Microstructure Evolution in the Cemented Carbides WC-Co I. Effect of the C/W Ratio on the Morphology and Defects of the WC Grains

The morphology and the interface features of WC grains are examined by SEM and TEM in cemented carbides WC-8 wt% Co. Three compositions — the mixture {WC + Co binder} and the mixtures with graphite or η — are studied after treatments at 1200 and 1450 °C. The effect of the C content is observed both on the WC crystal features and on the microstructure evolution. In all the alloys, large faceted grains that are defect free single crystals are formed at 1450 °C. On the C rich side, the increase in number and size of the large grains is more regular, the WC grains are more faceted and grow already during heating. On the W rich side, the WC grains have slightly rounded corners and interface steps. The C content influence on the interface energy anisotropy and the growth process of the WC grains is discussed from the microstructure results.