An isothermal section of the Mg-Nd-Gd ternary system at 723 K was established by diffusion triple technique and electron probe microanalysis(EPMA). Mg3Gd and Mg3Nd form a continuous solid solution(Gd,Nd)3Mg, and a continuous solid solution(Gd,Nd)Mg is also formed between MgGd and MgNd. Mg7Gd, Mg5Gd, Mg2Gd, Mg41Nd5,(Gd,Nd)3Mg and(Gd,Nd)Mg are found in the ternary system. In these intermetallic phases, Mg7Gd has been reported to be a metastable phase in previous literatures. The solubilities of Mg, Gd and Nd in all the phases were detected. Furthermore, four three-phase equilibria, α(Mg)+Mg7Gd+ Mg41Nd5, Mg7Gd+Mg5Gd+Mg41Nd5, Mg5Gd+Mg41Nd5+(Gd,Nd)3Mg and(Gd,Nd)3Mg+(Gd,Nd)Mg+Mg2Gd, were identified in the isothermal section.采用三元扩散偶技术,利用电子探针成分分析,建立Mg-Nd-Gd三元系723 K的等温截面。Mg3Gd和Mg3Nd在三元系中形成连续固溶体(Gd,Nd)3Mg,MgGd和MgNd也形成连续固溶体(Gd,Nd)Mg。在三元系中出现的金属间化合物有Mg7Gd、Mg5Gd、Mg2Gd、Mg41Nd5、(Gd,Nd)3Mg和(Gd,Nd)Mg,其中Mg7Gd在以往的报道中认为是亚稳相。测量了Mg,、Gd和Nd在每相中的溶解度,发现在Mg-Nd-Gd三元系中存在4个三相平衡,它们分别是α(Mg)+Mg7Gd+Mg41Nd5,Mg7Gd+Mg5Gd+Mg41Nd5,Mg5Gd+Mg41Nd5+(Gd,Nd)3Mg和(Gd,Nd)3Mg+(Gd,Nd)Mg+Mg2Gd。
Like Al3Sc,the Al30Dy7Zr3compound has an L12structure,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-xZrx(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 agreementhas been reached between the calculated phase relations and the experimental results,which indicates that the current thermodynamic description is reasonable.
