Nb-Al Binary System: Reevaluation of the Solubility Limits of the (Nb), Nb3Al, Nb2Al and NbAl3 Phases at High Temperatures

In this work a re-investigation of the solubility limits of the (Nb), Nb3Al, Nb2Al and the Nb-rich side of the NbAl3 phases on the Nb-Al system is presented. Alloys in the binary fields ((Nb)+Nb3Al, Nb3Al+Nb2Al and Nb2Al+NbAl3) were arc-melted, and then equilibrated at 1000, 1200 and 1400 ºC. The phases were confirmed via X-ray powder diffractometry, and their compositions were determined via EPMA measurements. The results showed agreement with the literature concerning the solubility limits of (Nb), Nb3Al and NbAl3 phases, while important differences in the values were found for the Nb2Al phase. In addition, the lattice parameters of the Nb2Al phase were determined via Rietveld refinement. This new set of more accurate experimental information indicates that a thermodynamic reassessment is necessary to precisely describe this system.本研究针对Nb-Al体系中的铌（Nb）相、Nb3Al相、Nb2Al相以及NbAl3相的富铌侧溶解度极限开展了重新探究。制备了[(Nb)+Nb3Al、Nb3Al+Nb2Al及Nb2Al+NbAl3]二元相区内的合金，经电弧熔炼后分别在1000℃、1200℃及1400℃下进行平衡热处理。通过X射线粉末衍射法确认物相，并利用电子探针显微分析（EPMA）测定合金成分。研究结果显示，铌（Nb）、Nb3Al及NbAl3相的溶解度极限与已有文献报道相符，但Nb2Al相的溶解度极限数值与文献存在显著差异。此外，通过里特维尔德（Rietveld）精修法测定了Nb2Al相的晶格参数。这套更为精准的全新实验数据表明，需开展热力学重新评估以精准描述该Nb-Al合金体系。