Corrosion Behavior of High Velocity Oxygen Fuel Sprayed WC-CoCr and WC-Ni Coatings in NaCl Solution

The phase composition and microstructure of high velocity oxygen fuel (HVOF) sprayed WC-CoCr and WC-Ni cermet coatings were analyzed by metallographic microscope, scanning electron microscope, X-ray diffractometer and so on. The potentiodynamic polarization curves and the Nyquist impedance spectra of the coatings in 3.5% (mass fraction) NaCl solution were measured by electrochemical workstation and compared with those of the chromium layer. The results show that: the coatings consisted of WC hard phase and metal binder phase, with a homogeneous and dense microstructure and porosity less than 1.5%; in NaCl solution, the corrosion resistance from high to low was that of WC-CoCr coating, WC-Ni coating, chromium layer; the structure of the HVOF coatings was dense, which prevented the coatings from Cl^-, thus the corrosion resistance of the coatings was better; the addition of a little chrome promoted the formation of a passive film on the surface of CoCr binder phase, thus the corrosion resistance of WC-CoCr coating was better than that of WC-Ni coating.