Influence of cavitation in seawater on the etching attack of manganese-aluminum-bronzes (MAB)

Abstract

During cavitation investigations with manganese-aluminum-bronzes (MAB) in seawater, it was found that the microstructure of the bronze was developed by etching [1]. To investigate this phenomenon in more detail, metallographically polished MAB samples were treated with pulsed ultrasound in a beaker with synthetic seawater (Fig. 1a). Fig. 1b shows a sample after 3 minutes of ultrasonic treatment in seawater and Fig. 1d after 5 minutes. The stronger etching after 5 min attack can be seen clearly. It is striking that a halo forms around the kappa phase, which can reach a diameter of up to 200 µm. SEM images (Fig.1c, f) show that the kappa phase is more strongly attacked. This could be due to preferential local steam bubble formation and cavitation, where the kappa phase is dissolved or breaks out.