Criteria for the prevalence of grain boundary sliding as a deformation mechanism

Abstract

Grain boundary sliding (GBS) is an important deformation mechanism that is known to activate at high temperatures, low strain rates, and for materials with small grain sizes. While crystalline slip has been extensively studied, investigations of GBS has been mostly restricted to nanocrystalline materials and loading in high-temperature environments. This study is aimed at improving our understanding of deformation mechanism relationships, specifically those between slip transmission and GBS, by examining interactions between mechanisms in high-purity aluminum with a through-the-specimen-thickness grain structure. Digital image correlation experiments are performed to measure 2D strains, which are used to resolve individual slip bands and the onset of grain boundary sliding. Onset of GBS is observed in the first loadstep (the first loadstep was collected just after macroscopic yield), which suggests that the mechanism is driven by high stress as opposed to only being active to accommodate large values of plastic strain. Further, GBS is observed in cases where slip impingement is present, as well as at boundaries that do not interact with obvious slip events. A temperature-dependent crystal plasticity model is used to study the constitutive response, which is then compared to full-field strain response experimentally obtained at the microscale-level. From this analysis, it is determined that a combination of the resolved shear stress at the grain boundary plane and boundary straightness form a set of criteria for predicting sliding propensity. These results improve the sophistication and accuracy of deformation modeling by establishing a set of criteria to describe the GBS mechanism.