HAADF imaging of the omega (ω) phase in a gum metal-related alloy

Nanosized precipitates have been observed in a Nb-lean gum metal-related alloy, Ti–20.0Nb–0.6Ta–1.7Zr–1.1O at.% (Ti–31.9Nb–2.0Ta–2.7Zr–0.3O wt.%) using probe-corrected high-resolution scanning transmission electron microscopy with a high-angle annular dark-field detector (HAADF). This characterization yields three distinct atomic motifs and STEM multislice simulations are semi-quantitatively used to verify that each motif can be attributed to the widely observed “athermal” omega phase. However, the presence of chemical ordering cannot be unambiguously ruled out in this system. Data presented here, demonstrate the complexity of interpreting HAADF images of multiphase, multicomponent alloys when complementary experimental data are unavailable.