Cr5Si3B and Hf5Si3B: New MAB phases with anisotropic electrical, mechanical properties and damage tolerance

Through a combination of electronic structure, chemical bonding and mechanical property investigations, anisotropic electrical and mechanical properties, and damage tolerant ability of MAB phases Cr5Si3B and Hf5Si3B are predicted. The anisotropic electrical conductivity is due to the anisotropic distribution of Cr in Cr5Si3B and Hf in Hf5Si3B, which mainly contribute to the electrical conductivity. The anisotropic mechanical properties are underpinned by the anisotropic chemical bonding within the crystal structures of Cr5Si3B and Hf5Si3B. The high stiffness is determined by the strong covalent-ionic Cr1BCr1 and Cr1Si bonds in Cr5Si3B and the ionic-covalent Hf1BHf1 and SiB bonds in Hf5Si3B; while the low shear deformation resistance is attributed to the presence of metallic CrCr, HfHf and SiSi bond. Based on the low Pugh's ratio, Cr5Si3B and Hf5Si3B are predicted tolerant to damage. The possible cleavage plane is (0001) and the possible slip systems are <1 1¯00>|{11 2¯0} and <11 2¯0>|{0001} for both Cr5Si3B and Hf5Si3B.