Accelerated Cavitation Damage of Steels and Superalloys in Sodium and Mercury

An investigation was conducted to study cavitation damage in liquid-metal environments of materials under consideration for components of liquid-metal power conversion systems. The materials investigated included AISI Types 316 and 318 stainless steels, Sicromo 9M, Inconel 600, A-286, Hastelloy X, L-605, René 41, and Stellite 6B. A magnetostrictive apparatus was used to perform accelerated cavitation damage tests with liquid sodium at 800 F and mercury at 300 F. Cavitation damage determined by volume loss and surface roughness measurements was used to rank the various materials and to compare the effects of the different fluids on the degree of damage sustained. Metallographic studies were made to determine the nature of the early stages of cavitation damage. The materials tested in both sodium and mercury ranked in the same order of resistance to cavitation damage, but the degree of damage to all materials was consistently greater when tested in mercury. The most resistant material was Stellite 6B; the least resistant material was annealed Sicromo 9M. Surface roughness measurements provided the same ranking of materials as that provided by conventional volume loss measurements. Visual observation of sodium pump impeller blades of three materials operated under cavitating conditions for 250 hr indicated the same ranking of the materials with respect to resistance to cavitation damage that was determined from the accelerated cavitation tests.