WC-Ni-Cr cemented carbides have been used even under corrosive condition because of its excellent corrosion resistance. The corrosion characteristics of this alloy in acidic and neutral solution had been investigated by immersion test and polarization test, and reported that corrosion resistance was improved in the low carbon and high Cr3C2 content alloy.In this report, these corrosion tests were carried out in 1N NaOH solution . In immersion test, most of the dissolved element in the solution was W. The corrosion rate of WC-Ni-Cr was the higher with the lower carbon and the lower Cr3C2 contents, and these results were quite opposite to the tendency in acidic and neutral solutions . In polarization test, a large difference in polarization curves by the change of carbon content was not observed . The passivation region, which was observed in acidic solution , was not observed. In the vicinity of the corrosion potential, the corrosion current density (irorr) decreased with the increase in the carbon and Cr3C2 contents . The difference of corrosion rate with carbon and Cr3C2 contents of WC-Ni-Cr in 1N NaOH solution was considered to be caused by the difference in the amount of W dissolved in the binder Ni phase .
Ti-30mass%Mo alloy is characterized by far better corrosion resistance than pure titanium in non-oxidizing acid such as 35% HC1 solution. This alloy was newly developed in this work by a powder metallurgical process, because the conventional melting-casting process had difficulties in manufacturing the alloy owing to its heavy gravity segregation. The corrosion behavior of sintered Ti-30Mo alloy was studied by both immersion test and electro-chemical measurement. The corrosion rate of 1.3• was obtained by immersion test in 35% HC1 solution, which was 103 times superior to that of pure titanium. The potentio-dynamic polarization curve of this alloy in 35% HC1 solution showed more noble corrosion potential and lower anodic current density than those of pure titanium. The passive film formed on the alloy, in which Mo was enriched by preferential dissolution of titanium, thought to suppress the anodic reaction and improve its corrosion resistance.
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