Pitting and Incubation Period

This chapter is devoted to the initial stage of cavitation erosion known as the incubation period. During this period, failure and material removal are negligible and the damage consists in isolated pits that result from plastic deformation for metallic samples. Typical distributions of pits with respect to their diameter are presented and the effects of various parameters such as flow velocity and material properties are discussed. The characteristic time of the erosion process is defined as the time needed for the pits to fully cover the eroded area without any overlap, and the characteristic pit size is defined as the size of those pits whose contribution to the covered surface is the largest. A new technique for estimating impulsive pressures from pitting tests is suggested. It is based on the similarity between a cavitation erosion pit and a conventional spherical nanoindentation imprint. This technique allows for the determination of the load spectrum in a wide range of pressure amplitudes by combining pitting tests on different materials of various cavitation resistances. The impulsive load associated with a pit can be deduced and correlated with pit volume.