Miscible chemical ordering in Ti-Cr-Mo quinary system by solid solution of Mo2Ti2AlC3 and Cr2.5Ti1.5AlC3 o-MAXs

Out-of-plane ordering is promising for separately adjusting the heterodesmic chemical bonding inside the MAX phase thus tuning their properties, while constructing the out-of-plane ordered-MAX (o-MAX) is still a challenge. In this work, a strategy towards o-MAX by solid solutions of two existing o-MAXs is verified, i.e., Cr_2.5Ti_1.5AlC₃ and Mo₂Ti₂AlC₃, with controllable stoichiometric ratios (1:2, 1:1, and 2:1). A miscible chemical ordering is observed in three Ti-Cr-Mo quinary MAXs, which inherits the out-of-plane ordering from both parental o-MAXs. Meanwhile, through density functional theory (DFT) calculations, the electronic structure and bonding states inside the quinary o-MAXs are analyzed. Based on the calculations, anisotropic and improved mechanical properties are predicted, which agree with the experimental observed high compressive strength and tunable capacity of energy dissipation. The present work proves a promising way for synthesizing multicomponent o-MAXs.