Direct observation of grain boundary formation in bcc iron through TEM in situ compression test

The formation of grain boundary (GB) by non-homogeneous plastic deformation was captured directly through transmission electron microscopy in situ compression test for body centered cubic iron. Stress inhomogeneity was purposely induced by a concaved grain shape using a focused ion beam, leading to enhanced interaction of dislocations by the activation of various slip systems. Wall-like tangled dislocations were gathered around the boundary at the apex or the bottom of the concaved surface with various stress/strain fields in an early deformation stage. The wall-like tangled dislocations further evolved into sharp grain boundaries with increasing plastic strain, analogous to the array of geometrically necessary dislocations. In contrast, the adjacent grain with a simple smooth shape in the same specimen formed no sharp GB. The results of this study indicate that the non-homogeneous stress/strain field is critical for the formation of the GB. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

The study observed the formation of grain boundaries through non-homogeneous plastic deformation in body centered cubic iron, indicating the critical role of non-homogeneous stress/strain field in grain boundary formation. The activation of various slip systems due to stress inhomogeneity led to the gathering of wall-like tangled dislocations around the boundary, evolving into sharp grain boundaries with increasing plastic strain.Adjacent grains with simple smooth shapes in the same specimen did not form sharp grain boundaries.