An investigation was made of the grain growth and other microstructural changes occurring during the liquid-phase sintering of NbC alloys with similar to 20 wt % cobalt. The effects of sintering time, sintering temperature, and small alloying additions were studied. It was found that the grain growth of NbC in liquid cobalt, at 1420 degrees C, can be described by the equation: (d) over bar3 - (d) over bar (3)(0) = Kt where (d) over bar is the mean linear intercept of the grains after time t, and (d) over bar (0) the initial mean intercept, K being a temperature-dependent constant with an "activation energy" of 95 +/- 15 kcal/mole. This equation suggests that grain growth occurs by a solution/precipitation process controlled by diffusion in the liquid phase. Small alloying additions of WC, TiC or NbB(2) inhibit the growth and/or alter the growth process, as well as affecting such properties as the shape and contiguity of the carbide grains. The relative significance of grain coalescence to grain growth in a liquid phase is discussed. By examining theoretically the effect of anisotropy of interface energy on the cube reversible arrow sphere grain-shape change, it has been possible to explain the observed sensitivity of grain shape towards sintering conditions.
