Copper–beryllium metal fiber brushes in high current density sliding electrical contacts

The use of copper–beryllium (UNS C17200) was demonstrated as a low wear, highly compliant material for the construction of high current density metal fiber brushes. Testing was conducted in a humidified carbon dioxide environment. Brush linear wear rates of 4 × 10−11 m/m were achieved at sliding speeds and current densities as high as 7.5 m/s and 215 A/cm2 (2 MA/m2). Contact resistance values were on the order of 10 mΩ and friction coefficients varied from 0.30 at 2.5 m/s to 0.15 at 7.5 m/s. Characterization of the brush and slip-ring surfaces using SEM as well as the slip-ring subsurface using TEM is presented as evidence in favor of fatigue dominated wear of the copper–beryllium fiber tips. Debris flakes were observed forming on the fiber tips with characteristic widths in the range 10–100 μm and thickness on the order of 1 μm, in stark contrast to 1–10 μm wide flakes of thickness on the order of 1 μm observed forming on the slip-ring surface. Relatively clean contact resistance data at the end of the test is indicative of the robustness of the brush design and the ability of the fiber tips to remain in contact with the evolving slip-ring surface. The importance of material selection, particularly in regard to fatigue and yield strength, is highlighted in this work as key factors in improving brush design and understanding the wear phenomena observed in high current density sliding electrical contacts.