(1) 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.
(2) High intensity
Titanium alloys are currently used in aircraft engine components, skeletons, skins, fasteners and landing gear. The density of titanium alloy is generally about 4.5g/cm3, which is only 60% of steel. The strength 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, which can produce zero-components with high unit strength, good rigidity and light weight.
(3) Good low temperature performance
Titanium alloys are also an important low temperature structural material. 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.
(4) high heat intensity
Titanium alloys can operate at temperatures up to 500 ° C and aluminum alloys at temperatures below 200 ° C. 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.
(5) Small thermal conductivity and small elastic modulus
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. 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.
(6) Large chemical activity
Titanium has a large chemical activity and produces strong chemical reactions with O, N, H, CO, CO2, water vapor, and ammonia in the atmosphere. 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.