Cavitation Damage Studies With Rotating Disk in Water

The cavitation damage resistance of alloys of aluminum, columbium (niobium), tantalum, molybdenum, and stainless steel was evaluated in water using a rotating disk apparatus that simulated the cavitation vortex patterns encountered in pumps operating at high suction specific speed. The alloys in decreasing order of cavitation resistance were Ta-8W-2Hf, Cb-18W-8Hf, Ta-10W, 316SS, Mo-.5Ti, Cb-1Zr, Al-4Cu-.7Mn-.5Mg, and Al-2.5Mg-.25Cr. The damage resistance order does not follow the variation of any single property such as strain energy to failure, yield strength, or hardness, but appears to be a combination of mechanical properties and phase structure. Photomicrographs show predominant intergranular cracking for the molybdenum alloy and transgranular erosion and cracking for the remaining alloys tested. The second phase precipitate in the aluminum alloy appears to hinder the erosion of material. Investigation of small variations in the grain size of the heat-treated Cb-1Zr alloys resulted in some variation in damage resistance, with the largest grain structure exhibiting the highest resistance. Correlation curves of volume loss as a function of the peripheral velocity are presented for all materials tested. In addition, the operation of the rotating disk apparatus itself was examined in considerable detail and the effects of various design changes were evaluated.