Lubrication mechanisms of a sliding contact by simultaneous action of electric current and magnetic field

This paper reports the friction tests results performed in open air of 20–30% relative humidity (RH) at room temperature of steel/graphite in sliding contact crossed by a DC electric current and submitted to a DC magnetic field. Magnetic field is applied normally to the sliding contact area. As have been elucidated by numerous friction tests in various experimental conditions, it was shown that the simultaneous effects of an electric current and that of a magnetic field decrease the friction coefficient of the couple and enhance the slope of the high friction–low friction state transition according to their intensities. This effect, similar to the lubrication of the contact, is attributed to the oxidation of the steel material, leading also to a reduction of the real contact area and to a carbon transfer on the steel friction track. Facilitation of this carbon transfer by the change of magnetic properties of the graphite friction track and by the reorientation process due to the magneto-mechanical effects, explains the low friction state and wear rate characteristic in the case of high electric–magnetic field intensity and high contact pressure.