The Progression of Engine Bearing Overlays 2002-01-1316
Due to their adaptability and embeddability soft lead-based sliding layers with additions of tin, copper or indium were common and sufficient for many years to overcome problems like seizure, corrosion and wear which occurred with non-coated copper based bearing metals in modern engines.
The last fifteen years of diesel engine evolution put new innovation pressure on the development of bearing materials. PVD-processes, especially sputtering of AlSn layers, were utilized to generate highly wear resistant overlays with increased load carrying capacity allowing for small sized engines with high cylinder pressures resulting in higher fuel efficiency and reduced emissions.
While the advent of PVD-coated bearings created new possibilities in engine design, it also caused a large performance and cost gap between PVD-coated bearings and electroplated bearings. For this reason, efforts were made to develop improved electroplated layers to cover the low end of the high performance market segment.
The performance of lead based layers was improved by utilizing new MSA electrolytes allowing for increased Cu and Sn contents in lead or by codeposition of hard particles. Currently, the use of lead as an alloy component is questioned under environmental and health aspects. Therefore, a new SnCu6-SnNi-Ni overlay system was developed which not only overcomes the lead problem but moreover represents a significant improvement in the performance of electroplated bearings.
