Effect And Mechanism Of Electric-pulse Current On Microstructure And Deformation Behavior Of GH4169 Superalloy

The superalloy serves at high temperature with high strength.The superalloy has excellent combination properties including good fatigue property,good oxidation resistance and corrison property,and its microstructure is stable with long-term aging.The superalloy is widely used at aerospace.It is one of the most important metal materials,representing the level of scientific and technological development.In order to satisfy the hard serve condition,the strength of superalloy improves continually.However,the resistance increases and ductility decreases during hot deforming with the increasing strength,which restricts the development of superalloy.Since electroplastic was first reported in 1963,electric-pulse current(EPC)had been widely used in metal,such as grain refinement through recrystallization,crack healing and phase transformation,amorphous nano-crystallization.The advantages of EPC includes high energy density,and precise quantify control.EPC has been applied to assist in deforming of various brittle alloys due to decreasing of flow stress and increasing of elongation in the alloy with EPC during hot deforming.In the present research,in order to clarify the plastic deforming behavior and the microstructure variation characteristics of GH4169 alloy with EPC.The mechanisms of EPC on plastic deformation behavior and microstructure evolution of the alloy are also discussed.It is meaningful for providing theory support for EPC application in sueralloy.The tensile tests were conducted to investigate the dynmic strain aging(DSA)of GH4169 alloy with EPC,and mechanisms of EPC on defect motion behavior were discussed.The results show that DSA is restrained during tensile deforming with EPC.The ?" phase and ? phase are improved to grow up with atom diffusing quickly under EPC.Therefore the amount of atoms pinning the dislocation decreases,leading to DSA to be restrained.In present research,the tensile tests were conducted to investigate the effect of EPC on tensile deforming,discussing the mechanisms of EPC on tensile deforming.The results show that EPC induces the decreasing of flow stress and the improving of plasticity compared with that without EPC.The fracture mechanism transforms from intergranular(without EPC)to transgranular(with EPC).The flow stress instantaneously increases/decreases without any delay with removing/recovering EPC during deformation.It is found that the thermal vibration of atoms enhances leading to decreasing of Peierls stress with in-situ EPC,which is the essential factor on flow stress decrease.Although,with in-situ EPC,the y" phases are induced to precipitate and then grow up,resulting in changing dislocation motion mode with ?" phase.And dynamic recrystallization has assist on the alloy softening,which leads to flow stress decrease during deforming.EPC induces grain boundary strengthening at high temperature,the granular ? phases pin and enhance the grain boundary.The ?" phase inside grian is induced to transform to ? phase at high temperature.When the alloy deformed with EPC,both increasing of defect concentration and atom energy account for ?" phase growing up and ? phase precipitating on grain boundary in the alloy deformed with EPC.The microstructure characteristics of GH4169 alloy aging treated with electric-pulse treatment(EPT)were investigated and tensile properties were examined at high temperature.The tensile test results indicate that the yield strength,the ultimate tensile strength and total elongation increase simultaneously in the alloy aged with EPT compared with normal aged.The vacancy concentration increases in the alloy induced with EPT proved by position annihilation spectrometer.Compared with normal aged,?" phases precipitate along dislocation in chain morphology and granular ? phases pin on the grain boundary in the alloy aged with EPT.The Joule heat effect enhances in the area with dislocation induced by EPT which leads to ?" phase nucleate and precipitate along dislocation.Vacancy concentration increase leads to yield strength increasing at the initial deforming.And the vacancies induces ultrafine nm-sized?" phase to precipitate from ? matrix with a dense distribution during tension deformation at high temperature,which is the key factor on improving strength and ductility.Based on discussing mechanisms of electric pulse on deforming behavior in GH4169 alloy,and electric pulse aged treatment on micro structure evolution,it is found that the strength and plasticity could be improved simultaneously with reasonably applied electric pulse on GH4169 alloy.On one hand,the flow stress decreases and enlogation increases with electric pulse during tensile deforming,which is useful for hot deformation of GH4169 alloy.On the other hand,the the strength and ductility could be improved simultaneously with nm-sized ?" phase precipitating.It will provide a new method for hot deformation and strength improving,meanwhile it is other new application of EPC.