The Synergistic Effects of Cavitation Erosion–Corrosion in Ship Propeller Materials

Abstract

Synergy tests were performed for two most common propeller materials, duplex stainless steel (DSS) and nickel aluminium bronze (NAB), by means of an indirect ultrasonic vibratory system. Tests were conducted for pure cavitation erosion in distilled water, pure corrosion using in situ electrochemistry under 3.5 % NaCl solution and a combination of cavitation erosion-corrosion to understand the overall synergism existing between the two. The results were analysed using gravimetric as well as volumetric analysis. Alicona and Talysurf were employed for the surface topography, and scanning electron microscope was used to see the microstructural morphologies of the samples under different conditions. As a result, the electrochemical tests held at open circuit potential showed that, although DSS exhibited higher resistance to corrosion under seawater alone, NAB exhibited much higher resistance to corrosion when subjected to cavitation. From the experiments conducted, it was concluded that synergy had measurable impact on the cavitation erosion-corrosion of both NAB and DSS. NAB was found to be more susceptible to erosion under both the conditions as compared to DSS with prominent selective cavitation erosion of alpha phase in the microstructure. The overall synergism of NAB was found to be higher than that of DSS.

Different methods of measuring synergy between cavitation erosion and corrosion for nickel aluminium bronze in 3.5% NaCl solution

“…The test samples were tested using the experimental conditions and procedure as given in previous work conducted, found in Ref [44] using indirect ultrasonic vibratory transducer operating at a frequency of 19.5 kHz and an amplitude of 80 μm ± 0.2 μm (peak-to-peak). The ultrasonic vibratory apparatus was used for the research as it is the most commonly used device that produces a periodic pressure field, inducing the periodic growth and collapse of a cloud of cavitation bubbles [54].…”

“…The alloy's property comes from a very complex network of microstructures. It generally consists of columnar grains of face centred cubic (FCC) copper-rich solid solution known as α-phase and a small volume fraction of β-phase or retained martensitic β'-phase, surrounded by a series of intermetallic Fe-rich kappa phases [14], [16], [44]- [46].…”

“…κIII phase is a fine lamellar "finger-like" eutectoid structure and forms at the boundary of κI phase [14], [44], [45], [47], [48].…”

“…Reports have also been made where the synergy results seemed to be dependent more on techniques and test conditions adopted during the tests as well as the impact of corrosive solution, the material property, and also the type of materials itself. For most alloys and metal samples the most significant impact was found at a mild corrosive environment [25], [26], [34], [40]- [44].…”

“…Furthermore, synergy is also highly dependent on the microstructure of the material, the environment, and the duration exposure, hence spatial and temporal aspects of Tribocorrosion testing must be considered. The cavitation experiments were conducted by means of an indirect ultrasonic vibratory system as presented in Ref [44] at room temperature.…”