Influence of processing methods on residual stress evolution in coated conductors

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Several processing methods are under study for deposition of different layers of YBa 2 Cu 3 O 7− x - (YBCO-) coated conductors. The effect of these processing techniques on residual stress evolution in thin films of yttria-stabilized zirconia (YSZ) and YBCO was evaluated by measurement of the residual stresses using x-ray diffraction (XRD). The YSZ films (textured and nontextured) were deposited on Hastelloy C substrates by ion-beam-assisted deposition (IBAD), and the YBCO films were deposited on lanthanum aluminate (LaAlO 3 ) substrates by pulsed laser deposition (PLD) and sol–gel techniques. The measured residual stresses in the YSZ films (both textured and nontextured) were more compressive than the calculated thermal mismatch stress between Hastelloy C and YSZ, apparently due to intrinsic compressive stresses induced in the YSZ films during IBAD processing. In addition, a lower compressive residual stress was measured in the textured YSZ film compared to the nontextured film because of a reduction in the intrinsic compressive stress in the textured film. PLD processing of YBCO films on LaAlO 3 substrate resulted in a lower tensile residual stress (in the YBCO film) than the calculated thermal mismatch stress between YBCO and LaAlO 3 . This difference is attributed to the generation of intrinsic compressive stresses in the YBCO film during PLD, in a manner similar to IBAD. In comparison to IBAD and PLD, sol–gel processing apparently generated negligible intrinsic stresses, resulting in a good agreement between the measured residual stress in the YBCO film and the calculated thermal mismatch stress between YBCO and LaAlO 3 .