Mechanisms of Formation of Spheroids Produced by Cavitation Erosion

The prediction, control, and prevention of unscheduled downtime due to wear of industrial equipment is an important engineering problem. The characterization of wear particles and the study of the mechanism of their formation will aid in preventive maintenance. Of particular interest is the mechanism of formation of spherical particles during wear and erosion. It has been suggested that cavitation erosion is a mechanism of formation for these spherical particles. Using both a vibratory apparatus and a jet erosion facility, spherical particles were produced on various materials including aluminum and 52100 steel. Special techniques for isolating and mounting the eroded particles were developed. Spheroids ranging from 0·5 μ (microns) to 30 μ in diameter were observed in the vibratory cavitation method both in distilled water and in SAE 10W nondetergent oil. Much larger spheroids up to 150μ in diameter were observed in clusters with the jet erosion method. Scanning electron microscope studies revealed craters, plastic flow, overflowing lips, and splashing stems. Based on these observations, it is theorized that the high strain rate indentation of the cavitation bubbles leads to the splash of metal into the surrounding liquid where surface tension produces spherical particles. Supporting experimental evidence and calculations are also presented.