Paper SE+AS+NS+TR-MoM2
Mo₂BC Coatings for Metal Forming: Interactions Between Tool Surface and Aluminium by Theory and Experiment

Monday, October 19, 2015, 8:40 am, Room 212A

Low temperature growth strategies for Mo₂BC coatings are reviewed and initial theoretical and experimental data pertaining to the applicability of these coatings during forming of Al based alloys are discussed. A Mo₂BC(040) surface was exposed to O₂. The gas interaction was investigated using ab initio molecular dynamics and x-ray photoelectron spectroscopy (XPS) of air exposed surfaces. The calculations suggest that the most dominating physical mechanism is dissociative O₂ adsorption whereby Mo – O, O – Mo – O and Mo₂ – C – O bond formation is observed. To validate these results, Mo₂BC thin films were synthesised utilizing high power pulsed magnetron sputtering and air exposed surfaces were probed by XPS. MoO₂ and MoO₃ bond formation is observed and is consistent with here obtained ab initio data. Additionally, the interfacial interactions of O₂ exposed Mo₂BC(040) surface with an Al nonamer is studied with ab initio molecular dynamics to describe on the atomic scale the interaction between this surface and Al to mimic the interface present during cold forming processes of Al based alloys. The Al nonamer was disrupted and Al forms chemical bonds with oxygen contained in the O₂ exposed Mo₂BC(040) surface. Based on the comparison of here calculated adsorption energy with literature data, Al – Al bonds are shown to be significantly weaker than the Al – O bonds formed across the interface. Hence, Al-Al bond rupture is expected for a mechanically loaded interface. Therefore the adhesion of a residual Al on the native oxide layer is predicted. This is consistent with experimental observations. The data presented here may also be relevant for other oxygen containing surfaces in a contact with Al or Al based alloys for example during forming operations.