Mechanical Properties of Superpower and Sunam Rebco Coated Conductors

High Temperature superconductors (HTS) are the only way to achieve elds with superconducting magnets higher than the 25 T of Low Temperature Superconductors (LTS). No-Insulation (NI) REBCO magnets using REBa2Cu3Ox as the superconductor require less copper stabilizer than insulated magnets and thin (30 m) substrates have now become available. In our recent small coil attack on elds greater than 40 T, we have seen that overstrain damage can easily occur even at frequently used design strain of 0.4%. Here we present an experimental study of the uniaxial stress () characteristics of SuperPower and SuNAM coated conductors and also do strain-critical current (Ic()) measurements to nd the onset of permanent damage to Ic. We found considerable variability in their 77 K mechanical properties. The cold-rolled Hastelloy C-276 substrate of the SuperPower is much stronger than the cold-rolled 310 stainless steel substrate used by SuNAM, but of more concern is the variability of the strength of dierent batches of SuNAM tape. Mechanical variability in the dierent SuNAM batches creates a challenge when designing for magnets. We also examined the eects of strain on critical current performance, nding that the critical current of the SuNAM conductor becomes irreversible over a wide range of strains from 0.3-0.6%. Suspecting that some annealing of the substrates occurs during REBCO deposition in the vicinity of 750 C, we performed short heat treatments at 700, 750, and 800 C of samples of the as-delivered substrates used by manufacturers. We found that there was little change to strength of the Hastelloy used by SuperPower but substantial change to the 310 stainless steel used by SuNAM. Our results show that any high eld operation at strains of 0.4% or more requires detailed knowledge of the mechanical properties of the tapes being used, especially for magnets using SuNAM tapes with cold-rolled 310 stainless steel substrates.