Titanium is a new type of metal, and its properties are related to the impurity content of carbon, nitrogen, hydrogen, oxygen, etc. The purest titanium iodide impurity content does not exceed 0.1%, but its strength is low and its plasticity is high. The performance of 99.5% industrial pure titanium is: density ρ= 4.5g/cm3, melting point 172, silicon titanium alloy wear-resistant floor 5 ℃ thermal conductivity λ= 15.24W/(m.K), tensile strength σ B=539MPa, elongation δ= 25%, reduction in area ψ= 25%, elastic modulus E=1.078 × 105MPa, hardness HB195.

(1) High strength

The density of titanium alloy is generally around 4.5g/cm3, which is only 60% of that of steel. The strength of pure titanium is only 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 higher than that of other metal structural materials, as shown in Table 7-1, which can produce components with high unit strength, good rigidity, and light weight. At present, titanium alloy is used for the engine components, frame, skin, fasteners, and landing gear of aircraft.

(2) High thermal intensity

The usage temperature is several hundred degrees higher than that of aluminum alloy, and it can still maintain the required strength at medium temperatures. It can work for a long time at temperatures of 450-500 ℃. These two types of titanium alloys still have high specific strength in the range of 150-500 ℃, while aluminum alloy has a significant decrease in specific strength at 150 ℃. 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 atmospheres and seawater media, and its corrosion resistance is much better than stainless steel; Has particularly strong resistance to pitting, acid corrosion, and stress corrosion; Has excellent corrosion resistance to organic substances such as alkali, chloride, chlorine, nitric acid, sulfuric acid, etc. 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 ℃. 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, and other gases in the atmosphere. When the carbon content is greater than 0.2%, hard TiC will form in the titanium alloy; When the temperature is high, the interaction with N will also form a TiN hard surface layer; At temperatures above 600 ℃, titanium absorbs oxygen to form a hardened layer with high hardness; An increase in hydrogen content can also form a brittle layer. 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 prone to adhesion with the friction surface.

(6) Low thermal conductivity and elastic modulus

Thermal conductivity of titanium λ= 15.24W/(m.K) titanium alloy products are about 1/4 of nickel, 1/5 of iron, and 1/14 of aluminum, and the thermal conductivity of various titanium alloys is about 50% lower than that of titanium. The elastic modulus of titanium alloy is about half of that of steel, so it has poor rigidity and is prone to deformation. It is not suitable for making slender rods and thin-walled parts. During cutting, the amount of rebound on the machined surface is large, about 2-3 times that of stainless steel, causing severe friction, adhesion, and adhesive wear on the back face of the cutting tool.