Extensive nanoprecipitate morphology transformation in a nanostructured ferritic alloy due to extreme thermomechanical processing. (November 2020)

• Record Type: Journal Article
• Authors: Massey, Caleb P.; Hoelzer, David T.; Unocic, Kinga A.; Osetskiy, Yury N.; Edmondson, Philip D.; Gault, Baptiste; Zinkle, Steven J.; Terrani, Kurt A.
• Is Part Of: Acta materialia. Volume 200(2020)
• Page Start: 922
• Page End: 931
• Publication Date: 2020-11
• Subjects: Atom probe tomography (APT) -- Scanning transmission electron microscopy (S/TEM) -- Precipitation -- Oxide dispersion–strengthened (ODS) alloys; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2020.09.020
• Languages: English
• ISSNs: 1359-6454

Abstract

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 (> 10 23 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. Graphical abstract: Image, graphical abstract