Planetary low‐temperature high‐energy ball mill was used for preparing the mixed powders with different particle sizes by adjusting the milling time. The ultrafine grain gradient cemented carbides were prepared by sinter‐HIP treatment. The effects of milling time on the gradient formation, grain growth, and mechanical properties of ultrafine grain gradient cemented carbides were investigated. The results show that the high‐energy ball milling cannot effectively reduce the particle size of mixed powder with short milling time. In addition, the particle size of the mixed powder is significantly reduced, while the specific surface area is significantly increased when the ball milling time exceeds 25 hours. The gradient layer thickness and the grain size increase at the beginning and then decrease when the mixed powder particle size was decreased. Simultaneously, the density, hardness, and fracture toughness of the alloy increase gradually. On the contrary, the number of WC with abnormal grain growth is significantly increased. The thickness of the gradient layer reached 32 μm, and the mean WC grain size is 314 nm. Based on the analyzed results, an optimized gradient layer thickness, grain size, density, and hardness can be obtained when the ball milling time is 35 hours.

No abstract

In this study, ultrafine WC powder was used as raw material, cubic carbonitrides Ti(C,N) and (W,Ti)C were added as gradient former, the cemented carbides with cubic carbide free layer (CCFL) structure was prepared by two-step sintering which was pre-sintering combined gradient sintering. The effect of gradient sintering temperature on the free-cubic layer structure formation and grain growth was studied. The results show that the layer structure gradient-cemented carbide with free-cubic phase in the surface can be prepared by two-step sintering when the ultrafine WC powder was used as raw material. However, many abnormal WC grains appeared after pre-sintering and gradient sintering. In the process of gradient sintering, with the increase of gradient sintering temperature, the thickness of free-cubic phase layer does not increase obviously, but the grain size of WC increases more, especially the number and size of abnormal WC grains growth increased.