Investigation of the Pressure Dependent Physical Properties of MAX Phase Ti2AlX (X = B, C, and N) Compounds: A First-Principles Study

The physical properties and their pressure dependence of recently synthesized Ti2AlX (X = B, C, and N) MAX phases are investigated for the very first-time applying density functional theory (DFT). The optimized lattice parameters are in good agreement with the existing literature. The metallic character of the phases is supported by the Fermi level overlap of the conduction band and valence band. Structural parameters of competing phases, elastic constants, and phonon calculations revealed that all three compounds are structurally, mechanically, and dynamically stable under pressure. The materials are brittle in nature at 0 GPa and start exhibiting ductility at around 8 GPa, confirmed by both Pugh's and Poisson's ratios. All three compounds possess good level of hardness. The compounds have moderate machinability. The Debye temperature, phonon thermal conductivity, and melting temperature are moderate; with the highest value observed for Ti2AlN. The lattice thermal conductivity decreases with increasing pressure (up to 10 GPa) and temperature (up to 1500 K). Directional anisotropies in mechanical, optical, and thermal features are at moderate level for all three MAX phases. All the compounds under study exhibit potential as promising TBC (thermal barrier coating) materials. They are also suitable for optical applications.