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The influence of the Al layer thickness on the critical current density Jc of transformation-processed \Nb3\Al superconductors was investigated. The Al layer thickness in the jerry-roll filaments of precursor wires was varied from 120 to 250 nm; the Nb layer thickness is proportional to the Al thickness, keeping the Nb–Al composition ratio to 3. The rapid heating and quenching (RHQ) operation condition was varied within a range of the conditions to form the ductile body-centered cubic (BCC) Nb–Al phase. The RHQ wires were also followed by an areal reduction process prior to the \Nb3\Al phase transformation. Thinner Al thickness wires show a steeper increase in Jc with reduction in the area, whereas thicker Al thickness wires show a slower increase. The best Jc performance was obtained for the thinnest Al thickness sample. Without areal reduction, there was not much difference in the optimum Jc with respect to the Al thickness. [ABSTRACT FROM PUBLISHER]

The effects of thermal aging of stainless steel weld-overlay claddings of nuclear reactor pressure vessels on the microstructure and hardness of the claddings were investigated using atom probe tomography and nanoindentation testing. The claddings were aged at 400°C for periods of 100-10,000 h. The fluctuation in Cr concentration in the d-ferrite phase, which was caused by spinodal decomposition, progressed rapidly after aging for 100 h, and gradually for aging durations greater than 1000 h. On the other hand, NiSiMn clusters, initially formed after aging for less than 1000 h, had the highest number density after aging for 2000 h, and coarsened after aging for 10,000 h. The hardness of the d-ferrite phase also increased rapidly for short period of aging, and saturated after aging for longer than 1000 h. This trend was similar to the observed Cr fluctuation concentration, but different from the trend seen in the formation of the NiSiMn clusters. These results strongly suggest that the primary factor responsible for the hardening of the d-ferrite phase owing to thermal aging is Cr spinodal decomposition. [ABSTRACT FROM AUTHOR]

The microstructures and the hardness of stainless steel weld overlay cladding of reactor pressure vessels subjected to neutron irradiation at a dose of 7.2×1019 ncm−2 (E >1MeV) and a flux of 1.1×1013 ncm−2 s−1 at 290°C were investigated by atom probe tomography and by a nanoindentation technique. To isolate the effects of the neutron irradiation, we compared the results of the measurements of the neutron-irradiated samples with those from a sample aged at 300°C for a duration equivalent to that of the irradiation. The Cr concentration fluctuation was enhanced in the δ-ferrite phase of the irradiated sample. In addition, enhancement of the concentration fluctuation of Si, which was not observed in the aged sample, was observed. The hardening in the δ-ferrite phase occurred due to both irradiation and aging; however, the hardening of the irradiated sample was more than that expected from the Cr concentration fluctuation, which suggested that the Si concentration fluctuation and irradiation-induced defects were possible origins of the additional hardening. [ABSTRACT FROM AUTHOR]

Microstructural changes in the stainless steel weld overlay cladding of reactor pressure vessels subjected to neutron irradiation with a fluence of 7.2×1023 nm−2 (E>1MeV) and a flux of 1.1×1017 nm−2 s−1 at 290°C were investigated by atom probe tomography. The results showed a difference in the microstructural changes that result from neutron irradiation and thermal aging. Neutron irradiation resulted in the slight progression of Cr spinodal decomposition and an increase in the fluctuation of the Si, Ni, and Mn concentrations in the ferrite phases, with formation of γ′-like clusters in the austenite phases. On the other hand, thermal aging resulted in the considerable progression of the Cr spinodal decomposition, formation of G-phases, and a decrease in the Si and an increase in the Ni and Mn concentration fluctuations at the matrix in the ferrite phases, without the microstructural changes in the austenite phases. [ABSTRACT FROM AUTHOR]

Abstract: V3Ga compound has a shorter radioactive decay time compared with Nb-based compounds and it will be one of the candidate superconducting magnet materials for advanced low activation fusion reactor systems.!Recently, we succeeded in developing new V3Ga wires, fabricated via the PIT process using high Ga content Cu-Ga compounds above Cu-Ga solid solution composition. Jc and Hc2 enhancements of V3Ga wire due to increasing three times of the V3Ga volume fraction were also confirmed. For the further microstructure control, in-situ observation of diffusion reaction with increase of temperature using High-Temperature X-ray diffraction (HT-XRD) was measured. Various high Ga content Cu-Ga compounds were composed with Cu3Ga (β phase: ∼30at%Ga), Cu9Ga4 (γ phase: ∼40at%Ga) and CuGa2 (δ phase: ∼64at%Ga) compounds. Especially, CuGa2 compound has much lower melting point (254°C) compared with various Cu-Ga compounds. In the case of diffusion reaction including CuGa2 phase, V3Ga phase was formed by the second step diffusion reactions; the first one is solid-liquid diffusion between the dissociated Ga liquid phase and metal V, the second one is soild-solid diffusion reaction between solid phase formed by the first step reaction and metal V [Copyright &y& Elsevier]

Abstract: The natural boron has two kinds of isotopes which are existed 20 wt% boron-10 (10B) and 80 wt% boron-11 (11B).11B isotope is stable against the neutron irradiation without nuclear transformation. For an advanced fusion application, in-situ PIT process using 11B isotope powder as the boron source material was desirable to enhance low induced radio-activity of MgB2 superconducting wire. We tried to fabricate the in-situ Cu addition MgB2/Ta/Cu multifilamenatry wire using boron isotope powder as the boron source material. In this study, superconductivity and microstructure of MgB2 wire using boron isotope powder were investigated. Tc value of MgB2 wire using 11B powder was shown to about 37K by the low temperature diffusion reaction, and its value was higher than commercial natural powder. However, Jc value of MgB2 wire using 11B isotope powder was remarkably lower than that of commercial natural powder. This is caused by the forming of much impurity phase and decrease of MgB2 volume fraction due to the remaining of much non-reactive 11B isotope powder. [Copyright &y& Elsevier]

Abstract: Jelly Roll (JR) processed Nb3Sn wires have been fabricated from laminated composites of Sn-based alloy and Nb sheets. The wires show an offset Tc of 18.1K with a transition width of less than 0.1K, and an offset Bc2 (4.2K) of 26.5T. The wire keeps Bc2 of ∼13T at 12K. Large non-Cu Jc values have been obtained at 4.2K and above 21T. Relative sheet thickness of the Sn-based alloy and Nb yields significant effect on the structure and Jc of the JR wire. [Copyright &y& Elsevier]

Abstract: The effect of thermal aging on microstructural changes in stainless steel submerged arc weld-overlay cladding of reactor pressure vessels was investigated using atom probe tomography (APT). In as-received materials subjected to post-welding heat treatments (PWHTs), with a subsequent furnace cooling, a slight fluctuation of the Cr concentration was observed due to spinodal decomposition in the δ-ferrite phase but not in the austenitic phase. Thermal aging at 400°C for 10,000h caused not only an increase in the amplitude of spinodal decomposition but also the precipitation of G phases with composition ratios of Ni:Si:Mn=16:7:6 in the δ-ferrite phase. The degree of the spinodal decomposition in the submerged arc weld sample was similar to that in the electroslag weld one reported previously. We also observed a carbide on the γ-austenite and δ-ferrite interface. There were no Cr depleted zones around the carbide. [Copyright &y& Elsevier]

Abstract: The effect of thermal aging on microstructural changes was investigated in stainless steel weld-overlay cladding composed of 90% austenite and 10% δ-ferrite phases using atom probe tomography (APT). In as-received materials subjected to cooling process after post-welding heat treatments (PWHT), a slight fluctuation of the Cr concentration was already observed due to spinodal decomposition in the ferrite phase but not in the austenitic phase. Thermal aging at 400°C for 10,000h caused not only an increase in the amplitude of spinodal decomposition but also the precipitation of G phases with composition ratios of Ni:Si:Mn=16:7:6 in the ferrite phase. The chemical compositions of M23C6 type carbides seemed to be formed at the austenite/ferrite interface were analyzed. The analyses of the magnitude of the spinodal decomposition and the hardness implied that the spinodal decomposition was the main cause of the hardening. [Copyright &y& Elsevier]

V3Ga compound has a shorter radioactive decay time compared with Nb-based compounds and it will be one of the candidate superconducting magnet materials for advanced low activation fusion reactor systems including shutdown scenario and material recycle. Recently, we succeeded in developing new V3Ga multifilamentary wires fabricated via the Powder In-Tube (PIT) process using high Ga content Cu-Ga binary phase compounds. We also found that high Ga content in the precursor promoted the formation of the stoichiometric V3Ga phase and it was effective in improving superconducting properties. [ABSTRACT FROM AUTHOR]

Sn-based sheets with Ta, B or Nb particle dispersion have been prepared from consolidated alloys. A small amount of Ti addition strengthened the bonding between dispersed particles and the Sn matrix, which improved the workability of the sheet. The sheet was laminated with a Nb sheet, and wound into a Jelly Roll (JR) composite. The composite was easily fabricated to a wire without intermediate annealing. Thick and uniform \ Nb3{{\ {Sn}}} layers with nearly stoichiometric Sn concentration were synthesized by the mutual diffusion between Nb and Sn-based alloy layers. An offset Tc of \sim18.1 K and an offset Bc2 (4.2 K) of \sim26.5 T have been obtained after the heat treatment. The non-Cu Jc of the wires increased with decreasing the wire diameter. A non-Cu Jc of \sim \ 150 A/mm^2 has been obtained at 4.2 K and 22 T. The Sn–Ta, Sn–B and Sn–Nb based sheet JR wires exhibited similar microstructures and superconducting performances. [ABSTRACT FROM AUTHOR]

Abstract: The correlation of microstructure evolution and hardening was studied in two kinds of A533B-1 steel with high and low levels of Cu irradiated in a range of dose from 0.32 to 9.9×1019 ncm−2 (E >1MeV) under a high flux of about 1.7×1013 ncm−2 s−1 using three-dimensional local electrode atom probe (3DAP), positron annihilation (PA) techniques, and Vickers microhardness. The early rapid hardening was found to be caused by mainly matrix defects such as mono- or di-vacancies (V 1 − V 2) and/or dislocations indicated by the PA analysis. The 3DAP analysis showed that dense dispersion of dilute Cu rich clusters and lean distribution of Mn–Ni–Si rich clusters, whichwereidentified to possess the same dislocation-pinning effectby applying a Russell and Brown model,were responsible for large and small hardening in high- and low-Cu steels irradiated above 0.59×1019 ncm2, respectively. [Copyright &y& Elsevier]

The authors have been developing the Nb3Al conductors through transformation process, where the Nb3AL phase forms from the BCC (body-centered cubic) Nb(Al) supersaturated solid solution phase; the BCC phase is quenched by rapid-cooling from a temperature around 2000°C. It was reported several times that deformation to the quenched BCC Nb(AI) phase influences the superconducting properties, usually improving Jc. But, the results have not been discussed in detail so far from a metallurgical viewpoint. This work investigates the fundamental relationship between the BCC-deformation, transformation temperature, microstructure and superconducting properties. The transformation temperature is identified by DTA measurement, detecting the release of the free energy between the BCC and the Nb3Al phases. It was found that the transformation temperature has a tendency of monotonic decrease with the deformation. But, the transformation temperature does not seem to go down below a temperature of about 720°C even by strong deformation. The microstructures observed by FESEM suggests that the grain size is reduced almost proportionally with the deformation. In case of reduction in area of 99%, the grain size is reduced down to about 250 nm from 1.2 μm. The Jc increases with deformation, not showing a peak. The Jc of the wire (ME365) with reduction in area of 86% shows the best performance of the Nb3A1 wire ever reported. But, at least high-field Jc seems to saturate at a certain value. [ABSTRACT FROM AUTHOR]

We have studied about annealing effect on V-based Laves phase compound multifilamentary superconducting wire using the Rapidly Heating and Quenching (RHQ) process in order to improve superconducting property. We found that the reaction layer within 10 microns was formed between powder mixture filament and V matrix after the RHQ process. The transport Jc values of samples post-annealed at 600°C for 10 hours were increased remarkably compared with as-quenched samples, and then Hc2 value calculated by Kramer's formula was increased from 14 T to 16 T by additional annealing. In this paper, the post-annealing condition effect on both microstructure and Jc-B property of V-based Laves phase compound superconductor made through RHQ process was investigated. [ABSTRACT FROM AUTHOR]

Sn-Ta-Cu buttons with enough ductility to be fabricated into thin sheets were synthesized by melting a mixture of Sn+Ta+(Cu) powder. (Nb, Ta)3Sn wires have been prepared by a Jelly Roll (JR) process and a filamentary process. In the JR process a Sn-Ta(-Cu) sheet was laminated with a Nb sheet forming a JR composite. In the filamentary process a Sn-Th(-Cu) sheet was wrapped around thirteen Nb-1.0 at%Ta rods forming a filamentary composite. Both composites were fabricated into wires without intermediate annealing, and then heat treated. The effect of Ge and Ti addition to the Sn-Ta-Cu sheet has been studied in the JR wires. A small amount of Ge addition improves the workability of the sheet, while that of Ti addition enhances appreciably the Jc of the JR wires. Meanwhile, the 13-core filamentary wires exhibit equivalent high-field performance as that of the JR wires. Present new (Nb, Ta)3Sn wires can be fabricated through a relatively easy process, and show attractive Jc in the field range of 22-23 T at 4.2 K and that of 24-25 Tat 2.1 K. [ABSTRACT FROM AUTHOR]

We have developed a nearly-stoichiometric Nb/sub 3/Al multifilamentary superconductor by exploiting the transformation from bcc supersaturated-solid-solution Nb(Al)/sub ss/. This is a candidate conductor for 1 GHz NMR magnets. Flat-roll forming, an effective way to increase the packing factor of the coil and thereby the coil-current-density, has been carried out on the multifilamentary Nb(Al)/sub ss//Nb wire, and its effects are compared with that of the conventional Nb tube processed conductor. A Nb(Al)/sub ss//Nb wire, 0.74 mm in diameter, was successfully deformed into a tape conductor (the thinnest case: 0.15/sup t//spl times/2.2/sup w/ mm) without mechanical fracture. The flat-roll forming creates very little anisotropy in critical parameters and scarcely degrades the J/sub c/ properties. Excess flat-rolling causes a wide distribution of Nb(Al)/sub ss/ filament areas and thus reduces the n-index in the voltage-current characteristic. However, it is probably possible to retain the high value of the n-index of a wire, by appropriately designing the overall-aspect-ratio of a flattened conductor. [ABSTRACT FROM PUBLISHER]

Abstract: Post-irradiation annealing (PIA) behavior of irradiation-induced microstructural changes and hardening of an A533B (0.16wt.% Cu) steel after neutron-irradiation of 3.9×1019 n cm−2 (0.061 displacement per atom (dpa)) at 290°C was studied by positron annihilation spectroscopy (PAS), atom probe tomography (APT) and Vickers microhardness measurements. Coincidence Doppler broadening and positron lifetime measurements clearly reveal two recovery stages; (i) as-irradiated state to annealing at 450°C and (ii) annealing from 450 to 600°C. The first stage is due to annealing out of the most of irradiation-induced vacancy-related defects, while the second stage corresponds to dissolving of irradiation-induced solute nanoclusters (SCs). APT observations reveal that the SCs are enriched with Cu, Mn, Ni and Si and that their number densities decrease with increasing annealing temperature without coarsening to give almost complete recovery at 550°C. The experimental hardening is almost twice the SC hardening estimated by the Russell–Brown model below 350°C, whereas it is almost the same as that estimated in the range 400–550°C. [Copyright &y& Elsevier]

Abstract: Based on a study low activation superconducting materials, we have selected the V-based Laves phase (V2(Hf, Zr)) compound superconductor from many V-based compound superconductors because of its high upper critical field (H c2) exceeding 20T. The fabrication, microstructure and superconductivity of V2(Hf, Zr) multifilamentary wire made through rapidly heating/quenching (RHQ) process were investigated. Based on the SEM observations, it was confirmed that the thick reaction layer within about 10μm was formed on the boundary of powder mixture filament and V matrix after the RHQ. The T c values were increased by additional annealing and showed about 8K which value agreed well with that of arc-melted V2(Hf, Zr). [Copyright &y& Elsevier]