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.

Key words: MAB phase, Cr₄AlB₄, First-principles, Mechanical properties, Thermal properties