Effects of Cr,V,Ta additives on electrochemical corrosion behaviors of extra coarse and super extra coarse cemented carbides

The electrochemical corrosion behaviors of WC–8.4Co,WC–8.4Co–0.4Cr3C2,WC–8.4Co–0.4VC and WC–8.4Co–0.4TaC extra coarse and super extra coarse cemented carbides were investigated by means of Tafel curves and Nyquist plots.Electrochemical experiments were carried out in H2SO4 solution(pH=1),Na2SO4 solution(pH=7) and NaOH solution(pH=13).Corrosion surface of the alloys were observed by scanning electron microscopy(SEM).The results show that,comparing with WC–8.4Co referential alloy,the corrosion resistances of WC–8.4Co–0.4Cr3C2,WC–8.4Co–0.4VC and WC–8.4Co–0.4TaC alloys in all the three kinds of corrosion solutions are improved.Among the three additives,Cr3C2 demonstrates the strongest ability in the improvement of the corrosion resistance.All the four alloys exhibit better corrosion resistance in NaOH solution(pH=13) than that in H2SO4 solution(pH=1).The corrosion mechanism is as following: while the alloy is in contact with the corrosion solution,a preferential corrosion and active dissolution take place in the Co binder phase and the corrosion reaction also takes place in the local region of WC grains.