基于Miedema模型和Toop模型的Al-Si-Er合金热力学参数计算

运用Miedema混合焓模型计算了Al-Er、Si-Er和Al-Si二元合金的部分热力学性质，选择Er为非对称性组元，在此基础上结合Toop模型计算出Al-Si-Er三元合金的混合焓、过剩熵与过剩自由能。结果表明，Al-Si-Er三元合金的混合焓、过剩熵与过剩自由能在整个浓度范围内均为负值，在富Er和贫Er区域各热力学参数变化趋势较大。通过计算Al、Si和Er 3种组元的偏摩尔过剩自由能得到Al-Si-Er三元合金各组元的等活度值曲线。曲线显示各组元随着摩尔分数的减少其活度值都急剧减小，在三元系成分三角形的中心部分Al、Si和Er的活度值都很小，这表明Al、Si和Er 3种组元之间存在很强的相互作用，易形成三元金属间化合物，这一结论与Al-Si-Er三元相图的实际情况相符合。

Calculation of Thermodynamic Parameters of Al-Si-Er Alloy Based on Miedema Model and Toop Model

Based on the Miedema formation enthalpy model, thermodynamic properties of Al-Er, Si-Er and Al-Si binary alloy were calculated, and Er was chosen as the asymmetric component in asymmetric model. Combining with Toop model, the enthalpies of formation, excess entropies and excess free-energy of Al-Si-Er ternary alloy were calculated. The results show that the enthalpies of formation, excess entropies and excess free-energy of the ternary alloy are all negative in the whole content range, and their values change obviously in the zone where the content of Er is high or low. Through calculating partial molar excess Gibbs energy of three components (Al, Si, Er), isoactivity curves of all components of Al-Si-Er ternary alloy at 1073 K were obtained. The curves show that these values of all components of Al-Si-Er ternary alloy decreased dramatically along with the diminishing of molar fraction, and these activity values of Al, Si and Er were slight in the central zone of composition triangle of ternary system. It indicates that there was strong interaction among the three components, and they were easy to form ternary intermetalic compound, which coincided with the ternary phase diagram.