Titanium alloy elements can be divided into three categories according to their influence on the phase transition temperature:
①The element that stabilizes the α phase and raises the phase transition temperature is the α stable element, including aluminum, carbon, oxygen and nitrogen. Among them, aluminum is the main alloy element of titanium alloy, which has obvious effects on improving the normal temperature and high temperature strength of the alloy, reducing the specific gravity, and increasing the elastic modulus.
②The element that stabilizes the β phase and lowers the phase transition temperature is the β stable element, and can be divided into two types: isomorphic and eutectoid. Products using titanium alloys include molybdenum, niobium, vanadium, etc .; the latter include chromium, manganese, copper, iron, silicon, etc.
③ Elements that have little effect on the phase transition temperature are neutral elements, such as zirconium and tin.
Oxygen, nitrogen, carbon and hydrogen are the main impurities of titanium alloys. Oxygen and nitrogen have greater solubility in the α phase, which has a significant strengthening effect on titanium alloys, but reduces the plasticity. Generally, the content of oxygen and nitrogen in titanium is 0.15 to 0.2% and 0.04 to 0.05%, respectively. Hydrogen has very little solubility in the alpha phase. Too much hydrogen dissolved in the titanium alloy will produce hydrides, making the alloy brittle. Usually the hydrogen content in titanium alloy is controlled below 0.015%. The dissolution of hydrogen in titanium is reversible and can be removed by vacuum annealing.