High-Energy/High-Rate Consolidation of Copper-Graphite Composite Brushes for High Current Applications
MetadataShow full item record
This paper reviews some of the important materials structure-property relationships that exist for copper-graphite composites, as they influence this class of materials in high current applications. Commercial composite brushes fail in high-speed/high-current duty by loss of the low-melting-temperature, metallic binder, usually lead-tin, caused by the high flash temperature at the sliding interface combined with the softening due to I2R heating. The virtues of binderless copper-graphite brush materials have driven the development of a novel high-energy/high-rate processing approach employing a homopolar generator as a '1 MJ in 1 s' pulsed power source. The discharge of such an energy pulse through a powder mixture under pressure produces a dense product with improved mechanical and electrical properties compared to conventionally sintered commercial material. The rapid processing minimizes internal oxidation, and the fast postpulse cooling promotes the freezing of the copper matrix and tight micro-encapsulation of the graphite particles due to localized energy deposition at the copper-graphite interface. High and low speed testing have been used in the preliminary tribological evaluation. The behavior of these materials has compared favorably to commercial materials for pulsed high-speed, high-current duty.