Investigation Of Solidification And High-Temperature Deformation Behavior Of Ni-base Alloy ??151

Ni-base alloy ??151 is a ?'-Ni3(Ti,Al)precipitation-strengthened wrought superalloy and it is widely applied as the gas turbine components of Russian fifth-generation fighter jets,due to the outstanding properties such as the great resistance to creep and fatigue,and good resistance to oxidation and corrosion.However,the element segregation is extremely severe in the alloy,because of its highly alloyed degree,especially the sum of precipitation elements(Nb,Ti,Al)alredy reaching 10 wt.%,which is the heighest among all the wrought alloy.Thus,it is quite difficult to be deformed and forged for the alloy.In this paper,the solidification behavior,high-temperature deformation behavior and the effects of trace element carbon have been investigated,which could provide theoretic ground for the homogenization and forging process.The precipitations of(Nb,Ti)C,?-Ni3(Ti,Nb),eutectic(?+?'),Laves in the inter-denditic region of as-cast ??151 alloy are firstly observed herein.Through the 'high-temperature freezing' test,the solidification sequence of each phases is determined.Accroding to incipient temperatures of the inter-dendritic phases and diffusion mechanism of some specific elements,a three-step homogenization treatment is designed to eliminate minor phases and segregated elements.Through the in-depth study of the high-temperature deformation behavior of ??151 alloy,it is found that in the as-cast alloy,the coarse ?'and inter-dendritic phases inhibite the movements of dislocation,which cause the strain localization and shear bands.The dynamic recrystallization will then be induced by the accumulation of dislocation at coarse ?' and inter-dendritic phases.In homogenized alloy,dislocation will pile up around the(Nb,Ti)C carbides and grain boundaries,which lead to the strain localization and shear bands,and dynamic recrystallization will also occur at these regions.The effects of C on the solidification segregation of ??151 alloy has been investigated.It has been found that C addition promotes the formation of(Nb,Ti)C,which largely consume the contents of Nb and Ti in residual liquids,diminishing the components gap between liquids and y dendrites.Thus,y dendrites are induced to be precipitated from the liquids.Also,the precipitation of ?-Ni3(Ti,Nb)and Laves are inhibited due to the lack of Nb and Ti in residual liquids.