Titanium is a new type of bai metal. The performance of titanium is related to the content of impurities such as carbon, nitrogen, hydrogen, and oxygen. The purest titanium iodide contains no more than 0.1% dao, but its strength and plasticity are low. high. The performance of 99.5% industrial pure titanium is: density ρ=4.5g/cubic centimeter, melting point is 1725℃, thermal conductivity λ=15.24W/(mK), tensile strength σb=539MPa, elongation δ=25%, section Shrinkage ψ=25%, elastic modulus E=1.078×105MPa, hardness HB195.
1. High strength
The density of titanium alloy is generally about 4.51g/cm3, which 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 greater than that of other metal structural materials. See Table 7-1, which can produce parts with high unit strength, good rigidity and light weight. The aircraft’s engine components, skeleton, skin, fasteners and landing gear all use titanium alloys.
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. It 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 seawater 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 ; 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 0.1～0.15mm, 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. Low thermal conductivity
The thermal conductivity of titanium λ=15.24W/(m.K) is about 1/4 of nickel, 1/5 of iron, and 1/14 of aluminum. 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 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, resulting in severe friction, adhesion, adhesive wear on the flank of the tool.
Comparison table of commonly used titanium and titanium alloy grades in various countries
|International standard ISO||USA
|Material Name||Chinese standard||USA standard|
|Titanium and titanium alloy sheet||GB/T3621||ASTM B265|
|Titanium and titanium alloy bars||GB/T2965||ASTM B348|
|Titanium and titanium alloy tube||GB/T3624||ASTM B337|
|Titanium and titanium alloy tubes for heat exchangers and condensers||GB/T3625||ASTM B338|
|Titanium and titanium alloy strips and foils||GB/T3622||ASTM B265|
|Titanium and titanium alloy cakes and rings||GB/T16598||ASTM B381|
|Titanium and titanium alloy wire||GB/T3623||ASTM B863|
Titanium and titanium alloy processed materials for surgical implants
Commonly used titanium and titanium alloy grades and chemical composition（GB/T 3620.1-2007）
|Alloy grade||Chemical composition group||Main ingredients/%|
|Chinese standard||USA standard||Russia standard||Janpan Standard|
|TA1ELI||Industrial pure titanium||–||–||–||–||–||–||–||–||–|
|TA1||GR1||BT1-0||TP270||Industrial pure titanium||–||–||–||–||–||–||–||–||–|
|TA1-1||GR1||BT1-00||Industrial pure titanium||≤0.20||–||–||–||–||–||–||–||–|
|TA2ELI||Industrial pure titanium||–||–||–||–||–||–||–||–||–|
|TA2||GR2||TP340||Industrial pure titanium||–||–||–||–||–||–||–||–||–|
|TA3ELI||Industrial pure titanium||–||–||–||–||–||–||–||–||–|
|TA3||GR3||TP450||Industrial pure titanium||–||–||–||–||–||–||–||–||–|
|TA4ELI||Industrial pure titanium||–||–||–||–||–||–||–||–||–|
|TA4||GR4||TP550||Industrial pure titanium||–||–||–||–||–||–||–||–||–|
|Main ingredients/%||Impurities, not more than/%|