OBRABOTKAMETALLOV Vol. 27 No. 1 2025 technology metal is ejected from the sample, resulting in the formation of a microcrater. The ejected molten metal rapidly solidifies, forming a characteristic bead around the crater’s perimeter. Figs. 4, a and 4, b show no pronounced zones of melt in the form of craters, beads, depressions, or sharp peaks. Fig. 5 shows the surface topography of the sample after processing in mode No. The average surface roughness (Ra) was 1.53 μm. Examination of the sample surface, machined according to mode No.1, using a confocal scanning laser microscope (CSLM) Lext OLS4000, revealed a relatively flat surface with a characteristic microrelief formed by melting of the sample material during machining. No pores or cracks were observed on the processed surface. With increasing pulse energy (mode No.2), an intensification of the material melting process was observed. The molten alloy spreads randomly across the surface, creating irregularities of different shapes and sizes. This process results in variations in the roughness of the surface layer. Due to the intense thermal impact on the workpiece surface layer during WEDM, secondary structures form on the surface. It has been established that increasing WEDM power in mode No.2, while maintaining the height of the machined sample at 10 mm, does not lead to significant qualitative changes in the overall surface morphology (Fig. 6, a). However, at higher magnifications (Fig. 6, b), microcracks are revealed on the processed surface. These microcracks likely formed during rapid cooling of the molten metal from elevated temperatures due to the more intense energy input compared to mode No.1. Fig. 6, b shows the presence of microcracks within the craters on the surface of a 10 mm high specimen machined in mode No.2. Fig. 7 shows a representative section of the heat-resistant nickel alloy VV751P sample surface after machining in mode No.2. A less pronounced temperature gradient is observed compared to mode No.1. The average surface roughness (Ra) was determined to be 1.62 μm, which is consistent with the roughness value obtained in mode No.1, placing both surfaces within the same roughness class. Increasing the height of the machined sample to 15 mm intensifies microcrack formation on its surface during WEDM, regardless of the machining power (Fig. 8, a-f). The effect of secondary discharges is illustrated in Fig. 8. The final stage is characterized by cavitation phenomena and a plasma luminous plume (with a characteristic lifetime of 5 ms) that exists due to the increased frequency of high-frequency discharges near the cathode. At the beginning of the third stage, vapor-gas layer bubbles begin to collapse due to the equilibration of internal and external pressure as a result of increasing local temperature, which is a derivative of the applied pressure. This leads to a large cavitation shock (approximately 1010 MPa), which further increases the surface roughness parameter and promotes the growth of technological cracks during WEDM of heat-resistant nickel alloy VV751P. а b Fig. 4. Surface of the specimen made of heat-resistant nickel alloy VV751P after WEDM according to mode No. 1, obtained using SEM: a – 100× magnification; b – 1,000× magnification
RkJQdWJsaXNoZXIy MTk0ODM1