Development of the microstructure during gradient sintering of a cemented carbide

A gradient sintered WC–Ti(C,N)–Co-based cemented carbide has been studied. The material was sintered in a nitrogen-free atmosphere, resulting in an outward diffusion of nitrogen. Due to the strong thermodynamic coupling between nitrogen and titanium, an inward diffusion of titanium is created. As a result of the diffusion processes the material develops a cubic carbide depleted and binder phase enriched surface zone, and inside this zone a region enriched in cubic carbide. The structure of the gradient surface zone has been studied, where variations in volume fractions of the different phases present have been investigated by scanning electron microscopy (SEM) and image analysis, and elemental variations have been studied with electron probe microanalysis (EPMA). Computer simulations of the gradient formation, based on diffusion and thermodynamic properties, show good agreement with the experimental results, and the gradient formation can be reasonably well predicted. Also studies of grain composition have been performed. In the rim of the cubic carbide grains, variations in composition are found which can be related to the sintering process. The composition of cubic carbide grains has been studied with SEM and analytical electron microscopy.