Berlin 2012 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe

O: Fachverband Oberflächenphysik

O 67: Metal surfaces: Adsorption of H/O and inorganic molecules

O 67.9: Vortrag

Donnerstag, 29. März 2012, 12:30–12:45, MA 043

Exceptionally low friction of CrN/TiN multilayer coatings -- a combined experimental and theoretical study — •David Holec, Jörg Paulitsch, and Paul H. Mayrhofer — Department of Physical Metallurgy and Materials Testing, University of Leoben, Leoben, Austria

Recently we have have demonstrated that CrN/TiN multilayer coatings, deposited using the hybrid high power impulse magnetron sputtering (HIPIMS)/direct current magnetron sputtering (DCMS), exhibit extremely low friction coefficients below 0.1 when tested at room temperature and ambient air conditions. By performing dry-sliding tests in an atmosphere with reduced humidity we identified relative humidity of approximately 13% as the necessary condition for the friction to drop to values below 0.1. Density functional theory was used to study the properties of the CrN/TiN system. While the surface energy of the (100) surface is lower than that of (111) in TiN, the situation reverses in CrN. Subsequently we studied the binding energies of H and O atoms on the (100) surfaces. It has turned out that both atoms are weaker bonded on TiN than on CrN. Moreover, the barrier for surface diffusion of H on TiN is significantly lower (~0.5eV) than on CrN (~0.8eV), thus suggesting that H atoms are more mobile on TiN surfaces while stronger bonded on CrN surfaces. Based on both evidences we therefore speculate that the extraordinary low friction coefficient of the CrN/TiN multilayer may be related to accumulation of water molecules from humid air (creation of water droplets) on the CrN on the expense of the TiN surfaces, thus providing a bearing-like effect.