Sequence of phase transformations in metastable ? Zr-12Nb alloy studied in situ by HEXRD and complementary techniques

Phase transformations in a metastable beta Zr-12Nb alloy were investigated by high-energy X-ray diffraction (HEXRD) measured simultaneously with thermal expansion in situ during linear heating from room temperature to 800 degrees C. Complementary in-situ methods of elec-trical resistance and differential scanning calorimetry, which were performed using the same heating conditions as in the HEXRD experiment, provided additional information on the transformation sequence occurring in the Zr-12Nb alloy. Two bcc phases with a different lattice parameter, l3Zr and l3Nb, were observed in the investigated temperature range and identified using the phase diagram of the Zr-Nb system. In the initial solution-treated condition, metastable l3Zr phase and athermal u particles are present in the material. At about 300 degrees C, Nb-rich l3Nb phase starts to form in the material and the original l3Zr phase gradually disappears. Ex-situ observations of the microstructure using transmission elec-tron microscopy revealed a cuboidal shape of the u particles, which is related to a relatively large misfit between the u and l3 phases. At 560 degrees C, u solvus was observed, identified by an abrupt dissolution of u particles which was followed by growth of the a phase.(c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).