Atomic force microscopy reveals thermally induced grain growth via shear-coupled migration

Grain boundary (GB) migration is typically assumed to proceed by diffusive atomic events following curvature-driven flow. However, recent 4D (3D plus time) experiments and atomic-to-mesoscale simulations have shown that thermally induced grain growth in polycrystals deviates from this assumption. GB migration mediated by disconnections—producing both boundary translation and shear—may resolve this discrepancy, although such shear is usually restricted by surrounding grains. We directly demonstrate shear-coupled migration during grain growth in 10μm-sized nickel by measuring surface displacements associated with GB migration using atomic force microscopy. Migrated GBs induced significant surface topography changes, clearly differing from grooves observed for stationary GBs.

晶界（Grain Boundary, GB）迁移通常被认为遵循曲率驱动流动的扩散原子机制。然而，近期开展的四维（三维加时间）实验以及原子至介观尺度的模拟研究表明，多晶体中的热致晶粒长大过程并不符合这一经典假设。由脱离位错（disconnection）介导的晶界迁移——可同时引发晶界平移与剪切效应——或可解释这一理论偏差，尽管这类剪切效应通常会受到周围晶粒的约束。本研究通过原子力显微镜（Atomic Force Microscopy, AFM）测量与晶界迁移相关的表面位移，直接证实了10微米级镍晶粒长大过程中的剪切耦合迁移现象。经迁移改造的晶界会引发显著的表面形貌变化，与静止晶界所观测到的沟槽结构存在明显差异。