Creep Properties and Deformation Mechanisms of a FGH95 Ni-based Superalloy

Abstract

By means of full heat treatment, microstructure observation, lattice parameters determination, and the measurement of creep curves, an investigation has been conducted into the microstructure and creep mechanisms of FGH95 Ni-based superalloy. Results show that after the alloy is hot isostatically pressed, coarse γ′ phase discontinuously distributes along the previous particle boundaries. After solution treatment at high temperature and aging, the grain size has no obvious change, and the amount of coarse γ′ phase decreases, and a high volume fraction of fine γ′ phase dispersedly precipitates in the γ matrix. Moreover, the granular carbides are found to be precipitated along grain boundaries, which can hinder the grain boundaries’ sliding and enhance the creep resistance of the alloy. By x-ray diffraction analysis, it is indicated that the lattice misfit between the γ and γ′ phases decreases in the alloy after full heat treatment. In the ranges of experimental temperatures and applied stresses, the creep activation energy of the alloy is measured to be 630.4 kJ/mol. During creep, the deformation mechanisms of the alloy are that dislocations slip in the γ matrix or shear into the γ′ phase. Thereinto, the creep dislocations move over the γ′ phase by the Orowan mechanism, and the $\left\langle { 1 10 } \right\rangle$ super-dislocation shearing into the γ′ phase can be decomposed to form the configuration of (1/3) $\left\langle { 1 12 } \right\rangle$ super-Shockleys’ partials and the stacking fault.