CalPhaD Coffee Lecture – From Heat Capacity to Gibbs Energy: Experimental Thermodynamics of High-Entropy Alloys

Understanding phase stability in complex alloys requires experimentally grounded thermodynamic data. In this lecture, I will present an experimental approach to derive temperature-dependent enthalpy, entropy, and Gibbs energy functions for single-phase high-entropy alloys, using the AlxCoCrFeNi system as a model. The approach combines heat-capacity measurements over a broad temperature range, high-temperature oxide-melt solution calorimetry for enthalpies of formation, physically based configurational entropy models, and comparisons with CALPHAD thermodynamic databases. Special attention will be given to challenges associated with metastable single-phase states, FCC/B2 ordering, magnetic contributions, and the use of experimental thermodynamics as a benchmark for database development. In the second part of the lecture, I will briefly introduce THERIS - the Thermal Research Institute of Israel at Ben-Gurion University of the Negev. THERIS was established to provide advanced capabilities for high-temperature materials characterization, including DSC/TGA, high-temperature calorimetry, oxide-melt solution calorimetry, dilatometry, thermal diffusivity and thermal conductivity measurements, controlled-atmosphere experiments, and characterization of ceramic and metallic materials under extreme conditions.

The lecture will show how integrated thermal analysis can transform measured heat-flow, heat-capacity, and calorimetric signals into thermodynamic insight. This connection among measurement, thermodynamic modeling, and materials design is essential for developing high-entropy alloys, ceramic materials, and other high-temperature materials for demanding technological applications.