Thermodynamic assessment of the Al–Dy, Dy–Zr and Al–Dy–Zr systems

Abstract

Like Al3Sc, the Al30Dy7Zr3 compound has an L12 structure, implying that it could probably be used to improve the strength of aluminum alloys at elevated temperatures. Thus, it is extremely important to understand the phase relations of the Al–Dy–Zr system in the Al-rich corner. Firstly, the phase diagram of the Al–Dy binary system was re-assessed with the C15_Laves phase treated as a stoichiometric compound. Then, using the special quasirandom structure containing 16 atoms (SQS_16) to simulate Dy1−x Zr x (x = 0.25, 0.5, and 0.75) hcp_A3 solid solutions, their enthalpies of mixing at 0 K were calculated by the first-principles method. Based on these results and the evaluated phase diagram in literature, the Dy–Zr binary system was optimized thermodynamically. Integrating the thermodynamic descriptions of the three constituent binary systems, the phase diagram of the Al–Dy–Zr ternary system in the Al-rich corner was optimized finally by coupling the first-principles calculation with the CALculation of PHAse Diagram method. A good agreement has been reached between the calculated phase relations and the experimental results, which indicates that the current thermodynamic description is reasonable.