Electropolishing of an Fe-Ni-Co Alloy in Acetic Acid-Perchloric Acid Mixture

Abstract

Among Fe-Ni-Co alloys, Kovar (53%Fe-29%Ni-17%Co) designated as ASTM F-15 (1), is a well-known glass-sealing alloy. It is also classified as low–expansion alloy (2). Low expansion is required to avoid internal stresses in applications that involve strong ceramic to metal joining such as in vacuum systems (3-6). Electropolishing is applied to obtain smooth metallic surfaces to gain low outgassing rates from the chamber walls in vacuum applications (7-9). The effects of current density, perchloric acid concentration and bath temperature on surface roughness and thickness change were investigated in acetic acid-perchloric acid electrolyte. It was found that current density, perchloric acid concentration and temperature of the bath had a decreasing influence on surface roughness in the given order. On the other hand, thickness change was found to have a direct correlation with the current density and was independent of bath concentration and temperature.