A novel electrical contact material with improved self-lubrication for railway current collectors

A new series of copper–graphite composite materials (CGCMs), which show improved electrical conductivity and tribological properties without the need for lubrication, were developed. The materials reported herein were prepared by the powder metallurgy (P/M) route and present a higher density (6.3–7.6 g/cm3) than other P/M prepared contact materials. The new materials differ from other sintered carbon–copper composite material (CCMs) used as contacts, in which an intermediate alloy is used in order to introduce carbon into the copper phase, resulting in high electrical contact resistance and/or high wear of the counterpart due to hardening of the copper matrix. The CGCMs exhibit a self-lubricating function, which works by formation of a carbonaceous layer (believed to be graphite) onto the counterpart surface, as confirmed by Auger analysis. The coefficient of friction was reduced during the wear test under 13.5 N constant normal load without lubrication from 0.220 to 0.185. The wear mechanism of the CGCMs versus Cu was identified as a combination of mechanisms that changes with variations in composition. The wear on contact wire was below a measurable rate, and the wear rate of CGCM samples against pure copper was also very low, in the range of 3.2×10−6 to 2×10−8 mm3/N m. The high electrical conductivity of the new series of materials is attributed to ‘network conduction’ channels which result in electrical conductivity values of 60% IACS (international annealed copper standard) in some samples. Based on these properties, the new materials show a clear advantage for use in applications such as pantographs, contact brushes and other electrical contact components.