J. Eickemeyer

Cube textured nickel alloy tapes as substrates for YBa2Cu3O7−δ-coated conductors

Abstract Suitable substrates for biaxially textured high temperature superconducting YBa 2 Cu 3 O 7−δ -thin films, which are necessary to carry high currents, are highly cube ({001}〈100〉) textured Ni-tapes that can be produced by heavy cold rolling and succeeding recrystallization annealing. At high temperatures which are necessary for the deposition of the YBa 2 Cu 3 O 7−δ -film such tapes often tend to abnormal grain growth destroying the cube texture. It was found that this can be avoided by microalloying Ni with 0.1 at.% of different elements each leading to a texture improvement with increasing annealing temperature. YBa 2 Cu 3 O 7−δ -films deposited on these microalloyed tapes reach critical current densities up to 0.5×10 6 A/cm 2 . Also non-magnetic Ni-alloys, namely Ni–13 at.%Cr and Ni–9 at.%V, were successfully processed to highly cube textured tapes. Tapes made of these alloys are not only an improvement because magnetic losses are avoided but also because of a three times enhanced yield strength which is due to solid solution hardening.

Highly cube textured Ni–W-RABiTS tapes for YBCO coated conductors

Abstract The investigation of Ni–W alloys in the concentration range of solid solubility of tungsten in nickel proved the potential of this metallurgical system for rolling assisted biaxially textured substrate (RABiTS) tapes of high performance. The cube texture of Ni+5 at.%W was characterized by a maximum of the deviation frequency at about 4°. For this material the beneficial effect of the initial grain size on the final texture quality was shown. The YBCO (YBa 2 Cu 3 O 7− δ ) type coatings on CeO 2 buffer layers carried absolute currents up to I =130 A at 77 K. A critical current density of j c =1.2 MA/cm 2 was achieved at 77 K and zero field on tapes up to 20 cm long.

Biaxially textured Ni-alloy tapes as substrates for buffer and YBCO film growth

Abstract Impurities in Ni processed by cold rolling and annealing for the purpose of producing a cube textured substrate for YBCO film deposition (RABiTS) often evoke secondary recrystallisation that destroys the cube texture at a temperature below the deposition temperature of the buffer. By adding small amounts of a second element the secondary recrystallisation can be suppressed and very strong cube textures with a FWHM below 10° and less than 1% highly misoriented grains are achieved. The suitability of such substrates is proved by superconducting films with a critical current density exceeding 0.5×10 6 A/cm 2 . The disadvantages of ferromagnetism and the low tensile strength of Ni as substrate material have been overcome by alloying with 13 at.% Cr or 9 at.% V. The yield strength of these well textured non-magnetic substrates is almost three times higher than that of Ni tapes.

Grain boundary networks in Y123 coated conductors: Formation, properties and simulation

The grain boundary (GB) network in biaxially textured YBa/sub 2/Cu/sub 3/O/sub x/ (Y123) coated conductors is the key to their transport properties and determines the upper limit for the critical current density. In this contribution we report on detailed EBSD (electron backscattering diffraction) investigations of the formation of these GB networks in Y123 films deposited on highly biaxially textured metallic substrates and the comparison of the measured critical current density with simulations based on the exact knowledge of the underlying GB network. Highly cube textured Ni-tapes were prepared by rolling and recrystallization and detailed texture maps were determined by EBSD before and after the deposition of Y123 films by thermal evaporation or pulsed laser deposition. This allowed the quantitative evaluation of both the Y123-growth on different oriented Ni-grains and the GB misorientation network which determines the critical current density. This exact texture information was also used to calculate the critical current density based on the well known exponential j/sub c/-dependence across Y123 tilt GBs and is compared to the measured transport j/sub c/ across the same substrate area.

Elongated grains in textured substrate tapes and their effect on transport currents in superconductor layers

The development of cube textured flexible metallic substrate tapes is of basic interest for the economic production of YBa2Cu3Ox (YBCO) coated superconductors. Nickel tapes microalloyed with silver were prepared with the specific feature of an elongated grain structure. Cube textured NiO films were grown by surface oxidation epitaxy on these tapes retaining the elongated grains. Further, buffer layers and YBCO were deposited thereon. The YBCO layer transports an up to four times higher critical current density (Jc=2.35MA∕cm2) in the direction of grain elongation compared to the transversal one (Jc=0.55MA∕cm2).

On the development of high strength and bi-axially textured Ni-3%W/Ni-10%Cr-1.5%Al composite substrate for coated conductor application

Abstract Ni and Ni base alloys are good candidate substrate materials in the development of coated conductors. The present paper reports the development of a high strength (Ni–3%W/Ni–10%Cr–1.5%Al) composite tape of 80 μm thickness with strong cube texture.

Biaxially textured Ni-alloy tapes as substrates for buffer and Y-Ba-Cu-O film growth

Highly cube ({001} ) textured Ni- and Ni-alloy tapes are produced by heavy cold rolling and recrystallisation annealing. Due to impurities in Ni, abnormal grain growth destroying the cube texture often occurs at temperatures above 600/spl deg/C. This could be prevented by alloying Ni with 0.1 at.% of different elements each leading to a texture improvement with increasing annealing temperature. YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//-films deposited on these tapes reach critical current densities up to 0.5/spl times/10/sup 6/ A/cm/sup 2/. Also Ni-Cr and Ni-V were successfully processed to highly cube textured tapes. Their magnetic and mechanical properties were characterized. Ni-13 at.% Cr and Ni-11 at.% V have a Curie temperature below 77 K. Their yield strength is three times higher than that of unalloyed Ni.

Continuous YBa2Cu3O7-tape deposition by thermal evaporation

Abstract Ni and Ni-alloy rolling assisted biaxially textured substrates provided both from IFW Dresden and an industrial partner (Plansee GmbH) were employed for the deposition of YBCO-coated conductors by thermal evaporation. The main advantages of this process are high volume deposition rates and relatively low substrate temperatures of 680 °C. As a consequence, a simple, economic, and very thin 100 nm CeO 2 buffer layer has turned out to be sufficient for high quality YBCO growth. For samples up to 20 cm long, critical current densities of 1.2 MA/cm 2 were achieved at 77 K and 2 μm thick films sustained transport currents beyond 150 A. Recently, the first continuously operating prototype tape deposition system based on thermal evaporation has been put into operation. A reel-to-reel tape winding mechanism is capable of handling YBCO and buffer layer deposition on tape 10 mm wide and up to 100 m long has been implemented. The YBCO-deposition speed of 4 m/h for a 1 μm layer.

Effect of silver on cube texture formation in nickel substrate tapes

The effect of silver in pure nickel on the quality of the primary recrystallization cube texture was investigated after intense cold rolling and annealing. Texture sharpness and thermal stability in the nickel tapes could be improved by micro-alloying with silver in the range of 100–500 at. ppm Ag. The sharpest cube texture was observed for the Ni + 100 at. ppm Ag material after annealing at 550 °C (FWHM(111) = 4.4°). Further, the nickel oxide layer grown thereon had a sharp cube texture rotated by 45° relative to the metallic substrate. Grain boundaries showed a typical zigzag image and the grain form was fractal-like.

Dispersion strengthened and highly cube textured Ni alloy tapes as possible substrates for coated conductors

Abstract Ni and Ni base alloys are good candidate substrate materials in the development of long lengths of coated superconductors due to the development of strong cube texture following heavy cold working and recrystallisation. Increasing the tape strength is an important issue in order to facilitate the production of very thin and long lengths of high current carrying superconductors. The present paper reports the development of strongly cube textured and thin tapes (40 and 20 μm thickness) of an Ni–1 at.% Al alloy and strengthening of these tapes through controlled internal oxidation. Precipitation of finely dispersed Al 2 O 3 particles increased the yield strength by a factor of 3–5 compared to pure Ni tapes without losing the strong cube texture. The problem of surface degradation due to precipitation of Al 2 O 3 particles during internal oxidation was sought to overcome by the design of an Ni–Ni–1.5 at.% Al composite tape.