Experimental Study of Bismuth Alloy Overlays for Automotive Engine Bearing 2021-01-0685

Bismuth has been applied successfully as sliding bearing overlay material in internal combustion engines, where a good combination of sliding properties, mechanical strength and corrosion resistance can be attained. However, environmental pressures driving towards lower emission and higher fuel efficiency are set to raise firing loads above the capability of many state-of-the-art bismuth materials in the market. At the same time, in order to meet increasingly stringent environmental regulations modern engines are adapting to more efficient and economic designs which put bearing materials under ever growing pressure to provide enhanced oxidation resistance and robustness to cope with elevated engine operating temperature and tighter oil clearance.

In this study bismuth overlays alloyed with various elements, such as tin, copper, indium and antimony are proposed to enhance load-carrying property and improve oxidation resistance at higher engine operating temperature, whilst still maintain good robustness for high performance engine applications. To understand the newly developed bismuth alloy overlay materials various investigations including microstructure and composition assessments, basic property evaluation, and fatigue and oxidation tests were carried out to evaluate their suitability under harsh engine operation conditions. The results have proved that bismuth-copper and bismuth-antimony alloy overlays provide much improved fatigue strength and oxidation resistance respectively compared to current market material and other candidate alloy overlays, which offers hope and promising future development route. Furthermore, the excellent fatigue and oxidation performances were achieved without compromising the key properties required for robustness.