OBRABOTKAMETALLOV technology Vol. 27 No. 2 2025 Fig. 7. Dynamics of surface changes during chemical treatment process Thus, when an abrasive is added to the liquid, a uniform effect is ensured over all surface areas due to the combined action of cavitation clusters and abrasive particles. Dynamics of changes in the surface layer during various types of treatment In CT, the oxide film is initially removed by the etching solution. Subsequently, the etching solution begins to interact with the alloy, dissolving the contacting surface areas at a low rate (Fig. 7). During CT, the size of the spheres decreases, and the boundaries between spheres in clusters become less distinct, leading to the formation of larger areas. As the CT time increases, these areas partially combine to form large areas. Simultaneously, depressions of the surface irregularities are etched, appearing as unfocused regions in the photographs. When ultrasonic vibrations are introduced into the solution, the dynamics of the treatment change significantly (Fig. 8). Cavitation clusters form and perform work at the locations of the greatest surface irregularity. When bubbles collapse in these clusters, shock waves and cumulative jets occur, accompanied by instantaneous pressures reaching up to 700 MPa and temperatures up to 4,000 °C [48–49]. As a result of the cumulative effect, plastic deformation of the treated surface occurs [50–51]. In the case of CET+CT, these instantaneous high temperatures further intensify the chemical reaction at the bubble collapse sites. Consequently, after 3 minutes of treatment with CET+CT, the resulting surface is similar to the surface treated with CT for 20 minutes, indicating an acceleration of the process by almost a factor of 7. The main difference between CET+CT and CT alone is that, with increasing treatment time, the number of protrusions of irregularities decreases, and the unfocused area increases in each subsequent photo, indicating the removal of surface defects. Starting from minute 7 of treatment, a portion of the surface becomes clearly visible, showing an alternation of powder melting tracks. After 15 minutes of treatment, defects such as metal splashes and spheres are completely removed from the surface. Adding abrasive particles during CAT also changes the nature of the treatment (Fig. 9).
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