A THEORETICAL INVESTIGATION OF THE MECHANISMS OF FRACTURE IN METALS AND ALLOYS

A fundamental understanding of the atomic mechanisms responsible for t he stress-induced bond failure of solid-state materials will facilitat e the synthesis of materials with desired mechanical properties. Outsi de of a small group of network solids and polymers, no such understand ing is available. By adopting an appropriate model for solid-state bon ding, based on features of the total charge density, it is possible to apply chemical reaction theory to an investigation of this process. F irst-principle local-density-functional techniques were used to model the transgranular fracture of two alloys with the same crystal structu re but different mechanical properties, a hitherto unexplained observa tion. It was found that the transition state for decohesion occurs ear lier in the reaction path for the brittle than for the ductile alloy. This observation is argued to be the result of a comparatively flat ch arge density at a few special points within the alloy. The success fou nd in the application of reaction theory toward an understanding of de cohesion suggests that reaction theory might be profitably employed in more complex and technologically important investigations of mechanic al properties of solids.