# Effect of Marine Coolant Additives on Cavitation Erosion-Corrosion of Diesel Engine Cylinder Liner
## 3 Results and Discussion
### Cavitation Erosion Behavior  
Figure 4 shows the weight loss and cavitation erosion rate curves over the duration of the cavitation erosion test and the scanned images of the surface specimen after the test. In the case of the weight loss curve in Figure 4a, it can be seen that all experimental solutions show a gradually increasing trend as the experimental time elapses, indicating that cumulative damage from continuous cavitation erosion has occurred. In particular, the DW+C specimen exhibited a steeper slope compared to the DW + A and DW + A + C specimens, indicating that its cavitation erosion resistance was relatively low. In the case of the cavitation erosion rate in Figure 4b, an unstable curve trend was observed in all conditions until about 10 min of the experimental time, but a stable curve trend was observed thereafter. The average rate in the stabilized cavitation erosion rate section was similar at 4.2 mg/h and 4.4 mg/h for DW + A and DW + A + C, respectively, whereas DW + C was confirmed to be more than twice as large at 9.3 mg/hour. The reason for the relatively high  
Figure 3: [PERSON]’s curves after electrochemical experiments. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Coolant** & **Corrosion Potential [V]** & **Corrosion Current Density** \\  & & [\(\mu\)A/cm\({}^{2}\)] \\ \hline DW + A & \(-\)0.22 & 0.671 \\ DW + C & \(-\)0.50 & 20.000 \\ DW + A + C & \(-\)0.26 & 0.631 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Corrosion potential and corrosion current density by [PERSON]’s analysis. -cavitation erosion in the DW + C specimen is that when the cavitation phenomenon occurs in a corrosive solution, such as Cl\({}^{-}\) ions, both physical cavitation erosion and chemical corrosion occur simultaneously, leading to a synergistic effect due to their interaction [47; 48; 49; 50]. This synergistic effect is a common issue observed in engineering alloys used in marine environments, such as ship propellers, pump impellers, and valves [51; 52]. Meanwhile, the DW + A and DW + A + C specimens showed almost identical trends in cavitation erosion rate, indicating that cavitation resistance is not significantly affected by the presence of Cl\({}^{-}\) ions. Accordingly, upon observing the surface images of DCI after the cavitation erosion tests, only circular surface damage caused by cavitation erosion was predominantly observed on the DW + A (Figure 4d) and DW + A + C (Figure 4e) specimens. In contrast, the DW + C specimen (Figure 4c) exhibited not only circular cavitation erosion damage but also a red coloration across the surface due to corrosion products from the corrosion damage. To observe the surface damage in more detail over the duration of the cavitation erosion test, SEM images of the central part of the circular surface damage on the DW + A and DW + C specimens are presented in Figures 5-8. First, Figure 5 shows the surface morphology after 1 min of cavitation erosion test. In Figure 5a,c, the DW + A and DW + C specimens exhibit a relatively uniform distribution of spherical graphite across the surface. In the high magnification images (Figure 5b,d), the DW + A specimen mostly maintained its original surface morphology, while the DW + C specimen showed partial erosion damage to the spherical graphite in some areas. After 3 min of cavitation erosion test, as shown in Figure 6, the 200\(\times\) magnification images (Figure 6a,c) revealed that spherical graphite was removed from the entire surface of both the DW + A and DW + C specimens, and small crater-like depressions with hemispherical shapes were observed due to cavitation erosion attack. In this way, during the early stages of the cavitation erosion test, when subjected to short periods of cavitation erosion attack, the exposed spherical graphite on the DCI surface is primarily damaged and removed. This is believed to occur because spherical graphite has relatively softer and more brittle structural characteristics compared to the ferrite-pearlite matrix [53].