THE EFFECT OF ULTRASONICALLY INDUCED CAVITATION CONDITIONS ON THE BEHAVIOR OF NI-RESIST CAST ALLOY IN SEAWATER

A cavitation facility was used to study the cavitation corrosion behavior of Ni-Resist cast alloy in seawater. The work included measurements of free corrosion potentials, and mass loss in presence and absence of cavitation.  The cavitation tests were made at a frequency of 20 KHz and at temperatures of 25⁰C.  Cavitation conditions caused a noble shift in the free corrosion potential for Ni-Resist alloy. 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 were also carried out for this ally 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 a over riding role in 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).  Mechanical factors were determined to be the leading cause of metal loss.