This paper reports a novel work on the synergetic effects of microscale surface texturing and lubricant friction modifier additive of molybdenum dialkyldithiophosphate (MoDDP) subject to both flooded and starved lubrication conditions. The experiments were performed on reciprocating ball-on-disk friction in GTL8 base oil with and without MoDDP. In the flooded lubrication condition, the test results demonstrated that the presence of the MoDDP additive contributed to lower friction coefficients, and also more pronounced effect of surface textures on friction than in the case of the bare base oil. In the starved lubrication experiments, textured and texture-free surfaces in the oils with and without MoDDP additive were tested until an abrupt rising of friction coefficient was detected. The results showed that the magnitude of friction coefficient before terminating each test was the almost same for various tests, while the endurance time in different test conditions was significantly different. The textured surface exhibited longer endurance time than the texture-free surface, especially when the MoDDP additive was used. The mechanism of the synergetic effects of surface textures and MoDDP additive has been discussed based on the experimental observations in the following sections. This study provides a new idea for the application of surface texture in boundary lubrication when lubricant additive is contained in the lubricating oils.
Experimental investigations have been conducted to study the effects of surface topography on ZDDP (zinc dialkyldithiophospahte) chemical tribofilm formation during runningin stage under boundary lubrication conditions. The scope of presented work has been limited and focused on reciprocating motion under boundary lubrication to simulate upper and lower dead center of piston ring movement, which is prone to adhesive wear failure. Several surface topographies were designed and fabricated to measure, compare coefficient of friction and ZDDP time critical tribofilm formation. Rubbing surfaces and their corresponding tribofilms were characterised by SEM and EDX. Mechanisms of surface topography effects on ZDDP time critical tribofilm formation is presented and discussed. Results from this study have demonstrated that the surface topography has a significant influence on the ZDDP time critical tribofilm formation during running-in process and corresponding wear performance. This research provides an opportunity to augment anti-wear performance under boundary lubrication condition. This can be achieved by optimising surface morphology design to influence the formation of anti-wear tribofilms during the running-in stage.In turn, this will result in interacting components' service life enhancement and significant cost savings from mitigated wear.
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