Pitting Corrosion of Amorphous Ni–Zr Alloys in Chloride Ion Containing Sulfuric Acid Solutions

Abstract

The pitting corrosion behavior of the melt-spun amorphous Ni-Zr alloys with 30-75 at% zirconium, the crystalline arc-melted counterparts and the sputter-deposited Ni-Zr alloys with 20-84 at% zirconium was examined by electrochemical measurements in deaerated 0.5 kmol/ m 3 H 2 SO 4 with and without 0.1 kmol/m 3 NaCl at 303 K. In the sulfuric acid solution without Cl - , these alloys were spontaneously passive and their potentiodynamic behavior was similar to each other. In the Cl - -containing solution, all the melt-spun amorphous alloys suffered pitting during anodic polarization and the pitting potential decreased with an increase in zirconium content. On the other hand, the crystalline arc-melted low zirconium alloys suffered pitting but no pitting observed for the crystalline alloys containing 70 at% zirconium or more. In addition, the pitting potential increased with the zirconium content of crystalline alloys. All the sputter-deposited alloys did not suffer pitting regardless of the amorphous and crystalline structures. Therefore, the melt-spun amorphous alloys were the most susceptible to pitting corrosion. A marked difference was observed in the pitting behavior between the shiny side (top side) and the dull side (wheel side) surfaces of the melt-spun ribbon. The pits initiated from the dull side surface. Thus, the dull side surface could be responsible for such an unusual pitting behavior of the melt spun ribbon.