Evaluation of microstructures of Nb-Cr-Ti alloy system by means of analytical transmission electron microscopy

The phase diagram of Cr-rich portion of ternary Nb-Cr-Ti alloy system at 15 23 K is investigated by means of X-ray diffraction, optical microscopy and analytical transmission electron microscopy. In the region of single phase of (Nb, Ti)Cr-2 intermetallics, Laves phase s hows C36 dihexagonal structure in the Nb concentration between 0 mol%Nb and 4 mol%Nb. In the range of the Nb concentration more than 12 mol%Nb, Laves phase shows C15 face centered cubic structure. On the other hand, the regio n of duplex structure consisting of C36 and C15 phase is within the range o f the Nb concentration between 4 mol%Nb and 12 mol%Nb. The solubility limit of Nb in Cr solid solution is as small as less than 0.5 mol%Nb. The maximu m solubility limit of Cr in Laves phase equilibrated with Cr-b.c.c. solid s olution is in a range of about 67 similar to 69 mol%Cr depending on a conte nt of Nb and Ti elements. The eutectic path on the Cr-rich portion of the t ernary Nb-Cr-Ti alloy system lies in the Cr concentration line between 75 m ol%Cr and 80 mol%Cr, and ends at the point of Nb concentration between 10 m ol%Nb and 15 mol%Nb.