Effect of tribo-layer on the corrosion behavior of WC-Co and WC-Ni cemented carbides in synthetic mine water
J. Jayaraj, Mikael Olsson
Abstract
For rock drilling applications, the cemented carbides containing hard WC grains in a ductile Co binder are commonly used as drill buttons. In considering the environmental and health aspects an alternate to Co-binder is pursued. In the present work, using standard scratch testing the friction and wear properties of the WC-20 vol% Ni grade is studied and compared to that of WC-20 vol% Co grade. The deformation and wear characteristics of the cemented carbide grades are evaluated and correlated to the microstructural changes during scratch testing. Also, the electrochemical impedance spectroscopy (EIS) behavior of the as-polished and scratch-tested cemented carbides was studied at the open circuit potential condition of simulated mine water (SMW) for 1 h. The obtained polarization resistance and charge transfer resistance values from the EIS analysis are correlated to the corrosion resistance of the samples. In both as-polished and scratch-tested conditions the WC-Ni grade exhibited higher polarization resistance values indicating high corrosion resistance than the WC-Co. In comparison to the as-polished sample, both the scratch-tested cemented carbides exhibited higher corrosion activity in particular within the scratch-induced tribo-layer. Severe corrosion and complete removal of the tribo-layer was observed for the WC-Co grade when exposed to SMW for 15 h. Site-specific scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX) analysis were carried out to get insight into the corrosion behavior of as-polished and scratch-tested cemented carbides.