# Effect of Marine Coolant Additives on Cavitation Erosion-Corrosion of Diesel Engine Cylinder Liner
## 3 Results and Discussion
### Cavitation Erosion Behavior
The primary destruction mechanism observed at this stage is related to fatigue, with the particles removed by cavitation erosion being attributed to the coalescence and growth of micro cracks. Thus, in the high magnification images (Figure 8b,d), the crater interior and surrounding areas in the DW + C specimen are judged to have a relatively more complex surface damage pattern. Figure 5: SEM images after cavitation erosion test during 1 min; (**a**) DW + A image (\(\times\)200), (**b**) high-magnification image of the marked area in (**a**), (**c**) DW + C image (\(\times\)200), and (**d**) high-magnification image of the marked area in (**c**). Figure 6: SEM images after cavitation erosion test during 3 min; **(a)** DW + A image (\(\times\)200), **(b)** high-magnification image of the marked area in **(a)**, **(c)** DW + C image (\(\times\)200), and **(d)** high-magnification image of the marked area in **(c)**. Figure 7: SEM images after cavitation erosion test during 10 min; **(a)** DW + A image (\(\times\)200), **(b)** high-magnification image of the marked area in **(a)**, **(c)** DW + C image (\(\times\)200), and **(d)** high-magnification image of the marked area in **(c)**. Figure 9 shows the graph of surface roughness and maximum surface damage depth over time during the cavitation erosion test, obtained using a confocal 3D laser microscope. Both surface roughness (Figure 9a) and maximum surface damage depth (Figure 9b) exhibited a general increasing trend over time during the cavitation erosion test. This trend is consistent with the weight loss curve in Figure 4a, indicating that as the cavitation erosion test progresses, surface damage also increases due to material detachment damage caused by cavitation erosion attacks. In the initial stage of the cavitation erosion test, up to approximately 5 min, both surface roughness and maximum surface damage depth showed a sharp increase. This is because, as shown in Figure 6, the graphite exposed on the DCI surface was preferentially removed. In the case of the DW + C specimen, there was a sharp increase in surface damage depth at 30 min of test time, which is attributed to the growth of depth-oriented damage, such as micro tunnels, typical of cavitation erosion characteristics. Throughout the remainder of the test, the surface roughness of all specimens continued to increase, while the surface damage depth exhibited a more gradual slope. This is due to the coalescence of adjacent craters, as observed in the DW + C specimen in Figure 8, leading to a tendency for damage to progress in the width direction. Furthermore, as shown in Figure 4a, the sharp increase in weight loss of the DW + C specimen towards the end of the cavitation erosion test is attributed to significant material detachment damage in the form of large bulks during the coalescence of the craters. In contrast, for the DW + A specimen, surface roughness continued to increase steadily until the end of the cavitation erosion test, but the surface damage depth showed a relatively mild slope. This is because, as seen in Figure 8a, the number of micro tunnel damages in the depth direction continued to increase over test time, while damage in the width direction occurred relatively less. On the other hand, the DW + A + C specimen exhibited relatively higher surface roughness and surface damage depth compared to the DW + A specimen, though the difference was not significant, and the weight loss in Figure 4a was also almost identical. This surface damage trend can also be confirmed through the 3D profile data obtained by analyzing the surface damage after the cavitation erosion test, as shown in Figure 10. In the DW + A  
Figure 8: SEM images after cavitation erosion test during 90 min; **(a)** DW + A image (\(\times\)200), **(b)** high-magnification image of the marked area in **(a)**, **(c)** DW + C image (\(\times\)200), and **(d)** high-magnification image of the marked area in **(e)**.