Grain growth behaviour and mechanical properties of coarse-grained cemented carbides with bimodal grain size distributions

Abstract

The WC grain growth behaviour and mechanical properties of coarse-grained cemented carbides with bimodal grain size distributions were investigated using WC-5Co composite powders with accurately controlled WC grain size distribution. The composite powders were prepared by a Sol-Gel process and ultrafine WC (UF-WC, 300 nm) was added to coarse WC (C-WC, 6.0 μm) to adjust the WC grain size distribution. It indicated that the WC grains undergo 2-D nucleation with 2-D growth at low UF-WC addition (≤6 wt%), resulting in a truncated trigonal prisms shape, whereas the WC grains grow up through 2-D nucleation with 3-D growth at high UF-WC addition (≥9 wt%), leading to a pyramid-like shape with a layer-by-layer structure of WC grains. Vickers hardness and fracture toughness tests indicated that the cemented carbide containing 6 wt% UF-WC present significant improvements in the hardness (1281.7 ± 1.6 HV10) and the fracture toughness (25.4 ± 0.2 MPa m 1/2 ). • 2-D nucleation and growth is the primary coarsening mechanism for coarse-grain WC in the liquid phase cobalt matrix. • Grain growth behaviours of WC depends on the driving force of nucleation and growth. • The mechanical properties of cemented carbides are affected by the shape and size distributions of WC grains.