Powder Metallurgy Preparation And Properties Of High Si Content High Temperature Titanium Alloy

High temperature titanium alloy is one of the main development directions of aerospace materials.At present,the research of 600 ? high temperature titanium alloy in China is backward and cannot meet the requirements of future aerospace vehicles development.The high temperature titanium alloy with high Si content cast by Ukraine has reached the international advanced level in design and application,which has good strength,but the plasticity is slightly worse.The purpose of this study is to improve the mechanical properties of high temperature titanium alloy with high Si content by powder metallurgy method.Firstly,Ti-8Al-2Si-2Zr and Ti-6.5Al-1.4Si-0.5Mo-2Zr-2Sn alloys were designed and the titanium alloy ingots were prepared by vacuum arc remelting(VAR).Then,the powders were prepared by plasma rotating electrode process(PREP)with different rotating speed.The relationship between rotating speed and physical and chemical properties of powder was studied.Investigate the phase composition,morphology and microstructure of the powder.Near fully density titanium alloy was prepared by hot isostatic pressing technique.Finally,in order to reduce the size of silicide and get uniform structure,the samples were forged at different temperatures.Then,different heat treatment process were designed to deal with the sample,and trying to find the best heat treatment process,in order to obtain better mechanical properties.The result shows that the composition distribution of titanium alloy ingot prepared by VAR is uniform and the content of alloy elements meets the requirements of national standard,through a unique way for pressing electrode.Microstructure of the ingot is lamellar structure with small amounts of silicide particles disperse in the matrix.The size distribution of the powders accords with the normal distribution.The sphericity of the powder is excellent,and almost no hollow ball and satellite ball.With the increasing of rotating speed,the proportion of small particles increases dramatically.The phase composition of powder is ?' phase.And it is mainly composed of peritectic and small amount of dendrite structures.Compared with the alloy ingot,the elements of the powders have a slight loss;the content of O is less than 0.1%.It is beneficial to obtain high-performance powder titanium alloy,and the ?transition temperatures of two kinds of pre-alloyed powders are 1047 ? and 997 ?respectively.The densification of alloy powder affected by the parameter of hot isostatic pressing process.In the study,the powder metallurgy reach to near full density after hot isostatic pressing,and the mechanical properties of the alloy are much better than those of the cast alloy.After forging and heat treatment,the Ti5Si3 phase is uniformly distributed in the alloy matrix,and the tensile strength and plasticity of the alloy are obviously improved.