A Fundamental Study on Cavitation Erosion Using a Magnesium Oxide Single Crystal

空化侵蚀是固体表面的原始材料由于持续暴露于空化而逐渐失去质量的现象，但目前尚不清楚压力如何作用于表面。在本研究中，利用氧化镁单晶(100)表面的空化来分析压力分布。测量了塑性变形区的大小和位错蚀坑的距离。结果表明，压力作用于表面是垂直于表面的，而不是平行的，因此表面上不存在空蚀的剪应力。最大压力范围为500-1000兆帕。高压区很大，但受影响的区域很大。通过与一些不同屈服强度金属上观察到的凹坑进行比较，证实了压力分布的合理性。此外，当一种材料长时间暴露在气蚀中时，表面会像海绵一样被侵蚀。对用四种砂纸抛光的氧化镁单晶进行了空化处理。结果表明，海绵状冲蚀表面的生长是不平坦表面凹陷处产生密集位错排的原因。

Cavitaion erosion is a phenomenon of progressive mass loss of original material from a solid surface due to continued exposure to cavitation, but it remains unclear how the pressure act on the surface. In this study, the pressure distribution was analyzed by using a magnesium oxide single crystal (100) surface exposed to cavitation. The size of the plastically deformed region and the distances of dislocation-etch-pits were measured. The results shows that the pressure acts normal to the surface, but not parallel, thus no shear stress acts on the surface for cavitation erosion. The maximum pressure ranges from 500MPa to 1000MPa. The high pressure region is very large, but the affected region is very large. The pressure distribution was confirmed to be reasonable by comparing it with pits observed on some metals with different yield strength. Moreover, when a material is exposed to cavitation for a long time, the surface is eroded like a sponge. Magnesium oxide single crystal polished with four grades of emery paper were exposed to cavitation. It is concluded that the growth of spongelike eroded surface is responsible for the dense dislocation rows initiated at the dents of uneven surface.