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Preparation and formation mechanism of cube textured Ag substrate for coated high-Tc superconductor
Physica C 337 Ž2000. 75–78 www.elsevier.nlrlocaterphysc
Preparation and formation mechanism of cube textured Ag substrate for coated high-Tc superconductor Danmin Liu ) , Meiling Zhou, Yancao Hu, Tieyong Zuo Department of Materials Science and Engineering, Beijing Polytechnic UniÕersity, 100 Pingleyuan, Chaoyang District, Beijng 100022, People’s Republic of China
Abstract A strong cube, 1004²100:, textured silver tape for coated high-Tc superconductor was obtained. The hot-rolling textures and annealed textures of silver were studied systematically. Cube texture can be obtained by hot-rolling. In the process of rolling, twin formation must be avoided in order to increase the strength of the 2114²111:orientation. The crystals in 2114²111:orientation transforms into cube orientation by dynamic recrystallization and subsequent annealing. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Formation mechanism; Cube textured Ag; Coated high-Tc superconductor
1. Introduction Because silver does not react with oxide superconductors, of which thin films can be expitaxially deposited directly on a single crystal Ag or a textured Ag tape w1–3x. It has been shown that the texture in polycrystalline substrate strongly affects the orientation distribution of thin film. For some kinds of oxide superconductors a sharp cube textured silver tape is the best substrate for thin film deposition w4x. However, As a low stacking fault energy ŽSFE. f.c.c. metal, both slipping and twinning may take place during the rolling process. This fact leads to the rolling texture of Ag differents from that of high SFE f.c.c. metals, such as Al, Ni and Cu. After annealing the rolling texture of Ag transforms into
brass-type recrystallization texture and, hence, a cube textured Ag tape is very difficult to be obtained. Besides, texture transforms of silver involve complicated technology of rolling and annealing. Silver is very sensitive to rolling and annealing parameters. Any condition changes will lead to transforming of textures. It has been confirmed that rolling at elevated temperature may promote cube texture formation w5x. However, the exact conditions to obtain strong cube texture are not clear. In this paper, we studied the forming regularity and the processing technology of textured Ag tape possessing cube orientation. From the results, we would like to suggest a mechanism of cube texture formation.
2. Experiments ) Corresponding author. Tel.: q86-10-67391761; fax: q86-1067395281. E-mail address: [email protected] ŽD. Liu..
A 0.48-mm-thick 99.99% silver plate was used as starting material. The original texture is mainly
0921-4534r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 3 4 Ž 0 0 . 0 0 0 5 9 - 9
D. Liu et al.r Physica C 337 (2000) 75–78
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Fig. 1. The ODF sections of the silver samples rolled at different temperatures Ž79%..
0234²023:. Silver plate was rolled to thin sheets at different temperatures Ž258C, 508C, 808C, 1208C, 1308C, 1408C, 1508C and 1908C.. Rolling sheets were annealed at 7008C for 30 min in a vacuum furnace. Three incomplete pole figures Ž111., Ž200. and Ž220. were measured from the samples after rolling and annealing. The ODFs Žorientation distribution function. were calculated using series expansion method of Bunge’s system w6x.
3. Results and discussion 3.1. The effect of the rolling temperature The rolling textures of Ag rolled at different temperatures are shown in Fig. 1, total reductions of them are 79%. As the rolling temperature rising, the
strength of the orientation 1104²211: Ž w 1 s 358, f s 458, w 2 s 08. decreased and the plane of most crystallites which parallel to the rolling-plane rotated from 1104 to 0124 . The recrystallization temperature of silver is very low w5,7x. It is obvious that dynamic recrystallization has happened in the process of hot-rolling. Because most superconductor films are deposited at about 7008C, we annealed the rolled samples at 7008C. The recrystallization textures rolled at different temperatures and annealed at 7008C for 30 min are shown in Fig. 2. It shows that, as the rolling temperature rising, the density of the cube orientation increased. When the rolling temperature reached at 1408C, a strong cube texture was obtained after annealed at 7008C for 30 min. When the rolling temperature increased further, the density of the cube
Fig. 2. The ODF sections of silver samples rolled at different temperatures Žreduction 79%. and annealed Ž7008Cr30 min...
D. Liu et al.r Physica C 337 (2000) 75–78
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in this sample. Therefore, it is a silver tape having strong cube texture. As the experiments show, strong cube textured silver substrates can be prepared from hot-rolling and annealing at high temperature. The suitable rolling temperature is 1408C. 3.2. The formation mechanism of cube texture of silÕer
Fig. 3. The ODF values of the cube orientation of silver samples rolled at different temperatures and annealed at 7008C for 30 min.
orientation decreased and the 0124² uÕw : components occur strongly. Fig. 3 shows the ODF values of the cube orientation as a function of rolling temperatures. It can been seen that the ODF value of the cube texture after rolled at 1408C and annealed reached 44.81 = random distribution. Since texture is distributed continuously, cube texture should be defined as the orientation 1004²100: Ž w 1 s 08, f s 08, w 2 s 08. with some spread around it. However, the spread degree is defined in different ways. In this work, the spread around cube orientation is shown in Fig. 4, i.e., the maximum deviation from cube orientation is ; 188. This is corresponding to the 98 FWHM determined from F-scanning. No other orientation has been found
Fig. 4. F Ž g . values around the cube orientation as a function of Euler angle w 1 in ODF w 2 s 08 section.
Fig. 5 shows the distribution of orientation densities of silver samples rolled at different temperatures. It is seen in Fig. 5 that the density of the 2114²111: orientation increased as the rolling temperature increased. When the rolling temperature reached 1408C, the 2114²111: orientation became strongest. When the rolling temperature reached 1908C, the density of the 2114²111: orientation decreased. The increasing and the decreasing of the density of cube orientation in Fig. 3 accords well with the increasing and the decreasing of the strength of the 2114²111: orientation. This result indicates an important fact, i.e., the cube nuclei are formed by consuming mostly the orientation 2114²111:. This result agrees with previous works w8x. It is well known that for f.c.c. metal the orientations of texture are determined by SFE, for high and
Fig. 5. Distribution of orientation densities of silver samples rolled at different temperatures, ²110: parallel to TD Žtransverse direction., w 1 s908, F s 08 908, w 2 s 458.
™
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D. Liu et al.r Physica C 337 (2000) 75–78
medium SFE metals slipping is the main process during cold-rolling and, hence, the orientation 2114²111: becomes the dominative one in texture. For low SFE metal, such as silver, twinning occurs easily during cold-rolling and, hence, the orientation 2114²111: in deformation texture is not dominative. By elevated temperature rolling, the resistance to slipping is reduced, slipping is easier than twinning; similar to high SFE metals, the orientation 2114²111: becomes stronger, therefore rolling at 1408C a strong cube texture can be obtained after annealing. However, when the rolling temperature is too high, say 1908C, then the dynamic recrystallization is very strong, this effect causes the texture change from 2114²111: to 1004²100: instantaneously, the cube orientation which is transformed from 2114²111: through dynamic recrystallization changes into other orientation during further rolling. Surely after annealing cube texture cannot be obtained. The key to obtain a strong cube texture is that by rolling, twinning process and strong dynamic recrystallization should be avoided.
4. Conclusions Strong cube textured silver substrates can be prepared from hot-rolling and annealing at higher temperature. The suitable rolling temperature is 1408C. It is because the density of the 2114²111: orientation became strongest when rolled at this tempera-
ture and the dynamic recrystalliaztion is not too strong.
Acknowledgements This work is supported by the National Science Foundation of China under Grant No. 59771010 and by the National Center for Research and Development on Superconductivity in China. The authors wish to express the most sincere thanks to Dr. Liu Weipeng for his helpful discussions.
References w1x M. Yamazaki, Y. Kudo, H. Yoshino, K. Ando, K. Inoue, Proc. 8th Int. Symp. Superconductivity ŽISS’95., Springer-Verlag, 1995, p. 759. w2x Y. Niiori, Y. Yamada, I. Hirabayashi, T. Fujiwara, K. Higashiyama, Physica C 301 Ž1998. 104. w3x M. Yamazaki, T.D. Thanh, Y. Kudo, H. Kubota, H. Yoshino, K. Inoue, Proc. 10th Int. Symp. Superconductivity ŽISS’97., Springer-Verlag, 1997, p. 123. w4x J.L. MacManus-Driscoll, Annu. Rev. Mater. Sci. 28 Ž1998. 421. w5x H. Hu, R.S. Cline, S.R. Goodman, J. Appl. Phys. 32 Ž1961. 1392. w6x H.J. Bunge, Texture Analysis in Material Science, Butterworth, London, 1982. w7x J.W.H.G. Slakhorst, C.A. Verbraak, Proc. 4th Int. Conf. Texture Mater., Cambridge England, 1975, p. 160. w8x W.P. Liu, H.J. Bunge, ICOTOM-11, Xian, China, 1996, 509.
Preparation and formation mechanism of cube textured Ag substrate for coated high-Tc superconductor Danmin Liu ) , Meiling Zhou, Yancao Hu, Tieyong Zuo Department of Materials Science and Engineering, Beijing Polytechnic UniÕersity, 100 Pingleyuan, Chaoyang District, Beijng 100022, People’s Republic of China
Abstract A strong cube, 1004²100:, textured silver tape for coated high-Tc superconductor was obtained. The hot-rolling textures and annealed textures of silver were studied systematically. Cube texture can be obtained by hot-rolling. In the process of rolling, twin formation must be avoided in order to increase the strength of the 2114²111:orientation. The crystals in 2114²111:orientation transforms into cube orientation by dynamic recrystallization and subsequent annealing. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Formation mechanism; Cube textured Ag; Coated high-Tc superconductor
1. Introduction Because silver does not react with oxide superconductors, of which thin films can be expitaxially deposited directly on a single crystal Ag or a textured Ag tape w1–3x. It has been shown that the texture in polycrystalline substrate strongly affects the orientation distribution of thin film. For some kinds of oxide superconductors a sharp cube textured silver tape is the best substrate for thin film deposition w4x. However, As a low stacking fault energy ŽSFE. f.c.c. metal, both slipping and twinning may take place during the rolling process. This fact leads to the rolling texture of Ag differents from that of high SFE f.c.c. metals, such as Al, Ni and Cu. After annealing the rolling texture of Ag transforms into
brass-type recrystallization texture and, hence, a cube textured Ag tape is very difficult to be obtained. Besides, texture transforms of silver involve complicated technology of rolling and annealing. Silver is very sensitive to rolling and annealing parameters. Any condition changes will lead to transforming of textures. It has been confirmed that rolling at elevated temperature may promote cube texture formation w5x. However, the exact conditions to obtain strong cube texture are not clear. In this paper, we studied the forming regularity and the processing technology of textured Ag tape possessing cube orientation. From the results, we would like to suggest a mechanism of cube texture formation.
2. Experiments ) Corresponding author. Tel.: q86-10-67391761; fax: q86-1067395281. E-mail address: [email protected] ŽD. Liu..
A 0.48-mm-thick 99.99% silver plate was used as starting material. The original texture is mainly
0921-4534r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 3 4 Ž 0 0 . 0 0 0 5 9 - 9
D. Liu et al.r Physica C 337 (2000) 75–78
76
Fig. 1. The ODF sections of the silver samples rolled at different temperatures Ž79%..
0234²023:. Silver plate was rolled to thin sheets at different temperatures Ž258C, 508C, 808C, 1208C, 1308C, 1408C, 1508C and 1908C.. Rolling sheets were annealed at 7008C for 30 min in a vacuum furnace. Three incomplete pole figures Ž111., Ž200. and Ž220. were measured from the samples after rolling and annealing. The ODFs Žorientation distribution function. were calculated using series expansion method of Bunge’s system w6x.
3. Results and discussion 3.1. The effect of the rolling temperature The rolling textures of Ag rolled at different temperatures are shown in Fig. 1, total reductions of them are 79%. As the rolling temperature rising, the
strength of the orientation 1104²211: Ž w 1 s 358, f s 458, w 2 s 08. decreased and the plane of most crystallites which parallel to the rolling-plane rotated from 1104 to 0124 . The recrystallization temperature of silver is very low w5,7x. It is obvious that dynamic recrystallization has happened in the process of hot-rolling. Because most superconductor films are deposited at about 7008C, we annealed the rolled samples at 7008C. The recrystallization textures rolled at different temperatures and annealed at 7008C for 30 min are shown in Fig. 2. It shows that, as the rolling temperature rising, the density of the cube orientation increased. When the rolling temperature reached at 1408C, a strong cube texture was obtained after annealed at 7008C for 30 min. When the rolling temperature increased further, the density of the cube
Fig. 2. The ODF sections of silver samples rolled at different temperatures Žreduction 79%. and annealed Ž7008Cr30 min...
D. Liu et al.r Physica C 337 (2000) 75–78
77
in this sample. Therefore, it is a silver tape having strong cube texture. As the experiments show, strong cube textured silver substrates can be prepared from hot-rolling and annealing at high temperature. The suitable rolling temperature is 1408C. 3.2. The formation mechanism of cube texture of silÕer
Fig. 3. The ODF values of the cube orientation of silver samples rolled at different temperatures and annealed at 7008C for 30 min.
orientation decreased and the 0124² uÕw : components occur strongly. Fig. 3 shows the ODF values of the cube orientation as a function of rolling temperatures. It can been seen that the ODF value of the cube texture after rolled at 1408C and annealed reached 44.81 = random distribution. Since texture is distributed continuously, cube texture should be defined as the orientation 1004²100: Ž w 1 s 08, f s 08, w 2 s 08. with some spread around it. However, the spread degree is defined in different ways. In this work, the spread around cube orientation is shown in Fig. 4, i.e., the maximum deviation from cube orientation is ; 188. This is corresponding to the 98 FWHM determined from F-scanning. No other orientation has been found
Fig. 4. F Ž g . values around the cube orientation as a function of Euler angle w 1 in ODF w 2 s 08 section.
Fig. 5 shows the distribution of orientation densities of silver samples rolled at different temperatures. It is seen in Fig. 5 that the density of the 2114²111: orientation increased as the rolling temperature increased. When the rolling temperature reached 1408C, the 2114²111: orientation became strongest. When the rolling temperature reached 1908C, the density of the 2114²111: orientation decreased. The increasing and the decreasing of the density of cube orientation in Fig. 3 accords well with the increasing and the decreasing of the strength of the 2114²111: orientation. This result indicates an important fact, i.e., the cube nuclei are formed by consuming mostly the orientation 2114²111:. This result agrees with previous works w8x. It is well known that for f.c.c. metal the orientations of texture are determined by SFE, for high and
Fig. 5. Distribution of orientation densities of silver samples rolled at different temperatures, ²110: parallel to TD Žtransverse direction., w 1 s908, F s 08 908, w 2 s 458.
™
78
D. Liu et al.r Physica C 337 (2000) 75–78
medium SFE metals slipping is the main process during cold-rolling and, hence, the orientation 2114²111: becomes the dominative one in texture. For low SFE metal, such as silver, twinning occurs easily during cold-rolling and, hence, the orientation 2114²111: in deformation texture is not dominative. By elevated temperature rolling, the resistance to slipping is reduced, slipping is easier than twinning; similar to high SFE metals, the orientation 2114²111: becomes stronger, therefore rolling at 1408C a strong cube texture can be obtained after annealing. However, when the rolling temperature is too high, say 1908C, then the dynamic recrystallization is very strong, this effect causes the texture change from 2114²111: to 1004²100: instantaneously, the cube orientation which is transformed from 2114²111: through dynamic recrystallization changes into other orientation during further rolling. Surely after annealing cube texture cannot be obtained. The key to obtain a strong cube texture is that by rolling, twinning process and strong dynamic recrystallization should be avoided.
4. Conclusions Strong cube textured silver substrates can be prepared from hot-rolling and annealing at higher temperature. The suitable rolling temperature is 1408C. It is because the density of the 2114²111: orientation became strongest when rolled at this tempera-
ture and the dynamic recrystalliaztion is not too strong.
Acknowledgements This work is supported by the National Science Foundation of China under Grant No. 59771010 and by the National Center for Research and Development on Superconductivity in China. The authors wish to express the most sincere thanks to Dr. Liu Weipeng for his helpful discussions.
References w1x M. Yamazaki, Y. Kudo, H. Yoshino, K. Ando, K. Inoue, Proc. 8th Int. Symp. Superconductivity ŽISS’95., Springer-Verlag, 1995, p. 759. w2x Y. Niiori, Y. Yamada, I. Hirabayashi, T. Fujiwara, K. Higashiyama, Physica C 301 Ž1998. 104. w3x M. Yamazaki, T.D. Thanh, Y. Kudo, H. Kubota, H. Yoshino, K. Inoue, Proc. 10th Int. Symp. Superconductivity ŽISS’97., Springer-Verlag, 1997, p. 123. w4x J.L. MacManus-Driscoll, Annu. Rev. Mater. Sci. 28 Ž1998. 421. w5x H. Hu, R.S. Cline, S.R. Goodman, J. Appl. Phys. 32 Ž1961. 1392. w6x H.J. Bunge, Texture Analysis in Material Science, Butterworth, London, 1982. w7x J.W.H.G. Slakhorst, C.A. Verbraak, Proc. 4th Int. Conf. Texture Mater., Cambridge England, 1975, p. 160. w8x W.P. Liu, H.J. Bunge, ICOTOM-11, Xian, China, 1996, 509.