Hydrostatic pressure tuned grain boundary mobility in polycrystalline metals

Abstract

Grain boundary (GB) plasticity plays a pivotal role in the mechanical behaviours of polycrystalline materials. The kinetics and deformation of GBs depend on both GB geometry and local stress states. While classic GB theories primarily focus on shear-driven GB kinetics, the fundamental mechanism by which hydrostatic pressure influences GB plasticity remains largely unclear, despite the evidence that polycrystalline materials subjected to substantial pressures can exhibit distinct mechanical properties. Here, we investigate pressure-tuned GB kinetics in polycrystalline metals through a series of atomistic simulations combined with experimental validations. We demonstrate that under constant temperature annealing, the application of pressure can reduce GB mobility and thus the rate of grain growth, which originates from the pressure-enhanced activation energies for disconnection nucleation and gliding. More importantly, pressure can shift GB deformation mechanism from disconnection-annihilation-mediated GB migration to disconnection-accumulation-mediated GB rotation, resulting in an asymmetry-to-symmetry GB structural transformation and generating a large volume of special GBs. An energetic model based on pressure-dependent disconnection dynamics is proposed to interpret the pressure-tuned GB mobility, offering insights into the understanding of pressure-assisted grain growth retardation in polycrystalline metals widely reported in the literature.