The 3D images of the steel ball wear scars are shown in Figure 6 and the ball total displaced wear volumes are shown in the below Table 4.
Table 3. Steel ball total displaced volume based on 3D images by profilometry.
In the case of steel–steel sliding contact, PFM 1 and PFM 2 were able to provide lower friction and reduced wear compared to the reference oil. GMO provided no friction reduction under the same conditions and caused a significant increase in wear when compared to the reference oil. In a steel–steel contact both the disc and the ball experience wear.
Hydrogenated DLC Disc - Steel Ball In a hydrogenated DLC disc–steel ball configuration, the reference oil showed a lower coefficient of friction compared to a steel-steel contact.
In this configuration and under pure sliding conditions, GMO gave the greatest reduction in steel ball wear volume (65%). PFM2 also gave an excellent reduction in steel ball wear (46%) and was also the most effective in reducing friction. Whilst providing similar friction performance to GMO, PFM2 was less effective than GMO in reducing steel ball wear but was still able to reduce wear in comparison to the reference oil.
All the oils tested showed some waviness to the friction curves, a phenomena which is yet to be clearly understood. Whilst it might be related to wear, this waviness is actually observed even with virgin surfaces when little or no wear has taken place. Additional experiments and analysis is required to determine the reason behind this observed waviness.
Figure 7. MTM graph - friction of EU Oil with and without 0.5% FM in non-hydrogenated DLC disc- steel ball pure sliding contact at 120 minutes rubbing.
Figure 6. Steel ball wear scar after 120 minutes in hydrogenated DLC disc-steel ball contact.
3D images of the surface of the non-hydrogenated DLC discs are shown in Figure 8. No significant wear was observed on any of the non-hydrogenated DLC discs, only a small wear track measured in the order of nanometres was observed with the addition of PFM1. Longer duration tests would be required to determine if this is of significance.
Figure 4. MTM graph - friction of EU Oil with and without 0.5% FM in hydrogenated DLC disc-steel ball pure sliding contact at 120 minutes rubbing.
In the hydrogenated disc–steel ball contact PFM2 gave an outstanding reduction in friction (56%).
With the addition of 0.5% GMO, a 15% reduction in friction was observed after 120 mins rubbing. PFM1 demonstrated similar performance to GMO.
3D Images of the discs surface are shown in Figure 5. The images for the hydrogenated DLC discs indicate little or no wear for the reference oil and the reference oil containing either PFM 1 or 2. GMO showed evidence of a very small wear track, measureable in the order of nanometres. Longer duration tests would be required to determine if this is of significance.
Table 4. Steel ball total displaced volume based on 3D images by profilometry.
In a hydrogenated DLC disc–steel ball configuration it is the steel ball that is worn, whilst the hydrogenated DLC disc retains its integrity.
Non-hydrogenated DLC Disc–Steel Ball Compared to the behaviour shown by the hydrogenated DLC disc–steel ball configuration, the non-hydrogenated DLC disc–steel ball contact lubricated with the same reference oil showed a higher coefficient of friction in the boundary and mixed lubrication regimes. In comparison to steel–steel contact the non-hydrogenated DLC disc–steel ball configuration demonstrates similar friction at very slow sliding speeds but lower friction at medium sliding speeds.
Figure 5. Hydrogenated DLC disc track after 120 minutes in hydrogenated DLC disc–steel ball contact.
PFM1 and PFM2 gave significant friction reduction after two hours rubbing, with PFM2 providing the greatest reduction in friction in both the boundary and mixed lubrication regimes. Whilst GMO provided some friction reduction, compared to the reference oil it was not as significant as either PFM1 or PFM2.
Figure 8. Non-hydrogenated DLC disc track after 120 minutes in non-hydrogenated DLC disc-steel ball contact.
3D images of the ball are shown in Figure 9 and the ball total displaced volumes given in Table 5.
The addition of PFM1 gave an outstanding wear reduction of 90% for the steel ball. PFM2 gave a very good reduction of 29%, whilst GMO was only able to provide 12% wear reduction on the steel ball.
Figure 9. Steel Ball wear scar after 120 minutes in non-hydrogenated DLC disc–steel ball contact.
LUBE MAGAZINE NO.134 AUGUST 2016
15
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