Effect of sol-gel boehmite infiltration on tribological and mechanical behavior of brake lining materials

This paper studies the effect of vacuum infiltration boehmite gel on tribological and mechanical behavior of brake lining materials. Experimental results indicate that open porosity decreased and bulk density increased with the numbers of infiltration cycle. The hardness of the infiltrated specimen increases with the infiltration cycle and sample depth but seem less sensitive to the number of infiltration cycle at higher infiltration cycle. The friction coefficient and weight loss of the infiltrated specimen are more stable and lower than that of the green specimen. As the number of infiltration cycle increase, average friction coefficients at different sample depth are more similar. Mass losses of specimens at different sample depth were directly related to their average friction coefficient values. The higher the average friction coefficient, the larger were the mass loss. According to the cross-section SEM observations, the pores decreased as the infiltration cycle progressed. X-ray mapping analyses reveal that the efficiency of infiltration decreases with the deeper sample depth. Morphological observations also show that the number of open pores at surface site for these materials decreases and they exhibit a denser and smoother morphology as the number of infiltration cycle increases. Furthermore, as the number of infiltration cycle increases, the friction behavior at the surface site of infiltrated specimens becomes more sensitive to the presentation of γ-Al₂O₃ particles. The γ-Al₂O₃ particle with higher density and hardness on the sliding surface was more easily to break loose during the wear test and cause the larger mass loss.