Study of surface hydrophilicity of metallic materials modified by ultraviolet laser radiation
Authors:   Institute of High Current Electronics of the Siberian Branch of the Russian Academy of Sciences, Tomsk, Sablina Tatyana , Panchenko Marina ,   Institute of High Current Electronics of the Siberian Branch of the Russian Academy of Sciences, Tomsk, Zyatikov Ilya ,   Institute of High Current Electronics of the Siberian Branch of the Russian Academy of Sciences, Tomsk, Puchikin Aleksey ,   Institute of High Current Electronics of the Siberian Branch of the Russian Academy of Sciences, Tomsk, Konovalov Ivan ,   Institute of High Current Electronics of the Siberian Branch of the Russian Academy of Sciences, Tomsk, Panchenko Yurii ,   Institute of High Current Electronics of the Siberian Branch of the Russian Academy of Sciences, Tomsk
Published: December 2024

Introduction. Surface modification using laser radiation is a promising direction in the field of creating new technologies for treatment metal materials, including those for medical purposes. The ability of lasers to change the surface characteristics of a material and, consequently, its interaction with the environment has attracted great interest among researchers. Despite numerous recommendations for the use of laser surface treatment, there is still lack of systematic and detailed studies on the influence of parameters on the structural-phase state and properties of the modified surface, especially concerning ultraviolet laser exposure. The purpose of this work is to study the hydrophilicity of the surface of TiNi alloy and stainless steel after UV laser treatment. Materials and methods of the study: experimental samples made of TiNi (TN-10) alloy and 12KH18N9T (AISI 321) stainless steel were locally (beam diameter 0.5 cm) exposed to a solid-state Nd:YAG laser at the wavelength of 266 nm, with a pulse duration of ~ 5 ns, and pulse repetition rate of 10 Hz. The material was exposed to a constant output radiation energy density of 0.1 J/cm2, with a change in the exposure duration from 10 to 600 s. Before and after UV laser treatment, the wettability of the material surface and free surface energy were determined. The structure, elemental and phase composition, and surface topography of TiNi and steel were studied using scanning electron microscopy with the determination of the elemental composition by energy-dispersive spectroscopy, X-ray phase analysis, and profilometry. Results and discussion. Ultraviolet laser treatment of the surface of TiNi alloy and steel samples leads to an increase in their hydrophilicity. In the initial state, the contact angle of wetting is ≈75° for both materials, and after ultraviolet laser treatment it decreases to ≈11-13° for TiNi and to ≈22° for steel. The phase composition of steel does not change during laser treatment, and phases belonging to oxides are recorded on the surface of TiNi after 420 seconds of treatment. Ultraviolet laser treatment of TiNi alloy and steel leads to an increase in free surface energy, a change in the ratio of its components (a decrease in the dispersed component and a significant increase in the polar component), an increase in the oxygen content on the surface of both materials. With long laser exposure times (more than 300 seconds), microcracking occurs on the surface of the processed material, leading to an increase in roughness. The change in the surface topography (roughness) of TiNi alloy does not have a noticeable effect on the wettability of the surface of metal materials, and for steel samples, there is an insignificant tendency to reduce the contact wetting angle with increasing roughness. The degree of hydrophilicity of metal materials, characterized by the contact wetting angle, increases with an increase in the duration of laser exposure due to saturation of the surface with free oxygen and an increase in free surface energy (its polar component). Based on the studies, it can be concluded that ultraviolet laser treatment is an effective way to change the wettability of metal materials.