Effect of Type and Relative Amount of Solid Lubricants and Abrasives on the Tribological Properties of Brake Friction Materials

Abstract

The effects of graphite and hexagonal boron nitride (h-BN) as solid lubricants and aluminum oxide (Al₂O₃) and boron carbide (B₄C) as abrasives on brake friction performance were evaluated. Friction material samples were produced based on an experimental formulation, and the lubricants and abrasives were added to the raw materials mixture at a total volume fraction of 10.5%. The composites had a fixed composition of 25% resin, 22% fibers, and 42.5% fillers. The friction tests were performed on a Chase friction material testing machine according to the brake lining quality test procedure as per SAE J661. The friction materials containing h-BN–B₄C and h-BN–Al₂O₃ showed better friction stability and improved fade resistance compared to those containing graphite–Al₂O₃ and graphite–B₄C. The results also indicated that the friction coefficient and specific wear rate of the composites increased with decreasing solid lubricant and increasing abrasive content. The worn surfaces and wear debris of the composites were examined using a scanning electron microscope (SEM) coupled with an energy-dispersive X-ray spectrometer (EDS). The atomic fraction of Fe on the worn surfaces and wear debris of the composites increased with decreasing solid lubricant and increasing abrasive content.

KEY WORDS:

• Brakes
• Friction
• Friction Modifiers
• Wear Particle Analysis
• Wear Mechanisms

ACKNOWLEDGEMENT

The authors gratefully acknowledge the financial support of this study by the Karadeniz Technical University Research Fund under Grant No. 2007.112.010.1.

Review led by David Burris