INTRODUCTION: Friction and wear are recognized to greatly influence the efficiency and lifespan of mechanical components in industry. Therefore, it is important to control the friction and wear properties of mechanical components by using lubricants and other surface modification techniques. Specifically, lubricants can provide a low-frictional fluid film that avoids direct contact between the solid surfaces, and at the same time, lubricants containing chemical additives promote the formation of a thin solid film called “tribofilm,” that can also avoid wear and improve frictional properties of the system. Recently, low-viscosity and low-shear lubricants have been commonly used as engine oils. Although the use of low-viscosity lubricants can reduce the energy losses that arise due to viscous resistance, they also expand the operation of the sliding components in the boundary lubrication regime; thus, contact between the solid surfaces may increase and cause more friction and wear. Therefore, the formation of a lubricant/additive-derived tribofilm with low-friction and high wear resistance on surfaces is an important factor to achieve desired tribological performances under boundary lubrication r.
One of the most effective analytical techniques to determine the chemical composition of tribofilms is XPS, which in fact provided crucial information about tribofilm composition in previous studies]. However, it has to be considered the oxidation of tribofilms and the removal of compounds at the outer-most surface during washing process when used high-vacuum analytical techniques such as XPS analysis. Precisely identifying the chemical composition of non-contaminated tribofilms is necessary in order to reveal the relationship between the tribological properties and the tribofilm formation. In this context, we used Raman spectroscopy as an in situ analytical technique. Our laboratory-built Raman tribometer allows us to easily monitor the formation process and the composition of MoDTC tribofilms within the rubbing test apparatus without having to remove the solution. Preliminary findings on this regard have already been reported by our group [1].On the other hand, many researchers reported that SLIM (spacing layer imaging method) is also one of in situ analytical techniques to monitor the film thickness of tribofilms on sliding surfaces under lubricated conditions [2]. Analysis of as much time-dependent information related to tribological phenomena as possible are needed to clarify tribological phenomena under boundary lubrication.
In this study, we will propose a lab-built tribometer with multiple analytical methods: Raman and SLIM that is called an in-situ Raman-SLIM tribometer as shown in Fig.1. The tribometer can evaluate time-dependent tribological information: friction, wear, the chemical composition and film thickness of tribofilms at the same time. We will report results obtained by using the in-situ Raman-SLIM tribometer.