- Email: [email protected]
Fabrication of biaxially textured Cu–Ni alloy tapes for YBCO coated conductor
Physica C 386 (2003) 353–357 www.elsevier.com/locate/physc
Fabrication of biaxially textured Cu–Ni alloy tapes for YBCO coated conductor K. Shi
a,b,*
, Y. Zhou a, J. Meng a, J. Yang b, G.Y. Hu b, H.W. Gu b, G.S. Yuan a
b
Applied Superconductivity Research Center, Tsinghua University, Beijing 100084, China b General Research Institute for Nonferrous Metals, Beijing 100088, China
Abstract Nickel is well suited as a substrate material for YBa2 Cu3 O7x coated conductors. However, nickelÕs ferromagnetism leads to AC losses when it is used in AC applications. In this paper, Cu–Ni non-magnetic tapes were made for YBa2 Cu3 O7x film deposition. The biaxially textured Cu–Ni alloy tapes were formed through heavy cold rolling followed by recrystallization heat treatment. Cu–Ni alloy tapes with sharp cube texture, full width at half maximum (FWHM) less than 9° for X-ray (1 1 1) u-scan, were obtained. The NiO(2 0 0) buffer layer was formed on Cu–Ni alloy tapes by using surface-oxidation epitaxy method. The textures of the substrate and the NiO(2 0 0) buffer layer were characterized by X-ray diffraction h–2h-scan, u-scan and pole figures. The surface morphology of NiO buffer layer on the Cu–Ni alloy tapes was observed by scanning electron microscope. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 85.25.K; 81.65.M; 81.40.E Keywords: Biaxially textured Cu–Ni tape; Non-magnetic; NiO; Surface-oxidation epitaxy
1. Introduction The rolling assisted biaxially textured substrates (RABiTS) technique is a very promising route for HTS coated conductor production [1,2]. In a large portion of the work on RABiTS, nickel has been used as the substrate material [3]. However, for YBa2 Cu3 O7x coated conductor on Ni, additional hysteretic losses could occur when it uses in AC applications, i.e. the ferromagnetism of Ni may contribute to losses in that case [4,5]. Several * Corresponding author. Address: Applied Superconductivity Research Center, Tsinghua University, Beijing 100084, China. Fax: +86-10-62785913. E-mail address: [email protected] (K. Shi).
studies have been carried out on non-magnetic substrates, such as Ni–Cu alloy substrate [6]. In comparison with nickel, Cu–Ni alloy is non-magnetic material. In this work, Cu–Ni non-magnetic tapes were made for high critical current density YBa2 Cu3 O7x film deposition. In the RABiTS method, biaxially textured buffer layers are deposited on the substrate in order to suppress the diffusion of Ni. In previous study, the randomly orientation NiO(1 1 1) would be formed in some oxidation atmosphere when buffer layers such as CeO2 or YSZ were deposited on Ni substrate, resulting in the degradation of the superconducting properties. The random NiO(1 1 1) layer can be avoided by using a reducing atmosphere (Ar/ H2 ) in the process of buffer layers deposition [7,8].
0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0921-4534(02)02197-4
354
K. Shi et al. / Physica C 386 (2003) 353–357
In 1997, the surface-oxidation epitaxy (SOE) method was invented by Matsumoto et al. in order to realize a biaxially textured NiO layer on a nickel tape surface [8,9]. This method seems to be useful for speeding up tape manufacturing, since the SOE batch process can easily form the biaxially textured NiO(2 0 0) layer. Meanwhile, this method is more advantageous than other methods from the viewpoint of simplification of the buffer layer formation. In this paper, SOE method was used to form NiO(2 0 0) on the Cu–Ni alloy tapes.
2. Experimental The Cu–Ni alloy was prepared by using high purity (>99.99%) Cu and Ni, and was melted in a high-frequency induction furnace. Finally, ingots with the original geometric shape of 80 38 14 mm3 were obtained. The ingots were cut into several bars. These bars were successively rolled to tapes with thickness of 125–150 lm. Total cross-section reduction of the tapes was larger than 98%. After rolling, the tapes were annealed at different temperatures between 750 and 1000 °C for 2–4 h in a high vacuum (106 – 107 Torr) furnace. The biaxially oriented NiO layer by oxidation of the f1 0 0gh0 0 1i textured Cu–Ni tape obtained above as the first buffer layer for YBa2 Cu3 O7x coated conductor. The oxidation process was carried out in a vacuum furnace, at 400–800 °C for 1–2 h in flowing Ar, O2 , or Ar/O2 gas at a flow rate of 40–100 cc/min. The orientation of the biaxially textured NiO films and Cu–Ni alloy substrates were measured by X-ray diffraction (XRD) h–2hand u-scan. The surface morphology of NiO buffer layer on the Cu–Ni alloy tapes was observed by scanning electron microscopy (SEM).
3. Results and discussion Fig. 1 shows an X-ray (1 1 1) pole figure of the as rolled Cu–Ni alloy tapes. Fig. 2 shows orientation density function (ODF) sections of the deformation texture (u2 ¼ 45°: left column and u2 ¼ 60°: right column). The C component f1 1 2gh1 1 1i that
Fig. 1. X-ray (1 1 1) pole figure for an as rolled Cu–Ni alloy sheet. C and S are the main components of the rolling texture of the Cu–Ni alloy substrate.
represents the main characteristic of copper-type texture is shown. The S component f1 2 3gh6 3 4i is also shown in the ODF section (the right column of Fig. 2). When samples were annealed at low temperature such as 400 °C, a considerable amount of deformation texture still remained. For a 600 °C annealing temperature, cube texture development was observed, indicating that the recrystallization behavior of the Cu–Ni alloy is similar to that of the higher stacking fault energy FCC metals such as nickel. There is a large amount of S component in the deformation texture. The orientation relation between S f1 2 3gh6 3 4i component and cube texture can be described as [1 1 1] rotations of about 40°. According to the theory of oriented-growth (OG), the preferential growth gives rise to a significant amount of cube texture [10]. The full width at half maximum (FWHM) of (1 1 1) u-scans decreased with the increasing annealing temperature (Fig. 3). At higher temperatures such as 850 °C and above, sharp cube textured Cu–Ni alloy substrate was obtained. The pole figure of Cu–Ni (1 1 1) diffraction for the samples annealed at 1000 °C for 1 h is shown in
K. Shi et al. / Physica C 386 (2003) 353–357
355
Fig. 2. ODF sections (u2 ¼ 45° and u2 ¼ 60°) of deformation texture in as rolled Cu–Ni alloy tapes. The lines are iso-ODF value lines with intensities of the step of 2.
Fig. 3. (1 1 1) u-scan of the Cu–Ni substrate annealed at different temperatures. The FWHM of the (1 1 1) u-scan decreases with increasing annealing temperature.
Fig. 4. It indicated that the Cu–Ni alloy substrate was sharp cube textured. The FWHM of (1 1 1) uscan was less than 9° (Fig. 3). After the sharp cube textured Cu–Ni alloy tapes were obtained, the SOE method was used to form
Fig. 4. X-ray (1 1 1) pole figure for a rolled and recrystallized Cu–Ni alloy substrate. (1 1 1) peak positions indicate the presence of only the f1 0 0gh0 0 1i cube orientation.
NiO(2 0 0) film as the first buffer layer on the Cu–Ni alloy substrate.
356
K. Shi et al. / Physica C 386 (2003) 353–357
Fig. 6. Typical XRD h–2h-scan and (1 1 1) u-scan of NiO film fabricated on the Cu–Ni alloy substrate. Under Po2 of 1 Pa and 800 °C. Fig. 5. Typical XRD h–2h-scans for Cu–Ni alloy substrates oxidized in different gas atmospheres: B is pure Ar; C is Ar/O2 atmosphere; D is O2 .
Fig. 5 shows XRD h–2h results from samples that were oxidized in different atmospheres at 400 °C for 1 h. In the figure, the plot B, C and D denote samples that were oxidized in Ar, Ar/10%O2 and O2 atmospheres respectively. With decreasing content of oxygen, different oxides were obtained. At this temperature, sharp cube textured NiO buffer layer can be fabricated in the lowest Po2 atmosphere (Ar). However, the NiO(2 0 0) buffer layer that fabricated under these conditions is too thin to prevent the diffusion of the Cu–Ni substrate. The reason may lie in that the content of oxygen in the Ar is too low. A precise control of the Po2 in the atmosphere is a key factor to get a suitable final cube textured NiO(2 0 0) buffer layer. An optimized pure cube oriented NiO(2 0 0) buffer layer was fabricated in oxygen partial pressure of 1 Pa, using a flow rate of 40 cc/min and a temperature of 800 °C. This NiO(2 0 0) buffer layer fabricated on the Cu–Ni substrate exhibited a high degree of texturing as examined by XRD h–2h-scan and (1 1 1) u-scan. Fig. 6 shows a typical XRD h–2h spectrum for the NiO/Cu–Ni under this condition. It also exhibits the u-scan spectrum of the NiO(1 1 1). The FWHM of the (1 1 1) u-scan is less than 10°, demonstrating good in-plane alignment. SEM investigation of the NiO(2 0 0) layer on the Cu–Ni substrate at a magnification of 2400
Fig. 7. SEM micrograph of the NiO on the Cu–Ni substrate (2400) showing a crack free surface.
shows no evidence of any micro cracking (Fig. 7). But the surface quality needs to be improved, indicating the necessity of an oxide cap layer to improve the surface qualities of the NiO layer. MgO may be fabricated on the NiO/Cu–Ni substrate as the cap layer [11]. Such structure would provide a promising candidate for developing YBa2 Cu3 O7x film on Cu–Ni tapes.
4. Summary Non-magnetic cube textured substrates were fabricated in order to avoid the ferromagnetism of
K. Shi et al. / Physica C 386 (2003) 353–357
Ni substrate at 77 K. A sharp cube textured Cu–Ni alloy substrate was obtained through heavy cold rolling followed by recrystallization heat treatment. The FWHM of the (1 1 1) u-scan is less than 9°. The cube texture was strengthened with the increasing annealing temperature. NiO(2 0 0)/Cu–Ni substrates were produced by using SOE method. The partial pressure of oxygen plays important role in the development of the NiO(2 0 0). The NiO buffer layer on the Cu–Ni tape shows good in plane and c-axis alignment. The FWHM of the u-scan is less than 10°. The NiO layer serves as a template for epitaxial growth of YBa2 Cu3 O7x film, and as a barrier layer to prevent the interaction between the Cu–Ni alloy substrate and YBa2 Cu3 O7x film. Acknowledgement This research work was supported by China National Center for Research and Development of Superconductivity.
357
References [1] A. Goyal et al., Appl. Supercond. 403–427 (1996) 4. [2] Q. He, D.K. Christen, R. Feenstra, D.P. Norton, M. Paranthaman, E.D. Specht, D.F. Lee, A. Goyal, D.M. Kroeger, Physica C 314 (1999) 105. [3] D.P. Norton, A. Goyal, J.D. Budai, D.K. Christen, D.M. Kroeger, E.D. Specht, Q. He, B. Saffian, M. Paranthaman, C.E. Klabunde, D.F. Lee, F.A. List, Science 274 (1996) 755. [4] P.R. Morris, Adv. X-ray Anal. 18 (1975) 514. [5] W.T. Norris, J. Phys. D. Appl. Phys. 3 (1970) 489. [6] B.De. Boer, J. Eickemeyer, N. Reger, L. Fernandez G.-R., J. Richter, B. Holzapfel, L. Schultz, W. Prusseit, P. Berberich, Acta Mater. 49 (2001) 1421–1428. [7] J. Yang, D. Shi, X.H. Wang, A.S. Liu, G.S. Yuan, Physica C 337 (2000) 67–70. [8] K. Matsumoto, S.B. Kim, K. Yamagiwa, Y. Koike, I. Hirabayashi, T. Watanabe, N. Uno, M. Ikeda, Physica C 335 (2000) 39–43. [9] K. Matsumoto, Y. Niiori, I. Hirabayashi, N. Koshizuka, T. Watanabe, Y. Tanaka, M. Ikeda, in: K. Osamura, I. Hirabayashi (Eds.), Advances in Superconductivity, vol. 10, Springer, Tokyo, 1998, p. 611. [10] B. Liebmann, K. Lucke, G. Masing, Z. Metallkd. 47 (1956) 57. [11] T. Watanabe, K. Matsumoto, T. Maeda, T. Tanigawa, I. Hirabayashi, Physica C 357–360 (2001) 914–922.
Fabrication of biaxially textured Cu–Ni alloy tapes for YBCO coated conductor K. Shi
a,b,*
, Y. Zhou a, J. Meng a, J. Yang b, G.Y. Hu b, H.W. Gu b, G.S. Yuan a
b
Applied Superconductivity Research Center, Tsinghua University, Beijing 100084, China b General Research Institute for Nonferrous Metals, Beijing 100088, China
Abstract Nickel is well suited as a substrate material for YBa2 Cu3 O7x coated conductors. However, nickelÕs ferromagnetism leads to AC losses when it is used in AC applications. In this paper, Cu–Ni non-magnetic tapes were made for YBa2 Cu3 O7x film deposition. The biaxially textured Cu–Ni alloy tapes were formed through heavy cold rolling followed by recrystallization heat treatment. Cu–Ni alloy tapes with sharp cube texture, full width at half maximum (FWHM) less than 9° for X-ray (1 1 1) u-scan, were obtained. The NiO(2 0 0) buffer layer was formed on Cu–Ni alloy tapes by using surface-oxidation epitaxy method. The textures of the substrate and the NiO(2 0 0) buffer layer were characterized by X-ray diffraction h–2h-scan, u-scan and pole figures. The surface morphology of NiO buffer layer on the Cu–Ni alloy tapes was observed by scanning electron microscope. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 85.25.K; 81.65.M; 81.40.E Keywords: Biaxially textured Cu–Ni tape; Non-magnetic; NiO; Surface-oxidation epitaxy
1. Introduction The rolling assisted biaxially textured substrates (RABiTS) technique is a very promising route for HTS coated conductor production [1,2]. In a large portion of the work on RABiTS, nickel has been used as the substrate material [3]. However, for YBa2 Cu3 O7x coated conductor on Ni, additional hysteretic losses could occur when it uses in AC applications, i.e. the ferromagnetism of Ni may contribute to losses in that case [4,5]. Several * Corresponding author. Address: Applied Superconductivity Research Center, Tsinghua University, Beijing 100084, China. Fax: +86-10-62785913. E-mail address: [email protected] (K. Shi).
studies have been carried out on non-magnetic substrates, such as Ni–Cu alloy substrate [6]. In comparison with nickel, Cu–Ni alloy is non-magnetic material. In this work, Cu–Ni non-magnetic tapes were made for high critical current density YBa2 Cu3 O7x film deposition. In the RABiTS method, biaxially textured buffer layers are deposited on the substrate in order to suppress the diffusion of Ni. In previous study, the randomly orientation NiO(1 1 1) would be formed in some oxidation atmosphere when buffer layers such as CeO2 or YSZ were deposited on Ni substrate, resulting in the degradation of the superconducting properties. The random NiO(1 1 1) layer can be avoided by using a reducing atmosphere (Ar/ H2 ) in the process of buffer layers deposition [7,8].
0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0921-4534(02)02197-4
354
K. Shi et al. / Physica C 386 (2003) 353–357
In 1997, the surface-oxidation epitaxy (SOE) method was invented by Matsumoto et al. in order to realize a biaxially textured NiO layer on a nickel tape surface [8,9]. This method seems to be useful for speeding up tape manufacturing, since the SOE batch process can easily form the biaxially textured NiO(2 0 0) layer. Meanwhile, this method is more advantageous than other methods from the viewpoint of simplification of the buffer layer formation. In this paper, SOE method was used to form NiO(2 0 0) on the Cu–Ni alloy tapes.
2. Experimental The Cu–Ni alloy was prepared by using high purity (>99.99%) Cu and Ni, and was melted in a high-frequency induction furnace. Finally, ingots with the original geometric shape of 80 38 14 mm3 were obtained. The ingots were cut into several bars. These bars were successively rolled to tapes with thickness of 125–150 lm. Total cross-section reduction of the tapes was larger than 98%. After rolling, the tapes were annealed at different temperatures between 750 and 1000 °C for 2–4 h in a high vacuum (106 – 107 Torr) furnace. The biaxially oriented NiO layer by oxidation of the f1 0 0gh0 0 1i textured Cu–Ni tape obtained above as the first buffer layer for YBa2 Cu3 O7x coated conductor. The oxidation process was carried out in a vacuum furnace, at 400–800 °C for 1–2 h in flowing Ar, O2 , or Ar/O2 gas at a flow rate of 40–100 cc/min. The orientation of the biaxially textured NiO films and Cu–Ni alloy substrates were measured by X-ray diffraction (XRD) h–2hand u-scan. The surface morphology of NiO buffer layer on the Cu–Ni alloy tapes was observed by scanning electron microscopy (SEM).
3. Results and discussion Fig. 1 shows an X-ray (1 1 1) pole figure of the as rolled Cu–Ni alloy tapes. Fig. 2 shows orientation density function (ODF) sections of the deformation texture (u2 ¼ 45°: left column and u2 ¼ 60°: right column). The C component f1 1 2gh1 1 1i that
Fig. 1. X-ray (1 1 1) pole figure for an as rolled Cu–Ni alloy sheet. C and S are the main components of the rolling texture of the Cu–Ni alloy substrate.
represents the main characteristic of copper-type texture is shown. The S component f1 2 3gh6 3 4i is also shown in the ODF section (the right column of Fig. 2). When samples were annealed at low temperature such as 400 °C, a considerable amount of deformation texture still remained. For a 600 °C annealing temperature, cube texture development was observed, indicating that the recrystallization behavior of the Cu–Ni alloy is similar to that of the higher stacking fault energy FCC metals such as nickel. There is a large amount of S component in the deformation texture. The orientation relation between S f1 2 3gh6 3 4i component and cube texture can be described as [1 1 1] rotations of about 40°. According to the theory of oriented-growth (OG), the preferential growth gives rise to a significant amount of cube texture [10]. The full width at half maximum (FWHM) of (1 1 1) u-scans decreased with the increasing annealing temperature (Fig. 3). At higher temperatures such as 850 °C and above, sharp cube textured Cu–Ni alloy substrate was obtained. The pole figure of Cu–Ni (1 1 1) diffraction for the samples annealed at 1000 °C for 1 h is shown in
K. Shi et al. / Physica C 386 (2003) 353–357
355
Fig. 2. ODF sections (u2 ¼ 45° and u2 ¼ 60°) of deformation texture in as rolled Cu–Ni alloy tapes. The lines are iso-ODF value lines with intensities of the step of 2.
Fig. 3. (1 1 1) u-scan of the Cu–Ni substrate annealed at different temperatures. The FWHM of the (1 1 1) u-scan decreases with increasing annealing temperature.
Fig. 4. It indicated that the Cu–Ni alloy substrate was sharp cube textured. The FWHM of (1 1 1) uscan was less than 9° (Fig. 3). After the sharp cube textured Cu–Ni alloy tapes were obtained, the SOE method was used to form
Fig. 4. X-ray (1 1 1) pole figure for a rolled and recrystallized Cu–Ni alloy substrate. (1 1 1) peak positions indicate the presence of only the f1 0 0gh0 0 1i cube orientation.
NiO(2 0 0) film as the first buffer layer on the Cu–Ni alloy substrate.
356
K. Shi et al. / Physica C 386 (2003) 353–357
Fig. 6. Typical XRD h–2h-scan and (1 1 1) u-scan of NiO film fabricated on the Cu–Ni alloy substrate. Under Po2 of 1 Pa and 800 °C. Fig. 5. Typical XRD h–2h-scans for Cu–Ni alloy substrates oxidized in different gas atmospheres: B is pure Ar; C is Ar/O2 atmosphere; D is O2 .
Fig. 5 shows XRD h–2h results from samples that were oxidized in different atmospheres at 400 °C for 1 h. In the figure, the plot B, C and D denote samples that were oxidized in Ar, Ar/10%O2 and O2 atmospheres respectively. With decreasing content of oxygen, different oxides were obtained. At this temperature, sharp cube textured NiO buffer layer can be fabricated in the lowest Po2 atmosphere (Ar). However, the NiO(2 0 0) buffer layer that fabricated under these conditions is too thin to prevent the diffusion of the Cu–Ni substrate. The reason may lie in that the content of oxygen in the Ar is too low. A precise control of the Po2 in the atmosphere is a key factor to get a suitable final cube textured NiO(2 0 0) buffer layer. An optimized pure cube oriented NiO(2 0 0) buffer layer was fabricated in oxygen partial pressure of 1 Pa, using a flow rate of 40 cc/min and a temperature of 800 °C. This NiO(2 0 0) buffer layer fabricated on the Cu–Ni substrate exhibited a high degree of texturing as examined by XRD h–2h-scan and (1 1 1) u-scan. Fig. 6 shows a typical XRD h–2h spectrum for the NiO/Cu–Ni under this condition. It also exhibits the u-scan spectrum of the NiO(1 1 1). The FWHM of the (1 1 1) u-scan is less than 10°, demonstrating good in-plane alignment. SEM investigation of the NiO(2 0 0) layer on the Cu–Ni substrate at a magnification of 2400
Fig. 7. SEM micrograph of the NiO on the Cu–Ni substrate (2400) showing a crack free surface.
shows no evidence of any micro cracking (Fig. 7). But the surface quality needs to be improved, indicating the necessity of an oxide cap layer to improve the surface qualities of the NiO layer. MgO may be fabricated on the NiO/Cu–Ni substrate as the cap layer [11]. Such structure would provide a promising candidate for developing YBa2 Cu3 O7x film on Cu–Ni tapes.
4. Summary Non-magnetic cube textured substrates were fabricated in order to avoid the ferromagnetism of
K. Shi et al. / Physica C 386 (2003) 353–357
Ni substrate at 77 K. A sharp cube textured Cu–Ni alloy substrate was obtained through heavy cold rolling followed by recrystallization heat treatment. The FWHM of the (1 1 1) u-scan is less than 9°. The cube texture was strengthened with the increasing annealing temperature. NiO(2 0 0)/Cu–Ni substrates were produced by using SOE method. The partial pressure of oxygen plays important role in the development of the NiO(2 0 0). The NiO buffer layer on the Cu–Ni tape shows good in plane and c-axis alignment. The FWHM of the u-scan is less than 10°. The NiO layer serves as a template for epitaxial growth of YBa2 Cu3 O7x film, and as a barrier layer to prevent the interaction between the Cu–Ni alloy substrate and YBa2 Cu3 O7x film. Acknowledgement This research work was supported by China National Center for Research and Development of Superconductivity.
357
References [1] A. Goyal et al., Appl. Supercond. 403–427 (1996) 4. [2] Q. He, D.K. Christen, R. Feenstra, D.P. Norton, M. Paranthaman, E.D. Specht, D.F. Lee, A. Goyal, D.M. Kroeger, Physica C 314 (1999) 105. [3] D.P. Norton, A. Goyal, J.D. Budai, D.K. Christen, D.M. Kroeger, E.D. Specht, Q. He, B. Saffian, M. Paranthaman, C.E. Klabunde, D.F. Lee, F.A. List, Science 274 (1996) 755. [4] P.R. Morris, Adv. X-ray Anal. 18 (1975) 514. [5] W.T. Norris, J. Phys. D. Appl. Phys. 3 (1970) 489. [6] B.De. Boer, J. Eickemeyer, N. Reger, L. Fernandez G.-R., J. Richter, B. Holzapfel, L. Schultz, W. Prusseit, P. Berberich, Acta Mater. 49 (2001) 1421–1428. [7] J. Yang, D. Shi, X.H. Wang, A.S. Liu, G.S. Yuan, Physica C 337 (2000) 67–70. [8] K. Matsumoto, S.B. Kim, K. Yamagiwa, Y. Koike, I. Hirabayashi, T. Watanabe, N. Uno, M. Ikeda, Physica C 335 (2000) 39–43. [9] K. Matsumoto, Y. Niiori, I. Hirabayashi, N. Koshizuka, T. Watanabe, Y. Tanaka, M. Ikeda, in: K. Osamura, I. Hirabayashi (Eds.), Advances in Superconductivity, vol. 10, Springer, Tokyo, 1998, p. 611. [10] B. Liebmann, K. Lucke, G. Masing, Z. Metallkd. 47 (1956) 57. [11] T. Watanabe, K. Matsumoto, T. Maeda, T. Tanigawa, I. Hirabayashi, Physica C 357–360 (2001) 914–922.