Influence of Steel Surface Composition on ZDDP Tribofilm Growth Using Ion Implantation

This paper examines the influence of steel surface composition on antiwear tribofilm formation by ion-implanting typical steel alloying elements, Ni, Mo, Cr, V and W, into AISI 52100 bearing steel surfaces. Such implantation changes the chemical composition of the steel surface but has relatively little effect on its mechanical properties or topography. The behaviour of zinc dialkyldithiophosphate (ZDDP) antiwear additive was studied. The study employs a ball on disc tribometer with ability to monitor tribofilm development and a range of analytical tools including STEM-EDX, XPS and FIB-TEM to analyse the formed tribofilms. It was found that Ni implantation promotes ZDDP tribofilm formation while Mo and Cr implantation deters tribofilm growth. V and W implantation do not significantly change tribofilm formation. Results on the influence of ZDDP concentration on tribofilm formation rate with different implanted metals suggest that one important mechanism by which steel composition influences tribofilm formation may be by controlling the extent of ZDDP adsorption. This study shows the importance of steel surface composition on ZDDP response and also demonstrates a powerful way to study and potentially improve the tribological performance of machine components via a combination of lubricant formulation and surface modification.

Lubricant and Lubricant Additives

Lubricants have been used by humans for thousands of years in their simple machines such as wheel-axle bearings and sledges. Modern machines are much more complicated and are composed of many different machine elements which are in relative motion under varying loads, speeds and temperatures. Industrial lubricants are significant for all kinds of industries whether machine building, chemical, textile, wood, food-processing, automotive, or wind power. Today’s lubricants have evolved to a complex mixture of chemical structures that ensure not only lower friction but also provide various other functionality such as lower wear, improved heat transfer, sealing, as well as control of soot, impurities, sludge and deposit formation in the mechanical equipment. Lubricant research and development has become indispensable in automotive engines and drive trains as these have been rapidly advancing towards smaller sizes, increased power, better fuel economy and lesser emissions. Development of lubricant additives and lubricant formulation has led to extended service intervals, enhanced fuel efficiency and improved machine durability. Future trends of lubricant development and use in the Industry 4.0 era and rise of electric vehicles look promising where several stakeholders already have taken their first steps.

Experimental and Molecular Level Analysis of the Tribological and Oxidative Properties of Chaulmoogra Oil

This study introduces chaulmoogra oil as a base stock for lubricant formulation. The tribological properties of chaulmoogra oil are evaluated by quantitative structure-property relation (QSPR) technique using the molecular modelling package Spartan 18. The quantum chemical calculations were performed on a typical molecule of chaulmoogra oil and its constituent fatty acids. The orbital energy gap of the constituent fatty acids in chaulmoogra oil is 7.37 eV and that of chaulmoogra oil molecule is 6.8 eV, which is less than that of the lauric acid, the main constituent of coconut oil (7.78 eV). Orbital energy gap predicts a better tribological performance for chaulmoogra oil, and the four ball test result is in agreement with this prediction. Oxidative property of chaulmoogra oil is tested by isothermal thermogravimetric/differential thermal analysis (TGA/DTA) and compared with different oils. Weight gain in oxygen is only 0.02% for chaulmoogra oil and showed better oxidative stability among all other tested oils.

Effect of turmeric oil and halloysite nano clay as anti-oxidant and anti-wear additives in rice bran oil

Mineral oils, which are mainly used as lubricant base oils in industries and automobiles, are non-bio degradable, toxic and cause harm to our environment. A large quantity of the lubricants, approximately 150 million barrels are used per year. In order to tackle the adverse effects of mineral oils on the environment, an idea emerged to replace mineral oils with an environmentally friendly bio lubricant. Vegetable oils having good lubricating properties, biodegradability and non-toxicity became the forerunners in these new bio lubricant formulation methods. In this paper, physical, chemical, tribological properties and oxidative stability of rice bran oil with two non-toxic additives, namely turmeric oil and halloysite nano clay, were evaluated. The gas chromatography method was used for structure elucidation. The tribological properties were evaluated by a four-ball apparatus as per ASTM D4172-94. Rice bran oil with 0.1% halloysite nano clay and 1.5% turmeric oil has shown 16.1% and 13.4% reduction in coefficient of friction and wear scar diameter, respectively, whereas the acid and peroxide value has reduced to 49% and 52%, respectively, when compared with the pure rice bran oil. The effect of turmeric oil in rice bran oil was evaluated using DFT-based quantum chemical studies using Gaussian 09, and it was found that the curcumin, which is the major component of turmeric oil, has shown good anti-oxidant behaviour. The properties of rice bran oil were observed to increase at a synergic combination of turmeric oil and halloysite nano clay.

The influence of lubricant formulation on early thrust and radial bearing damage associated with white etching cracks

In the past, results have shown the influence of oil-additive systems in the life of rolling bearings, also hypotheses have been formulated on the influence of lubricant formulation on the development of early bearing damage associated with white etching cracks. In some earlier work of the authors with different operating conditions, early damage, and white etching cracks had been generated by mechanical stresses. In this study, tests with custom-made lubricants have been performed on thrust as well as radial bearings to clarify some assumptions. The tested oils differ only by the presence of three additives, but only one oil has led systematically to white etching cracks despite the fact that both oils lead to similar mechanical stresses. The results confirm that under mixed lubrication conditions with certain lubricant formulations, early damage, in particular white etching cracks, can be influenced by the oil-additive system likely affecting the bearing steel. Hypotheses are formulated and the influence of different parameters is discussed. This paper, combined with earlier work of the authors, confirms that the understanding and solution to an early bearing damage associated with white etching cracks can only be validated using the appropriate test method.