%0 Journal Article
%T Corrosion of WC-VC-Co Hardmetal in Neutral Chloride Containing Media
%A C. N. Machio
%A D. S. Konadu
%A J. H. Potgieter
%A S. Potgieter-Vermaak
%A J. Van der Merwe
%J ISRN Corrosion
%D 2013
%R 10.1155/2013/506759
%X The effect of varying VC content on the corrosion behavior of WC-10 wt% Co hardmetals in sodium chloride (NaCl) and synthetic mine water (SMW) solutions has been investigated using anodic polarization scans and surface analytical methods. It is shown that the polarization behavior is active-pseudopassive in NaCl and active in SMW regardless of the VC content, while the corrosion resistance is poorer and independent of VC content in NaCl but better at high VC contents in SMW. The corrosion behavior of samples is explained using the effect of VC on the chemical composition of the binder. 1. Introduction Corrosion is an important surface degradation process in some, if not all, applications of tungsten-carbide-(WC-) cobalt- (Co-) based hardmetals. Applications like tools for machining of metals [1] and for wear resistance in the mining industry [1] expose the WC-Co to fluids that can be corrosive, leading to a reduced useful life. The Co binder is the least corrosion resistant constituent [2], and efforts to improve WC-Co corrosion resistance have involved altering the chemical composition of the binder by introducing more corrosion resistant elements. Nickel [3], and chromium [4] especially, and recently, ruthenium [5] have been shown to markedly improve the corrosion resistance of WC-Co-based hardmetals. The corrosion resistance of WC-Co can also be improved by some transition carbides, which have been usually added in small amounts. Chromium carbide (Cr3C2), for example, added to WC-Co in amounts of about 0.5£¿wt.% markedly improves corrosion resistance [6]. The effect of vanadium carbide (VC) has not been as straight forward as that of chromium carbide. Earlier studies [6] found small additions of VC to WC-Co had at best a neutral effect on the corrosion resistance. Subsequent studies by other researchers, using higher amounts of VC have indicated otherwise. For example, studies in hydrochloric and sulphuric acids have indicated that 10£¿wt% VC improves the corrosion resistance of high Co content WC-Co [7]. This result has been confirmed by the current authors [8] who have shown that the corrosion resistance, determined from the corrosion current density at the free corrosion potential, increases with increasing VC content. The current article is extending the corrosion study of the materials to neutral chloride electrolytes to determine whether the improved corrosion resistance is solution independent. It has happened that observations made on the corrosion of WC-Co in acidic electrolytes do not appear to be reproduced in tests that use neutral chloride
%U http://www.hindawi.com/journals/isrn.corrosion/2013/506759/