High Speed Si-DLC Coatings on Mg-alloy with Higher Repetition Bi-polar Pulses of a PBII System

In order to improve poor corrosion protection property of Mg-alloy, we have been studied about Si incorporated DLC (Si-DLC) coatings with our bi-polar PBII (Plasma Based Ion Implantation) system. Recently, we have introduced new pulse power supply and studied the effects of the repetition frequency (R.F.) up to 20 kHz on the deposition rate of Si-DLC coatings and corrosion protection ability of the Si-DLC coatings on AZ31 (Mg-3%Al-1%Zn) alloy. On deposition rate, the deposition rate increases with the increase of the repetition frequency and gas pressure of precursor gas, generally. Delay time of -pulse application after +pulse application, pulse width and the peak pulse voltage of -pulse are also affected to the deposition rate. On corrosion protection ability, the coating made at 8 kHz of R.F. for 120 min with 1000 nm in thickness, the thickest coating is the best. Unfortunately, the higher deposition rate of higher R.F. can not make better corrosion protection property. Si-DLC coatings of several hundred nm in thickness are relatively transparent, which was confirmed by an optical measurement.