AN ENERGY DISPERSIVE-X-RAY AND IMAGING X-RAY PHOTOELECTRON SPECTROSCOPICAL STUDY OF TRANSFER FILM CHEMISTRY AND ITS INFLUENCE ON FRICTION COEFFICIENT

The nature of the 'third-body layer' formed at the interface between the two elements of a friction couple in an automotive braking system has been the subject of much speculation. The development of the imaging x-ray photoelectron spectrometer is now allowing detailed studies of this layer. This investigation has examined the influence of temperature on the composition of transfer films (third-body layers) formed on grey cast iron after rubbing against asbestos-free friction materials in a friction assessment screening test (FAST). Evidence will be presented to show the strong dependence between transfer film composition and the coefficient of friction over a range of temperatures. The information obtained in this investigation may provide a partial solution to the problem of 'early morning sharpness' and also poor cold friction coefficient, the latter is often referred to in the industry as 'low cold mu'. These slight changes in friction coefficient are occasionally encountered by some drivers whose vehicles have a particular cast iron-friction material combination.