WC grain growth and grain growth inhibition in nickel and iron binder hardmetals

Abstract

WC grain growth and growth inhibition of an 0.6 μm FSSS WC powder (average SEM size: 0.35 μm) were studied in WC–10 wt% Ni alloys by adding 0–2 wt% of inhibitor carbides (VC, Cr 3C 2, TaC, TiC and ZrC). Alloy gross carbon content turned out to be a crucial factor for WC growth in Ni alloys, even with high inhibitor additions. Coarsening was more pronounced in high carbon alloys, compared with low carbon grades, resulting in a significantly lower hardness. VC proved to be by far the most effective grain growth inhibitor in WC–Ni hardmetals, followed by TaC, Cr 3C 2, TiC and ZrC. Hardness increased with increasing amount of additive but reached a maximum above which it remained about the same. Experiments on WC–Fe–(VC) alloys revealed that WC grain growth is strongly restricted in Fe-binder alloys, even without additions of growth inhibitors. Binder chemistry thus strongly influences both continuous and discontinuous WC grain growth. This chemistry is determined by the nature of the binder matrix (Fe, Co, Ni), the alloy gross carbon content (which determines the composition of the binder matrix) as well as the inhibitor additive.