Hard yet tough V-Al-C-N nanocomposite coatings: Microstructure, mechanical and tribological properties

Hard coatings have been widely used in industrial applications as wear-resistant coatings, but are prone to failure due to the high intrinsic brittleness. In order to improve toughness without significantly sacrificing hardness, here we designed the V-Al-C-N nanocomposite coatings, and the microstructures consisting of V-based nanocrystalline hard phases and sp2-riched amorphous carbon soft phases were successfully manipulated by sputtering V2AlC target under various N2 flow rates. Results indicated that the coating hardness was almost independent on the N2 flow rate and maintained around ~ 30 GPa as changing N2 flow rate from 5 to 20 sccm, while the toughness was significantly improved, and the high H/E ratio of 0.11 and elastic recovery of 69% could be obtained, respectively. In addition, the V-Al-C-N nanocomposite coatings showed low wear rate (< 1.5 × 10− 16 m3/Nm) under a normal load of 10 N. The hard yet tough characteristic and high wear resistance for the deposited coatings were attributed to the special nanocomposite microstructures as well as the synergistic lubricant effect derived from both sp2-riched amorphous carbon and V2O5 Magnéli phases formed during friction stage.