According to the phase composition, titanium alloys can be divided into three categories: α alloy, (α + β) alloy and β alloy, which are represented by TA, TC and TB respectively in China.
The results are as follows: 1. The α alloy contains a certain amount of elements with stable α phase, which is mainly composed of α phase in equilibrium state. Alpha alloy has low specific gravity, good thermal strength, good weldability and excellent corrosion resistance, but it has low strength at room temperature. It is usually used as heat-resistant and corrosion-resistant materials. α - alloys can be divided into total α - alloys (TA7), near α - alloys (ti-8al-1mo-1v) and α - alloys with a small amount of compounds (Ti-2.5Cu).
2. (α + β) alloy contains a certain amount of stable α phase and β phase elements, and the microstructure of the alloy in equilibrium state is α phase and β phase. (α + β) alloy has medium strength and can be strengthened by heat treatment, but its weldability is poor. (α + β) alloys are widely used, and Ti-6Al-4V Alloy accounts for more than half of all titanium products.
3. β alloy contains a lot of stable β phase elements, which can keep all high temperature β phase to room temperature. In general, β alloys can be divided into heat treatable β alloys (metastable β alloys and near metastable β alloys) and heat stable β alloys. The heat treatable β - alloy has excellent plasticity in quenched state, and its tensile strength can reach 130-140 kgf / mm ~ 2 by aging treatment. Beta alloys are usually used as high strength and toughness materials. The disadvantages are heavy ratio, high cost, poor welding performance and difficult machining.