Vacancy-induced omega phase fluctuations in body-centered cubic Ti and Zr

S Issa and G Treglia and H Amara and C Varvenne, COMPUTATIONAL MATERIALS SCIENCE, 260, 114251 (2025).

DOI: 10.1016/j.commatsci.2025.114251

The precipitation of wphase in body-centered cubic (bcc) metastable Ti and Zr alloys can occur athermally, with a typical high density of homogeneously distributed wparticles. We propose in this work that vacancies can act as an important source of w-phase fluctuations in bcc Ti and Zr matrices, which are mechanically unstable at zero temperature but dynamically stabilized at finite T. Using ab initio calculations we highlight the similarities between the relaxation field of the vacancy in a bcc mechanically unstable matrix and the LA 2/3111 phonon mode, through a detailed analysis of the local atomic and electronic structure around the vacancy. Then, empirical potential simulations suggest a complex vacancy structure at finite temperature, alternating over time between standard cubic and linear w-like vacancy configurations. The linear, symmetry-broken, vacancy configuration involves the relaxation of many atoms, and is very close to the best structural model explaining the characteristic of the diffuse scattering distribution observed experimentally in many bcc Ti and Zr alloys. We therefore suggest that the nucleation of athermal w precipitates could occur heterogeneously on thermal vacancies. This scenario is consistent with the spatial homogeneity of athermal w particles seen in TEM images, and with the estimate of particle density; it also suggests a way to reduce this wprecipitation.

Return to Publications page