Effect of Bionic Surface Architecture and Ultrasonic Power Density on Wear Resistance of Ni–AlN Nanoparticle-Reinforced Composite Coatings

First, three bionic surface architectures (pit, hexagonal, and coupled) were compared to identify the optimal geometry; subsequently, the effect of ultrasonic power density (UPD, 0–35 W/cm2) on coating microstructure and dry-sliding wear performance was evaluated on the selected coupled structure. In this study, using dung beetle pit structures and many-banded krait hexagonal dorsal scales as bio-inspiration, pit-type (S1), hexagonal-type (S2), and coupled-type (S3) Ni–AlN nanocomposite coatings were deposited on AISI 1045 carbon structural steel by ultrasonic-assisted jet electrodeposition. The effect of ultrasonic power density (UPD, 0–35 W/cm2) on coating microstructure and dry-sliding wear performance was investigated by combining ANSYS finite element simulation with tribological experiments (ASTM G133). The coupled structure (S3) reduced peak contact stress by 45.8% and cumulative wear volume by 11.4%. At UPD = 25 W/cm2, AlN nanoparticles (43.6 nm) were uniformly dispersed, Ni grains were refined to 32.5 nm, and the coating achieved a microhardness of 794 ± 22 HV, a COF of 0.32 ± 0.01, and the lowest wear loss rate among the tested UPD conditions (approximately 0.025% mass loss). Hall–Petch analysis (R2 = 0.96) supports an important contribution of grain refinement to coating strengthening, with a smaller contribution from Orowan strengthening. This work provides a bio-inspired morphology–nanoparticle reinforcement approach for surface wear protection of carbon structural steel.