CHEMICALLY-INDUCED MIGRATION OF LIQUID-FILM IN W-NI-FE ALLOY

Abstract

The rate of chemically induced migration of liquid films analogous to DIGM is shown to vary with the amount of the solute atom added. Molten Ni-Fe films between spherical W particles or W-Ni grains formed by liquid phase sintering have been observed to migrate during heat-treatment at 1550°C, and the migration rate increases with the amount of Fe added until the total Fe Ni ratio exceeds about 2 3 by weight. The result is attributed to increasing Fe concentration and, hence, increasing coherency strain energy in thin diffusion layer on the surface of retreating W or W-Ni grains. Upon prolonged heat-treatments, the curvature of liquid films increases sufficiently to cause a reversal of their migration.