In this study, we investigate the scandium-containing Sc-Hf-Nb-Ta-Ti-Zr system of refractory high-entropy alloys (HEAs). Using the arc-melting method, we synthesized nine equimolar alloys (five 4-, three 5- and one 6-component), with all of them containing Sc. The alloys were characterized by XRD, electron microscopy and EDS, while superconductivity was investigated via electrical resistivity, specific heat and the Meissner effect. The results were compared to the parent Hf-Nb-Ta-Ti-Zr refractory HEAs, forming a single-phase body-centered cubic (bcc) structure and quite homogeneous microstructure. The addition of Sc produces a two-phase structure in the Sc-Hf-Nb-Ta-Ti-Zr alloys, with one phase being bcc and the other hexagonal close-packed (hcp). The hcp phase absorbs practically all Sc, whereas the Sc-poor bcc phase is identical to the bcc phase in the Hf-Nb-Ta-Ti-Zr parent system. Upon the Sc addition, the microstructure becomes very inhomogeneous. Large bcc dendrites (10–100 µm) are homogeneous in the central parts, but become a fine dispersion of sub-micron precipitates of the bcc and hcp phases close to the edges. The interdendritic regions are also a fine dispersion of the two phases. Superconductivity of the Sc-Hf-Nb-Ta-Ti-Zr alloys originates from the bcc phase fraction, which demonstrates identical superconducting parameters as the bcc Hf-Nb-Ta-Ti-Zr parent alloys, while the Sc-containing hcp phase fraction is non-superconducting.

In the quest for climate neutrality in the aviation industry by 2050, technology development is one of the main pathways for Airbus. Owing to their high efficiency and current density, use of superconducting DC and AC distribution lines are a potential enabler for fully electric propulsion in a longer range aircraft, in particular in the scenario where liquid hydrogen provides a cold source on board of the aircraft. The ground-based Advanced Superconducting and Cryogenic Experimental power traiN Demonstrator (ASCEND) at Airbus intends to demonstrate the potential and feasibility of a cryogenic and superconducting powertrain as a breakthrough electric propulsion solution on future electric aircraft. A direct current distribution network is used in a generic propulsion system to transfer 500 kW power from the DC supply to an electrical converter, which transforms the energy into an alternating voltage/current to drive the superconducting motor. A relatively low voltage level of 300 V, and a current of 1700 A, is chosen to optimize the safety and installation in a future aircraft by operating at relatively low voltage. The DC link consists of a 10 m long two-pole superconducting Conductor on Round Core (CORC) cable, and demountable current leads, that transfer the power from the room temperature environment to the cryogenically cooled motor control unit. Downstream of this unit a 3-phase AC link operating at 500 Hz delivers power to a superconducting motor. Both the AC and DC links are cooled with a flow of subcooled LN ₂ . The components of the DC and AC links have been designed, manufactured and recently integrated into the ASCEND test bench in Ottobrunn, Germany. We present the powering of the DC link up to nominal current, as well as commissioning and integration experience.

This paper investigates transport AC loss in CORC cables for the ground-based demonstrator ASCEND at Airbus, which studies the feasibility of a superconducting powertrain for electric aircraft. The demonstrator includes a three-phase AC link consisting of three parallel cables operating at 500 Hz and 2350 A peak current. The transport AC loss of the three-phase cable is estimated using a 2D model assuming equal current in all tapes. The model predicts an AC loss of 40 W at 77.5 K and 0.4 W at 65 K. A second model is proposed, which computes the current distribution between the tapes in a single cable using mutual inductance matrices for helical tape conductors. This model predicts that, at 500 Hz, the outer two layers of a CORC cable carry a disproportionate fraction of the current. This will lead to additional AC loss if the critical current in the outer layers is exceeded. AC transport loss was measured on single CORC cables. Both models significantly underestimate the measured loss. Also, a frequency-dependent quench current below the DC critical current was observed at 48 Hz and 96 Hz.

In an attempt to incorporate tin (Sn) into high-entropy alloys composed of refractory metals Hf, Nb, Ti and Zr with the addition of 3d transition metals Cu, Fe, and Ni, we synthesized a series of alloys in the system HfTiZrSnM (M = Cu, Fe, Nb, Ni). The alloys were characterized crystallographically, microstructurally, and compositionally, and their physical properties were determined, with the emphasis on superconductivity. All Sn-containing alloys are multi-phase mixtures of intermetallic compounds (in most cases four). A common feature of the alloys is a microstructure of large crystalline grains of a hexagonal (Hf, Ti, Zr)₅Sn₃ partially ordered phase embedded in a matrix that also contains many small inclusions. In the HfTiZrSnCu alloy, some Cu is also incorporated into the grains. Based on the electrical resistivity, specific heat, and magnetization measurements, a superconducting (SC) state was observed in the HfTiZr, HfTiZrSn, HfTiZrSnNi, and HfTiZrSnNb alloys. The HfTiZrSnFe alloy shows a partial SC transition, whereas the HfTiZrSnCu alloy is non-superconducting. All SC alloys are type II superconductors and belong to the Anderson class of “dirty” superconductors.