Study On Thermal Deformation Behavior And Microstructure And Properties Of Sheet Of High Temperature Titanium Alloy Reinforced By Nano-Y₂O₃

Due to its low density,high specific strength and good thermal strength,high temperature titanium alloys have become important structural materials in aerospace.Replacing a large amount of nickel-based alloys with titanium alloys can reduce the weight of the components at the same strength without affecting its service performance,so it has considerable application potential in the high temperature resistant part of the aircraft engine.However,at present,high-temperature titanium alloys have limited performance due to poor stability and insufficient antioxidant capacity above 600°C.In this study,the research object is Ti-6Al-4Sn-7Zr-0.8Mo-1Nb-1W-0.25Si near-αhigh-temperature titanium alloy with 0.5wt%nano-Y₂O₃ added;as-cast alloy deformed at high temperature to study the microstructure evolution and drawn the hot-worked drawing;on this basis,the as-cast alloy is directly rolled to study the microstructure and properties of the annealed sheet after rolling and the microstructure of the heat-treated annealed sheet.The thermophysical simulation of high-temperature titanium alloy with nano-Y₂O₃reinforced Ti-Al-Sn-Zr-Mo-Nb-W-Si shows that it has temperature and strain rate sensitivity,and the thermal deformation activation energies of the alloys were caculated is 657.849 kJ/mol and 405.997 kJ/mol in the（α+β）andβphase region,respectively;and the constitutive equations of the corresponding phase regions were calculated.Analysis of the hot deformed microstructure shows that the main deformation mechanism in the（α+β）phase region is the dynamic spheroidization of theαphase and the dynamic recovery of theβphase;and theβphase region is mainly the Dynamic recrystallization（DRX）and part of theβphase Dynamic recover（DRV）.The analysis of the thermal processing map shows that in the（α+β）phase region,950℃⁹65℃,0.001⁰.4s-1 and965℃¹010℃,0.02⁰.4s-1（region I and II）and the regions of 1010℃¹070℃and0.03¹s-1（region III）in theβphase region are suitable for hot working.On this basis,the as-cast alloy is directly spliced,and the rolling processes are three-pass rolling at 950℃,three-pass rolling at 1050℃,and two passes at 1050℃.A high-temperature titanium alloy sheet with good denaturing ability and no crack is obtained.In the annealed sheet microstructure,the basket structure is mainly composed,and the equiaxedαphase and the sheetαphase appear in different processes,forming a mixed structure,and the three-pass rolling at 950℃to 1050℃occurs.Micro-texture of[21?1?0]and[0001]directions.The tensile strength at room temperature of the three-pass rolled annealed sheet at 1050℃reached 1168 MPa,which was 23.3%higher than that of the as-cast alloy,and the tensile strength at 650℃was 642 MPa,which was 15.1%higher than that of the as-cast alloy.The heat treatment of the three-pass rolled annealed sheet at 1050℃was carried out.It was found that with the increase of solid solution temperature,the content of primaryαphase decreased,and theαphase of grain boundary decreased gradually.With the increase of cooling rate,the content of primaryαphase decreased,and the length decreased and the ratio is reduced,and the amount of secondary phase precipitation decreases;after aging,more secondaryαphase precipitates.And the aging temperature increases,the width of the secondaryαincreases.Comparing the average hardness of the heat treated and the original annealed sheets,it was found that 970℃+2h+AC solid solution,700℃+4h aging hardness value maximum 457.75HV,990℃+2h+AC aging after the minimum hardness of 379.5HV,and the hardness of the annealed sheet was424.5HV.It was found that the changes in the morphology and content of primary alpha and secondary alpha phases under different conditions have an effect on the hardness properties of the heat treatment annealed sheets.