GALVANIC CORROSION BEHAVIOUR OF COMMERCIALLY PURE TITANIUM/Cu-Ni ALLOY/LOW ALLOYING STEEL IN MULTIMATERIAL SYSTEM IN MARINE ENVIRONMENT

摘要

The galvanic corrosion of commercially pure titanium titanium (TA2), Cu-Ni alloy (B10) and low alloying steel (921A) in multimaterial system has been studied under open circuit conditions using potentiodynamic polarisation measurements and a multi pass zero-resistance ammeter (DL-1) in seawater, then effects of elevated dissolved oxygen and temperature have been analysed. After the tests, the surface morphology of the samples has been characterised using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) techniques. Results show that 921A acts as the anode and both TA2 and B10 act as the cathodes in multimaterial system. TA2/B10/921A generates the higher galvanic current density. Galvanic corrosion process involves a higher rate of anodic dissolution for 921A and dissolved oxygen reduction reaction on cathodes. The strength of the galvanic coupling effect is typically controlled by the oxidation rate of 921A. Galvanic corrosion behaviour of TA2/B10/921A fulfills the mixed potential theory. The galvanic current density and galvanic potential of galvanic corrosion has been compared with results estimated from the polarisation curves according to the mixed potential theory (imposed potential measurements). Two methods reflecting the severity of galvanic corrosion are basically in agreement.