Program No. ：S-15-NI-43
Program Type ：Collaboration work
Program Title (English) ：Growth of graphene-based two dimensional materials
Username (English) ：Hemant Sagar1), Sachin Shinde2), Kalita Golap2), Masaki Tanemura2),
Bettar el Moctar1)
Affiliation (English) ：1) Institute of Ship Technology, Ocean Engineering and Transport Systems,
University of Duisburg-Essen, Germany 2) Department of Frontier Materials, Nagoya Institute of Technology, Japan.

1．Summary
In current study, ultrasonic vibrating apparatus was used to generate the cavitation. The aluminum alloy sample surface and graphene-based two dimensional materials coated surfaces were exposed to the cavitation and the erosion effect on the surface was characterized in material science point of view. The coating of 2D material have not shown resistance against the cavitation erosion and get easily removed. The further characterization of the metal surface was performed with optical Microscope, SEM, FE-SEM. EDS, XPS and Raman.

2. Experimental
Experimental setup was consists of ultrasonic horn with electronic control unit, double wall beaker, sample holder accompanied with the height measuring gauge. The ultrasonic horn is transduced with the oscillating frequency of 20 kHz. The peak to peak amplitude was 40 um for the current tests. The erosion fluid was distilled water. Double wall of beaker distinguish the inner pot containing the erosion fluid and test setup whereas the cavity between walls is used to circulate the cooling fluid. The temperature of the water during the experiment was measured by thermometer. The original temperature before the experiment was 20 0C, and this temperature was kept constant during the experiment by circulating the water around the inner pot. A cylindrical shaped and 16 mm diameter sonotrode tip was is positioned with the vertical axis aligned with the beaker axis and 10 mm deep from the water surface. The test sample fitted in the sample holder accompanied with the vertical gauge was arranged below the sonotrode tip. The gap between the sonotrode tip and the test surface was 2.5 mm. Cylindrical aluminum alloy samples and samples coated with graphene based 2D material coating with diameter of 16 mm and height of 15 mm (±0.05 mm) was considered for testing as per the G32-10 standards methods cavitation-erosion using Vibratory apparatus. The test surface was smooth and flat. The tests were conducted for 70 minutes and the after every 10 minute the mass loss was measured. After 70 minutes.

3. Results and Discussion
The graphene based material coatings on the metal surface were easily removed by cavitation erosion process (within 10 minutes of exposure to cavitation). This could be result of bonding between coating and base surface. This results will able to develop the further coating process in order to achieve optimum bonding between substrate and coating. Significant increase in oxygen amount and stable oxide formation was seen on metal surface. After removal of the natural oxide layer, the existence of oxygen content indicate the oxide formation process on the surface. This confirms the high temperature impacts on the surface during the cavitation bubble collapse. Thermal cracks on the pit ribs were also observed. The erosion mechanism was also explained from this assumption and the mass loss curve is also explained based on this mechanism. Finally, this study concluded that the erosion is not only mechanical process but it is mechanically accelerated chemical process. Erosion resistance coating characteristics can be also defined with the further research.

4. Others (reference, acknowledgements and so on)
4.1 References
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4.2 Acknowledgement
Financial support provided by Nagoya Institute of Technology and University of Duisburg-Essen is highly acknowledge. The experimental facility to perform ultrasonic cavitation tests provided by Materials Department, University of Bochum is also appreciated.

5. Publication/Presentation/Award/Press-presentation list (if any)
(1) H. Sagar, S. Shinde, K. Golap, M. Tanemura, B. el Moctar, “Characterization of the surface eroded by the ultrasonic cavitation”, WEAR, (Under preparation, expected submission: end May)

6. Patents (if any)
None