Effect of Grain Size and Local Chemical Order on Creep Resistance in MoNbTaW Refractory High-Entropy Alloy: A Molecular Dynamics Study

TL;DR

This study uses atomistic simulations to analyze how grain size and local chemical order influence creep resistance in MoNbTaW refractory high-entropy alloys, emphasizing microstructural control for extreme environments.

Contribution

It demonstrates that larger grain size and local chemical order improve creep resistance by reducing grain boundary mechanisms, guiding alloy design.

Findings

Larger grain size reduces creep deformation by limiting grain boundary mechanisms.

Local chemical order enhances creep resistance by strengthening grain boundaries.

Microstructural control is crucial for designing RHEAs for extreme environments.

Abstract

Refractory high-entropy alloy (RHEA) is a promising class of materials with potential applications in extreme environments, where the dominant failure mode is thermal creep. The design of these alloys, therefore, requires an understanding of how their microstructure and local chemical distribution affect creep behavior. In this study, we performed high-fidelity atomistic simulations using machine-learning interatomic potentials to explore the creep deformation of MoNbTaW RHEA under a wide range of stress and temperature conditions. We parametrized grain size and local chemical order (LCO) to investigate the effects of these two important design variables, which can be controlled during the alloy fabrication process, on creep deformation process. Our investigation revealed that resistance to creep deformation is enhanced with larger grain size due to the reduced grain boundary area, which limits grain-boundary dominated deformation mechanisms such as Coble creep and grain boundary sliding. Introducing LCO in the microstructure has the same effect of increasing resistance to creep deformation by strengthening grain boundary. This study highlights the importance of utilizing LCO in conjunction with other microstructural properties when designing RHEAs for extreme environmental applications.