Phase stability of the laves phase Cr₂Nb in a two-Phase Cr-Cr₂Nb alloy

The phase stability of the Laves phase Cr₂Nb in a two-phase Cr-Cr₂Nb alloy produced by arc-melting was investigated using X-ray diffraction, transmission electron microscopy and selected area electron diffraction. The experimental results indicated that the as-cast ingot was consisted of C15-Cr₂Nb and Cr phases; the intermediate C36 and high-temperature C14 modifications of Cr₂Nb, reported in literatures, were not detected in this study. These results, combined with a detailed analysis of the actual solidification conditions, revealed that the C14-Cr ₂Nb was a metastable rather than a stable high-temperature modification. Moreover, a kind of extremely fine lamellar structure was found to be randomly distributed in the eutectic cells, which may be formed by decomposition of the supersaturated C15-Cr₂Nb via a discontinuous precipitation reaction.