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

Abstract

By means of creep curve measurements and microstructure observation, the microstructure evolution and creep properties of [001] and [111] oriented single crystal nickel-based superalloys are investigated. Results show that, after full heat treatment, the microstructure of both the oriented single crystal nickel-based superalloys consist of the cuboidal γ′ phase embedded coherently in the γ matrix phase, and arranged regularly along the <100> direction. During tensile creep, the cuboidal γ′ phase in the [001] oriented superalloy is transformed into the rafted structure along the direction vertical to the stress axis, while rafting orientation of the γ′ phase in the [111] oriented alloy is at an angle of about 40°–60° relative to the stress axis. During steady-state creep, the deformation mechanism of the [001] oriented alloy is mainly dislocations being activated in γ matrix channels and climbing over the rafted γ′ phase, while that of the [111] oriented alloy is dislocations slipping in γ matrix channels and shearing into the rafted γ′ phase. As creep goes on, dislocations concentrate to form the subgrain structure in the [111] oriented alloy. From the study of this paper, the creep anisotropy, especially the microstructure-evolution anisotropy and its effect on creep properties of single crystal superalloys, are further specified, which are expected to provide useful data for the design and production of single crystal superalloys.