Classification of titanium alloys

Titanium is a homoisomer, melting point of 1720℃, in less than 882℃ in a dense hexagonal lattice structure, known as α titanium; At 882℃ above the body - centered cubic structure, known as β titanium. By using the different characteristics of the above two structures of titanium and adding appropriate alloying elements, the phase transition temperature and phase separation content of titanium were gradually changed to obtain different microstructure of itanium alloys. At room temperature, titanium alloy has three kinds of matrix structure, titanium alloy is also divided into the following three types: α alloy '(α+β) alloy and β alloy. China is represented by TA, TC and TB respectively.

Alpha titanium alloy
It is a single-phase alloy composed of α phase solid solution, whether at general temperature or at high practical application temperature, are α phase, stable structure, wear resistance is higher than pure titanium, strong oxidation resistance. At the temperature of 500℃ ~ 600℃, it still maintains its strength and creep resistance, but can not be enhanced by heat treatment, the room temperature strength is not high.

Beta titanium alloy
It is a single phase alloy composed of β phase solid solution. It has high strength without heat treatment. After quenching and aging, the alloy is further strengthened, and the strength of the alloy at room temperature can reach 1372 ~ 1666 MPa. But the thermal stability is poor, should not be used at high temperature.

Alpha + beta titanium alloy
It is a two-phase alloy, has good comprehensive properties, good structure stability, good toughness, plasticity and high temperature deformation properties, can be better for hot pressure processing, quenching, aging to strengthen the alloy. The strength after heat treatment is about 50% ~ 100% higher than that of annealing state. High temperature strength, can work at 400℃ ~ 500℃ for a long time, its thermal stability is inferior to α titanium alloy.

The most commonly used of the three titanium alloys are α titanium alloy and α+β titanium alloy; The machinability of α titanium alloy is the best, α+ P titanium alloy is the second, β titanium alloy is the worst. α titanium alloy is code-named TA, β titanium alloy is code-named TB, α+β titanium alloy is code-named TC.

Titanium alloy can be divided into heat resistant alloy, high strength alloy, corrosion resistant alloy (titanium-molybdenum, titanium-palladium alloy, etc.), low temperature alloy and special function alloy (titanium-iron hydrogen storage material and titanium - nickel memory alloy), etc. The composition and properties of typical alloys are shown in the table. Different phase composition and microstructure of titanium alloy can be obtained by adjusting heat treatment process. It is generally believed that the fine equiaxed structure has good plasticity, thermal stability and fatigue strength. The acicular structure has high endurance strength, creep strength and fracture toughness. Equiaxed and acicular mixed tissues have better comprehensive properties.