Corrosion behavior of TaC/Ta composite coatings on C17200 alloy by plasma surface alloying and CVD carburizing

Abstract In order to obtain the combination of improved abrasion and corrosion resistances, TaC/Ta composite coatings were made on C17200 beryllium copper alloy by two steps, surface Ta-alloying at 800 °C for 2 h followed by carburizing at 670 °C for 0.5 h. The corrosion property of TaC/Ta coatings in H 2 SO 4 solution (10%) was investigated by polarization curves and electrochemical impedance spectroscopy. The microstructure of the composite coatings and corroded surface were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope equipped with energy dispersive spectrometer, respectively. The results showed that the composite coating, 8.79 μm in thickness, was composed of the TaC top layer and Ta-Cu intermediate layer. The untreated bare C17200 alloy substrate revealed a poor corrosion resistance. After Ta-alloying and carburizing, the corrosion resistance of C17200 alloy increased due to a higher self-corrosion potential and lower self-corrosion current of TaC/Ta coatings. In addition, TaC/Ta coatings had wider frequency scope, larger radius of capacitive semi-circles, phase angle and |Z| value compared with bare alloy. The protection efficiency of TaC/Ta coatings calculated from electrochemical impedence and potentiodynamic polarization was over 90%. The dense corroded surface and Ta oxide formed in the corroded surface caused an improved anti-corrosion property of TaC/Ta coatings.