Although the properties of titanium alloy castings are different from those of other metals, such as steel and aluminum, many properties such as strength, plasticity and fatigue properties are lower than those of forgings.The main reason is that there are holes in titanium casting, which seriously affect the strength, plasticity and fatigue strength of the casting.On the other hand, the microstructure of the casting is large.Because castings are cooled at high temperatures, especially in two-phase alpha + beta castings, the grain size is so large that it seriously affects the properties of the castings.In order to improve and improve the performance of castings and ensure the reliability of castings, the following treatment processes can be used:
1. Thermal isostatic pressure treatment
Thermal isostatic treatment is to make the defects in the casting diffused and welded together under a certain high temperature and high pressure, improve the thick structure of the casting, and improve the plasticity and fatigue strength of the casting.Microstructure of ZT4 titanium alloy cast before and after thermal isostatic pressure.Mechanical properties of titanium alloy castings before and after thermal isostatic pressure treatment.Because of this, in recent years, thermostatic pressure treatment technology has been used as a necessary procedure to produce high-quality titanium alloy castings for aerospace.With the extensive application of thermostatic treatment in titanium alloy castings, the application range of titanium alloy precision castings in aerospace will be further expanded.
2. Heat treatment
Changes in the microstructure of alloys by heat treatment have been noticed in recent years.Although for two phase microstructure of titanium alloy castings in alpha + beta temperature range is very stable, but as long as the heating temperature is close to, or more than one beta transition temperature, can through the beta solid solution treatment, then take the medium speed or fast cooling, or loop heat treatment, resulting in low proportion of alpha, tiny slice of flake alpha and alpha cluster, even get basket weaving structure, so as to greatly improve the performance of high frequency fatigue on the titanium alloy castings.
3. Thermochemical treatment
This is a new process developed in recent years. The basic principle of this process is to dissolve about 3% hydrogen in titanium alloy casting, form a kind of low eutectic gold with titanium, and then conduct various heat treatment and hydrogen action on titanium alloy casting, so as to obtain a kind of very fine microstructure completely different from the cast microstructure.Because of the improvement of the internal structure of titanium alloy casting, the plasticity of its tensile strength shed at room temperature can be comparable to that of the deformed alloy.Therefore, it is a new technology which has great pioneering significance for titanium casting.
It is absolutely believed that, with the development of a series of research work, titanium alloy precision casting technology currently existing in all aspects of the ideal problem, will be solved, the production will be rapidly increased, titanium alloy precision casting will be used throughout all sectors of industry, especially in the civil industry