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

Abstract

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.

Keywords:

• STEM
• titanium alloys
• phase transformations
• ordered intermetallics
• Ti₂Nb

Acknowledgements

The authors gratefully acknowledge useful discussions with Y. Hanlumyuang.

Additional information

Funding

Funding. The authors acknowledge the support of the National Science Foundation [grant number DMR-0706554], [grant number DMR-1105081]; Toyota Research and Development. All HRSTEM imaging and image processing were performed at the National Center for Electron Microscopy which is supported by the Office of Science, Office of Basic Energy Sciences of the US Department of Energy under Contract No. DE-AC02-05CH11231. VRR acknowledges supports of Nanotechnology and Functional Materials Center at faculty of Technology and Metallurgy, University of Belgrade, and from the Ministry of Education and Science of the Republic of Serbia, project No. 172054.