Effect of carbon activity and powder particle size on WC grain coarsening during sintering of cemented carbides

• We investigated the effect of carbon activity on WC grain coarsening in cemented carbides.
• A more homogenous grain size distribution is seen in alloys with a high carbon activity compared with a low.
• A lower carbon activity seems to lead to an increased tendency for developing a bimodal size distribution.
• The initial powder particle size distribution is important to consider in order to predict WC grain coarsening.

Liquid-phase sintering is an important step in the production of cemented carbides. During sintering, the average WC grain size increases, leading to a coarser structure, which affects the performance of the final product. The coarsening occurs by dissolution of small grains and growth of large grains. In the present work, the effect of high carbon activity during sintering on the WC grain coarsening has been evaluated using electron backscattered diffraction (EBSD) and the results have been compared with a previous work where sintering was performed at a lower carbon activity. A more homogeneous grain size distribution was observed in alloys sintered at a high carbon activity. In addition, the effect of the initial powder particle size distribution was investigated. It was found that the coarsening rate of a WC powder with an initial small average grain size is significantly higher as compared to the coarsening rate for a powder with a larger initial average grain size. The results obtained emphasize the importance of considering the complete particle size distribution in order to predict coarsening.