Superplastic deformation carried by grain boundaries

A model of plastic deformation based on grain rolling is proposed for the interpretation of large superplastic strains that may be reached in some metallic as well as ceramic materials in certain ranges of high temperatures and strain rates. The deformation process is modelled by the motion of grain boundary dislocations that glide on the grain facets when sliding takes place and climb on the facets with normal stresses. A constitutive equation for the strain rate is derived for steady state deformation when the emission rate of climbing dislocations is a constant determined by the dislocations climb velocity.