Microstructural evolution and mechanical behaviors of graded cemented carbides

Graded cemented carbides have been developed by pre-sintering carbon-deficient compacts and subsequently carburizing in this work. The microstructures and the mechanical behaviors of the graded cemented carbides were studied. The formation mechanism of the graded structure can be attributed to the Ostwald ripening induced by the carbon diffusion. The difference of the Ostwald ripening rate in areas of different carbon contents leads to the variation in the WC grain-packing structure, hence driving the flow of the liquid Co from the surface to interior. Theoretical results based on the carbon diffusion in the liquid Co match well with the experimental measurements. The graded cemented carbides possess a good combination of high hardness and high toughness, and indicate an excellent performance in the engineering test. The results also show that a high carburizing temperature and a long soaking time lead to an excessive growth of WC grains in the outer layer, which will block the further diffusion of carbon into the alloy body, and will deteriorate the mechanical behaviors as well.