OBRABOTKAMETALLOV Vol. 26 No. 2 2024 technology Equipment Surfacing was carried out by the direct laser deposition method. With this method, laser radiation is focused by means of a lens onto the substrate, forming a “bath” of melt. The powder mixture is supplied coaxially to the laser radiation through a coaxial nozzle. As the laser beam moves, the melt bath solidifies to form a deposited bead. Formation of single tracks was carried out on the equipment “Cladding and welding complex on the basis of a multi-axis arm and fiber laser” with the power of ytterbium laser 3 kW (produced by IPGphotonics) and wavelength of radiation 1.07 μm (Fig. 1). Argon was used as a carrier gas and as a protective medium during the growth process. The Olympus LEXT OLS 3000 optical microscope and Carl Zeiss EVO 50 XVP scanning electron microscope (core facility “Structure, mechanical and physical properties of materials” NSTU) were used to determine the size and quality of the formed tracks. Cross-sections of specimens for the study were prepared according to the standard grinding and polishing technique. Etching was performed using a chemical etchant of the composition HNO3 : HCl = 1 : 3 Experimental conditions Equipment parameters, energy density, scanning speed, gas flow rate and other parameters play an important role in determining microstructure features, part quality and process performance. Therefore, to determine the optimal modes of building a steel product by direct laser deposition, it is necessary to investigate the material behavior during the formation of single tracks. The choice of initial parameter values is based on literature data [16–23]. The range of values of the main parameters was as follows: laser power 1.000–1.500 W, scanning speed 15–35 mm/s, powder flow rate 12–36 g/min (feed disk speed 4–12 % respectively) and laser spot size 2.9–5.6 mm. Such parameters as powder flow rate and laser spot size were changed after determining the optimal power and scanning speed. Selection conditions In the additive manufacturing process, various surfacing defects may occur due to peculiarities of the study material, equipment parameters and growing modes. Therefore, to determine the optimal building mode, the geometric dimensions, wetting angle with the substrate, the presence of pores and cracks in the junction zone of the obtained single tracks and the substrate were analyzed. In this work, the ratio between the thickness and width of the surfaced layer equal to 1:3 is evaluated, since if this ratio is not met in the process of the solid formation interlayer pores may form [8, 24]. Also, in this paper the concept of effective build-up ratio is introduced – the coefficient of effective materials consumption, based on the ratio of the surfaced metal mass to the rate of powder consumption. This characteristic evaluates the loss of material during the surfacing process. Results and discussion Macrostructure and geometrical dimensions of the obtained tracks The geometric dimensions and the presence of defects in the zone of the surfaced layer at single tracks should be evaluated to determine the most suitable build-up mode for solid construction. Table 2 shows the geometric characteristics of the surfaced steel powder. The macrostructure of the cross sections of steel 316L is presented in Fig. 2–6. As one can see, with increasing speed, the height of the investigated tracks decreases, which further increases the width of the Fig. 1. Automated laser complex
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