| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016) | |
| Thin Films | Thursday Sessions |
| Session TF-ThM |
| Session: | Advanced Protective Coatings/Stress Evolution, Nanostructure, and Physical Properties of Thin Films |
| Presenter: | Motonori Tamura, The University of Electro-Communications (UEC-Tokyo), Tokyo, Japan |
| Correspondent: | Click to Email |
Diamond-like carbon (DLC) is an amorphous carbon with a significant fraction of CC sp3 bonds. Tetrahedral amorphous carbon (ta-C) is the DLC with the maximum sp3 content. These hydrogenated amorphous carbons have been classified into several types, such as a-C:H and ta-C:H.
Films of a-C:H with the highest H content (40–60 at. %) can have up to 70% sp3. However, most of the sp3 bonds are hydrogen terminated and this material is soft and has low density. Films of a-C:H with intermediate H content (20–40 at. %) have better mechanical properties. Even if these films have lower overall sp3 content, they have more C-C sp3 bonds. These films have the advantage of possessing high hardness levels –in the range of conventional tribological PVD coatings (1500 – 3200 HV), coupled with a coefficient of friction that is less than half of the conventional coatings.
In this study, hydrogen permeability of a-C:H films with intermediate H content was measured. Films were deposited by PVD + plasma-assisted CVD (PACVD) on stainless-steel substrates Type 316L. Hydrogen-permeation tests were performed on the coated stainless steel samples. These tests were based on the differential-pressure methods described in ISO15105-1:2007, the international standard for determination of gas-transmission rates.
The permeation of hydrogen through solid materials involves a series of steps including adsorption, dissociation, diffusion, and recombination coupled with desorption. In our experimental conditions, it was indicated from the relation between the permeation flux and driving pressure of hydrogen (100〜800 kPa) that hydrogen passed through the samples in the diffusion-limited permeation mode.
Hydrogenated amorphous carbon films (2.0-mm-thick) were effective to reduce the rate of hydrogen permeation through stainless steel (0.1-mm-thick) less than 1/100 at 573-773 K. Effect of hydrogen content in films to hydrogen permeation behavior was studied.