Effect of post-spray annealing on the microstructure and corrosion resistance of nano-(Ti,V)N coatings

To improve the microstructure and properties of a nano-(Ti,V)N composite coating prepared by reactive plasma spray deposition, post-spray annealing was performed at 600 °C for durations of 1, 5, and 10 h, respectively. The microstructure and phase of the heat-treated coatings were analyzed by scanning electron microscopy, X-ray diffraction, and transmission electron microscopy, and the change in the residual stress of the coating at different holding times was measured using the sin2ψ method. The corrosion resistances of the coatings were evaluated by electrochemical testing. The main phases of the reactive plasma sprayed nano- (Ti,V)N coating were determined to be TiVN2 and Ti3O. With an increase in the holding time, the proportion of the Ti3O phase increased and an oxide TiVO4 appearred. The TiVN2 grain size gradually increased. The coating with the lowest porosity and best corrosion resistance was obtained with an annealing time of 1 h. The maximum corrosion potential was −0.345 V, and the minimum corrosion rate was 8.24 × 10−2 mm/y. The (Ti,V)N coating did not form primary cells like metals when exposed to 3.5 wt% NaCl, but electrolyte solvents penetrated into the coating through pores and microcracks and corroded the substrate. The corrosion resistance of the annealed (Ti,V)N coatings was significantly improved, exhibiting a first immersion stage 48 times longer than that of the untreated coating.