V3Ga Compound Research Articles

Microstructure of V3Ga Superconducting Wire Using High Ga Content Ti-Ga/V Precursor Composite Material

Our co-workers, Hishinuma et. al. have fabricated the V3Ga compound wire by a new process using a high Ga content Ti-Ga compound in order to improve the superconducting property of the wire. In this study, we investigated microstructures of this wire to clarify the existence of V3Ga phase. The different contrasts of the matrix, two V-Ga phases and Ti-Ga core were observed by SEM observation. Two V-Ga phases were also confirmed. The ratio of V to Ga for two V-Ga phases was respectively 3:1 and 6:5 according to the EDS result. And these two phases were confirmed as V3Ga and V6Ga5.

Effect of Cu Addition Into $\hbox{TiGa}_{3}$ Compound on Superconducting Properties and Microstructure of $ \hbox{V}_{3}\hbox{Ga}$ Multifilamentary Wires Synthesized Through High Ga Content Diffusion Process

The decay time of induced radioactivity in V3Ga is remarkably shorter than in Nb-based compounds, making the V3Ga compound as one of the candidate and suitable superconducting magnet materials for the future nuclear fusion system. In order to improve the superconducting properties of V3Ga multifilamentary wires, we investigated high Ga content TiGa3 compound with various Cu addition as the Ga source material. The Cu additions into TiGa3 compounds were 10, 30, and 50 wt.%, respectively. The volume fraction of V3Ga phase was increased with increasing of Cu addition. We confirmed that Cu addition into TiGa3 compound promoted the formation of the V3Ga phase. The optimum Cu addition into TiGa3 compound on superconducting properties was obtained to be 30 wt. %, and Hc2 value of the 30 wt.%Cu sample was estimated to be above 24 T. This value was 3 T higher than conventional “Bronzed route” processed V3Ga wires.

Microstructure of the New Route Wire Fabrication of V<sub>3</sub>Ga Compound Superconducting Wire Using High Ga Content Cu-Ga/V Precursor Composite Material

Our co-worker, Hishinuma et. al. has established a new route Powder-In-Tube (PIT) process using a high Ga content Cu-Ga compound in order to improve the superconducting property of the V3Ga compound wire. In this study, we investigated microstructure of this high Ga content Cu-Ga/V composite superconducting wire. The different contrasts of matrix, V-Ga phase and Cu-Ga core were observed by SEM observation in cross section of 19 multifilamentary wire. And V-Ga phase was confirmed by SEM mapping. The area fraction of V-Ga phase increased when Ga content increased from 30% to 50%. Thin film sample with V-Ga phase for TEM was fabricated by FIB and observed by TEM in detail. Selected area diffraction pattern was obtained for V matrix, V-Ga phase and Cu-Ga core. The ratio of V to Ga for V-Ga phase was probably V3Ga according to the EDS result. There was a linear interface between V matrix and V-Ga phase, while the interface between Cu-Ga core and V-Ga phase was not linear. On the other hand, there were some granular grains observed in V-Ga phase wear Cu-Ga core.

The Formation Mechanism of the Higher Performance V3Ga Phase on the High Ga Content Cu-Ga Compound/V Diffusion Reaction Through the High-Temperature XRD Analysis

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

Microstructure of the New Route Wire Fabrication of V<sub>3</sub>Ga Compound Superconducting Wire Using High Ga Content Cu-Ga/V Precursor Composite Material

Our co-worker, Hishinuma et. al. has established a new route Powder-In-Tube (PIT) process using a high Ga content Cu-Ga compound in order to improve the superconducting property of the V3Ga compound wire. In this study, we investigated microstructure of this high Ga content Cu-Ga/V composite superconducting wire. The different contrasts of matrix, V-Ga phase and Cu-Ga core were observed by SEM observation in cross section of 19 multifilamentary wire. And V-Ga phase was confirmed by SEM mapping. The area fraction of V-Ga phase increased when Ga content increased from 30% to 50%. Thin film sample with V-Ga phase for TEM was fabricated by FIB and observed by TEM in detail. Selected area diffraction pattern was obtained for V matrix, V-Ga phase and Cu-Ga core. The ratio of V to Ga for V-Ga phase was probably V3Ga according to the EDS result. There was a linear interface between V matrix and V-Ga phase, while the interface between Cu-Ga core and V-Ga phase was not linear. On the other hand, there were some granular grains observed in V-Ga phase wear Cu-Ga core.

Superconducting Properties and Microstructure of ${\rm V}_{3}{\rm Ga}$ Wires Using High Ga Content ${\rm TiGa}_{3}$ and ${\rm V}_{2}{\rm Ga}_{5}$ Compounds

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.

The new route process of V3Ga mono-cored and multifilamentary wires using high Ga content Cu-Ga compound and V matrix precursor

V3Ga compound is one of the attractive low activation materials for high magnetic field superconducting magnet in the several V-based compounds because V-based superconducting materials have shorter decay time of induced radioactivity and high field property above 20 T. V3Ga compound has not only high upper critical magnetic fields (Hc2) above 20 T as well as Nb3Sn but also better mechanical property. However, the present critical current density (Jc) property of V3Ga compound wire is insufficiency to apply for large high field magnet such as fusion application. In the previous study, V3Ga compound wire was mainly investigated ‘Diffusion process’ between Cu-Ga solid solution matrix within 20 at% Ga composition and V filament. Recently, we investigated the new route PIT process using high Ga content Cu-Ga compound to fabricate V3Ga mono-cored and multifilamentary wires in order to increase a volume fraction of synthesized A15 phase. It was confirmed that the thicker V3Ga layer formed along the boundary of Cu-Ga powder core and V matrix compared with previous diffusion processed samples in the case of the both mono-cored and mltifilamentary wires. And Hc2 property of the samples using high Ga content Cu-Ga compounds was increased with increasing of Ga content into Cu-Ga compounds, and it showed about 23.0 T which value was 2.0 T higher than conventional processed samples.

Fabrication and superconducting properties ofPIT-V3Ga mono-cored wires using high Ga content Cu–Ga compound powders

V-based superconducting material has a shorter decay time of induced radioactivity and itsmechanical properties are better than Nb-based materials. We thought that theV3Ga compound was one of the most promising materials in ‘low activation and higher fieldsuperconductors’ for an advanced fusion reactor. However, the present critical current density(Jc) propertyof the V3Ga compound wire is insufficient to apply to fusion magnet applications.We investigated a new route powder-in-tube (PIT) process using a highGa content Cu–Ga compound in order to improve workability and theJc propertyof the V3Ga compound wire. It was confirmed that a thicker reaction layer formed along the boundaryof the Cu–Ga compound powder filament and V matrix. Critical transition temperature(Tc) values were shown to be almost 15 K, which was higher thanconventional bronze processed samples. Comparisons of the transportJc property and microstructure between different Ga content Cu–Ga compounds areinvestigated in this paper.

V3Ga 超伝導線材における高 Ga 濃度 Cu-Ga 化合物粉末を経由した新製法

A superconducting magnet system is also one of the important components in an advanced magnetic confinement fusion reactor. Then it is required to have a higher magnetic field property to confine and maintain the steady-state burning deuterium (D)-tritium (T) fusion plasma in the large interspace during the long term operation. Burning plasma is sure to generate 14 MeV fusion neutrons during deuterium-tritium reaction, and fusion neutrons will be streamed and penetrated to superconducting magnet through large ports with damping neutron energy. Therefore, it is necessary to consider carefully not only superconducting property but also neutron irradiation property in superconducting materials for use in a future fusion reactor, and a “low activation and high field superconducting magnet” will be required to realize the fusion power plant beyond International Thermonuclear Experimental Reactor (ITER). V-based superconducting material has a much shorter decay time of induced radioactivity compared with the Nb-based materials. We thought that the V3Ga compound was one of the most promising materials for the “low activation and higher field superconductors” for an advanced fusion reactor. However, the present critical current density (Jc) property of V3Ga compound wire is insufficient for apply to fusion magnet applications. We investigated a new route PIT process using a high Ga content Cu-Ga compound in order to improve the superconducting property of the V3Ga compound wire.

Mechanically induced phase transformation in the Nb3Au intermetallic compound

The A15 intermetallic compound Nb3Au was subjected to grinding in a high-energy ball mill. A phase transformation from the A15 phase to the high-temperature BCC solid solution of gold in niobium was observed after milling. Differential scanning calorimetry revealed an exothermic peak with a heat content of 4.6 kJ mol-1. The activation energy was 435 kJ mol-1. The present result is very similar to the previous results on the V3Ga compound. The energies involved in the order-disorder reactions for these two compounds scale very well. These results, together with similar results obtained by other authors, strongly support the concept of energy storage by ball milling mainly in the form of atomic disorder.

Arrhenius behaviour of the degradation of the superconducting transition temperature

Abstract The degradation of the superconducting transition temperature in A15 compounds produced by quenching from high temperatures is ascribed to site-antisite disorder. An Arrhenius relation is derived between this degradation and the quenching temperature. It is shown that measurements on the A15 compound V3Ga and A15-like compound Yb3Rh4Sn13 are in excellent agreement with this relation. From the slope of the Arrhenius plots the disordering energies are obtained.

Knight Shift in the V3Ga Compound at High Temperatures

The temperature dependence of the Knight shift of both 51V and 71Ga in the V3Ga compound has been measured over the entire range from 300 K to 1300 K. The results are discussed using a model based on the assumption that the core polarization contribution to the total Knight shift is the temperature dependent term.

Multifilamentary Stranded Compound Superconductor

This paper summarizes our works on newly-developed multifilamentary V3Ga and Nb3Sn compound superconductors, including their designing, processing, and characteristics such as mechanical and superconducting properties, and coil performances.

複合加工法によるV<SUB>3</SUB>Ga超電導線材の作製

Superconducting V3Ga tapes and multifilamentary wires have been fabricated by a composite process in which a composite of the Cu-Ga alloy matrix and vanadium cores is mechanically deformed and then heat treated. Cu-Ga solid-solution alloys with less than 20 at%Ga are ductile enough to be deformed into thin tapes or wires. Above the solid-solubility limit of ∼20 at%Ga, the deformability of the alloy rapidly decreases due to the precipitation of phase. Diffusion reaction between the Cu-Ga alloy and the vanadium have been investigated in relation to the heat treatment condition and the composition of the Cu-Ga alloy. In the composite processed specimen, only the V3Ga compound layer is formed by the diffusion reaction and any other compounds richer in gallium are not formed. The lower limit of the matrix gallium concentration for obtaining the V3Ga layer at 700°C is about 13 at%. Growth rate of the V3Ga layer increases with increasing matrix gallium concentration, heat treatment temperature and time. The V3Ga growth rate at 700°C in the composite processed specimen with 18–20 at% gallium matrix is nearly two orders larger than that in the V-Ga diffusion couple and is the same order as that in the surface diffusion processed specimen.

V-Ga系中間相の拡散生成

Compositions and structures of V-Ga intermediate phases formed by diffusion at high temperatures were studied using electron probe microanalysis, optical metallography and X-ray diffraction. Superconducting transition temperatures, Tc, of the intermediate phases were also measured.Five different intermediate phases, V3Ga, 2V-Ga, V3Ga2, VGa and VGa2 were formed in the V-Ga diffusion couples. The V3Ga compound, having the cubic (A-15) structure, is stable below 1300°C and transforms to V-Ga solid solution above 1300°C. The 2V-Ga phase, which is a V-Ga solid solution, decomposes into V3Ga and V3Ga2 by an eutectoid reaction at 1100°C. The hexagonal V3Ga2 compound is stable below 1200°C. The VGa compound is stable between 1050°C and 1200°C and decomposes into V3Ga2 and VGa2 at 1050°C. The tetragonal VGa2 compound is stable below 1050°C.The formation rates of V3Ga, V3Ga2 and VGa2 show maxima at 1100°C, 1000°C and 700°C, respectively. The formation rates of V3Ga2 and VGa2 are more than one order of magnitude larger than that of V3Ga. Tc of V3Ga formed at 800°C is 14.5°K. Tc decreases as the heat treatment temperature increases. V3Ga is the only phase in V-Ga ststem which becomes superconducting above 4.2°K.