Lead-free frictional materials are important components in safety and power transmission parts of automobiles. In order to avoid using lead-containing friction modifiers, non-toxic ceramic particles are considered to be used as reinforcements. In this research work, copper-based friction materials have been developed by using press and sinter method. Pre-alloyed bronze (Cu-10Sn) powder was admixed with iron (Fe), graphite (C) and varied amounts of silicon carbide (SiC) powders. The admixed powders were compacted into disc-shape samples, which were then sintered at different temperatures in the range of 800-950 °C. It was found that sintered density and hardness of the sintered copper-based friction materials reduced with increasing SiC content. Microstructures of the sintered materials showed inhomogeneity due to uneven distribution of coarse Fe and SiC particles. The coarse SiC particles also prohibited bonding between metal powder particles. However, the sintered materials showed high room-temperature friction coefficients, which were in the range of 0.50-0.90, particularly the materials containing 4 wt. % of SiC particles.
Experimental sintered Fe-Mo-Mn-Si-C composites were prepared from 3 different pre-alloyed Fe-Mo-Mn powders, namely Fe-0.50Mo-0.15Mn, Fe-0.85Mo-0.15Mn and Fe-1.50Mo-0.15Mn, mixed with fixed 4 wt.% silicon carbide powder. Sintered Fe-SiC composite was also prepared, as a reference material, from pure Fe powder mixed with fixed 4 wt.% silicon carbide powder. All specimens were processed by using the ‘press and sinter’ method. Sintering was performed in a vacuum furnace at 1250ºC for 45 minutes and slow cooling in the furnace. The microstructures of most sintered alloys showed a common feature consisting of a black particle enveloped with ferrite and pearlite. Sintered composites produced from high-molybdenum powders showed different matrices, in which some pearlite regions were replaced by BF/M- A structures. The Tensile and hardness test showed that the sintered alloys exhibited an increase of tensile strength, yield strength, and hardness with increasing molybdenum content. The pearlite + BF/M-A fractions of sintered composites played important roles in material strengthening. In the sintered composites produced from high-molybdenum powders, the carbide-free BF/M-A structure showed a promising strengthening effect.
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