In this work, tribological characteristics of thin films composed of entangled carbon nanotubes (CNTs) were investigated. The surface roughness of CNT thin films fabricated via a dip-coating process was controlled by squeezing during the process with an applied normal force ranging from 0 to 5 kgf. Raman spectra and scanning electron microscopy (SEM) images of the thin films were obtained to estimate the influence of the squeezing process on the crystallinity of the CNTs. The analysis revealed that squeezing could reduce surface roughness, while preserving the crystallinity of the CNTs. Moreover, the surface energy of the cover glass used to press the CNT thin film was found to be the critical factor controlling surface roughness. A micro-tribometer and macro-tribometer were used to assess the tribological characteristics of the CNT thin film. The results of the tribotest exhibited a correlation between the friction coefficient and surface roughness. Dramatic changes in friction coefficient could be observed in the micro-tribotest, while changes in friction coefficient in the macro-tribotest were not significant. Friction 6(4): 432-442 (2018) 433 |www.Springer.com/journal/40544 | Friction http://friction.tsinghuajournals.comFriction 6(4): 432-442 (2018) | https://mc03.manuscriptcentral.com/friction Advances 2(2): e1500969 (2016)

The reliability and durability of devices that operate in vacuum and are subjected to wear are critical issues. The concerns rise at the macroscale wherein the contact area is large, yet the contact stress is in the GPa range. This paper reports on the design and fabrication of a coating comprising nitridized molybdenum disulfide (MoSN) supported by a novel nanolayered coating composed of carbon with subnanometer‐thick periodic albeit discrete Cr interlayers. The MoSN coatings are deposited onto mating surfaces using pulsed‐DC magnetron sputtering in an atmosphere with varying N2 to argon (Ar) ratios. Pulsed‐DC parameters, such as pulse duty and frequency, together with nitrogen content, are systematically optimized to achieve superior mechanical and tribological properties. The results reveal the importance of optimizing pulsing parameters during deposition as they significantly alter the properties of MoS2. The outcome is fabrication of a coating that despite having a low thickness, exhibits extremely low friction and record‐breaking macroscale wear rate in high vacuum compared to the values reported in the literature by date. Lastly, the analysis confirms the prediction of theoretical studies regarding the release of entrapped nitrogen in gaseous form during the wear process without disrupting the formation of a stable solid lubricant tribofilm.

A one-step method was developed to create a highly biocompatible micropatterned surface on a diamond-like carbon (DLC) through irradiation with a nitrogen ion beam and thus enhance the biocompatibility of osseointegrated surfaces and biotribological performance of articular surfaces. The biocompatibility and biotribological mechanisms were analyzed in terms of the structure and morphology of DLC. It was demonstrated that a layer enriched in sp3 C−N bonds was formed on the surface of the DLC after nitrogen ion beam irradiation. Moreover, with an increase in the radiation dose, the content of sp3 C−N on the DLC surface increased significantly, and the biocompatibility was positively correlated with it. The adhesion of the MC3T3 osteoblasts increased significantly from 32% to 86% under an irradiation dose of 8 × 1015 ions/cm2. In contrast, the micropattern had a significant negative effect on the adhesion of the osteoblasts as it physically hindered cell expansion and extension. The micropattern with a depth of 37 nm exhibited good friction properties, and the coefficient of friction was reduced by 21% at relatively high speeds.