The Study On Tensile Behavior Of Ti-Al-Sn-Zr-Mo-Nb-W-Si High Temperature Titanium Alloy At 700℃

With the rapid development of space industry in China,the flying speed of short-time high-speed aircraft has been continuously improved.The traditional long-term high temperature titanium alloys have been unable to meet the requirements of high-speed aircraft,while the short-term high-temperature titanium alloy applied at 650～700 ℃ has become a research hotspot.In the early stage,novel Ti-Al-Sn-Zr-Mo-Nb-W-Si short-term high temperature titanium alloys was designed by adding different contents of Nb,Mo and W to the Ti-Al-Sn-Zr-Mo-Si high temperature titanium alloy,the effects of alloy composition and heat treatment on microstructure and mechanical properties were studied systematically,but the properties of alloys above 650 °C and even 700 °C have not been studied.Therefore,the Ti-6.5Al-2Sn-4Zr-x(Mo-Nb-W)-Si short-time high-temperature titanium alloy was studied in this paper,and the relationship between composition-microstructure-performance at 700 ℃ and the effect of heat treatment on the microstructure of the alloy were investigated systematically.And the research on the deformation and fracture behavior of the alloy at 700 ℃ was carried out.The main results were drawn as follows:The microstructure and properties of the invesgated alloys after single-stage annealing℃βtreatment were studied,it was found that after simple annealing,the alloy obtained bimodal structure composed of equiaxed ap phase and lamellarβt structure.The proper addition of Mo can increase the tensile strength of the alloy at 700 ℃,and the addition of Nb,W can improve the yield strength of the alloy at 700 ℃.Moreover,compared to 600 ℃and 650 °C,the strengthening effect of Mo element is weakened at 700 ℃,and that of Nb element and W element on the alloy is enhanced.When the Kp value was between 0.3-0.4 and the contents of Mo,Nb,W were controlled in 2 wt%,2-4 wt%,1-2 wt%respectively,the mechanical properties of the alloy at 700 ℃ are well matched,the yield strength exceeds 330 MPa,the tensile strength exceeds 530 MPa,and the elongation is greater than 3 5%.The microstructure and mechanical properties of the alloy treated by different heat treatment processes were studied,it was found that after solution aging treatment,the alloy obtained a lamellar structure composed of coarse original β grains and a phase.With the increase of Kp value,the content and size of a phase in the alloy decrease,the tensile strength and yield strength increase at room temperature,and the elongation decreases.And at 700 ℃,the tensile strength of the alloy increases,and the yield strength shows a fluctuating trend.Compared with the single stage annealed alloy,the phase size of the alloy treated by solution aging treatment is larger,and the high temperature property is better at 700 ℃,but the performance at room temperature is worse.The in-situ tensile deformation behavior of alloys at high temperature were studied.It is found that when tensiled at 700 ℃,1M2N1W alloy presented microvoid coalescence intergranular fracture characteristic,2M2N2W alloy has both intergranular fracture characteristics and transgranular fracture characteristics,4M2N1W alloy has no obvious cracks in the whole process,but only deformation occurs.As the Kp value increases,the difficulty of alloy nucleation increases,and fracture is less likely to occur.