Micro-to-nano triboactivity of hydrogenated DLC films

Abstract

In this paper, we present the results of a systematic study directed toward submicrometric scale triboactivity of a range of hydrogenated diamond-like-carbon (H : DLC) films derived from source gases with different hydrogen-to-carbon ratios. The H : DLC films were deposited on Si substrates in a plasma enhanced chemical vapour deposition system. Specifically, we produced three kinds of H : DLC films, using pure acetylene, pure methane and 25% methane + 75% hydrogen as the precursor source gases. Samples were subjected to wettability and depth sensing ultramicroindentation tests, and micro-to-nanoscale friction and wear studies using a nanotribometer and an atomic force microscope. The results of our study revealed a very close correlation between the wettability and the tribo-mechanical response of the H : DLC films at micro-to-nanoscales and their hydrogen-to-carbon ratio, i.e. lower hydrogen-to-carbon ratio leads to higher hardness (H) and lower water contact angles. Moreover, our results indicated a strong correlation between the hardness of the films and the threshold for severe wear damage. This threshold can be expressed by the ratio between the average Hertzian contact stress and the hardness which, in this study, is close to unity.