Properties of Titanium Alloys

Titanium is a new type of metal, titanium properties and the content of carbon, nitrogen, hydrogen, oxygen and other impurities, the purest titanium iodide impurity content of no more than 0.1%, but its strength is low, high plasticity. 99.5% industrial pure titanium properties are: density ρ = 4.5g/cm3, the melting point of 1800 ° C, the coefficient of thermal conductivity λ = 15.24W / (m.K), the tensile strength of σb = 539MPa. Elongation δ=25%, section shrinkage ψ=25%, modulus of elasticity E=1.078×105MPa, hardness HB195.

  (1)High specific strength

  Titanium alloy density is generally in 4.5g/cm3 or so, only 60% of steel, pure titanium strength close to the strength of ordinary steel, some high-strength titanium alloys more than many alloy structural steel strength. Therefore, the specific strength of titanium alloys (strength / density) is much greater than other metal structural materials, see Table 7-1, can produce unit of high strength, good rigidity, lightweight parts and components. Currently aircraft engine components, skeleton, skin, fasteners and landing gear, etc. are using titanium alloys.

  (2)High thermal strength

  The use of temperature than the aluminum alloy a few hundred degrees higher in the medium temperature can still maintain the required strength, can be in the temperature of 450-500 ℃ long-term work of these two types of titanium alloys in the range of 150 ℃ to 500 ℃ still have a high specific strength, and aluminum alloy at 150 ℃ than the strength of the obvious decline. The working temperature of titanium alloy can reach 500 ℃, aluminum alloy is below 200 ℃.

  (3)Good corrosion resistance

  Titanium alloy in the humid atmosphere and seawater media work, its corrosion resistance is far better than stainless steel; pitting, acid corrosion, stress corrosion resistance is particularly strong; alkali, chloride, chlorine organic items, nitric acid, sulfuric acid, etc. have excellent corrosion resistance. But titanium has a reducing oxygen and chromium salt media corrosion resistance is poor.

  (4) Good low-temperature performance

  Titanium alloy in low temperature and ultra-low temperature, can still maintain its mechanical properties. Good low-temperature performance, the gap element is very low titanium alloy, such as TA7, in -253 ℃ can also maintain a certain degree of plasticity. Therefore, titanium alloy is also an important low-temperature structural materials.

  (5) Great chemical activity

  Titanium's chemical activity, and the atmosphere O, N, H, CO, CO2, water vapor, ammonia and other strong chemical reactions. Carbon content greater than 0.2%, will form hard TiC in titanium alloys; higher temperature, and N role will also form TiN hard surface layer; in 600 ℃ or more, titanium absorbs oxygen to form a hardened layer of high hardness; hydrogen content rises, but also the formation of embrittlement layer. Absorption of gas and the resulting hard brittle surface layer depth of up to 0.1 ~ 0.15 mm, the degree of hardening is 20% ~ 30%. Titanium's chemical affinity is also large, easy to produce adhesion with the friction surface.

  (6) small thermal conductivity, small modulus of elasticity

  Titanium's thermal conductivity λ = 15.24W/(m.K) is about 1/4 of nickel, 1/5 of iron, 1/14 of aluminum, and various titanium alloys have a thermal conductivity of about 50% lower than that of titanium. The modulus of elasticity of titanium alloy is about 1/2 of steel, so its rigidity is poor, easy to deform, not suitable for making slender rods and thin-walled parts, and the rebound of the machined surface when cutting is very large, about 2 to 3 times as much as stainless steel, resulting in intense friction, adhesion and bonding wear of the tool after the cutter surface.

  Titanium alloy has high strength and low density, good mechanical properties, toughness and corrosion resistance is very good. In addition, titanium alloys have poor process performance, cutting and machining difficulties, in thermal processing, very easy to absorb impurities such as hydrogen, oxygen, nitrogen and carbon. There is also poor abrasion resistance, the production process is complex. The industrialized production of titanium was started in 1948. The needs of the aviation industry development, so that the titanium industry to an average annual growth rate of about 8% development. At present, the world's annual output of titanium alloy processing materials has reached more than 40,000 tons, titanium alloy grade nearly 30 kinds. The most widely used titanium alloy is Ti-6Al-4V (TC4), Ti-5Al-2.5Sn (TA7) and industrial pure titanium (TA1, TA2 and TA3).

  Titanium alloys are mainly used to make aircraft engine compressor parts, followed by structural parts for rockets, missiles and high-speed aircraft.In the mid-1960s, titanium and its alloys have been applied in general industry to make electrodes for the electrolysis industry, condensers for power stations, heaters for petroleum refineries and seawater desalination as well as environmental pollution control devices, etc. Titanium and its alloys have become a kind of resistant material. Titanium and its alloys have become a corrosion-resistant structural material. It is also used to produce hydrogen storage materials and shape memory alloys.