Degradation and anisotropy characteristics of fracture toughness in Ni-based superalloys after phase coarsening

Abstract

The effect of phase coarsening on the crack propagation characteristics and the corresponding fracture toughness in Ni-based superalloys is investigated by integrating with the finite element method simulations and related mechanism analysis, and the relationship between the macroscopic mechanical properties of alloys and the evolution in their microstructures are discussed in detail. Related analysis shows that the fracture toughness of alloys degraded considerably with phase coarsening. Moreover, the fracture toughness also demonstrates an anisotropic characteristic. Specifically, when the volume fraction of precipitate is low or the degree of phase coarsening is relatively low, the fracture toughness of alloys increases first and then decreases gradually along with increasing the loading angle, showing an inverted "V" shape. In comparison, in the case of a higher volume fraction of precipitate or higher degree of phase coarsening, the fracture toughness displays an opposite variation trend, and reaches the minimum value at the loading direction of 45°. The corresponding variation characteristics of fracture toughness are correlated with the evolutions of precipitate shape, size, and distribution within the alloys. The change in the microstructure or that in the loading direction affects remarkably the initiation and growth of micro-voids within the alloys, and it further affects the crack propagation characteristics, resulting in the degradation and anisotropy characteristics of macroscopic fracture toughness in the alloys. Related work is of great significance for the structure design of Ni-based superalloys components, the mechanical property evaluation and the life prediction during their service process.