Analysis on Phase Stability and Mechanical Property of Newly-discovered Ternary Layered Boride Cr4AlB4
(2.Beijing Power Machinery Research Institute, Beijing, China 100074)
【Abstract】As newly-discovered member of the MAB phases, Cr4AlB4, has much potential for high-temperature structural applications due to possible formation of a protective oxide scale. By use of “linear optimization procedure” and theoretical model of “bond stiffness” based on first-principle calculations, the phase stability and mechanical behavior of Cr4AlB4 were investigated. No imaginary frequencies in phonon dispersion indicate the intrinsic stability. The lower energy as compared with the set of other competing phases also shows the thermodynamic stability. Based on the quantificationally calculated bond stiffness by use of the model of “bond stiffness”, strong covalent bonding is present between Cr and B atoms as well as between B and B atoms, while the Cr-Al (625 GPa) and B-Al (574 GPa) bonds are relatively weak. It follows that Cr4AlB4 can be described as the layered structure of strong covalently bonded Cr-B blocks interleaved by Al atomic planes where the bonding is relatively weak, similar to the well-known MAX phases. This demonstrates the similar damage tolerance and fracture toughness of Cr4AlB4 with the MAX phases.
【Keywords】 MAB phases; density functional theory; phase stability; mechanical property;
(Translated by LI ZP)
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