Stainless Steel as Substrate Material for High-Temperature Superconducting Tapes Processed Via the ISD MgO Route

Second-generation high-temperature superconducting (HTS) tapes strongly rely on the substrate material, in many cases Hastelloy C276 ('H-C276'). In order to ameliorate performance (and reduce the price) of superconducting tapes, replacement of H-C276 has been investigated. In this paper, the potential of the readily available austenitic stainless steels X2CrNiMo17-12-2 ('CrNiMo') and X11CrNiMnN19-8-6 ('CrNiMnN') as substrates is assessed. It was found that CrNiMnN is not suitable as a replacement for H-C276. Tensile stresses occurring at elevated temperatures during the HTS tape production result in plastic deformation of the CrNiMnN substrate. In the case of CrNiMo, however, plastic deformation was not observed after processing of the HTS tape. Electrical losses as a result of alternating currents beyond those of H-C276 did not occur due to the paramagnetic nature of CrNiMo. It is demonstrated that, for the very same processing parameters, HTS films deposited on electrochemically polished and buffered CrNiMo substrates exhibit similarly high critical current densities as on polished and buffered H-C276 substrates. The application of CrNiMo stainless steel reduces substrate costs considerably. More importantly, tapes processed on CrNiMo substrates withstand higher tension strains with respect to the reduction of the critical current compared to H-C276 substrates. This effect is interpreted to be a result of the matching coefficients of thermal expansion of the HTS layer and CrNiMo, resulting in lower residual tensile stress in the HTS layer after processing.