Precipitation behavior during the solution-aging process of Ti-15V-3Cr-3Sn-3Al titanium alloy

Type titanium alloy has good cold and hot processing performance, and can obtain higher mechanical properties through solid solution - aging treatment.At the same time, the heat treatment and deep quenching and penetration of titanium alloy make it gradually replace + two-phase titanium alloy as the main material of large forgings, playing an increasingly important role in aerospace and civil industry.

In recent years, in order to understand the effect of solution-aging treatment on the properties of titanium alloy and its strengthening mechanism, a large number of scholars in various countries have studied the microstructure, mechanical properties and formation process of precipitation phase of titanium alloy of different grades.The type, quantity and distribution of precipitated phase during aging process are closely related to aging process.The precipitation behavior of Ti-5Al-5Mo-5V-3Cr-O.5Fe titanium alloy during aging was studied on the nanometer scale by TEM and 3DAP.The results showed that the alloy in phase region quenching will form stable precipitated phase, at lower temperature isothermal annealing, these precipitated phase coarsing and forming ordered components precipitated phase, accompanied by stable phase formation.

The precipitated phase was decomposed and phase of different morphology was further formed when annealed at higher temperature.On the other hand, the content and morphology of the precipitated phase also have a direct impact on the mechanical properties of the material. Different heat treatment processes were carried out on Ti-5Al-4zr-4Mo-2Cr-2SN-1Fe titanium alloy.It has been found that alpha lath in the original tissue can effectively improve the strength and plasticity.In the + two-phase solution, the percentage of phase decreased and the size of spherical phase increased, but no significant change in the performance was observed. After a long time of solid solution above the phase transition point, the destructive strain decreases greatly.The +(+B) spicular phase after solid solution continuously reduces the strength, but has no effect on the plasticity. The aging sample has better compression performance than other samples.The formation of precipitated phase in aging is a complicated process.The solid solution aging of TI-10V-2Fe-3Al was applied to the nucleation position of the precipitated phase during the precipitation process.The process is studied and it is proved that phase provides the core for the heterogeneous nucleation of phase.In the study of Ti-6.8Mo-4.5Fe-1.5Al, it was found that phase nucleated at a certain distance near the/interface.Since phase precipitation tends to ostracize Al (which is stable but not stable), it helps to nucleate a region of Al enrichment near phase during isothermal aging.

Ti-15V-3Cr-3Sn-3Al titanium alloy selected in this study is a new type of titanium alloy, which has high specific strength and good cold forming property. After multiple aging treatment, it can obtain high strength and plastic toughness, and has good welding performance. At present, it has been widely used in many fields.In order to obtain excellent strength/toughness matching for the alloy, the alloy was subjected to the strength/toughness treatment of deformable heat treatment, the microstructure of the material and the precipitation behavior during the aging process were studied, and the internal relations and mutual influence rules among the aging process, precipitation behavior and mechanical properties were revealed.The results showed that after solution treatment at 980°C/ 0.5h, a large number of metastable Martensite 'phases appeared in the tissue, and different amounts and forms of phase were precipitated by subsequent aging treatment.