## 3 Results and Discussion  
### Cavitation Curves  
According to laboratory convention [28], cavitation erosion is evaluated based on diagrams (cumulative mass loss of expelled material, erosion rates, and the v(t) curve representing the averaged values of the erosion rates) and characteristic values (the maximum value of the cumulative mass M\({}_{\text{max}}\), and the final erosion rate \(v_{s}\), toward which the averaged velocity curve v(t) tends to stabilize); see Figure 4.  
Since laboratory customs require justification of the experiment's accuracy and data processing, the velocity diagram (Figure 4b) includes the dispersion band of the experimental values, corresponding to the standard deviation \(\sigma=7.881\times 10^{-3}\), which represents an error of \(\pm 1.5\%\), bounded above and below by the curves S(t) and I(t), respectively. The formulas used are as follows:  
* Cumulative mass loss [28]: \[\text{M}_{\text{i}}=\frac{n}{\text{i}=1}\Delta\text{m}_{\text{i}}\] (1)  
Figure 4: Variation in mass loss (**a**) and mean penetration rate of erosion (**b**) with the duration of cavitation exposure. * Erosion rate: \[\mathrm{v_{i}}=\frac{\sum_{i=1}^{n}\Delta\mathrm{m_{i}}}{\sum_{i=1}^{12}\Delta \mathrm{t_{i}}}\] (2)
* Mean rate curve: \[\mathrm{v(t)}=\mathrm{A}\cdot\left(1-\mathrm{e}^{-\mathrm{B}\cdot\mathrm{t}} \right)+\mathrm{A}\cdot\mathrm{B}\cdot\mathrm{t}\cdot\mathrm{e}^{-\mathrm{B} \cdot\mathrm{t}}\] (3)
* Standard deviation: \[\sigma=\left[\frac{\sum_{i=1}^{n}\left(\mathrm{v_{i}}-\mathrm{v(t)_{i}} \right)^{2}}{n-1}\right]^{\frac{1}{2}}\] (4)
* Curves defining the width of the dispersion band (approximation error of \(\pm\) 1.5%): \[\mathrm{S(t)}=\mathrm{v(t)}+1.5\cdot\sigma;\mathrm{I(t)}=\mathrm{v(t)}-1.5\cdot\sigma\] (5) Explanation of terms: \(\Delta\mathrm{mi}\)--mass of material lost due to erosion during the period \"i\", in mg; \(\mathrm{v_{i}}\)--velocity value determined for the intermediate period \"i\", in mg/min; \(\Delta\mathrm{ti}\)--duration of the intermediate period \"i\" of cavitation (the first 5 min, the second 10 min, and the remaining 15 min); \(n=12\)--total number of intermediate periods; A, B--scale and shape parameters, calculated iteratively to minimize the deviations of the experimental values (i.e., the standard deviation \(\sigma\) relative to the mean curve). The dispersions of the experimental values, obtained from the three samples tested over 165 min, as well as their evolutions with cavitation exposure time--whether referring to mass losses (Figure 4a) or erosion rates (Figure 4b)--show dependence on the amount of fragile intermetallic phases, grain sizes, and uniformity of mechanical properties in the surface structure, especially hardness, which is the parameter with the greatest influence, as demonstrated in the studies of [PERSON] [28], [PERSON] [29], [PERSON] [30], [PERSON] [31], [PERSON] [32], etc. From the viewpoint of the behavior of the three samples over the cavitation attack duration, the two diagrams show interference and even overlaps of experimental values. These aspects are well highlighted by the erosion rate values at 60, 90, 120, and 165 min, Figure 4b. Of particular interest is the identical behavior of the three samples at 60, 75, 80, and 120 min, when erosion rates and mass losses decrease, and at 45, 105, and 150 min, when these increase. These similarities, even the identities in the behavior of the three samples, reflect the technological heat treatment regime with well-chosen and controlled technological parameters. Based on research data by other authors on austenitic structured metallic alloys [4; 5; 6; 9; 10], increases in mass loss are explained by the elimination of grains of fragile intermetallic phases and the \(\gamma\) solid solution phase. During the 0-15 min period, the losses are primarily due to the removal of surface roughness peaks and parts of the fragile intermetallic phases.