Electrochemically activated wear of metal fibre brushes

Abstract

The electrical and tribological properties of metal fibre sliding contacts are studied. The Cu-Cd fibres have a diameter of 50 μm. They slide on Cu-Cr tracks with optional surface treatments (gold electroplated on a nickel underplate). The working atmosphere is generally wet pure nitrogen. Several types of experimental results are reported in the first section. A microcomputer-controlled test bench is described first. It allows long duration tests on devices fitted with a large number of brushes. Results obtained with this set-up show that the temperature and the polarity of the electric field at the brush-track interface have an influence on the mechanisms and speed of wear. The electric field part is confirmed by complementary experiments where the current polarity is reversed. The electrochemical nature of the phenomena occurring at the sliding interface is then shown. In the second section the authors present a model adapted from Cabrera and Mott's copper oxidation theory. The part played by temperature and by the electrochemical electric field are described. After defining values for these two parameters, results obtained with the model are presented and are in very good agreement with the experimental results.