Theoretical investigation on the stability, mechanical and thermal properties of the newly discovered MAB phase Cr4AlB4

Abstract

The nanolaminated MAB phases have attracted great research interests in recent years due to their similarities to MAX phases, which display both metallic and ceramic-like properties. In the present work, a newly discovered MAB phase Cr4AlB4 was investigated by first principles calculations. Energy evaluations indicate that Cr4AlB4 can be synthetized in Al lean condition, which can further transform to Cr2AlB2 in Al rich condition. The full set of elastic properties and their dependences on temperature, ideal strengths under different tensile and shear deformations, and thermal expansions of Cr4AlB4 were predicted. The results reveal that the properties of Cr4AlB4 are dominated by the layered crystal structure and weak bonding nature between Al and Cr2B2 layers, including low elastic stiffness and large thermal expansion along [010] direction (the stacking direction of Al and Cr2B2 layers), low shear resistances in (010) plane, and preferentially cleavage along and/or shear in (010) plane. Therefore, it suggests that Cr4AlB4 displays similar mechanical properties to MAX phases, including readily machinable, thermal shock resistant, and damage tolerant. In combination with the fact that Cr, Al and B all can form dense oxides to protect the material from further oxidation, Cr4AlB4 is regarded as a promising high temperature ceramic.