Pure titanium, also called industrial pure titanium or commercial pure titanium, is graded according to the content of impurity elements. It has excellent stamping process performance and welding performance, is insensitive to heat treatment and organizational type, and has a certain strength under satisfactory plastic conditions. Its strength mainly depends on the content of interstitial elements oxygen and nitrogen. The properties of 99.5% industrial pure titanium are: density P=4.5g/cm3, melting point is 1800°C, thermal conductivity coefficient λ=15.24W/(M.K), tensile strength σ b=539MPa, elongation: δ =25%, cross-sectional shrinkage ψ=25%, elastic modulus E=1.078×105MPa, hardness HB195. Titanium alloy is an alloy composed of titanium and other elements. It is a relatively young metal with a history of only sixty or seventy years from its discovery to the present. Titanium alloy materials have the characteristics of light weight, high strength, low elasticity, high temperature resistance and corrosion resistance. They are mainly used in aircraft engines, rockets, missiles and other components.
Titanium has two isomorphs. Titanium is an isomer with a melting point of 1720°C. When it is below 882°C, it presents a close-packed hexagonal lattice structure, called a titanium; when it is above 882°C, it presents a body-centered cubic lattice structure, called B titanium. By using the different characteristics of the above two structures of titanium, appropriate alloying elements are added to gradually change its phase transition temperature and phase content to obtain titanium alloys with different structures (itanium alloys).
Titanium alloy elements can be divided into three categories according to their influence on the phase transition temperature: ① Elements that stabilize the a phase and increase the phase transition temperature are a stabilizing elements, including aluminum, magnesium, oxygen and nitrogen. Among them, aluminum is the main alloying element of titanium alloy, which has a significant effect on improving the room temperature and high temperature strength of the alloy, reducing the specific gravity and increasing the elastic modulus. ② Elements that stabilize the B phase and reduce the phase transition temperature are B stabilizing elements. It can be divided into two types: isomorphous and eutectoid. The former includes molybdenum, niobium, vanadium, etc.; the latter includes chromium, manganese, copper, silicon, etc. ③ Elements that have little effect on the phase transition temperature are neutral elements, such as zirconium and tin.
