Boundary defects, and atomistic aspects of boundary sliding and diffusional creep

The paper describes behavior of atoms in a grain or phase boundary when the boundary slides (when the crystals which meet at the boundary suffer a relative shear displacement parallel to the boundary plane) and during diffusional creep (when the crystals which meet at the boundary suffer both a normal and a shear translation). Boundary defects are involved. They are dislocations, with Burgers' vectors which need not be lattice vectors of either crystal. If they are sufficiently numerous and mobile, the rate of sliding and diffusional creep is given by the classical, continuum models. But if their density is low, or their motion is hindered, the rate of sliding and of creep is less than that predicted by the classical treatments. Equations for sliding and creep rates are developed.