Titanium alloy is an alloy based on titanium and added with other elements. Titanium has two isomorphous crystals: below 882°C, it is α-titanium with a close-packed hexagonal structure, and above 882°C, it is β-titanium with a body-centered cubic structure.
Alloying elements can be divided into three categories based on their influence on phase transformation temperature:
1. Elements that stabilize the α phase and increase the phase transition temperature are α-stabilizing elements, including aluminum, carbon, oxygen, and nitrogen. Among them, aluminum is the main alloying element of titanium alloy. It has obvious effects on improving the normal and high temperature strength of the alloy, reducing the specific gravity and increasing the elastic modulus.
2.Elements that stabilize the β phase and reduce the phase transition temperature are β-stabilizing elements, which can be divided into two types: isomorphous and eutectoid. Products using titanium alloy
The former includes molybdenum, niobium, vanadium, etc.; the latter includes chromium, manganese, copper, iron, silicon, etc.
3.Elements that have little effect on the phase transition temperature are neutral elements, including zirconium, tin, etc.
Oxygen, nitrogen, carbon and hydrogen are the main impurities in titanium alloys. Oxygen and nitrogen have a large solubility in the α phase and have a significant strengthening effect on titanium alloys, but they reduce the plasticity. It is usually stipulated that the oxygen and nitrogen contents in titanium are below 0.15~0.2% and 0.04~0.05% respectively. The solubility of hydrogen in the α phase is very small. Excessive hydrogen dissolved in titanium alloys will produce hydrides, making the alloy brittle. Usually the hydrogen content in titanium alloys is controlled below 0.015%. The dissolution of hydrogen in titanium is reversible and can be removed by vacuum annealing.