Studies On Hot Work Ability Of Ti53311S,TP650 And Zr-4 Alloy

In order to determine the hot working parameter,optimize the structure and property of alloy,hot work ability of the alloy must be studied.In this work,the near-alpha titanium alloy Ti53311S,TiC particles reinforced titanium matrix composite TP650 and Zr-4 alloy were hot compressed in a broad range of temperature.The flow behavior was described by the constitutive equation and numerical simulation,the deformation activation energy were calculated and the relationship between the flow stress and deformation parameters was studied systematically.The microstructure of the deformed specimens were studied by the optical microscope and the transmission electron microscope,the effect of deformation temperature,strain rate and deformation ratio on the microstructure of deformed specimens and the deformation mechanism were analyzed,and the relationship between the deformation parameter and the microstructure evolution was defined.The processing maps of Ti53311S,TP650 and Zr-4 alloy were plotted by Dynamic Material Model and the principle of system stability analysis,and the different regime in processing map was analyzed by the microstructure observation,the hot work ability was studied profoundly and the deformation parameters were optimized,in order to select the "safety" regime and instruct the hot procedure.Lastly,the deformation mechanism map for Ti53311S, TP650 and Zr-4 alloy were plotted,which is the guide for the hot procedure of like-kind alloy.From this work,it was found that:The hot deformation behaviors of Ti53311S,TP650 and Zr-4 alloy were described by the power exponent and hyperbolic sine constitutive equation respectivly,and the deformation activation energy of Ti53311S alloy were calculated to be 507KJ/mol in (α+β)phase field and 241KJ/mol inβphase field,the deformation activation energy of TP650 alloy were calculated to be 691KJ/mol in(α+β)phase field and 202KJ/mol inβphase field,and the deformation activation energy of Zr-4 alloy were calculated to be 387KJ/mol.In addition,the flow stress model of Ti53311S,TP650 and Zr-4 alloy were established,and the fitting precision of which is satisfying.Ti53311S alloy is sensitive to the strain rate and different softening mechanism occurred at(α+β)phase.Superplasticity was observed at the strain rate of 0.001s^-1,it is mean that this alloy can be superplastic forged.At middle strain rate of 0.1～1s^-1,the microstructure of the specimens is spheroidization,and with the increase of deformation ratio,spheroidizing is strengthening.Dynamic recrystallization occurred at 980℃and 0.001-0.1s^-1,and the nucleation is related with the redistribution of dislocations and the subgrain which created by polygonization.However,dynamic recovery which controlled by climb motion and cross slip is the deformation mechanism of Ti53311S alloy above the transformation temperature.Superplasticity was observed in TP650 alloy also at 900～980℃and 0.001～0.01s^-1.Dynamic recrystallization and spheroidizing of small quantity ofαphase occurred at 0.01-10s^-1,and the dynamic recrystallization is related with the formation, rotation and aggregation of subgrain.The addition of TiC particles is help for the formation of structure cell and stabilization of subgrain and close grain by drageffect. Above the transformation temperature,the director softening mechanism is dynamic recovery at low strain rate of 0.001s^-1,dynamic recrystallization is the primary softening mechanism at 0.01-10s^-1,and the recrystal grain generated priority at the cross point and grain boundary.The deformation characteristic of TP650 alloy atβphase field is depending on the deformation of titanium matrix,it is due to the softening of matrix by the start of more slip system atβphase,the TiC particles turned in the matrix and the hardening effect is weakening.Dynamic recrystallization of Zr-4 alloy occurred inαphase and(α+β)phase,and the nucleation mechanism is intercrystal projection.The precipitated phase of Zr(CrFe)₂ play an important role in the recrystallization nucleation by hindering the interface migration.The effect of strain rate on the softening mechanism is important at high temperature rang of(α+β)phase,the softening mechanism is not obvious at low strain rate of 0.005-0.05s^-1and dynamic recrystallization occurred at high strain rate.When deformed in high temperatureαphase regime and middle strain rate,the higher efficiency of power dissipation is result form the inconsistent of the intercrystalline deformation,and the deformation shear zone is obvious at 850℃,50s^-1. Thus,in order to form the uniform structure,high strain rate should be avoided in the deformation of Zr-4 alloy.The research for Ti53311S and TP650 alloy showed that the good hot work ability of near-alpha titanium alloy and near-alpha titanium matrix composite can be obtained at(α+β)phase.The addition of TiC particles in near-alpha titanium alloy expended the field of dynamic recrystallization.Adiabatic shear zone is easy to occur at high strain rate and low temperature due to the low heat conductivity of titanium alloy.The non-uniform delivery of heat which produced by plastic deformation created phase transformation shear zone in Ti53311S alloy.