Coarse-grained WC–6Co hardmetals with dual-scale and plate-like WC structures fabricated by convention powder metallurgy process

Abstract

In this work, coarse-grained WC–6Co hardmetals featuring dual-scale and plate-like structures were successfully fabricated via conventional powder metallurgy process using W, ultrafine WC, Co and carbon black as raw materials. The investigation focuses on the effects of two critical factors, sintering temperature and ultrafine WC powder content, on the microstructures, densities, and mechanical properties. The results demonstrate that increasing the sintering temperature accelerates the growth of WC grains via 2D nucleation growth mechanism, thus enhancing the plate-like structure of WC grains. The addition of ultrafine WC powder reduces the mean WC grain size and eliminates the preferential orientation of WC grains because of its separating effect on coarse WC grains. Moreover, the dual-scale and plate-like structures can be achieved with sufficient ultrafine WC content (≥ 20 wt%) and adequate sintering temperature (≥ 1500 °C). Notably, the coarse-grained WC–6Co alloy sintered at 1550 °C with the addition of 20 wt% ultrafine WC powder exhibits good comprehensive mechanical properties: hardness of 1493 ± 7 HV30, transverse rupture strength of 2698 ± 58 MPa and fracture toughness of 16.93 ± 0.65 MPa·m1/2.