A Fundamental Study on Cavitation Erosion Using a Magnesium Oxide Single Crystal. Effect of Surface Roughness.

Abstract

When a material is exposed to cavitation for a long time, the sueface is eroded like a sponge, which is one of the evidences of cavitation damage. However, the mechanism of the spongelike surface formation remains unclear. A magnesium oxide single crystal is useful to understand the fundamental mechanisms of cavitation erosion. In this study, magnesium oxide single crystal(100)surface were polished with four grades of emery paper to prepare test specimens. The test specimens were exposed to vibratory cavitation. Many dislocation rows with various lengths which intersect the specimen surface at 45 degrees were observed uniformly on a(010)or(001)cross section for an as-cleaved specimen. On the other hand, the dense dislocation rows were localized at the roots of surface irregularity for rough specimens. The depht of surface roughness increases with exposure time and the acceleration is hogher for rougher specimens. It is concluded that the dense dislocation rows intiated at the roots of irregular surface is responsible for the growth of the spongelike eroded surface.