Abstract
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.
Highlights
Corrosion is an important surface degradation process in some, if not all, applications of tungsten-carbide-(WC-) cobalt- (Co-) based hardmetals
As was the case in a previous study, the anodic polarization behavior for each specimen was repeatable (Figure 3). e anodic polarization behavior in NaCl, where all samples showed pseudopassive behavior, is similar to that observed in HCl acid solutions [8]. e pseudopassive behavior was more pronounced for the base alloy WC-10Co, the specimen with the least magnetic saturation (Table 1)
E pseudopassive behavior observed for WC-10Co hardmetal in the NaCl test solution is in contrast with other literatures [27] where dilute (0.1 M) NaCl solutions were used. is is because the higher Cl− anion concentration used in this study compared to literature favours passivation [28]
Summary
Corrosion is an important surface degradation process in some, if not all, applications of tungsten-carbide-(WC-) cobalt- (Co-) based hardmetals. Nickel [3], and chromium [4] especially, and recently, ruthenium [5] have been shown to markedly improve the corrosion resistance of WC-Co-based hardmetals. E corrosion resistance of WC-Co can 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]. Earlier studies [6] found small additions of VC to WC-Co had at best a neutral effect on the corrosion resistance. Studies in hydrochloric and sulphuric acids have indicated that 10 wt% VC improves the corrosion resistance of high Co content WC-Co [7]. T 1: Nominal chemical composition and magnetic properties of test specimens
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