Mechanical and tribological properties of (AlCoCrNiSi)_100-xN_x thin films

High entropy thin films of (AlCoCrNiSi)(100-x)N-x were deposited on silicon wafers using a pulsed DC magnetron sputtering technique, with nitrogen gas flow ratios (R-N) of 0, 0.33, and 0.50. The structure and properties of these films were analyzed for elemental composition, surface and cross-sectional morphologies, microstructure, roughness, and mechanical properties. The coatings were primarily composed of an amorphous structure with a minor presence of a BCC structure and exhibited periodic variations in chemical composition from the substrate to the free surface. An increase in R-N enhances crystallinity of the materials. Nanoindentation results showed that the films deposited at R-N = 0.50 displayed the highest hardness (10.7 +/- 0.5 GPa) and reduced modulus (176 +/- 5 GPa), which were the highest among the films. Microtribology testing was conducted using a 20 mu m radius spherical diamond tip under ambient air and normal loads ranging from 0.5 to 9 mN. Worn surfaces were characterized using atomic force microscopy. The coefficient of friction was evaluated to investigate the elastic and plastic behaviors of films using Schiffmann's model. The coating without nitrogen displayed a predominant plastic behavior during the initial cycles, while the coating deposited at R-N = 0.33 demonstrated a more elastic behavior, particularly at lower loads.