Role of Ag added together with Sn to Cu-Sn-Ag alloy bearing for heavy dutydiesel engine

A higher seizure resistant Cu-5Sn-1Ag alloy bearing was previously develope d for heavy duty diesel engines. This study, therefore, was conducted to cl arify the anti-seizure mechanism of the bearing by analyzing the sliding su rface, using EPMA, AES and XRD. Excess amounts of Sn and Ag supersaturated in the alloy were found to segregate the surface and form an enriched thin 5Sn-1Ag layer of 0.1 mu m in thickness during the sliding test at 160 degre es C. Just above the 5Sn-1Ag layer, surface contamination, mainly of carbon , and reaction products with engine oil were also found. They, however, wer e considered not to contribute the anti-seizure property of the alloy. On t he other hand, a sputtered 5Sn-1Ag him of 0.1 mu m on Cu-5Sn alloy was foun d to show low frictional coefficient of 0.15-0.20 and good anti-seizure per formance under dry condition at higher temperature of 180 degrees C, since sliding surface layer was consisted of very thin soft 5Sn-1Ag (16HV0.2 at R .T.) layer on the harder Cu-5Sn alloy (120HV0.2). It was, therefore, conclu ded that anti-seizure performance of Cu-5Sn-1Ag alloy bearing was caused by the formation of enriched thin and soft 5Sn-1Ag layer on the harder bearin g alloy (125HV0.2) surface.