The physical metallurgy and electrical contact resistance of mechanically alloyed CuRu composites

Abstract

Mechanical alloying (high energy attrition milling) has been used to create a novel type of electrical contact material, a Cu-15vol.%Ru composite consisting of a fine (micron-scale) distribution of ruthenium in copper. Because these elements are mutually insoluble, mechanical alloying is one of the only ways of creating such a non-equilibrium microstructure. Consolidation of the composite powders into strip was carried out by warm and cold rolling, to preserve the metastable microstructure. The removal of surface copper from the consolidated strip gives rise to a “sandpaper” structure in which the hard, refractory and conductive ruthenium particles, now protruding from the surface, serve as the electrical contacts, whereas the copper matrix supports these particles and provides electrical continuity. The fact that this is so is borne out by the observation that in contact resistance versus exposure time tests, the Cu-15vol.%Ru composite behaves much more like pure ruthenium than like pure copper. Thus, we have developed a procedure for producing a base metal-ruthenium composite with electrical contact properties similar to those of ruthenium, without the difficulties (i.e. hot forging) or expense of working with pure ruthenium. This processing is applicable to an unlimited number of alloy systems.