Investigation of thermodynamic properties of high entropy (TaNbHfTiZr)C and (TaNbHfTiZr)N

Based on density functional theory calculation in conjunction with quasi-harmonic Debye-Gruneisen model, thermodynamic properties of (TaNbHfTiZr)C and (TaNbHfTiZr)N are studied, in which the chemical disorder is modeled with the special quasi-random structure. Thermodynamic entropies for both materials rise significantly due predominantly to vibrational contribution, and (TaNbHfTiZr)N is more stable at high temperatures because its entropy increment is more dramatic with increasing temperature. Although the high temperature softening effect is very similar, (TaNbHfTiZr)N is more beneficial for higher temperature applications because of the much larger bulk modulus. Thermal expansion coefficients for both materials increase first rapidly then slowly, and (TaNbHfTiZr)N is more slightly susceptible to temperature. For (TaNbHfTiZr)C and (TaNbHfTiZr)N, the heat capacities at constant volume and pressure demonstrate similar behaviors, being larger than metal high entropy HfNbTaTiZr. The present investigations provide helpful insights into the thermodynamic behaviors for both materials.