A model of thermodynamic stabilization of nanocrystalline grain boundaries in alloy systems

TL;DR

This paper presents a simple 2D model and kinetic Monte Carlo simulations that demonstrate how solute segregation can fully stabilize nanocrystalline grain boundaries, preventing grain growth.

Contribution

It introduces a coupled grain boundary migration and solute diffusion model that predicts and reproduces the fully stabilized nanocrystalline state.

Findings

Simulations show zero grain boundary free energy at stabilization

Emergence of stabilization via divergence of capillary wave amplitudes

Fragmentation of large grains into smaller stable grains

Abstract

Nanocrystalline (NC) materials are intrinsically unstable against grain growth. Significant research efforts have been dedicated to suppressing the grain growth by solute segregation, including the pursuit of a special NC structure that minimizes the total free energy and completely eliminates the driving force for grain growth. This fully stabilized state has been predicted theoretically and by simulations but is yet to be confirmed experimentally. To better understand the nature of the full stabilization, we propose a simple two-dimensional model capturing the coupled processes of grain boundary (GB) migration and solute diffusion. Kinetic Monte Carlo simulations based on this model reproduce the fully stabilized polycrystalline state and link it to the condition of zero GB free energy. The simulations demonstrate the emergence of a fully stabilized state by the divergence of capillary wave amplitudes on planar GBs and by fragmentation of a large grain into a stable ensemble of smaller grains. The role of solute diffusion in the full stabilization is examined. Possible extensions of the model are discussed.