Effect of crack on morphology evolution of the precipitates in Nickel-based superalloys under applied stress

Abstract

Nickel-based superalloys are widely used in turbine blades and aviation engine due to their outstanding mechanical property at elevated temperatures. The superior mechanical property of nickel-based superalloys is highly relevant to the morphology evolution of γ′ precipitates in the γ matrix phase. At high temperature, the directional coarsening of γ′ precipitates may result in rafting behavior under applied stress. In addition, defects such as the cavities, inclusions and micro-cracks introduced during the manufacturing process in superalloys have significant influence on the evolution of the γ′ precipitates. In this work, a phase field model with crack and precipitate as order parameters has been proposed to investigate the effect of crack on the morphology evolution of the γ′ precipitates. The morphology evolution and volume fraction evolution of the γ′ precipitates in the Nickel-based superalloys with different cracks have been investigated under the tensile and shear stresses. It is found that the local high equivalent stress and high elastic strain energy near the crack lead to the migration of solute atoms from the high stress region to the low stress region. The migration of solute atoms results in the disappearance of the γ' phases in the vicinity of cracks, which is consistent with the experimental observation. The disappearance of the γ' phases around the crack reduces the volume fraction of the γ′ precipitates, which will affect the mechanical property of the superalloys.