Characterization of Erosion of Metallic Materials Under Cavitation Attack in a Mineral Oil

Abstract

Cavitation erosion and erosion rates of eight metallic materials representing three crystal structures were studied. The erosion experiments were conducted with a 20-kHz ultrasonic electrostrictive oscillator in a viscous mineral oil. The erosion rates of the metals and alloys varied over three orders of magnitude. The erosion rates of brittle metals, iron, and molybdenum were higher than that of the titanium alloy but lower than the rest of the soft ductile metals and alloys. Studies with scanning electron microscopy indicated that the cavitation pits were initially formed at the grain boundaries and precipitates and that the pits formed at the junction of grain boundaries grew faster than the others. Transcrystalline craters formed by cavitation attack over the surface of grains and roughened the surfaces by multiple slip and twinning. Surface roughness measurements showed that the pits formed over the grain boundaries deepened faster than other pits. Computer analysis revealed that a geometric expression describes the normalized erosion curves during the time period 0.5 t0 < t < 2.5 t0, where t0 is the incubation period. The fcc metals had very short incubation periods; the titanium alloy had the longest incubation period.