THE ROLE OF ALLOY MICROSTRUCTURE ON THE CAVITATION CORROSION BEHAVIOR OF IRON-BASED, NICKEL-BASED AND COBALT-BASED ALLOYS IN SEAWATER

摘要

UNS F33800, UNS N08825 and UNS R30016 alloys of known microstructures were exposed to cavitation conditions using a vibratory cavitation testing apparatus utilizing seawater as a testing medium. The cavitation tests were made at a frequency of 20 KHz and at temperatures of 25°C. Cavitation made the surface of these alloys very rough, exhibiting large cavity pits in the middle region of the attacked area as revealed by the scanning electron microscope (SEM). The cavitation damage initiated at interfaces of high energy such as that of the ferrite/graphite interfaces of UNS F33800 and the grain boundaries/interfaces of UNS N08825 and UNS R30016 alloys. Mechanical, electrochemical and metallurgical factors were determined to be the leading cause of metal loss.