Microstructure and properties of WC-11.5%Fe-4%NbH-0.5%C cemented carbides produced by spark plasma sintering

Abstract

This study investigates the influence of milling parameters and sintering cycle on the microstructure and properties of cemented carbides with an overal WC–11.5wt%Fe–4wt%NbH–0.5wt%C starting powder composition. The raw material powders were milled and mixed in a ring mill or planetary ball mill and sintered at 1150, 1200 or 1250 °C using spark plasma sintering (SPS). The cemented carbide density, Vickers hardness and fracture toughness were evaluated. The microstructure was investigated by optical and scanning electron microscopy using wavelength dispersive X-ray spectroscopy for elemental mapping. The transition from NbH to NbC was identified for all sintered materials. Moreover, microstructural gradients were formed creating bi-layered structured materials with higher hardness edges and tougher cores. The highest microstructural homogeneity and hardness were found for planetary ball milled starting powder sintered at 1250 °C. For these samples, the highest density recorded was 13.69 g/cm3, which also obtained highest hardness values of 1620 Hv and 1589 Hv, on the surface and center regions, respectively.