Deposition of DLC films on the inner wall of U-type pipes by hollow cathode PECVD

There are many defects in the bending part of U-type pipe, which will directly affect its safety and service life. DLC (Diamond Like Carbon) film is considered as an effective protective film because of its excellent properties. However, it is very difficult to deposit DLC films on the inner wall of U-type pipes with double stress. The purpose of this paper is to deposit DLC film with high hardness, wear resistance and corrosion resistance on the inner wall of U-type pipes by hollow cathode PECVD. The microstructure, mechanical properties, tribological and corrosive behaviors were characterized by the Raman spectroscopy, ATR-FTIR, SEM, nano-indention, polarization, electrochemical impedance spectroscopy and ball-on-disk tribological tests. Results indicates that the U-type pipe inner DLC films shows the lower stress level. Compared with the bare substrate, it presents the higher hardness (7- 14 GPa), elastic factor (>0.1) and plastic factor (>0.1) and the above DLC film exhibits the lower corrosion current density, which is about 1-2 orders of magnitude lower than the bare substrate. Moreover, the DLC films also possesses the lower friction coefficient (0.04- 0.06) and wear rate (2.67- 5.93E-7 mm(3) N-1 m(-1)). Therefore, the DLC films exhibits the greater mechanical, tribological and anti-corrosion performance, indicating that the above DLC films effectively protects U-shaped pipe and prolongs its service life.