The influence of alumina whiskers content on friction and wear properties of copper-based friction materials

【Objective】 This study aims to systematically investigate the effect of alumina whisker content on the friction and wear properties of copper-based friction materials, clarify the evolution law of hardness, density, friction coefficient and wear rate with whisker addition, and reveal the corresponding wear mechanism transformation, so as to provide experimental support and theoretical reference for optimizing the composition and performance of copper-based powder metallurgy friction materials.
【Method】 Copper-based friction materials reinforced with 0、0.25、0.50, 0.75 wt% alumina whiskers were prepared by powder metallurgy including cold pressing and vacuum hot‑press sintering. The hardness and density were measured by Brinell hardness tester and Archimedes drainage method. The friction and wear tests were carried out on an MM3000 tester under braking speeds of 150-350 km/h to obtain friction coefficient and wear mass loss. The microstructure and worn surface morphology were observed by scanning electron microscopy (SEM) to analyze the dispersion state of whiskers and wear characteristics.
【Result】 The hardness first increases and then decreases with the rise of alumina whisker content, reaching the maximum at 0.25 wt%, while the density decreases linearly. At 0.25 wt% alumina whiskers, the friction coefficient increases by about 3% and the wear mass loss decreases by about 5% compared with the unreinforced sample. As the whisker content further increases, both friction coefficient and hardness decline, whereas wear loss increases obviously. SEM observations show that appropriate alumina whiskers disperse uniformly and reduce spalling pits and cracks. With increasing content, whisker agglomeration occurres, causing interface defects and pores. The wear mechanism gradually transforms from delamination wear to oxidative wear, and further evolves into abrasive wear and finally adhesive wear when the content exceeds 0.50 wt%.
【Conclusion】 An appropriate addition of 0.25 wt% alumina whiskers significantly improves the hardness, friction coefficient and wear resistance of copper‑based friction materials by pore filling and load transfer strengthening. Excessive alumina whiskers lead to serious agglomeration, poor interface bonding and increased defects, which degrade mechanical and tribological properties. The wear mechanism is highly dependent on alumina whisker content. This study confirms that moderate alumina whisker reinforcement is an effective strategy to enhance the comprehensive performance of copper‑based friction materials for braking applications.