| AVS 62nd International Symposium & Exhibition | |
| Tribology Focus Topic | Thursday Sessions |
| Session TR-ThP |
| Session: | Tribology Poster Session |
| Presenter: | Kazuki Ikoma, Tohoku University, Japan |
| Authors: | K. Ikoma, Tohoku University, Japan K. Adachi, Tohoku University, Japan T. Takeno, Tohoku University, Japan |
| Correspondent: | Click to Email |
Solid lubricants are usually used at severe environment (ex. vacuum). Among these lubricants, MoS2 is widely used for many mechanical systems and shows low friction by forming transferred layer with MoS2 lamellar structure. However, one of the drawbacks of MoS2 is that it must be kept in dry nitrogen condition to avoid oxidation of molybdenum-disulfide.
We have proposed amorphous carbon coatings containing Molybdenum disulfide (MoS2-DLC) as a new solid lubricant. It is well known that amorphous carbon coating is used for a gas barrier coating decreasing gas permeability. So, we have made the coatings with nanocomposite structure that MoS2 clusters with several nm in diameter are embedded in hydrogenated amorphous carbon (a-C:H) host matrix. It was reported that friction coefficient obtained by MoS2 sliding against SiC ball decreased with increasing MoS2 concentration It is worth noting that MoS2-DLC with proper MoS2 concentration showed lower friction than MoS2 coatings. Further reduction of friction could be obtained by changing a deposition parameter leading to a modification of host matrix of amorphous carbon. Therefore, not only concentration of MoS2 but also properties of amorphous carbon host matrix are very important for achieving low friction.
This study focuses on hydrogenated amorphous carbon host matrix to achieve low friction. Especially, deposition parameter that controls properties of carbon host matrix was changed to produce various amorphous hydrogenated carbon host matrix containing MoS2 nano-clusters. After the friction tests, a thin transferred layer proving low friction is well analyzed by various analytical techniques including transmission electron microscope (TEM), secondary ion mass spectrometer (SIMS) and Auger electron spectroscopy (AES). It was clarified that thin transferred layer was composed of two phases. Dominant one contains mainly MoS2 with lamellar structure. It is worth noting that there is very thin carbon-rich layer with ~ 5 nm between MoS2-rich layer and the counter material of SiC, and carbon at thin carbon layer comes from carbon host matrix. Taking into account the selective transfer of carbon from the coating and the possibility that such carbon-rich layer becomes a kind of support for forming lubricious MoS2 layer, friction properties could be controlled by the properties of carbon. In this study, formation mechanisms of such two-phase thin layer are clarified, first. Then, we try to achieve very low friction with low MoS2 concentration with optimized phase of carbon phase in the coating. Finally, design guideline for achieving low friction utilizing MoS2-DLC coatings is proposed.