Effect of nitrogen flow rate on the structure and mechanical properties of ZrN thin films on Si(1 0 0) and stainless steel substrates

Nanocrystalline ZrN films were successfully deposited on Si(1 0 0) and AISI 304 stainless steel substrates using hollow cathode discharge ion-plating (HCD-IP). The effect of nitrogen flow rate (ranging from 5 to 35 sccm) was investigated on the N/Zr ratio, structure, and mechanical properties of the ZrN films. The results showed that the variation of nitrogen flow rate did not significantly affect the film thickness, preferred orientation and hardness. The major effects of the nitrogen flow rate were on the N/Zr ratio, packing factor, and grain size of the ZrN films. The N/Zr ratio increased (0.6–0.9) with increasing nitrogen flow rate. The grain sizes of the ZrN films, measured by both X-ray diffraction (XRD) and scanning electron microscopy (SEM), ranging from 15 to 30 nm, generally increased with increasing nitrogen flow rate. The hardness of the nanocrystalline ZrN films, ranging from 23.3 to 26.6 GPa, was not related to the variation of the residual stress. The deformation mechanism of the nanocrystalline ZrN films may be through grain rotation or grain boundary sliding instead of slip by dislocations. Since the electric conductivity of 304 stainless steel is higher than that of Si, the stainless steel substrate can attract more Zr ions than Si substrate. This led to larger deposition rate, roughness, and residual stress for the ZrN film deposited on stainless steel than on Si substrate.