Surface oxidation of manganese and silicon in nickel-iron alloys

Abstract

A nickel-iron alloy containing 51 wt. % Ni, 49 wt. % Fe, and small additions of Mn and Si is used commercially in applications where soft magnetic properties and good glass-sealing characteristics are required. This alloy is also used, after plating with a precious metal, as an electrical contact material. For the latter application, the surface condition of the material is important. Accordingly, a study has been made of the surface oxidation characteristics of the commercial alloy and a series of silicon-free experimental alloys to which various manganese additions were made. Experiments were performed at 915°C in atmospheres of hydrogen with various moisture contents. The onset of surface oxidation was found to occur at conditions which were predicted from available thermodynamic data. The degree of surface oxidation was determined metallographically and through reflectivity measurements.