Study On Hot Deformation Behavior And Deformation Mechanism Of Hot Extruded FGH96 Superalloy

FGH96 superalloy is aγ’-phase precipitation-reinforced Nickel-based powder high-temperature superalloy with excellent properties such as homogeneous microstructure,high strength,creep resistance and fatigue resistance.It is of great interest in aviation and aerospace and is commonly used in the manufacture of hot end components for high performance engines.FGH96 superalloy has the advantages of high alloying degree,narrow hot working window,high deformation resistance and poor plasticity.During the deformation process,problems such as mixed crystal,cracking and structural instability are easy to occur,which seriously affects the properties of the alloy and makes it difficult to process and prepare the superalloy.Hot extrusion technology is beneficial to improve the formability of the alloy,make the grain of the alloy finer and more uniform,and improve the mechanical properties and organizational stability.Therefore,in this paper,the hot extruded FGH96 superalloy is taken as the research object,and mainly studies the hot deformation behavior and microstructure evolution law of the hot extruded FGH96 superalloy.The R-W-S deformation mechanism diagram of nickel-based superalloy was drawn,the deformation mechanism of hot extruded FGH96 superalloy was determined and the constitutive equation of mechanism was established.Due to the difference of initial microstructure between the center and the edge of extruded bar,the hot deformation behavior and deformation mechanism of different initial microstructures are compared,which provides theoretical basis for optimizing the hot process parameters of hot extruded FGH96 superalloy.The main work of this paper includes:The flow stress curves of the hot extruded FGH96 superalloy were obtained by hot compression simulation experiments at deformation temperatures of 1020～1090℃and strain rates of 0.001～1s^-1.The flow stress of hot extruded FGH96 superalloy decreases with the increase of deformation temperature and the decrease of strain rate.The strain rate sensitivity index varies from 0.05～0.61.The region of m≥0.3 decreases with the increasing strain.The deformation activation energy of hot extruded FGH96 superalloy is 700.539 k J/mol.Arrhenius constitutive equation is established by peak stress.The results show that the correlation coefficient R²between the predicted flow stress and the measured flow stress is 0.9824,and the average absolute relative error AARE is 6.13%.Dynamic recrystallization occurs during deformation,and the grain size of recrystallization increases with the increase of deformation temperature and decreases with the increase of strain rate and strain.The deformation mechanism of hot extruded FGH96 superalloy at different deformation temperatures was established by solving the characteristic parameters required for the mechanism-based intrinsic constitutive equation through stress-strain curves,and two deformation mechanisms were obtained for the hot extruded FGH96superalloy in this experiment.The two deformation mechanisms are grain boundary slip mechanism controlled by grain boundary diffusion and grain boundary slip mechanism controlled by dislocation pipeline diffusion.And the constitutive equations of the superalloy under two different deformation mechanisms are obtained.Combined with the observation of microstructure,it can be seen that there are few dislocations in the grain boundary slip mechanism controlled by grain boundary diffusion,and the dislocations are mainly distributed in the small grains at the intersection of grain boundary and grain boundary.In the grain boundary slip mechanism controlled by dislocation pipeline diffusion,the dislocation density inside the grain is large,and the high-density dislocation around the grain provides a diffusion channel for the hot deformation of the material.The difference in grain size and the size and distribution of the second phase between the initial microstructure of the bar at the edge and the center has a certain influence on the hot deformation behavior and deformation mechanism.The strain rate sensitivity index m in the center of bar is generally smaller than that in the edge position.The deformation activation energy at the center of FGH96 superalloy（Q=874.649k J/mol）is greater than that at the edge（Q=700.539 k J/mol）.The deformation mechanism at the center of the bar includes dislocation pipeline diffusion-controlled grain boundary slip mechanism and dislocation pipeline diffusion-controlled dislocation slip mechanism;the deformation mechanism at the edge of the bar includes grain boundary diffusion-controlled and dislocation pipeline diffusion-controlled grain boundary slip mechanism.