Improvement of Delamination Strength of REBCO Coated Conductors

Recent progress in development of RE₁Ba₂Cu₃O_x (REBCO, RE: Y and Rare Earth) coated conductors has been remarkable, which makes practical applications realistic. Considering the major applications, long coated conductors are expected to be used as coils. Improvement of delamination strength throughout the long tape is important issue as well to meet the requirements of those applications. Effect of processing on delamination strength was analyzed in this work. The delamination strength can be distinguished into 3 groups depending on the origins of delamination; weak strength (<30 MPa) occurred from MOD-GZO due to pores in it. Densification of the layer by using higher calcination temperature in the heat treatment eliminated this type of delamination. Middle strength (30- 50 MPa) was due to cracks near the bed layer/substrate interface which were caused by the oxygenation of metallic substrate due to exposure to high temperature during GdBCO deposition. It was clarified that shortening the deposition time is effective to minimize the effect. High strength (>50 MPa) was realized by elimination of those defects which can be controlled by optimization of the process. Statistical analysis showed the improved process gives only one weak spot per thousands of kilometers long tape. The improvement of processing was effective to obtain high delamination strength throughout long wires.