Diffusion parameters of grain-growth inhibitors in WC based hardmetals with Co, Fe/Ni and Fe/Co/Ni binder alloys

The diffusion behaviour of the grain-growth inhibitors (GGI) Cr and V during early sintering stages from 950 to 1150 °C was investigated bymeans of diffusion couples of the typeWC-GGI-binder/WC-binder. Besides Co, also alternative Fe/Ni and Fe/Co/Ni binder alloyswere investigated. Itwas found that the diffusion in green bodies differs significantly fromsintered hardmetals. Diffusivities in the binder phasewere determined fromdiffusion couples prepared from model alloys and were found to be almost equal for Co and alternative binder alloys. The diffusion parameters determined fromgreen bodies allowed to estimate the GGI distribution in a hardmetal during heat up. This was subsequently used to estimate an appropriate grain size of VC and Cr ₃C ₂ in hardmetals, which is required to ensure a sufficient GGI distribution during sintering beforeWC grain-growth initiates.