INVESTIGATION ON FRICTION AND WEAR CHARACTERISTICS OF ADVANCED ALUMINUM ALLOY MATRIX COMPOSITE UNDER VARIOUS LUBRICATING CONDITIONS

研究了铝硅合金浸渍石墨复合材料(ALGR-MMC)及其基体(石墨和铝硅合金)在润滑滑动条件下与轴承钢接触时的摩擦磨损特性。采用SAE30型内燃机油，在干滑动、滑动前滴加润滑(0.005~1.00 cm^3)和浸没润滑(90 cm^3)条件下，进行销盘式摩擦磨损试验。在整个试验过程中，持续监测摩擦和磨损的变化。对于Al-Si合金，油膜击穿发生在油滴0.03 cm^3以下。油膜破裂后，摩擦系数(F)和磨损率(W)急剧上升，对端面造成损坏。石墨的f和w随油量的增加而减小，但均高于Al-Si合金和AlGR-MMC在浸泡润滑下的f和w。结果表明，随着加油量的增加，AlGR-MMC的摩擦磨损逐渐减小，但没有发生油…的分解。更多的胶片和柜台表面的损坏。摩擦系数f和w远低于基体的f和w，说明ALGR-MMC是一种优良的滑动材料，即使在润滑不足的条件下也可以使用。研究了空气相对湿度对ALGR-MMC摩擦磨损性能的影响。磨损曲线可分为三种类型。在类型1曲线中，销抬起出现在测试开始之后，然后是稳态磨损。在类型2曲线中，在类型1过程之后，再次出现销钉提升，随后是油膜破裂。在类型3的曲线中，在试验的早期阶段，销被提起后不会发生磨损。RH=50%~80%时，1型的出现频率较高。第二类曲线仅在相对湿度[小于或等于]5%时出现，表明油膜破裂发生在非常低的湿度下。类型3曲线出现在RH=10%到50%的低湿度下。为了研究接触载荷对ALGR-MMC在微动条件下摩擦磨损特性的影响，对复合材料(平板)与轴承钢(球)在不同载荷下的平球微动磨损性能进行了试验研究。从实验结果可以看出，微动过程分为两种。在A型中，动摩擦系数(F_K)在初始阶段较高，在稳态阶段f_k急剧下降至恒定值。在B型中，f_k在整个测试过程中是恒定的。在75~100N的较高载荷范围内，相对滑移幅度在50μm的范围内不能保持恒定，而在5~60N的较低载荷范围内保持不变。在整个试验过程中，B类材料的平均磨损率低于A类材料。两种材料的平均磨损率随着接触载荷从5增加到100N而增加。这两种微动过程的发生是由于每次试验时铝硅合金和石墨的接触面积不同所致。较少

Friction and wear characteristics of Al-Si alloy impregnated graphite composite (ALGR-MMC) and its matrices (graphite and Al-Si alloy) in contact with bearing steel were investigated under lubricated sliding conditions. Pin-on-disk type friction and wear tests were conducted under dry sliding, drop-feed lubrication (0.005 to 1.00cm^3) before sliding and immersion lubrication (90cm^3) by using SAE 30 engine oil. Changes in friction and wear were monitored continuously throughout the tests. For the Al-Si alloy, a breakdown of oil film occurs below 0.03cm^3 of oil drop. After the oil film has broken down, the friction coefficient (f) and wear rate (w) rise drastically, causing damage to the counter surface. The f and w for the graphite decrease with increasing amount of oil but the values are higher than those of the Al-Si alloy and ALGR-MMC under immersion lubrication. A gradual decrease in friction and wear for ALGR-MMC with increasing amount of oil is found without the breakdown of oil … More film and the damage to the counter surface. The f and w are much lower than those for the matrices, indicating that ALGR-MMC is an excellent sliding material that can be used even under insufficiently lubricated sliding conditions. The f and w of ALGR-MMC go up with increasing X-ray intensity of Al and C of adhered films on the counter surface.The effects of relative humidity (RH) in air on the wear of ALGR-MMC were investigated under drop-feed lubrication. The wear curves were classified into three types. In Type 1 curves, the pin lifting appears just after the start of tests followed by steady state wear. In Type 2 curves, after the process of Type 1 the pin lifting appears again, followed by the breakdown of oil film. In Type 3 curves, wear dose not occur after the pin lifting in the early stage of the tests. The occurrence frequency of Type 1 is high at RH=50 to 80%. The Type 2 curves appear only at RH【less than or equal】5%, indicating that the oil film breakdown takes place at very low humidity. The Type 3 curves appear at low humidity of RH=10 to 50%. The steady-state wear rate is higher at high humidity and shows a maximum at RH=70% in the Type 1 curves.In order to investigate the effects of contact load on the friction and wear characteristics of an ALGR-MMC under fretting conditions, flat-against-ball type fretting wear tests for the composite (flat) in contact with bearing steel (ball) were conducted in moist air at various loads. From the results two types of fretting process were found to occur. In Type A, the coefficient of kinetic friction (f_k) was high in the initial stage followed by a drastic decrease in f_k to a constant value in the steady-state stage. In Type B, f_k was constant throughout the tests. The amplitude of relative slip could not be kept constant at a desired value of 50μm in the higher load range from 75 to 100N but kept in the lower load range from 5 to 60N. The mean wear rates throughout the tests in Type B were lower those that in Type A. The mean wear rate for both the types was increased with contact load from 5 to 100N. The occurrence of the two types of fretting process is due to a difference in the contact area portion of Al-Si alloy and graphite for each test. Less