Adhesion of hydrogenated amorphous carbon films on ferrous alloy by intermediate nitrogen plasma treatment in silicon-containing interlayers

Abstract

Hydrogenated amorphous carbon (a-C:H) thin films show low adhesion on ferrous alloys. The addition of a silicon-containing interlayer could minimize the problem but traditionally high deposition temperatures are still needed (at least 300 °C). However, recently, plasma modifications of interlayers deposited under lower temperatures could promote similar results. In order to investigate if nitrogen plasma treatment could also be responsible for better interaction of interfaces and, consequently, better adhesion, different times of this treatment were performed on the outermost interface of silicon-containing interlayers deposited at 150 °C on AISI 52100 steel prior to a-C:H films deposition. The results show that nitrogen plasma modifies the chemical bonding and composition of the interlayer in function of time but without thickness changes. An finest treatment time was found in 20 min, promoting better adhesion of a-C:H when compared with the same conditions without N2 treatment. Finally, a chemical mechanism due to nitrogen plasma treatment is proposed, where a-C:H coatings adhesion is maximized in high N/O and low Si/C ratios.