Fabrication of anisotropic sliding surfaces on polyamide via femtosecond laser oblique ablation.

Femtosecond laser oblique ablation provides a flexible approach for fabricating asymmetric surface structures with directional functionality. In this work, asymmetric groove arrays were fabricated on polyamide (PA) surfaces using femtosecond laser oblique processing to achieve anisotropic sliding behavior. A simplified numerical model based on the two-temperature framework was developed to qualitatively analyze the influence of pulse energy, laser incident angle, and pulse number on ablation morphology. The simulation results indicate that pulse energy and pulse number mainly control the groove depth through energy input and accumulation effects, while the incident angle governs the spatial distribution of energy and induces structural asymmetry. Experimental results confirm that the groove geometry can be effectively tailored by adjusting processing parameters, showing good agreement with the simulation trends. Directional sliding performance was characterized by the sliding angle in three directions (along the groove, with the groove, and against the groove). The results reveal a stable anisotropic behavior, where the sliding resistance is strongly dependent on the asymmetric groove geometry and lubricant distribution. A pronounced anisotropy is achieved at a moderate incident angle, where directional resistance differences are maximized. The study demonstrates that processing parameters influence sliding behavior indirectly through morphology control, and provides an effective strategy for designing anisotropic low-friction surfaces using femtosecond laser oblique ablation.