Superior engineering critical current density obtained via hot isostatic pressing of MgB2 wires manufactured using nano-amorphous isotopic boron

• Published in: Journal of alloys and compounds 2021-08, Vol.871, p.159579, Article 159579
• Main Authors: Gajda, D., Zaleski, A.J., Morawski, A.J., Babij, M., Szymański, D., Gajda, G., Rindfleisch, M.A., Shahbazi, M., Hossain, M.S.A.
• Format: Article
• Language: English
• Subjects: Annealing; Boron; Connectivity; Critical current density; Critical field (superconductivity); Engineering critical current density; Grain connectivity; Heat treatment; High temperature; HIP process; Hot isostatic pressing; Isostatic pressure; Magnesium compounds; Magnetic fields; Magnets; Mg11B2 wires; Nano amorphous 11B; Pinning centers; Superconductivity; Transition temperature
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2021.159579

•Long annealing time and high annealing temperature allow to obtain a dense longitudinal layer.•The dense longitudinal layer significantly increases the number of connections between grains.•Heat treatment under high isostatic pressure allows to obtain more dense longitudinal layersHeat treatment under high isostatic pressure (HIP) increase density of high fields pinning centers. The effects of heat treatment temperature, time and isostatic pressure on the grain connectivity and superconducting properties of Mg11B2 wires prepared using nano-amorphous isotopic boron powder (11B) have been investigated. The article presents detailed studies of the Mg11B2 material structure of the wires using scanning electron microscope (SEM). Heat treatment at low and high temperature for different annealing time and isostatic pressure does not create an internal macro-defect that disrupts connectivity in the Mg11B2 superconducting wires. Our study shows that dense longitudinal superconducting layers are formed at high annealing temperature of 800 °C for 60 min. Formation of dense longitudinal superconducting layers under high isostatic pressure (HIP) allow improved grain connectivity and high density of pinning centers and as a result, high engineering critical current density, Jec, at 4.2 K has been achieved. Also, high upper critical field (Bc2) and high irreversible magnetic field (Birr) were obtained using HIP process while superconducting transition temperature (Tc) was not significantly affected. Better grain connectivity obtained using high annealing temperature and long annealing time under low isotopic pressure leads to Jec enhancement at high magnetic fields at 20 K. Our results show that the annealing temperature of 800 °C for 60 min under isostatic pressure of 1 GPa yields the required Jec of 25 A/mm2 and 50 A/mm2 for ITER applications in magnetic fields of 8 T and 7 T, respectively. The promising results obtained in this work could pave the way for designing low activation superconducting Mg11B2 wires to be considered for next generation fusion magnets.