Titanium is a new metal, the performance of titanium is related to the content of impurities such as carbon, nitrogen, hydrogen, oxygen, etc. The impurity content of pure titanium iodide is not more than 0.1%, but its strength is low and plasticity is high. 99.5% industrial pure titanium has the following properties: density ρ=4.5g/cm3, melting point 1800℃, thermal conductivity λ=15.24W/(m.K), tensile strength σb=539MPa, elongation δ=25%, sectional shrinkage ψ=25%, modulus of elasticity E=1.078×105MPa, and hardness HB195.
(1)High specific strength
The density of titanium alloy is generally around 4.5g/cm3, only 60% of steel, the strength of pure titanium is close to the strength of ordinary steel, some high strength titanium alloy exceeds the strength of many alloy structural steel. Therefore, the specific strength (strength / density) of titanium alloy is much greater than other metal structural materials, can be made of high strength, good rigidity, light weight parts, components. At present, the aircraft engine components, skeleton, skin, fasteners and landing gear, etc. are used titanium alloy.
(2) High thermal strength
The use of temperature than the aluminum alloy several hundred degrees, in the medium temperature can still maintain the required strength, can be in 450 ~ 500 ℃ temperature long-term work of these two types of titanium alloys in 150 ℃ ~ 500 ℃ range still has a very high than the strength, while the aluminum alloy in 150 ℃ than the strength dropped significantly. The working temperature of titanium alloy can reach 500℃, while aluminum alloy is below 200℃.
(3)Good corrosion resistance
Titanium alloy working in the humid atmosphere and seawater medium, its corrosion resistance is far better than stainless steel; pitting, acid corrosion, stress corrosion resistance is particularly strong; excellent corrosion resistance to alkali, chloride, chlorine organic substances, sulfuric acid, etc.. But titanium has a reduction of 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) Chemical activity is large
The chemical activity of titanium is large, and the atmosphere O, N, H, CO, CO2, water vapor, ammonia, etc. produce strong chemical reaction. When the carbon content is greater than 0.2%, it will form hard TiC in titanium alloy; when the temperature is higher, the action with N will also form TiN hard surface layer; above 600 ℃, titanium absorbs oxygen to form a hardened layer with high hardness; hydrogen content rises, it will also form a brittle layer. Absorption of gas and the resulting hard and brittle surface layer depth of up to 0.1 ~ 0.15 mm, the degree of hardening of 20% to 30%. The chemical affinity of titanium is also large, easy to produce adhesion phenomena with the friction surface.
(6) Small thermal conductivity, small modulus of elasticity
The thermal conductivity of titanium λ=15.24W/(m.K) is about 1/4 of nickel, 1/5 of iron and 1/14 of aluminum, while the thermal conductivity of various titanium alloys is about 50% lower than that of titanium. The modulus of elasticity of titanium alloy is about 2 to 3 times that of stainless steel, causing severe friction, adhesion and bonding wear on the tool's rear face.
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