Tailoring the Properties of (TiZrHfV)B₂ High-Entropy Diboride via Elemental Concentration: A First-Principles Approach

Abstract

High entropy diboride ceramics (HEB) are prospective materials for thermal protection systems, and high temperature structural materials due to their excellent heat resistance, high temperature stability, super hardness, and wear resistance. Properties of high entropy ceramics can be enhanced by tuning the stoichiometry of the constituent elements. Therefore, the present study uses first principles methods to provide a comprehensive evaluation of enhancement in structural, mechanical, and thermal properties of Ti, Hf, Zr, and V based high entropy diborides (HEB) by tuning atomic fractions of constituent metals. Total 18 HEB compositions were evaluated with varied atomic fractions of Ti, Zr, Hf and V. The thermodynamic phase stability parameters demonstrated that all the 18 HEB compositions tend to form single phase solid solutions. The occupied and bonding state analysis confirmed the structural stability of the HEBs. High Vickers’ hardness values of 35.72 ‒ 43.22 GPa suggests the super-hardness properties of the studied HEBs. HEBs with highest Ti and Hf concentrations (Ti0.42Zr0.17Hf0.25V0.17B2 and Ti0.42Zr0.25Hf0.25V0.08B2) showed highest hardness of 43.22 GPa and 42.75 GPa respectively. HEBs having low concentrations of Ti and high concentration of V showed lowest hardness (Ti0.08Zr0.25Hf0.25V0.42B2 and Ti0.17Zr0.25Hf0.25V0.33B2). Except Ti0.08Zr0.33Hf0.33V0.25B2 (Tm=3465 K), all non-equiatomic compositions displayed higher melting points than the equiatomic Ti0.25Zr0.25Hf0.25V0.25B2 (Tm=3488 K). Ti0.33Zr0.25Hf0.25V0.17B2 exhibited highest melting point of 3934 K. HEB having highest Ti concentration and lowest V concentration (Ti0.42Zr0.25Hf0.25V0.08B2) exhibited remarkable elastic rigidity and superior resistance to shape and volume deformation due to highest Young's, shear, and bulk moduli. The findings conclusively accentuate that compositional complexity of HEBs govern the mechanical, thermodynamic, and structural stability. The results also highlight the significance of computational studies in evaluating structure-property relationships to identify optimum HEB composition for targeted applications. The present study also emphasizes the need for exploring non-equiatomic compositions as they have potential to exhibit superior properties compared to the widely explored equiatomic compositions.