Heterogeneous γ′ microstructures in nickel-base superalloys and their influence on tensile and creep performance

Mechanical properties of nickel-base superalloys can be greatly influenced by spatial variation of γ′ microstructure, calling for models at mesoscale to study additional complexity in the underlying microstructure/property relationship. We combine a FFT-based elasto-viscoplasticity (FFT-EVP) model with a phase-field (PF) model to study plastic deformation of γ/γ′ superalloys. The model is applied to Haynes 282 (H282), where the low volume fraction (<20%) of dispersed spherical γ′ particles results in a dislocation-particle interaction of either Orowan looping at tensile conditions or climb-bypass at creep conditions. The incorporation of these mechanisms is achieved through the framework of a dislocation density based constitutive model in FFT-EVP, together with the introduction of a location-dependent inter-particle spacing based on the k-nearest neighbor algorithm. Features of non-uniform γ′ microstructures, including γ′ volume fraction variation and non-uniform γ′ distribution due to element microsegregation observed in welded H282 samples, are modeled using the PF method and then passed to FFT-EVP to explore their influence on the tensile and creep properties in a parametric manner. It is found that if the particle distribution is uniform, γ′ volume fraction variation can exhibit a nonlinear effect on both the tensile strength and creep rate; for a given overall γ′ volume fraction, the degree of particle distribution non-uniformity can also exhibit nonlinear influence on the tensile strength and creep rate. It is also shown that the location-dependent inter-particle spacing serves as a better microstructure descriptor than the conventional analytical expression of the average inter-particle spacing in terms of establishing a homogenized but microstructure-sensitive constitutive microstructure-property relationship for fast-acting engineering applications.