The development of copper-free brake pads poses a significant challenge because copper plays a critical role in tribofilm formation and friction stability. This study proposes a novel approach using a recycled flake iron oxide material, characterized by high thermal stability and a unique plate-like morphology, as a sustainable alternative. The material acts as a friction modifier, promoting the formation of stable tribofilms and serving either as a copper substitute or a functional additive. Its iron-oxide composition ensures strong compatibility with the counterface tribofilm, enhancing adhesive friction, while its role as a primary plateau contributes to friction stability and reduced wear.
Three application scenarios were investigated: (i) copper substitution in Low-Steel (LS) and Non-Asbestos Organic (NAO) formulations, (ii) partial replacement of steel fibers in copper-free LS formulations, and (iii) synergistic use with iron sulfide in copper-free NAO formulations. Tribological performance was evaluated using a tribometer, and worn surfaces were analyzed by SEM and EDS to characterize tribofilm formation.
Results demonstrate that the proposed material provides friction stability and wear resistance comparable to copper in both LS and NAO formulations. Partial substitution of steel fibers improved wear resistance by up to 75%, while synergistic addition with iron sulfide further enhanced friction and wear performance in copper-free NAO pads.
These findings highlight the potential of this recycled material as a sustainable and effective alternative for copper-free brake pads, offering both environmental benefits and high tribological performance while reducing reliance on critical raw materials.