Tribological Performance of Femtosecond Laser-Fabricated Biomimetic Sinusoidal-Circular Composite Textures on 40Cr Steel Under Oil Lubrication

To improve the tribological performance of 40Cr steel, a biomimetic composite micro-texture consisting of sinusoidal grooves and circular dimples was designed based on the periodic corrugated structures on the shell surface of Fimbria fimbriata. The texture parameter ranges were determined through microscopic characterization of the shell surface and orthogonal design. The composite micro-textures were fabricated on 40Cr steel by femtosecond laser processing and characterized by confocal microscopy, white light interferometry (WLI), and scanning electron microscopy (SEM). Their tribological behavior was evaluated under oil-lubricated reciprocating sliding conditions against a GCr15 counter-body in a ball-on-flat contact configuration. The results showed that laser power significantly affected the forming quality of the sinusoidal textures, and 4.50 W provided the best overall cross-sectional morphology. All textured specimens exhibited lower steady-state average coefficients of friction (COF) than the untextured specimen, with the textured groups ranging from 0.1678 to 0.1905. Among them, specimen L6 showed the lowest steady-state average COF of 0.1678, corresponding to a reduction of approximately 19.4%, together with the best wear resistance as indicated by the relative displacement volume ratio (Kw). Surface analyses revealed that abrasive wear and adhesive wear were the dominant wear mechanisms, while the optimized composite micro-texture effectively suppressed wear-groove development, material pile-up, and transfer-layer formation. Overall, the biomimetic sinusoidal-circular composite micro-texture effectively improved the tribological performance of 40Cr steel under oil lubrication through the synergistic effects of contact-state regulation, lubricant retention, and wear-debris capture. This study provides theoretical and experimental support for the engineering application of biomimetic composite micro-textures on mechanical surfaces.