Nanoindentation and nanoscratch behaviors of DLC films growth on different thickness of Cr nanolayers

- 10, 20, 40 and 80 nm Cr layers applied as an interlayer to improve the adhesion and mechanical behavior of DLC films.
- Surface roughness of Cr interlayer changed with its thickness which depended both on sputter time and deposition condition.
- Lower surface roughness with a normal distribution of Cr particles caused better adhesion and hardness of DLC films.
- The thermal stress of the DLC film decreases in the lower roughness which cause better adhesion strength.
- The mechanism of mechanical interlocking between Cr and DLC which is affected by roughness, also improve the adhesion.

Metal interlayer is a promising method for improving the adhesion of DLC film to the substrate. In this study, Cr thin film, with different thickness of 10, 20, 40 and 80 nm was applied as an interlayer, to investigate the influences on the tribological behavior of DLC films. Cr nanolayers were deposited by DC magnetron sputtering and DLC films were deposited by plasma enhancement chemical vapor deposition (PECVD) using methane and argon as precursors. Surface roughness and particle size distribution of Cr nanolayers were investigated by atomic force microscopy (AFM), which showed increasing the roughness from 0.17 nm to 0.69 nm by increasing Cr nanolayer thickness. Thickness and microstructure of DLC films obtained by cross-sectional field emission scanning electron microscopy images and Raman spectroscopy, respectively. Nanotribological behaviors of DLC films such as scratch resistance, adhesion strength, friction coefficient, hardness and wear resistance were investigated by nanoscratch and nanoindentation tests. Good adhesion for all samples was observed in which samples with Cr thickness of 10 and 20 nm had the best hardness of 17 GPa and 24 GPa, respectively. The results indicated lower surface roughness and better particle distribution in Cr interlayer cause better tribological behavior.

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