Theoretical investigation of the mechanisms of fracture in metals and alloys

A fundamental understanding of the atomic mechanisms responsible for the stress-induced bond failure of solid-state materials will facilitate the synthesis of materials with desired mechanical properties. Outside of a small group of network solids and polymers, no such understanding is available. By adopting an appropriate model for solid-state bonding, based on features of the total charge density, it is possible to apply chemical reaction theory to an investigation of this process. First-principle local-density-functional techniques were used to model the transgranular fracture of two alloys with the same crystal structure but different mechanical properties, a hitherto unexplained observation. It was found that the transition state for decohesion occurs earlier in the reaction path for the brittle than for the ductile alloy. This observation is argued to be the result of a comparatively flat charge density at a few special points within the alloy. The success found in the application of reaction theory toward an understanding of decohesion suggests that reaction theory might be profitably employed in more complex and technologically important investigations of mechanical properties of solids.