On the structure and chemistry of complex oxide nanofeatures in nanostructured ferritic alloy U14YWT

The remarkable radiation damage resistance of nanostructured ferritic alloys (NFAs) is attributed to the large numbers of matrix nanofeatures (NFs) of various types, which can enhance the recombination of displacement defects and trap transmutant helium in fine scale bubbles. Characterizing the chemistry, crystallographic structure and orientation relationships of the NFs is critical to understanding how they enhance the radiation damage resistance of NFAs. Conventional and high-resolution transmission electron microscopy and energy-dispersive spectroscopy were used to characterize the various types of NF and larger oxide phases in a model 14Cr-3 W-0.4Ti-0.25Y(2)O(3) NFA (14YWT) hot isostatic pressed (HIP-ed) at 1150 degrees C. Large CrTiO3 precipitates (50-300 nm) and small diffracting NFs (<5 nm) were found in this alloy. One major new result is the observation of an additional type of nanofeature (10-50 nm), ortho-rhombic in structure, with a square center cross-section, which constitutes a new kind of Y-Ti-oxide phase with lattice parameters different from those of known Y and Ti complex oxides. The interfaces of these particles seem to be semicoherent, while manifesting a possible orientation relationship with the BCC matrix. The ratio of Y to Ti varies between <1 and 2 for these larger NFs.