Magnetotribology of ferromagnetic/ferromagnetic sliding couple

Abstract

Applied magnetic field around the rotating sliding ferromagnetic steel/steel modifies the friction and the wear behaviour of the contact. The friction tests where conducted in ambient air or in high vacuum chamber 10 −5 Pa. The applied normal loads are 0.1, 18.5 and 37 N. Without magnetic field, the contact is ductile steel against steel in a severe adhesive grooving mode. When a magnetic field is applied, the contact in ambient air progressively became black, covered by a brittle thick black layer of oxides which leads to a low friction and a low wear mode after some hundred cycles. Under the low normal load P = 0.1 N, a positive wear rate for the pin and for the disc was measured for magnetized contact. This mass increase is due to the activation by applied magnetic field of the oxygen chemisorption. X-ray diffraction analysis of magnetized wear particles reveals the existence of ferromagnetic Fe 3O 4 oxide. This result shows that the magnetized contact enhances the ferromagnetic oxide Fe 3O 4 growth to the detriment of the non-ferromagnetic oxides Fe 2O 3 and FeO, following the electronic spin conservation theory. The magnetotribological behaviour phenomenon occurs especially in ferromagnetic/ferromagnetic sliding couples as it was shown by different experimental studies on different couples. The contact asperities of rotated disc in magnetic field are continuously submitted to the high magnetic flux variation from zero to B and from B to zero, which leads to electrical field creation E. Then, tribochemical activation can be explained by the Cabrera's and Mott's model related to the induced electrical field E. This study will present the tribological behaviour in ambient air and in vacuum, the experimental results of the nucleation and the growth of oxide layer in magnetized contact. A model of magnetotribological behaviour of ferromagnetic contact will be presented.