难熔金属-低熔点金属Hf-Sb二元系局部相平衡研究

Study on local phase equilibrium of Hf-Sb binary system with refractory metal Hf and low melting point metal Sb

Hf-Sb二元系作为热电材料Half-Heusler合金的重要组元,因Hf(2227℃)与Sb(630℃)熔点相差1597℃,为Hf-Sb二元相图的测定带来极大困难。本研究采用螺纹密封在室温下制成固−液Hf-Sb二元扩散偶,在750~950℃五个温度点恒温退火14 d,获得了五组扩散偶样品,并对其进行了相平衡组织分析和成分测定。结果表明:经电子探针组织观察和成分分析,发现了严格计量比化合物HfSb_(2)、有溶解度范围的(HfSb)和固溶体相(Hf)三个平衡相,获得了相应温度下的Hf-Sb二元系的相平衡关系和共轭平衡成分。其中,化合物(HfSb)成分范围为48.41%~52.23%Sb,随着温度的增高,Hf-Sb互溶范围有扩大趋势;化合物HfSb_(2)高温下不稳定,在900℃以上发生偏晶分解。

As an important component of thermoelectric Half-Heusler alloys,the melting point difference between Hf(2227℃)and Sb(630℃)is 1597℃,which makes it very difficult to build the Hf-Sb binary phase diagram.In this work,the solid-liquid Hf-Sb binary diffusion couples were fabricated by screw seal at room temperature.After annealing at five temperature points from 750℃to 950℃for 14 d,five groups of diffusion couple samples were obtained,and their phase equilibrium structure and composition were analyzed.The results show that three equilibrium phases,strictly stoichiometric compound HfSb_(2),(HfSb)with solubility range and solid solution(Hf),are found,the phase equilibrium relationship and the conjugate equilibrium compositions of Hf-Sb binary system at corresponding temperature were obtained by electron probe microanalysis(EPMA).The composition range of(HfSb)compound is 48.41%−52.23%Sb,the mutual solubility range of Hf-Sb tends to expand with the increase of temperature.The compound HfSb_(2) is unstable at high temperature and undergo monotectic decomposition above 900℃.