Effects of Negative Bias Voltage and Ratio of Nitrogen and Argon on the Structure and Properties of NbN Coatings Deposited by HiPIMS Deposition System

The NbNx>1 coatings were deposited on Si wafer and SUS 304 stainless steel substrates by a high power impulse magnetron sputtering (HiPIMS) system at various bias voltages and the ratios of nitrogen and argon (N2/Ar). By virtue of electron probe microanalysis (EPMA), X-ray diffraction pattern (XRD), scanning electron microscope (SEM), atomic force microscope (AFM) and nano indentation test, the relationships between deposition parameters and coatings properties were examined in detail. These coatings show a strong preferred orientation of (200) plane at free bias voltage. With increasing bias voltage, the intensity of (200) plane peak became weaker and the full width at half maximum of peaks ((200) and (111) peaks) became broader, implying the crystalline grain size were decreased. The (200) plane almost is disappeared at −150 V bias voltage and the phase transition maintains the same change tendency with the increase of N2/Ar gas ratio. The coating microstructure gradually evolved from coarse columnar to dense columnar, and then to compact featureless structure with increase of the bias voltage, corresponding to the decreased surface roughness. The columnar structure of coatings is unrelated to N2/Ar gas ratio and the thickness is minimum at high N2/Ar ratio, which is attributed to the poor sputtering capability of nitrogen compared with argon instead of target poisonous effect. The higher hardness (H) and elastic recovery value are obtained for NbNx>1 (H = 31.3 GPa and We = 69.2%) at −150 V bias voltage, suggesting considerable influence of bias voltage on hardness than that of the N2/Ar gas ratio.