Tribological properties of neat 150 SN mineral base oil and the oils doped with different contents of tricresyl phosphate(TCP) under magnetic field or non-magnetic field were evaluated on a four-ball tribotester, on which an external magnetic field was applied. Furthermore, the morphology and the tribochemical characteristics of the worn surfaces were examined with a scanning electron microscope(SEM) and an X-ray photoelectron spectrograph(XPS). The tribological test results showed that the magnetic field improved anti-wear properties but impaired the friction-reducing properties of neat base oil and the TCP-doped oils. The worn surfaces tested in magnetic field were characterized by a slighter wear than those tested in normal condition, especially for the surfaces lubricated with the TCP-doped oils. Furthermore, the results of XPS analysis indicated that tribochemical films on the surfaces tested with TCP-doped oils were mainly composed of ferriccontaining compounds such as Fe_2O_3, Fe_3O_4 and FePO_4. Under the influence of a magnetic field, the atomic concentrations of oxygen and phosphorous in the frictional sub-surfaces were higher than those without magnetic impact. Thus it can be inferred that the improved anti-wear properties and impaired friction-reducing capabilities of lubricating oils with TCP under a magnetic field were related to the diffusion of phosphorus and oxygen into the substrate induced by magnetism.
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