ALKALI-Mg METAL INCORPORATED 211-MAX COMPOUNDS: Hf2MgY (Y=B, C, N)

211-MAX phases are an important material family which is widely considered, because they form a bridge between physical properties of metals and ceramics [1]. They have wide range of physical properties such as most readily machinable, high efficiency engines, damage tolerant thermal systems, wear and corrosion protection, good electric and thermal conductivity [2, 3] . In this study, to reveal the effects of the alkali and light elements especially boron on the actual properties of 211-MAX phases, the structural, electronic, mechanical and dynamic properties of alkali metal (Mg)-incorporated Hf2MgY, Y= B, C, and N compounds with nanolaminated Cr2AlC-type structure (see Fig.) have been investigated by CASTEP based on firstprinciples density functional plane-wave pseudopotential calculations within generalized gradient approximation. From calculated formation enthalpies, all compounds are thermodynamically stable, and they have metallic behavior. From calculated elastic constants and phonon dispersion curves, it is shown that all compounds are mechanically stable, and Y=C, and N-incorporated compounds are dynamically stable. Boron-incorporated one is dynamically unstable due to the negative frequency around the Γ. At the same time, related mechanical properties such as bulk and shear moduli are calculated, and anisotropic properties are investigated. It is shown that Hf2MgN has higher mechanical properties and lower anisotropic character. For further mechanical characterization, hardnesses of the compounds are determined theoretically