Transformation of chemical ordering and configuration entropy in quaternary Cr <sub> <i>x</i> </sub>Ti <sub>0.75</sub>Mo <sub>0.75</sub>V <sub>1.5− <i>x</i> </sub>AlC <sub>2</sub> MAX system
Yaqing Xue, Hong Yu, Hongwei Liang, Xiaomei Wang, Lili Xue, Shiyao Lei, Conghui Meng, Long Wang, Cheng‐Feng Du
Abstract
Two new quaternary Cr<em><sub>x</sub></em>Ti<sub>0.75</sub>Mo<sub>0.75</sub>V<sub>1.5−<em>x</em></sub>AlC<sub>2</sub> (<em>x</em> = 1.25, 1) MAXs and Cr<sub>0.75</sub>Ti<sub>0.75</sub>Mo<sub>0.75</sub>V<sub>0.75</sub>AlC<sub>2</sub> are synthesized by hot pressing. Interestingly, an unprecedented transition in M-site atomic occupancy from out-of-plane order to solid solution is observed along with the composition variation, which also increases the configurational entropy from medium- to high-entropy. Through experimental observation and theoretical calculation, the influence of the atomic distribution on their properties is analyzed. Eventually, about 40% increment on the Vickers hardness than that of the Cr<sub>2</sub>TiAlC<sub>2</sub> and low thermal conductivities are detected from the three MAXs, which can be ascribed to the solid solution strengthening effects and the enhanced scattering of both electrons and phonons from the high-entropy structure.