The investigation of the effect of using graphite, molybdenum disulfide and boron nitride as solid lubricants on brake pad friction performance

As the most important component of the braking system used in automobiles, brake pads are composed of composite materials, and the added materials to their composition provide various contributions. It is not enough for the materials in the brake pads to contribute only to performance; they are also expected to have minimal impact on the environment or even achieve a zero-carbon footprint when used. The banning of harmful materials added to the brake pad composition, such as asbestos, by countries and global organizations, encourages manufacturers to turn towards more sustainable, environmentally friendly, efficient, and performance-oriented alternative materials. Concerns are also raised about graphite, a carbon-based material used as a solid lubricant in brake pads, and its potential environmental impact. In this study, nine different samples were produced by using Graphite, Molybdenum Disulfide, and Boron Nitride as solid lubricants in the brake pad composition, and one reference sample was created by adding a filler material instead of a solid lubricant. The solid lubricants were added to the samples in mass ratios of 3%, 6%, and 9% to evaluate their effects on performance. The materials were manufactured using powder metallurgy method, where specific formulations were combined, and preforming and pressing processes were applied. To simulate the braking event, a gray cast iron brake disc was used in the friction test setup. Friction coefficient data were obtained from the samples by providing specific parameters (pressure, temperature, time, and disc rotational speed) in the test setup. Physical properties of the brake pad samples, such as specific wear rate, hardness, and density, were determined. After the friction test, the worn surfaces of the samples were examined using a Scanning Electron Microscope (SEM). In the conducted study, the samples with added Molybdenum Disulfide and Boron Nitride as solid lubricants exhibited friction performance close to that of Graphite. The sample with 3% mass ratio of Graphite showed the highest average friction coefficient. Subsequently, the reference sample and the sample with 9% mass ratio of Molybdenum Disulfide followed with the next best performances