Cavitation is described as the formation and collapse of gas bubbles in fluids due to local pressure changes. The implosion of these bubbles in the immediate vicinity of a surface can lead to shock waves and microjets, inducing plastic deformation and erosion of the material. The wear resistance of materials is highly influenced by the surface properties of the material. One simple way to change these properties is to change the surface topography via the final manufacturing step. For cavitation erosion it is oftentimes assumed that a smoother surface finish will yield better erosion resistance. In other cases, surface structuring is attempted to reduce the aggressiveness of cavitation attack on a surface. Nevertheless, the effects of surface properties on cavitation erosion are not fully understood to date.

In this study the damage evolution during ultrasonic cavitation of an austenitic steel (316L; 1.4441) and a nickel-aluminium bronze (CuAl10Ni5Fe5) at two different surface roughness values (ground with 80 grit sandpaper and polished with silica) were investigated, using light microscopy, confocal microscopy, as well as scanning electron microscopy. Additionally, the mass loss curves were recorded during the experiment. For both materials investigated, the mass loss curves of the polished samples show a tendency of a slightly higher mass loss over cavitation time. This phenomenon is mainly visible in the early damaging stages of the material and is also evident from the microscopic analysis. After short ultrasonic cavitation times the polished samples show plastic deformation e.g., slip lines, whereas the ground samples show a later onset of the plastic deformation alongside maintaining large parts of the original surface for a long time compared to the polished samples. Apparently, the surface finishing by polishing did not improve the cavitation resistance of the materials. On the contrary, strain hardening induced by grinding appears to delay the onset of erosion under cavitation.