Experimental Investigation And Thermodynamic Optimization Of The Nd-Sn Phase Diagram,and The Thermodynamic Optimization Of The Mg-Sn-Pr Ternary System

The CALculation of PHAse Diagram（CALPHAD method）based on a reasonable thermodynamic database is an efficient tool for new material design.Reliable and accurate phase diagram experimental data is a prerequisite for obtaining reasonable thermodynamic parameters.The Mg-Sn-RE system is regarded as a magnesium alloy system with good creep resistance.The phase diagram and reasonable thermodynamic parameters of the Mg-Sn-RE system play an important role in the design and development of novel high-strength magnesium alloys.In this paper,the phase equilibria of the boundary binary system Nd-Sn in the Mg-Sn-RE system is studied by combining experiments and thermodynamic optimization methods.The thermodynamic optimization of the Pr-Sn binary system and Mg-Sn-Pr ternary system have also been carried out,and the following research results were obtained:1.Experimental studies and thermodynamic optimization of the Nd-Sn phase diagram.The Nd-Sn phase diagram has been studied in the range of 20–67 at.%Sn by X-ray diffraction（XRD）,scanning electron microscope equipped with energy dispersive spectrometer（SEM-EDS）,and differential scanning calorimetric（DSC）.In addition to five known compounds:Nd₅Sn₃,Nd₅Sn₄,Nd₁₁Sn₁₀,Nd Sn and Nd₃Sn₅,three new compounds:Nd₃Sn,Nd₄Sn₅ and Nd₂Sn₃,have been identified in this range.Nd₃Sn,Nd₄Sn₅ and Nd₂Sn₃ were formed by the peritectic reaction at 1148℃,1169℃and 1146℃,respectively.While Nd₃Sn₅ was formed by the peritectic reaction at 1153℃and decomposed at1136℃.The Nd-Sn system was modeled using the CALPHAD approach based on the experimental data of this work,and all other available literature data.A complete thermodynamic description of the Nd-Sn system is obtained and extensive comparisons between calculated and experimental data are presented,indicating that almost every available experimental and theoretical data are fitted satisfactorily.2.Thermodynamic optimization of the Pr-Sn binary system by Calphad method.In this work,the phase diagram and thermodynamic experimental data of the Pr-Sn binary system were carefully reviewed.Based on reliable experimental literature data,the Pr-Sn The binary system is thermodynamically optimized,and the reasonable thermodynamic parameters of the Pr-Sn binary system are obtained.3.Thermodynamic optimization of the Mg-Sn-Pr ternary system by combining first-principles calculations and the CALPHAD method.Combining the thermodynamic parameters of the Pr-Sn binary system obtained in this work,and the thermodynamic parameters of the Mg-Pr and Mg-Sn binary systems from the literature,a thermodynamic database of the Mg-Sn-Pr ternary system was constructed.The formation enthalpy of two ternary compounds（τ₁ andτ₂）were calculated by first principles.Basing on these thermodynamic data and the equilibrium phase relationship of the Mg-Sn-Pr ternary system at 500℃determined by our group,the thermodynamic optimization of the Mg-Sn-Pr ternary system was carried out by CALPHAD method,and the optimization results were consistent with the experimental data.