PITTING CORROSION BEHAVIOUR OF AUSTENITIC STAINLESS-STEEL COATED ON Ti6Al4V ALLOY IN CHLORIDE SOLUTIONS

This study aims to investigate the influence of adding a coating layer of austenitic stainless steel type 316L on Ti6Al4V alloy on corrosion behaviour. Samples of 316L, Ti6Al4V, and 316L on Ti6Al4V were prepared by hot-press sintering of their powders. The potentiodynamic polarization technique was used to characterize the corrosion behaviour of the samples in 0.9 and 3.5 wt. % NaCl concentrations. The corrosion potential (E-corr.), current density (i(corr)) and corrosion rate (CR) of the sintered samples were compared in this study. The results showed that 316L samples had the best corrosion resistance, although micropits were observed on the surface, while Ti6Al4V samples had the lowest. This corrosion behaviour of sintered 316L samples can be interrelated to the existence of a passive layer on stainless steel alloys that can be attacked by chloride ions and causing localized corrosion. In general, the CR values of Ti6Al4V samples coated by 316L were between the 316L and Ti6Al4V samples. The CR values of the samples, in 0.9 wt. % NaCl, did not show significant changes with increasing time, as the CR for 316L values were around 0.003 mm/year, while for Ti6Al4V the CR values changed noticeably from 0.018 mm/year of 0 hr, to 0.015 mm/year for 24 hours. However, the changes were less than that of Ti6Al4V. For 3.5 wt. % NaCl solution, although the same order of CR remained, i.e., the CR values of coated Ti6Al4V samples were between 316L (lowest) and Ti6Al4V (highest), the overall CR values for the samples were higher than 0.9 wt. % NaCl.