The use of contact resistance measurements to study oxide films developed during high-temperature sliding

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Abstract
Contact resistance measurements have been made during like-on-like reciprocating sliding of two commercial Fe-12% Cr alloys and an electrodeposited cobalt composite in air at high temperatures, when thick, mechanically-stable, wear-protective oxides have been established on the metal surfaces. It has been shown that such measurements can provide information on the characteristics of the contacting oxide-oxide junctions and on the frictionally-induced temperature increases during sliding. The contact resistance is very dependent on ambient temperature and applied load, but much less dependent on sliding speed. Analysis indicates that the constriction resistance associated with the points of real contact between the oxide surfaces makes the major contribution to the measured contact resistance. The results are consistent with the oxide surfaces being deformed plastically during sliding and with relatively small increases in surface temperature. At a frequency of 500 double traversals per minute and load of 1.5 kg, a mean flash temperature rise of only 7 degrees C is indicated at an ambient temperature of 100 degrees C. A linear relationship ln(RcW)=(A/T)+B, where Rc is contact resistance, T is absolute temperature, W is load, A and B are constants, was found to hold for measurements taken between 300 degrees C and 600 degrees C. Analysis confirms this relationship and relates A and B to fundamental oxide parameters.