Phase transition and mechanical properties of ZrNxOy thin films on AISI 304 stainless steel

ZrN x O y thin films were deposited on AISI 304 stainless steel (304SS) substrates by reactive magnetron sputtering. The specimens were produced by sputtering a Zr target at 500 °C and the reactive gasses were N 2 and O 2 at various flow rates (ranging from 0 to 2 sccm). The purpose of this study was to investigate the effect of oxygen flow rate on the phase transition and accompanying mechanical properties of the ZrN x O y thin films. The oxygen contents of the thin films increased significantly with increasing oxygen flow rate. X-ray diffraction (XRD) revealed that the characteristics of the films can be divided into three zones according to the major phase with increasing oxygen content: Zone I (ZrN), Zone II (Zr 2 ON 2 ) and Zone III (m-ZrO 2 ). The hardness of the ZrN x O y films decreased with increasing oxygen content due to the formation of the soft oxide phase. Modified XRD sin 2 ψ method was used to respectively measure the residual stresses of ZrN, Zr 2 ON 2 and m-ZrO 2 phases. The results showed that the residual stress in ZrN was relieved as the oxygen content increased, and Zr 2 ON 2 and m-ZrO 2 were the phases with lower residual stress. Compositional depth profiles indicated that there was a ZrO 2 interlayer near the film/substrates interface for all samples except the mononitride ZrN specimen. Contact angle was used as an index to assess the wettability of the film on substrate. The contact angles of ZrN, Zr 2 ON 2 and m-ZrO 2 on stainless steel were indirectly measured using Owens–Wendt method. The results showed that ZrO 2 possessed the lowest wettability on 304SS among the three ZrN x O y phases, indicating that the ZrO 2 interlayer may account for the spallation of the ZrN x O y films after salt spray tests.