## 3 Results and Discussion
### Cavitation Curves
The large losses after 45 min are also affected by the solid solution losses, as the coalescence of generated cracks enabled the expulsion of large amounts of material, forming craters. Decreases at various cavitation attack durations, with relative constancy after 75 min, are explained by a reduction in impact force intensity due to hardening by work hardening and the damping effect of air and subsequently of the air/water mixture in the formed cavities. This information is supported by macroscopic images in Figure 5 at 105 and 165 min. The low value of the standard deviation \(\sigma=7.881\times 10^{-3}\) of the experimental erosion rate values relative to the mean curve shows not only the accuracy of the technological heat treatment regime but also that of experimental cavitation testing program management. A first assessment of the surface structure's behavior under cyclic loading from shock waves and microjets generated by bubble implosion in the cavitation cloud can be made based on the photographic images in Figure 5 at significant durations, correlated with the erosion rate values from Figure 4b. These images were taken with a Canon PowerShot A480 camera. The dark color of the surface after 15 min of cavitation exposure is the effect of the destruction of roughness peaks, removal of abrasive dust, and plastic deformations generating shadows and a crack network created by the pressure force from the surface impact with shock waves and microjets. The microscopic cavities formed during this time are few and caused by the expulsion of grains of fragile intermetallic phases. With increasing cavitation attack duration (at 45 and 60 min), the structure yields, with typical local fatigue-type stresses [29; 30; 31; 32; 33; 34], more pronounced toward the periphery where the erosion ring forms. This ring, analyzed via scanning electron microscopy, besides deformations and deep interconnected cracks, shows multiple cavities of varying sizes, characteristic of both the expulsion of \(\gamma\) solid solution grains and intermetallic phases, which led to increased erosion rate values and a maximum in the curve v(t) (Figure 4b). Continued cavitation attack leads to intensified destruction through increasing geometric dimensions (in plane and depth) of formed cavities, intensification of deformations, and cracks propagating into the surface, as a result of fatigue loading mechanisms, without major variations in erosion velocity and mass loss values (Figure 4) during the intermediate durations. This behavior also explains the slight asymptotic decrease in the curve v(t) toward the stabilization value \(\mathrm{v_{s}}=0.026\) mg/min, corresponding to the linear evolution of cumulative losses over the 60-165 min interval (Figure 4a). The slight changes in the shape, size, and aspects of the exterior ring and central zone, shown in images at 105 and 165 min, correspond to erosion velocity values over the 90-165 min interval. This is due to the fact that the intensity of pressure forces, although contributing to cavity growth by smaller material expulsions, is dampened by water and air penetrating the cavities during  
Figure 5: Macroscopic images of erosion evolution at various cavitation exposure durations. the compression phase of the mechanical vibrator system on one hand and by hardening through mechanical work of the stressed layer on the other hand.