Tribological Characteristics of the Aluminum-Silicon Alloy Impregnated Graphite Composite Under Insufficiently Lubricated Reciprocating Sliding Conditions

Tribological characteristics of Al-Si alloy impregnated graphite composite (ALGR-MMC) in contact with bearing steel were investigated under insufficiently lubricated reciprocating sliding conditions. Ball (JIS SUJ2 bearing steel) on disk (ALGR-MMC) type wear tests were conducted under unlubricated conditions, i.e., in air with high (70%) and low (≤ 1%) relative humidity (RH), under drop-feed lubrication, i.e., oil-drops were deposed on the disk surface before commencing the tests, and under immersion lubrication, i.e., the ball-on-disk contact was submerged in a oil (SAE30) bath. Reciprocating sliding movement was maintained, under a contact load of 40 N at a frequency of 3.3 Hz and amplitude of 3.5 mm, for 100,000 cycles. Tribological properties were continuously monitored. Variation of the kinetic friction coefficient (KFC) versus the number of reciprocating cycles (NRC) was obtained for various amounts of oil (lubrication conditions) and two values of the air RH. For drop-feed lubrication the KFC has at beginning the same value as that under immersed lubrication, but if breakdown of the oil film has occurred after a certain NRC, it increases towards the value corresponding to unlubricated conditions. Connected to the oil film breakdown, there is a certain transition range, expressible both in terms of the oil amount and NRC. Minimum quantity of oil to avoid the film breakdown was found. Due to its self-lubricating properties, ALGR-MMC was able to endure adverse lubrication conditions such as insufficiently lubricated reciprocating sliding.