We present results on the in-field critical current (I c ) performance of 4.0 µm thick REBCO film with 15% Hf addition with fields up to 31.2 T and field orientations in the B∥ab plane and B∥c axis. Unlike the behavior at B∥c, the critical current at B∥ab is only very weakly dependent on field, decreasing from self-field to 31.2 T by only 22%, i.e. from the self-field value of ∼7700 A/4 mm width to ∼6300 and 5812 A/4 mm width at 14 and 30 T, respectively. These values are remarkably 3 and 5.7x higher than the corresponding critical currents at B∥c. The in-field behavior of the present 15% Hf sample at field orientation B∥c axis is nearly identical to the previously reported record values found in 4.3 and 4.6 µm thick 15% Zr samples in terms of critical current density. In contrast to the pinning force behavior in the B∥c orientation, which saturates to a constant value of 1.7 TN m −3 above ∼5-6 T, the pinning force in the B∥ab orientation increases near-linearly, reaching a remarkable value of over 11.5 TN m −3 at 31.2 T. These results demonstrate the potential of thick REBCO conductors at 4.2 K for high field and energy density applications, in particular where the magnetic field is contained near the ab-plane.

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High-temperature superconductors (HTS) make it possible to achieve magnetic fields beyond the 23.5 T limit of low-temperature superconductors (LTS). For higher energy density, high-performance HTS with Je > 1000 A/mm2 enable reduction in coil winding length and a smaller magnet size. Among HTS, REBa2Cu3O7-δ (REBCO, RE = rare earth) exhibits excellent mechanical properties and superior performance over a wide range of temperatures and magnetic fields. REBCO tapes can be converted to various formats, including round wires. The state-of-the-art REBCO superconductors for ultra-high field magnets, including cable/wire architectures, are reviewed. R&D needs to address remaining challenges with REBCO superconductors for ultra-high magnetic field applications are discussed.

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In the present work, 6061Al-TiB2 composites were synthesized using two types of base 6061Al powder (prealloyed and premixed) through powder metallurgy route. Dry sliding wear test was performed on the specimens using pin on disk apparatus to investigate the effect of TiB2 content on tribological characteristics. The microstructure, worn surface, and subsurface were also characterized using scanning electron microscope to examine the wear mechanism of prealloyed- and premixed-based composites. A mathematical model was developed using parameters (composition and applied load) to predict wear rate and correlated with experimental results. Adequacy of developed model has been validated using analysis of variance. Results indicated that premixed 6061Al-TiB2 composites have superior tribological properties as compared to the prealloyed 6061Al-TiB2 composite.

RE-Ba-Cu-O (REBCO, RE=rare earth) Symmetric Tape Round (STAR®) wires of 1.5 – 2.5 mm in diameter have been fabricated with 4 – 12 strands of symmetric REBCO tapes made by Advanced Metal Organic Chemical Vapor Deposition (MOCVD). 1.5 mm diameter STAR® wires made with just four Advanced MOCVD tape strands are able to sustain nearly the same critical current (Ic ) as 2.5 mm diameter STAR® wires made with 12 commercial-grade tape strands. An Ic of 1070 A, corresponding to an engineering current density (Je ) of 597 A/mm2, has been demonstrated at 4.2 K, 30 T in 1.5 mm diameter, 4-strand STAR® wire at a bend radius of 15 mm. This Ic value exactly matches the Ic expected from the lift factor of the tape strands used in the wire. The 2.5 mm diameter STAR® wires made with 12 Advanced MOCVD tape strands exhibit an Ic of 1,075 A at 77 K, self-field and sustained currents of 2,500 to 2,750 A at 4.2 K, 30 T before burnout, corresponding to a Je greater than 500 A/mm2. These results show that the cost of STAR® wires can be substantially reduced using fewer tape strands of high-performance Advanced MOCVD tapes and that the superior bend performance of STAR® wires can be maintained even using 12 strands of Advanced MOCVD tapes with 4-µm-thick REBCO films.

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