Effect of substrate bias on the structure and properties of ion-plated ZrN on Si and stainless steel substrates

This research studied the effect of bias on the microstructure and properties of zirconium nitride (ZrN) deposited on Si (1 0 0) and AISI stainless steel 304. The ZrN films were deposited using hollow cathode discharge ion plating (HCD-IP) method. The optimum coating conditions were first determined using Taguchi experimental method. Based on the optimum conditions, the single-variable experiments on the effect of bias were conducted. The cross-sectional microstructure revealed that the columnar structure of the ZrN film became denser with increasing bias. The results of X-ray diffraction (XRD) showed that all the coating samples exhibited (1 1 1) preferred orientation both on Si and SS304 substrates. To avoid substrate effect, the hardness of the ZrN films was measured by nanoindentation. The hardness values of ZrN films deposited on Si were ranged from 27 to 30 GPa, and on stainless steel 304 were from 32.5 to 40.8 GPa. The ZrN films deposited on the stainless steel were very smooth with a roughness number ranging from 1.1 to 3.9 nm. The N:Zr ratios were determined using X-ray photoelectron spectrometry (XPS) and the results indicated that the films were close to the stoichiometric composition. The resistivity of ZrN films gradually decreased with increasing bias until −120 V and then abruptly increased. The corrosion resistance of ZrN-coated stainless steel was evaluated by standard salt spray test and potentiodynamic scanning in two kinds of solution environments: 5% NaCl and 1N H2SO4 +0.05 M KSCN, respectively. The results showed a consistent trend between salt spray test and potentiodynamic scanning. The corrosion resistance increased with bias at bias ranging from 0 to −90 V, then abrupt decreased at −120 V, and then increased again at −150 V. The properties changes of resistivity and corrosion resistance can be explained by the change of film structure due to bias-induced ion bombardment.