Effect of bimodal WC particle size and binder composition on the morphology of WC grains in WC–Co–Ni3Al cemented carbides

Abstract

In addition to dispersed nanoparticles in the binder phase, the effect of Ni3Al on the growth mechanism of tungsten carbide (WC) grains is also essential for the fabrication of high-quality of cemented carbides. In this work, WC–Co–Ni3Al cemented carbides with different combinations of Co and Ni3Al binders was studied by using the original artificial bimodal WC grain size distribution. The WC particle sizes of medium 4 μm, fine 1 μm and ultrafine 0.2 μm were adopted. A series of WC–Co–Ni3Al alloys were firstly designed based on thermodynamic calculations and then liquid-sintered at 1450 °C for 1 h. Subsequently, the morphology and grain size distribution of WC grains were studied. By increasing the proportion of Ni3Al in the Co–Ni3Al composite binder phase, the solid–liquid interfacial energy increases significantly, which may provide a higher driving force for abnormal grain growth (AGG) through 2-dimension (2D) nucleation. However, the increase of Ni3Al proportion conversely greatly raises the energy barrier for the migration of W and C atoms into liquid binder phase, which finally retards the AGG of WC. Consequently, the AGG of WC decreases and the number of crystallites with blunt faces increases on WC particles with the increase of Ni3Al proportion, which can be well accounted for by the presently detected WC morphology evolution.