Self-pinning mechanism for grain boundary stabilization

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.