| TiAl-based alloys have drawn increasing attention due to their excellent properties,such as low density,high specific strength,high specific stiffness,etc..They have developed into a novel candidate of light high temperature structural materials in a wide array of applications,like hypersonic aircraft and thermal protection materials.However,inherent brittleness and high temperature oxidation of TiAl-based alloys have extremely limited their applications as large size excellent thin sheets,and so on.The powder metallurgy,especially the pre-alloyed powder technology,can eliminate casting defects and provide excellent raw materials.Therefore,obtaining high-purity low-oxygen spherical gas atomized powder and preparing powder metallurgy sheets with superior performance would be the key to further expand the application range of TiAl-based alloys.In this paper,Ti43.5Al5Nb1V1Y pre-alloyed powders,which were densified by vacuum hot-pressing sintering,were prepared by gas atomization process.OM,laser particle size analyzer,SEM with BSE mode and EDS spectra,TEM,X-ray diffraction and other analytical methods were used to characterize and analyze the pre-alloyed powders,Ti43.5Al5Nb1V1Y alloys after the vacuum hot-pressing sintering and Ti43.5Al5Nb1V1Y alloys after high temperature deformation.Isothermal hot compression simulation tests for Ti43.5Al5Nb1V1Y alloys were carried out at the conditions of deformation temperature of 1050 ?-1200 ?,strain rate of 0.001 s-1-0.5 s-1 and deformation of 50 % by Gleeble-3500 thermal physical simulation tester.The results show that the Ti43.5Al5Nb1V1Y pre-alloyed powders prepared by the gas atomization process have fine particle size and high sphericity.The compact macrostructure of Ti43.5Al5Nb1V1Y alloy prepared by vacuum hot-pressing sintering is dense and the surface morphology is flat without pores.The microstructure is uniform and the internal microstructure is nearly ? microstructure characteristics,mainly composed of the ? phase,?2 phase and YAl2 phase.The changes of flow stress were inversely proportional and proportional to the deformation temperature and strain rate,respectively.The initial strain flow curves show obvious work hardening characteristics,and compared to other alloys,the dynamic recrystallization curve features of the alloy were more obvious.According to the Arrhenius relation,the material constants ?,?,n,A and Q are calculated and the constitutive equation of the vacuum hot-pressing sintering Ti43.5Al5Nb1V1Y alloy is established.The thermal deformation activation energy of the vacuum hotpressing sintering Ti43.5Al5Nb1V1Y alloy is 320.861 k J/mol.The experimental data of the constitutive model of peak stress are in good agreement with the calculated values.The Ti43.5Al5Nb1V1Y alloy deformation depends mainly on the ? phase.The dynamic recrystallization is the main softening mechanism of the Ti43.5Al5Nb1V1Y alloy.Dynamic recrystallization ? grain size is proportional to the change of deformation temperature and inversely proportional to the change of strain rate.Cracking is the main instability method for Ti43.5Al5Nb1V1Y alloy.When true strain is 0.5,the hot processing map of Ti43.5Al5Nb1V1Y alloys is based on the Prasad instability criterion and Dynamic Material Model,and the ideal deformation conditions are deformation temperatures of 1080 ?-1200 ? and strain rates of 0.0015 s-1-0.04 s-1. |
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