Microstates and defects of incoherent S3 [111] twin boundaries in aluminum

In the last few decades, it has been recognized that a single grain boundary (GB) may exist in several different stable and metastable states, which differ in their atomic structure. However, experimental in-sights at the atomic structure level are rarely reported. In this study, two different microstates of inco-herent Sigma 3 [111] (11 (2) over bar) GBs from two different orientation relationships (ORs) in an aluminum thin film grown on sapphire, comprised of slightly different structural units, are reported. The structural units in ORII exhibit hexagonal units while in ORI the hexagonal units are slightly distorted. Molecular statics simulations are utilised to understand the difference in excess properties of both states, which suggest that strain could potentially contribute to the stability of the ORII GB microstate over the ORI microstate. In addition, the atomic structure of the two ORs along the ( 110 ) zone axis reveal the rigid body microscopic translations of different magnitude of {111} planes across the GB experimentally. Furthermore, in the case of asymmetric variants of the same GBs, different types of Sigma 3 [111] disconnections with Burgers vectors ( b(1) = 1/6[(1) over bar (1) over bar 2]), ( b(2) = 1/2[ (1) over bar 01]) and varying step heights ( h = 2a(dsc), 5a(dsc)) are investigated and their implications on the GB mobility are discussed. (c) 2022 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc.

Automated summary

In the past few decades, it has been discovered that a single grain boundary can exist in different stable and metastable states with different atomic structures. However, experimental insights into the atomic structure are rarely reported. This study reports two different microstates of incoherent Sigma 3 [111] (11 (2) over bar) grain boundaries in an aluminum thin film grown on sapphire, which have slightly different structural units. Molecular statics simulations are used to understand the differences between these states and strain is found to potentially contribute to the stability of one state over the other.