The effect of the 2D internal strain state on the critical current in GdBCO coated conductors

Abstract

A reversible effect of strain on the critical current (Ic) has been reported for REBa2Cu3O7−δ (REBCO) coated conductors. In this study, the strain sensitivity of Ic was compared for GdBCO coated conductors with different crystal orientations. Extremely small strain sensitivity was confirmed from tensile and bending tests at 77 K for a GdBCO film with the [110] direction parallel to the tape length (Gd-F), while a GdBCO film with the [100] or [010] direction parallel to the tape length (Gd-I) has much stronger strain dependence of Ic. To compare the strain sensitivity of Ic based on internal strain, the lattice strain was evaluated for a GdBCO film in a composite conductor by employing a diffraction technique using synchrotron radiation. The lattice strain was determined along both the a- and b-axes for the orthogonal domains that are generated by the twin structure of GdBCO film. A distinct difference in the 2D strain state that depended on the crystal orientation was revealed for the GdBCO coated conductors. In Gd-I, the lattice strains along the axial and lateral directions are tensile and compressive under tensile loading, respectively, that is, the 2D internal strain state is anisotropic. On the other hand, an almost isotropic 2D strain state was confirmed in Gd-F. In addition, the strain components along the crystal axes in Gd-F are much smaller than the axial strain components in Gd-I. This difference in the internal strain state is attributed to the difference in strain sensitivity between the GdBCO coated conductors with different crystal orientations. The contributions of the strain components along the a- and b-axes to Ic are discussed on the basis of the measured strain sensitivities and internal strains for two conductors.

Review of progress in electromechanical properties of REBCO coated conductors for electric device applications

“…For samples having Hastelloy substrate, the intrinsic strain response of I c /I cmax under bending was well correlated with those under uniaxial tension. The intrinsic strain sensitivity of I c in GdBCO CC tapes depends on the crystal orientation of the GdBCO coating film as have been reported by Sugano et al and van der Laan et al [34,35]. RCE-DR and MOCVD processed GdBCO CC samples investigated have similar crystal orientation parallel to the tapes length and this might be the reason that they showed similar strain sensitivity.…”

“…Exponent of this function varies in some reports [33]. For GdBCO CC tapes, the strain sensitivity value obtained in the RCE-DR and MOCVD processed samples is 0.177 similarly with a=0.199 in PLD processed sample having the same GdBCO film crystal orientation as reported by Sugano et al [34]. For samples having Hastelloy substrate, the intrinsic strain response of I c /I cmax under bending was well correlated with those under uniaxial tension.…”

Strain Distribution in REBCO-Coated Conductors Bent With the Constant-Perimeter Geometry

“…For REBCO tapes fabricated with the metal-organic chemical-vapor deposition route, both axial and transverse strains lead to the highest strain sensitivity of the I c through the impact on the critical temperature of REBCO [51][52][53]. The transverse and axial strain in the helical configuration can be varied with the winding angle (section IV-A).…”

Investigation on the electromechanical properties of RCE-DR GdBCO CC tapes under transversely applied load

“…From the pressure dependence of I c , it is not much affected along the c-axis. However, based on these results, it appears that I c is also affected by stress at transverse loading direction (c-axis orientation) similar with the uniaxial tension test (a-b plane) [9,10]. However, in regards to this study, further examinations on the occurrence of micro cracks, debonding zones and other I c degradation related deformations are needed for better understanding of the mechanism.…”