Effect of Substrate Bias Voltage on Microstructure and Mechanical Properties of Cr-Nb-Ti-Zr-N-O Ceramic Thin Films Produced by Reactive Sputtering

Hard coatings are applied in various applications to protect substrates from wear and corrosion. In the present study, multi-element ceramic films are deposited by reactive sputtering. The level of substrate bias voltage (-50, -125 and -200 V) is changed to investigate the structural and mechanical properties of Cr-Nb-Ti-Zr-N thin films. Chemical analysis (using EDS, XRD and Raman spectroscopy) reveals that these thin films (with a high amount of oxygen) are composed of a nanocomposite phase structure (amorphous and nano-crystalline phases). CrO2 and NbxN crystalline phases exist in an amorphous matrix in the coatings. By increasing the substrate voltage (from -50 to -200 V), the nitrogen content (from 30 to 40 at. %) increases, and CrxN crystalline phases are generated in S125 and S200. Morphological, topological and image analysis (employing FESEM and AFM) data show that the intermediate level of substrate bias voltage (sample S125) can produce a uniform surface with minimum defect density (15%). In addition, S125 has the minimum level of roughness (16.6 nm), skewness (0.2) and kurtosis (2.8). Therefore, the hardness, toughness and wear resistance (extracted from indentation and scratch tests) of this sample is maximum (H is 24.5 GPa and H/E is 0.107), while sample S50 shows complete fracture and delamination.