The clarification of low friction mechanism in oil lubrication for B-DLC coating by in-situ observation of friction area

The Clarification of Friction Mechanism in Oil Lubrication for CN<i>_x</i> Coating by <i>In-Situ</i> Observation of Friction Area with Reflectance Spectroscopy

“…Further, we studied the loading ratio for the boundary lubrication area. The results showed that as the number of friction cycles increased, the composite root mean roughness σ for the CN x film and its counterpart, the sapphire hemisphere decreased from 11.1 nm to 7.6 nm, and the minimum oil film thickness increased Table 1 Pearson's correlation coefficient (µ b and composite root mean square roughness, thickness of transformed layer and oil film, polarizability of transformed layer and oil film); reproduced with permission form [19] Copyright (2018) Japanese Society of Tribologists from 13.5 nm to 19.7 nm; therefore, the film thickness ratio increased from 1.2 to 1.7. When calculating the loading ratio for the boundary lubrication area from the film thickness ratio, it decreased from 90% to 65%.…”

“…Fig. 2 Modeling of surface roughness layer by effective medium approximation; reproduced with permission form [19] Copyright (2018) Japanese Society of Tribologists is applied when there is a light adsorption range in a thin film layer within the range of the measured wavelength [9].…”

“…15 Friction coefficient and polarizability of transformed layer; reproduced with permission form [19] Copyright (2018) Japanese Society of Tribologists Fig. 17 Friction coefficient and polarizability of oil film; reproduced with permission form [19] Copyright (2018) Japanese Society of Tribologists coefficient decreased, only the transformed layer, which has high polarizability at 1.4 × 10 -24 cm 3 , increased from 2.0 nm to 5.7 nm. Accordingly, the decrease from 0.028 to 0.022 of the friction coefficient after cycle 400 is believed to be caused by the increase of the thickness of the transformed layer, which has high polarizability.…”

“…Fig.8Friction coefficient and arithmetic average roughness of CN x coating and sapphire hemisphere; reproduced with permission form[19] Copyright (2018) Japanese Society of Tribologists…”

“…Fig.10Relationship between loading ratio of boundary lubrication and film thickness ratio; reproduced with permission form[19] Copyright (2018) Japanese Society of Tribologists…”