The instability of solid-liquid interface in MoNi alloy induced by diffusional coherency strain

Abstract

In an alloy of 85Mo-15Ni by weight prepared by liquid phase sintering for a long time, the relatively large spherical MoNi grains are in chemical equilibrium with the surrounding liquid matrix and are separated from each other by bulk liquid. When the chemical equilibrium between the grain and the liquid is broken either by heat-treating at a temperature different from that of the sintering or by adding Fe to the liquid, some grain surface zones become convex by reprecipitation of a new equilibrium solid, while others become concave by dissolution of the initial solid solution. An instability of the grain-liquid interface in the form of an undulating structure thus develops. It is demonstrated that the driving force for this solution-reprecipitation process arises from the coherency strain energy in the solute diffusion zone at the dissolving grain surface.