Effect of heat treatment on the microstructure and corrosion behaviors of reactive plasma sprayed TiCN coatings

In the present study, TiCN coatings were developed by atmosphere reactive plasma spraying, and micro-defects, e.g. pores, cracks, cavities, inevitably existed in the as-sprayed coatings. Heat treatment as one of key method to improve corrosion resistance of coatings has attracted widely interests. The microstructure, corrosion properties of samples with different heat treatment temperatures were studied using XRD, EPMA, EIS measurement and Potentiodynamic polarization curves. Results show that the sample with higher heating temperature can form more Ti2O, Ti3O and TiO2, and the porosity of coatings was decreased, which results in an increment of energy or potential for the corrosive ions into the coatings. It found that the one heat-treated at 600 degrees C exhibits a better corrosion resistance with an ccorrosion potential (E-corr) of -517 mV and low corrosion current (i(corr)) of 2.18 mu A.cm(-2), compared with other samples. The results also identify that local corrosion originates from the microdefects, and the first formed oxides provide an infiltrated channel for latter corrosion.