Sputtering and Characterization of MAX-Phase Forming Cr–Al–C and Ti–Al–C Coatings and Their Application on γ-Based Titanium Aluminides

Abstract

MAX-phases are of increasing interest as coating material for high temperature applications due to their unique metallic as well as ceramic properties. Herein, the deposition of Cr2AlC and Ti3AlC2 or Ti2AlC MAX-phase forming coatings by magnetron sputtering is demonstrated. Using pure elemental targets, the manufacturing with a coating thickness of above 7 μm is established. The MAX-phase forming coatings are characterized by high-temperature X-ray diffraction (HT-XRD) measurements and provide a good oxidation behavior due to the development of protective thermally grown oxide layers. The performance of the MAX-phases is strongly depended on the substrate material and the accompanying interdiffusion processes. Therefore, the Ti–Al–C coating is favored for TiAl alloys due to the thermodynamic stability of the Ti2AlC MAX phase in particular in the presence of the γ-TiAl phase. An excellent oxidation behavior is confirmed up to 300 h at 850 °C due to the development of an alumina layer above a homogenous Ti2AlC phase coating. The Cr2AlC MAX-phase coating degrades after 100 h at 800 °C due to interdiffusion processes between coating and substrate and the accompanying development of carbides and nitride phases. Nevertheless, the oxidation resistance of the Cr–Al–C-coated TiAl alloy is given by the formation of the Ti2AlC MAX-phase.