Classification of titanium alloy elements

Titanium alloy is an alloy composed of titanium and other elements. Titanium has two kinds of homogeneous and heterogeneous crystals: close packed hexagonal structure below 882 ℃ α Titanium, body centered cubic above 882 ℃ β Titanium.

Alloy elements can be divided into three categories according to their influence on phase transformation temperature:

① Steady α The elements that increase the phase transition temperature are α Stable elements include aluminum, carbon, oxygen and nitrogen. Aluminum is the main alloying element of titanium alloy. It has an obvious effect on improving the strength at room and high temperature, reducing the specific gravity and increasing the elastic modulus.

② Steady β The elements that reduce the phase transition temperature are β Stable elements can be divided into isomorphic and eutectoid types. Products with titanium alloy

The former includes molybdenum, niobium, vanadium, etc; The latter includes chromium, manganese, copper, iron, silicon, etc.

③ The elements that have little effect on the phase transition temperature are neutral elements, such as zirconium, tin and so on.

Oxygen, nitrogen, carbon and hydrogen are the main impurities in titanium alloys. Oxygen and nitrogen in α It has a large solubility in the phase, which has a significant strengthening effect on titanium alloy, but reduces the plasticity. It is generally specified that the contents of oxygen and nitrogen in titanium are less than 0.15 ~ 0.2% and 0.04 ~ 0.05% respectively. Hydrogen in α The solubility in the phase is very small. Too much hydrogen dissolved in titanium alloy will produce hydride and make the alloy brittle. Generally, 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.