High strength: The density of titanium alloys is generally around 4.51g/cm3, which is only 60% of that of steel. Some high-strength titanium alloys exceed the strength of many alloy structural steels. Therefore, the specific strength (strength/density) of titanium alloys is much greater than that of other metal structural materials, and parts with high unit strength, good rigidity and light weight can be made. Aircraft engine components, skeletons, skins, fasteners and landing gear all use titanium alloys.
Good corrosion resistance: Titanium alloys work in humid atmospheres and seawater media, and their corrosion resistance is much better than that of stainless steel; they are particularly resistant to pitting, acid corrosion and stress corrosion; they have excellent corrosion resistance to alkali, chloride, chlorine organic substances, nitric acid, sulfuric acid, etc. However, titanium has poor corrosion resistance to reducing oxygen and chromium salt media.
Good low-temperature performance: Titanium alloys can still maintain their mechanical properties at low and ultra-low temperatures. Titanium alloys with good low-temperature performance and extremely low interstitial elements, such as TA7, can still maintain a certain plasticity at -253°C. Therefore, titanium alloys are also an important low-temperature structural material.
High chemical activity: Titanium has high chemical activity and reacts strongly with O2, N2, H2, CO, CO2, water vapor, ammonia, etc. in the atmosphere. When the carbon content is greater than 0.2%, hard TiC will be formed in the titanium alloy; when the temperature is high, it will also form a hard TiN surface layer when it reacts with N; above 600°C, titanium absorbs oxygen to form a hardened layer with high hardness; when the hydrogen content rises, a brittle layer will also be formed. The depth of the hard and brittle surface layer produced by absorbing gas can reach 0.1-0.15 mm, and the degree of hardening is 20%-30%. Titanium also has high chemical affinity and is prone to adhesion to the friction surface.
Low thermal conductivity elasticity: The thermal conductivity coefficient 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 coefficients of various titanium alloys are about 50% lower than that of titanium. The elastic modulus of titanium alloy is about 1/2 of that of steel, so it has poor rigidity and is easy to deform. It is not suitable for making slender rods and thin-walled parts. The springback of the processed surface is very large during cutting, about 2 to 3 times that of stainless steel, causing severe friction, adhesion, and bonding wear on the back face of the tool.
