Abstract
Nano-oxide precipitates in a modern nanostructured ferritic alloy were investigated after extreme thermomechanical processing into a thin-walled tube geometry. It was found that the morphology of the precipitates changed from spherical to rod-shaped, with some increasing to aspect ratios of up to 9, despite the precipitate volume fraction (0.3%) and number density (> 1023 m−3) of precipitates remaining unchanged. High-resolution electron microscopy showed that the precipitates likely remained coherent with the Fe-matrix, while atom probe tomography confirmed that the precipitate compositions remained unaffected by the transformation. The morphological change was attributed to the shearable nature of the (Y,Ti,O)-rich precipitates, indicating they should be considered as “soft” obstacles to dislocation motion. The elongation was most pronounced in larger (>5 nm) precipitates, which may be caused by preferential dissolution of the smallest (1–3 nm) precipitates followed by the competition between re-precipitation and solute diffusion to larger precipitates during recovery heat treatments.
| Original language | English |
|---|---|
| Pages (from-to) | 922-931 |
| Number of pages | 10 |
| Journal | Acta Materialia |
| Volume | 200 |
| DOIs | |
| State | Published - Nov 2020 |
Funding
This work was supported by US Department of Energy , Office of Nuclear Energy, Advanced Fuels Campaign. A part of the microscopy research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility, and part of the microscopy was supported by the Office of Nuclear Energy, Fuel Cycle R&D Program and the Nuclear Science User Facilities. The author would like to thank Dorothy Coffey, James Burns, Jonathan Poplawsky, and Anoop Kini for assistance with the experimental work (assistance in preparing TEM and APT specimens) and Chad Parish and Rachel Seibert for comments on the manuscript. This work was supported by US Department of Energy, Office of Nuclear Energy, Advanced Fuels Campaign. A part of the microscopy research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility, and part of the microscopy was supported by the Office of Nuclear Energy, Fuel Cycle R&D Program and the Nuclear Science User Facilities. The author would like to thank Dorothy Coffey, James Burns, Jonathan Poplawsky, and Anoop Kini for assistance with the experimental work (assistance in preparing TEM and APT specimens) and Chad Parish and Rachel Seibert for comments on the manuscript.
Keywords
- Atom probe tomography (APT)
- Oxide dispersion–strengthened (ODS) alloys
- Precipitation
- Scanning transmission electron microscopy (S/TEM)