Effect of nonhydrostatic stresses on solid-fluid equilibrium. I. Bulk thermodynamics

We present a thermodynamic analysis of the effect of nonhydrostatic stresses on solid-fluid equilibrium in single-component systems. The solid is treated in the small-strain approximation and anisotropic linear elasticity. If the latent heat of the solid-fluid transformation is nonzero and pressure in the fluid is fixed, the shift of the equilibrium temperature relative to hydrostatic equilibrium is shown to be quadratic in nonhydrostatic components of the stress. If atomic volumes of the phases are different and temperature is fixed, the shift of the equilibrium liquid pressure relative to a hydrostatic state is quadratic in nonhydrostatic components of the stress in the solid. The stress effects at special points, at which either the latent heat or the volume difference turn to zero, have also been analyzed. Our theoretical predictions for the temperature and pressure shifts are quantitatively verified by atomistic computer simulations of solid-liquid equilibrium in copper using molecular dynamics with an embedded-atom potential. The simulations also demonstrate spontaneous crystallization of liquid on the surface of a stressed solid with the formation of solid-solid interfaces with the same crystallographic orientation of the solid layers. The lattice mismatch between the stressed and unstressed regions is accommodated by misfit dislocations dissociated in a zigzag pattern.