Abstract
The corrosion mechanism of WC-Ni-Cr cemented carbides and TiC-Ti-Mo sintered hard alloys were studied through investigating their corrosion behavior by the electrochemical method such as immersion test and polarization test in various solutions. For WC-Ni-Cr cemented carbides, the corrosion was mainly caused by the dissolution of binder Ni phase in both neutral and acidic solutions, and by the dissolution of W from WC phase and binder Ni-phase in alkaline solution. From the polarization curves of WC-Ni-Cr cemented carbide, the corrosion rate was found to depend on the carbon and Cr3C2 content of the alloy because of the difference in both the ability of passive film formation and the W content in the binder Ni phase. For TiC-Ti-Mo sintered hard alloy, the corrosion was mainly caused by the dissolution of fl-Ti phase in every test solutions. In the TiC-Ti-Mo sintered hard alloy, the spontaneously passivated film adapting to each environment was formed, causing the alloy to show an excellent corrosion resistance in every test solutions. In addition, the corrosion rate of the TiC-Ti-Mo sintered hard alloy increased in 5%HNO3 solution because the chemical decomposition of TiC phase itself might be occurred.
