Whisker and hillock growth via coupled localized Coble creep, grain boundary sliding, and shear induced grain boundary migration

Abstract A model incorporating the effects of grain geometry and size and grain boundary properties on the growth of whiskers and hillocks has been developed based on coupling between localized Coble creep and grain boundary sliding. For both whiskers and hillocks accretion of atoms by Coble creep on grain boundary planes normal to the growth direction is limited by grain boundary sliding on planes parallel to the direction of whisker growth. If the accretion-induced shear stresses are not coupled to grain boundary migration a whisker forms when sliding occurs. In the case of hillocks an additional coupling between grain boundary sliding and shear-induced grain boundary migration leads to the observed lateral growth. By incorporating grain size and geometry, a structure-dependent grain boundary sliding coefficient and measured film stresses the local conditions for whisker growth, including the growth rates, can be calculated. As described here, other commonly observed whisker and hillock morphologies and geometries are consistent with this model, as are the effects of a surface oxide film and thermal cycling.