MgB2 is one of the practical superconductors that has been widely studied over the past two decades. The internal magnesium diffusion (IMD) method serves as a promising method because it can enhance the grain connectivity of MgB2 phase and thereby improve the superconducting current of MgB2 wires. Here, we present the fabrication of 30-filament MgB2 wires using the IMD method. The wires have a diameter of 1.00 mm and length more than 1 km. The filling factor of MgB2 is around 10% and the superconducting current I-c (4.2K, 3T) reaches 650 A. The highest layer-superconducting current density J(c) (4.2K, 3T) is 8.9 x 10(3) A mm(-2) and engineering superconducting current density J(e) (4.2K, 3T) is 8.3 x 10(2) A mm(-2). Meanwhile, the percentage of copper in the MgB2 wire is 28% and the residual resistivity ratio RRR(300K/40K) is 60. This can enhance the thermal stability for the low-temperature application. All of these indicate the great potential for the application of our MgB2 wires in the future.

Reducing the AC loss of MgB2 wire is significant for its possible AC engineering applications. In this study, the multi-filaments MgB2 wires possessed of various filaments diameter were fabricated via in-situ PIT (Powder in Tube) method. The effects of filaments diameters on the superconducting properties and magnetic hysteresis loss of MgB2 wires were studied systematically. With the filaments diameters decrease from 120 mu m to 40 mu m, the critical current density (J(c)) decreases by 20% (4.2 K, 3 T), the critical transition temperature (T-c) shows a consistent trend, while the magnetic hysteresis losses (Q(m)) decrease from 1230 mJ/cm(3) to 650 mJ/cm(3). The above results demonstrate that the smaller filaments diameter is beneficial to reduce the Q(m) of MgB2 wire, but the attenuation of current capacity can also not be ignored.

Internal Mg diffusion (IMD) method is proposed to overcome the drawbacks of powder in tube (PIT) method for the improvement of the MgB2 superconducting wires. To enhance the current carrying capacity of the IMD wire, 100 m class 30 filaments structure IMD MgB2 superconducting wires were fabricated. We precisely controlled the diameter of the wire, initial material parameters, annealing time and characterized optical metallographic and superconducting properties. The reduction of the Monel proportion from 37.25% to 19.16% made MgB2FF increase from 10.25% to 14.07%. The experimental results revealed that the 1.0 mm outer diameter (OD) of the wire exhibited the best current carrying capacity and longer annealing time could both enhance J(c) and J(e). The excellent J(e) were 7.6 x 10(4) A cm(-2) (4.2 K, 4 T) and 9.5 x 10(3) A cm(-2) (4.2 K, 8 T) which the wire was annealed at 650 degrees C for 3.5 h in vacuum with 1.0 mm OD. This study revealed that the IMD MgB2 wire is suitable for further practical applications compared with PIT MgB2 wire and NbTi wire.

Facility for Rare Isotope Beams (FRIB) is a scientific user facility for the U.S. Department of Energy Office of Science (DOE-SC), supporting the mission of the DOE-SC Office of Nuclear Physics, and Michigan State University is home to FRIB. The superconducting magnet is used for focusing and steering the heavy ion beams for FRIB driver linac. The magnet is made of NbTi wire, and cooled by liquid helium. The testing results show that all the 81 sets of the FRIB magnet achieved 100

NbTi superconducting Wire exhibits the advantages of excellent processing characteristics, stable superconducting properties and low cost. It has been widely applied and extensively used for low magnetic fields of < 9 T. To expand the application range in higher magnetic fields, it is vital to improve the upper critical fields (Hc2) and the critical current density (Jc) at high magnetic fields (≥ 9 T) of NbTi superconducting material. This study aims to add Ta element, obtaining both higher Jc and higher upper critical fields (Hc2). After the addition of Ta element, the critical current density of NbTiTa superconducting wire reaches 681.3, 527.5, and 381.4 A/mm2 at (4.2 K, 9 T), (4.2 K, 9.5 T) and (4.2 K, 10 T), respectively and the upper critical field Hc2 is also higher than that of NbTi superconducting wire. In addition, the NbTiTa superconducting wire also exhibits the striking second magnetization peak effect at high fields, and the flux pinning mechanism changes from the surface pinning at low fields to the Δκ pinning at high fields. This study demonstrates that the NbTiTa superconducting wire can expand the application range in higher magnetic fields (≥ 9 T) by improving the critical current density at high magnetic fields (≥ 9 T) and the upper critical fields of the NbTi superconducting wire.

We prepared Nb 3 Al superconducting wires doped with nano-size SnO 2 (n-SiO 2 ) particles through a multi-time rapid heating and quenching process and investigated their microstructure and superconducting properties. All the samples showed a highly homogeneous A15 Nb 3 Al phase. Compared with pure Nb 3 Al, the n-SnO 2 doped Nb 3 Al wires presented a larger Δ T c value and a higher J c value. The best J c at 4.2 K was found in the 1 wt% n-SnO 2 doped Nb 3 Al sample, with 3.37 × 10 5 A cm −2 , 2.55 × 10 5 A cm −2 and 1.80 × 10 5 A cm −2 at 8 T, 10 T and 12 T, respectively. These results were an improvement of about 60% compared with pure Nb 3 Al at the same applied fields. The maximum irreversible field value was obtained in the 1 wt% SnO 2 -doped Nb 3 Al wire, with a result of 29.5 T at 4.2 K. The improvement of J c performance in the n-SnO 2 doped Nb 3 Al wires might be attributed to the formation of artificial nanoparticles in the grain, which act as extra effective flux pinning centers.

This research introduced nano-scale particles into the RHQT Nb3Al superconducting wires, which was confirmed by TEM that nanoparticles with size of 5-25 nm distributed in the wires and might act as the extra flux pinning centers. The precursor wires were fabricated by powder in tube process with nano-sized MgO (n-MgO) doped in the raw powder. Uniform microstructure and chemical composition were obtained in the superconducting wires. Besides nanoparticles, high density stacking faults with spacing of 5-20 nm were observed in the Nb3Al superconducting wire, which acted as the dominant flux pinning centers. It had great importance that nanoparticles were introduced into the RHQT Nb3Al wires and combined with the high density stacking faults to significantly improve the critical current density (Jc) of the wires. The magnetic Jc results of 1 wt% n-MgO doped Nb3Al wire were about twice of the non-doped sample, corresponding to Jc values of 3.18 x 105 A/cm2, 2.38 x 105 A/cm2 and 1.72 x 105 A/cm2 at 4.2 K and 8 T, 10 T and 12 T.

This paper investigated the microstructure and superconductivity of the powder-in-tube (PIT) Nb3Al short samples with different rapid heating and quenching (RHQ) treatment. Single RHQ processed Nb3Al wires showed inhomogeneous microstructure and the superconductivity were sensitive to rapid heating temperature (Tmax), showing significant fluctuation with a slight change of Tmax. Multi-time RHQ treatment was performed to homogenize the Nb3Al superconductors. The highly uniform microstructure and composition distribution were found in 5-time RHQ processed Nb3Al wires, which exhibited significantly stable and excellent Jc performance. Reproducible stable Jc results of Nb3Al wires were realized in three samples of 5-time RHQ treatment with a difference of Tmax reaching about 200 & DEG;C. Jc of the three samples fluctuated less than 20% with results of 1.1 x 105 A/cm2, 9.87 x 104 A/cm2 and 9.51 x 104 A/cm2 at 4.2 K and 12 T. The insensitivity of Jc to Tmax in 5-time RHQ processed Nb3Al samples might attribute to the highly homogeneous Nb3Al A15 phase.

Sparking plasma sintering (SPS) technique has the characteristics of rapid heating and cooling rate, high mass density, and grain activation sintering. Therefore, it may be used to improve the grain connection, refine the grains, and enhance the superconducting current-carrying capacity of MgB2. In this paper, the MgB2 wire prepared by the in-situ method is rapidly treated by the SPS method, and the effects of different SPS sintering conditions on the phase formation, microstructure characteristics and superconductivity of the MgB2 material are studied, and compared with the MgB2 prepared by conventional sintering and the ex-situ SPS method. It was found that the SPS-treated samples were in a rapidly changing non-equilibrium state during the entire sintering process, so there are existing both flake particles and nanoparticles in the samples, which significantly improves the connection of the grains and refine the grains, resulting in significantly improved superconducting performance for MgB2. The critical current densityJ(c) of SPS-treated sample at 850 celcius reached 1354 A/cm(2) @ (10 K, 5 T) and 1615 A/cm(2) @ (20 K, 3 T), which were 3.7 times and 2.6 times that of conventional sintering sample. Our research shows that SPS is an effective method to improve the superconductivity of in-situ MgB2 wire. (C) 2021 Elsevier B.V. All rights reserved.

Herein, the microstructure and composition of the Ti‐ and Ta‐doped Nb3Al superconductor fabricated by rapid heating, quenching, and transformation (RHQT) process are compared. After rapid heating and quenching (RHQ) process, body‐centered cubic (bcc) phase is formed in all the wires, showing dark stripe and bright contrast morphology in the backscattered electron (BSE) images. After transformation heat‐treatment, all wires consist of A15 phase and show the same morphology as that of the quenched samples. Near‐stoichiometric composition is shown in 3 at% Ti‐ and Ta‐doped Nb3Al samples, but when doping amount is 10 at%, Ti‐doped sample has constant Nb content of 67 at% and Ta‐doped sample has Al + Ta content of 25 at%. Superconducting properties of both 3 at% Ti‐ and Ta‐doped Nb3Al samples are comparable and much superior than that of 10 at% doped samples, including critical temperature (Tc), critical current density (Jc), and irreversible field (Birr). Though 10 at% Ta‐doped Nb3Al has higher Tc than 10 at% Ti‐doped sample, it presents wider ΔTc value and lower Jc performance. When increasing the measurement temperature from 8 to 10 K, the decay ratio of Birr value for Ti‐doped Nb3Al superconductor follows the scaling law; however, the Ta‐doped samples are not the case.

In response to the growing demand for critical current density (J(c)) in superconducting wires, Sn-Ge co-doped Nb3Al wires were fabricated by the rapid-heating, quenching and transformation (RHQT) method. Physical Property Measurement System-Vibrating Sample Magnetometer (PPMS-VSM) was used to perform magnetic measurements at low-temperature and external field to estimate J(c) and superconducting transition temperature (Tc). Backscattered electron (BSE) image acquisition and EDS analysis of the polished surface by FESEM were used to determine phase homogeneity and elemental distribution. A significant positive correlation was found between J(c) (up to 7 T at 8 K) and delta T-c. Compared with binary sample, doubled J(c) was obtained in the low-dose Sn-Ge co-doped Nb3Al wire, reaching 3.01 x 10(3) A/mm(2), 1.46 x 10(3) A/mm(2) and 0.39 x 10(3) A/mm(2) at 5 T and 8 K, 10 K and 12 K, respectively. The increase in J(c) can be attributed to the enhancement of the homogeneity of the superconducting phase, especially the distribution of Al element therein.

Tungsten-based materials with high melting point, high thermal conductivity, low vapor pressure and low tritium retention have become plasma oriented materials with broad application prospects. Due to its shortcomings in low temperature brittleness, recrystallization brittleness and irradiation damage, its application in engineering is limited, and it has become a research hotspot in the field of nuclear fusion materials. In this paper, the research status of tungsten-oriented plasma-oriented materials was reviewed, the damage caused by four kinds of particle irradiation and four kinds of commonly used methods to improve the properties of tungsten materials were described, and the problems that need to be solved were also discussed.

This work compared the phase structure and superconducting properties of Nb3Al wires fabricated by static and dynamic rapid heating and quenching (RHQ) process. Single A15 Nb3Al phase was formed in transformed wires under rapid heating current (IRHQ) from 67 A to 69 A and from 120 A to 123 A for static and dynamic RHQ operation. The Tc-onset of RHQT Nb3Al wires are sensitive to IRHQ. Dynamic RHQT Nb3Al wires show much narrower ΔTc (~1.1 K) than that of static samples (>2.1 K), indicating better uniformity of the Nb3Al phase. Critical current density (Jc) at 4.2 K, 6.5 T of the single phase Nb3Al wires ranges from 4.7 × 10 4 to 6.9 × 10 4 A/cm 2 for the dynamic RHQ samples, and ranges from 1.5 × 10 4 to 3.4 × 10 4 A/cm 2 for the static RHQ wires. The precursor wires operated at other IRHQ conditions, that was below 65 A for static RHQ and 124 A for dynamic RHQ, exhibit much lower Jc results for including of Nb2Al impurity phase in the Nb3Al wires. The Birr reaches maximum values of 19.5 T and 19.1 T at 4.2 K, 10.5 T and 11.8 T at 10 K for the best static and dynamic RHQT Nb3Al wires. The main pinning mechanism of Nb3Al superconductor was surface pinning where grain boundaries or stacking faults acted as the pinning centers.

This work investigated the effect of post heat treat time on the structure and superconducting properties of Nb3Al wires prepared around the current condition of getting T-c peak. Properties of Nb3Al wires rapidly heated at much lower current of 76 A were also studied for comparison. M-T results show that prolongation of post-heat treatment time can elevate the T-c value of all Nb3Al wires because of the stoichiometry improvement of Nb3Al phase. The best J(c) of post heat treated Nb3Al wires rapidly heated at 76 A and 272 A were obtained after post heat treated for 2 hat 800 degrees C, compared to that of 10 h for the 276 A samples. The different optimism post heat treatment time to get best J(c) of the wires might attribute to the disorder degree difference of the Nb(Al)(ss) phase fabricated under different rapid heating current. The main pinning mechanism of Nb3Al superconducting wires was grain boundary pinning, as deduced from the fitting of pinning curve. Gradually degrade of J(c) of the Nb3Al wire performed at longer heat treatment time was attributed to the coarse of Nb3Al grain that attenuated grain boundary pinning.

The phase evolution of Bi-2223 precursor powder prepared by spray pyrolysis method is studied with different heat treatment parameters. The results show that the reaction temperature and phase composition of precursor powder depend on heat treatment atmosphere. Phase assemblage of (Bi,Pb)-2212, AEC, CuO, and small Bi-2201 can be obtained by heat-treated in N-2-0.1%O-2 atmosphere. For precursor powder, there is sufficient reaction process at 770 degrees C, and the dimension of Bi-2212 phase increases rapidly with the increase of heat treatment temperature and time. The dimension of AEC phase also increases by extending heat treatment time. As a balance among phase assemblage, dimension of particle and adequate reaction, a reasonable precursor powder can be obtained by heat-treated at 770 degrees C for 12 h-16 h in N-2-0.1%O-2 atmosphere. Critical current of 37-filament Bi-2223 tape is about 120 A, which confirms that these heat treatment parameters are reasonable.

With extremely high critical current density (Jc) and excellent strain tolerance, Nb 3 Al superconductor is considered as an alternative to Nb 3 Sn for application of high-filed magnets. However, complexity in the phase formation of Nb 3 Al hinders the Nb 3 Al superconducting wires to satisfy the requirement of engineering applications at present. Here, we have reported the improved performance of simple-structured 18-filamnet jelly-roll Nb 3 Al precursor long wires fabricated with rapid heating and quenching (RHQ) process. After processed with RHQ heat-treatment under various heating conditions, the Nb 3 Al wire were post-heat treated at a temperature between 700 °C to 1100 °C. The phase formation and the superconducting properties of the wires were investigated. It has been found that, even if the RHQ process deviates from the optimum processing state, the superconducting properties of the wire can be improved by appropriately selecting post-heat treatment conditions.

Ag-duped Nb3Al samples, Nb-3(Al1.05-xAgx), with x = 0, 0.05, 0.1, 0.15, and 0.2 are synthesized using high-energy ball milling method. At first, the raw materials are found to form Nb(Al, Ag)(ss) solid solution after 3 h of high-energy ball milling. With subsequent heat treatment, sintered at 900 degrees C for 5 h, a transformation from Nb(Al, Ag)(ss) into A15 Nb3AI phase occurred. The or-phase Nb2Al diffraction peaks have been observed in the XRD patterns of pure Nb3Al. However. with Ag doping, no sigma-phase Nb3Al has been detected. SEM images show an obvious difference, where the crystalline grain can he clearly observed in the matrix Nb3Al phase, but the grain boundary was blurred in the doped samples. The M-T curve illustrated that the superconducting transition temperature of the Ag doped Nb3Al compounds decreased with increasing dopants, but slight Ag doping can be effective to stabilize the Nb3Al A15 lattice.

In this paper, we compare the superconducting properties of Nb3Al wires prepared by two different techniques. The first is the in situ powder-in-tube method: first, the powder of the Nb-Al saturated solid solution, Nb(Al)ss, prepared by mechanical alloying is filled into a metal niobium tube, and then subjected to cold working such as swaging and drawing to form a wire. Heat treatment at 800-1000 °C converts the Nb(Al)ss phase to the Nb3Al phase. Another method is to use the jelly-roll technology to make the Nb-Al precursor wire, then use the rapid heating and quenching (RHQ) process to form the Nb(Al)ss phase, and finally, to transform the Nb(Al)ss phase into Nb3Al by heat-treatment at 800-900 °C. We found that although both the mechanical alloying method and the RHQ technique can make the Nb(Al)ss phase, the properties of the finally obtained Nb3Al wire have a big gap: the Nb3Al wire prepared by the RHQ process has much higher Tc and Jc. Phase structure analyses show that the RHQ energy density in the RHQ method plays a similar role as the milling time does in the mechanical alloying method, both of these parameters play important roles in controlling the crystal structure and microstructure of the Nb3 Al wires.