Physical characteristics and properties of one of the hardest metals - titanium. Titanium is metal. properties of titanium. Application of titanium. Grades and chemical composition of titanium
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Titanium and its alloysTitanium widely distributed in the earth's crust, where it contains about 6%, and in terms of prevalence, it ranks fourth after aluminium, iron and magnesium. However, the industrial method of its extraction was developed only in the 40s of the twentieth century. Thanks to progress in the field of aircraft and rocket manufacturing, the production of titanium and its alloys has been intensively developed. This is due to a combination of such valuable properties of titanium as low density, high specific strength (s in /r × g), corrosion resistance, manufacturability in pressure treatment and weldability, cold resistance, non-magneticness and a number of other valuable physical and mechanical characteristics listed below.
Characteristics of the physical and mechanical properties of titanium (VT1-00)
| Density r, kg / m 3 | 4.5 × 10 -3 |
| Melting temperature T pl , °C | 1668±4 |
| Linear expansion coefficient a × 10 –6 , deg –1 | 8,9 |
| Thermal conductivity l , W/(m × deg) | 16,76 |
| Tensile strength s in, MPa | 300–450 |
| Conditional yield strength s 0.2 , MPa | 250–380 |
| Specific strength (s in /r×g)× 10 –3 , km | 7–10 |
| Relative elongation d, % | 25–30 |
| Relative contraction Y , % | 50–60 |
| Modulus of normal elasticity E´ 10 –3 , MPa | 110,25 |
| Shear modulus G´ 10 –3 , MPa | 41 |
| Poisson's ratio m, | 0,32 |
| Hardness HB | 103 |
| Impact strength KCU, J/cm2 | 120 |
Titanium has two polymorphic modifications: a-titanium with a hexagonal close-packed lattice with periods a= 0.296 nm, with= 0.472 nm and a high-temperature modification of b-titanium with a cubic body-centered lattice with a period a\u003d 0.332 nm at 900 ° C. The temperature of the polymorphic a "b-transformation is 882 ° C.
The mechanical properties of titanium significantly depend on the content of impurities in the metal. There are interstitial impurities - oxygen, nitrogen, carbon, hydrogen and substitutional impurities, which include iron and silicon. Although impurities increase strength, they simultaneously sharply reduce ductility, and interstitial impurities, especially gases, have the strongest negative effect. With the introduction of only 0.003% H, 0.02% N, or 0.7% O, titanium completely loses its ability to plastic deformation and becomes brittle.
Especially harmful is hydrogen, which causes hydrogen embrittlement titanium alloys. Hydrogen enters the metal during melting and subsequent processing, in particular, during pickling of semi-finished products. Hydrogen is sparingly soluble in a-titanium and forms lamellar hydride particles, which reduce impact strength and are especially negative in delayed fracture tests.
An industrial method for the production of titanium consists in the enrichment and chlorination of titanium ore, followed by its recovery from titanium tetrachloride with metallic magnesium (magnesium thermal method). Obtained by this method titanium sponge(GOST 17746–79), depending on the chemical composition and mechanical properties, the following grades are produced:
TG-90, TG-100, TG-110, TG-120, TG-130, TG-150, TG-T V (see Table 17.1). The numbers mean Brinell hardness HB, T B - hard.
To obtain monolithic titanium, the sponge is ground into powder, pressed and sintered or remelted in arc furnaces in a vacuum or inert gas atmosphere.
The mechanical properties of titanium are characterized by a good combination of strength and ductility. For example, commercially pure titanium grade VT1-0 has: s in = 375–540 MPa, s 0.2 = 295–410 MPa, d ³ 20%, and these characteristics are not inferior to a number of carbon and Cr-Ni corrosion-resistant steels.
The high ductility of titanium compared to other metals with an hcp lattice (Zn, Mg, Cd) is explained by a large number of slip and twinning systems due to the small ratio with/a= 1.587. Apparently, this is the reason for the high cold resistance of titanium and its alloys (see Chap. 13 for details).
When the temperature rises to 250 ° C, the strength of titanium decreases by almost 2 times. However, heat-resistant Ti-alloys have no equal in terms of specific strength in the temperature range of 300–600 °C; at temperatures above 600°C, titanium alloys are inferior to iron and nickel based alloys.
Titanium has a low modulus of normal elasticity ( E= 110.25 GPa) - almost 2 times less than that of iron and nickel, which makes it difficult to manufacture rigid structures.
Titanium is one of the reactive metals, but it has a high corrosion resistance, since a stable passive TiO 2 film is formed on its surface, which is firmly bonded to the base metal and excludes its direct contact with a corrosive environment. The thickness of this film usually reaches 5–6 nm.
Due to the oxide film, titanium and its alloys do not corrode in the atmosphere, in fresh and sea water, are resistant to cavitation corrosion and stress corrosion, as well as to organic acids.
The production of products from titanium and its alloys has a number of technological features. Due to the high chemical activity of molten titanium, its melting, casting and arc welding are carried out in a vacuum or in an atmosphere of inert gases.
During technological and operational heating, especially above 550–600 °C, it is necessary to take measures to protect titanium from oxidation and gas saturation (alpha layer) (see Chap. 3).
Titanium is well processed by pressure in the hot state and satisfactorily in the cold. It is easily rolled, forged, stamped. Titanium and its alloys are well welded by resistance and argon arc welding, providing high strength and ductility of the welded joint. The disadvantage of titanium is poor machinability due to sticking, low thermal conductivity and poor anti-friction properties.
The main purpose of alloying titanium alloys is to increase strength, heat resistance and corrosion resistance. Wide application found alloys of titanium with aluminum, chromium, molybdenum, vanadium, manganese, tin, and other elements. Alloying elements have a great influence on the polymorphic transformations of titanium.
Table 17.1
Grades, chemical composition (%) and hardness of spongy titanium (GOST 17746–79)
| Ti, not less | Hardness HB, 10/1500/30, no more |
||||||||
Table 17.2
Grades and chemical composition (%) of wrought titanium alloys (GOST 19807–91)
| Notation | ||||||||||||||
Note. The sum of other impurities in all alloys is 0.30%, in the VT1-00 alloy - 0.10%.
The formation of the structure and, consequently, the properties of titanium alloys is decisively influenced by phase transformations associated with titanium polymorphism. On fig. 17.1 shows diagrams of the "titanium-alloying element" state diagrams, reflecting the division of alloying elements according to the nature of their influence on the polymorphic transformations of titanium into four groups.
a - Stabilizers(Al, O, N), which increase the temperature of the polymorphic transformation a «b and expand the range of solid solutions based on a-titanium (Fig. 17.1, a). Considering the embrittlement effect of nitrogen and oxygen, only aluminum is of practical importance for alloying titanium. It is the main alloying element in all industrial titanium alloys, reduces their density and tendency to hydrogen embrittlement, and also increases strength and modulus of elasticity. Alloys with a stable a-structure are not hardened by heat treatment.
Isomorphic b-stabilizers (Mo, V, Ni, Ta, etc.), which lower the temperature of a "b-transformation and expand the range of solid solutions based on b-titanium (Fig. 17.1, b).
Eutectoid-forming b-stabilizers (Cr, Mn, Cu, etc.) can form intermetallic compounds of the TiX type with titanium. In this case, when cooled, the b-phase undergoes a eutectoid transformation b ® a + TiX (Fig. 17.1, in). Majority
b-stabilizers increases the strength, heat resistance and thermal stability of titanium alloys, somewhat reducing their ductility (Fig. 17.2.). In addition, alloys with (a + b) and pseudo-b structure can be hardened by heat treatment (hardening + aging).
Neutral elements (Zr, Sn) do not significantly affect the temperature of polymorphic transformation and do not change the phase composition of titanium alloys (Fig. 17.1, G).
Polymorphic b ® a -transformation can occur in two ways. With slow cooling and high mobility of atoms, it occurs according to the usual diffusion mechanism with the formation of a polyhedral structure of a solid a-solution. With rapid cooling - by a diffusionless martensitic mechanism with the formation of an acicular martensitic structure, denoted by a ¢ or with a higher degree of alloying - a ¢ ¢ . The crystal structure of a , a ¢ , a ¢ ¢ is practically of the same type (HCP), however, the lattice of a ¢ and a ¢ ¢ is more distorted, and the degree of distortion increases with increasing concentration of alloying elements. There is evidence [1] that the lattice of the a ¢ ¢ -phase is more orthorhombic than hexagonal. When aging phases a ¢ and a ¢ ¢ are separated b-phase or intermetallic phase.
Rice. 17.1. State diagrams of "Ti-alloying element" systems (schemes):
a) "Ti-a-stabilizers";
b) “Ti-isomorphic b-stabilizers”;
in) "Ti-eutectoid-forming b-stabilizers";
G) "Ti-neutral elements"
Rice. 17.2. Influence of Alloying Elements on the Mechanical Properties of Titanium
Unlike martensite of carbon steels, which is an interstitial solution and is characterized by high strength and brittleness, titanium martensite is a substitutional solution, and quenching of titanium alloys for martensite a ¢ leads to slight hardening and is not accompanied by a sharp decrease in plasticity.
Phase transformations that occur during slow and rapid cooling of titanium alloys with different contents of b-stabilizers, as well as the resulting structures, are shown in a generalized diagram (Fig. 17.3). It is valid for isomorphic b-stabilizers (Fig. 17.1, b) and, with some approximation, for eutectoid-forming b-stabilizers (Fig. 17.1, in), since the eutectoid decomposition in these alloys is very slow and can be neglected.
Rice. 17.3. Scheme of change in the phase composition of alloys "Ti-b-stabilizer" depending on the speed
cooling and hardening from the b-region
With slow cooling in titanium alloys, depending on the concentration of b-stabilizers, structures can be obtained: a, a + b or b, respectively.
During quenching as a result of martensitic transformation in the temperature range M n -M k (shown in dotted line in Fig. 17.3), four groups of alloys should be distinguished.
The first group includes alloys with a concentration of b-stabilizing elements up to C 1, i.e., alloys that, when quenched from the b-region, have exclusively a ¢ (a ¢ ¢)-structure. After quenching these alloys from temperatures (a + b)-region in the range from polymorphic transformation to T 1 , their structure is a mixture of phases a ¢ (a ¢ ¢), a and b, and after quenching from temperatures below T cr they have an (a + b)-structure.
The second group consists of alloys with a concentration of alloying elements from C 1 to C cr, in which, when quenched from the b-region, the martensitic transformation does not occur to the end and they have the structure a ¢ (a ¢ ¢) and b. Alloys of this group after quenching from temperatures from polymorphic transformation to T kr have the structure a ¢ (a ¢ ¢), a and b, and with temperatures below T cr - structure (a + b).
Hardening of alloys of the third group with a concentration of b-stabilizing elements from C cr to C 2 from temperatures in the b-region or from temperatures from polymorphic transformation to T 2 is accompanied by the transformation of part of the b-phase into the w-phase, and alloys of this type after quenching have the structure (b + w). Alloys of the third group after hardening from temperatures below T 2 have the structure (b + a).
Alloys of the fourth group after quenching from temperatures above the polymorphic transformation have exclusively b-structure, and from temperatures below the polymorphic transformation - (b + a).
It should be noted that the b ® b + w transformations can occur both during quenching of alloys with a concentration of (С cr –С 2) and during aging of alloys with a concentration of more than С 2 that have a metastable b-phase. In any case, the presence of the w-phase is undesirable, since it strongly embrittles titanium alloys. The recommended heat treatment regimes exclude its presence in industrial alloys or its appearance under operating conditions.
For titanium alloys, the following types of heat treatment are used: annealing, hardening and aging, as well as chemical-thermal treatment (nitriding, siliconizing, oxidation, etc.).
Annealing is carried out for all titanium alloys in order to complete the formation of the structure, leveling the structural and concentration inhomogeneity, as well as mechanical properties. The annealing temperature should be higher than the recrysallization temperature, but lower than the transition temperature to the b-state ( T pp) to prevent grain growth. Apply conventional annealing, double or isothermal(to stabilize the structure and properties), incomplete(to relieve internal stresses).
Quenching and aging (hardening heat treatment) is applicable to titanium alloys with (a + b) structure. The principle of hardening heat treatment is to obtain metastable phases b , a ¢ , a ¢ ¢ during quenching and their subsequent decay with the release of dispersed particles a - and b -phases during artificial aging. In this case, the strengthening effect depends on the type, quantity, and composition of the metastable phases, as well as the fineness of the a- and b-phase particles formed after aging.
Chemical-thermal treatment is carried out to increase hardness and wear resistance, resistance to "seizure" when working under friction conditions, fatigue strength, as well as improve corrosion resistance, heat resistance and heat resistance. Nitriding, siliconizing and some types of diffusion metallization have practical applications.
Titanium alloys, compared with technical titanium, have a higher strength, including at high temperatures, while maintaining a sufficiently high ductility and corrosion resistance.
Brands and chemical composition of domestic
alloys (GOST 19807–91) are presented in Table. 17.2.
According to the manufacturing technology, titanium alloys are divided into wrought and casting; according to the level of mechanical properties - for alloys low strength and high ductility, middle strength, high strength; according to the conditions of use - on cold-resistant, heat-resistant, corrosion-resistant . According to the ability to harden by heat treatment, they are divided into hardened and non-hardened, according to the structure in the annealed state - into a -, pseudo-a -, (a + b) -, pseudo-b - and b-alloys (Table 17.3).
Separate groups of titanium alloys differ in the value of the conditional stabilization coefficient Kb, which shows the ratio of the content of b-stabilizing alloying element to its content in an alloy of critical composition with cr. When the alloy contains several b-stabilizing elements, their Kb summed up.
< 700 MPa, namely: a - alloys of grades VT1-00, VT1-0 (technical titanium) and alloys OT4-0, OT4-1 (Ti-Al-Mn system), AT3 (Ti-Al system with small additions of Cr, Fe, Si, B), related to pseudo-a-alloys with a small amount of b-phase. The strength characteristics of these alloys are higher than those of pure titanium due to impurities in VT1-00 and VT1-0 alloys and slight alloying with a- and b-stabilizers in OT4-0, OT4-1, AT3 alloys.
These alloys are distinguished by high ductility both in hot and cold states, which makes it possible to obtain all types of semi-finished products: foil, strip, sheets, plates, forgings, stampings, profiles, pipes, etc. The mechanical properties of semi-finished products from these alloys are given in tab. 17.4–17.6.
Table 17.3
Classification of titanium alloys by structure
| Alloy group | Alloy grade |
| VT1-00, VT1-0, VT5, VT5-1, PT-7M |
|
| Pseudo-a-alloys | OT4-0, OT4-1, OT4, VT20, AT3 |
| (a + b)-martensitic class ( Kb= 0,3–0,9) | VT6S, VT6, VT14, VT8, VT9, PT-3V, VT3-1, AT3 |
| (a + b)-Transition class alloys ( Kb= 1,0–1,4) | |
| Pseudo-b-alloys ( Kb= 1,5–2,4) | VT35*, VT32*, VT15 |
| b-Alloys ( Kb= 2,5–3,0) |
* Experimental alloys.
Table 17.4
Mechanical properties of titanium alloy sheets (GOST 22178–76)
| Titanium grades | Sample condition | sheet thickness, | Tensile strength, s in, MPa | Relative elongation, d, % |
| annealed | ||||
| St. 6.0–10.5 | ||||
| St. 6.0–10.5 | ||||
| annealed | ||||
| St. 6.0–10.5 | ||||
| St. 6.0–10.5 | ||||
| St. 6.0–10.5 | ||||
| 885 (885–1080) | ||||
| annealed | 885 (885–1050) | |||
| St. 5.0–10.5 | 835 (835–1050) | |||
| tempered and | ||||
| St. 7.0–10.5 | ||||
| annealed | 930 (930–1180) | |||
| St. 4.0–10.5 | ||||
| annealed | 980 (980–1180) | |||
| St. 4.0–10.5 | ||||
Note. Figures in parentheses are for sheets with a high surface finish.
Table 17.5
Mechanical properties of bars made of titanium alloys (GOST 26492–85)
| Alloy grade | State | Bar diameter | Limit | Relative | Relative | percussion |
| Annealed | ||||||
| Annealed | ||||||
| Annealed | 885 (905–1050) | |||||
| 835 (835–1050) | ||||||
| Hardened and aged | ||||||
| Annealed | ||||||
| Hardened and aged | ||||||
| Annealed | 930 (980–1230) | |||||
| 930 (930–1180) | ||||||
| 980 (980–1230) | ||||||
| 930 (930–1180) | ||||||
| 980 (1030–1230) | ||||||
| 930 (980–1230) | ||||||
| Annealed | 885 (885–1080) | |||||
| 865 (865–1080) | ||||||
| Hardened and aged | ||||||
| Annealed | 885 (930–1130) | |||||
| 885 (885–1130) | ||||||
| 1030 (1080–1230) | ||||||
| 1030 (1080–1280) | ||||||
Note. Data in parentheses are for higher quality bars.
Table 17.6
Mechanical properties of titanium alloy plates (GOST 23755–79)
| Alloy grade | State | plate thickness, | Tensile strength s in, MPa | Relative elongation d, % | Relative contraction y , % | Impact strength KCU, J/cm2 |
| Without | ||||||
| annealed | ||||||
| annealed | ||||||
| Hardened and aged | ||||||
| annealed | ||||||
| Without heat treatment | ||||||
Forging, volumetric and sheet stamping, rolling, pressing are carried out in a hot state according to the modes indicated in Table. 17.7. Final rolling, sheet stamping, drawing and other operations are carried out in a cold state.
These alloys and products from them are subjected only to annealing according to the modes indicated in Table. 17.8. Incomplete annealing is used to relieve internal stresses resulting from machining, sheet stamping, welding, etc.
These alloys are well welded by fusion welding (argon-arc, submerged arc, electroslag) and contact (spot, roller). In fusion welding, the strength and ductility of the welded joint are almost the same as those of the base metal.
The corrosion resistance of these alloys is high in many media (sea water, chlorides, alkalis, organic acids, etc.), except for solutions of HF, H 2 SO 4 , HCl and some others.
Application. These alloys are widely used as structural materials for the manufacture of almost all types of semi-finished products, parts and structures, including welded ones. Their most effective use is in aerospace engineering, in chemical engineering, in cryogenic engineering (Table 17.9.), as well as in units and structures operating at temperatures up to 300–350 ° C.
This group includes alloys with tensile strength s in = 750–1000 MPa, namely: a - alloys of grades VT5 and VT5-1; pseudo-a-alloys of grades OT4, VT20; (a + b)-alloys of grades PT3V, as well as VT6, VT6S, VT14 in the annealed state.
Alloys VT5, VT5-1, OT4, VT20, PT3V, VT6S, containing a small amount of the b-phase (2–7% of the b-phase in the equilibrium state), are not subjected to hardening heat treatment and are used in the annealed state. Alloy VT6S is sometimes used in a thermally hardened state. Alloys VT6 and VT14 are used both in the annealed and in the thermally hardened state. In the latter case, their strength becomes higher than 1000 MPa, and they will be considered in the section on high-strength alloys.
The alloys under consideration, along with increased strength, retain satisfactory ductility in the cold state and good ductility in the hot state, which makes it possible to obtain all types of semi-finished products from them: sheets, strip, profiles, forgings, stampings, pipes, etc. The exception is the VT5 alloy, from which sheets and plates are not produced due to low technological plasticity. Modes of hot pressure treatment are given in table. 17.7.
This category of alloys accounts for the bulk of the production of semi-finished products used in mechanical engineering. Mechanical characteristics of the main semi-finished products are given in table. 17.4–17.6.
All medium-strength alloys are well welded by all types of welding used for titanium. The strength and ductility of a welded joint made by fusion welding is close to the strength and ductility of the base metal (for VT20 and VT6S alloys, this ratio is 0.9–0.95). After welding, incomplete annealing is recommended to relieve internal welding stresses (Table 17.8).
The machinability of these alloys is good. Corrosion resistance in most aggressive environments is similar to technical titanium VT1-0.
Table 17.7
Modes of hot forming of titanium alloys
| Alloy grade | Ingot forging mode | Forging mode pre | Press stamping mode | Hammer stamping mode | Mode |
|||||||||
| temperature | thickness, | temperature | temperature | temperature | temperature |
|||||||||
| the ending | the ending | the ending | the ending |
|||||||||||
| All | ||||||||||||||
| 40–70 | ||||||||||||||
| 40–70 | ||||||||||||||
| 40–50** | ||||||||||||||
| 40–50** | ||||||||||||||
| 850 | 40–50** | |||||||||||||
| All | ||||||||||||||
* Degree of deformation for one heating, %.
** Deformation in the (a + b) region.
*** Deformation in the b-region.
Table 17.8
Annealing modes for titanium alloys
| Alloy grade | Annealing temperature, ° С | Note |
|
| Sheets | Bars, forgings, stampings, |
||
| 445–585 ° С* |
|||
| 445–585 ° С* |
|||
| 480–520 ° С* |
|||
| 520–560 ° С* |
|||
| 545–585 ° С* |
|||
| Isothermal annealing: heating to 870–920°C, holding, cooling to 600–650°C, cooling with furnace or transfer to another furnace, holding 2 h, air cooling |
|||
| Double annealing, holding at 550–600°C for 2–5 hours. Annealing at 850°C, air cooling is allowed for power parts |
|||
| 550–650 ° С* |
|||
| Annealing is allowed according to the modes: 1) heating up to 850 ° C, holding, cooling with a furnace up to 750 ° C, holding for 3.5 hours, cooling in air; 2) heating up to 800°C, holding for 30 min, cooling with an oven up to 500°C, then in air |
|||
| Double annealing, exposure at 570–600 ° С - 1 h. Isothermal annealing is allowed: heating up to 920–950°C, holding, cooling with a furnace or transfer to another furnace with a temperature of 570–600°C, holding for 1 h, cooling in air |
|||
| Double annealing, exposure at 530–580 °C - 2–12 h. Isothermal annealing is allowed: heating up to 950–980 °С, holding, cooling with a furnace or transfer to another furnace with a temperature of 530–580 °С, holding for 2–12 h, cooling in air |
|||
| 550–650 ° С* |
|||
| Isothermal annealing is allowed: heating up to 790–810°C, holding, cooling with a furnace or transfer to another furnace up to 640–660°C, holding for 30 min, cooling in air |
|||
| Annealing of sheet parts is allowed at 650–750 ° С, (600–650 ° С)* |
|||
| (depending on the section and type of semi-finished product) | Cooling with an oven at a rate of 2–4 °C/min to 450 °C, then in air. Double annealing, exposure at 500–650 ° С for 1–4 hours. Double annealing is allowed for parts operating at temperatures up to 300 ° С and duration up to 2000 h |
||
| (545–585°C*) |
|||
* Incomplete annealing temperatures.
Table 17.9
Mechanical characteristics of titanium alloys at low temperatures
| s in (MPa) at temperature, ° С | d (%) at temperature, ° С | KCU, J / cm 2 at temperature, ° С |
||||||
Application. These alloys are recommended for the manufacture of products by sheet stamping (OT4, VT20), for welded parts and assemblies, for stamp-welded parts (VT5, VT5-1, VT6S, VT20), etc. The VT6S alloy is widely used for the manufacture of vessels and pressure vessels. Parts and assemblies made of alloys OT4, VT5 can work for a long time at temperatures up to 400 ° C and for a short time - up to 750 ° C; from alloys VT5-1, VT20 - for a long time at temperatures up to 450–500 ° C and for a short time - up to 800–850 ° C. Alloys VT5-1, OT4, VT6S are also recommended for use in refrigeration and cryogenic technology (Table 17.9).
This group includes alloys with a tensile strength s > 1000 MPa, namely (a + b)-alloys of grades VT6, VT14, VT3-1, VT22. High strength in these alloys is achieved by hardening heat treatment (hardening + aging). The exception is the high-alloy alloy VT22, which even in the annealed state has s B > 1000 MPa.
These alloys, along with high strength, retain good (VT6) and satisfactory (VT14, VT3-1, VT22) technological ductility in the hot state, which makes it possible to obtain various semi-finished products from them: sheets (except VT3-1), rods, plates, forgings, stampings, profiles, etc. Hot forming modes are given in Table. 17.7. Alloys VT6 and VT14 in the annealed state (s in » 850 MPa) can be subjected to cold sheet forging with small deformations. The mechanical characteristics of the main semi-finished products in the annealed and hardened states are given in Table. 17.4–17.6.
Despite the heterophasic structure, the alloys under consideration have satisfactory weldability by all types of welding used for titanium. To ensure the required level of strength and plasticity, complete annealing is mandatory, and for the VT14 alloy (with a thickness of the welded parts of 10–18 mm), it is recommended to carry out hardening followed by aging. In this case, the strength of the welded joint (fusion welding) is at least 0.9 of the strength of the base metal. The ductility of the welded joint is close to the ductility of the base metal.
Machinability is satisfactory. Machining of alloys can be carried out both in the annealed and in the thermally hardened state.
These alloys have high corrosion resistance in the annealed and thermally hardened states in a humid atmosphere, sea water, and in many other aggressive environments, like commercial titanium.
Heat treatment . Alloys VT3-1, VT6, VT6S, VT14, VT22 are subjected to hardening and aging (see above). The recommended heating modes for hardening and aging for monolithic products, semi-finished products and welded parts are given in Table. 17.10.
Cooling during quenching is carried out in water, and after aging - in air. Full hardenability is provided for parts made of VT6, VT6S alloys with a maximum cross section of up to 40–45 mm, and of VT3-1, VT14, VT22 alloys - up to 60 mm.
To ensure a satisfactory combination of strength and ductility of alloys with an (a + b) structure after quenching and aging, it is necessary that their structure be equiaxed or "basket weave" before hardening heat treatment. Examples of initial microstructures providing satisfactory properties are shown in Figs. 17.4 (types 1–7).
Table 17.10
Modes of Strengthening Heat Treatment of Titanium Alloys
| Alloy grade | Temperature of polymorphic transformation T pp, ° С | Temperature | Temperature | Duration |
The initial acicular structure of the alloy with the presence of primary grain boundaries of the b-phase (types 8–9) during overheating after quenching and aging or annealing leads to marriage - a decrease in strength and ductility. Therefore, it is necessary to avoid heating (a + b) alloys to temperatures above the polymorphic transformation temperature, since it is impossible to correct the overheated structure by heat treatment.
Heating during heat treatment is recommended to be carried out in electric furnaces with automatic temperature control and registration. To prevent the formation of scale, the heating of finished parts and sheets must be carried out in furnaces with a protective atmosphere or with the use of protective coatings.
When heating thin sheet parts for hardening, to equalize the temperature and reduce their warping, a steel plate 30–40 mm thick is placed on the furnace floor. For hardening parts of complex configuration and thin-walled parts, locking devices are used to prevent warping and leashes.
After high-temperature processing (quenching or annealing) in a furnace without a protective atmosphere, semi-finished products that are not subjected to further processing must undergo hydro-sandblasting or corundum sanding, and sheet products must also be pickled.
Application. High-strength titanium alloys are used for the manufacture of critical parts and assemblies: welded structures (VT6, VT14), turbines (VT3-1), stamp-welded assemblies (VT14), highly loaded parts and stamped structures (VT22). These alloys can work for a long time at temperatures up to 400 ° C and for a short time up to 750 ° C.
A feature of high-strength titanium alloys as a structural material is their increased sensitivity to stress concentrators. Therefore, when designing parts from these alloys, it is necessary to take into account a number of requirements (improved surface quality, increase in transition radii from one section to another, etc.), similar to those that exist when high-strength steels are used.
Physical and chemical properties of titanium, obtaining titanium
The use of titanium in pure form and in the form of alloys, the use of titanium in the form of compounds, the physiological effect of titanium
Section 1. History and occurrence of titanium in nature.
Titan -This an element of a secondary subgroup of the fourth group, the fourth period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 22. The simple substance titanium (CAS number: 7440-32-6) is a light silver-white metal. It exists in two crystalline modifications: α-Ti with a hexagonal close-packed lattice, β-Ti with a cubic body-centered packing, the temperature of the polymorphic transformation α↔β is 883 °C. Melting point 1660±20 °C.
History and presence in nature of titanium
Titan was named after the ancient Greek characters Titans. The German chemist Martin Klaproth named it this way for his personal reasons, unlike the French, who tried to give names in accordance with the chemical characteristics of the element, but since the properties of the element were unknown at that time, such a name was chosen.
Titanium is the 10th element in terms of number of it on our planet. The amount of titanium in the earth's crust is 0.57% by weight and 0.001 milligrams per 1 liter of sea water. Titanium deposits are located on the territory of: the Republic of South Africa, Ukraine, Russia, Kazakhstan, Japan, Australia, India, Ceylon, Brazil and South Korea.
In terms of physical properties, titanium is a light silvery metal, in addition, it is characterized by high viscosity during machining and is prone to sticking to the cutting tool, so special lubricants or spraying are used to eliminate this effect. At room temperature, it is covered with a translucent film of TiO2 oxide, due to which it is resistant to corrosion in most aggressive environments, except for alkalis. Titanium dust has the ability to explode, with a flash point of 400 °C. Titanium shavings are flammable.
To produce pure titanium or its alloys, in most cases, titanium dioxide is used with a small number of compounds included in it. For example, a rutile concentrate obtained by beneficiation of titanium ores. But the reserves of rutile are extremely small, and in connection with this, the so-called synthetic rutile or titanium slag, obtained during the processing of ilmenite concentrates, is used.
The discoverer of titanium is considered to be 28-year-old English monk William Gregor. In 1790, while conducting mineralogical surveys in his parish, he drew attention to the prevalence and unusual properties of black sand in the valley of Menaken in the south-west of England and began to explore it. In the sand, the priest found grains of a black shiny mineral, attracted by an ordinary magnet. Obtained in 1925 by Van Arkel and de Boer by the iodide method, the purest titanium turned out to be a ductile and technological metal with many valuable properties, which attracted the attention of a wide range of designers and engineers. In 1940, Croll proposed a magnesium-thermal method for extracting titanium from ores, which is still the main one at the present time. In 1947, the first 45 kg of commercially pure titanium were produced.
Titanium has the atomic number 22 in Mendeleev's periodic table of elements. Atomic mass natural titanium, calculated from the results of studies of its isotopes, is 47.926. So, the nucleus of a neutral titanium atom contains 22 protons. The number of neutrons, that is, neutral uncharged particles, is different: more often 26, but can vary from 24 to 28. Therefore, the number of titanium isotopes is different. In total, 13 isotopes of element No. 22 are now known. Natural titanium consists of a mixture of five stable isotopes, titanium-48 is the most widely represented, its share in natural ores is 73.99%. Titanium and other elements of the IVB subgroup are very similar in properties to the elements of the IIIB subgroup (scandium group), although they differ from the latter in their ability to exhibit a large valence. The similarity of titanium with scandium, yttrium, as well as with elements of the VB subgroup - vanadium and niobium, is also expressed in the fact that titanium is often found in natural minerals together with these elements. With monovalent halogens (fluorine, bromine, chlorine and iodine), it can form di-tri- and tetra compounds, with sulfur and elements of its group (selenium, tellurium) - mono- and disulfides, with oxygen - oxides, dioxides and trioxides.
Titanium also forms compounds with hydrogen (hydrides), nitrogen (nitrides), carbon (carbides), phosphorus (phosphides), arsenic (arsides), as well as compounds with many metals - intermetallic compounds. Titanium forms not only simple, but also numerous complex compounds; many of its compounds with organic substances are known. As can be seen from the list of compounds in which titanium can participate, it is chemically very active. And at the same time, titanium is one of the few metals with exceptionally high corrosion resistance: it is practically eternal in the air, in cold and boiling water, it is very resistant in sea water, in solutions of many salts, inorganic and organic acids. In terms of its corrosion resistance in sea water, it surpasses all metals, with the exception of noble ones - gold, platinum, etc., most types of stainless steel, nickel, copper and other alloys. In water, in many aggressive environments, pure titanium is not subject to corrosion. Resists titanium and erosion corrosion resulting from a combination of chemical and mechanical effects on the metal. In this regard, it is not inferior to the best grades of stainless steels, copper-based alloys and other structural materials. Titanium also resists fatigue corrosion well, which often manifests itself in the form of violations of the integrity and strength of the metal (cracking, local corrosion centers, etc.). The behavior of titanium in many aggressive environments, such as nitrogen, hydrochloric, sulfuric, "aqua regia" and other acids and alkalis, is surprising and admirable for this metal.
Titanium is a very refractory metal. For a long time it was believed that it melts at 1800 ° C, but in the mid-50s. English scientists Diardorf and Hayes established the melting point for pure elemental titanium. It amounted to 1668 ± 3 ° C. In terms of its refractoriness, titanium is second only to such metals as tungsten, tantalum, niobium, rhenium, molybdenum, platinoids, zirconium, and among the main structural metals it is in first place. The most important feature of titanium as a metal is its unique physical and Chemical properties: low density, high strength, hardness, etc. The main thing is that these properties do not change significantly at high temperatures.
Titanium is a light metal, its density at 0°C is only 4.517 g/cm8, and at 100°C it is 4.506 g/cm3. Titanium belongs to the group of metals with a specific gravity of less than 5 g/cm3. This includes all alkali metals (sodium, cadium, lithium, rubidium, cesium) with a specific gravity of 0.9–1.5 g/cm3, magnesium (1.7 g/cm3), aluminum (2.7 g/cm3) and etc. Titanium is more than 1.5 times heavier than aluminum, and in this, of course, it loses to it, but it is 1.5 times lighter than iron (7.8 g/cm3). However, taking specific gravity an intermediate position between aluminum and iron, titanium surpasses them many times in its mechanical properties.). Titanium has a significant hardness: it is 12 times harder than aluminum, 4 times harder than iron and copper. Another important characteristic of a metal is its yield strength. The higher it is, the better the parts made of this metal resist operational loads. The yield strength of titanium is almost 18 times higher than that of aluminum. The specific strength of titanium alloys can be increased by a factor of 1.5–2. Its high mechanical properties are well preserved at temperatures up to several hundred degrees. Pure titanium is suitable for all types of processing in hot and cold states: it can be forged like iron, drawn and even made into wire, rolled into sheets, tapes, and foils up to 0.01 mm thick.
Unlike most metals, titanium has significant electrical resistance: if the electrical conductivity of silver is taken as 100, then the electrical conductivity of copper is 94, aluminum is 60, iron and platinum is -15, and titanium is only 3.8. Titanium is a paramagnetic metal, it is not magnetized like iron in a magnetic field, but it is not pushed out of it like copper. Its magnetic susceptibility is very weak, this property can be used in construction. Titanium has a relatively low thermal conductivity, only 22.07 W / (mK), which is approximately 3 times lower than the thermal conductivity of iron, 7 times lower than magnesium, 17–20 times lower than aluminum and copper. Accordingly, the coefficient of linear thermal expansion of titanium is lower than that of other structural materials: at 20 C, it is 1.5 times lower than that of iron, 2 - for copper, and almost 3 - for aluminum. Thus, titanium is a poor conductor of electricity and heat.
Today, titanium alloys are widely used in aviation technology. Titanium alloys were first used on an industrial scale in the construction of aircraft jet engines. The use of titanium in the design of jet engines makes it possible to reduce their weight by 10...25%. In particular, compressor discs and blades, air intake parts, guide vanes and fasteners are made from titanium alloys. Titanium alloys are indispensable for supersonic aircraft. The growth of flight speeds aircraft led to an increase in the temperature of the skin, as a result of which aluminum alloys no longer meet the requirements that are imposed by aviation technology at supersonic speeds. The skin temperature in this case reaches 246...316 °C. Under these conditions, titanium alloys turned out to be the most acceptable material. In the 70s, the use of titanium alloys for the airframe of civil aircraft increased significantly. In a medium-haul aircraft TU-204 total weight parts made of titanium alloys is 2570 kg. The use of titanium in helicopters is gradually expanding, mainly for parts of the main rotor system, drive, and control system. An important place is occupied by titanium alloys in rocket science.
Due to the high corrosion resistance in sea water, titanium and its alloys are used in shipbuilding for the manufacture of propellers, ship plating, submarines, torpedoes, etc. Shells do not stick to titanium and its alloys, which sharply increase the resistance of the vessel when it moves. Gradually, the areas of application of titanium are expanding. Titanium and its alloys are used in the chemical, petrochemical, pulp and paper and food industries, non-ferrous metallurgy, power engineering, electronics, nuclear technology, electroplating, in the manufacture of weapons, for the manufacture of armor plates, surgical instruments, surgical implants, desalination plants, racing car parts , sports equipment (golf clubs, climbing equipment), watch parts and even jewelry. Nitriding of titanium leads to the formation of a golden film on its surface, which is not inferior in beauty to real gold.
The discovery of TiO2 was made almost simultaneously and independently by the Englishman W. Gregor and the German chemist M. G. Klaproth. W. Gregor, studying the composition of magnetic ferruginous sand (Creed, Cornwall, England, 1791), isolated a new "earth" (oxide) of an unknown metal, which he called menaken. In 1795, the German chemist Klaproth discovered a new element in the mineral rutile and named it titanium. Two years later, Klaproth established that rutile and menaken earth are oxides of the same element, behind which the name "titanium" proposed by Klaproth remained. After 10 years, the discovery of titanium took place for the third time. The French scientist L. Vauquelin discovered titanium in anatase and proved that rutile and anatase are identical titanium oxides.
The first sample of metallic titanium was obtained in 1825 by J. Ya. Berzelius. Due to the high chemical activity of titanium and the complexity of its purification, the Dutch A. van Arkel and I. de Boer obtained a pure Ti sample in 1925 by thermal decomposition of titanium iodide TiI4 vapor.
Titanium is the 10th most abundant in nature. The content in the earth's crust is 0.57% by mass, in sea water 0.001 mg / l. 300 g/t in ultrabasic rocks, 9 kg/t in basic rocks, 2.3 kg/t in acid rocks, 4.5 kg/t in clays and shales. In the earth's crust, titanium is almost always tetravalent and is present only in oxygen compounds. It does not occur in free form. Titanium under conditions of weathering and precipitation has a geochemical affinity for Al2O3. It is concentrated in bauxites of the weathering crust and in marine clayey sediments. The transfer of titanium is carried out in the form of mechanical fragments of minerals and in the form of colloids. Up to 30% TiO2 by weight accumulates in some clays. Titanium minerals are resistant to weathering and form large concentrations in placers. More than 100 minerals containing titanium are known. The most important of them are: rutile TiO2, ilmenite FeTiO3, titanomagnetite FeTiO3 + Fe3O4, perovskite CaTiO3, titanite CaTiSiO5. There are primary titanium ores - ilmenite-titanomagnetite and placer - rutile-ilmenite-zircon.
Main ores: ilmenite (FeTiO3), rutile (TiO2), titanite (CaTiSiO5).
In 2002, 90% of the mined titanium was used for the production of titanium dioxide TiO2. World production of titanium dioxide was 4.5 million tons per year. The confirmed reserves of titanium dioxide (without Russia) are about 800 million tons. For 2006, according to the US Geological Survey, in terms of titanium dioxide and excluding Russia, the reserves of ilmenite ores amount to 603-673 million tons, and rutile - 49.7- 52.7 million tons. Thus, at the current rate of production, the world's proven reserves of titanium (excluding Russia) will be enough for more than 150 years.
Russia has the world's second largest reserves of titanium after China. The mineral resource base of titanium in Russia is made up of 20 deposits (of which 11 are primary and 9 are alluvial), fairly evenly dispersed throughout the country. The largest of the explored deposits (Yaregskoye) is located 25 km from the city of Ukhta (Komi Republic). The reserves of the deposit are estimated at 2 billion tons of ore with an average titanium dioxide content of about 10%.
The world's largest titanium producer is the Russian company VSMPO-AVISMA.
As a rule, the starting material for the production of titanium and its compounds is titanium dioxide with a relatively small amount of impurities. In particular, it can be a rutile concentrate obtained during the beneficiation of titanium ores. However, the reserves of rutile in the world are very limited, and the so-called synthetic rutile or titanium slag, obtained during the processing of ilmenite concentrates, is more often used. To obtain titanium slag, ilmenite concentrate is reduced in an electric arc furnace, while iron is separated into a metal phase (cast iron), and not reduced titanium oxides and impurities form a slag phase. Rich slag is processed by the chloride or sulfuric acid method.
In pure form and in the form of alloys
Titanium monument to Gagarin on Leninsky Prospekt in Moscow
The metal is used in: chemical industry (reactors, pipelines, pumps, pipeline fittings), military industry (body armor, armor and fire barriers in aviation, submarine hulls), industrial processes (desalination plants, pulp and paper processes), automotive industry, agricultural industry, food industry, piercing jewelry, medical industry (prostheses, osteoprostheses), dental and endodontic instruments, dental implants, sporting goods, jewelry (Alexander Khomov), mobile phones, light alloys, etc. It is the most important structural material in aircraft, rocket, shipbuilding.
Titanium casting is carried out in vacuum furnaces in graphite molds. Vacuum investment casting is also used. Due to technological difficulties, it is used in artistic casting to a limited extent. The first monumental cast titanium sculpture in the world is the monument to Yuri Gagarin on the square named after him in Moscow.
Titanium is an alloying addition in many alloy steels and most special alloys.
Nitinol (nickel-titanium) is a shape memory alloy used in medicine and technology.
Titanium aluminides are very resistant to oxidation and heat-resistant, which in turn determined their use in aviation and automotive industry as structural materials.
Titanium is one of the most common getter materials used in high vacuum pumps.
White titanium dioxide (TiO2) is used in paints (such as titanium white) as well as in the manufacture of paper and plastics. Food additive E171.
Organotitanium compounds (eg tetrabutoxytitanium) are used as a catalyst and hardener in the chemical and paint industries.
Inorganic titanium compounds are used in the chemical, electronic, glass fiber industries as additives or coatings.
Titanium carbide, titanium diboride, titanium carbonitride are important components of superhard materials for metal processing.
Titanium nitride is used to coat tools, church domes and in the manufacture of costume jewelry, because. has a color similar to gold.
Barium titanate BaTiO3, lead titanate PbTiO3 and a number of other titanates are ferroelectrics.
There are many titanium alloys with different metals. Alloying elements are divided into three groups, depending on their effect on the temperature of polymorphic transformation: beta stabilizers, alpha stabilizers and neutral hardeners. The former lower the transformation temperature, the latter increase it, and the latter do not affect it, but lead to solution hardening of the matrix. Examples of alpha stabilizers: aluminum, oxygen, carbon, nitrogen. Beta stabilizers: molybdenum, vanadium, iron, chromium, nickel. Neutral hardeners: zirconium, tin, silicon. Beta stabilizers, in turn, are divided into beta-isomorphic and beta-eutectoid-forming. The most common titanium alloy is the Ti-6Al-4V alloy (in Russian classification- BT6).
60% - paint;
20% - plastic;
13% - paper;
7% - mechanical engineering.
$15-25 per kilo, depending on purity.
The purity and grade of rough titanium (titanium sponge) is usually determined by its hardness, which depends on the content of impurities. The most common brands are TG100 and TG110.
The price of ferrotitanium (minimum 70% titanium) as of 12/22/2010 is $6.82 per kilogram. On 01.01.2010 the price was at the level of $5.00 per kilogram.
In Russia, titanium prices at the beginning of 2012 were 1200-1500 rubles/kg.
Advantages:
low density (4500 kg / m3) helps to reduce the mass of the material used;
high mechanical strength. It should be noted that at elevated temperatures (250-500 °C) titanium alloys are superior in strength to high-strength aluminum and magnesium alloys;
unusually high corrosion resistance, due to the ability of titanium to form thin (5-15 microns) continuous films of TiO2 oxide on the surface, firmly bonded to the metal mass;
the specific strength (ratio of strength and density) of the best titanium alloys reaches 30-35 or more, which is almost twice the specific strength of alloyed steels.
Disadvantages:
high production cost, titanium is much more expensive than iron, aluminum, copper, magnesium;
active interaction at high temperatures, especially in the liquid state, with all the gases that make up the atmosphere, as a result of which titanium and its alloys can only be melted in a vacuum or in an inert gas environment;
difficulties involved in the production of titanium waste;
poor antifriction properties due to titanium sticking to many materials, titanium paired with titanium cannot work for friction;
high propensity of titanium and many of its alloys to hydrogen embrittlement and salt corrosion;
poor machinability similar to that of austenitic stainless steels;
high reactivity, a tendency to grain growth at high temperature and phase transformations during the welding cycle cause difficulties in welding titanium.
The main part of titanium is spent on the needs of aviation and rocket technology and marine shipbuilding. Titanium (ferrotitanium) is used as an alloying additive to high-quality steels and as a deoxidizer. Technical titanium is used for the manufacture of tanks, chemical reactors, pipelines, fittings, pumps, valves and other products operating in aggressive environments. Grids and other parts of electrovacuum devices operating at high temperatures are made from compact titanium.
In terms of use as a structural material, titanium is in 4th place, second only to Al, Fe and Mg. Titanium aluminides are very resistant to oxidation and heat-resistant, which in turn determined their use in aviation and automotive industry as structural materials. The biological safety of titanium makes it an excellent material for the food industry and reconstructive surgery.
Titanium and its alloys are widely used in engineering due to their high mechanical strength, which is maintained at high temperatures, corrosion resistance, heat resistance, specific strength, low density and other useful properties. The high cost of titanium and its alloys is in many cases offset by their greater performance, and in some cases they are the only material from which it is possible to manufacture equipment or structures capable of operating under given specific conditions.
Titanium alloys play an important role in aviation technology, where the aim is to obtain the lightest design combined with the required strength. Titanium is light compared to other metals, but at the same time it can work at high temperatures. Titanium alloys are used to make skin, fastening parts, a power set, chassis parts, and various units. Also, these materials are used in the construction of aircraft jet engines. This allows you to reduce their weight by 10-25%. Titanium alloys are used to produce compressor disks and blades, air intake and guide vane parts, and fasteners.
Titanium and its alloys are also used in rocket science. In view of the short-term operation of the engines and the rapid passage of dense layers of the atmosphere in rocket science, the problems of fatigue strength, static endurance, and partly creep are largely removed.
Technical titanium is not suitable for aviation applications due to its insufficiently high heat resistance, but due to its exceptionally high corrosion resistance, in some cases it is indispensable in the chemical industry and shipbuilding. So it is used in the manufacture of compressors and pumps for pumping such aggressive media as sulfuric and hydrochloric acid and their salts, pipelines, valves, autoclaves, various containers, filters, etc. Only titanium has corrosion resistance in environments such as wet chlorine, aqueous and acidic chlorine solutions, therefore equipment for the chlorine industry is made from this metal. Titanium is used to make heat exchangers that operate in corrosive environments, for example, in nitric acid (not fuming). In shipbuilding, titanium is used for the manufacture of propellers, plating of ships, submarines, torpedoes, etc. Shells do not stick to titanium and its alloys, which sharply increase the resistance of the vessel when it moves.
Titanium alloys are promising for use in many other applications, but their use in technology is constrained by the high cost and scarcity of titanium.
Titanium compounds are also widely used in various industries. Titanium carbide has a high hardness and is used in the manufacture of cutting tools and abrasive materials. White titanium dioxide (TiO2) is used in paints (such as titanium white) as well as in the manufacture of paper and plastics. Organotitanium compounds (eg tetrabutoxytitanium) are used as a catalyst and hardener in the chemical and paint industries. Inorganic titanium compounds are used in the chemical, electronic, fiberglass industry as an additive. Titanium diboride is an important component of superhard metalworking materials. Titanium nitride is used to coat tools.
With the current high prices for titanium, it is mainly used for the production of military equipment, where the main role belongs not to cost, but to technical characteristics. Nevertheless, cases of using the unique properties of titanium for civil needs are known. As the price of titanium declines and its production grows, the use of this metal in military and civilian purposes will expand more and more.
Aviation. The low specific gravity and high strength (especially at elevated temperatures) of titanium and its alloys make them highly valuable aviation materials. In the field of aircraft construction and the production of aircraft engines, titanium is increasingly replacing aluminum and stainless steel. As the temperature rises, aluminum quickly loses its strength. On the other hand, titanium has a clear strength advantage at temperatures up to 430°C, and elevated temperatures of this order occur at high speeds due to aerodynamic heating. The advantage of replacing steel with titanium in aviation is to reduce weight without sacrificing strength. The overall reduction in weight with increased performance at elevated temperatures allows for increased payload, range and maneuverability of aircraft. This explains the efforts aimed at expanding the use of titanium in aircraft construction in the manufacture of engines, the construction of fuselages, the manufacture of skins and even fasteners.
In the construction of jet engines, titanium is mainly used for the manufacture of compressor blades, turbine disks and many other stamped parts. Here, titanium is replacing stainless and heat-treated alloy steels. A saving of one kilogram in engine weight saves up to 10 kg in the total weight of the aircraft due to the lightening of the fuselage. In the future, it is planned to use sheet titanium for the manufacture of casings for engine combustion chambers.
In aircraft construction, titanium is widely used for fuselage parts operating at elevated temperatures. Sheet titanium is used for the manufacture of all kinds of casings, protective sheaths of cables and guides for projectiles. Various stiffening elements, fuselage frames, ribs, etc. are made from alloyed titanium sheets.
Shrouds, flaps, cable sheaths and projectile guides are made from unalloyed titanium. Alloyed titanium is used for the manufacture of the fuselage frame, frames, pipelines and fire barriers.
Titanium is increasingly used in the construction of the F-86 and F-100 aircraft. In the future, titanium will be used to make landing gear doors, hydraulic piping, exhaust pipes and nozzles, spars, flaps, folding struts, etc.
Titanium can be used to make armor plates, propeller blades, and shell boxes.
At present, titanium is used in the construction of military aircraft Douglas X-3 for skin, Republic F-84F, Curtiss-Wright J-65 and Boeing B-52.
Titanium is also used in the construction of civil aircraft DC-7. The Douglas company, by replacing aluminum alloys and stainless steel with titanium in the manufacture of the engine nacelle and fire barriers, has already achieved savings in the weight of the aircraft structure of about 90 kg. Currently, the weight of titanium parts in this aircraft is 2%, and this figure is expected to be increased to 20% of the total weight of the aircraft.
The use of titanium makes it possible to reduce the weight of helicopters. Sheet titanium is used for floors and doors. A significant reduction in the weight of the helicopter (about 30 kg) was achieved by replacing alloyed steel with titanium for sheathing the blades of its rotors.
Navy. The corrosion resistance of titanium and its alloys makes them a highly valuable material at sea. The US Department of the Navy is extensively investigating the corrosion resistance of titanium against exposure to flue gases, steam, oil, and sea water. The high specific strength of titanium is of almost the same importance in naval affairs.
The low specific gravity of the metal, combined with corrosion resistance, increases the maneuverability and range of the ships, and also reduces the cost of maintaining the material part and its repair.
Applications of titanium in the navy include exhaust mufflers for submarine diesel engines, instrument discs, thin-walled tubes for condensers and heat exchangers. According to experts, titanium, like no other metal, is able to increase the life of exhaust mufflers on submarines. For gauge discs exposed to salt water, gasoline or oil, titanium will provide better durability. The possibility of using titanium for the manufacture of heat exchanger tubes is being investigated, which should be corrosion resistant in sea water washing the tubes from the outside, and at the same time withstand the effects of exhaust condensate flowing inside them. The possibility of manufacturing antennas and components of radar installations from titanium, which are required to be resistant to the effects of flue gases and sea water, is being considered. Titanium can also be used for the production of parts such as valves, propellers, turbine parts, etc.
Artillery. Apparently, the largest potential consumer of titanium may be artillery, where intensive research is currently underway on various prototypes. However, in this area, the production of only individual parts and parts made of titanium is standardized. The rather limited use of titanium in artillery with a large scope of research is explained by its high cost.
Various parts of artillery equipment were investigated from the point of view of the possibility of replacing conventional materials with titanium, subject to a reduction in titanium prices. The main attention was paid to parts for which weight reduction is essential (parts carried by hand and transported by air).
Mortar baseplate made from titanium instead of steel. By such a replacement and after some alteration, instead of a steel plate from two halves with a total weight of 22 kg, it was possible to create one part weighing 11 kg. Thanks to this replacement, it is possible to reduce the number of service personnel from three to two. The possibility of using titanium for the manufacture of gun flame arresters is being considered.
Titanium-made gun mounts, carriage crosses and recoil cylinders are being tested. Titanium can be widely used in the production of guided projectiles and missiles.
The first studies of titanium and its alloys showed the possibility of manufacturing armor plates from them. Replacing steel armor (12.7 mm thick) with titanium armor of the same projectile resistance (16 mm thick) makes it possible, according to these studies, to save up to 25% in weight.
High-quality titanium alloys give hope for the possibility of replacing steel plates with titanium plates of equal thickness, which saves up to 44% in weight. Industrial Application titanium will provide greater maneuverability, increase the range of transportation and durability of the gun. Modern level The development of air transport makes obvious the advantages of light armored cars and other vehicles made of titanium. The Artillery Department intends to equip infantry with helmets, bayonets, grenade launchers and hand flamethrowers made from titanium. Titanium alloy was first used in artillery for the manufacture of the piston of some automatic guns.
Transport. Many of the benefits of using titanium in the production of armored materiel apply to vehicles as well.
The replacement of structural materials currently consumed by transport engineering enterprises with titanium should lead to a reduction in fuel consumption, an increase in payload capacity, an increase in the fatigue limit of parts of crank mechanisms, etc. railways it is essential to reduce dead weight. A significant reduction in the total weight of the rolling stock due to the use of titanium will save in traction, reduce the dimensions of the necks and axle boxes.
Weight is also important for trailers. Vehicle. Here, the replacement of steel with titanium in the production of axles and wheels would also increase the payload capacity.
All these opportunities could be realized by reducing the price of titanium from 15 to 2-3 dollars per pound of titanium semi-finished products.
Chemical industry. In the production of equipment for the chemical industry, the corrosion resistance of the metal is of the utmost importance. It is also essential to reduce the weight and increase the strength of the equipment. Logically, it should be assumed that titanium could provide a number of benefits in the production of equipment for transporting acids, alkalis and inorganic salts from it. Additional possibilities for the use of titanium are opening up in the production of such equipment as tanks, columns, filters and all kinds of high-pressure cylinders.
The use of titanium piping can improve the efficiency of heating coils in laboratory autoclaves and heat exchangers. The applicability of titanium for the production of cylinders in which gases and liquids are stored under pressure for a long time is evidenced by the use in microanalysis of combustion products instead of a heavier glass tube (shown in the upper part of the image). Due to its small wall thickness and low specific gravity, this tube can be weighed on smaller, more sensitive analytical balances. Here, the combination of lightness and corrosion resistance improves the accuracy of chemical analysis.
Other applications. The use of titanium is expedient in the food, oil and electrical industries, as well as for the manufacture of surgical instruments and in surgery itself.
Tables for food preparation, steaming tables made of titanium are superior in quality to steel products.
In the oil and gas drilling industry, the fight against corrosion is of great importance, so the use of titanium will make it possible to replace corroding equipment rods less often. In catalytic production and for the manufacture of oil pipelines, it is desirable to use titanium, which retains mechanical properties at high temperatures and has good corrosion resistance.
In the electrical industry, titanium can be used to armor cables due to its good specific strength, high electrical resistance and non-magnetic properties.
In various industries, fasteners of one form or another made of titanium are beginning to be used. Further expansion of the use of titanium is possible for the manufacture of surgical instruments, mainly due to its corrosion resistance. Titanium instruments are superior in this respect to conventional surgical instruments when repeatedly boiled or autoclaved.
In the field of surgery, titanium proved to be better than vitallium and stainless steels. The presence of titanium in the body is quite acceptable. The plate and screws made of titanium for fastening the bones were in the body of the animal for several months, and the bone grew into the threads of the screws and into the hole in the plate.
The advantage of titanium also lies in the fact that muscle tissue is formed on the plate.
Approximately half of the titanium products produced in the world are usually sent to the civil aircraft industry, but its decline after the well-known tragic events is forcing many industry participants to look for new applications for titanium. This material represents the first part of a selection of publications in the foreign metallurgical press devoted to the prospects of titanium in modern conditions. According to one of the leading American manufacturers of titanium RT1, out of the total volume of titanium production on a global scale at the level of 50-60 thousand tons per year, the aerospace segment accounts for up to 40 consumption, industrial applications and applications account for 34, and the military area 16 , and about 10 accounted for the use of titanium in consumer products. Industrial applications of titanium include chemical processes, energy, oil and gas industry, desalination plants. Military non-aeronautical applications include primarily use in artillery and combat vehicles. Sectors with significant use of titanium are the automotive industry, architecture and construction, sporting goods, and jewelry. Almost all titanium in ingots is produced in the USA, Japan and the CIS - Europe accounts for only 3.6 of the global volume. Regional markets for the end use of titanium vary greatly - the most striking example of originality is Japan, where the civil aerospace sector accounts for only 2-3 using 30 of the total consumption of titanium in equipment and structural elements of chemical plants. Approximately 20 of the total demand in Japan comes from nuclear power and in solid fuel power plants, the rest is in architecture, medicine and sports. The opposite picture is observed in the US and Europe, where exclusively great importance has consumption in the aerospace sector - 60-75 and 50-60 for each region, respectively. In the US, traditionally strong end markets are chemicals, medical equipment, industrial equipment, while in Europe the largest share is in the oil and gas industry and the construction industry. The heavy reliance on the aerospace industry has been a long-standing concern for the titanium industry, which is trying to expand titanium applications, especially in the current downturn in civil aviation on a global scale. According to the US Geological Survey, in the first quarter of 2003 there was a significant decline in imports of titanium sponge - only 1319 tons, which is 62 less than 3431 tons in the same period in 2002. The aerospace sector will always be one of the leading markets for titanium, but we in the titanium industry must rise to the challenge and do everything we can to make sure our industry does not development and recession cycles in the aerospace sector. Some of the titanium industry's leading manufacturers see growing opportunities in existing markets, one of which is the subsea equipment and materials market. According to Martin Proko, Sales and Distribution Manager for RT1, titanium has been used in power generation and underwater applications for a long time, since the early 1980s, but only in the last five years have these areas become steadily developing with a corresponding growth in the market niche. In the subsea sector, the growth is primarily driven by drilling operations at greater depths, where titanium is the most suitable material. Its, so to speak, underwater life cycle is fifty years, which corresponds to the usual duration of underwater projects. We have already listed the areas in which an increase in the use of titanium is likely. Howmet Ti-Cast sales manager Bob Funnell notes that the current state of the market can be seen as growth opportunities in new areas such as rotating parts for truck turbochargers, rockets and pumps.
One of our ongoing projects is the development of BAE Butitzer XM777 light artillery systems with a caliber of 155 mm. Nowmet will supply 17 of the 28 structural titanium assemblies for each gun mount, supplied in part marines The US is due to start in August 2004. With a total gun weight of 9,800 pounds of approximately 4.44 tons, titanium accounts for about 2,600 pounds of approximately 1.18 tons of titanium in its design - a 6A14U alloy with a large number of castings is used, says Frank Hrster, head of fire support systems BAE Sy81et8. This XM777 system is to replace the current M198 Newitzer system, which weighs about 17,000 pounds and approximately 7.71 tons. Mass production is planned for the period from 2006 to 2010 - deliveries to the USA, Great Britain and Italy are initially scheduled, but the program may be expanded for deliveries to NATO member countries. John Barber of Timet points out that examples of military equipment that use significant amounts of titanium in their construction are the Abramé tank and the Bradley fighting vehicle. For the past two years, a joint program between NATO, the US and the UK has been underway to intensify the use of titanium in weapons and defense systems. As has been noted more than once, titanium is very suitable for use in the automotive industry, however, the share of this direction is rather modest - about 1 of the total volume of titanium consumed, or 500 tons per year, according to the Italian company Poggipolini, a manufacturer of titanium components and parts for Formula- 1 and racing motorcycles. Daniele Stoppolini, head of research and development at this company, believes that the current demand for titanium in this market segment is at the level of 500 tons, with the massive use of this material in the construction of valves, springs, exhaust systems, transmission shafts, bolts, could potentially rise to the level of almost not 16,000 tons per year He added that his company is just beginning to develop automated production of titanium bolts in order to reduce production costs. In his opinion, the limiting factors, due to which the use of titanium does not expand significantly in the automotive industry, are the unpredictability of demand and the uncertainty with the supply of raw materials. At the same time, a large potential niche for titanium remains in the automotive industry, combining optimal weight and strength characteristics for coil springs and exhaust gas systems. Unfortunately, in the American market, the wide use of titanium in these systems is marked only by a fairly exclusive semi-sport model Chevrolet Corvette Z06, which can in no way claim to be a mass car. However, due to the ongoing challenges of fuel economy and corrosion resistance, the prospects for titanium in this area remain. For approval in the markets of non-aerospace and non-military applications, the UNITI joint venture was recently created in its name, the word unity is played up - unity and Ti - the designation of titanium in the periodic table as part of the world's leading titanium producers - American Allegheny Technologies and Russian VSMPO-Avisma. These markets have been deliberately excluded, said Carl Moulton, president of the new company, as we intend to make the new company a leading supplier to industries using titanium parts and assemblies, primarily petrochemicals and power generation. In addition, we intend to actively market in the fields of desalination devices, vehicles, consumer products and electronics. I believe that our production facilities complement each other well - VSMPO has outstanding capabilities for the production of end products, Allegheny has excellent traditions in the production of cold and hot titanium rolled products. UNITI's share of the global titanium products market is expected to be 45 million pounds, approximately 20,411 tons. The market of medical equipment can be considered a steadily developing market - according to the British Titanium International Group, the annual content of titanium worldwide in various implants and prostheses is about 1000 tons, and this figure will increase, as the possibilities of surgery to replace human joints after accidents or injuries. In addition to the obvious advantages of flexibility, strength, lightness, titanium is highly compatible with the body in a biological sense due to the absence of corrosion to tissues and fluids in the human body. In dentistry, the use of prostheses and implants is also skyrocketing - three times in the last ten years, according to the American Dental Association, largely due to the characteristics of titanium. Although the use of titanium in architecture dates back more than 25 years, its widespread use in this area began only in last years. The expansion of Abu Dhabi Airport in the UAE, scheduled for completion in 2006, will use up to 1.5 million pounds of approximately 680 tons of titanium. Quite a lot of various architectural and construction projects using titanium are planned to be implemented not only in the developed countries of the USA, Canada, Great Britain, Germany, Switzerland, Belgium, Singapore, but also in Egypt and Peru.
The consumer goods market segment is currently the fastest growing segment of the titanium market. While 10 years ago this segment was only 1-2 of the titanium market, today it has grown to 8-10 of the market. Overall, titanium consumption in the consumer goods industry grew at about twice the rate of the entire titanium market. The use of titanium in sports is the longest running and holds the largest share of the use of titanium in consumer products. The reason for the popularity of titanium in sports equipment is simple - it allows you to get a ratio of weight and strength superior to any other metal. The use of titanium in bicycles began about 25-30 years ago and was the first use of titanium in sports equipment. Ti3Al-2.5V ASTM Grade 9 alloy tubes are mainly used. Other parts made from titanium alloys include brakes, sprockets and seat springs. The use of titanium in the manufacture of golf clubs first began in the late 80s and early 90s by club manufacturers in Japan. Prior to 1994-1995, this application of titanium was virtually unknown in the US and Europe. That changed when Callaway introduced its Ruger Titanium titanium stick, called the Great Big Bertha. Due to the obvious benefits and well-thought-out marketing from Callaway, titanium sticks became an instant hit. Within a short period of time, titanium clubs have gone from the exclusive and expensive equipment of a small group of golfers to being widely used by most golfers while still being more expensive than steel clubs. I would like to cite the main, in my opinion, trends in the development of the golf market; it has gone from high-tech to mass production in a short period of 4-5 years, following the path of other industries with high labor costs such as the production of clothing, toys and consumer electronics, the production of golf clubs has gone into countries with the cheapest labor first to Taiwan, then to China, and now factories are being built in countries with even cheaper labor, such as Vietnam and Thailand, titanium is definitely used for drivers, where its superior qualities give a clear advantage and justify a higher price . However, titanium has not yet found very widespread use on subsequent clubs, as the significant increase in costs is not supported by a corresponding improvement in the game. Currently, drivers are mainly produced with a forged striking surface, a forged or cast top and a cast bottom. Recently, the Professional Golf Association ROA allowed an increase the upper limit of the so-called return factor, in connection with which all club manufacturers will try to increase the spring properties of the striking surface. To do this, it is necessary to reduce the thickness of the impact surface and use stronger alloys for it, such as SP700, 15-3-3-3 and VT-23. Now let's focus on the use of titanium and its alloys on other sports equipment. Race bike tubes and other parts are made from ASTM Grade 9 Ti3Al-2.5V alloy. A surprisingly significant amount of titanium sheet is used in the manufacture of scuba diving knives. Most manufacturers use Ti6Al-4V alloy, but this alloy does not provide blade edge durability like other stronger alloys. Some manufacturers are switching to using BT23 alloy.
The retail price of titanium scuba knives is approximately $70-80. Cast titanium horseshoes provide a significant reduction in weight compared to steel, while providing the necessary strength. Unfortunately, this use of titanium did not materialize because the titanium horseshoes sparkled and frightened the horses. Few will agree to use titanium horseshoes after the first unsuccessful experiments. Titanium Beach, based in Newport Beach, California Newport Beach, California, has developed Ti6Al-4V alloy skate blades. Unfortunately, here again the problem is the durability of the edge of the blades. I think that this product has a chance to live if manufacturers use stronger alloys such as 15-3-3-3 or BT-23. Titanium is very widely used in mountaineering and hiking, for almost all items that climbers and hikers carry in their backpacks bottles, cups $20-$30 retail, cooking sets about $50 retail, dinnerware mostly made from commercially pure titanium Grade 1 and 2. Other examples of climbing and hiking equipment are compact stoves, racks and tent mounts, ice axes and ice screws. Arms manufacturers have recently begun producing titanium pistols for both sport shooting and law enforcement applications.
Consumer electronics is a fairly new and rapidly growing market for titanium. In many cases, the use of titanium in consumer electronics is not only due to its excellent properties, but also due to the attractive appearance of the products. Commercially pure Grade 1 titanium is used to make cases for laptop computers, mobile phones, plasma flat screen TVs and other electronic equipment. The use of titanium in speaker construction provides better acoustic properties due to titanium being lighter than steel resulting in increased acoustic sensitivity. Titanium watches, first introduced to the market by Japanese manufacturers, are now one of the most affordable and recognized consumer titanium products. World consumption of titanium in the production of traditional and so-called wearable jewelry is measured in several tens of tons. Increasingly, you can find titanium wedding rings, and of course, people wearing jewelry on the body are simply obliged to use titanium. Titanium is widely used in the manufacture of marine fasteners and fittings, where the combination of high corrosion resistance and strength is very important. Los Angeles-based Atlas Ti manufactures a wide range of these products in VTZ-1 alloy. The use of titanium in the production of tools first began in the Soviet Union in the early 80s, when, on the instructions of the government, light and convenient tools were made to facilitate the work of workers. The Soviet giant of titanium production, the Verkhne-Saldinskoye Metal Processing Production Association, at that time produced titanium shovels, nail pullers, mounts, hatchets and keys.
Later, Japanese and American tool manufacturers began to use titanium in their products. Not so long ago, VSMPO signed a contract with Boeing for the supply of titanium plates. This contract undoubtedly had a very beneficial effect on the development of titanium production in Russia. Titanium has been widely used in medicine for many years. The advantages are strength, corrosion resistance, and most importantly, some people are allergic to nickel, a necessary component of stainless steels, while no one is allergic to titanium. The alloys used are commercially pure titanium and Ti6-4Eli. Titanium is used in the manufacture of surgical instruments, internal and external prostheses, including critical ones such as a heart valve. Crutches and wheelchairs are made from titanium. The use of titanium in art dates back to 1967, when the first titanium monument was erected in Moscow.
At the moment, a significant number of titanium monuments and buildings have been erected on almost all continents, including such famous ones as the Guggenheim Museum, built by architect Frank Gehry in Bilbao. The material is very popular with people of art for its color, appearance, strength and resistance to corrosion. For these reasons, titanium is used in souvenirs and costume jewelry haberdashery, where it successfully competes with such precious metals as silver and even gold. . According to Martin Proko of RTi, the average price of titanium sponge in the US is 3.80 per pound, in Russia it is 3.20 per pound. In addition, the price of metal is highly dependent on the cyclicality of the commercial aerospace industry. The development of many projects could accelerate dramatically if ways can be found to reduce the costs of titanium production and processing, scrap processing and smelting technologies, said Markus Holz, managing director of the German Deutshe Titan. British Titanium agrees that titanium product expansion is being held back by high production costs and many improvements need to be made before titanium can be mass produced. modern technologies.
One of the steps in this direction is the development of the so-called FFC process, which is a new electrolytic process for the production of metallic titanium and alloys, the cost of which is significantly lower. According to Daniele Stoppolini, the overall strategy in the titanium industry requires the development of the most suitable alloys, production technology for each new market and application of titanium.
Sources
Wikipedia - The Free Encyclopedia, WikiPedia
metotech.ru - Metotechnics
housetop.com - House Top
atomsteel.com – Atom technology
domremstroy.ru - DomRemStroy
Since titanium is a metal with good hardness, but low strength, titanium-based alloys have become more widespread in industrial production. Alloys with different grain structure differ in structure and type of crystal lattice.
They can be obtained by providing certain temperature regimes in the production process. And by adding various alloying elements to titanium, it is possible to obtain alloys characterized by higher operational and technological properties.
When adding alloying elements and various types crystal lattices in structures based on titanium can be obtained higher than in pure metal heat resistance and strength. At the same time, the resulting structures are characterized by low density, good anticorrosion properties and good plasticity, which expands the scope of their use.
Characteristics of titanium
Titanium is a light metal that combines high hardness and low strength which complicates its processing. Melting temperature of this material is on average 1665°C. The material is characterized by low density (4.5 g/cm3) and good anti-corrosion ability.
An oxide film with a thickness of several nm is formed on the surface of the material, which excludes corrosion processes titanium in sea and fresh water, atmosphere, oxidation by organic acids, cavitation processes and in structures under tension.
In the normal state, the material does not have heat resistance, it is characterized by the phenomenon of creep at room temperatures. However, in conditions of cold and deep cold, the material is characterized by high strength characteristics.
Titanium has a low modulus of elasticity, which limits its use for the manufacture of structures that require rigidity. In a pure state, the metal has high anti-radiation characteristics and does not have magnetic properties.
Titanium is characterized by good plastic properties and easy to process at room temperature and above. Welded seams made of titanium and its compounds have ductility and strength. However, the material is characterized by intensive processes of absorption of gases when in an unstable chemical state that occurs when the temperature rises. Titanium, depending on the gas with which it combines, forms hydride, oxide, carbide compounds, which have a bad effect on its technological properties.
The material is characterized poor machinability, as a result of its implementation, he within a short period of time sticks to the tool, which reduces its resource. Machining of titanium by cutting is possible using intensive cooling at high feed rates, at low machining speeds and a significant depth of cut. In addition, high-speed steel is selected as a tool for processing.
The material is characterized by high chemical activity, which leads to the use of inert gases when smelting, casting titanium or arc welding.
During use, titanium products must be protected from the possible absorption of gases in the event of an increase in operating temperatures.
titanium alloys
Structures based on titanium with the addition of such alloying elements as:
Structures obtained by deformation of alloys of the titanium group are used for the manufacture of products that undergo mechanical processing.
By strength, they distinguish:
- High-strength materials, the strength of which is more than 1000MPa;
- Structures with medium strength, in the range of values from 500 to 1000 MPa;
- Low strength materials, with strength below 500MPa.
By area of use:
- Structures with corrosion resistance.
- Construction materials;
- Heat resistant structures;
- Structures with high cold resistance.
Types of alloys
According to the alloying elements included in the composition, six main types of alloys are distinguished.
Alloys type α-alloys
Alloys type α-alloys based on titanium with application for alloying aluminum, tin, zirconium, oxygen characterized good weldability, lowering the freezing point of titanium and increasing its fluidity. These properties allow the use of so-called α-alloys for obtaining blanks in a shaped way or when casting parts. The resulting products of this type have high thermal stability, which allows them to be used for the manufacture of critical parts, working in temperature conditions up to 400°С.
With minimal amounts of alloying elements, the compounds are called technical titanium. It is characterized by good thermal stability, and has excellent welding characteristics when carrying out welding work on various machines. The material has satisfactory characteristics for the possibility of cutting. It is not recommended to increase the strength for alloys of this type using heat treatment, materials of this type are used after annealing. Alloys containing zirconium have the highest cost and are highly manufacturable.
Forms of delivery of the alloy are presented in the form of wire, pipes, rolled bars, forgings. The most used material of this class is alloy VT5-1, characterized by medium strength, heat resistance up to 450 ° C and excellent performance when working at low and ultra-low temperatures. This alloy is not practiced to be strengthened by thermal methods, however, its use at low temperatures requires a minimum amount of alloying materials.
Alloys type β-alloys
β-type alloys obtained by alloying titanium vanadium, molybdenum, nickel, in this case, the resulting structures are characterized increased strength in the range from room to negative temperatures in comparison with α-alloys. When using them, the heat resistance of the material increases, its temperature stability, however, reduction of plastic characteristics of alloys of this group.
To obtain stable characteristics, the alloys of this group must be doped with a significant amount the specified elements. Based on the high cost of these materials, the structures of this group have not received wide industrial distribution. Alloys of this group are characterized by resistance to creep, the possibility of increasing strength different ways, the possibility of mechanical processing. However, as the operating temperature rises to 300°С alloys of this group acquire fragility.
Pseudo α-alloys
Pseudo α-alloys, most of whose alloying elements are α-phase components with additions of up to 5% elements of the β group. The presence of the β-phase in alloys adds to the advantages of alloying elements of the α-group the property of plasticity. An increase in the heat resistance of this group of alloys is achieved by using aluminum, silicon and zirconium. The last of the listed elements has a positive effect on the dissolution of the β-phase in the alloy structure. However, these alloys also have limitations, among which good absorption of hydrogen by titanium and the formation of hydrides, with the possibility of hydrogen embrittlement. Hydrogen is fixed in the compound in the form of a hydride phase, reduces the viscosity and plastic characteristics of the alloy and contributes to an increase in the brittleness of the joint. One of the most common materials in this group is titanium alloy brand VT18, which has heat resistance up to 600°C, has good plasticity characteristics. These properties make it possible to use the material for manufacture of compressor parts in the aircraft industry. Heat treatment of the material includes annealing at temperatures of about 1000°C with further air cooling or double annealing, which allows a 15% increase in its tear resistance.
Pseudo β-alloys
Pseudo β-alloys are characterized by the presence after quenching or normalization by the presence of only the β-phase. In the state of annealing, the structure of these alloys represented by the α-phase with a significant amount of alloying components of the β group. These alloys are characterized the highest specific strength index among titanium compounds, have low thermal stability. In addition, the alloys of this group are little susceptible to brittleness when exposed to hydrogen, but they are highly sensitive to the content of carbon and oxygen, which affects the reduction in the ductile and ductile properties of the alloy. These alloys are characterized by poor weldability, a wide range of mechanical characteristics due to the heterogeneity of the composition and low stability at work at high temperatures.The form of release of the alloy is represented by sheets, forgings, rods and strip metal, with the recommended use for a long time at temperatures not exceeding 350°C. An example of such an alloy is BT 35, which is characterized by pressure treatment when exposed to temperature. After hardening, the material is characterized by high plastic characteristics and the ability to deform in the cold state. Carrying out the operation of aging for this alloy causes multiple hardening in the presence of high viscosity.
α+β type alloys
α+β type alloys with possible inclusions of intermetallic compounds are characterized by less brittleness when exposed to hydrites compared to alloys of groups 1 and 3. In addition, they are characterized by greater manufacturability and ease of processing using various methods compared to α-group alloys. When welding using this type of material, annealing is required after the operation is completed to increase the ductility of the weld. The materials of this group are made in the form of strips, sheet metal, forgings, stampings and bars. The most common material in this group is alloy VT6, is characterized by good deformability during heat treatment, reduced probability of hydrogen embrittlement. From this material produce aircraft bearing parts and heat-resistant products for engine compressors in aviation. The use of annealed or heat-hardened VT6 alloys is practiced. For example, parts of a thin-walled profile or sheet blanks are annealed at a temperature of 800 ° C, then cooled in air or left in a furnace.
Titanium alloys based on intermetallic compounds.
Intermetallics are an alloy of two metals, one of which is titanium.
Receipt of products
Structures obtained by casting, carried out in special metal molds under conditions of limited access of active gases, taking into account the high activity of titanium alloys with increasing temperature. Alloys obtained by casting have poorer properties than alloys obtained by deformation. Heat treatment to increase strength is not carried out for alloys of this type, since it has a significant effect on the plasticity of these structures.
Titanium (Titanium), Ti, is a chemical element of group IV of the periodic system of elements of D. I. Mendeleev. Ordinal number 22, atomic weight 47.90. Consists of 5 stable isotopes; artificially radioactive isotopes have also been obtained.
In 1791, the English chemist W. Gregor found a new "earth" in the sand from the town of Menakan (England, Cornwall), which he called Menakan's. In 1795, the German chemist M. Klairot discovered in the mineral rutile a still unknown earth, the metal of which he called Titan [in Greek. mythology, the titans are the children of Uranus (Heaven) and Gaia (Earth)]. In 1797, Klaproth proved the identity of this land with that discovered by W. Gregor. Pure titanium was isolated in 1910 by the American chemist Hunter by reducing titanium tetrachloride with sodium in an iron bomb.
Being in nature
Titanium is one of the most common elements in nature, its content in the earth's crust is 0.6% (weight). It occurs mainly in the form of TiO 2 dioxide or its compounds - titanates. More than 60 minerals are known, which include titanium. It is also found in the soil, in animal and plant organisms. Ilmenite FeTiO 3 and rutile TiO 2 serve as the main raw material for the production of titanium. As a source of titanium, slags from smelting are becoming important titanium magnetites and ilmenite.
Physical and chemical properties
Titanium exists in two states: amorphous - dark gray powder, density 3.392-3.395 g / cm 3, and crystalline, density 4.5 g / cm 3. For crystalline titanium, two modifications are known with a transition point at 885° (below 885°, a stable hexagonal form, above - cubic); t° pl about 1680°; t° kip above 3000°. Titanium actively absorbs gases (hydrogen, oxygen, nitrogen), which make it very brittle. Technical metal lends itself to hot pressure treatment. Perfectly pure metal can be cold rolled. In air at ordinary temperature, titanium does not change; when heated, it forms a mixture of oxide Ti 2 O 3 and nitride TiN. In a stream of oxygen at red heat, it is oxidized to dioxide TiO 2. Reacts with carbon, silicon, phosphorus, sulfur, etc. at high temperatures. Resistant to sea water, nitric acid, wet chlorine, organic acids and strong alkalis. It dissolves in sulfuric, hydrochloric and hydrofluoric acids, best of all in a mixture of HF and HNO 3 . The addition of an oxidizing agent to acids protects the metal from corrosion at room temperature. Tetravalent titanium halides, with the exception of TiCl 4 - crystalline bodies, fusible and volatile in an aqueous solution, hydrolyzed, prone to the formation of complex compounds, of which potassium fluorotitanate K 2 TiF 6 is important in technology and analytical practice. Of great importance are TiC carbide and TiN nitride - metal-like substances, which are distinguished by high hardness (titanium carbide is harder than carborundum), refractoriness (TiC, t ° pl = 3140 °; TiN, t ° pl = 3200 °) and good electrical conductivity.
Chemical element number 22. Titanium.
The electronic formula of titanium is: 1s 2 |2s 2 2p 6 |3s 2 3p 6 3d 2 |4s 2 .
The serial number of titanium in the periodic system of chemical elements D.I. Mendeleev - 22. The element number indicates the charge of a yard, therefore, titanium has a nuclear charge of +22, the mass of the nucleus is 47.87. Titanium is in the fourth period, in a secondary subgroup. The period number indicates the number of electron layers. The group number indicates the number of valence electrons. A side subgroup indicates that titanium belongs to the d-elements.
Titanium has two valence electrons in the s-orbital of the outer layer and two valence electrons in the d-orbital of the pre-outer layer.
Quantum numbers for each valence electron:
4s4sWith halogens and hydrogen, Ti(IV) forms compounds of the TiX 4 type, having sp 3 → q 4 hybridization type.
Titanium is metal. Is the first element of the d-group. The most stable and common is Ti +4. There are also compounds with lower oxidation states -Ti 0, Ti -1, Ti +2, Ti +3, but these compounds are easily oxidized by air, water or other reagents to Ti +4. The detachment of four electrons requires a lot of energy, so the Ti +4 ion does not really exist and Ti(IV) compounds usually include covalent bonds. Ti(IV) is in some respects similar to the elements -Si, Ge, Sn and Pb, especially with Sn.
The most significant for National economy there were and still are alloys and metals that combine lightness and strength. Titanium belongs to this category of materials and, in addition, has excellent corrosion resistance.
Titanium is a transition metal of the 4th group of the 4th period. Its molecular weight is only 22, which indicates the lightness of the material. At the same time, the substance is distinguished by exceptional strength: among all structural materials, it is titanium that has the highest specific strength. Color is silvery white.
What is titanium, the video below will tell:
Concept and features
Titanium is quite common - it takes 10th place in terms of content in the earth's crust. However, it was only in 1875 that a truly pure metal was isolated. Prior to this, the substance was either obtained with impurities, or its compounds were called metallic titanium. This confusion led to the fact that the metal compounds were used much earlier than the metal itself.
This is due to the peculiarity of the material: the most insignificant impurities significantly affect the properties of a substance, sometimes completely depriving it of its inherent qualities.
Thus, the smallest fraction of other metals deprives titanium of heat resistance, which is one of its valuable qualities. And a small addition of a non-metal turns a durable material into a brittle and unsuitable for use.
This feature immediately divided the resulting metal into 2 groups: technical and pure.
- First are used in cases where strength, lightness and corrosion resistance are most needed, since titanium never loses the last quality.
- High purity material used where a material is needed that works at very heavy loads and high temperatures, but at the same time characterized by lightness. This, of course, is aircraft and rocket science.
The second special feature of matter is anisotropy. Some of its physical qualities change depending on the application of forces, which must be taken into account when applying.
Under normal conditions, the metal is inert, does not corrode either in sea water or in sea or city air. Moreover, it is the most biologically inert substance known, due to which titanium prostheses and implants are widely used in medicine.
At the same time, as the temperature rises, it begins to react with oxygen, nitrogen, and even hydrogen, and absorbs gases in liquid form. This unpleasant feature makes it extremely difficult both to obtain the metal itself and to manufacture alloys based on it.
The latter is possible only when using vacuum equipment. The most complex production process has turned a fairly common element into a very expensive one.
Bonding with other metals
Titanium occupies an intermediate position between the other two well-known structural materials - aluminum and iron, or rather, iron alloys. In many respects, the metal is superior to its "competitors":
- the mechanical strength of titanium is 2 times higher than that of iron, and 6 times higher than that of aluminum. In this case, the strength increases with decreasing temperature;
- corrosion resistance is much higher than that of iron and even aluminum;
- at normal temperature titanium is inert. However, when it rises to 250 C, it begins to absorb hydrogen, which affects the properties. In terms of chemical activity, it is inferior to magnesium, but, alas, it surpasses iron and aluminum;
- the metal conducts electricity much weaker: its electrical resistivity is 5 times higher than that of iron, 20 times higher than that of aluminum, and 10 times higher than that of magnesium;
- thermal conductivity is also much lower: 3 times less than iron 1, and 12 times less than aluminum. However, this property results in a very low coefficient of thermal expansion.
Advantages and disadvantages
In fact, titanium has many disadvantages. But the combination of strength and lightness is so in demand that neither the complex manufacturing method nor the need for exceptional purity stop metal consumers.
The undoubted advantages of the substance include:
- low density, which means very little weight;
- exceptional mechanical strength of both the titanium metal itself and its alloys. With increasing temperature, titanium alloys outperform all aluminum and magnesium alloys;
- the ratio of strength and density - specific strength, reaches 30–35, which is almost 2 times higher than that of the best structural steels;
- in air, titanium is coated with a thin layer of oxide, which provides excellent corrosion resistance.
Metal also has its drawbacks:
- Corrosion resistance and inertness only applies to non-active surface products. Titanium dust or shavings, for example, spontaneously ignite and burn at a temperature of 400 C;
- a very complex method of obtaining titanium metal provides a very high cost. The material is much more expensive than iron, or;
- the ability to absorb atmospheric gases with increasing temperature requires the use of vacuum equipment for melting and obtaining alloys, which also significantly increases the cost;
- titanium has poor antifriction properties - it does not work for friction;
- metal and its alloys are prone to hydrogen corrosion, which is difficult to prevent;
- titanium is difficult to machine. Welding it is also difficult due to the phase transition during heating.
Titanium sheet (photo)
Properties and characteristics
Strongly dependent on cleanliness. Reference data describe, of course, pure metal, but the characteristics of technical titanium can vary markedly.
- The density of the metal decreases when heated from 4.41 to 4.25 g/cm3. The phase transition changes the density by only 0.15%.
- The melting point of the metal is 1668 C. The boiling point is 3227 C. Titanium is a refractory substance.
- On average, the tensile strength is 300–450 MPa, but this figure can be increased to 2000 MPa by resorting to hardening and aging, as well as the introduction of additional elements.
- On the HB scale, the hardness is 103 and this is not the limit.
- The heat capacity of titanium is low - 0.523 kJ/(kg K).
- Specific electrical resistance - 42.1 10 -6 ohm cm.
- Titanium is a paramagnet. As the temperature decreases, its magnetic susceptibility decreases.
- Metal as a whole is characterized by ductility and malleability. However, these properties are strongly influenced by oxygen and nitrogen in the alloy. Both elements make the material brittle.
The substance is resistant to many acids, including nitric, sulfuric in low concentrations and almost all organic acids except formic. This quality ensures that titanium is in demand in the chemical, petrochemical, paper industries, and so on.
Structure and composition
Titanium - although a transition metal, and its electrical resistivity is low, nevertheless, it is a metal and conducts electric current, which means an ordered structure. When heated to a certain temperature, the structure changes:
- up to 883 C, the α-phase is stable with a density of 4.55 g / cu. see It is distinguished by a dense hexagonal lattice. Oxygen dissolves in this phase with the formation of interstitial solutions and stabilizes the α-modification - pushes the temperature limit;
- above 883 C, the β-phase with a body-centered cubic lattice is stable. Its density is somewhat less - 4.22 g / cu. see. Hydrogen stabilizes this structure - when it is dissolved in titanium, interstitial solutions and hydrides are also formed.
This feature makes the work of the metallurgist very difficult. The solubility of hydrogen decreases sharply when titanium is cooled, and hydrogen hydride, the γ-phase, precipitates in the alloy.
It causes cold cracks during welding, so manufacturers have to work extra hard after melting the metal to clean it of hydrogen.
About where you can find and how to make titanium, we will tell below.
This video is dedicated to the description of titanium as a metal:
Production and mining
Titanium is very common, so with ores containing metal, and in quite large quantities, there are no problems. The raw materials are rutile, anatase and brookite - titanium dioxide in various modifications, ilmenite, pyrophanite - compounds with iron, and so on.
But it is complex and requires expensive equipment. The methods of obtaining are somewhat different, since the composition of the ore is different. For example, the scheme for obtaining metal from ilmenite ores looks like this:
- obtaining titanium slag - the rock is loaded into an electric arc furnace together with a reducing agent - anthracite, charcoal and heated to 1650 C. At the same time, iron is separated, which is used to obtain cast iron and titanium dioxide in the slag;
- slag is chlorinated in mine or salt chlorinators. The essence of the process is to convert solid dioxide into gaseous titanium tetrachloride;
- in resistance furnaces in special flasks, the metal is reduced with sodium or magnesium from chloride. As a result, a simple mass is obtained - a titanium sponge. This is technical titanium quite suitable for the manufacture of chemical equipment, for example;
- if a purer metal is required, they resort to refining - in this case, the metal reacts with iodine in order to obtain gaseous iodide, and the latter, under the influence of temperature - 1300-1400 C, and electric current, decomposes, releasing pure titanium. Electricity is fed through a titanium wire stretched in a retort, onto which a pure substance is deposited.
To obtain titanium ingots, the titanium sponge is melted down in a vacuum furnace to prevent hydrogen and nitrogen from dissolving.
The price of titanium per 1 kg is very high: depending on the degree of purity, the metal costs from $25 to $40 per 1 kg. On the other hand, the case of an acid-resistant stainless steel apparatus will cost 150 rubles. and will last no more than 6 months. Titanium will cost about 600 r, but is operated for 10 years. There are many titanium production facilities in Russia.
Areas of use
The influence of the degree of purification on the physical and mechanical properties forces us to consider it from this point of view. So, technical, that is, not the purest metal, has excellent corrosion resistance, lightness and strength, which determines its use:
- chemical industry– heat exchangers, pipes, casings, pump parts, fittings and so on. The material is indispensable in areas where acid resistance and strength are required;
- transport industry- the substance is used to make vehicles from trains to bicycles. In the first case, the metal provides a smaller mass of compounds, which makes traction more efficient, in the latter it gives lightness and strength, it is not in vain that a titanium bicycle frame is considered the best;
- naval affairs- titanium is used to make heat exchangers, exhaust silencers for submarines, valves, propellers, and so on;
- in construction widely used - titanium - an excellent material for finishing facades and roofs. Along with strength, the alloy provides another advantage important for architecture - the ability to give products the most bizarre configuration, the ability to shape the alloy is unlimited.
The pure metal is also very resistant to high temperatures and retains its strength. The application is obvious:
- rocket and aircraft industry - sheathing is made from it. Engine parts, fasteners, chassis parts and so on;
- medicine - biological inertness and lightness makes titanium a much more promising material for prosthetics, up to heart valves;
- cryogenic technology - titanium is one of the few substances that, when the temperature drops, only become stronger and does not lose plasticity.
Titanium is a structural material of the highest strength with such lightness and ductility. These unique qualities provide him with an increasingly important role in the national economy.
The video below will tell you where to get titanium for a knife: