Anodic behaviour of WC-Co type hardmetal

An understanding of the anodic behaviour of WC-Co type hard-metals is vital for the functional behaviour of this class of materials. The anodic oxidation of WC-13Co grade hardmetal in 0.1 M H2SO4 was investigated. This study is based on electrochemical (linear sweep voltammetry, cyclic voltammetry, impedance spectroscopy), compositional (energy dispersive spectroscopy), structural (X-ray diffraction) and morphological (scanning electron microscopy) investigations. The potential range in which the oxidation of the Co-alloy takes place with respect to the nobler carbide phase was defined. Within this potential interval a passivating behaviour for the binder alloy was shown. The potential threshold for WC oxidation was identified by monitoring the inception of the electrochromic loop. The anodic attack gives rise to the formation of hydrous WO3. The attack morphology is characterised by the alteration of the grain shape with formation of jelly-like microscopic and flaky macroscopic structures.