Open Access

Fundamental mechanisms of friction and wear on the atomic scale were studied for different oxidation states of metallic glass surfaces. Bulk metallic glass was prepared by suction casting and characterised by X-Ray Diffraction and Dynamic Scanning Calorimetry. Surfaces were oxidised in controlled atmosphere and characterised by Electron Microscopy and X-ray Photoelectron Spectroscopy. Tribological experiments on the nano-scale were performed by Atomic Force Microscopy in ultra-high vacuum on a continuous load scale extending over three decades with different cantilevers. The oxide layer on Zr60Cu30Al10 consists mainly of an amorphous matrix of ZrO2 and Al2O3 with embedded crystalline Cu2O nanoparticles. Stick-slip friction was found on both, the metallic glass and on the oxidised surface. Comparative experiments revealed higher friction and wear after oxidation. Due to the surface roughness, friction is scale dependent on the oxidised surface. Sharp indenters were found to penetrate the oxide surface resulting in cutting wear. Indenters with larger contact areas initiate plowing and eventually delamination from the surface of metallic glass. On the clean metallic glass, plastic deformation was attributed to plowing mechanisms, independent on the contact area.