First-principles study on high-temperature thermodynamic and mechanical properties of intermetallic phases in Mg–RE alloys (RE = Tb, Dy, Ho)

The thermodynamic and elastic moduli of secondary phases play a crucial role in governing the high-temperature mechanical performance of magnesium alloys. This strengthening mechanism originates from high-modulus precipitates that remain fine and uniformly dispersed at elevated temperatures, persistently pinning dislocations and impeding their motion while maintaining microstructural stability. However, technical challenges have significantly limited experimental characterization of elastic moduli. This study investigates the thermodynamic and mechanical properties of Mg–RE (RE = Tb, Dy, Ho) intermetallic phases via first-principles calculations using quasi-harmonic and quasi-static approximations. Specifically, heat capacity, thermal expansion, and elastic moduli are calculated from 0 to 850 K. Results reveal thermal expansion coefficients increase monotonically with temperature, with MgHo showing the lowest thermal expansion. Heat capacity follows classical Dulong-Petit behavior at high temperatures, with all phases approaching theoretical limits. As temperature rises, elastic moduli generally decrease. Among the studied systems, MgDy retains superior mechanical properties, exhibiting the highest Young’s modulus retention at elevated temperatures and minimal shear modulus degradation across the investigated range. In contrast, MgHo displays the highest bulk moduli throughout, indicating excellent volumetric stability under thermal loading.