Tribology of Sliding Contacts Within Plain Bearing Overlays Subject To Corrosion.

Abstract

The increasing global awareness and legislative restrictions has influenced the design within Internal Combustion (IC) engines. In addition to meeting environmental requirements the specified materials should be suitable to withstand extreme operating conditions such as high combustion pressures that attains the optimum fuel economy whilst reducing the exhaust emissions. The lead-free materials exhibit near analogous mechanical and tribological properties to the traditional lead-based materials. The plain bearings are subjected to many different laboratory-based performance tests for instance, ring-on-disc, pin-on-disc that screen candidate materials as cost effectively as possible prior to much more expensive full engine-based tests. However, it is still uncertain how these lead-free bearing materials behave in different lubrication regimes such as mixed and boundary lubrication regime. The corrosion resistance of these materials also need to be especially within used lubricant conditions. In advance of tribology experiments a static immersion test is employed to investigate the corrosion resistance of lead-free lining and overlay materials in both new oil and degraded oil environments. The surface topography and chemical composition of the tested materials are examined using a scanning electron microscope in-built with energy dispersive x-ray spectroscopy. A digital optical microscope was also used to understand tested surface damage mechanisms. Furthermore, X-ray photoelectron spectroscopy was used to understand the chemical composition at the surface of tested materials. With aid of these characterization techniques the corrosion mechanisms of the tested materials are investigated. A newly designed and developed test-rig module was used to investigate the tribological performance of hydrodynamic bearing shells. This test-rig simulates automotive engine representative conditions experienced plain bearings during operation. Wear rate of these materials were explored using this new test methodology. The materials considered are tin based lead-free overlay and lead based overlays considered as a reference.