Effects of Ultrafine Nanograins on the Fracture Toughness of Nanocrystalline Materials

Abstract

For the purpose of evaluating the effects of ultrafine nanograins (UFNGs) on the fracture toughness of conventional nanocrystalline (nc) materials, we developed a theoretical model comprised of UFNGs (with a grain size d between 2 and 4 nm) evenly distributed in the conventional nc matrix. The UFNGs could be treated as a part of triple junctions, denoted as super triple junctions (STJ). In the framework of our model, stress concentration near crack tip initiates intergrain sliding that leads to the generation of edge dislocations at STJ. The dependence of critical crack intensity factors on grain size was calculated. It was demonstrated that the existence of the UFNGs approximately doubles the critical crack intensity factors.