Computational and experimental investigation of non-equimolar high-entropy diborides: structural, mechanical, and thermodynamic insights

This work presents the design, modeling, and experimental investigation of high-entropy diboride ceramics based on (TiZrHfNbTa)B2 with varying nonequimolar compositions. The study aims to understand the impact of different atomic ratios on the structural, energetic, and mechanical properties of high-entropy boride systems. Density Functional Theory (DFT) calculations were performed using VASP with structural disorder modeled via the Special Quasirandom Structures (SQS) approach. Key parameters, such as formation energy, and vacancy formation energy were evaluated to identify the most stable compositions. Experimentally, three selected non-equimolar compositions were synthesized using boro/carbothermal reduction followed by Spark Plasma Sintering (SPS) at 1800–2000 °C [1]. Microstructural analysis was conducted using TEM and SEM, and mechanical properties—including hardness, Young’s modulus, and wear resistance—were assessed via nanoindentation and tribological testing. The combined theoretical and experimental results offer insight into the structure– property relationships of high-entropy diborides and support their potential application in extreme environments.