Cyclic-loading microstructure-property relations from a mesoscale perspective: An example of single crystal Nickel-based superalloys

TL;DR

This paper introduces a mesoscale phase-field framework to model the microstructure evolution and property relations in single crystal Nickel-based superalloys under cyclic loading, capturing both short-term and long-term microstructural changes.

Contribution

It develops a novel mesoscale phase-field model that directly links microstructure evolution to cyclic loading response, advancing beyond traditional macroscopic models.

Findings

Cyclic dislocation motion produces experimental-like cyclic loops.

Plastic strains are much smaller than total strains, explaining thin cyclic loops.

Microstructures exhibit directional coarsening similar to creep, influenced by cyclic parameters.

Abstract

Past models of stress-strain response under cyclic loading mainly rely on macroscopic equations which consider microstructure evolution indirectly or simply discard microstructure information. Modern materials science, on the other hand, seeks quantitive descriptions for the relations between microstrucutre and loading response. In the present work, we show a promising mesoscale phase-field framework which can describe co-evolution of phase/grain and defect microstructures, reveal microstructure mechanisms and simultaneously predict deformation properties as a natural outcome of microstrucuture interactions. The energy functionals for phase/grain and defect microstructures are constructed, followed by functional variation which leads to governing equations. Applying the developed framework to high temperature cyclic loading of single crystal Nickel-based superalloys, the simulated results show that cyclic loading-microstructure-property relations can be principally revealed. In the short term perspective (in one cycle), dislocations move back and forth, leading to cyclic loops consistent with characteristics observed in experiments. The plastic strains are one order of magnitude smaller than total strains, which explains why the cyclic loops are very "thin". In the long term perspective, all $\gamma\gamma'$ microstructures exhibit directional coarsening similar to creep under zero cyclic loading ratio, with the extent of rafting slight dependent on cyclic waveform, period, etc. The plastic strains are sensitive to cyclic loading conditions both in terms of curve shape and in terms of magnitude.