Uwe Gaitzsch

Highly alloyed Ni–W substrates for low AC loss applications

Cube texture formation has been studied in Ni?W alloys with a W content of 9?at.% and above. These alloys show a low magnetization at 77?K and below, and are therefore excellent candidates for use as substrates of coated conductors in AC applications. The application of a modified deformation and annealing sequence leads to a highly textured surface of Ni9W and Ni9.5W tapes with cube texture fractions above 96%. YBCO (YBa2Cu3O7??) layers obtained on these substrates using a standard buffer architecture showed a critical current density exceeding 1.5?MA?cm?2 at 77?K, similar to those for films on commercial Ni5W tapes. In contrast, only a weak cube texture was achieved in Ni10W tapes. The rolling texture of this alloy showed a significantly increased Goss component, which could not be reduced by applying intermediate annealing treatments. The influence of this texture on the cube texture formation will be discussed in detail.

Acoustic Assisted Magnetic Field Induced Strain in 5M Ni-Mn-Ga Polycrystals

Magnetic shape memory alloys can be deformed in an external magnetic field by twin boundary motion. By coupling in acoustic energy the strain can be enhanced significantly, especially if the twinning stress is just above the magnetically achievable stress level. Two percent of strain can be achieved in a polycrystalline material, which showed only 0.3% strain without acoustic assistance.

-Doped Thick Films on Highly Alloyed Textured Ni-W Tapes

YBa₂Cu₃O_7-δ (YBCO) films with a thickness of up to 2 μm containing nano-sized BaHfO₃ (BHO) have been grown on biaxially textured metal tapes by pulsed laser deposition. Transmission electron microscopy revealed the inclusion of Y₂O₃ platelets and rod-like BHO structures. A c-axis oriented growth of the YBCO layer and biaxial oriented incorporation of BHO is confirmed by X-Ray diffraction. BHO expands the c-axis of YBCO, flattens the surface of YBCO and densifies the films. Y₂O₃ inclusions get smaller and finer distributed, possibly with a positive influence on pinning effects. A superconducting transition temperature T_c of about 89 K was determined, decreasing slightly with increasing BHO content. Transport current measurements in the maximum Lorentz force configuration showed an increased irreversibility field H_irr and higher pinning force density F_p with increasing BHO content in high magnetic fields.