Formation and evolution of hierarchical microstructures in a Ni-based superalloy investigated by in situ high-temperature synchrotron X-ray diffraction

Hierarchical microstructures are created when additional gamma particles form in gamma' precipitates and they are linked to improved strength and creep properties in high-temperature alloys. Here, we follow the formation and evolution of a hierarchical microstructure in Ni86.1Al8.5Ti5.4 by in situ synchrotron X-ray diffraction at 1023 K up to 48 h to derive the lattice parameters of the gamma matrix, gamma' precipitates and gamma particles and misfits between phases. Finite element method-based computer simulations of hierarchical microstructures allow obtaining each phase's lattice parameter, thereby aiding peak identification in the in situ X-ray diffraction data. The simulations further give insight into the heterogeneous strain distribution between gamma' precipitates and gamma particles, which gives rise to an anisotropic diffusion potential that drives the directional growth of gamma particles. We rationalize a schematic model for the growth of gamma particles, based on the Gibbs-Thomson effect of capillary and strain-induced anisotropic diffusion potentials. Our results highlight the importance of elastic properties, elastic anisotropy, lattice parameters, and diffusion potentials in controlling the behavior and stability of hierarchical microstructures. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

The formation and evolution of hierarchical microstructures in high-temperature alloys play a crucial role in improving material strength and creep properties.