Surface modification of 9Cr18 bearing steels by a metal and carbon co-plasma immersion ion implantation

In the aerospace industry, 9Cr18 martensitic stainless steel (AISI 440) is commonly used as a bearing material. Because of its ability to rapidly treat irregular industrial components, plasma immersion ion implantation (PIII) is an effective method to improve the wear resistance of 9Cr18 precision bearings and prolong their working lifetime. Vacuum arc plasma sources provide a good means of introducing metal ions into the bearing steel to create a special surface to enhance its surface properties. In this work, tungsten and titanium PIII was performed on 9Cr18 bearing steel using a vacuum arc plasma source, followed by carbon PIII using acetylene (C2H2) plasma, without breaking the vacuum. The surface properties were evaluated by measuring the microhardness, wear properties and friction coefficient, as well as the elemental depth profiles and chemical composition of the modified layer. It was found that the microhardness of the treated samples was much higher. The tribological characteristics were also significantly improved, as demonstrated by the reduced friction coefficient and wear track width. This improvement can be attributed to the diamond-like-carbon (DLC) surface layer, as well as favorable ion mixing caused by the implanted metal ions.