Influence of Nano lubricants on Laser Surface Texturing (LST) to minimize Coefficient of Friction

Demófilo Maldonado-Cortés1, Laura Peña-Parás¹, Jaime Taha-Tijerina1, Gerardo Tadeo Garza-García1 

1Departamento de Ingeniería, Universidad de Monterrey, Monterrey, México

INTRODUCTION: There are many surface engineering techniques in order to improve the tribological parameters and reduce friction coefficient (COF) and wear as: coatings, surface treatments and more recently surface texturing techniques, being one of the most versatile the use of the laser (LST)¹ to make different geometries² that allow improving the aforementioned parameters. Among the geometries are circles³ like the most common used because their ease of manufacture, squares, ovals and channels. On the other hand, the tribological use of nanoparticles in lubricants to create nano lubricants has been and is well researched⁴ since several phenomena have been found that allow the reduction of the coefficient of friction and wear: nano particles can function as nano bearings, spacers, valley fillers or creating exfoliation that generates a tribofilm. However, the effect in synergy of the use of LST and nano lubricants has been little studied. This paper presents the tribological benefits in reduction of friction force that this combination can bring when analyzing nano particles of CuO and TiO₂ at 0.05% Wt. Finally, the results are explained by 3D surface analysis techniques and EDAX analysis that allow to determine the type of tribological mechanism presented.

METHODS: The frictional pair block on ring in conformal⁵ mode was used for this study following the ASTM G77 test standard in the triboster called T-05. The curved surface of the block (probe) was exposed to the LST technique. The test parameters were: reciprocating disc movement⁶ of 90 degrees in each direction of rotation at a frequency of 250 rpm, a load of 150 newtons applied perpendicular to the center of the disc at a total test time of 900 seconds. Only a few drops of the nano lubricant were applied at the beginning of the test (synthetic fluid was used). A total of 3 repetitions were made following the statistical method of DIXON to a trusted novel of 95%. Due to the reciprocating movement of the disc on the specimen, almost symmetric values ​​of the friction force in newtons were obtained (positive and negative values). To explain the tribological phenomenon of wear, 3D surface analyzer equipment and EDAX chemical analysis were used.

RESULTS: Figure 1 shows the results by pairs of the 3 variables compared against not using the LST technique, in Figure 1A) the combination of non-LST and presence of LST is observed. It is also observed that when the LST technique is not used, the friction force increases considerably from the second 500, and the LST probe, although maintaining a tendency to the high, has a much lower slope and reaches maximum values ​​of friction force up to 50 newtons; while the probe with LST do not exceed 20 newtons of friction force in the last 10% of the test time. Figure 2A) shows the combination of not using LST vs the use of nano fluid with CuO nano particles at 0.05 Wt% . Friction force values ​​of less than 10 newtons are observed in the first 230 seconds of the test to increase the slope to approximately 19 newtons. Figure 1C) shows the combination of not using LST against the TiO₂ nano fluid at 0.05% Wt. A start is observed in the same way with a band even smaller than that shown with the nano particles of CuO with values ​​lower than 6 newtons in the same period of time (230 seconds), however the slope increases considerably in the second 750 and reaches values ​​almost as high as the test tube without LST at the end of the test. The 3D surface analysis studies show the changes in the surface finish (Ra) and the EDAX to show the traces of the components on the surface helps us understand the tribological mechanism presented in each of the nano particles used.

Figure 1 - Friction force of 3 different conditions vs NO LST application A) With LST, B) LST and CuO NP´s and C) LST and TiO NP´s

DISCUSSION: The benefit of the use of LST^7,8,9 is evidenced by the reduction of the friction force up to 70%, in addition the use of nano particles slightly improves these values ​​with additional consequences in the wear and surface finish. But the most important contribution in the case of CuO nanoparticles is the control of low amplitude of the friction force values during almost all the test. The analysis of 3D surface images and EDAX explain the tribological mechanism that this generates the benefits on friction force values as well roughness (Ra) and wear reductions.

REFERENCES: 1. Etsion, J. Tribol (2005),  2. Yu, H., Wang, X., & Zhou, F. Tribol Lett (2009), 3. Taha Maldonado, Garza, Ind. Lubr. Tribol. (2018), 4. Nakano, Tribol Lett,(2007),. 5. Haiwu, Tribology Letters (2010, 6.Vladescu Trib. International (2015), 7. Jones Procedia Manuf (2016), 8. Cobias, Journal of  Eng. Tribology (2015), 9. Etsion Tribol International (2009).