Effect of Fe addition on the growth of W solid grains dispersed in Ni-W liquid matrix at 1540℃ has been studied. Mixtures of fine W and Ni powders containing 12.4 wt.% Ni have been sintered for 30 min and 4 h until W grains have grown considerably. Then each specimen has been resintered for various times up to 32 h after adding some Fe powder to make the composition of W-12 wt.% Ni-3 wt.% Fe (group Ⅰ). After the Fe addition, the grains grow more rapidly and the stationary particle size distribution cannot be maintained for a short period. The grain growth rate and the particle size distribution are returned to those of Ostwald ripening in agreement with LSW and Ardell's theory. Original W-Ni grain and newly growing region, which is expected to contain some Fe, can be differentiated by strong etching. Equilibrium composition of solid grains is calculated thermodynamically and is W-0.13 wt.% Ni-0.08 wt.% Fe. And when more Fe is added to W-9.6 wt.% Ni with the final composition of W-9 wt.% Ni-6 wt.% Fe (group Ⅱ), the grains not only grow more rapidly, but also lose their sphericity by forming regions with negative curvature. The spherical grain shape is restored after prolonged sintering. Calculated equilibrium composition of solid grains of group Ⅱ is W-0.09 wt.% Ni-0.23 wt.% Fe. The enhanced grain growth and the grain shape change (for group Ⅱ) are attributed to the precipitation of a W-Ni-Fe phase with lower chemical free energy than the original W-Ni grain. As the magnitude of the chemical free energy can be varied by the amount of added Fe, it is expected that the difference between group Ⅰ and group Ⅱ in microstructural change arises from the competition between the driving force by the solid-liquid interfacial free energy and the chemical driving force. As the chemical driving force diminishes rapidly, the grains grow by normal Ostwald ripening again.
