Classification of titanium alloy
Titanium is an isomer of isotopes with a melting point of 1668 ° C. It is a close-packed hexagonal lattice structure below 882 ° C and is called α titanium. It is a body-centered cubic lattice structure above 882 ° C and is called β titanium. Titanium alloys with different microstructures are obtained by adding appropriate alloying elements and gradually changing the phase transition temperature and phase content by using the different characteristics of the above two structures of titanium. At room temperature, titanium alloys have three kinds of matrix structures, and titanium alloys are classified into the following three types: α alloys, (α + β) alloys and β alloys.
Alpha titanium alloy
It is a single-phase alloy composed of α phase solid solution. It is α phase at normal temperature or at a higher practical application temperature. It is structurally stable and has higher wear resistance than pure titanium and has strong oxidation resistance. At 500 ° C ~ 600 ° C temperature, its strength and creep resistance are maintained, but heat treatment can not be strengthened, the room temperature strength is not high.
Beta titanium alloy
It is a single-phase alloy composed of a β-phase solid solution.
It has higher strength without heat treatment. After quenching and aging, the alloy is further strengthened. The room temperature strength can reach 1372~1666 MPa. However, the thermal stability is poor and it is not suitable for use at high temperature.
++β titanium alloy
It is a dual-phase alloy with good comprehensive properties, good structural stability, good toughness, plasticity and high temperature deformation properties. It can perform hot pressure processing well, and can be quenched and aged to strengthen the alloy. The strength after heat treatment is about 50% to 100% higher than that of the annealed state; the high temperature strength is high, and it can work for a long time at a temperature of 400 ° C to 500 ° C, and its thermal stability is inferior to that of the α titanium alloy.
The most commonly used of the three titanium alloys are α-titanium alloy and α+β-titanium alloy; the α-titanium alloy has the best machinability, the α+β-titanium alloy is the second, and the β-titanium alloy is the worst. The alpha titanium alloy is coded as TA, the beta titanium alloy is coded as TB, and the alpha + beta titanium alloy is coded as TC.
Titanium alloys can be classified into heat-resistant alloys, high-strength alloys, corrosion-resistant alloys (titanium-molybdenum, titanium-palladium alloys, etc.), low-temperature alloys, and special functional alloys (titanium-iron hydrogen storage materials and titanium-nickel memory alloys). . The composition and properties of typical alloys are shown in the table.
Heat Treatment Titanium alloys can be obtained by adjusting the heat treatment process to obtain different phase compositions and microstructures. It is generally believed that the fine equiaxed structure has good plasticity, thermal stability and fatigue strength; the needle-like structure has high durability, creep strength and fracture toughness; the equiaxed and needle-like mixed structure has better comprehensive performance.