Hardness and residual stress in nanocrystalline ZrN films: Effect of bias voltage and heat treatment

The purpose of this study was to investigate the effects of both bias voltage and heat treatment on the composition, microstructure, and associated mechanical properties of the zirconium nitride (ZrN) thin films deposited on AISI 304 stainless steel substrates by a filtered cathodic arc ion-plating (FCA-IP) system. The depositions were carried out by varying negative substrate bias voltage, from −40 Vb to −80 Vb. The deposited film specimens were heat-treated at 800 °C for 1 h. X-ray diffraction (XRD) revealed that (a) texture coefficients of (1 1 1) plane increased with negative bias, and (b) the grain size was approximately less than 15 nm, i.e. nano-scale grain size. The hardness of the deposited ZrN films was correlated with point defects, (1 1 1) texture coefficient, and crystallinity characterized for the films. For the as-deposited films, it was found that the hardness increased with decreasing (1 1 1) full width of the peak at half maximum (FWHM) and increasing (1 1 1) texture coefficient, suggesting a better crystallinity and lower grain boundary mobility in the highly textured films. The decrease in film hardness after heat treatment may be attributed mainly to the reduction of point defects present in the films. Measurements performed for the intrinsic residual stress reported a significant 5.5 GPa release in the heat-treated films, due to recovery of point defects by heat treatment.