Microstructures in ZrC-doped WC-Co alloys, which were prepared by liquid-phase and solid-phase sintering, were investigated mainly by high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectrometry (EDS). HRTEM study has revealed that multi facet structures, which are often observed in VC-doped alloys, were not formed in ZrC-doped alloys. In addition, the segregation of Zr at WC/Co interfaces could not be detected by EDS analysis even with nano size electron probe. Doped ZrC was found to exist as other carbide grains without dissolving into γ-phase, i.e., Co phase by EDS-mapping performed for liquid-phase sintered alloys. In the case of liquid-phase sintering, the inhibition effect for the grain growth caused by ZrC-doping was confirmed to be very small as previously reported. In contrast, it was found that ZrC-doping largely retards WC grain growth in the case of solid-phase sintering. The retardation of WC grain growth observed in solid-phase sintered alloys was considered to be closely related to a low sinterbility due to a low wettability between Co and ZrC.
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