Characterization and Microstructural Evolution of WC-Co Cemented Carbides

Abstract

Two types of cemented carbides have been elaborated from three mixtures of WC and Co powders containing 3, 5 and 6% of cobalt mass. Three samples of these mixtures have been obtained by liquid phase sintering and three others of the same composition have been sintered then densified by hot isostatic pressing (HIP). Observations by scanning electronic microscope have allowed to note that the samples elaborated by sintering followed by an HIP densification have a more homogeneous structure than that observed in the sintered samples. Under the compression, the WC grains flattens and interlock more easily from one another which gives a uniform surface appearance. Energy dispersion analysis shows that these samples contain a very small voluminal fraction of graphite and residual porosities, these are more pronounced in sintered samples, especially in the case of alloys with a low Co content (3 and 5%). X rays diffraction analysis allowed to show clearly the existence of cobalt type carbide in the sintered samples. Measurement of the closed porosity allows to observe that the sintering process followed by densification by HIP leads to the elaboration of alloys with a low rate of closed porosity. Microhardness of these samples have improved hardnesses.