Enhanced sulfur segregation in plastically deformed OFHC Cu and the effect of surface segregated sulfur on electric contact resistance

The effects of thermally segregated sulfide films on the contact resistance of OFHC copper specimens have been examined. Contact resistances were measured in situ in UHV for SiC abraded and POL polished copper specimens at dry circuit levels. It was found that at low sulfur concentrations (<10 a/o) the segregated sulfide films did not have an appreciable effect on the contact resistance. Above a critical sulfur surface concentration of about 10 a/o, a sharp increase was observed in the contact resistance values. A saturation effect was observed at higher sulfur concentrations. A model was proposed to explain the growth mechanism of the segregated sulfide film that explains the contact resistance behavior. Sulfur was found to disappear from specimen surfaces after air exposure of about 72 hours. Contact resistance values obtained after air exposure showed a steady increase with exposure due to the growth of an oxide layer. The values of the contact resistance increased at about 2.13%/h for both SiC and POP specimens.<>