The properties of titanium alloys

Titanium is a new type of metal. The performance of titanium is related to the content of impurities such as carbon, nitrogen, hydrogen, and oxygen. The purest titanium iodide has an impurity content of no more than 0.1%, but its strength is low and its plasticity is high. The performance of 99.5% industrial pure titanium is: density ρu003d4.5g/cm3, melting point 1800℃, thermal conductivity λu003d15.24W/(mK), anti-titanium is a new type of metal, and the performance of titanium is related to the carbon and nitrogen contained in it. , Hydrogen, oxygen and other impurity content, the purest titanium iodide impurity content does not exceed 0.1%, but its strength is low, and its plasticity is high. The properties of 99.5% industrial pure titanium are: density ρu003d4.5g/cm3, melting point 1800℃, thermal conductivity λu003d15.24W/(mK), tensile strength σbu003d539MPa, elongation δu003d25%, and section shrinkage Rate ψu003d25%, elastic modulus Eu003d1.078×105MPa, hardness HB195. '(1) High specific strength' 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, and some high-strength titanium alloys exceed the strength of many alloy structural steels. Therefore, the specific strength (strength/density) of titanium alloy is much greater than that of other metal structural materials. See Table 7-1, which can produce parts and components with high unit strength, good rigidity, and light weight. At present, titanium alloys are used in aircraft engine components, skeletons, skins, fasteners, and landing gear. (2) High thermal strength. The service temperature is several hundred degrees higher than that of aluminum alloy. It can still maintain the required strength at medium temperature. It can work for a long time at a temperature of 450～500℃. These two types of titanium alloys are in the range of 150℃～500℃ There is still a high specific strength inside, while the specific strength of aluminum alloy decreases significantly at 150°C. The working temperature of titanium alloy can reach 500℃, while that of aluminum alloy is below 200℃. (3) Good corrosion resistance. Titanium alloy works in humid atmosphere and sea water. Its corrosion resistance is far better than stainless steel. It has strong resistance to pitting corrosion, acid corrosion and stress corrosion. It is resistant to alkali, chloride and chlorine. The organic materials, nitric acid, sulfuric acid, etc. have excellent corrosion resistance. However, titanium has poor corrosion resistance to reducing oxygen and chromium salt media.　　(4) Good low-temperature performance 　　Titanium alloy can still maintain its mechanical properties at low and ultra-low temperatures. Titanium alloys with good low temperature performance and extremely low interstitial elements, such as TA7, can maintain a certain degree of plasticity at -253°C. Therefore, titanium alloy is also an important low-temperature structural material.　　(5) High chemical activity 　　 Titanium has high chemical activity, and it produces a strong chemical reaction with O, N, H, CO, CO2, water vapor, ammonia, etc. in the atmosphere. When the carbon content is more than 0.2%, it will form hard TiC in the titanium alloy; when the temperature is higher, it will also form a hard surface layer of TiN when it interacts with N; when the temperature is above 600℃, titanium absorbs oxygen to form a hardened layer with high hardness ; When the hydrogen content increases, an embrittlement 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 a high chemical affinity and is easy to adhere to the friction surface. (6) The thermal conductivity is small and the modulus of elasticity is small. The thermal conductivity of titanium λu003d15.24W/(mK) is about 1/4 of nickel, 1/5 of iron, 1/14 of aluminum, and the thermal conductivity of various titanium alloys The coefficient is about 50% lower than the thermal conductivity of titanium. The modulus of elasticity 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 springback of the machined surface during cutting is very large, about 2～3 of stainless steel. Times, resulting in severe friction, adhesion, and adhesive wear on the flank of the tool. Previous: Classification of titanium alloys Next: Uses of titanium alloys