Passivity characteristics on Ni(Cr)(Fe)SiB glassy alloys in phosphate solution

AbstractPassivity characteristics of three nickel-metalloids glassy alloys (Ni92.3Si4.5B32, Ni82.3Cr7Fe3Si4.5B3.2 and Ni75.5Cr13Fe4.2Si4.5B2.8) and the immersion time effect on the corrosion resistance were carried out by AC and DC electrochemical methods and SEM and XPS analyses. The study also focused on the effect of H3PO4 concentration and its role on the corrosion rate, passivation ability of nickel base glassy alloys surface. The present investigation revealed (i) corrosion resistance of Cr-free alloy shows pseudo passivity at all examined H3PO4 concentrations, (ii) high corrosion resistance of Cr contains alloys due to the formation of protective layer of chromium oxyhydroxide on the surface which acts as a diffusion barrier against alloy dissolution, (iii) the negative resistance observed in the case Ni75.5Cr13Fe4.2Si4.5B2.8 alloy revealed the sudden transition of metal/solution interface from a state of active dissolution to the passive state