Abstract
Solid lubrication in tribological applications was studied on hard metal specimens with micropits fabricated using metal injection molding (MIM). This study investigated synergy effects of paraffin wax mixed with 5 wt% MoS2 on the lubricating potential both under normal and elevated temperatures. Pin-on-plate sliding tests were performed on a CSM tribometer in which WC–Co pins oscillated against microstructured and flat reference WC–Co specimens under 10 N applied normal load. Surface morphology characterization of test specimens was carried out before and after tribological tests using scanning electron microscopy. Solid paraffin wax displayed enhanced lubrication compared to solid paraffin wax mixed with 5 wt% MoS2 on micropit specimens under normal temperature. On the contrary, under heating conditions, solid paraffin mixed with 5 wt% MoS2 significantly reduced the dynamic coefficient of friction (COF) values for both flat and micropit specimens. The results showed that the micropits in textured specimens can be used as a reservoir for the lubricant that can significantly reduce friction compared to flat reference specimens.Graphical
Highlights
Solid lubrication is important for reducing friction and wear between rubbing surfaces in various tribological systems [1]
The influence of M oS2 on the lubrication properties of solid paraffin was tested by the addition of 5 wt% M oS2 into solid paraffin, and the results were compared to paraffin in terms of coefficient of friction (COF) values on both flat and textured WC–Co specimens
A steady increase in the COF values was observed for the flat specimens with paraffin in Fig. 5a similar to all COF curves in Fig. 5b that may result from a reduced lubricant amount between the tip and surface as the distance was increased
Summary
Solid lubrication is important for reducing friction and wear between rubbing surfaces in various tribological systems [1]. Surface texturing and patterning have been studied with solid lubricants for enhanced performance [4] with materials ranging from soft polymers to hard metals. Lamellar crystalline materials such as MoS2 have been studied in combination with microscale surface patterning for enhanced tribological performance [5]. Paraffin wax was combined with MoS2 to study the synergetic effects of layered lubrication additives with surface texturing under solid and liquid conditions in the elevated temperature. Materials with characteristic lamellar crystalline structure having long-range van der Waals forces are typically used in solid lubrication. Adjacent sulfur sheets are bound by weak van der Waals forces at bond lengths of about 3.08 Å. In previous studies [6, 15], MoS2 has been used as an additive to liquid paraffin with enhanced tribological properties. Surfaces of the test specimens were characterized using the scanning electron microscope (SEM)
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