Vacuum annealing-driven microstructural densification and synergistic mechanical-tribological enhancement of MAIP-deposited CrNiCN coatings

Nanocomposite coatings deposited by multi-arc ion plating (MAIP) usually suffer from intrinsic microstructural defects, such as droplets and micropores, which disrupt matrix densification and reduce fatigue resistance under cyclic shear stresses. Herein, this work proposes a vacuum annealing strategy to repair these inherent deposition defects and synergistically improve the mechanical and tribological properties of MAIP-deposited CrNiCN coatings. Thermal annealing induces the formation of Ni₃C phase and refines the grain size to 40–75 nm. Meanwhile, surface diffusion promotes the coalescence of droplets and the elimination of inherent micropores, resulting in significant structural densification. Therefore, the hardness of the coating increases substantially from 11.87 GPa (D1 coating) to 15.13 GPa (A1 coating) after vacuum annealing, accompanied by elevated H/E (0.0675) and H³/E² (0.0690) ratios. In addition, it is found that the steady-state coefficient of friction (COF) decreases from 0.58 to 0.44, while the wear rate reduces from 4.28 × 10⁻⁶ to 1.39 × 10⁻⁶ mm³ N^-1 m⁻¹. This enhanced wear performance is attributed to the synergistic effects of nanophase strengthening, grain-refinement and structural densification. This thermal-driven microstructural evolution effectively suppresses friction-induced micro-cracking, shifting the failure mechanism from severe abrasive and fatigue wear to mild abrasive wear. These findings provide an effective post-treatment paradigm for eliminating MAIP-induced structural defects and offer critical engineering guidelines for designing durable, fatigue-resistant protective coatings for tools used in precision glass molding and high-speed machining.