Tribological and wear behavior of phenolic matrix brake pads reinforced with hybrid fibers and graded sulfide solid lubricant additives

Purpose This study aims to investigate the synergistic influence of fiber architecture and sulfide-based solid lubricant chemistry on the tribological and mechanical performance of phenolic resin-based brake friction composites. The objective is to optimize wear resistance, friction stability, and thermal durability for advanced automotive braking systems. Design/methodology/approach Six brake pad formulations were developed by systematically varying steel fiber and potassium titanate (KT) fiber ratios and incorporating low-temperature (CuS, FeS2, Bi2S3) and high-temperature (MoS2, SnS, SnS2, CaF2) sulfide-based solid lubricants. Pads were fabricated via compound molding followed by controlled thermal post-curing. Tribological evaluation was conducted under SAE J661-specified fade and recovery cycles using a Chase tribometer. Characterization included surface roughness (Ra = 1.71–3.74 µm), shear strength (>42 kg/cm²), hardness, wear loss, and scanning electron microscopy (SEM)-energy-dispersive X-ray spectroscopy wear mechanism analysis. Findings BP4 (10 Wt.% KT fiber) exhibited the lowest wear loss (∼3%), while BP3 (5 Wt.% KT + 5 Wt.% steel fiber) achieved the highest performance friction coefficient (µPerformance = 0.60). BP2 demonstrated the highest recovery rate (105%), highlighting the role of low-temperature sulfides in restoring frictional capacity after thermal degradation. SEM analysis revealed distinct variations in tribo-film stability, plateau morphology, and matrix degradation across formulations. Originality/value This work establishes a direct correlation between microstructural wear mechanisms and macroscale tribological responses in brake friction composites. It introduces a fiber–lubricant hybrid design framework that enables the development of eco-friendly, durable, and thermally stable braking materials, addressing both performance and sustainability in modern automotive applications. Peer review The peer review history for this article is available at: Link to the cited article.