OBRABOTKAMETALLOV Vol. 27 No. 1 2025 technology As the pulse energy increases, process cracks resulting from WEDM are nucleated, in addition to increasing the surface roughness. Rapid heating of the workpiece to a temperature of 5,000 °C, followed by rapid cooling to the temperature of the distilled water (20 °C), promotes crack formation on the machined surface. This phenomenon is caused by thermal stresses that lead to cracking of the metal. An important factor affecting crack formation is the presence of depressions and holes, which act as stress concentrators. After surface machining of a 15 mm high specimen in mode No.3, relatively large microcracks are detected by SEM even at relatively low magnifications (Fig. 8, a). At slightly higher magnifications, it becomes evident that microcracks on the machined surface, compared to the surfaces of 10 mm high specimens machined in modes No.1 and No.2, become deeper and more branched (Fig. 8, c). More detailed studies of the machined surface at ×5,000 magnification revealed fine crystalline formations of submicron size along the boundaries of which zigzag-shaped microcracks are observed, as indicated by arrows in Fig. 8, d. No significant qualitative changes in the microrelief of the specimen surface with a height of 15 mm machined in mode No.3 were observed compared to the microrelief of the surface of the specimen with a height of 10 mm machined in mode No.2 (Fig. 9). The surface roughness parameter Ra after WEDM in mode No.3 was 2.6. On the surface of the specimen machined in mode No.4, a significant number of cracks and cracking are also observed (Fig. 8, b, d). As shown by CSLM studies of the sample surface (Fig. 10), the depth of these cracks and cracking exceeds 1 µm. No macroscopic defects in the form of large pores or cavities were detected. a b с Fig. 7. CSLM at 500× magnifcation: a – a random area of the sample surface after processing in mode No. 2 with a secant line; b – 3D model with a temperature map of heights; c – graph of microrelief variation along the secant line
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