Numerical correlation of the cavitation bubble collapse load and frequency with the pitting damage of flame quenched Cu–9Al–4.5Ni–4.5Fe alloy

In this study, the collapsing loads of cavitation bubbles generated by an ultrasonic vibratory device have been quantitatively evaluated for the as-casted and flame-quenched Cu–8.8Al–4.5Ni–4.5Fe (Al–bronze) alloys and their effects on the surface pitting after a short cavitation exposure have been numerically studied. The cavitation bubble collapsing loads were determined by measuring the cavitation pulse signal (Vout) and converting it into the impact load (F) by a ball drop test. A linear relation (F = A′Vout) between Vout and F was established with a different slope of A′ for both materials. According to the impact load measurements, the flame-quenched Al–bronze underwent lower impact intensities compared to the as-cast one. For the flame-quenched Al–bronze the critical impact load (Lc) required to form a pit more than 5 μm (minimum observable size) was 12.9–13.5 N which is slightly lower compared to that of the as-casted Al–bronze (13–13.8 N). The cavitation bubbles with the impact load value above Lc were very small, suggesting that the cavitation erosion leading a significant material loss is due to the surface fatigue by cumulative small impact loads.