Small-scale plasticity of ultra-fine grained alloy and nanostructured nanocomposite: Ambient and elevated-temperature nanoindentation

Abstract

Abstract This article presents the experimental and modeling results of nanoindentation testing at ambient and elevated temperatures (i.e. 300 to 523\xa0K), examining the small-scale plasticity of ultra-fine grained (UFG) alloy and nanostructured nanocomposite (NS) materials. The complex small-scale deformation mechanisms are highlighted to assess the material flow behavior under the indenter, which involves the interaction of dislocations and nanoparticles restricting the slip/glide of dislocations. Combined with UFG band propagation and transition stages, these lead to a stabilized mechanical strength at elevated temperatures. Accordingly, the activation energy for softening during localized deformation behavior of the nanocomposite is increased compared to the UFG alloy. It is attributed to a shift in the dislocations activation volume and energy aided by altered grain boundary diffusion and sliding mechanisms. It is shown that the straining role of nanoparticles leads to substantial grain size refinement to the nano-scale with enhanced generation of geometrically necessary dislocations. However, these nanoparticles presence on the boundaries of nano-sized sub-grains can reduce the migration energy and restrict the sliding-based deformation mechanism.