Experimental Investigation and Thermodynamic Modeling of the Nd-Zr and the Mg-Nd-Zr Systems

The Nd-Zr phase diagram was first constructed through the investigation of nine Nd-Zr alloys by means of X-ray diffraction, scanning electron microscopy, electron probe microanalysis, and differential scanning calorimetry (DSC). Three diffusion couples and four alloys were then prepared and analyzed to investigate the phase relations at 773 K (500 °C) in the Mg-Nd-Zr system. No ternary compound was found at 773 K (500 °C). The solubility of αZr in the Mg-Nd intermetallics (Mg₄₁Nd₅, Mg₃Nd, and MgNd) was determined to be negligible. DSC measurement was performed on the Mg-Nd-Zr alloys to measure the phase transition temperatures. Based on the current experimental results, the Nd-Zr and Mg-Nd-Zr systems are evaluated through CALPHAD-type assessment. Comprehensive comparisons between the calculated and the measured phase diagrams show that the current thermodynamic description can satisfactorily reproduce the experimental results. Further study on the partial liquidus surface in Mg-rich region of the Mg-Nd-Zr system can offer a better understanding of the recent processing technique of creep-resistant magnesium alloys.