Microstates and defects of incoherent Σ3 [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 insights at the atomic structure level are rarely reported. In this study, two different microstates of incoherent Σ3 [111] (112¯) 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 Σ3 [111] disconnections with Burgers vectors (b1 = 1/6[1¯1¯2]), (b2 = 1/2[1¯01]) and varying step heights (h = 2adsc, 5adsc) are investigated and their implications on the GB mobility are discussed.