Phase and microstructure evolution patterns at combustion synthesis of high-entropy M2AlC (M=Ti/Ta/V/Nb/Cr) MAX phase

High-entropy (HE) MAX phases represent an emerging family of multi-constituent solid solutions that provide large compositional variations and, therefore, a wide variety of properties. Here, we report the experimental realization of M 2 AlC (M=Ti/Ta/V/Nb/Cr) MAX phase by an energy-efficient self-propagating high-temperature synthesis, which enables facile scalability to an environmentally friendly industrial production. The HE-MAX phase was developed according to crystal size, electronegativity, and valence electron concentration of corresponding metals required to form a substitutional single-phase material. Variations in initial mixture composition, inert gas pressure, additive amount and sample diameter played a decisive role in HE-MAX formation. The combustion of the stoichiometric mixture favors the formation of the HE-carbide. Deviation from the stoichiometry has resulted in the formation of 211 and/or 413 type HE-MAX phases. Fine-tuning the aluminum and carbon content in the initial mixture, facilitated the formation of a layered structure, characteristic of MAX phases. DSC/TG analysis proved an enhanced oxidation resistance of HE-MAX phases, which outperforms conventional MAX phases and several previously studied HE-MAX phases.