Abstract
The purpose of this study was to investigate the oxidation behavior and corrosion resistance of the vacuum annealed ZrN-coated stainless steel (SS) deposited by two deposition methods. ZrN thin films were deposited on AISI 304SS by hollow cathode discharge ion-plating (HCD-IP) and unbalanced magnetron sputtering (UBMS). Afterwards, the specimens were annealed at 1000°C in vacuum (4×10-6 Torr) for a duration ranging from 1 to 4 hr. The XRD results indicated that ZrN remained as the major phase in the oxidized thin films even after heat treating at 1000 °C for 4 hr in vacuum. Since the grain size of the as-deposited ZrN films by UBMS was larger than that by HCD-IP, the surface grain size of the oxidized film showed the similar results, which also affected the phase formation after vacuum annealing. The oxidized ZrN thin film on 304SS formed two oxide layers, the outer layer on the film surface and the inner layer nearby the film/substrate interface, which could be attributed to the simultaneous diffusion of oxygen from film surface and the edge of film/substrate interface, respectively. The results of potentiodynamic polarization scan showed that the corrosion resistance of the oxidized ZrN-coated SS was excellent and increased by about 1000 times relative to that of bare 304SS. The corrosion area after 500-hr salt spray test was less than 6.7 % for the oxidized ZrN-coated SS, and the oxidized ZrN films deposited by UBMS had better durability in salt spray test. The fully oxidized ZrN thin film deposited by UBMS showed great corrosion resistance and remained intact on 304SS substrate after potentiodynamic polarization scan and 500-hr salt spray test, which was associated with the enhanced adhesion by the interdiffusion layer from heat treatment. The results indicated that ZrN thin films deposited by both UBMS and HCD-IP could be used for the growth of oxidized layer by vacuum annealing. Therefore, UBMS could replace HCD-IP to deposit ZrN thin films on 304SS to produce an oxidized ZrN layer with excellent corrosion resistance.