Properties of titanium alloy
Titanium is a new type of metal. The properties of titanium are related to the content of impurities such as carbon, nitrogen, hydrogen and oxygen. The purest titanium iodide impurity content does not exceed 0.1%, but its strength is low and its plasticity is high. The performance of 99.5% industrial pure titanium is: density ρ=4.5g/cm3, melting point is 1725°C, thermal conductivity λ=15.24W/(mK), tensile strength σb=539MPa, elongation δ=25%, section The shrinkage ratio ψ = 25%, the elastic modulus E = 1.078 × 105 MPa, and the hardness HB 195.
The density of titanium alloy is generally around 4.51g/cm3.
It is only 60% of steel. The density of pure titanium is close to that of ordinary steel. Some high-strength titanium alloys exceed the strength of many alloy structural steels. Therefore, the specific strength (strength/density) of titanium alloy is much larger than that of other metal structural materials. See Table 7-1 for parts with high unit strength, good rigidity and light weight. Titanium alloys are used for aircraft engine components, skeletons, skins, fasteners and landing gear.
High heat strength
The use temperature is several hundred degrees higher than that of aluminum alloy, and the required strength can be maintained at moderate temperatures. The long-term operation of these two types of titanium alloys at temperatures of 450 to 500 ° C is still high in the range of 150 ° C to 500 ° C. Specific strength, while the specific strength of aluminum alloy at 150 ° C is significantly reduced. Titanium alloys can operate at temperatures up to 500 ° C and aluminum alloys at temperatures below 200 ° C.
Good corrosion resistance
Titanium alloy works in moist atmosphere and seawater medium, and its corrosion resistance is much better than that of stainless steel; it is particularly resistant to pitting, acid etching and stress corrosion; organic substances for alkali, chloride and chlorine, nitric acid, sulfuric acid Such as excellent corrosion resistance. However, titanium has poor corrosion resistance to a medium having a reducing oxygen and a chromium salt.
Good low temperature performance
Titanium alloys retain their mechanical properties at low and ultra-low temperatures. Titanium alloys with good low-temperature properties and extremely low interstitial elements, such as TA7, retain a certain degree of plasticity at -253 °C. Therefore, titanium alloy is also an important low temperature structural material.
Large chemical activity
Titanium has great chemical activity, and it is O, N, H in the atmosphere.
Titanium alloy products
Titanium alloy products
, CO, CO2, water vapor, ammonia, etc. produce a strong chemical reaction. When the carbon content is more than 0.2%, hard TiC is formed in the titanium alloy; when the temperature is high, the TiN hard surface layer is formed by the action of N; when it is above 600 ° C, the titanium absorbs oxygen to form the hard layer with high hardness. When the hydrogen content rises, an embrittlement layer is also formed. The hard and brittle surface layer produced by absorbing gas can reach a depth of 0.1 to 0.15 mm and a degree of hardening of 20% to 30%. Titanium also has a large chemical affinity and is liable to adhere to the friction surface.
Low thermal conductivity
The thermal conductivity of titanium λ = 15.24 W / (m. K) is about 1/4 of nickel, 1 / 5 of iron, 1 / 14 of aluminum, and the thermal conductivity of various titanium alloys is about 50% lower than that of titanium. The elastic modulus of titanium alloy is about 1/2 of that of steel, so its rigidity is poor and easy to deform. It is not suitable to make slender rods and thin-walled parts. The amount of springback of the machined surface during cutting is very large, about 2 to 3 of stainless steel. Double, causing severe friction, adhesion, and bond wear on the flank of the tool