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

Fu-Zhi Dai¹，Haiming Zhang^1,2，Huimin Xiang¹，Yanchun Zhou¹

1. Science and Technology on Advanced Functional Composite Laboratory, Aerospace Research Institute of Materials & Processing Technology2. School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University

摘 要：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.

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