Titanium is an important structural metal developed in the 1950s. Titanium alloy has high strength, good corrosion resistance and high heat resistance. From the 1950s to the 1960s, it was mainly the development of high-temperature titanium alloys used in aero-engines and structural titanium alloys for the body.
In the 1970s, a number of corrosion resistant titanium alloys were developed. Since the 1980s, corrosion resistant titanium alloys and high strength titanium alloys have been further developed. Titanium alloy is mainly used for the manufacture of aircraft engine compressor components, followed by the rocket, missile and high-speed aircraft structure
Titanium alloy is titanium-based alloy with other elements. Titanium has two kinds of homogeneous crystals: 882 ° C for the close-packed hexagonal structure α titanium, 882 ° C above the body-centered cubic β titanium.
Alloying elements according to their impact on the phase transition temperature can be divided into three categories:
① stable α-phase, phase transition temperature to improve the elements of α-stable elements, aluminum, carbon, oxygen and nitrogen. Among them, aluminum is the main alloying element of titanium alloy, which has obvious effect on improving the strength at room temperature and high temperature of the alloy, reducing the specific gravity and increasing the elastic modulus.
② stable β-phase, lower phase transition temperature of the element is β-stable element, and can be divided into two types of crystal and eutectoid. The former is molybdenum, niobium, vanadium, etc .; the latter is chromium, manganese, copper, iron, silicon and so on.
③ phase transition temperature is not a significant element of neutral elements, zirconium, tin and so on.
Oxygen, nitrogen, carbon and hydrogen are the major impurities of titanium alloys. Oxygen and nitrogen in the α phase has a greater solubility, the titanium alloy has a significant strengthening effect, but the plasticity decreased. It is generally stipulated that the content of oxygen and nitrogen in titanium should be 0.15-0.2% and 0.04-0.05% respectively. Hydrogen solubility in the α phase is very small, titanium dissolved in excess of hydrogen will produce hydride, the alloy becomes brittle. Hydrogen content of titanium alloy is usually controlled below 0.015%. The dissolution of hydrogen in titanium is reversible and can be removed by vacuum annealing.