OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 4 2024 medical materials and implants with shape memory (Tomsk) (identifi cation mark — TiNi) and stainless steel 0.12 C-18 Cr-9 Ni-Ti (GOST 5632-72) (AISI 321) (identifi cation mark — steel) were taken for the study. The specimens were previously polished on SiC grinding paper of various grits P600–2500 (ISO6344) and then polished to gloss with diamond pastes ASM or ASN 3/2, 2/1, 1/0. To remove surfactant contamination after polishing, the specimens were washed in an ultrasonic bath (VGT-1620QTD, China) successively in alcohol and acetone for 10 minutes. Ultraviolet laser treatment was carried out in air at normal atmospheric pressure and room temperature (22 ± 3 °C). Experimental specimens were exposed to radiation of the 4th harmonic of Q-smart 850 Nd:YAG laser (Quantel, France) at the wavelength of 266 nm. Pulse duration was ~ 5 ns, pulse repetition rate was 10 Hz. Experimental scheme of laser treatment is shown in Fig. 1, a. The material was treated stationary, without moving the specimen and laser beam, at a constant radiation energy density of 0.1 J/cm2, and the duration of treatment was varied from 10 to 600 s. The area of exposure on the surface of the experimental specimens was limited by the diameter of the laser beam d = 0.5 cm (Fig. 1, b). a b Fig. 1. Experimental scheme of UV laser treatment of specimen surface Before and after UV laser treatment, the wettability of the materials surface was determined using the sessile drop method of test liquids (deionized water, glycerin) with known properties of surface energy at the contact angle. Contact angle was measured by photographing a drop on the surface of the material. To do this, a 3 μl drop of liquid from a micropipette was applied to the horizontal surface of the metallic material, after which the drop was photographed so that the optical axis coincided with the plane of the material surface and the drop. The height h and the length of the baseline 2r of the drop were measured from the obtained photographs (Fig. 2), and the contact angle (Θ) was calculated using the semi-angle method using formulas (1, 2): 1 1Þ Þtan / , h r − Θ = (1) 1, Þ Þ 2 Θ= Θ (2) where h is the height; r is the half of baseline length. At least 5 series of contact angle measurements were carried out for the original surface and for each treatment mode. Fig. 2. Scheme of measuring the wetting contact angle
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