Study on Cavitation Erosion-Corrosion Behavior of Mild Steel under Synergistic Vibration Generated by Ultrasonic Excitation

In order to simulate the real condition of a ship sailing in seawater, a cavitation apparatus of ultrasonic excitation was set up with variable temperature field and self-vibration of a Q235 steel sample. The sample self-vibration in a cavitation environment was firstly measured and its erosion-corrosion behaviors at ultrasonic generator output powers of 40, 70, and 100 W were fully investigated. It is found that the displacement fluctuation of sample is enhanced with increasing output power. The temperature rise by cavitation bubble collapse and sample vibration is proved by the higher temperature of the sample than that of the corrosive solution. The surface morphologies of samples in cavitation erosion-corrosion tests show more extensive and worse local corrosion than that in the static case. The maximum depths of erosion-corrosion pits are 39.5, 31.8, and 24.6 mu m, corresponding to output powers of 100, 70, and 40 W, respectively, which are higher than that in the static case. The content of Fe in the corrosive solution increases as corrosion time lasts and output power increases, revealing the progressive corrosion of the steel sample. The collapse of cavitation bubbles, sample vibration, as well as electrochemical reaction enhanced by temperature rise are considered to be the main reasons for worse cavitation erosion-corrosion of the sample in an ultrasonic excitation environment.