Influence of heat treatment regimes on microstructure and creep properties of FGH95 nickel base superalloy

Abstract

Abstract By means of creep curves measurement and microstructure observation, an investigation has been made into the influence of heat treatment regimes on microstructure and creep properties of FGH95 nickel base superalloy. Results show that, after the alloy is solution treated and cooled in oil bath, coarser γ′ precipitates are distributed in the previous particle boundaries (PPB) regions in which appears the γ′-free phase zone. No coarser γ′ phase is detected in the alloy cooled in molten salt, the grain size of which increases slightly and fine γ′ phase is dispersedly distributed in the grains, in addition, some (Nb, Ti)C particles are precipitated along the boundaries. In the ranges of the experimental stresses and temperatures, the alloy cooled in molten salt possesses a better creep resistance and longer creep life, the creep activation energy of the alloy is measured to be Q = 590.3 kJ/mol. During creep, the deformed mechanism of the alloy cooled in oil bath is that the slipping dislocations with double orientations are activated in the matrix, and some finer carbide particles are precipitated along the slipping traces. Moreover, the wider PPB regions are broken into finer grains due to the severe plastic deformation. However, not only dislocations tangle but also stacking fault appears in the alloy cooled in molten salt. The fact that the carbide particles precipitate along the boundary may effectively restrain the movement of dislocation slipping, which is one important factor for the alloy possessing better creep resistance and longer creep life.