The coarsening mechanism for the system of grains immersed in liquid matrix has been investigated by analyzing the growth patterns and kinetics of individual grains. 85Mo-13.5Ni-1.5Fe and 96Mo-3.5Ni-0.5Fe (by wt.pct.) alloy specimens have been prepared by sintering a mixture of fine powders in the presence of liquid phase. When annealed in two or more cycles at $1430^\circ{C}$, etch boundaries are formed at the grain matrix interface during cooling and reheating, which have revealed the growth pattern of individual grains. These boundaries are attributed to slight composition changes of solid phase precipitated on large grains at lower temperatures. With 85Mo-13.5Ni-1.5Fe composition, spherical grains are dispersed in the liquid matrix. The isolated grains grow in a nearly concentric growth pattern in agreement with the solution-reprecipitation process through the liquid matrix. The thickness of growth layer which represents the growth rate of individual grains increases with grain size and reaches maximum at the largest grain. These results are also consistent with the theoretical predictions of Ostwald ripening. The grain boundaries between some grains in contact migrate to the direction of smaller grains, and the rate is expected to be determined by the movement of grooves formed at the junctions of the grains and the matrix, which is in turn dependent on solution-reprecipitation through the matrix. The overall coarsening process is thus shown to be determined by the solution-reprecipitation through the matrix. With 96Mo-3.5Ni-0.5Fe composition, anhedral grains are in contact with the neighbors across grain boundaries or thin liquid films. The coarsening behavior of individual anhedral grains is expected to be determined by the local flux with the nearest neighbors, resulting in a asymmetric growth pattern. The grain boundary migration with low liquid contents can, therefore, be explained based upon the pore drag mechanism suggested by Evans et al. Since the grain boundary migration is inhibited by the continuous liquid prism at the three grain junction, the grain coarsening rate is determined by the solution and reprecipitation at the grain surfaces in contact with the liquid. This coarsening model can be applied to the grain contacts with a thin film of liquid since their movement is controlled by the rate of material transport through the liquid layers at the three grain junctions. Therefore, the effective diffusion distance of solute atoms should correspond to the average linear dimension of the liquid prisms.
