Schematic of a nano-void coalescence model. Vacancy clusters coalesce into nano-voids, which, when large enough, and closely spaced enough, coalesce similar to microvoids in traditional macroscale ductile fracture. This is proposed to happen in areas of intense strain localization, such as slip bands. In (a) a plastic zone, including the locally hydrogen-affected region, is shown forming ahead of the crack tip. (b) Plasticity leads to enhanced vacancy formation, and the vacancies coalesce to form voids, leading to bulk failure. Adapted from Neeraj et al., Acta Mater. 60, 5160 (2012).136 Copyright 2012 Elsevier.