Liquid metal assistant self-propagating high-temperature synthesis of S-containing high-entropy MAX-phase materials

Due to their high-entropy effects, the high-entropy (HE) MAX-phase materials improve the comprehensive performance of MAX phases, opening up more possibilities for practical engineering applications. However, it is still challenging to obtain S-containing high-entropy MAX phases because of the high volatilization behavior of sulfur, suffering from issues such as high reaction temperature and long reaction time of traditional synthesis methods. This paper proposes a novel process named as liquid metal assistant self-propagating high-temperature synthesis (LMA-SHS) for efficient synthesis of high-purity S-containing high-entropy MAX-phase materials. Low-melting-point metal (Sn or In) has been introduced into the raw mixture and melted into a liquid phase during the early stage of the SHS reaction. By serving as a "binder" between transition metal atoms of the M-site due to the negative mixing enthalpy, this liquid phase can accelerate mass and heat transfer during the SHS process, ensuring a uniform solid solution of each element and realizing the synthesis of high-purity (TiNbVZr)2SC in an extremely short time. The synthesis method for high-entropy MAX-phase materials developed in this study, i.e., LMA-SHS, showing very short reaction time, low energy consumption, high yield, and low cost, has the promise to be a general energy- and resource-efficient route towards high-purity HE materials.