Diffusive crack-grain interplay in freestanding nanocrystalline silver thin film

Abstract Crack dynamics typically controls the deformation and fracture in nanocrystalline (NC) metallic materials, while the ubiquitous interplay between nanograins and propagating cracks remains unclear. Here, using in situ nanomechanical testing inside transmission electron microscope, we clarify the atomistic interplay between GB evolution and crack propagation in NC silver (Ag) thin films, where the cooperative GB migration, GB re-orientation and nanograin nucleation activated ahead of the crack tip result in conspicuous crack blunt. This grain-crack interplay is critically facilitated by the diffusive plasticity associated with crack propagation, which yields dynamically modified crack tip morphology and rate-limiting intragranular cracking. These atomistic mechanisms of diffusive crack-grain interplay enrich our understanding of the cooperative deformation behaviors in nanograin regime and hold general implications to enhance the fracture resistance of NC metallic materials.