Improvement of Friction and Wear Characteristics for Advanced Al-Si Alloy Matrix Composites

点击翻译按钮获取中文摘要

Unlubricated pin-on-disk type wear tests of an Al-Si alloy impregnated graphite composite in contact with a bearing steel were conducted in dry and wet gas environments of argon, nitrogen, air and oxygen. The properties of an adhered film generated on the sliding surface of the bearing steel were investigated and then friction and wear characteristics of the composite were elucidated. The composite, having a humidity dependency, exhibits wear resistance and friction performance better than the matrices (Al-Si alloy and graphite) in wet gases, indicating that the improvement of tribological characteristics has been made by composing the matrices. The adhered film is generated on the sliding surface of the bearing steel just after the start of the tests and serves as an effective solid lubricating film, especially in wet gases. The mixture of Al-Si alloy wear particles in graphite powder promotes the formation of the films under press-slide fattening action. More compared films are gener … More ated with decreasing oxygen in the wet gas environment and contribute to the improvement of wear resistance of the composite. Pin lifting i.e. negative wear takes place in wet gases during the initial stage and subsequently lower wear occurs with increasing pin lifting height.In order to investigate the good mating materials in sliding contact with the Al-Si alloy impregnated graphite, pin-and-disk type wear tests were conducted and the material combination showing minimum friction and wear was obtained. The composite in contact with itself yields low friction and wear, indicating the best material combination. Ferrous metals such as mild steel, cast iron, bearing steel and commercial thrust bearing in contact with the composite exhibit low friction and middle levels of wear rate, showing better material combinations. The composite in contact with its matrices gives the middle levels of friction and wear, showing bad combinations. Titanium in contact with the composite brings about high friction and wear, resulting in an inadequate combination. Graphite, copper, brass and titanium in contact with the composite causes wear damage to themselves, leading to the most inadequate combinations for sliding surfaces.Unidirectional sliding wear tests of the Al-Si alloy impregnated graphite composite and it matrices (pin) in contact with the bearing steel (disk) were conducted using engine base oil to investigate the tribological characteristics under the lubrication methods of immersion feed or oil-drop feed only before the tests. In the case of the composite pin, as the amount of oil drop is increased, the friction coefficient and wear rate reach the values for the immersion test. The breakdown of oil film does not occur even with very small amount of oil-drop. For the Al-Si alloy pin, the sliding distance to the breakdown of an oil film tends to increase with the amount of oil drop. The wear scarcely occurs but the friction coefficient fluctuates greatly before the oil film breakdown and afterwards the friction and wear rapidity increase. In the case of the graphite pin, the friction coefficient and wear rate under oil-drop feed are lower than those under the immersion feed but the wear rate does not change irrespective of the amount of oil drop. These results suggest that the composite is one of the good sliding materials even under severe lubricating conditions compared with the matrices. Less