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/cm(3)) 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 x 10(-6) to 2 x 10(-8) mm(3)/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. (C) 2001 Published by Elsevier Science B.V.