Influence of microstructure on dielectric strength of CuCr contact materials in a vacuum

The influence of microstructure of CuCr contact materials on dielectric strength in a vacuum is investigated. Experimental results show that breakdown selectively occurs on dielectrically weak phases. For the Cu50Cr50 alloy, it first takes place on Cr particles, and for the CuCr50Sel alloy, on the Cu2Se phase. As a result of conditioning of breakdown, the dielectric strength of these phases increases, and breakdown occurs simultaneously. Breakdown roughens the surface of the cathode, but produces a small melt layer on the surface which has much finer microstructures and more homogeneous micro-compositions. The effect of conditioning of breakdown to increase dielectric strength, according to the present work, is to produce much finer microstructures and more even micro-compositions on the contact surface.