Evaluation of Cavitation Erosion based on Erosion Particles

Abstract

Cavitation erosion mechanisms were studied through the observation of removed particles for annealed S15C (equivalent to AISI 1015) steel and heat-treated S55C (AISI 1055) steels. In the initial and the incubation stages, single impact loads removed many small sharply-edged particles. During the acceleration and the maximum rate stages, large striated particles were observed due to cyclic loads. The volume fraction of particles exhibiting fatigue fracture in these stages amounts to 70 or 80% irrespective of the material including pure copper and pure aluminum. The exponent of the crack growth rate determined from the fracture is almost the same as that obtained from a regular fatigue test. The fatigue crack growth rate for many metals is inversely proportional to the square of Young's modulus, E^(-2). The particles fall off from the protrusive surface and their sizes depend on the unevenness in relation to the hardness of the material. The average diameter of erosion particles decreases inversely with the square root of Vickers hardness, HV^(-1/2). Therefore, the volume is proportional to HV^(-3/2). Thus, the dependence of the volume loss rate in the maximum rate stage is well described by HV^(-3/2)•E^(-2). The conclusion is that cavitation erosion can be evaluated in terms of the hardness of the material and the fatigue crack growth rate.