Phase stability and mechanical properties of Nb-rich Nb-Mo-Al ternary system at elevated temperatures

Nb3Al base intermetallic compounds have become attractive as structural mat erials for ultra high temperature use. To improve high temperature strength , molybdenum (Mo) has been selected as the third element. Phase stability a nd fundamental mechanical properties of Nb-Al-Mo system have been investiga ted. Based on the phase and the microstructure observations in the various alloys, ternary phase diagrams have been calculated, applying a modified Th ermo-calc database. Mo addition stabilizes both the bcc and A15 phases in t he all composition range. The total solid solution of both bcc and A15 (Mo3 Al-Nb3Al) phases exists in the ternary phase diagram. The solution hardenin g effect of Mo atoms on A15 structure is clarified. The high temperature st rength of bcc-Nb alloys and Nb3Al intermetallic compounds is closely relate d to the phase stability of the Nb-Al-Mo ternary system. The Mo doped A15 s tructure exhibits the highest tensile strength in the Nb-Al-Mo ternary syst em at 1873 K. TEM observations revealed the role of dynamic re-crystallizat ion on the high temperature deformation process.