Effect of Hydrogen Doping for ta-C on Friction of ta-C:H Sliding Against Bearing Steel in High Temperature and High Vacuum

The ta-C coating, characterized by a high fraction of sp3 hybridized structure, was considered as low friction and high wear resistant coatings in oil with friction modifier as lubricant additives. However ta-C showed high friction in high vacuum. Therefore hydrogen contained DLC with CVD was developed and evaluated for low friction in high vacuum. Normally the hardness of CVD hydrogen contained DLC is about 10 GPa. So higher hardness hydrogenated ta-C than 10 GPa can be expected for low friction and high wear resistant in vacuum. Also such new materials should be used at high temperature up to 200 degrees C in high vacuum. In this research, ta-C:H coated bearing steel plates were prepared with Filtered CathodicArc Method (FCVA) with Hydrogen ion irradiationwith various Hydrogen atomic concentration. Their ta-C:H coatings were used for friction tests in atmospheric pressure and high vacuum from 23 to 200 degrees C. After friction results, it can be found that the enough amount of Hydrogen concentration is important for low friction at high vacuum and high temperature as 200 degrees C. Also the transfer films on Steel balls can affect to reduce friction.