Figure 19. Specimen scar depth vs. alloy type. Conclusions
Mechanical and tribological properties of bismuthized and leaded alloys have been analyzed and are discussed in this study. The main conclusions drawn from this project are:
1. The mechanical properties of the alloy containing 5% Bi were superior to those of the alloy contain- ing 10% Bi. This observation should be verified because of somewhat higher shrinkage porosity in the latter.
2. The structure of the bismuth-containing alloys is similar to that of the lead-containing alloy. Howev- er, the morphology of the lead is more favourable than that of the bismuth from a bearing characteris- tics point of view. A massive variation in grain size was observed in a given sample.
3. The lead-containing alloy has the highest fatigue limit.
4. The temperature in the rubbing area is similar for all the three materials.
5. The friction forces for the bismuth-containing alloys are slightly higher than those of the lead- containing bearing material. On the other hand, the friction force of the bismuth-containing alloys showed less fluctuation during the tests.
6. Based on the amount of material removed during the rub, the lead-free alloys seem to be softer than the leaded alloy.
7. Based on the microstructural characteristics and evaluation of mechanical properties and tribologi- cal behaviour, the lead-free alloy with 5% Bi ap- pears to be the alloy of choice for aerospace bear- ing applications.
8. Thermodynamic analysis may have to be per- formed to find a better substitute for Pb which would impart better bearing properties.
Figure 20. Removed material. Acknowledgements
The authors would like to thank the staff of CANMET- MTL’s the Experimental Casting Laboratory for their expert assistance in melting and casting, Bob Eagleson for mechan- ical testing, and Dr. Kumar Sadayappan for his input into technical discussions and project planning. Thanks are also extended to J.-P. Bédard, R. Payette and B. Liko and the staff at NRC for preparing the Falex machine and perform- ing the friction tests.
REFERENCES
1. “Cast Copper Alloy Sleeve Bearings,” Copper Devel- opment Association Inc., (1997).
2. Sahu S., “Friction and Wear Properties of Leaded and Bismuthized Bearing Bronzes,” Proceedings from Ma- terials Solutions ’97 on Wear of Engineering Materials, Indianapolis, Indiana (15-18 September 1997).
3. Whiting L.V., Sadayappan M., Sahoo M., “Bismuth and Selenium Impurities in Red Brasses (C83600, C84400, C89520)”, AFS Transactions, vol. 110, pp 563-578 (2003).
4. Plewes J.T., Loiacono D.N., “Free-Cutting Copper Al- loys Contain No Lead”, Advanced Materials & Process- es, vol. 140, no 4, pp 23-27 (1991).
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