Microstructure evolution and FEM analysis of a [111] oriented single crystal nickel-based superalloy during tensile creep

Abstract

By means of the elastic–plastic stress–strain finite element method (FEM), the distribution of the von Mises stress and strain energy density in the regions near the interfaces of the cuboidal γ/γ′ phases is calculated to investigate the rafted behaviors of γ′ phase in a [111] oriented single crystal (SC) nickel-based superalloy. Results show that, after fully heat treated, the microstructure of the superalloy consists of the cuboidal γ′ phase embedded coherently in the γ matrix and arranged regularly along the 〈100〉 orientation. And the parameters and misfits of γ′/γ phases in the alloy increase with the temperature. After crept for 50 h, the γ′ phase in alloy has transformed into the mesh-like rafted structure on (010) plane along [001] and [100] orientations. When the tensile stress is applied along [111] direction, the change of the strain energy on the planes of the cuboidal γ′ phase results in the directional diffusion of the elements. Thereinto, compared with (010) plane, the bigger expanding strain occurs on (100) and (001) planes along the [010], [001] and [010], [100] directions, which may trap the Al and Ti atoms with bigger radius to promote the directional growth of γ′ phase on (010) plane along [100] and [001] directions. This is thought to be the main reason for the γ′ phase directionally growing into the mesh-like rafted structure on (010) plane.