HRTEM Microstructure and Segregation Amount of Dopants at WC/Co Interfaces in TiC and TaC Mono-doped WC-Co Submicro-grained Hardmetals

Abstract

HRTEM (high resolution transmission electron microscope) microstructure and the segregation amount of dopants at WC/Co interfaces were investigated on TiC and TaC mono-doped WC-10mass%Co submicro-grained hardmetals, following the previous studies on VC, Cr₃C₂ and VC+Cr₃C₂ doped hardmetals. The dopant amounts in the specimen were nearly a half of the solubility limit in Co liquid phase. At WC(0001)/Co interface, Ti segregated in a small amount and Ta hardly segregated. At WC(1010)/Co interface, both Ti and Ta hardly segregated. The order of segregation amounts (at% of metal of carbide or mol% of carbide) of dopants at WC(0001)/Co interface (TaC<TiC<Cr₃C₂<VC≤VC+Cr₃C₂) were not necessarily positively correlated with the magnitude of grain growth inhibition effect (TiC<Cr₃C₂<TaC<VC≤VC+Cr₃C₂). This suggested that the segregation layers of dopants themselves were not directly related with WC grain growth inhibition mechanism and that the layer was not generated by an equilibrium segregation mechanism during the sintering stage, but by a heterogeneous precipitation mechanism during the cooling stage of sintering.