This project was initiated by the Gas Turbine Laboratory (GTL) of the Institute of Aerospace Research (IAR) of the National Research Council (NRC), Ottawa, Ontario and led to this collaborative project with CANMET Materials Technology Laboratory [CANMET-MTL (company A)]. The goal of this study was to develop a lead-free replace- ment bearing material to address environmental concerns and market demands resulting from expected future regu- lations that will prohibit the use of lead. It was decided to focus on alloy C93700 containing 9-11% Sn and 8-11% Pb which is usually used for bearings for high speed and heavy pressure. This alloy has typical mechanical properties of 241 MPa UTS, 124 MPa YS, 20% elongation and a compressive strength of 325 MPa. The project team decided to replace lead with bismuth in the following combinations:
• Cu – 5% Bi – 10% Sn, • Cu – 10% Bi – 10% Sn, and • Cu – 10% Pb – 10% Sn
(alloy C93700 base alloy for comparison).
Experimental Procedure and Specimen Preparation
All alloys were prepared in a clay-graphite crucible using a 100 kW, 3000 Hz push-up type induction furnace. Since there was no information in the literature on how these al- loys should be prepared, the procedure for preparing leaded alloys was followed. Pure electrolytic tough pitch (ETP) copper was melted under a graphite cover to minimize hy- drogen pick-up at 1100ºC, once the copper was liquid, bis- muth and tin were added. The temperature of the molten metal was raised to 1150ºC, then phosphorus was added (in the form of Cu-15% P) to de-oxidise the melt. The crucible was then lifted from the furnace, and the molds were poured.
For each composition, two melts were required due to the large amount of material needed. In each melt, five web bar sand molds were poured. Each mold yields two tensile speci- mens for a total of 10 per melt, thus 20 tensile bars were tested per composition. The full web casting is shown in Fig.
Table 1. Chemical Composition of the Alloys Tested
Figure 4. General view of the Falex tester. International Journal of Metalcasting/Winter 10
Figure 5. Close-up view of the test enclosure. 21
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