纳米及亚微米复合粉添加对超粗晶硬质合金晶粒长大的影响及机制

The synthesized WC-8Co composite powders with the particle sizes of 100, 250 and 400 nm were added to the coarse WC/Co powders. The mixture was sintered at different temperatures in an Ar atmosphere. The morphology, grain size and distribution of the sintered bulks were studied. The WC grain growth mechanism of the samples with composite powder additives at different sintering stages was analyzed. The result shows that the ultra-coarse cemented carbide can be prepared by WC/Co mixed powders to which the nano or submicron particle size composite powder additives are added. In particular, the cemented carbide with a grain size of 9.3 μm can be prepared by using the mixed powder with the nanocomposite powder additives as raw materials. At the initial sintering stage, the addition of the nano and submicron composite powders obviously increases the surface energy of the mixed powders, which is beneficial for promoting the growth of WC grains effectively. During the liquid sintering, the sintered bulks with the nanocomposite powder have a larger dissolution driving force, which causes the small grains to dissolve and precipitate on the surrounding large grains, further increasing the grain size of the sintered bulks. In the bulks where the submicron composite powder is added, the small grains WC are concentrated and the dissolution driving force is small, and the precipitation mainly occurs between the surrounding small grains, and the dissolved precipitate reaches a dynamic equilibrium, so that the average grain size of sintered bulk grows slowly.