A mathematical model incorporating the erosion process and the internal hardening mechanism is proposed to determine the cavitation erosion rate of alloys. It takes into account both the properties of the material being eroded and the cavitation flow conditions. This calculation approach assumes that during erosion the material is subjected to stress pulse loading conditions. The spatial and the temporal distributions of these pulses are statistical, but the mean level of their amplitude is controlled by the flow conditions. The mechanical properties of the materials (such as the elastic limit and the rupture limit) and the metallurgical parameters (such as the work-hardening coefficient and the stacking fault energy) are introduced into the erosion rate equation. This model can be applied to all types of cavitation in various hydraulic machines. It can also be extended to erosion by liquid drop impacts and to solid particle impact erosion. At this stage of development, only the mechanical aspect of erosion is considered and the effects of coroosion on the erosion rate are not included.