Abstract
N-doped ZrO2 thin films were deposited respectively on Si (Si-series) and 304 stainless steel (SS-series) substrates using hallow cathode discharge ion-planting (HCD-IP). The objectives of the present study were to understand the effect of substrate materials on phase transition and to provide a feasible approach to manufacture N-doped ZrO2 coatings with excellent corrosion resistance and good adhesion. By maintaining oxygen flow rate at 10 sccm and adjusting nitrogen flow rate, ranging from 0 to 12 sccm, the compositions and phase ratios of the N-doped ZrO2 thin films can be controlled. With increasing nitrogen flow rate, the XRD patterns showed that the phase content of c-ZrO2 increased while that of m-ZrO2 decreased, and then ZrN phase increased. The N solubility limit in ZrO2 for the formation of ZrN was 8.8 and 8.3 at% for the as-deposited thin film on SS and Si, respectively. After annealing in vacuum, different phase transitions were found for the specimens of different substrates. At higher nitrogen content, phase separation of ZrN from c-ZrO2 occurred in the SS-series specimens, while the main phase transformed from c-ZrO2 into Zr2ON2 in the Si-series specimens. The difference in defects between SSAD and SiAD-series specimens may be derived from the substrate effect, leading to different phase transitions after annealing. The corrosion resistance of SS-series specimens was evaluated by potentiodynamic scan in both 5% NaCl and in 1N H2SO4 solutions, and salt spray test was employed to access the durability of the films. Corrosion resistance was associated with film packing density and major phases. The HCD-IP method can effectively overcome the surface wetting problem of ZrO2 on stainless steel, and hence N-doped ZrO2 coating on stainless steel possesses excellent adhesion and corrosion resistance. N-doped ZrO2 thin films containing from 14.4 % to 28.8 % ZrN were found to have better corrosion resistance than pure ZrO2 thin films.