The Microstructure and Creep Behavior of a [001] Orientation Single Crystal Nickel-Base Superalloy

摘要

The microstructure and creep behavior of a [001] orientation single crystal nickel-base superalloy are investigated by the creep curve measurement and microstructure observation. Results show that, after fully heat treated, the microstructure of the [001] orientation single crystal nickel-base superalloy consists of the cubical γ' phase embedded coherently in the y matrix phase, and arranged uniformly along (100) orientation. During tensile creep at 850℃/500 MPa, the γ' phase is gradually transformed into the rafted microstructure, and the deformation mechanism of the alloy at the steady stage of creep is the deformation dislocations moving in the γ matrix channels. At the latter stage of creep, more dislocations shear into the γ' phase, and the γ' phase is twisted and broken until the creep fracture occurs. During the course of creep, the main/secondary slip systems start alternatively, which makes the formation of cavities at the interfaces of the γ/γ' phases, from which cracks spread radially. This accelerates the lose of the creep resistance of the alloy. The fracture mode of the [001] orientation superalloy under the experimental conditions is cleavage fracture.