Duplex DLC coatings fabricated on the inner surface of a tube using plasma immersion ion implantation and deposition

A duplex plasma immersion ion implantation and deposition (PIIID) process, involving carbon ion implantation and diamond-like carbon (DLC) deposition, is proposed to modify the inner surface of a tube. In the research, samples of GCr15 bearing steel were placed inside a tube in the vacuum chamber. After the vacuum chamber was evacuated to a base pressure of 6 × 10^{- 3} Pa, C₂H₂ gas was introduced into the chamber, and the tube was biased by a negative pulsed bias. Since a pulsed glow discharge (PGD) plasma can be formed by the bias, carbon ion implantation and DLC film deposition process can be obtained by biasing the tube with a high and low bias, respectively. To synthesize different DLC films, single PIIID processes employing a low voltage (several kV) PGD method and duplex PIIID processes combining the high (several tens kV) and low voltage PGD techniques were carried out. The as-synthesized films were characterized by Raman spectrum, nano-indentation, scratch, tribological and electrochemical tests. Raman results show that duplex DLC films were synthesized by this duplex PIIID process. In addition, compared with the single DLC film synthesized by the low voltage PGD process, the duplex DLC films can obtain a high wear and corrosion resistances. Furthermore, using this duplex PIIID method, batch treatment of outer-rings of the bearing was realized.