Optimised additive-surface material combinations for reduced friction & wear in internal combustion engines

There has been a general increase in the level of CO₂, NO_x and particulate emissions through the consumption of hydrocarbon fuels over the last 2-3 decades. These emissions have a detrimental effect on the environment and, as such, are undesirable. In an attempt to reduce emissions and to increase fuel efficiency of internal combustion engines there have been developments in two key areas: lubricant technology and materials technology. Improvements in lubricant formulation and/or improvements in the material technology performance of internal combustion engine components can potentially lead to an overall reduction in friction and wear. Because of the increased use of new materials and surface engineering in engines it is necessary to understand their lubrication requirements, which are anticipated to be different to those of conventional Fe-based materials. The work presented in this paper addresses aspects of lubrication of a traditional Cr-bearing steel and Al-Si alloy-based components. In particular, the interaction of surfaces with lubricant additives is investigated. Tribological tests have been performed and are supported by post-test examination using X-ray Photoelectron Spectroscopy (XPS), and Environmental Scanning Electron Microscope (ESEM) with Energy Dispersive X-ray analysis (EDX). Preliminary results show that fully formulated lubricant oils are effective in the reduction of wear and friction for ferrous-based systems but not for aluminium systems. Initial XPS and EDX data suggests that a relatively thick anti-wear film is formed on ferrous materials but is thin (and therefore unstable) for steel on aluminium systems. In completely non-ferrous systems the wear film is absent. In this paper the fundamental aspects of the film formation as well as the practical aspects of the results will be discussed.