Douglas T. Jayne

Effect of lubricant additives on the tribological behavior of aluminum alloy against steel

Abstract This study aims to understand the impact of various lubricant additives on the friction- and wear behavior of aluminum alloys against steel. Employing the aluminum alloy Al 6061 and the steel AISI E 52100 as representatives, we studied the effects of the main additives typically found in fully formulated lubricants individually by formulating model lubricants consisting of base oil and just one additive at a time. The additives we studied include sulfurized olefin, complex alkyl phosphate amine, alkyl phosphite, overbased calcium sulphonate, zinc dithiophosphate (ZDP), and calcium sulfonate detergents. For each model lubricant, as well as for the base oil and the fully formulated oil, we performed ball-on-disc experiments with aluminum alloy balls on steel discs. We obtained the friction coefficient, determined the wear volume of the aluminum alloy, and analyzed the composition of the wear surface. We found that all additives except calcium sulfonate detergents promote the formation of aluminum oxide. Among all individually tested additives, zinc dithiophosphate provides the best wear resistance, while sulfurized olefin provides the lowest friction. The lowest friction combined with the second lowest wear rate was actually observed for a fully formulated oil (containing an optimized mixture of several additives).

Microcharacterization of Tribo Layers on Al–Steel

In order to improve the efficiency of internal combustion engines, profound understanding of the tribological problems in the piston ring assembly is crucial. Relentless efforts have been made by the tribologists over the past one decade in understanding the tribological interaction in steel on steel counter-face materials in dry and lubrication conditions. These efforts were mostly limited in characterizing tribolayers through surface characterization techniques [1]. Quite a few have reported about the microsturctural aspects of tribolayer and sub-surface deformed regions in the tribocontacts [2]. In this research an effort has been made to understand the microstructural and chemical aspects of tribolayer and subsurface deformed regions formed during Pinon-disc (ball-on-disc) sliding wear test. The experiments were conducted on 6061 Aluminium (ball)-E52100 Steel (disc) tribopairs in dry and in the presence of novel lubricants such as Basil oil and Fully formulated oil. Microstructural changes in the tribopairs were characterized by conventional, analytical, and high-resolution TEM (transmission electron microscopy). TEM cross section specimens were prepared using a FIB (focused ion beam). The specimens were studied with a Zeiss Libra 200EF, a 200 kV instrument equipped with an in-column imaging energy filter of the Omega type. STEM images taken from the Al ball revealed the presence of continuous deformed sublayer in all testing conditions Fig (1). The depth of deformed layer in dry condirtion is much larger than the lubricated conditions. Also STEM studies showed discontinuous tribolayer formed on Al ball only in fully formulated lubricant condition Fig (1). Further ESI (electron spectroscopic imaging) and EELS (electron energy-loss spectrometry) results showed the presence of Ca and oxygen in tribo-layer region (Figure3 and 4). This results shows that Al has a tendency to react with lubricant and form a stable tribo-layer and this confirms that fully formulated lubricant could be considered as a potential wear modifier for this tribopair.