Investigations of the Deuterium Permeability of As-Deposited and Oxidized Ti2AlN Coatings

Aluminum containing Mn+1AXn (MAX) phase materials have attracted increasing attention due to their corrosion resistance, a pronounced self-healing effect and promising diffusion barrier properties for hydrogen. We synthesized Ti2AlN coatings on ferritic steel substrates by physical vapor deposition of alternating Ti- and AlN-layers followed by thermal annealing. The microstructure developed a {0001}-texture with platelet-like shaped grains. To investigate the oxidation behavior, the samples were exposed to a temperature of 700 °C in a muffle furnace. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) depth profiles revealed the formation of oxide scales, which consisted mainly of dense and stable α-Al2O3. The oxide layer thickness increased with a time dependency of ~t1/4. Electron probe micro analysis (EPMA) scans revealed a diffusion of Al from the coating into the substrate. Steel membranes with as-deposited Ti2AlN and partially oxidized Ti2AlN coatings were used for permeation tests. The permeation of deuterium from the gas phase was measured in an ultra-high vacuum (UHV) permeation cell by mass spectrometry at temperatures of 30–400 °C. We obtained a permeation reduction factor (PRF) of 45 for a pure Ti2AlN coating and a PRF of ~3700 for the oxidized sample. Thus, protective coatings, which prevent hydrogen-induced corrosion, can be achieved by the proper design of Ti2AlN coatings with suitable oxide scale thicknesses

Microstructural investigations of polycrystalline Ti2AlN prepared by physical vapor deposition of Ti-AlN multilayers

Ti2AlN is a prominent ternary nitride and belongs to the class of nanolaminated Mn + 1AXn phase materials which combine metallic and ceramic properties. In this work we report on the successful synthesis of polycrystalline Ti2AlN thin films with a preferential (000l) orientation on a polycrystalline Al2O3 substrate by depositing multiple Ti-AlN double layers and applying a subsequent annealing step. Investigations with scanning electron microscopy (SEM), X-ray diffraction (XRD), electron back scatter diffraction (EBSD) and Raman spectroscopy reveal a successful transformation of the multilayer system into a polycrystalline and dense Ti2AlN coating with a thickness of 2.7 μm. The observed grains are plate-like shaped with an in-plane size of about 100 to 300 nm and a thickness of 30 to 60 nm. Furthermore EBSD measurements proof that these macroscopic grains have a preferred orientation in the [000l] direction. We believe that a (000l)-textured microstructure will lead to new applications for protective coatings on polycrystalline substrates