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Silicon (Si) self-diffusivity in a Si nanopillar under dry oxidation was quantitatively evaluated by atom probe tomography of Si isotope heterostructure interfaces. Dry oxidation of a nanopillar with 200 nm diameter at 920 °C for 4 h revealed that the Si self-diffusivity was the same as the one measured for the standard planar oxidation despite the fact that the diffusion region probed in the pillar was surrounded by approximately seven times more oxidation interface areas than the simple planar oxidation case. This finding can be understood by considering the large diffusion length of ∼300 μm of the interstitials for our thermal oxidation condition. The excess interstitials injected by the pillar oxidation as well as those injected by the oxidation of the base (100) plane can easily diffuse through the sample, including interiors of the pillars, making the concentration of the excess interstitials practically equal to those injected for the (100) planar oxidation case. [ABSTRACT FROM AUTHOR]

Atom probe tomography (APT) and transmission electron microscopy (TEM)/scanning transmission electron microscopy (STEM) have been used correlatively to explore atomic-scale local structure and chemistry of the exactly same area in the vicinity of growth front of a long-period stacking ordered (LPSO) phase in a ternary Mg–Al–Gd alloy. It is proved for the first time that enrichment of Gd atoms in four consecutive (0001) atomic layers precedes enrichment of Al atoms so that the formation of Al6Gd8 clusters occurs only after sufficient Al atoms to form Al6Gd8 clusters diffuse into the relevant portions. Lateral growth of the LPSO phase is found to occur by 'ledge' mechanism with the growth habit plane either {1 1 ¯ 00} or {11 2 ¯ 0} planes. The motion of ledges that give rise to lateral growth of the LPSO phase is considered to be controlled by diffusion of Al atoms. [ABSTRACT FROM AUTHOR]

We have investigated a post-annealing effect on microscopic structural changes of kink boundaries (KBs), which have been initially introduced by a hot-extrusion of an Mg-Zn-Y alloy containing long period stacking/order (LPSO) phase, based on scanning transmission electron microscopy (STEM) and atom-probe tomography (APT). STEM observations show that most of the KBs appear to be segmented into several submicron-scale, each of which is composed of arrays of extended basal (a -) dislocations that are geometrically necessary to account for the LPSO crystalline rotations. Atomic-scale STEM/APT observations reveal significant reconstructions of these extended dislocation-core structures, which occur at the solute-enriched face-centered cubic layers in the LPSO structures and forms local hexagonal close-packed Mg region with distinct solute depletions. These recovery-like features indeed enhance the thermal stability of the KBs, and the corresponding driving force can be reasonably described according to disclinations, whose elastic energy is defined by crystal rotations and the relevant dipole distances. • Microscopic structures of kink boundaries in unique long-period structured Mg-Zn-Y alloys have been investigated. • Microscopic segmentations of kink boundaries have been promoted during the post-annealing of the hot-extruded specimen. • Dislocation-core structures at kink boundaries have been significantly reconstructed with distinct solute redistributions. • Driving force to promote the observed recovery features can be reasonably described according to disclinations. [ABSTRACT FROM AUTHOR]

To clarify the irradiation hardening behavior of neutron-irradiated tungsten(W), the formation behavior of rhenium(Re)-enriched cluster and W-Re precipitation with displacement damage in fission reactors environment was investigated by the atom probe tomography (APT) technique, and the results obtained by APT and microstructural observation by transmission electron microscopy (TEM) were compared. Neutron-irradiated pure W and W-10Re alloys were used for the analysis. These samples were irradiated to 0.96 dpa at 538 °C in a fast experimental reactor Joyo, and irradiated to 0.90 dpa at 500 °C in a mixed spectrum reactor HFIR. The chemical compositions of the matrix, Re clusters, and precipitates were determined by the AP analysis. The Joyo-irradiated samples contained lower levels of transmuted Re and Os, while the HFIR-irradiated samples contained higher levels of Re and Os. The Re-enriched clusters demonstrated characteristic spatial distribution related to defect cluster distribution in each irradiated specimen. [ABSTRACT FROM AUTHOR]

[Display omitted] • The addition of Re and Cr suppressed the formation of vacancy clusters in W after high-temperature irradiation, while no effect was observed for W-5 at.% Ta and W-2.5 at.% Mo alloys. • Fine Cr-rich and Re-rich precipitates were observed in W-0.3 at.% Cr and W-5 at.% Re alloys, respectively, where the distributions of Mo and Ta in W-2.5 at.% Mo and W-5 at.% Ta alloys were uniform even after irradiation. • Irradiation hardening was observed for all materials but that of W-5 at.% Re alloy was significantly smaller than the hardening of W, W-2.5 at.% Mo and W-5 at.% Ta alloys. • The stability of mixed dumbbells plays an important role in the vacancy cluster formation, precipitation and irradiation hardening of W alloys. Irradiation responses of binary W alloys were investigated systematically from the perspective of the binding energy of an alloying element with a W self-interstitial atom (W-SIA). Plates of W, W-0.3 at.% Cr, W-5 at.% Re, W-2.5 at.% Mo and W-5 at.% Ta alloys were irradiated at 1073 K with 6.4 MeV Fe ions to 0.26 dpa at the damage peak, where the binding energy of alloying element with W-SIA is in order of Cr > Re > Mo > Ta. The formation of vacancy-type defects (vacancies and vacancy clusters) was studied by using positron lifetime measurement. The precipitation of alloying elements was studied by using atom probe tomography (APT) and the hardness changes in the irradiated volumes were measured by the nanoindentation technique. The formation of vacancy-type defects was strongly suppressed by the addition of Cr and Re, while Ta and Mo had no noticeable suppression effect. The APT measurements showed fine Cr- and Re-rich precipitates in W-0.3 at.% Cr and W-5 at.% Re alloys, respectively, where the density of precipitates in the latter was clearly lower than that in the former. The distributions of Mo and Ta were uniform even after irradiation. Irradiation hardening was observed for all materials but that of W-5 at.% Re alloy was significantly smaller than the hardening of W, W-2.5 at.% Mo and W-5 at.% Ta alloys. These observations suggest that the irradiation hardening of W, W-2.5 at.% Mo, and W-5 at.% Ta alloys were mainly caused by vacancy-type defects. It was concluded that an alloying element with moderate binding energy with a W-SIA effectively suppresses vacancy formation without significantly enhanced precipitation and consequently mitigates irradiation hardening. [ABSTRACT FROM AUTHOR]

We investigate copper (Cu) precipitation at small-angle tilt boundaries on (220) in Czochralski-grown p-type silicon (Si) ingots using transmission electron microscopy, atom probe tomography, and ab initio calculations. In the initial stage of precipitation, Cu atoms agglomerate along the boundaries, forming coherent layers (less than about 2 nm thick) of Cu3Si with a body-centered-cubic structure in a metastable state (a = 0.285 nm). As the layers thicken, they become semicoherent with misfit dislocations on the (220) interphase boundaries, reducing coherency strains. Subsequently, the metastable layers convert into incoherent polyhedrons of orthorhombic η''-Cu3Si in the equilibrium state, forming interphase boundaries on {112} in Si. These results are similar to the Cu precipitation processes found in metallic alloys: the formation of Guinier-Preston zones followed by a conversion into the equilibrium θ phase. [ABSTRACT FROM AUTHOR]

• The role of Si content on irradiation embrittlement was clarified. • Solute atom clusters of highly neutron-irradiated Japanese pressurized water reactor surveillance test specimens were analyzed by atom probe tomography. • The cluster radius and number density decreased and increased, respectively, with increasing Si content, resulting in a constant volume fraction of SCs. • Increase in Si reduces the degree of irradiation embrittlement. This is consistent with the results of our previous study based on Bayesian statistical analysis. Solute clusters (SCs) formed in pressurized water reactor surveillance test specimens neutron-irradiated to a fluence of 1 × 1020 n/cm2 were analyzed via atom probe tomography to understand the effect of silicon on solute clustering and irradiation embrittlement of reactor pressure vessel steels. In high-Cu bearing materials, Cu atoms were aggregated at the center of cluster surrounded by the Mn, Ni, and Si atoms like a core-shell structure. In low-Cu bearing materials, Mn, Ni, and Si atoms formed cluster and these solutes were not comprised core-shell structure in SCs. While the number of Cu atoms in clusters was decreased with decreasing nominal Cu content, the number of Si atoms had clearly increased. The cluster radius (r) and number density (N d) decreased and increased with increasing nominal Si content, respectively. The shift in the reference temperature for nil-ductility transition (ΔRT NDT) showed a good correlation with the square root of volume fraction (V f) multiplied by ( V f × r). The negative relation between the nominal Si content and ΔRT NDT indicated that increasing of nominal Si content reduces the degree of embrittlement. [ABSTRACT FROM AUTHOR]