Determination of the Influence of Metal Sulphides on the Tribofilm and the Friction Behavior

Abstract

Metal sulphides are additives that are used in brake pad formulations because they help to stabilize the coefficient of friction, reduce wear and improve NVH. Previous rimsa studies have shown that the oxidation mechanism of metal sulphides is one of the key properties that explain their contribution to performance and wear. Depending on the metal sulphide, the oxidation mechanism is different and so is the tribochemistry. Hence, the transfer layer formed will strongly depend on the metal sulphide used. This work is focused on establishing a connection among the metal sulphide oxidation, the transfer layer formed and the performance. The friction behavior was determined through two tests, J2522 and J2707, using a NAO formula where only the metal sulphide was varied. While the transfer layer characterization was carried out through pad SEM-EDS cross-section analysis, after each test. The differences in thermal profile of J2522 and J2707 illustrate the correlation between performance and wear and different oxidation mechanisms depending on the metal sulphide used. SEM characterization of pad surface also shows that the transfer layer morphology varies depending on the metal sulphide used in the formulation. Hence, the results of this research indicate that the morphology of the transfer layer and the friction behaviour strongly depend on the oxidation mechanism of the metal sulphide.