Abstract
This research studied the effect of oxygen flow rate on the composition, microstructure and properties of Zr(N,O) thin films deposited on AISI 304 stainless steel substrate using hollow cathode discharge ion-plating (HCD-IP) method. The Zr:N:O ratios of the Zr(N,O) films were determined from X-ray photoelectron spectroscopy (XPS) and the results showed that there were three kinds of bonding, including ZrN, Zr(N,O) and m-ZrO2. X-ray diffraction (XRD) patterns revealed that phase separation (ZrN and m-ZrO2) occurred at the oxygen content ranging from 31.2 to 49.6 at. %. ZrN single phase existed in the Zr(N,O) films with lower oxygen contents (<18.1 at. %), while m-ZrO2 phase was prevailed as the oxygen content increased over 40.3 at. %. Glancing incidence X-ray diffraction (GIXRD) confirmed the occurrence of phase separation. The phase separation consistently affected hardness, residual stress and corrosion resistance of the Zr(N,O) films. Phase separation of ZrO2 from ZrN lowers the hardness of the Zr(N,O) films as the fraction of ZrO2 lower than 40 %. When ZrO2 is higher than 50 %, the hardness of the films is close to that predicted by Vigard’s law. This is possibly derived from the change of distribution of the ZrO2 phase when ZrO2 becomes the major phase. The residual stresses in ZrN phase was higher than that in ZrO2, and the residual stress decreased for the specimen containing 30 to 40 % of ZrO2. For the samples containing more than 44% of ZrO2, the residual stresses measured by optical method were very close to those measured by XRD in ZrO2 phase. The corrosion resistance of the Zr(N,O) films was evaluated by salt spray test and potentiodynamic scan in two kinds of solutions: H2SO4 + 0.05M KSCN and 5% NaCl solutions. From the results of potentiodynamic scan, it was found that Icorr of the Zr(N,O) films decreased as the packing density increased and the film thickness was not a crucial factor on Icorr; moreover, the electrical conductivity of the film was an another significant factor on corrosion resistance. The results also showed consistent trend in the two solutions.