Tribological investigation of titanium-based materials for brakes

Titanium alloys and their composites have the potential to reduce truck disc brake component weight and improve their resistance to road-salt corrosion. A titanium alloy rotor can weigh approximately 37% less than a conventional cast iron rotor with the same dimensions, while offering good high-temperature strength and much better resistance to corrosion from road-deicing salts. Friction coefficients and temperature rise data were obtained for two commercial Ti alloys, four experimental Ti-based hard particle composites, and a thermally spray-coated Ti alloy. Several commercially produced lining materials were used as counterfaces. Using a flat block pressed against a rotating disc, tests consisted of repetitive on-and-off drags at sliding speeds from 2 to 15 m/s, using nominal contact pressures of 1.0 or 2.0 MPa. Friction coefficients were affected by the choice of counterface (semi-metallic versus highly metallic lining composition) and by the friction-induced wear track temperature, which at times exceeded 800 °C. The wear rates of the Ti metal matrix composites exceeded that of the reference cast iron, but were significantly better that that of two Ti alloys. A thermal conversion parameter was used to compare the efficiency by which various material combinations convert frictional work into temperature rise. Several of the tested material combinations provided friction coefficients within the typical range for brake materials (0.35-0.55) and some showed excellent resistance to fade, a phenomenon in which braking effectiveness decreases as temperature rises. The thermally spray-coated Ti disc exhibited the least wear and merits further attention as a lightweight, corrosion-resistant brake rotor material.