Nitrogen-ion-beam-induced wear resistance improvement of AlCrN-coated SKH55 punches for hydraulic pistons in automobile brake systems

• Hot N₂ + /N + implantation (300°C) achieved 113% hardness increase (12.8→27.2 GPa) • Wear rate reduced 19–26× by suppressing brittle h-Cr₂N phase (24–26% decrease) • Angle-controlled beam (45°–90°) enables area-selective edge reinforcement • Field validation: 21% lifetime extension, zero defects (350 ton, >5,000/day) An area-selective enhancement process for complex-shaped high-speed steels is crucial for industrial applications. This study presents an angle-controlled composite nitrogen-ion hot implantation strategy (N₂⁺/N⁺ = 8:2) to improve the wear resistance of AlCrN-coated SKH55 punches by selectively reinforcing stress-concentrated regions such as edges and corners. Performance enhancement is achieved through hot implantation at 300°C, which activates radiation-enhanced nitrogen diffusion and produces continuous subsurface hardening, combined with beam-angle control (45°–90°) to localize the modified regions. Nitrogen-ion implantation at 120 keV and 5×10¹⁷ ions/cm² increases surface hardness from 12.8 GPa to 27.2 GPa and reduces wear rates by up to 26× compared to pristine AlCrN/SKH55. Structural analyses confirm suppression of the brittle h-Cr₂N phase and stabilization of fcc-AlN/CrN phases, providing a mechanistic basis for the improved tribological performance. Industrial field testing under actual hydraulic piston manufacturing conditions validates the laboratory results. Optimally treated punches exhibit a 21% increase in service lifetime and defect-free production. This scalable ion-implantation approach offers an effective route for selectively reinforcing vulnerable regions of complex-shaped tooling in industrial environments.