Materials qualification of a new process for manufacturing high temperature superconducting bulks
PI: Speller, Susannah
High temperature superconducting (HTS) materials in bulk form can be energised to form very strong and compact permanent magnets can potentially be used in a wide range of technologies from cheap, limb-scale magnetic resonance imaging to rotating machines with improved power-to-weight ratio for electric aircraft. However, they are very challenging to manufacture because it is essential to avoid high angle grain boundaries which act like dams, completely blocking the macroscopic flow of supercurrents that generate the magnetic field. This necessitates a complex and very slow melt-growth process using a seed crystal to nucleate the growth of the superconducting phase during solidification. This process was developed more than 30 years ago, but the crystal grows in 5 directions simultaneously from a seed placed on the top of the sample, leading to chemical inhomogeneities and intractable difficulties scaling up to the larger samples required for practical applications. CAN Superconductors, a commercial manufacturer of HTS bulks, are developing a new manufacturing process that involves growth in a single direction from a reusable seed plate, with the aim of avoiding both the issues that lead to growth failure and also enabling the growth of larger and hopefully more uniform samples. This project involves applying multi-scale, multi-technique characterisation and analysis methodologies devised by the secondee during her DPhil research to HTS bulk samples grown by this promising new process, and developing and translating suitable materials qualification protocols for routine application at CAN Superconductors. Analytic scanning electron microscopy techniques will be used to map macro- and microscopic chemical and crystallographic variations to determine the size and distribution of insulating particles (deliberately added to improve superconducting performance) and to identify how grain boundaries form, with the aim of modifying the growth process to avoid them.