A combinatorial approach for automotive friction materials: Effects of ingredients on friction performance

Raw materials used in automotive friction formulations were classified using a combinatorial approach into two groups in accordance with their ability to improve the wear properties of the mixture by two-phase friction composites. Components of group one, which improved the wear resistance, include softer additives (graphite, MoS2, and Twaron), harder additives (Al2O3 and steel wool), and organic binder (benzoxazine). Softer additives have low friction coefficient (μ), low wear, and easily transferred debris to the surface of disc. Harder additives have intermediate wear, intermediate μ, and formed iron-containing surface layer transferred from cast iron disc to friction material pad. Benzoxazine has high wear and high μ and there is no transferred layer formed either on disc or pad in the case of benzoxazine used as pad. The wear of two-phase friction materials can be improved by adding Al2O3, graphite, MoS2, steel wool, and Twaron to benzoxazine and four wear improvement mechanisms were proposed: (1) lubrication mechanism (graphite and MoS2); (2) abrasive mechanism (Al2O3); (3) friction layer mechanism (steel wool); (4) reinforced mechanism (Twaron). Components of group two, which produced poor wear resistance, include BaSO4, BN, B2O3, brass chips, CaCO3, Ca(OH)2, cashew, copper chips, CuS, Cu2S, H3BO3, iron powder, MgO, oxidized PAN fiber, PMF (SiO2 + CaO), Sb2S3, Ultrafibe (CaSiO3), and ZrSiO4.