Low-power Blue Diode Laser Nitriding of Ti-6Al-4V ELI and Ti-6Al-7Nb

Laser-induced nitriding was applied to Ti-6Al-4V ELI and Ti-6Al-7Nb alloys using a low-power blue diode laser (455 ± 5 nm, 22 W) under localized high-purity nitrogen delivery. The effect of laser power on the microstructure, phase composition, and microhardness of the treated layers was systematically investigated. A multilayer structure consisting of a TiN-rich compound layer, a remelted zone, and a heat-affected zone was formed. The total modified depth increased with increasing laser power, reaching approximately 160–170 µm. X-ray diffraction analysis confirmed the formation of titanium nitride phases, with TiN reflections becoming more pronounced at higher laser power levels. A substantial increase in surface hardness was achieved, with maximum values of approximately 1758 HV for Ti-6Al-4V ELI and 2233 HV for Ti-6Al-7Nb, compared with substrate hardness values of approximately 300–330 HV. The hardness gradually decreased with increasing depth, reflecting the transition from the nitride-rich compound layer toward the substrate. The results demonstrate that low-power blue diode laser processing enables the controlled formation of TiN-based surface layers on biomedical titanium alloys and represents an efficient approach for localized surface modification.