Failure of Silicon Bronze Impeller from Dealloying Via Desiliconification

Abstract

A cast silicon bronze (UNS C86700) impeller that had been severely corroded was submitted for failure analysis. The customer had informed that this impeller was used to pump potable water, but the service length and chlorine content of the water were unknown. The impeller displayed a Cu-rich red phase on its surfaces and showed a pattern very similar to dezincification. Further investigation to determine the cause of damage using various techniques, including light microscopy, scanning electron microscopy combined with energy dispersive x-ray spectroscopy, revealed that the microstructure consisted of multiple phases and that a Si-rich phase was being preferentially attacked, leading to a porous structure. After a thorough examination, it was concluded that this part had failed due to dealloying via desiliconification.