CALPHAD‐Guided Prediction and Interpretation of Phase Formation in Ta–Mo–Cr–Ti–Al Refractory High‐Entropy Alloys

This article presents new results on designing alloys with a disordered body‐centered‐cubic (BCC) A2 crystal structure within the refractory high‐entropy alloy (RHEA) system Ta–Mo–Cr–Ti–Al using equilibrium calculations, microstructure analysis, and differential scanning calorimetry (DSC). Thermodynamic calculation utilizing the calculation of the phase diagrams (CALPHAD) method is applied to predict alloy compositions with a dominant disordered A2 phase, which is considered favorable for enhancing room‐temperature ductility. Additionally, the reduced density and improved oxidation resistance are the target properties in the presented alloy design. DSC is used for the identification of the phase transitions taking place upon heating from the room temperature up to 1300 °C. Such phenomena as ordering, phase separation, and higher‐order phase transition occurring in two‐phase BCC RHEAs are discussed based on the results of microstructural characterization, X‐ray diffraction, thermal analysis, and selected area electron diffraction by transmission electron microscopy.