Investigation Of Cavitation Erosion Mechanism On Several Typical Materials

Cavitation erosion is a complex process and the mechanism of cavitation erosion is not established perfectly by now. The initiation of cavitation erosion is the important stages, but the fixed-point and multi-scale study on the early stage of cavitation erosion is very little. In this study, austenitic stainless steel, brass and industrial pure titanium are studied by systemically experimental method. The characteristics of initiation and development of cavitation erosion are investigated, and the image processing method was used to exhibit characteristics of surface deformation of the cavitation erosion. The main conclusions are as follow:1. Cavitation pit are produced in the polished surface of Austenitic stainless steel (0Cr18Ni9)by the effect of cavitation bubbles collapsed. Subsequently the pits pile up and extend. Plastic deformations of the surface occur, causing to yield hardening and stressing. However, plastic flow is prone to occur in the surface. 0Cr18Ni9 is not sensitive to the high strain rate, so the incubation period were prolonged, the cavitation erosion is difficult to develop, which indicates that 0Cr18Ni9 present an outstanding anti-cavitation property. Fatigue cracks are generated in the materials surface and extended inward, leading to fatigue fracture and abscission. Then the cracks continue to extend inward, resulting in the further damage. On the newborn cavitation erosion stage, the surface roughness raised significantly.2. Anti-cavitation performance of the materials have a closely relationship with the Ra value of surface roughness. Material surfaces with certain geometric morphology show a pronounced anti-cavitation performance.3. Common structural brass is prone to caused slip and cavitation damage along the grain boundary, and behaves a poor anti-cavitation performance. Industrially pure titanium is difficult to slip along the grain boundary, but is easy to get transcrystalline and cleavage fracture. Cracks and shedding increased in the cavitation processing. It indicated that industrially pure titanium has a poor anti-cavitation property. The anti-cavitation properties of the materials are more obviously affected by the crystal structure, plastic and toughness nature, and strength of surface.4. The images of the surfaces of materials on the initiation stage of cavitation erosion were treated with the colors-abstraction method. The Cavitation erosion curves by surface deformation and time are consistent with the model which based on the exponential distribution of cavitation pulse. It validates the cavitation erosion models. Four-color image processing can exhibit the inception of cavitation erosion process well, which can be used to analyze surface changes of the materials qualitatively.