Corrosion Behavior of a Fe-25at%Sn Supersaturated Solid Solution in H3PO4 Solution

Corrosion resistance of iron can be drastically improved by addition of passivating alloying elements. A supersaturated solid solution of Fe-25at%Sn was produced by mechanical alloying of commercially pure iron and tin powders for 24 hours using a planetary ball mill. Electrochemical measurements were performed on cold compacted unsintered specimens.. XRD investigation on produced alloy showed the characteristics of a supersaturated solid solution. Corrosion behavior of the solid solution alloy was investigated in 0.1M H3PO4 employing potentiodynamic and potentiostatic polarization techniques. The anodic behavior of mechanically alloyed specimens was compared with specimens prepared from individually compacted iron, tin and appropriate admixture of tin/iron powders. Potentiodynamic polarization of supersaturated specimen featured a gradual decrease in anodic current density, indicating a feature of quasi passivation which was attributed to the tin surface enrichment as a result of preferential iron dissolution. Anodic current density from the result of potentiostatic polarization of the prepared alloy also showed a gradual decrease with time following i¥t-0.45 relationships indicating a characterization of passivity. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) examination of the specimen surface after potentiostatic anodic polarization test confirmed the presence of high tin content on the surface.