Observation of MoDTC-derived tribofilm on the surface of Ta and Nb doped a-C:H coating by reflectance spectroscopic friction microscopy

Abstract

To enhance the friction reduction characteristics of MoDTC are desired to reduce a friction loss of automobile engines. In this research, we focused on the influence of doped metal of a-C:H coatings, specifically hydrogen-containing DLC coatings, as factors that affect the friction reduction effect of MoDTC. We prepared three types of DLC coatings: a metal-free a-C:H coating, a-C:H coating with Ta doped, and a-C:H coating with Nb doped, both belonging to the fifth group of elements. Friction tests were conducted to evaluate the friction characteristics, and Raman spectroscopy analysis was performed on the tribofilm formed after the friction tests. Among the three DLC coatings, the a-C:H:Nb coating exhibited the lowest friction. Raman spectroscopy analysis revealed clear peaks of MoS₂ in the tribofilm formed on the a-C:H:Nb coating. Based on our findings, we proposed that addition of metals, particularly Nb, to the a-C:H coating contributed more to the reaction of MoDTC, resulting in a larger friction reduction effect of the tribofilms derived from MoDTC.