Phase Stability and Mechanical Properties of Nb-rich Nb-Mo-Al Ternary System at Elevated Temperatures

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Nb3Al base intermetallic compounds have become attractive as structural materials for ultra high temperature use. To improve high temperature strength, molybdenum (Mo) has been selected as the third element. Phase stability and fundamental mechanical properties of Nb-Al-Mo system have been investigated. Based on the phase and the microstructure observations in the various alloys, ternary phase diagrams have been calculated, applying a modified Thermo-calc database. Mo addition stabilizes both the bcc and A15 phases in the all composition range. The total solid solution of both bcc and A15 (Mo3Al-Nb3Al) phases exists in the ternary phase diagram. The solution hardening effect of Mo atoms on A15 structure is clarified. The high temperature strength of bcc-Nb alloys and Nb3Al intermetallic compounds is closely related to the phase stability of the Nb-Al-Mo ternary system. The Mo doped A15 structure exhibits the highest tensile strength in the Nb-Al-Mo ternary system at 1873 K. TEM observations revealed the role of dynamic re-crystallization on the high temperature deformation process.

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