The Effect of Carbon Structure of DLC Coatings on Friction Characteristics of MoDTC-Derived Tribofilm by Using an In Situ Reflectance Spectroscopy

Abstract

In this study, six types of DLC coatings were prepared, featuring different carbon structures (including amorphous ta-C coatings and GNC coatings with nanocrystallites) and different doped Ta amounts, to investigate friction characteristics. The results of friction tests with MoDTC-added lubricant revealed a consistent trend: DLC coatings with a higher ID/IG ratio exhibited lower friction coefficients. In addition, in situ observations using reflectance spectroscopy highlighted that the tribofilm formed on DLC coatings with a higher ID/IG ratio maintained a higher MoS2/(MoS2+MoO3)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\ ext{MoS}}}_{2}/({{\ ext{MoS}}}_{2}+{{\ ext{MoO}}}_{3})$$\\end{document} ratio, which exhibited a strong correlation with the friction coefficient. Measurements of a work function of each DLC coating indicated that those with a higher ID/IG ratio had a higher work function, suggesting the inclusion of a larger amount of graphite structure defects. These active defects in the graphite structure were deemed responsible for enhancing the friction reduction effect of MoDTC. The outcomes of this study propose a material design approach for DLC coatings that amplifies the effectiveness of lubricant additives in friction reduction.Graphical abstract