| Powder superalloy has excellent mechanical properties at high temperature and is the preferred material for hot-end unit such as turbine disc of advanced aeroengine.However,due to its high degree of alloying,high volume fraction of precipitation strengthening phaseγ’phase,large deformation resistance,narrow hot working window,and difficult microstructure control.In this paper,a new powder superalloy CSU-A1（A1 alloy for short）for turbine disk was studied.The Gleeble thermal simulation compression test and electron backscattering diffraction（EBSD）and backscattered electron（BSE）microstructure characterization techniques were used.The thermal deformation behavior and microstructure evolution of A1 alloys in hot isostatic pressing（HIP）,hot extrusion（HEX）and slow cooling treatment（SC）were co MPared and analyzed,which provided theoretical basis and data support for microstructure control and optimization of hot working parameters of the key preparation process of the alloy.Specific research results are as follows:（1）The flow stress curves obtained from the thermal simulation experiments of A1alloy with three states were modified by friction-temperature.It was found that the flow curves under the condition of low temperature and high rate deformation had obvious dynamic recrystallization（DRX）characteristics,that is,the flow stress in the plastic deformation stage rose rapidly to the peak stress,and then gradually decreased to the steady state stage.Under the condition of high temperature and low rate deformation,it has obvious DRV characteristics,that is,the flow stress curve has no obvious peak stress,and the whole is relatively stable.The Arrenhius model is used to establish the peak stress constitutive model,the strain compensation constitutive model and the DRX dynamic model of the three states A1 alloy.From the evaluation results of the relative error between the predicted value and the revised value,the model can predict the deformation resistance of the alloy well.It is found that the flow stress of the HEX state is higher than that of the HIP state,while the flow stress of the SC state is lower than that of the HEX state at low temperature,indicating that adjusting the size ofγ’phase can reduce the deformation resistance at low temperature.（2）During the thermal deformation of A1 alloy,progressive subcrystal rotation continuous dynamic recrystallization（CDRX）is the auxiliary nucleation mechanism,and strain-induced discontinuous dynamic recrystallization（DDRX）is the main DRX mechanism.However,the dominant factors of DRX nucleation are different for A1 alloys with different states.HIP A1 alloy is the original particle boundary（PPB）induced DDRX nucleation,and increasing temperature and strain rate can promote higher dynamic recrystallization volume fraction(Xdrx)at the initial deformation stage.In the HEX A1 alloy,theγ’phase induced DDRX nucleation,and theγ’phase at the grain boundary promoted DRX,while theγ’phase delayed DRX.At low temperature and high rate,γ’phase induced CDRX and grain boundary induced DDRX nucleation are common,while at high temperature and low rate,grain boundary induced DDRX nucleation is dominant.（3）The grain size of A1 alloy is mainly affected by PPB andγ’phases.At the early stage of deformation,the unbroken PPB grains mainly grow,and PPB is more likely to be broken under the condition of high temperature,high rate and high strain.Under the condition of low rate and high temperature deformation,the critical strain ofγ’phase dissolution will be reduced,while large deformation will make the dissolution and precipitation ofγ’phase repeated,resulting in unstable microstructure,prone to abnormal grain growth（AGG）and secondary grain refinement.（4）Combined with the hot working diagram,the hot working parameters of A1 alloy were optimized.Extrusion parameters can be controlled in the temperature of1090°C～1123°C,strain rate of 100.27 s-1～10 s-1;The forging parameters can be controlled in 1065°C～1104°C,and the strain rate is 10-0.15 s-1～1 s-1.According to the microstructure analysis,the optimal parameters of A1 alloy forging in SC state are 0.1 s-1-1040°C/1070°C and 1 s-1-1100°C.Increasing theγ’phase size in the alloy is beneficial to reducing the forging temperature. |
