Thermodynamic modeling of the Hf-Ta-O system for the design of oxidation resistant HfC-TaC ceramics

• DOI: 10.1016/j.oceram.2024.100618
• Publication Date: 2024-06-07T17:41:52Z
• Authors: Rahim Zaman; Elizabeth J. Opila; Bi-Cheng Zhou
• Keywords: TP785-869; CALPHAD; High temperature oxidation; 0103 physical sciences; Thermodynamics; Clay industries. Ceramics. Glass; Ultra-high temperature ceramics; 01 natural sciences

An improved understanding of the oxidation resistance HfC-TaC ultra-high temperature ceramics (UHTCs) is developed through modeling phase equilibria in Hf-Ta-O system and HfO2-Ta2O5 isoplethal section. CALculation PHAse Diagrams (CALPHAD) thermodynamic models systems are conjunction with experimental data from literature first-principles calculations. Density functional theory (DFT) calculations accurately describe properties binary oxides predict cation disorder Hf(n-5)/2Ta2On. The ternary includes revised Hf–O existing Ta–O Hf–Ta systems. Hf(n-5)/2Ta2On oxide series modeled as three entropically stabilized solid solutions disordered sublattices that increase stability structure size. Hf4Ta2O13 considered a metastable based on present diagram, consistent lack supporting its stability. calculated diagrams improve upon prior ones optimal thermal at compositions between 3HfC-1TaC 4HfC-1TaC.