Ag-Sn-Zr三元系的热力学模拟和凝固显微组织

Thermodynamic modeling and solidified microstructure of Ag-Sn-Zr ternary system

采用关键实验和热力学模拟研究Ag–Sn–Zr三元系的相平衡。通过制备22个平衡合金,采用X射线衍射、扫描电子显微镜和能量色散X射线能谱测定Ag–Sn–Zr体系500、700和900℃的等温截面。通过制备8个铸态合金,研究合金的凝固行为。测定Zr、Sn和Ag在Ag–Sn、Ag–Zr和Sn–Zr体系中二元化合物的溶解度,未发现三元化合物存在。基于3个边际二元系的热力学描述及获得的相平衡数据,采用CALPHAD方法对Ag–Sn–Zr体系进行热力学优化,得到一套自洽的热力学参数。计算的等温截面与实验数据吻合较好。计算和构筑Ag–Sn–Zr体系在整个成分范围内的液相面投影图和希尔反应图,模拟Gulliver-Scheil非平衡条件下铸态合金的凝固行为。模拟结果与实验数据相一致。

The phase equilibria of the Ag−Sn−Zr ternary system were investigated over the whole composition via thermodynamic modeling coupled with key experiments.Twenty-two equilibrated alloys were prepared to determine the isothermal sections of the Ag−Sn−Zr system at 500,700 and 900°C by means of X-ray diffraction(XRD)and scanning electron microscopy with energy dispersive X-ray spectroscopy(SEM/EDS),and eight as-cast alloys were prepared to study the solidification behavior of the alloys.The solubilities of Zr,Sn and Ag in binary compounds of the Ag−Sn,Ag−Zr and Sn−Zr systems were measured.No ternary compound was found.Based on the thermodynamic descriptions of three constitutive binary systems as well as the experimental phase equilibria data obtained from the present work,thermodynamic assessment of the Ag−Sn−Zr system was carried out by the CALPHAD(Calculation of phase diagrams)approach.A set of thermodynamic parameters of the Ag−Sn−Zr system were obtained.The calculated isothermal sections are in good agreement with most of the reliable experimental data.The liquidus projection and reaction scheme of the Ag−Sn−Zr system over the whole composition were also presented.The solidification behaviors of as-cast alloys were simulated under Gulliver−Scheil non-equilibrium condition.The simulated and experimental results are consistent with each other.