Characterisation and performance optimisation of WC-MC/M(C,N)-Co hardmetals

Abstract

WC-MC/M(C,N)-Co hardmetals with 10 wt% Co were prepared in undoped, as well as in either Cr- or V-doped form. The starting formulations contained 5 wt% TiC or 5% (TiC+TiN), the latter with two different TiC/TiN ratios, and 10 wt% (Ta,Nb)C. For each composition, a low-C grade (Ms ≈ 75%) and a high-C grade (Ms ≈ 88%) was adjusted by C or W addition, to end up with 18 different hardmetal formulations, prepared in an industrial process. Model alloys, MC and M(C,N) phases with a composition reflecting the composition of these phases in the hardmetal were prepared, too. A variety of data was collected: binder phase and hard phase compositions of model alloys by wavelength-dispersive electron-probe microanalysis (WDS-EPMA), liquid phase formation temperatures in model alloys with free C and eta by differential thermal analysis (DTA), respectively, thermal conductivities of MC and M(C,N) phases and hardmetals by laser-flash temperature conductivity and heat capacity measurements up to 950 °C, crystallite-size distribution by electron backscatter diffraction EBSD, hardness HV30, Palmqvist-Shetty fracture toughness KIC, Weibull evaluation of the transverse rupture strength (TRS), oxidation resistance in air as well as milling tests on coated hardmetals with Ti(C,N)/Al2O3 and (Ti,Al)N layers.