51316-7377-The Effect Of Alloy UNS S32550 Microstructure On Its Cavitation Erosion Behavior In Seawater

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Product Number: 51316-7377-SG

ISBN: 7377 2016 CP

Author: Abdul Hameed Al-Hashem

Publication Date: 2016

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An ultrasonically-induced cavitation facility was used to study the cavitation corrosion behavior of UNS S32550 alloy in seawater. The work included measurements of mass loss in the presence and absence of cavitation and free corrosion potentials . The cavitation tests were made at a frequency of 20 KHz and at temperatures of 250C. Cavitation conditions caused an electrochemically active shift in the free corrosion potential for UNS S32550. Cavitation also increased the rate of mass loss of this alloy by several orders of magnitude with respect to stagnant conditions. Another set of cavitation experiments was also carried out for this alloy in a nonconductive medium in order to distinguish between the mechanical and electrochemical factors that contribute to metal loss. Results indicated that the mechanical factor has an overriding role of metal loss of this alloy. Cavitation made the surface of this alloy very rough exhibiting large cavity pits in the middle region of the attacked area as revealed by the scanning electron microscope (SEM). High magnification SEM microscopy revealed that small cavities initiated in the ferrite matrix and at the ferrite-austenite boundaries. With the progress of cavitation the attack concentrated in the austenite phase and then spread to the ferrite phase and was associated with cleavage-like facets ductile tearing river patterns and crystallographic steps at later stages. Mechanical factors were determined to be the leading cause of metal loss.