2026 Veverkova Zr15Nb Phase Transformations (1)

This study examines the phase transitions occurring during linear heating of the Zr15Nb alloy through a comprehensive, multi-technique methodology comprising in situ high-energy synchrotron X-ray diffraction (HEXRD), electrical resistance measurements, differential scanning calorimetry (DSC) and thermal expansion analysis, supplemented by ex situ transmission electron microscopy (TEM). The findings reveal a complex sequence of phase transformations and corresponding structural changes over a broad temperature range (from room temperature up to 800 °C). Two distinct body-centered cubic (bcc) β phases βZr and βNb with closely related lattice parameters are identified. At room temperature, the microstructure is characterized by a mixture of the metastable βZr + ωah phase. Upon heating, βZr progressively decomposes, giving rise to the formation of βNb. TEM observation revealed the cuboidal shape of the ωiso particles, resulting from the high lattice misfit between β and ω phase. The ω solvus temperature is determined to be approximately 555 °C, as evidenced by in situ HEXRD and abrupt changes in the alloy’s thermal and electrical properties. The growth of the α phase occurs after the dissolution of the ω phase, resulting in a pronounced increase in thermal expansion.