Deterioration of surface layers of tungsten and steel-containing materials in current collection sliding against molybdenum

Abstract

The possibility of improving the characteristics of a dry sliding electrical contact with a current density higher than 100 A/cm² by using a molybdenum counterbody is considered. It is shown that tungsten or metallic materials containing bearing steel (1.5 % Cr) in sliding against molybdenum at a speed of 5 m/s under electric current, forms a contact with low electrical conductivity and high wear intensity. This observation served as the basis of this work. Using optical and electron microscopy of sliding surfaces it was found that strong adhesion in the interface was the main reason for rapid surface layers deterioration and high wear intensity. A well-known statement was taken into account that adhesion is due to the low oxide content between the contact surfaces. Visual study of molybdenum sliding surface made it possible to establish formation of a thin transfer layer and absence of traces of oxide formation. The same was observed on sliding surface of tungsten that was caused by high temperature of tungsten and molybdenum oxides formation. A layer of iron oxides was observed on sliding surface of steel containing materials. In addition, traces of a thin tribolayer were find out. An increase in concentration of steel in the primary structure led to a slight increase in iron oxides on the sliding surface, but did not lead to a significant increase in electrical conductivity and wear resistance of the contact. Unsatisfactory characteristics of the contact allowed us to conclude that it is impossible to significantly improve sliding parameters with current collection against molybdenum and inappropriateness of its use as a counterbody for these conditions.