Thermodynamic analysis of cooling-induced segregation and grain growth inhibition in WC–Co cemented carbides

Understanding interfacial segregation is critical for controlling WC grain growth in ultrafine WC–Co cemented carbides. This study examines WC–Co alloys containing VC (0.5 mass%), TaC (0.5 mass%), and TiC (0.075 mass%) using phase diagram calculations and cooling simulations to clarify segregation mechanisms. Results demonstrate that VC dissolves completely during liquid-phase sintering and subsequently segregates to WC/Co interfaces during cooling. Based on these findings, we propose that VC repeatedly forms and dissolves as clusters on WC surfaces to inhibit grain growth. Subsequent layer formation during cooling is driven by solute enrichment and facilitated by a small lattice misfit (~1.4%). TaC exhibits similar cooling-induced segregation but to a much smaller extent because the solubility difference between liquid and solid Co is smaller than for VC, reducing the precipitation driving force, and its lattice misfit with WC is larger (~8.6%). TiC behaves differently: most TiC remains as stable particles throughout sintering, while a minor fraction dissolves and subsequently segregates to WC/Co interfaces during cooling. Despite these differences in initial phase state, TiC and VC share a common cooling-induced mechanism driven by solute pile-up during Co solidification. These findings provide a thermodynamic basis for distinguishing sintering-stage stability from cooling-induced segregation and guide additive selection and cooling control for ultrafine WC–Co grades. • Cooling-induced segregation forms interfacial layers in WC–Co cemented carbides. • Solubility drop during Co solidification drives solute enrichment at interfaces. • VC dissolves during sintering and precipitates significantly during cooling. • TiC remains stable during sintering with limited cooling-induced segregation. • Thermodynamic constraints govern grain growth inhibition, not segregation layers.