Segregation of Dopants at WC/Co and WC/WC Interfaces in Solid-State-Sintered WC-VC-Cr₃C₂-Co Cemented Carbides

Abstract

The segregation of V and Cr at WC/Co and WC/WC interfaces in ultrafine-grained WC-0.7VC-1.4Cr 3 C 2 -10Co (mass%) cemented carbides produced through solid-state sintering and semi-sintering was investigated. This segregation was compared against that of a liquid-statesintered specimen to elucidate the mechanism by which WC grain growth is inhibited by V and Cr. The V and Cr were found to segregate at the WC/Co and WC/WC interfaces during solid-state sintering and semi-sintering, but no differences were observed in the V and Cr concentrations at the interfaces among the liquid-state-sintered, solid-state-sintered and semi-sintered specimens. Furthermore, these concentrations were unchanged by quenching of the solid-state-sintered specimen. From these results, it was concluded that (V,W,Cr)C x segregation layers are stably formed at the WC/Co and WC/WC interfaces at a temperature below the solidus of the Co phase, but almost dissolve in the liquid Co phase once the temperature exceeds its liquidus. Thus, the (V,W,Cr)C x segregation layers observed at the WC/Co and WC/WC interfaces at room temperature are formed during the cooling that follows the liquid-state sintering. This supports the finding that WC grain growth is inhibited by the adsorption of dopant atoms onto steps/kinks on the WC surface during liquid-state sintering, as well as by the segregation layers formed on the WC surface during solid-state sintering.

First-principles derived complexion diagrams for phase boundaries in doped cemented carbides

“…During cooling in the end of the sintering cycle, most of the dissolved atoms leave the Co binder phase [36] and reprecipitate onto existing carbide grains. It is thus conceivable that experimentally observed atomic structures and dopant segregation correspond to a lowtemperature equilibrium or some frozen-in state from the end of the cooling [37,38]. However, experimental studies using rapid temperature quench of the samples give strong evidence for the existence of thin films in WC/Co interfaces at the holding temperature during liquid phase sintering [30].…”