Effect of WS₂ and TiO₂ nanoparticles on the tribological characteristics of ta-C coating
Tetrahedral amorphous carbon (ta-C) coating is one of the Diamond-like Carbon (DLC) coating which display some excellent properties of a diamond, such as high hardness properties, high wear resistivity and chemically inertness. It is widely used in engineering applications. The interaction of the lu...
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| Format: | Thesis |
| Language: | English English |
| Published: |
2017
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| Subjects: | |
| Online Access: | https://eprints.ums.edu.my/id/eprint/38894/1/24%20PAGES.pdf https://eprints.ums.edu.my/id/eprint/38894/2/FULLTEXT.pdf |
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| Summary: | Tetrahedral amorphous carbon (ta-C) coating is one of the Diamond-like Carbon (DLC) coating which display some excellent properties of a diamond, such as high hardness properties, high wear resistivity and chemically inertness. It is widely used in engineering applications. The interaction of the lubricant additive could affect the tribological performance of the ta-C coating layer with its intrinsic factor. This project was carried out to investigate the effect of tungsten disulphide (WS2) and titanium dioxide (TiO2) nanopowder separately in Poly-alpha-olefin (PAO4) oil on the friction and wear behavior of the ta-C coating films. PAO4 base oil blended with different weight ratio of a WS2 and TiO2 was used (0 wt%, 0.1 wt%, 0.5 wt%, and 1.0 wt% TiO2 blended with PAO4, and 0 wt%, 3.0 wt%, 4.0 wt%, and 5.0 wt% WS2 blended with PAO4). The ta-C coating was deposited on the bearing steel using the Filtered Cathodic Vacuum Arc (FCVA) method. The hardness and young modulus value of this coated films were measured to be 64.53 GPa and 418.23 GPa, respectively. A ball-on-disc tester was used to investigate the friction and wear behavior of ta-C films. Under boundary lubrication condition, the presence of the WS2 and TiO2 additives in the base oil reduced the wear of the ta-C films. The specific wear rate obtained under PAO4 lubrication was the highest at 0.2816 X 10-6 mm3/mN. This lubrication condition had the lowest lambda ratio of 0.551 indicating of boundary lubrication resulting in severe interaction of the asperities and a significant shear properties of the lubricant film onto the ta-C surface. In contrast, sliding under PAO4 containing 3.0 wt% of WS2 with lambda ratio of 0.851 resulted in micro-elastrohydrodynamic lubrication condition and a lower specific wear rate of 0.1494 X 10-5 mm3/mN. Among all the PAO4 blended with TiO2 lubricant, the lubricant containing 1.0 wt% of TiO2 with the highest lambda ratio value of 0. 989 gave the lowest wear rate of 0.1314 X 10-5 mm3/mN. The TiO2 and WS2 had different effects on the friction coefficient and the specific wear rate. Increasing the weight percentage of WS2 led to a reduction in the COF but an increasing specific wear rate. However, for PAO4 blended with TiO2 lubricants, higher content of TiO2 resulted in higher COF but lower specific wear rate. The Raman result showed that the presence of the additives had significant effect on the graphitization of the ta-C structure. Higher amount of additives caused more sp3 bond structure to break into sp2 bonds which had adverse effect on its wear resistance. On the other hand, the additives could form a protective layer capable of reducing the wear of the ta-C film. Overall effect was these was a reduction in wear. |
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