Phase constituent and granularity distribution of γ′phase in FGH95 nickel based superalloy

Abstract：In order to study the phase constituent and granularity distribution of γ′ phase,the γ′ phase in FGH95 nickel based superalloy subjected to heat treatment was extracted by means of an electrolytic extraction method,and the structural formula of γ ′ phase was tested.The lattice parameters and misfit of γ′ and γ phases were measured with XRD curves.Furthermore,the small-angle diffraction for the extracted γ′ phase powder in the superalloy was carried out,and the granularity distribution of γ′ phase was determined.The results show that after solid solution at 1 140 ℃ plus aging treatments,the microstructure of the superalloy consists of γ′ phase（mass fraction of 47.8%）,γ phase（mass fraction of 51.2%）,and carbides and borides（mass fraction of 1%） such as（Nb,Ti）C,（Nb,W）B2,Nb3B2and Cr23C6 phases.The structural formula of γ′ phase is identified as（Ni0.896Co0.055Cr0.017Fe0.031）3（Ti0.224Nb0.134Al0.473Mo0.038W0.066Cr0.064）,and the mass fractions of γ′ phase with granularity ranges of 36 to 60 nm and 60 to 96 nm are 30.6% and 29.1%,respectively.In addition,the fine γ′ phase dispersedly distributes inside the grains,while the coarse γ′ phase discontinuously precipitates along the wider grain boundaries.Moreover,the lattice parameters of γ′ and γ phases are determined as 0.359 86 nm and 0.359 12 nm,respectively.The lattice misfit between γ′ and γ phases is 0.205 8%.