As an important structural metal, titanium alloy has excellent comprehensive properties such as low density, high specific strength, corrosion resistance, high temperature resistance, non-magnetic, seawater resistance and marine atmospheric corrosion. It is widely used in aviation, aerospace, ships, weapons, nuclear, chemical, seawater desalination, medical devices, environmental protection and other fields. It is of great significance for equipment lightweight and improving equipment service performance. It is one of the important strategic materials for national defense.
There is a good correspondence between the type and performance of titanium alloy, as shown in Fig. 1. For example, α Titanium alloy has high heat resistance and weldability, while β Titanium alloys have high room temperature strength and cold formability, α+β Two phase titanium alloy has better comprehensive properties.
Heat treatment is an important step to optimize the structure and properties of titanium and titanium alloy in the process of processing. Selecting appropriate heat treatment standards and processes for titanium and titanium alloys is an important condition for titanium and titanium alloy products to obtain the best matching relationship between structure and properties that meet the use.
Currently, the commonly used heat treatment processes in the industry are as follows:
·Common annealing: in alloy β Air cooling or slower cooling after heating at a temperature of 20 ° C to 250 ° C below the transition temperature.
·Complete annealing: at temperatures above the recrystallization temperature but below β Heat treatment of heating and insulation at the transition temperature, followed by air cooling or furnace cooling.
·Double annealing: air cooling to alloy after complete annealing β Air cooled after heating at a temperature of 250 ° C to 450 ° C below the transition temperature.
·Isothermal annealing: in the alloy β Heat and hold at a temperature of 20 ℃ ~ 160 ℃ below the transition temperature, and then transfer to β Air cooling or furnace cooling shall be conducted in the furnace at 350 ℃ ~ 450 ℃ below the transition temperature or after the furnace is cooled to this temperature.
· β Annealing: in the alloy β Annealing is performed at an appropriate temperature above the transition temperature.
·Stress relief annealing: heat treatment that reduces the residual stress of the product without causing recrystallization of the structure.
·Solid solution treatment: heat treatment in which the alloy is heated to an appropriate temperature and kept at this temperature for a sufficient time to completely dissolve the soluble components into the solid solution and maintain an unstable state after quenching.
·Aging treatment: after the solution treatment, it is maintained at an appropriate temperature for a sufficient time to make it precipitate the second phase from the unstable solid solution and cause enhanced heat treatment. The intermetallic compound in the alloy can be precipitated to achieve high strengthening.
·Hot isostatic pressure treatment: in the sealed vessel, titanium and titanium alloy are subjected to high temperature and isotropic static pressure stress process through the simultaneous action of high temperature and high pressure (argon medium), so as to reduce or remove internal porosity, porosity and other defects of titanium and titanium alloy.
