Wear mechanisms of multilayer TiN/Ti/a-C:H coatings investigated by transmission electron microscopy technique

• Hybrid PLD allowed for the deposition of functional multilayer coatings.
• Wear on the multilayer coatings proceeded sequentially layer-by-layer.
• During the wear process some amount of carbon phase which was removed from the coating was transformed into graphite – the naturally formed lubricant.

Wear mechanisms of multilayer TiN/Ti/a-C:H coatings were investigated by transmission electron microscopy technique. Mechanical properties of the TiN/Ti/a-C:H multilayer coating were tested by a ball-on-disk. Microstructure of the coatings was analyzed after the mechanical treatment. Two types of wear mechanisms were discovered:-cracking-layer by layer remove and tribofilm formation.Cracking was performed by the ‘layers motion’ mechanism. After a one layer step movement they were fixed again.Tribofilm was built of two types of fractions. One was homogenous, the second one had layered structure. The qualitative chemical EDS analysis showed, that titanium oxide dominated in the homogenous area, while in the layered structure partial graphitization process was found. The graphite formation during the wear process, from the carbon phase presented in the coating, is a beneficial phenomenon due to the fact that graphite is a very good lubricant. The presence of the graphite phase in the tribofilm has been confirmed by the qualitative EDS chemical analysis, electron diffraction pattern and the high resolution technique.The article presents new ideas and techniques in materials science, especially in surface engineering, as well as in mechanics and mechanisms of wear of multilayer coatings.