OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 4 2024 of cleaning the surface from organic contaminants on its hydrophilicity [36, 37]. On the other hand, metal oxides have increased hydrophilicity and can chemically alter the surface wettability due to its strong affi nity for hydroxylation [27, 38]. An increase in hydrophilicity can also result from the process of photooxidation during surface treatment [35]. In particular, titanium dioxide becomes superhydrophilic when exposed to UV radiation due to its photocatalytic activity [39]. Several studies [26, 40] have reported on the laser oxidation of metal surfaces both during irradiation in water and in air, which is associated with possible processes of excitation, ionization, and dissociation of atmospheric oxygen. It is known that laser treatment, which causes surface oxidation and increases the oxygen content on the treated surfaces, can enhance its hydrophilicity [27]. However, a thin oxide fi lm on the surface of metals does not prevent further interaction with oxygen [15, 41–43]. Therefore, in this study, a change in the hydrophilicity of metallic materials can also be attributed to the saturation of the surface with atmospheric oxygen and its subsequent oxidation. The data on the change in the amount of oxygen on the surface of TiNi and steel after UV laser treatment, obtained using EDS during SEM study and XRD analysis, presented in Figs. 4–7, indicate the saturation of metallic surfaces with oxygen and the formation of an oxide fi lm during ultraviolet laser treatment. Figs. 4 and 5 show SEM images of TiNi and steel specimens with the results of EDS analysis in the initial state and after laser treatment. According to the data obtained from scanning electron microscopy, the structure of the TiNi specimens consists of a TiNi matrix (light areas) and a small amount of TiC precipitates (dark areas) (Fig. 4, a). The elemental composition of the matrix primarily consists of Ti and Ni in a ratio that is close to equiatomic, and an insignifi cant amount of Mo and Fe. Additionally, the matrix contains carbon and a small amount of oxygen. The secondary phase precipitates contain Ti, C and Ni (Fig. 4, b). After 300 s of laser treatment, there is an observed increase in the oxygen content by approximately 10 times (Fig. 4, c), and a further increase in the treatment duration to 600 s results in an even more substantial increase in oxygen levels on the material’s surface (Fig. 4, d). For the steel specimens subjected to UV laser treatment durations of 60–300 s, only minor changes in the oxygen concentration on the surface are observed, whereas after 600 s of treatment, the oxygen content increases to approximately 13 at. % (Fig. 5). UV laser treatment results in an increase in the amount of oxygen on the surface. When comparing the oxygen levels on the surfaces of TiNi and steel specimens after UV laser treatment, it is evident that, under identical treatment conditions, the oxygen concentration on the TiNi specimens is signifi cantly higher than that on the steel specimens. This diff erence may be attributed to the presence of a substantial amount of Fig. 3. The dependence of contact wetting angle on the duration of UV laser treatment
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