Co‐Optimization of Hardness–Hydrophobicity: Comparison of Homogeneous Versus N‐Gradient ZrN Films Prepared by HiPIMS

ZrN films are widely used as protective coatings due to high hardness and wear resistance. However, an increase in hardness often reduces hydrophobicity, limiting their multifunctional applications in biomedical and anti‐fouling coatings. In this work, we report on a comparative study of homogeneous and non‐uniform nitrogen‐gradient ZrN films synthesized using high‐power pulsed magnetron sputtering (HiPIMS) and examine their microstructure, mechanical properties, and hydrophobicity behaviors. In nitrogen‐gradient samples, the steeper gradient acted as an effective grain refiner, resulting in increased hardness. The high nitrogen‐gradient steepness ZrN film exhibited the highest hardness of 30 ± 1.39 GPa. This was ascribed to its high interface‐strengthening effect and increased micro‐hardness compared to homogeneous ZrN films, which was demonstrated in a ZrN/ZrN 1 − x heterostructure based on first‐principles simulations. In addition, an enhancement in hydrophobicity was also observed in the nitrogen‐gradient samples relative to the corresponding homogeneous‐structure ones. In particular, when the hydrophobicity of sample G8 was enhanced to 104.3 ± 1.3°, its hardness also increased to 23 ± 3.33 GPa. This work utilized the synergistic effect of interface‐strengthening mechanism and surface‐roughening mechanism to achieve a simultaneous increase in hardness and hydrophobicity, opening a pathway for developing a new generation of advanced protective coating materials.