OBRABOTKAMETALLOV Vol. 26 No. 2 2024 technology a b c Fig. 4. Cross sections of tracks obtained at a power of 1.500 W, powder flow rate 24 g/min, laser spot size 2.9 mm, speed 15 mm/s (a), 25 mm/s (b), 35 mm/s (c) The wetting angle of the deposited layer with the substrate is one of the most important parameters determining the track homogeneity. In some specimens, at minimum speed values, a negative lateral angle was detected (Fig. 2, a; 3, a; 3, b; 4, a), which can cause delamination of the material from the substrate and the presence of interlayer pores. With increasing power and scanning speed, the wetting angle increased to the contact with the substrate boundary due to changes in the geometric dimensions of the track (Fig. 2–4). Also, the main geometric parameter necessary to identify the optimal growth mode is the depth of penetration. With increasing power, the depth of the melted area increases, but the opposite effect occurs with increasing scanning speed (Fig. 2–4). The maximum penetration depth (1.286 μm) corresponds to the highest power value with the minimum scanning speed (1.500 W and 15 mm/s). The reason for this is the large amount of power applied to the local melting point. This effect indicates that when using the maximum scanning speed, the laser power should also be a maximum. Based on the analysis of the obtained data, the power and build-up rate of 1,250 W and 25 mm/s were chosen as the parameters of the optimal mode, respectively, since neat tracks without large pores were formed in this mode, and minimal sparking was present in the surfacing process (Fig. 3, b). However, the condition described in [8] was not fulfilled because not all parameters were varied. Therefore, based on this mode at constant scanning power and speed, the effect of powder consumption and laser spot size on single tracks was further investigated. When using a powder feed rate of 12 g/min, a minimum track height was formed, since with an increase in this characteristic, the mass consumption of the powder increases (Fig. 5). However, when the laser spot size was increased, the track height increased (Fig. 6). With increasing scanning power, the depth of the molten substrate increases due to an increase in the amount of laser energy penetrating the substrate (Fig. 7). However, as the scanning speed increases, the a b c Fig. 5. Cross sections of tracks produced at a power of 1.250 W, speed 25 mm/s, laser spot size 2.9 mm, powder consumption 12 g/min (a), 24 g/min (b), 36 g/min (c)
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