Shear-induced directional grain growth in Ag nanocrystalline films under nanoindentation

Nanocrystalline metallic materials exhibit different mechanical properties compared with coarse-grained counterparts. In essence, the high density of grain boundaries contributes to significant portion of plasticity, which is more pronounced in thin films. Due to intrinsic geometric limitation, the responses of nanocrystalline films under shear-dominant loading are seldom understood. Here, we take Ag film as an example, with a larger indentation depth than film thickness, the deformation beneath the pyramidal surfaces of the indenter is considered to be dominated by in-plane shear stress with gradient distribution. The shear-dominant loading leads to directional grain elongation within indentation region, accompanied with frequent formation of nanotwins across the grain boundaries. These findings enrich our understanding of stress induced grain growth under nanoindentation, and provide a novel way to study shear-dominated plastic deformation in metallic nanocrystalline films.

Automated summary

Nanocrystalline metallic materials have different mechanical properties compared with coarse-grained counterparts due to a high density of grain boundaries contributing to plasticity, especially in thin films. However, the responses of nanocrystalline films under shear-dominant loading are not well understood. In this study, using Ag film as an example, it was found that shear-dominant loading leads to directional grain elongation and frequent formation of nanotwins across grain boundaries within the indentation region. These findings contribute to our understanding of stress-induced grain growth and provide insights into the plastic deformation of metallic nanocrystalline films under shear loading.