Synchrotron radiation investigations of microstructural evolutions of ODS steels and Zr-based alloys irradiated in nuclear reactors

Abstract

Abstract

The Mechanism of Radiation-Induced Nanocluster Evolution in Oxide Dispersion Strengthened and Ferritic-Martensitic Alloys

“…In both cases, average nanocluster size decreases while number density increases with dose above 1 dpa. The inverse relationship between size and number density has been observed elsewhere in literature [72,84,88,101], and is akin to inverse Ostwald ripening, which has been previously described in the context of ion beaminduced size refinement of embedded metallic nanoparticles [58,75,77,78,205], an emerging research area in nanoelectronics. Through inverse Ostwald ripening, smaller nanoclusters nucleate and grow at the expense of larger nanoclusters, due to the competing mechanisms of ballistic dissolution and diffusion-driven nanocluster growth, with the net result being a reduced average cluster size and increased number density.…”

“…2.13 is proportional to φ), where φ is the irradiation flux [59,69]. Conversely, other irradiation studies have shown evidence of reduction in average nanocluster size [70] and even of haloing [71,72], in which a high density of smaller nanoclusters nucleate around, and at the expense of, larger nanoclusters. This trend is fundamentally the opposite that of Ostwald ripening, and is commonly referred to as inverse Ostwald ripening (Section 2.4.5).…”

“…The coherency between the oxide nanocluster and matrix interface is considered a critical attribute of nanoclusters, as this will directly influence the effectiveness of the interface as a sink for defects [101,110,111,125]. Using high resolution transmission electron microscopy (HRTEM), several studies have found oxides to generally be coherent with the matrix [69,79,88,96,128].…”

“…Oxide nanoclusters have been observed to amorphize to varying degrees upon irradiation [59,92,97,101,103,104,108,109,135]. The extent of amorphization is attributed to three factors: 1) the structure of the oxides, 2) irradiation dose, and 3) irradiation temperature [109,135].…”

“…A few other techniques including x-ray absorption fine structure (XFAS) spectroscopy [101], glancing-incident angle x-ray diffraction (GIXRD) [99] and small angle neutron scattering (SANS) [82,100,164,165] For this thesis, the primary focus is the characterization of nanocluster morphology (size and number density) and its evolution as a result of irradiation. Bright field images of the oxide clusters in Fe-9%Cr ODS were also obtained in TEM by reviewing areas having low dislocation contrast, allowing the z-contrast of the clusters to be more visibly prominent.…”