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Fabrication of cube textured Ni tapes by in situ thermal and magnetic annealing
Journal of Alloys and Compounds 449 (2008) 180–183
Fabrication of cube textured Ni tapes by in situ thermal and magnetic annealing Jun-Ki Chung a , Won-Jeong Kim a , Sung Gap Lee b , Cheol Jin Kim c,∗ a
Institute of Industrial Technology, Changwon National University, 9 Sarim-dong, Changwon, Kyeongnam 641-773, Republic of Korea b Department of Ceramic Engineering, Gyeongsang National University, 900 Gajwa-dong, Jinju 660-701, Republic of Korea c Information Technology Research Center for Energy Storage and Conversion, Gyeongsang National University, 900 Gajwa-dong, Jinju 660-701, Republic of Korea Received 4 November 2005; received in revised form 30 December 2005; accepted 13 January 2006 Available online 22 January 2007
Abstract The development of highly cube textured substrates is important for application of coated high-Tc superconductors. Pure Ni and Ni alloy are the most widely used substrates for coated conductors (CC) because they easily exhibit cube texture through cold rolling and annealing. The textured Ni tape was obtained through recrystallization heat treatment with the line focused infrared heater and the electromagnet. Magnetic field was applied up to 200 G during the heat treatment of Ni tape. Magnetically annealed Ni tape showed stronger cube texture than the samples without magnetic field. full width half maximum (FWHM) value of in-plane texture were 8.3◦ and 7.8◦ for the samples annealed without magnetic field and with magnetic field, respectively. © 2007 Elsevier B.V. All rights reserved. Keywords: High-Tc superconductors; Powder metallurgy; Domain structure; Atomic force microscope
1. Introduction It is well known that the bi-axially textured YBa2 Cu3 O7-δ (YBCO) film containing low angle grain boundaries is necessary to obtain high critical current densities. Suitable substrates for YBCO coated conductors (CC), which are necessary to carry high critical current, are strongly cube ({0 0 1}1 0 0) textured metal tapes. In order to improve the in-plane orientation and thereby the current transport properties of YBCO film, the conditions of YBCO epitaxial growth on the metal substrate should be strictly controlled. This has brought the evolution of several processes, including the rolling assisted bi-axially textured substrate (RABiTS) [1,2], the ion-beam assisted deposition (IBAD) [3,4], the inclined substrate deposition (ISD) [5], and the ionbeam structure modification (ISM) [6]. Among the processes developed so far, the RABiTS technique has been considered as an effective way to make substrate on which buffer layers and superconducting layers could be stacked with low cost. In recent years, critical current densities of more than 1 × 106 A/cm2 in ∗
Corresponding author. Tel.: +82 55 751 5331; fax: +82 55 761 1656. E-mail address: [email protected] (C.J. Kim).
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2006.01.114
bi-axially textured YBCO CC have been achieved using the RABiTS method [7,8]. This method is composed of fabrication of textured metal substrates by cold rolling, recrystallization heat treatment, and deposition of buffers and YBCO films on the bi-axially textured Ni substrates. In the RABiTS process, Ni has been the most widely used substrate for CC because it has good workability and easy formation of strong cube texture through cold rolling and annealing. It is well known that recrystallization cube texture is related to the rolling texture, annealing temperature, and heat treatment time, etc. In this work, we have fabricated Ni substrates by powder metallurgy process and cold rolling, and optimized the recrystallization condition by focused IR-heating with magnetic field. Also, we have evaluated the effects of focused IR-heating with or without magnetic field on the texture development, microstructure, and surface morphology. 2. Experimental Ni rods were fabricated from Ni powder of 99.99% purity by powder metallurgy process including powder compaction, cold isostatic pressing (CIP), and sintering. Ni powder was poured into the rubber mold with the inside diameter of 12 mm and compacted during CIP process with 2500 kg/cm2 . The dimension
J.-K. Chung et al. / Journal of Alloys and Compounds 449 (2008) 180–183
181
Fig. 1. Schematic diagram of the apparatus for the magnetic annealing with focused infrared heater. of the Ni compact after CIP process was ∼100 mm in length and ∼10.5 mm in diameter. The Ni green rods were densified by heat treatment in the tube furnace at 1000–1100 ◦ C for 1–6 h in 96%Ar–4%H2 atmosphere. Reducing atmosphere with 96%Ar–4%H2 gas mixture was employed to prevent the surface oxidation of Ni rods. The sintered Ni rods were cold-rolled into the final thickness of 60–80 m with 5% thickness reduction ratio at each cold-rolling stage using a hard metal roller with a diameter of 50 mm. The in situ thermal and magnetic annealing was carried out with the line focused infrared heater. The focused area of the infrared heater was less than 5 mm in width and 100 mm in length, and the stripe-shaped heating zone was applied along the tape width direction while the tapes were transferred at uniform speed of 6–60 mm/h. The infrared heating system with magnetic field is shown in Fig. 1. While Ni tapes were transferred in the tape length direction at a uniform speed, magnetic field of 200 G was applied to the tapes at perpendicular direction to the tape length. At the same time, narrow region less than 5 mm width of the Ni tapes heated up to 1000 ◦ C to induce recrystallization using the focused infrared heater in the reducing 96%Ar–4%H2 gas atmosphere. Since the infrared heating method has very steep temperature gradient in heating or cooling, magnetization below the Curie temperature of nickel and recrystallization at high temperature enough to induce the grain rearrangement could be synchronized by simply turning on and off the heater or magnetic coil. Recrystallization procedure has been repeated as shown in Fig. 2 to improve cube texture development. It is worth noting that the Curie temperature of nickel is known to be 354–358 ◦ C. The texture characteristics of Ni tapes were evaluated by pole-figure, φscan and ω-scan with General Area Detector Diffraction System (GADDS). In order to evaluate the influence of magnetic field on texture development, magnetic domain structures have been investigated with magnetic force microscopy (MFM).
3. Results and discussion Cube texture development after the recrystallization is clearly shown in Fig. 3, where XRD patterns of the cold-rolled sample
Fig. 2. Schematic illustration of heat treatment profile in magnetic field for recrystallization of Ni tapes.
Fig. 3. XRD θ–2θ patterns of the: (a) as-rolled Ni tapes, (b) annealed Ni tapes without magnetic field, and (c) annealed Ni tapes with magnetic field.
(Fig. 3(a)) exhibits various (h k l) peaks, such as (1 1 1), (2 0 0), and (2 2 0). However, samples annealed with/without magnetic field exhibit only (2 0 0) peak, which indicates strong (2 0 0) cube texture development by heat treatment. Recrystallization of nickel in the cold-rolled has been known to begin above ∼500 ◦ C. This result indicates that annealing of pure Ni tapes at 1000 ◦ C is sufficient for cube texture growth. After magnetic domain structures in the annealed samples were investigated using atomic force microscope (XE-100, PSIA Inc.). Fig. 4 shows AFM and MFM images of Ni tapes annealed with/without magnetic field. Annealed Ni tapes exhibit ordered domain patterns as shown in Fig. 4(c and d). The distance between the distinct bright and dark regions in the MFM images was longer in the magnetically annealed Ni tapes than the nonmagnetically annealed Ni tapes. The magnetic domain structure of the sample annealed with magnetic field was well defined, which demonstrates the magnetic field effect. Annealed Ni tape exhibits a root-mean-square roughness values (Rq) of 15 nm by AFM investigation. Since it is difficult to estimate the magnetic field effect using normal XRD θ–2θ patterns, the X-ray pole-figure analysis was carried out for the annealed Ni tapes to estimate the degree of the cube texture. The typical result obtained for pure Ni tape is shown in Fig. 5. The (1 1 1) pole-figure of the annealed Ni tape shows a good symmetry of the four peaks, which indicates the development of the (2 0 0) texture. However, annealing with/without magnetic field exhibited difference in texture development. The full width half maximum (FWHM) of in-plane (φ-scan) and out-of-plane (ω-scan) textures without magnetic field, estimated from the pole-figure data, were 8.3◦ and 5.5◦ , respectively. On the other hand, FWHM values of in-plane and out-of-plane for that annealed with magnetic field were 7.8◦ and 4.8◦ , respectively. Magnetically annealed Ni tape showed stronger cube texture than the samples without magnetic field. This clearly demonstrates that the additional magnetic driving force during annealing process could enhance the texture development.
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Fig. 4. Typical AFM and MFM images from 20 m × 20 m region on annealed Ni tape: AFM images of the annealed sample (a) without magnetic field and (b) with magnetic field. MFM images of the annealed sample (c) without magnetic field and (d) with magnetic field.
Fig. 5. X-ray analysis of textured Ni tapes annealed at 1000 ◦ C with magnetic field (a–c) and without magnetic field (d–f): (a) out-of-plane texture (FWHM = 5.5◦ ), (b) in-plane texture (FWHM = 8.3◦ ), (c) three-dimensional pole-figure of (1 1 1) planes (d) out-of-plane texture (FWHM = 4.8◦ ), (e) in-plane texture (FWHM = 7.8◦ ), and (f) three-dimensional pole-figure of (1 1 1) planes.
J.-K. Chung et al. / Journal of Alloys and Compounds 449 (2008) 180–183
4. Conclusions We applied the powder metallurgy to the fabrication of Ni tapes for the application of YBCO coated conductor substrates. The bi-axially textured Ni tape was successfully made by cold rolling of the Ni powder compacts and focused IR heat treatment with magnetic field. The Ni tape annealed by a focused IR-heating with magnetic field resulted in better texture development compared to that without magnetic field. The X-ray pole-figure analysis showed that the in-plane and out-of-plane texture of the Ni tape were as good as 7.8◦ and 4.8◦ , respectively. The evolution of the magnetic domain structure of the Ni tape annealed with magnetic field was better than that annealed without magnetic field. Acknowledgments This research was supported by a grant from Center for Applied Superconductivity Technology of the 21st Century
183
Frontier R&D Program funded by the Ministry of Science and Technology, Republic of Korea. References [1] 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, B.C. Sales, F.A. List, Science 274 (1996) 755. [2] A. Goyal, D.P. Norton, J.D. Budai, M. Paranthaman, E.D. Specht, D.M. Kroeger, D.K. Christen, Q. He, B. Saffian, F.A. List, D.F. Lee, P.M. Martin, C.E. Klabunde, E. Hatfield, V.K. Sikka, Appl. Phys. Lett. 69 (1996) (1795). [3] Y. Lijima, K. Onabe, N. Futaki, Y. Ikeno, Appl. Phys. Lett. 60 (1992) 69. [4] R.P. Reade, P. Berdahl, S.M. Garrison, R.E. Russo, Appl. Phys. Lett. 61 (1992) 2231. [5] K. Hasegawa, K. Fujino, H. Mukai, M. Konishi, K. Hayashi, K. Sato, S. Honjo, Y. Sato, H. Ishii, Y. Iwata, Appl. Supercond. 4 (1996) 487. [6] S.S. Wang, K. Wu, Y. Zhou, A. Godfrey, J. Meng, M.L. Liu, Q. Liu, W. Liu, Z. Han, Supercond. Sci. Technol. 16 (2003) L29. [7] S. Kreiskott, M. Getta, B. Monter, H. Piel, N. Pupeter, Phys. C 383 (2003) 306. [8] M. Parans Paranthaman, T. Izumi, MRS Bull. 29 (2004) 533.
Fabrication of cube textured Ni tapes by in situ thermal and magnetic annealing Jun-Ki Chung a , Won-Jeong Kim a , Sung Gap Lee b , Cheol Jin Kim c,∗ a
Institute of Industrial Technology, Changwon National University, 9 Sarim-dong, Changwon, Kyeongnam 641-773, Republic of Korea b Department of Ceramic Engineering, Gyeongsang National University, 900 Gajwa-dong, Jinju 660-701, Republic of Korea c Information Technology Research Center for Energy Storage and Conversion, Gyeongsang National University, 900 Gajwa-dong, Jinju 660-701, Republic of Korea Received 4 November 2005; received in revised form 30 December 2005; accepted 13 January 2006 Available online 22 January 2007
Abstract The development of highly cube textured substrates is important for application of coated high-Tc superconductors. Pure Ni and Ni alloy are the most widely used substrates for coated conductors (CC) because they easily exhibit cube texture through cold rolling and annealing. The textured Ni tape was obtained through recrystallization heat treatment with the line focused infrared heater and the electromagnet. Magnetic field was applied up to 200 G during the heat treatment of Ni tape. Magnetically annealed Ni tape showed stronger cube texture than the samples without magnetic field. full width half maximum (FWHM) value of in-plane texture were 8.3◦ and 7.8◦ for the samples annealed without magnetic field and with magnetic field, respectively. © 2007 Elsevier B.V. All rights reserved. Keywords: High-Tc superconductors; Powder metallurgy; Domain structure; Atomic force microscope
1. Introduction It is well known that the bi-axially textured YBa2 Cu3 O7-δ (YBCO) film containing low angle grain boundaries is necessary to obtain high critical current densities. Suitable substrates for YBCO coated conductors (CC), which are necessary to carry high critical current, are strongly cube ({0 0 1}1 0 0) textured metal tapes. In order to improve the in-plane orientation and thereby the current transport properties of YBCO film, the conditions of YBCO epitaxial growth on the metal substrate should be strictly controlled. This has brought the evolution of several processes, including the rolling assisted bi-axially textured substrate (RABiTS) [1,2], the ion-beam assisted deposition (IBAD) [3,4], the inclined substrate deposition (ISD) [5], and the ionbeam structure modification (ISM) [6]. Among the processes developed so far, the RABiTS technique has been considered as an effective way to make substrate on which buffer layers and superconducting layers could be stacked with low cost. In recent years, critical current densities of more than 1 × 106 A/cm2 in ∗
Corresponding author. Tel.: +82 55 751 5331; fax: +82 55 761 1656. E-mail address: [email protected] (C.J. Kim).
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2006.01.114
bi-axially textured YBCO CC have been achieved using the RABiTS method [7,8]. This method is composed of fabrication of textured metal substrates by cold rolling, recrystallization heat treatment, and deposition of buffers and YBCO films on the bi-axially textured Ni substrates. In the RABiTS process, Ni has been the most widely used substrate for CC because it has good workability and easy formation of strong cube texture through cold rolling and annealing. It is well known that recrystallization cube texture is related to the rolling texture, annealing temperature, and heat treatment time, etc. In this work, we have fabricated Ni substrates by powder metallurgy process and cold rolling, and optimized the recrystallization condition by focused IR-heating with magnetic field. Also, we have evaluated the effects of focused IR-heating with or without magnetic field on the texture development, microstructure, and surface morphology. 2. Experimental Ni rods were fabricated from Ni powder of 99.99% purity by powder metallurgy process including powder compaction, cold isostatic pressing (CIP), and sintering. Ni powder was poured into the rubber mold with the inside diameter of 12 mm and compacted during CIP process with 2500 kg/cm2 . The dimension
J.-K. Chung et al. / Journal of Alloys and Compounds 449 (2008) 180–183
181
Fig. 1. Schematic diagram of the apparatus for the magnetic annealing with focused infrared heater. of the Ni compact after CIP process was ∼100 mm in length and ∼10.5 mm in diameter. The Ni green rods were densified by heat treatment in the tube furnace at 1000–1100 ◦ C for 1–6 h in 96%Ar–4%H2 atmosphere. Reducing atmosphere with 96%Ar–4%H2 gas mixture was employed to prevent the surface oxidation of Ni rods. The sintered Ni rods were cold-rolled into the final thickness of 60–80 m with 5% thickness reduction ratio at each cold-rolling stage using a hard metal roller with a diameter of 50 mm. The in situ thermal and magnetic annealing was carried out with the line focused infrared heater. The focused area of the infrared heater was less than 5 mm in width and 100 mm in length, and the stripe-shaped heating zone was applied along the tape width direction while the tapes were transferred at uniform speed of 6–60 mm/h. The infrared heating system with magnetic field is shown in Fig. 1. While Ni tapes were transferred in the tape length direction at a uniform speed, magnetic field of 200 G was applied to the tapes at perpendicular direction to the tape length. At the same time, narrow region less than 5 mm width of the Ni tapes heated up to 1000 ◦ C to induce recrystallization using the focused infrared heater in the reducing 96%Ar–4%H2 gas atmosphere. Since the infrared heating method has very steep temperature gradient in heating or cooling, magnetization below the Curie temperature of nickel and recrystallization at high temperature enough to induce the grain rearrangement could be synchronized by simply turning on and off the heater or magnetic coil. Recrystallization procedure has been repeated as shown in Fig. 2 to improve cube texture development. It is worth noting that the Curie temperature of nickel is known to be 354–358 ◦ C. The texture characteristics of Ni tapes were evaluated by pole-figure, φscan and ω-scan with General Area Detector Diffraction System (GADDS). In order to evaluate the influence of magnetic field on texture development, magnetic domain structures have been investigated with magnetic force microscopy (MFM).
3. Results and discussion Cube texture development after the recrystallization is clearly shown in Fig. 3, where XRD patterns of the cold-rolled sample
Fig. 2. Schematic illustration of heat treatment profile in magnetic field for recrystallization of Ni tapes.
Fig. 3. XRD θ–2θ patterns of the: (a) as-rolled Ni tapes, (b) annealed Ni tapes without magnetic field, and (c) annealed Ni tapes with magnetic field.
(Fig. 3(a)) exhibits various (h k l) peaks, such as (1 1 1), (2 0 0), and (2 2 0). However, samples annealed with/without magnetic field exhibit only (2 0 0) peak, which indicates strong (2 0 0) cube texture development by heat treatment. Recrystallization of nickel in the cold-rolled has been known to begin above ∼500 ◦ C. This result indicates that annealing of pure Ni tapes at 1000 ◦ C is sufficient for cube texture growth. After magnetic domain structures in the annealed samples were investigated using atomic force microscope (XE-100, PSIA Inc.). Fig. 4 shows AFM and MFM images of Ni tapes annealed with/without magnetic field. Annealed Ni tapes exhibit ordered domain patterns as shown in Fig. 4(c and d). The distance between the distinct bright and dark regions in the MFM images was longer in the magnetically annealed Ni tapes than the nonmagnetically annealed Ni tapes. The magnetic domain structure of the sample annealed with magnetic field was well defined, which demonstrates the magnetic field effect. Annealed Ni tape exhibits a root-mean-square roughness values (Rq) of 15 nm by AFM investigation. Since it is difficult to estimate the magnetic field effect using normal XRD θ–2θ patterns, the X-ray pole-figure analysis was carried out for the annealed Ni tapes to estimate the degree of the cube texture. The typical result obtained for pure Ni tape is shown in Fig. 5. The (1 1 1) pole-figure of the annealed Ni tape shows a good symmetry of the four peaks, which indicates the development of the (2 0 0) texture. However, annealing with/without magnetic field exhibited difference in texture development. The full width half maximum (FWHM) of in-plane (φ-scan) and out-of-plane (ω-scan) textures without magnetic field, estimated from the pole-figure data, were 8.3◦ and 5.5◦ , respectively. On the other hand, FWHM values of in-plane and out-of-plane for that annealed with magnetic field were 7.8◦ and 4.8◦ , respectively. Magnetically annealed Ni tape showed stronger cube texture than the samples without magnetic field. This clearly demonstrates that the additional magnetic driving force during annealing process could enhance the texture development.
182
J.-K. Chung et al. / Journal of Alloys and Compounds 449 (2008) 180–183
Fig. 4. Typical AFM and MFM images from 20 m × 20 m region on annealed Ni tape: AFM images of the annealed sample (a) without magnetic field and (b) with magnetic field. MFM images of the annealed sample (c) without magnetic field and (d) with magnetic field.
Fig. 5. X-ray analysis of textured Ni tapes annealed at 1000 ◦ C with magnetic field (a–c) and without magnetic field (d–f): (a) out-of-plane texture (FWHM = 5.5◦ ), (b) in-plane texture (FWHM = 8.3◦ ), (c) three-dimensional pole-figure of (1 1 1) planes (d) out-of-plane texture (FWHM = 4.8◦ ), (e) in-plane texture (FWHM = 7.8◦ ), and (f) three-dimensional pole-figure of (1 1 1) planes.
J.-K. Chung et al. / Journal of Alloys and Compounds 449 (2008) 180–183
4. Conclusions We applied the powder metallurgy to the fabrication of Ni tapes for the application of YBCO coated conductor substrates. The bi-axially textured Ni tape was successfully made by cold rolling of the Ni powder compacts and focused IR heat treatment with magnetic field. The Ni tape annealed by a focused IR-heating with magnetic field resulted in better texture development compared to that without magnetic field. The X-ray pole-figure analysis showed that the in-plane and out-of-plane texture of the Ni tape were as good as 7.8◦ and 4.8◦ , respectively. The evolution of the magnetic domain structure of the Ni tape annealed with magnetic field was better than that annealed without magnetic field. Acknowledgments This research was supported by a grant from Center for Applied Superconductivity Technology of the 21st Century
183
Frontier R&D Program funded by the Ministry of Science and Technology, Republic of Korea. References [1] 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, B.C. Sales, F.A. List, Science 274 (1996) 755. [2] A. Goyal, D.P. Norton, J.D. Budai, M. Paranthaman, E.D. Specht, D.M. Kroeger, D.K. Christen, Q. He, B. Saffian, F.A. List, D.F. Lee, P.M. Martin, C.E. Klabunde, E. Hatfield, V.K. Sikka, Appl. Phys. Lett. 69 (1996) (1795). [3] Y. Lijima, K. Onabe, N. Futaki, Y. Ikeno, Appl. Phys. Lett. 60 (1992) 69. [4] R.P. Reade, P. Berdahl, S.M. Garrison, R.E. Russo, Appl. Phys. Lett. 61 (1992) 2231. [5] K. Hasegawa, K. Fujino, H. Mukai, M. Konishi, K. Hayashi, K. Sato, S. Honjo, Y. Sato, H. Ishii, Y. Iwata, Appl. Supercond. 4 (1996) 487. [6] S.S. Wang, K. Wu, Y. Zhou, A. Godfrey, J. Meng, M.L. Liu, Q. Liu, W. Liu, Z. Han, Supercond. Sci. Technol. 16 (2003) L29. [7] S. Kreiskott, M. Getta, B. Monter, H. Piel, N. Pupeter, Phys. C 383 (2003) 306. [8] M. Parans Paranthaman, T. Izumi, MRS Bull. 29 (2004) 533.