Mechanical Properties, Tribological Performance and Oxidation Resistance of HfCx/a-C:H Coatings Prepared by Pulsed DC Magnetron Sputtering

The development of protective coatings with simultaneously enhanced mechanical, tribological, and antioxidant properties remains a major challenge for micro-electro-mechanical systems operating under harsh environments. In this work, HfCx/a-C:H coatings with varying carbon contents were deposited by magnetron sputtering. Increasing the C2H2 flow rate from 12 to 20 sccm drove the coating structure to undergo two-stage evolution, from a composite structure dominated by HfC nanograins with a-C:H distributed at triple junctions of HfCx grain boundaries to a typical nanocomposite structure with ~8 nm HfCx nanograins embedded in a continuous a-C:H matrix. The coating deposited at 18 sccm exhibited the highest hardness (31.3 GPa) and effective Young’s modulus (392.3 GPa), owing to enhanced interface-mediated strengthening effect induced by the optimized nanocomposite structure. The coating prepared at 20 sccm showed the lowest friction coefficient (0.28), the lowest wear rate (6.82 × 10−6 mm3/N·m), and the best oxidation resistance. These improvements were supported by the enhanced mechanical properties and a-C:H fraction, the increased interface density and tortuosity, and the regulation of oxidation kinetics by the a-C:H matrix. This work provides an effective strategy for designing multi-functional protective coatings with balanced mechanical, tribological, and oxidation performance.