纳米尺度下Sm-Co合金体系中相组成与相稳定性的研究

建立了纳米晶合金相的热力学模型，可定量描述纳米尺度下合金体系中化合物相的热力学性质，并预测合金相的稳定性及其转变规律.利用该模型全面计算了纳米晶Sm-Co合金体系中各化合物相在不同晶粒尺寸下的摩尔吉布斯自由能随温度的变化关系，预测了纳米尺度下Sm-Co合金体系中各物相的相对稳定性及转变规律.模型预测结果示出，在室温附近，随着纳米晶粒尺寸的减小，某些纳米晶合金相的摩尔吉布斯自由能将由负值变为正值，预示着将向其他更稳定的纳米晶合金相转变，这是与传统粗晶材料中合金相的稳定性仅依赖于温度条件而完全不同的纳米晶合金 关键词： 纳米晶材料热力学 Sm-Co合金 相稳定性 相变

Phase configuration and stability in the nanocrystalline Sm-Co system

A thermodynamic model that describes the thermal properties of the compound phases in the nanocrystalline （NC） alloy systems has been developed，which provides quantitative predictions on the stabilities and transition features of different phases. By using the NC Sm-Co alloy system as an example，the temperature dependence of the mole Gibbs free energy of the NC alloy phases with different excess volumes in the nano-grain boundary regions were provided. Based on the model calculations，the relative stability of different phases and the phase transition rules in the NC Sm-Co system were analyzed. It was shown by the calculation results that near the room temperature，some of the NC alloy phases，whose mole Gibbs free energy values change from negative to positive due to the decrease of the nano-grain size，will transform into stable NC alloy phases. This is distinctly different from the phase transformation features in the coarse-grained alloy systems，whose thermodynamic properties are only dependent on the temperature. The experimental results on the phase configuration and the phase stability obtained from the prepared NC Sm-Co alloy confirmed the theoretical predictions of the present thermodynamic model.