Testing a Cu-8Cr-4Nb contact material in vacuum interrupters

GRCop-84 is a Cu-8 at.% Cr-4 at.% Nb alloy developed at NASA Glenn Research Center for use in rocket engine liners. Its high thermal and electrical conductivities make it a possible candidate for the electrical contact of a vacuum interrupter (VI). In this work, contacts were made from a warm rolled Cu-8Cr-4Nb plate and tested in a VI of the Axial Magnetic Field (AMF) type as well as a VI of the Transverse Magnetic Field (TMF) type. The material showed comparable performance in dielectric strength as well as current interruption to those of typical powder-metallurgically made or vacuum cast Cu-Cr contact materials. Contact resistance values are also in the same range as those of typical commercial Cu-Cr. Postmortem examinations of the VIs saw appearance of a significant melt depth, and rather fluid molten metal flow on the contact surface, and splashing on to the surrounding shields. The results of the testing are discussed in terms of the microstructure and properties of the GRCop-84 material. Future work to examine the addition of a fourth element and increased Cr₂Nb content is proposed.