Hybrid alumina-graphene oxide reinforced phenolic friction material

Friction materials play an important role in the safety of automobiles. In this work, we study the effects of graphene oxide and alumina with different mass ratios of micrometer-sized alumina to nanometer-sized alumina on tribological behavior of phenolic resin-based friction materials by friction tests. The experimental results reveal that the structural stability of the friction materials is dependent on the mass ratio of micro-sized alumina to nanometer-sized alumina. The friction coefficient varies in a range of 0.60–0.63 for the materials with high fractions of micro-sized alumina over the temperature of 100–350 °C and in a range of 0.4–0.5 (i.e., thermal recession) for those with high fractions of nano-sized alumina at 350 °C. The wear rate of the material without graphene oxide is within 0.13–0.36 × 10⁻⁷ cm³/(N·m) at 100 °C and within 0.5–0.7 × 10⁻⁷ cm³/(N·m) at 350 °C. A compromise needs to be taken between the friction coefficient and the wear rate. For wear at low temperatures, increasing the fraction of nano-sized alumina in the total alumina powders reduces the wear rate of the friction materials. The wear at temperatures higher than or equal to 200 ºC can cause the formation of friction film, which can alleviate wear and improve the friction performance. The tribological performance of the friction materials with graphene oxide deteriorates with increasing the fraction of nano-sized alumina. The optimal performance of the friction materials is achieved with the mass ratio of micrometer-sized alumina to nanometer-sized alumina being 13:5. 4-layer graphene oxide is preferable over 8-layer graphene oxide for the enhancement of the wear resistance of the friction materials.