Tribochemical reactions on sliding surface of the sintered metallic brake linings against SiC ceramic brake disk

The research presented in this paper is focused on formation, structure and chemical composition of friction layer on sintered metal–matrix brake linings sliding surface at early stage of braking against SiC ceramic. The character of the friction layer formed at sliding temperatures 200, 300 and 400 °C was investigated using scanning electron spectroscopy (SEM), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). In this starting stage of braking we confirmed the two-layer oxide structure of the friction layer composed from CuO on the top and Fe2O3 below. There is practically no change between structure, thickness and composition of the friction layer formed on sliding surface of the sample with only metallic matrix and the sample with the addition of graphite.

► The present investigation “Tribochemical reactions on sliding surface of the sintered metallic brake linings against SiC ceramic brake disk” involves a comprehensive study of formation, structure and chemical composition of friction layer on lining′s sliding surface at early stage of braking, using the AES, XPS and SEM analyses of the samples.
► The observations are discussed and correlated to observed tribochemical reactions on pad sliding surface.
► An extensive heat generation and high mechanical energy input during braking using the sintered metallic brake linings on SiC ceramic brake disk modify the surface of the brake lining.
► Due to plastic deformation, resulting in mixing of the metallic phases and the consequent enhanced oxidation, a friction layer is formed, which is composed of Fe- and Cu oxides, with the iron oxides mostly covered by oxidized copper.
► Tribochemical reaction together with the plastic deformation of metallic matrix is the reason for the formation and growth of friction layer on sliding surface of the lining.
► The smooth, two-layer structured oxide layer, consisting of CuO and Fe2O3, has an important influence on excellent friction properties of sintered metallic linings sliding against hard, heat and oxidation resistance SiC ceramic surface.