OBRABOTKAMETALLOV Vol. 27 No. 2 2025 technology Fig. 12. Surface Profile in Cross-Sectional Micrograph: 1, 2, 3, 4 – surface layer defects The submicrostructure of the control sample has a slightly rounded shape with undulating steps, which is probably a consequence of the crystallization of a spherical particle. The AFM image after CT shows a region with a boundary between a sphere (right corner of the image), which exhibits pronounced steps after etching, and a portion of the surface formed during normal crystallization of the melt track. After CET+CT, the banded submicrostructure results from directional heat dissipation during the crystallization of the melt track. The surface after CAT+CT differs from the others in its chaotic structure, formed by periodic exposure to abrasive particles. Wide steps, resembling surges, indicate the flow of metal perpendicular to the direction of deformation during ultrasonic SPD. Examination of the hardened layer after ultrasonic SPD The changes in the surface profile (Fig. 12) correspond to the surface profilometer traces presented in Table 2. The deformed layer is characterized by high microhardness (Fig. 14). The maximum hardening is achieved closer to the edge of the surface layer, reaching approximately 35 %. As the distance from the surface increases, the microhardness gradually decreases, reaching the base metal level after 100 µm. As a result, ultrasonic SPD leads to a significant reduction in surface roughness and the creation of a hardened layer. However, the resulting surface defects can significantly decrease the performance characteristics of the part. Therefore, it is advisable to perform ultrasonic SPD after removing surface defects using the aforementioned methods of CAT+CT or CET+CT. Description of the mechanisms of action during ultrasonic treatment Three-dimensional images of the sample surfaces, obtained by extended depth of field microscopy, are shown in Fig. 15. These images visualize the surface changes that occur during various types of treatment. Changes in the surface condition are determined by the type of ultrasonic treatment used and the corresponding mechanisms of action, schematically shown in Fig. 16. In the case of CET, the primary effect is exerted by cavitation clusters formed at locations of greatest surface inhomogeneity, which are spherical defects and depressions of micro-irregularities. The pressure and temperature formed during the collapse of clusters lead to plastic deformation of the surface, removal of spheres, and an increased depth of depressions. Since the depressions in the samples under consideration are mainly formed between the spheres, the roughness will decrease during treatment until all the spheres
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