Nano-mechanical properties of Cr-Zr-Nb-N medium entropy alloy films produced by reactive sputtering

Protective thin films have gained extensive applications in various industries, especially in machining. The present work investigates the structure-mechanical properties relations of Cr-Zr-Nb-N medium entropy films deposited by sputtering. First, chemical analysis (by means of EDS, GI-XRD and Raman spectroscopy), morphology (by SEM) and topology (by means of AFM) of the coatings are studied. By applying graphical methods, average and root mean square roughness, skewness, kurtosis, fractal dimension and texture characteristics are extracted from 2D-AFM images. In addition, hardness, toughness and friction coefficient of the films are reported by employing nano-indentation and nano-scratch tests. Finally, optimum sputtering conditions (substrate temperature = 500 degrees C, nitrogen flow rate = 15 sccm and - 10 V <= substrate bias voltage <= - 70 V) and fractal parameters necessary to obtain wear-resistant films are presented. The thin film deposited under the optimum condition demonstrates high hardness (21.3 GPa), toughness (H/E = 0.096 and H-3/E-2 = 0.195 GPa) and minimum wear characteristics (CoF < 0.2, wear width = 479 nm and wear depth = 56 nm).