Cavitation; ; Cave erosion is also called cave erosion. Cavitation is the surface damage caused by the relative movement between solid surface and liquid, which usually occurs on the surfaces of water pump parts, turbine blades and ship propellers. Under the condition of high-speed fluid flow and pressure change, the metal surface in contact with the fluid is corroded in caves. It often occurs in high-speed decompression areas such as centrifugal pump blade tips, forming cavities, which are crushed in high-pressure areas, generating impact pressure, destroying the protective film on the metal surface and accelerating the corrosion rate. Cavitation is characterized by forming many tiny pits on the metal surface, and then gradually expanding into caves.