Friction Characteristics Of NCD Vs Alumina Balls Analysis

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3.4. Friction Characteristics of the NCD, MCD and boron doped NCD Coatings against Alumina Balls
The friction coefficient curves of NCD, MCD and boron-doped diamond films sliding with Al2O3 balls are shown in figure 4, figure 5 and figure 6, respectively, for a sliding speed of 8 m/s and a load of 1N, 5N and 10N, respectively. Figure 4 (a), figure 5 (a) and figure 6 (a) show the friction coefficient of NCD, MCD and BDNCD at 1 N, respectively. Figure 4 (b), figure 5 (b) and figure 6 (b) show the friction coefficient of NCD, MCD and BDNCD at 5 N. Figure 4 (c), figure 5 (c) and figure 6 (c) show the friction coefficient of NCD, MCD and BDNCD at 10 N, respectively. Figure 4 (d), figure 5 (d) and figure 6 (d) show the average friction coefficient
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Among all the tested diamond films, friction tests suggest that the boron doped diamond films exhibit the lowest friction coefficient and wear rate, because of its diamond grain refinement effect. A lower friction coefficient is found in boron-doped diamond films than that of undoped ones. No variation of the total volume wear rate as a function of time was evidenced during the test since the vertical movement was negligible, a few micrometers at the end of the test. At this point, the final wear rate of the ball is indeed about 5x10-17 m3 (N/m). The wear of the diamond coated disc is too low to be measured and the wear track is just polished, as detected by SEM and confirmed by the AFM measurements. This lack of coating wear of the disc results from the short test duration due to the ball wearing more quickly. Alumina is a chemically inert ceramic compound and sliding interaction of diamond coatings against alumina material is purely mechanical. Low and stable friction coefficient values of around 0.0804 were observed with the boron doped NCD coating. The stable and low friction coefficient of the boron doped NCD coating was attributed to the chemical inertness of the mating materials and also due to the …show more content…
On the other hand, slightly high and unstable friction behavior was observed during the sliding of MCD coating against alumina ball. High run-in friction values of ~ 0.153 (average) were observed with the MCD coatings. The high run-in friction behavior of the MCD coating as compared to the NCD and BDNCD coatings was attributed to its sharp and rough surface asperities. When increasing the time, at a sliding speed of 8 m/s and a load of 10 N, the friction coefficient first increases and then decreases gradually after a time period of 5 minutes and remains constant after 12 minutes. The NCD, MCD and doped diamond films undergo similar friction coefficient advancement. Following the initial peak, the coefficient of friction transit to a lower value and at last reaches a steady state. In case of the boron-doped diamond films, the coefficient of friction also starts with a high value but falls to a low value quickly. An increasing regime then can be observed and ultimately the curve offers a reasonably steady state. The averaged

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