Ion Microprobe analysis of wear processes in ta-C coatings and contact areas on the counter bodies

Solid lubricants, like ta-C (hydrogen-free tetrahedral amorphous carbon) coatings, are an active area of research to replace liquid lubricants. This substitution is important because of the negative environmental impact and high material consumption of liquid lubricants. The influence of soft metal counter bodies on the unlubricated friction behaviour of hydrogen-free carbon coatings has mostly been studied for doped a-C coatings so far. All these studies show that low friction and wear can only be achieved if a tribolayer is formed to protect the contact. Even with a formed tribolayer, its composition is crucial for the frictional behaviour, making the investigation of this composition essential. A study currently underway aims to identify friction-induced surface changes like material loss of the coating, material transfer between the counter body and the coating, or the formation of a tribolayer.
The current work presents Ion Beam Analysis methods to deliver laterally and depth-resolved element analysis of the wear track on the coating and the contact area of the counter bodies (CB). In a first test, a ta-C coating has been subjected to pin-on-disk tests with various metallic and ceramic CBs. He and H ion microbeams have been used to scan over the tracks and the contact areas of the CBs. Both RBS and PIXE have been used and first results are presented. It is shown that, in this case, RBS yields the more useful information. Both, a 2 MeV He ion beam and a 3 MeV H ion beam provide valuable results. The advantages of each type of ion beam depend on the sample and the information needed. As shown in this work, RBS with a 2 MeV He ion beam is useful to determine the transfer layer of a (soft) metal CB to the ta-C coating, whereas 3 MeV H RBS can be used to determine the presence of C and O on the CB because of the increased non-Rutherford cross-sections for these elements.