Abnormal grain growth in ultrafine grained Ni under high-cycle loading

Abnormal grain growth can occur in polycrystalline materials with only a fraction of grains growing dras-tically to consume other grains. Here we report abnormal grain growth in ultrafine grained metal in a rarely explored high-cycle loading regime at ambient temperature. Abnormal grain growth is observed in electroplated Ni microbeams with average initial grain sizes less than 640 nm under a large number of loading cycles (up to 10(9)) with low strain amplitudes (< 0.3%). Such abnormal grain growth occurs predominantly in the family of grains whose < 100 > orientation is along the tensile/compressive loading direction. Micromechanics analysis suggests that the elastic anisotropy of grains dictates the thermody-namic driving force of abnormal grain growth, such that the lowest strain energy density of the < 100 > oriented grain family dominates grain growth. This work unveils a unique type of abnormal grain growth that may be harnessed to tailor grain microstructures in materials. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.