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 has an impurity content of not more than 0.1% but its strength is low and its plasticity is high. The properties of 99.5% industrial pure titanium are: density ρ=4.5g/cm3, melting point 172, silicon-titanium alloy wear-resistant floor 5℃ thermal conductivity λ=15.24W/(mK), tensile strength σb=539MPa, elongation δ=25%, reduction of area ψ=25%, elastic modulus E=1.078×105MPa, hardness HB195.
Performance advantages of titanium alloy
(1) High 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 the strength 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 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 intensity
The service temperature is several hundred degrees higher than that of aluminum alloy. It can still maintain the required strength at medium temperature, and can work for a long time at a temperature of 450～500℃. These two types of titanium alloys are still very high in the range of 150℃～500℃. Specific strength, 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 moist atmosphere and sea water medium, its corrosion resistance is far better than stainless steel; it is particularly resistant to pitting corrosion, acid corrosion, and stress corrosion; it is resistant to alkali, chloride, chlorine organic substances, nitric acid, sulfuric acid It has excellent corrosion resistance. However, titanium has poor corrosion resistance to media with reducing oxygen and chromium salts.
(4) 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 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 produces strong chemical reactions with O, N, H, CO, CO2, water vapor, ammonia, etc. in the atmosphere. When the carbon content is greater than 0.2%, it will form hard TiC in the titanium alloy; when the temperature is higher, it will also form a TiN hard surface layer when it interacts with N; when the temperature is above 600℃, titanium absorbs oxygen to form a hardened layer with high hardness ; The increase in hydrogen content will also form an embrittlement layer. The depth of the hard and brittle surface layer produced by absorbing gas can reach 0.1 to 0.15 mm, and the degree of hardening is 20% to 30%. Titanium also has a high chemical affinity and is easy to adhere to the friction surface.
(6) Small thermal conductivity and small elastic modulus
The thermal conductivity of titanium λ=15.24W/(mK) Titanium alloy products are about 1/4 of nickel, 1/5 of iron, and 1/14 of aluminum. The thermal conductivity of various titanium alloys is about lower than that of titanium. 50%. 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 to make slender rods and thin-walled parts. The springback of the processed surface during cutting is very large, about 2～3 of stainless steel. Times, causing severe friction, adhesion, and adhesive wear on the flank of the tool.