Kinetics and oxidation behavior of laser clad WC-Co and Ni/WC-Co coatings

In this study, the oxidation behavior of WC-12Co and electroless Ni/WC-Co coatings is investigated by Thermogravimetric analysis (TGA), X-Ray Diffraction (XRD), and scanning electron microscope (SEM). Time dependence of weight gain showed a linear behavior for WC-Co coating and a parabolic-like behavior for Ni/WC-Co coating. This behavior is related to the reaction-controlled and diffusion-controlled oxidation processes in the WC-Co and Ni/WC-Co coatings, respectively. Oxidation resistance of coatings was determined by phase composition and formation mechanism of the protective oxide layer. The results demonstrated that the use of Ni/WC-Co powder could reduce significantly the porosity and cracks and lead to a compact and protective (Ni, Co)WO₄ layer. The apparent activation energy was measured to be about 98.3 and 229.4 kJ/mol for WC-Co and Ni/WC-Co coatings, respectively.