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

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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