Self-pinning mechanism for grain boundary stabilization

TL;DR

This paper introduces a novel self-pinning mechanism for grain boundary stabilization in alloys, where solute clustering at moving boundaries intrinsically suppresses grain growth by coupling thermodynamics and kinetics, without needing second phase particles.

Contribution

It proposes a new self-pinning mechanism based on solute clustering at grain boundaries, shifting focus from external pinning particles to intrinsic phase behavior.

Findings

Self-pinning occurs via solute-rich cluster formation at grain boundaries.

The mechanism is demonstrated through kinetic Monte Carlo simulations.

Self-pinning effectively suppresses grain growth without second phase inclusions.

Abstract

Previous research focused on two different mechanisms of microstructure stabilization in alloys: thermodynamic stabilization by reducing the grain boundary (GB) free energy and kinetic stabilization by suppressing the GB mobility by solute drag or embedded pinning particles. Here, we propose a new GB stabilization mechanism, called self-pinning, in which the segregation atmosphere of a moving GB spontaneously breaks into solute-rich clusters, which produce a strong pinning effect in addition to the free energy reduction resulting from the segregation. The cluster formation is caused by strong solute-solute attraction at GBs, leading to a first-order transformation between solute-lean and solute-rich GB phases. The effect is demonstrated by kinetic Monte Carlo simulations capturing segregation thermodynamics, GB dynamics, and solute diffusion. The self-pinning provides an intrinsic stabilization mechanism for suppressing grain growth that couples thermodynamics and kinetics. The mechanism obviates the need for pre-existing second phase inclusions, refocusing the alloy design on GB phase behavior.