Classification of titanium alloys

Titanium is an allotrope with a melting point of 1720°C. When it is lower than 882°C, it has a close-packed hexagonal lattice structure, called α titanium; when it is above 882°C, it has a body-centered cubic lattice structure, called β titanium. Utilizing the different characteristics of the above two structures of titanium, adding appropriate alloying elements to gradually change the phase transition temperature and phase content. Titanium is an allotrope with a melting point of 1720°C and close packing below 882°C. The hexagonal lattice structure is called α titanium; the body-centered cubic lattice structure above 882℃ is called β titanium. Utilizing the different characteristics of the above two structures of titanium, adding appropriate alloying elements to gradually change the phase transformation temperature and phase content to obtain titanium alloys with different structures (itanium alloys). At room temperature, titanium alloys have three matrix structures, and titanium alloys are divided into the following three categories: α alloys, (α+β) alloys and β alloys. China is represented by TA, TC, and TB respectively. Alpha titanium alloy is a single-phase alloy composed of alpha phase solid solution. It is alpha phase regardless of normal temperature or higher practical application temperature. The structure is stable, the wear resistance is higher than that of pure titanium, and the oxidation resistance is strong. . At a temperature of 500°C to 600°C, it still maintains its strength and creep resistance, but cannot be strengthened by heat treatment, and its room temperature strength is not high. β titanium alloy is a single phase alloy composed of 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 to 1666 MPa; but the thermal stability is poor, so it is not suitable for Use at high temperature. α+β titanium alloy is a dual-phase alloy with good comprehensive properties, good structure stability, good toughness, plasticity and high-temperature deformation properties, and can perform hot press processing well, and can be quenched and aging to strengthen the alloy . The strength after heat treatment is about 50%-100% higher than the annealed state; the high-temperature strength is high, and it can work for a long time at a temperature of 400℃～500℃, and its thermal stability is inferior to that of α titanium alloy.　　 The three most commonly used titanium alloys are α titanium alloy and α + β titanium alloy; α titanium alloy has the best machinability, followed by α + p titanium alloy, and β titanium alloy is the worst. The alpha titanium alloy code is TA, the beta titanium alloy code is TB, and the alpha + beta titanium alloy code is TC. Titanium alloys can be divided 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), etc. . The composition and properties of typical alloys are shown in the table.　　 Heat treatment Titanium alloy can obtain different phase composition and structure by adjusting the heat treatment process. It is generally believed that the small equiaxed structure has better plasticity, thermal stability and fatigue strength; the needle-like structure has higher endurance strength, creep strength and fracture toughness; the equiaxed and needle-like mixed structure has better comprehensive properties. Previous: Titanium alloy elements Next: Properties of titanium alloys