Synergistic effects of cavitation erosion and corrosion for nickel aluminium bronze with oxide film in 3.5% NaCl solution

Cavitation erosion-corrosion of nickel aluminium bronze with oxide films formed under two different conditions, oxide formed in air for 1 week and oxide formed after 3 months immersion in 3.5% NaCl solution, was conducted using a 19.5 kHz indirect ultrasonic vibratory system at a peak-to-peak amplitude of 80 (±0.2) μm in 3.5% NaCl solution. The synergistic interactions between the cavitation erosion and corrosion were determined via experiment comprising of three different tests: pure cavitation erosion test in distilled water, pure in-situ electrochemical corrosion tests using open circuit potentials (OCP) and polarization scanning, and a combination of cavitation erosion-corrosion kept at OCP in 3.5% NaCl solution to understand the overall synergism existing between cavitation wear and corrosion. The results were then analysed and compared using mass loss analysis. Scanning electron microscopy was used to analyse microstructural characteristics of the cavitated sample surfaces, as well as the transverse-sections of the surface features. It was seen that samples with water formed film exhibited high synergy and was more susceptible to selective phase attack and phase boundary erosion in comparison to air-formed film.