| AVS 62nd International Symposium & Exhibition | |
| Tribology Focus Topic | Thursday Sessions |
| Session TR-ThP |
| Session: | Tribology Poster Session |
| Presenter: | Takanori Takeno, Tohoku University, Japan |
| Authors: | T. Takeno, Tohoku University, Japan H. Miki, Tohoku University, Japan T. Takagi, Tohoku University, Japan K. Adachi, Tohoku University, Japan |
| Correspondent: | Click to Email |
This study clarifies the formation mechanisms of thin layer on the counter material when nanocompsite coatings consisted of nanoparticles and diamond-like carbon were sliding against steel ball in air. When low friction was obtained in such combination, thin metallic film was formed on the counter material. What we could find is that such metallic film does not contain oxygen less than the one coming from native oxidized surface.
Hybrid deposition system composed of CVD and PVD sources allows us to make nanocomposite structure based on diamond-like carbon (DLC) coatings. Thanks to magnetron sputtering system, target material in sputtering source is extracted as a form of nanoparticle, and its size varies depending on deposition condition and type of material. During sputtering process, hydrocarbon plasma is generated, and hydrogenated amorphous carbon phase is formed. Typical structure of the composite coatings is that nanometer-sized metallic particles are well dispersed in amorphous carbon host matrix. Friction tests are conducted under vacuum or dry conditions. Various analytical techniques including transmission electron microscope (TEM), secondary ion mass spectrometer (SIMS), Raman spectroscopy, Scanning Electron Microscope equipped with energy dispersive X-ray spectrometer (SEM-EDS), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES).
Once iridium was selected as an inclusions in diamond-like carbon host matrix, Ir-containing DLC showed friction coefficient of less than 0.1 despite friction coefficients of Ir and DLC showed ~ 0.3. In-situ electrical contact resistance measurements revealed that such coating provides not only low friction coefficient but also low electrical contact resistance, several tens ohms. When low friction and electrical contact resistance was achieved, metallic thin film was formed on the counter material. EDS analyses revealed that chief material forming the metallic film is Ir. It could be understood that nanoparticles formed metallic thin film on the counter materials during friction. It is worth noting that such transfer film does not contain oxygen even friction tests were conducted under air. Same phenomena could be observed with Cu- and Ag-containing DLCs. Even for both cases, metallic transfer films were formed during friction tests, and we could not detect oxygen from the transfer by EDS. Possibly, tribochemical reaction occurred and oxygen from air reacts to carbon in DLC, then gas phase or wear particles of carbon-oxides were formed. Details on a possible chemical reaction between the coatings and air will be discussed at the conference.