ＷＣ‐Ｃｒ３Ｃ２‐Ｃｏ系超硬合金の腐食特性に及ぼすＣｏ含有量の影響

Abstract

Though WC-Co cemented carbides are widely used for a variety of machining, drilling, metallic mold and other applications because of their high strength, high hardness and excellent wear resistance, their poor corrosion resistance in aqueous solutions reduces the scope of their application. In this experiment, three kinds of WC-Cr3C2-Co cemented carbides were used, and the influence of Co content on corrosion characteristics of them was investigated by the electrochemical methods such as the potenitodynamic polarization test and electrochemical impedance spectroscopy (EIS), and the observation by scanning electron microscopy (SEM). All of the three specimens showed the similar active, passive and over passive regions during the polarization test, though the passivation was retarded with increasing amount of Co content. EIS test indicated that all of the three samples had the similar capacitance semicircle in the first quadrant. After that, the second capacitance semicircle which involve a film formation following the first capacitance semicircle and the induction semicircle following the second capacitance semicircle were confirmed. From this EIS test result, it was confirmed that the charge transfer resistance (Rct) decreased with an increase in Co content.