Room temperature preparation of Ti₂AlC MAX-phase films using the powder aerosol deposition method

The MAX-phase Ti2AlC is interesting as a temperature-stable electrical contact material and, due to the formation of a protective alumina scale on the surface, also as an oxidation-resistant and self-healing coating. For the first time, the powder aerosol deposition method (PADM) is applied to prepare homogenous Ti2AlC-films directly from the raw powder at room temperature. Besides the material's microstructure, initial tests address the thermal stability and the electrical resistivity of PADM-Ti2AlC. μm-sized Ti2AlC-particles are deposited as adhesive, up to 20 μm thick and dense Ti2AlC-films on electrically insulating alumina or turbine-relevant titanium aluminides. The PADM-Ti2AlC films with an average roughness of about 1 μm exhibit a nanocrystalline microstructure and retain the phase composition of the applied powder. Initial results on the thermal stability of PADM-Ti2AlC in air up to 800 °C are promising: The film-integrity is preserved and light discolorations as well as slight film growth indicate oxide formation at the surface. Moderate thermal annealing of PADM-films is known to relax microstrain that origins from the high-energy particle impact and limits electrical conductivity. Accordingly, the resistivity of PADM-Ti2AlC is reduced by 68 % after annealing at 800 °C in nitrogen atmosphere. The final value of 6.8 μΩm of the nanocrystalline PADM-films is one order of magnitude above those of common thin-films. Electrical measurements as well as SEM images indicate the formation of surficial oxide during heat treatment in air.