Tribological behavior of self-lubricating aluminium/SiC/graphite hybrid composites synthesized by the semi-solid powder-densification method

Abstract

The tribological behavior of self-lubricated aluminium/SiC/graphite hybrid composites with various amount of graphite addition synthesized by the semi-solid powder densification (SSPD) method has been studied. As the amount of graphite increases, the hardness and CTE of the composites decreases. Fracture toughness decreases monotonically as the graphite content increases. It was found that the seizure phenomenon which occurred with a monolithic aluminium alloy did not occur with the hybrid composites. The amount of graphite released on the wear surface increases as the graphite content increases, which reduces the friction coefficient. Graphite released from the composites bonded onto the wear surfaces of the counter faces. However, the amount bonded is small, and X-ray mappings showed no significant difference in the amounts bonded for different graphite additions. Wear becomes more stable, and wear debris particles become smaller as the graphite content increases, which is reflected by the lower electric contact resistance. More fracturing is shown on the wear surface of the composite with high graphite addition as a consequence of poor fracture toughness by comparison with composites with low graphite. There seems to be less abrasive wear on the composites than on the counter faces. The wear rate of the composite increases as the amount of graphite content increases up to 5% then falls to a lower value for an 8% addition. However, the wear rate of the counter face increases as the amount of graphite in the composites increases up to 8%.