Hot Deformation Behavior and Deformation Mechanism of Hot Extruded FGH96 Superalloy
FGH96 is the second generation of damage tolerance powder metallurgy superalloy in China,with a maximum service tem-perature of 700 ℃.Due to its excellent comprehensive mechanical properties,corrosion resistance and high temperature oxidation re-sistance,FGH96 superalloy has become the first choice for the preparation of high thrust ratio advanced aero-engine turbine disc,ring and other hot end parts in China.However,due to its high alloying degree,its thermal processing performance is poor,and its thermal deformation behavior has a great influence on its micro-structure evolution and properties.Therefore,researching the hot deformation behavior of this superalloy and its hot working window has great significance,and for FGH96 superalloy research focused on based on the hot compression experimental data,build the constitutive equation,to set up the hot processing maps,and for FGH96 superalloy energy dissipation,dislocation movement and deformation mechanism of content less reported.Therefore,the hot deformation behav-ior of hot extruded FGH96 superalloy was studied by hot compression experiment,and the change law of hot deformation activation en-ergy and strain rate sensitive index was analyzed in this paper.Based on dynamic materials model(DMM),the hot processing maps in-cluding the safety region and instability region was established.By introducing the material parameters of FGH96 superalloy into Rua-no-Wadsworth-Sherby(R-W-S)mechanism diagram,the deformation mechanism diagram of FGH96 superalloy at different tempera-tures was constructed,and the quantitative relationship between the flow stress value and the grain size during the high temperature de-formation was given.The micro-structure was observed by optical microscopy(OM)and transmission electron microscopy(TEM).The original micro-structure of FGH96 superalloy used in this paper was relatively uniform,and the average grain size was about 9 μm.The hot compression experiments of hot extruded FGH96 superalloy were carried out by Gleeble-3500 thermal simulation machine.The hot deformation behavior of the superalloy was investigated under the conditions of deformation temperature of 1020～1090 ℃,strain rate of 0.001～1 s 1,and deformation capacity of 60％(maximum true strain of 0.9).Based on the obtained true stress-strain curves and micro-structure,the strain rate sensitivity index m value,deformation activation energy Q value and grain index p value were calculated at different strain rates and deformation temperatures.Therefore,the flow stress of hot extruded FGH96 superalloy de-creased with the increase of deformation temperature and the decrease of strain rate.The true stress-strain curves under different tem-peratures and strain rates showed two different types:One was in the work hardening stage at the early stage of deformation,and the flow stress increased sharply with the increase of true strain.When the flow stress reached the peak value,it gradually decreased and entered the flow softening stage.The other was that with the increase of deformation,the work hardening and dynamic softening can-celled each other to achieve steady flow,and the flow stress curve approximated to the level to achieve steady flow.The m value of the alloy was 0.212～0.243,and with the increase of temperature,the m value of the alloy first increased and then decreased.The thermal deformation activation energy Q values ranged from 200～360 kJ·mol-1.With the increase of temperature,the deformation activation en-ergy first decreased and then increased.When the temperature was 1070 ℃,the deformation activation energy reached the minimum value.When the deformation temperature was 1070 ℃,m value was 0.243,p value was 2.76,and Q reached the minimum value of 201.185 kJ·mol-1,the forming property of the superalloy was good.It could be concluded from the hot processing maps of hot extruded FGH96 superalloy that the instability area was small and concentrated,generally located in the high strain rate area,and other loca-tions were safe areas.When the true strain was 0.35,the peak value was 0.53.When the true strain was 0.9,the peak value of power dissipation rate was 0.47.And two peak regions of dissipation rate were formed:(1)1035～1055 ℃,0.001～0.005 s-1;(2)1040～1060 ℃,0.05～0.1 s-1.Therefore,when the true strain was 0.35,the optimal hot working parameters of FGH96 alloy were 1020～1050 ℃,0.001～0.005 s-1.When the true strain was 0.9,the optimal thermal working parameters were 1035～1055 ℃,0.001～0.005 s-1.However,the area of 1040～1060 ℃ and 0.05～0.1 s-1 was close to the instability zone,which might cause instability and was not the best hot working area.Therefore,when the strain was 0.35 and 0.9,the optimal hot working parameters of FGH96 superalloy were lo-cated at 1035～1050 ℃ and 0.001～0.005 s-1.It could be observed from the micro-structure that the grain size decreased with the in-crease of strain rate at constant deformation temperature.From the R-W-S deformation mechanism diagram of hot extruded FGH96 su-peralloy,the deformation mechanism of the alloy was revealed under the grain size compensated by the modulus and the appropriate amount of compensation.Under the deformation condition of 1070 ℃,the dislocation slip mechanism was mostly controlled by lattice diffusion when the strain rate was low.At higher strain rates,the grain boundary slip mechanism of dislocation tube was mostly con-trolled by diffusion of dislocation tube.
FGH96 superalloystrain rate sensitivity index mgrain index phot processing mapsdeformation mechanism maps
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