Amorphous Carbon Nitride (a-CNx) coating is an attractive material that satisfies both relatively high hardness and ultra-low friction coefficient. We have tried to obtain a-CNx by using plasma-enhanced chemical vapor deposition (PECVD), which is more suitable for 3-dimensional coating than typical physical vapor deposition methods. However, considering the application of a-CNx coatings for real machine parts, ultra-low friction property is expected to express under oil lubrication. Thus in this work, the friction characteristic under oil lubricated of Si-containing a-CNxHy films deposited by PECVD was evaluated especially by analyzing the relation between the Raman spectrum, which is a proper index of carbon structure, and the friction coefficient of the films. In particular, the relation between friction coefficient and
ID/IG ratio from Raman spectroscopic analysis of Si-containing a-CNxHy films was focused on. The friction coefficient decreased with the increasing of
ID/IG ratio in the range of 0.63-0.78, and the minimum low friction coefficient of 0.055 was shown for the
ID/IG ratio of 0.78. However, even for a film with the
ID/IG ratio of 0.32, similar low friction coefficient of 0.051 was shown. Moreover, for a film with the
ID/IG ratio of 0.34, which is almost unchanged from 0.32, the increased friction coefficient of 0.105 was shown. In these films, the amount of hydrogen in Si-containing a-CNxHy film increased from 33% to 37%, which is considered to mainly cause the increased of friction from 0.051 to 0.105. Two more exceptions were seen for some films where the friction characteristic is not correlated with
ID/IG ratio, but may be affected by maximum height roughness (Rz) and C=N combination. When maximum height roughness (Rz) was in the range of 203 nm-414 nm, transfer layer formed on counter material, and it showed lowest friction coefficient of 0.02. In addition, the friction coefficient was linearly decreased with the increase of C=N bond amount; the friction coefficient of 0.027 was achieved for the
IC=N/IG ratio of 0.44.
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