A study of the distribution of Nb and Fe in two-phase Zr-2.5 wt% Nb alloys

An analytical transmission electron microscopy study of two-phase (α-β) structures in a Zr-2.5 wt% Nb pressure tube alloy was used to follow the distribution of Nb and Fe as a function of alloy heat treatment and tube processing. The presence of Fe (≅ 0.1 wt%) modifies the (α-β) phase equilibria as Fe is a β-stabilizing element. Significant segregation of Fe to βZr and βNb structures was measured and shown to be in good agreement with the prediction of a graphical method used to find the phase boundaries in the ternary diagram (at the Zr corner) from the binary data. Segregation of Fe at α-α subboundaries was found in the as-extruded and cold-worked plus stress-relieved treatments. The Fe profiles, measured across subboundaries, indicated a strong segregation of Fe to the core or near-core regions of the dislocations comprising the boundary structure. (orig.)