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Effect of initial cube texture on the recrystallization texture of cold rolled pure nickel
Materials Science & Engineering A 585 (2013) 66–70
Contents lists available at ScienceDirect
Materials Science & Engineering A journal homepage: www.elsevier.com/locate/msea
Effect of initial cube texture on the recrystallization texture of cold rolled pure nickel X.P. Chen n, X. Chen, J.P. Zhang, Q. Liu College of Materials Science and Engineering, Chongqing University, Chongqing 400030, China
art ic l e i nf o
a b s t r a c t
Article history: Received 22 March 2013 Received in revised form 14 June 2013 Accepted 17 July 2013 Available online 24 July 2013
High-purity nickel samples with different volume fractions of initial cube textures were cold rolled to 96% reduction and subsequently annealed at different temperatures. The survived cube orientation fractions in the cold-rolled samples were found to be in proportion to the volume fraction of the initial cube texture. The initial cube fraction could affect the recrystallization process significantly, which showed some huge differences in the case of low temperature annealing from that of high temperature annealing. & 2013 Elsevier B.V. All rights reserved.
Keywords: Nickel Cold-rolling Recrystallization Cube texture EBSD
1. Introduction The recrystallization texture has been a research subject by metallurgist for several decades. It is usually found that the cube texture ({001}〈100〉) is the strongest recrystallization texture component after annealing for most deformed face-centered cubic (FCC) metals. For metal-based substrates for coated superconductors (i.e. Ni and Ni–W alloys), the cube texture should be controlled. A very sharp cube texture is needed for metal substrates to overcome the “weak link” behavior so that YBCO coated conductors can get a high critical current density [1]. With respect to the origin of the cube texture both theories of oriented nucleation and oriented growth were given strong supports [2–4]. Oriented nucleation maintains that cube-oriented grains nucleate from a deformed matrix more frequently than grains with any other orientations [5]. There is a substantial evidence that in the cold deformed microstructure, cube orientation regions are located in some thin bands, which are parallel to the rolling direction (RD), these regions are called cube bands [6–9]. These cube bands are formed within cube oriented grains in pre-deformed metals undergoing deformation and retention [8]. It has been reported that cube orientation is metastable, a large orientation gradient develops during plastic deformation [8–10] and dislocation cells of cube oriented regions have larger size. All these characters lead to a larger nucleation rate of cube orientation grains and thus the cube bands become very potent
n
Corresponding author. Tel.: +86 23 65111547; fax: +86 23 65106407. E-mail address: [email protected] (X.P. Chen).
0921-5093/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msea.2013.07.028
nucleation sites during recrystallization annealing. In contrast, the oriented growth theory emphasizes that the origin of sharp cube texture lies in the selective growth of cube nuclei. That is to say, cube oriented grains grow faster than non-cube oriented grains during the recrystallization process [2], which is due to the high migration mobility of boundaries between cube grains and their surrounding deformation matrix. It is also suggested that certain misorientation relationships such as 401 around 〈111〉 have a high mobility. It is found that misorientation between the cubeorientation and the S-orientation ({123}〈634〉) conforms to this relationship. S is one of the dominating components of deformation texture in FCC metals. Since cube oriented grains in the cube bands grow faster than non-cube oriented grains [2,11], cube bands in the deformation microstructure were developed from cube-oriented grains in pre-deformed materials, therefore the content of cubeoriented grains in the pre-deformed materials plays an important role in the recrystallization cube texture component. It is well known that many factors influence the recrystallization cube textures. For polycrystalline nickel, numerous studies have focused on the effects of nickel purity, alloying elements, rolling reduction and annealing temperature on the recrystallization textures [11–17]. However, effect of initial cube texture has been paid little attention for nickel substrate. The initial cube texture prior to cold deformation is one of the structural parameters affecting the evolution of the microstructure and the texture of nickel during deformation and subsequent annealing. It is important to study the effect of initial cube texture on the as-deformed and recrystallized textures of pure nickel which is critical for texture control of nickel-based superconducting substrates. Not
X.P. Chen et al. / Materials Science & Engineering A 585 (2013) 66–70
only does it play an important role in enriching the theory of metalbased substrates but also it contributes to industrial production of metal-based substrates production.
2. Materials and methods The starting material used in the present investigation was highpurity nickel (99.999%), its thickness was 10 mm. It was processed to give an average grain size of 50 μm and a fairly random texture. A two-step rolling procedure was used to investigate the effect of initial cube texture on the recrystallization texture of the cold-rolled pure nickel. Firstly, the samples were rolled by a reduction of 80% to 2 mm in thickness, and two types of initial samples with different fractions of cube texture were prepared by different annealing procedures, marked as samples A and B. Then, they were cold rolled by 96% reduction to 80 μm in thickness. Finally, the samples were
67
annealed at certain temperature (300 1C, 700 1C or 900 1C) for 30 min in reducing atmosphere of argon and 4% hydrogen (heating rate of 300 1C per hour, water quench). The microstructures and textures of the deformed and recrystallized samples were characterized by a Channel 5 Electron BackScattering Diffraction (EBSD) detector attached to a FEI Nova 400 Nano scanning electron microscope (SEM). The measuring surface is RD-TD (RD is rolling direction and TD is transverse direction) and an area of 400 400 μm2 was characterized on each sample. At least three maps were taken for each condition. The horizontal direction is RD in all EBSD orientations maps.
3. Results and discussions Fig. 1 shows the microstructures and misorientation distribution of initial samples. EBSD analysis gives crystallographic orientation map for identifying orientations of each grain. Different
Fig. 1. (a) EBSD orientation map for initial sample A with initial texture (fraction of cube texture is 25.4%); (b) misorientation distribution of initial sample A; (c) EBSD orientation map for initial sample B with initial texture (fraction of cube texture is 9.1%); (d) misorientation distribution of initial sample B. In this EBSD map, grains in red have the orientation of cube texture (within a 151 deviation from {100}〈001〉), grains in purple are S orientation ({123}〈634〉), grains in green are goss texture ({011}〈100〉), grains in yellow are brass texture ({011}〈211〉), grains in blue are copper texture ({112}〈111〉), grains in white have random orientation, thin black lines refer to low angle grain boundaries, and thick black lines refer to high angle grain boundaries. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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Fig. 2. EBSD orientation maps of cold-rolling specimens (with a 96% reduction in thickness): (a) sample A and (b) sample B. In this EBSD map, grains in red have the orientation of cube texture (within a 151 deviation from {100}〈001〉), grains in purple are S orientation ({123}〈634〉), grains in green are goss texture ({011}〈100〉), grains in yellow are brass texture ({011}〈211〉), grains in blue are copper texture ({112}〈111〉), grains in white have random orientation, thin black lines refer to low angle grain boundaries, and thick black lines refer to high angle grain boundaries. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 3. The curve of micro-hardness for Ni after annealing at different temperatures for 1 h.
annealing temperature and time were used so as to get nearly same grain size and eliminate the effect of grain size on the intensity of cube texture after annealing. As shown in Fig. 1, two initial samples A and B are of similar grain size, which are 22.8 μm and 21.8 μm. The initial cube texture fractions of samples A and B are 25.4% and 9.1%, respectively. Moreover, the cube grains distribute randomly, and the misorientation distribution of sample A is similar to that of sample B. After 96% cold rolling reduction, the EBSD maps of two samples showing the typical deformation microstructure were given in Fig. 2. It is clearly observed that the remained cube grains are present within the long thin bands (cube bands), and the volume fraction of the cube texture reduces sharply after cold rolling by a reduction of 96%. However, there remain a few cube textures in all samples, the cube texture fractions of the deformed samples A and B are 4.7% and 0.7%, respectively. It is also interesting to note that the higher of the initial cube texture fraction, the higher is the cube texture fraction after rolling. The above results demonstrate that the cube-oriented grains rotate away from it and to other orientations after severe cold rolling. At the same time there are a few cube orientations surviving after large reduction cold rolling. It suggests that cube-oriented grains which were present in the initial materials prior to cold rolling are metastable through large reductions.
Fig. 3 shows the micro-hardness changes of pure nickel annealed at various temperatures, ranging from 100 1C to 900 1C. When annealed at 100–200 1C, hardness of both samples decreased slightly, indicating that only recovery took place. While annealed at a temperature between 250 1C and 300 1C, the hardness decreased sharply, which illustrates that the material partially recrystallized. Hardness of sample A decreased faster. After 300 1C, with temperature increasing, the hardness of sample A reduced a little, but the hardness of B diminished throughout the heat treatment. It suggests that severely sample A completes recrystallization at 300 1C, but it was uncertain of B. It is possible that thickness of Ni substrates produce an effect on hardness, and these substrates were 80 μm. The microstructures for annealed specimens were shown in Fig. 4. After annealing at 300 1C for 30 min, clearly, sample A is almost fully recrystallized, and the cube oriented grains were developed in most regions (Fig. 4a). While for sample B, only a few recrystallized grains were observed (Fig. 4b). The volume fractions of the recrystallized area were 77.6% in sample A only 29.0% in sample B. Our results suggest that the fraction of the initial cube texture significantly affects the recrystallization kinetics, the sample with a higher fraction of the initial cube texture exhibits a faster rate of formation of the recrystallization texture. After annealing at 700 1C and 900 1C, both samples recrystallized completely and achieved a strong cube textures. Fig. 5 shows the trends of the cube texture fractions in different state specimens. We note that, independent of the fractions of the initial cube texture, cube recrystallization texture fraction increases with increasing annealing temperature, indicating that a higher temperature is benefit to enhancing cube texture. On the other hand, the fraction of cube recrystallization texture increases with increasing initial cube texture fraction during annealing at the same temperature, namely samples with more initial cube texture can achieve more recrystallization cube texture after annealing. It appears that the recrystallization cube textures have much to do with the initial cube texture prior to cold deformation. Some related reports have stated that the origin of the cube-oriented bands appeared in the hot deformed Al alloys was “old” cube grains (presented in the starting material) which survived in the deformation process [8]. During deformation the old cube grains were flattened into bands which acted as nucleation sites for recrystallization upon annealing treatments. In our experiments, a higher fraction of initial cube texture can provide more potential nucleation sites during annealing and then enhance strength of recrystallized
X.P. Chen et al. / Materials Science & Engineering A 585 (2013) 66–70
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Fig. 4. EBSD orientation maps of samples annealed for 30 min at different temperatures: (a) sample A, 300 1C, (b) sample B, 300 1C, (c) sample A, 700 1C, (d) sample B, 700 1C, (e) sample A, 900 1C, and (f) sample B, 900 1C. In this EBSD map, grains in red have the orientation of cube texture (within a 151 deviation from {100}〈001〉), grains in purple are S orientation ({123}〈634〉), grains in green are goss texture ({011}〈100〉), grains in yellow are brass texture ({011}〈211〉), grains in blue are copper texture ({112}〈111〉), grains in white have random orientation, thin black lines refer to low angle grain boundaries, and thick black lines refer to high angle grain boundaries. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
cube texture in nickel. Besides that it should be noted that the effect of initial cube texture fractions on the recrystallization texture depends strongly on the annealing temperature. The fraction of cube recrystallization texture increases sharply at low annealing temperatures while it increase slightly at high annealing temperatures with the increases of initial cube texture fractions. The fraction of cube recrystallization texture depends on the initial cube texture to some degree. It is obvious that the cube texture
fraction in cold-rolled nickel is in proportion to the cube fraction of initial specimens, and similar result is also found in the as-annealed specimens. The cube recrystallization texture could be enhanced by a high initial cube fraction (or large amount of cube bands). The more initial cube texture in the initial sample, the more cube orientation remained after heavy cold rolling and the more cube recrystallization texture developed upon annealing. However, there are still some differences in recrystallization between low and high temperature
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fraction of initial cube texture make for stronger cube recrystallization texture. In the case of low-temperature annealing, fraction of initial cube texture has a pronounced effect on the cube recrystallization texture, but for high-temperature annealing, this effect is less.
Acknowledgment This project was supported by the National Natural Science Foundation of China (51171215). References [1] [2] [3] [4] Fig. 5. Fractions of cube texture of different state specimens.
annealing. When annealed at low temperatures, higher initial cube fraction is of more benefit to nucleation of cube grains, thus oriented nucleation is dominated. While annealed at high temperatures, the rates of recovery and growth are very fast and cube oriented grains grow faster as temperature increased [18]. Sample A developed a large number of cube nucleus within the cube bands at first, and more recrystallized grains were in these areas. Consequently, the grain growth will restrict due to the impingement of gains in these areas. Sample B developed less amount of nucleus, and the inhibition of each grain was small, so most grains could grow normally. Hence it presented a little difference in cube fractions after high temperature annealing. Some researchers thought that the structure and local misorientation environment surrounding of the cube bands in deformed matrix are more important for the formation of recrystallization cube texture [7,19]. Nonetheless, the present work indicates that large cube-oriented regions in the deformed microstructure make for the formation of recrystallization cube texture. 4. Conclusions In summary, we report the effects of the initial cube texture on the cube texture of cold rolling and subsequent annealing samples. In both deformed and recrystallized states, fractions of cube textures are commensurate with fractions of initial cube textures, higher
[5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
F. Yang, E. Narumi, S. Patel, D.T. Shaw, Physica C 244 (1995) 299–304. D.J. Jensen, Acta Metall. Mater. 43 (1995) 4117–4129. R.E. Smallman, C.S. Lee, Mater. Sci. Eng. A 184 (1994) 97–112. B.J. Duggan, M. Sindel, G.D. Köhlhoff, K. Lücke, Acta Metall. Mater. 38 (1990) 103–111. P.P. Bhattacharjee, R.K. Ray, N. Tsuji, Acta Mater. 57 (2009) 2166–2179. S. Zaefferer, T. Baudin, R. Penelle, Acta Mater. 49 (2001) 1105–1122. P.P. Bhattacharjee, Metall. Mater. Trans. A 41A (2010) 2856–2870. H.E. Vatne, R. Shahani, E. Nes, Acta Mater. 44 (1996) 4447–4462. Q. Liu, D. Juul Jensen, N. Hansen, Acta Mater. 46 (1998) 5819–5838. O. Daaland, E. Nes, Acta Mater. 44 (1996) 1389–1411. X.L. Li, W. Liu, A. Godfrey, D. Juul Jensen, Q. Liu, Acta Mater. 55 (2007) 3531–3540. J. Eickemeyer, D. Selbmann, R. Optiz, E. Maher, W. Prusseit, Physica C 341–348 (2000) 2425–2426. J. Eickemeyer, D. Selbmann, R. Opitz, H. Wendrock, S. Baunack, V.S. Sarma, B. Holzapfel, L. Schultz, E. Maher, Physica C 418 (2005) 9–15. A.L. Etter, M.H. Mathon, T. Baudin, V. Branger, R. Penelle, Scr. Mater. 46 (2002) 311–317. V. Subramanya Sarma, J. Eickemeyer, L. Schultz, B. Holzapfel, Scr. Mater. 50 (2004) 953–957. 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. H.L. Suo, Y. Zhao, M. Liu, Y. Zhang, D. He, L. Ma, Y. Ji, M. Zhou, Acta Mater. 56 (2008) 23–30. J. Humphreys, M. Hatherly, Recrystallization and Related Annealing Phenomena, second edition, Elsevier, New York, 2004. P.P. Bhattacharjee, Y. Takatsuji, Y. Miyajima, D. Terada, N. Tsuji, Mater. Sci. Forum 753 (2013) 293–296.
Contents lists available at ScienceDirect
Materials Science & Engineering A journal homepage: www.elsevier.com/locate/msea
Effect of initial cube texture on the recrystallization texture of cold rolled pure nickel X.P. Chen n, X. Chen, J.P. Zhang, Q. Liu College of Materials Science and Engineering, Chongqing University, Chongqing 400030, China
art ic l e i nf o
a b s t r a c t
Article history: Received 22 March 2013 Received in revised form 14 June 2013 Accepted 17 July 2013 Available online 24 July 2013
High-purity nickel samples with different volume fractions of initial cube textures were cold rolled to 96% reduction and subsequently annealed at different temperatures. The survived cube orientation fractions in the cold-rolled samples were found to be in proportion to the volume fraction of the initial cube texture. The initial cube fraction could affect the recrystallization process significantly, which showed some huge differences in the case of low temperature annealing from that of high temperature annealing. & 2013 Elsevier B.V. All rights reserved.
Keywords: Nickel Cold-rolling Recrystallization Cube texture EBSD
1. Introduction The recrystallization texture has been a research subject by metallurgist for several decades. It is usually found that the cube texture ({001}〈100〉) is the strongest recrystallization texture component after annealing for most deformed face-centered cubic (FCC) metals. For metal-based substrates for coated superconductors (i.e. Ni and Ni–W alloys), the cube texture should be controlled. A very sharp cube texture is needed for metal substrates to overcome the “weak link” behavior so that YBCO coated conductors can get a high critical current density [1]. With respect to the origin of the cube texture both theories of oriented nucleation and oriented growth were given strong supports [2–4]. Oriented nucleation maintains that cube-oriented grains nucleate from a deformed matrix more frequently than grains with any other orientations [5]. There is a substantial evidence that in the cold deformed microstructure, cube orientation regions are located in some thin bands, which are parallel to the rolling direction (RD), these regions are called cube bands [6–9]. These cube bands are formed within cube oriented grains in pre-deformed metals undergoing deformation and retention [8]. It has been reported that cube orientation is metastable, a large orientation gradient develops during plastic deformation [8–10] and dislocation cells of cube oriented regions have larger size. All these characters lead to a larger nucleation rate of cube orientation grains and thus the cube bands become very potent
n
Corresponding author. Tel.: +86 23 65111547; fax: +86 23 65106407. E-mail address: [email protected] (X.P. Chen).
0921-5093/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msea.2013.07.028
nucleation sites during recrystallization annealing. In contrast, the oriented growth theory emphasizes that the origin of sharp cube texture lies in the selective growth of cube nuclei. That is to say, cube oriented grains grow faster than non-cube oriented grains during the recrystallization process [2], which is due to the high migration mobility of boundaries between cube grains and their surrounding deformation matrix. It is also suggested that certain misorientation relationships such as 401 around 〈111〉 have a high mobility. It is found that misorientation between the cubeorientation and the S-orientation ({123}〈634〉) conforms to this relationship. S is one of the dominating components of deformation texture in FCC metals. Since cube oriented grains in the cube bands grow faster than non-cube oriented grains [2,11], cube bands in the deformation microstructure were developed from cube-oriented grains in pre-deformed materials, therefore the content of cubeoriented grains in the pre-deformed materials plays an important role in the recrystallization cube texture component. It is well known that many factors influence the recrystallization cube textures. For polycrystalline nickel, numerous studies have focused on the effects of nickel purity, alloying elements, rolling reduction and annealing temperature on the recrystallization textures [11–17]. However, effect of initial cube texture has been paid little attention for nickel substrate. The initial cube texture prior to cold deformation is one of the structural parameters affecting the evolution of the microstructure and the texture of nickel during deformation and subsequent annealing. It is important to study the effect of initial cube texture on the as-deformed and recrystallized textures of pure nickel which is critical for texture control of nickel-based superconducting substrates. Not
X.P. Chen et al. / Materials Science & Engineering A 585 (2013) 66–70
only does it play an important role in enriching the theory of metalbased substrates but also it contributes to industrial production of metal-based substrates production.
2. Materials and methods The starting material used in the present investigation was highpurity nickel (99.999%), its thickness was 10 mm. It was processed to give an average grain size of 50 μm and a fairly random texture. A two-step rolling procedure was used to investigate the effect of initial cube texture on the recrystallization texture of the cold-rolled pure nickel. Firstly, the samples were rolled by a reduction of 80% to 2 mm in thickness, and two types of initial samples with different fractions of cube texture were prepared by different annealing procedures, marked as samples A and B. Then, they were cold rolled by 96% reduction to 80 μm in thickness. Finally, the samples were
67
annealed at certain temperature (300 1C, 700 1C or 900 1C) for 30 min in reducing atmosphere of argon and 4% hydrogen (heating rate of 300 1C per hour, water quench). The microstructures and textures of the deformed and recrystallized samples were characterized by a Channel 5 Electron BackScattering Diffraction (EBSD) detector attached to a FEI Nova 400 Nano scanning electron microscope (SEM). The measuring surface is RD-TD (RD is rolling direction and TD is transverse direction) and an area of 400 400 μm2 was characterized on each sample. At least three maps were taken for each condition. The horizontal direction is RD in all EBSD orientations maps.
3. Results and discussions Fig. 1 shows the microstructures and misorientation distribution of initial samples. EBSD analysis gives crystallographic orientation map for identifying orientations of each grain. Different
Fig. 1. (a) EBSD orientation map for initial sample A with initial texture (fraction of cube texture is 25.4%); (b) misorientation distribution of initial sample A; (c) EBSD orientation map for initial sample B with initial texture (fraction of cube texture is 9.1%); (d) misorientation distribution of initial sample B. In this EBSD map, grains in red have the orientation of cube texture (within a 151 deviation from {100}〈001〉), grains in purple are S orientation ({123}〈634〉), grains in green are goss texture ({011}〈100〉), grains in yellow are brass texture ({011}〈211〉), grains in blue are copper texture ({112}〈111〉), grains in white have random orientation, thin black lines refer to low angle grain boundaries, and thick black lines refer to high angle grain boundaries. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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Fig. 2. EBSD orientation maps of cold-rolling specimens (with a 96% reduction in thickness): (a) sample A and (b) sample B. In this EBSD map, grains in red have the orientation of cube texture (within a 151 deviation from {100}〈001〉), grains in purple are S orientation ({123}〈634〉), grains in green are goss texture ({011}〈100〉), grains in yellow are brass texture ({011}〈211〉), grains in blue are copper texture ({112}〈111〉), grains in white have random orientation, thin black lines refer to low angle grain boundaries, and thick black lines refer to high angle grain boundaries. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 3. The curve of micro-hardness for Ni after annealing at different temperatures for 1 h.
annealing temperature and time were used so as to get nearly same grain size and eliminate the effect of grain size on the intensity of cube texture after annealing. As shown in Fig. 1, two initial samples A and B are of similar grain size, which are 22.8 μm and 21.8 μm. The initial cube texture fractions of samples A and B are 25.4% and 9.1%, respectively. Moreover, the cube grains distribute randomly, and the misorientation distribution of sample A is similar to that of sample B. After 96% cold rolling reduction, the EBSD maps of two samples showing the typical deformation microstructure were given in Fig. 2. It is clearly observed that the remained cube grains are present within the long thin bands (cube bands), and the volume fraction of the cube texture reduces sharply after cold rolling by a reduction of 96%. However, there remain a few cube textures in all samples, the cube texture fractions of the deformed samples A and B are 4.7% and 0.7%, respectively. It is also interesting to note that the higher of the initial cube texture fraction, the higher is the cube texture fraction after rolling. The above results demonstrate that the cube-oriented grains rotate away from it and to other orientations after severe cold rolling. At the same time there are a few cube orientations surviving after large reduction cold rolling. It suggests that cube-oriented grains which were present in the initial materials prior to cold rolling are metastable through large reductions.
Fig. 3 shows the micro-hardness changes of pure nickel annealed at various temperatures, ranging from 100 1C to 900 1C. When annealed at 100–200 1C, hardness of both samples decreased slightly, indicating that only recovery took place. While annealed at a temperature between 250 1C and 300 1C, the hardness decreased sharply, which illustrates that the material partially recrystallized. Hardness of sample A decreased faster. After 300 1C, with temperature increasing, the hardness of sample A reduced a little, but the hardness of B diminished throughout the heat treatment. It suggests that severely sample A completes recrystallization at 300 1C, but it was uncertain of B. It is possible that thickness of Ni substrates produce an effect on hardness, and these substrates were 80 μm. The microstructures for annealed specimens were shown in Fig. 4. After annealing at 300 1C for 30 min, clearly, sample A is almost fully recrystallized, and the cube oriented grains were developed in most regions (Fig. 4a). While for sample B, only a few recrystallized grains were observed (Fig. 4b). The volume fractions of the recrystallized area were 77.6% in sample A only 29.0% in sample B. Our results suggest that the fraction of the initial cube texture significantly affects the recrystallization kinetics, the sample with a higher fraction of the initial cube texture exhibits a faster rate of formation of the recrystallization texture. After annealing at 700 1C and 900 1C, both samples recrystallized completely and achieved a strong cube textures. Fig. 5 shows the trends of the cube texture fractions in different state specimens. We note that, independent of the fractions of the initial cube texture, cube recrystallization texture fraction increases with increasing annealing temperature, indicating that a higher temperature is benefit to enhancing cube texture. On the other hand, the fraction of cube recrystallization texture increases with increasing initial cube texture fraction during annealing at the same temperature, namely samples with more initial cube texture can achieve more recrystallization cube texture after annealing. It appears that the recrystallization cube textures have much to do with the initial cube texture prior to cold deformation. Some related reports have stated that the origin of the cube-oriented bands appeared in the hot deformed Al alloys was “old” cube grains (presented in the starting material) which survived in the deformation process [8]. During deformation the old cube grains were flattened into bands which acted as nucleation sites for recrystallization upon annealing treatments. In our experiments, a higher fraction of initial cube texture can provide more potential nucleation sites during annealing and then enhance strength of recrystallized
X.P. Chen et al. / Materials Science & Engineering A 585 (2013) 66–70
69
Fig. 4. EBSD orientation maps of samples annealed for 30 min at different temperatures: (a) sample A, 300 1C, (b) sample B, 300 1C, (c) sample A, 700 1C, (d) sample B, 700 1C, (e) sample A, 900 1C, and (f) sample B, 900 1C. In this EBSD map, grains in red have the orientation of cube texture (within a 151 deviation from {100}〈001〉), grains in purple are S orientation ({123}〈634〉), grains in green are goss texture ({011}〈100〉), grains in yellow are brass texture ({011}〈211〉), grains in blue are copper texture ({112}〈111〉), grains in white have random orientation, thin black lines refer to low angle grain boundaries, and thick black lines refer to high angle grain boundaries. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
cube texture in nickel. Besides that it should be noted that the effect of initial cube texture fractions on the recrystallization texture depends strongly on the annealing temperature. The fraction of cube recrystallization texture increases sharply at low annealing temperatures while it increase slightly at high annealing temperatures with the increases of initial cube texture fractions. The fraction of cube recrystallization texture depends on the initial cube texture to some degree. It is obvious that the cube texture
fraction in cold-rolled nickel is in proportion to the cube fraction of initial specimens, and similar result is also found in the as-annealed specimens. The cube recrystallization texture could be enhanced by a high initial cube fraction (or large amount of cube bands). The more initial cube texture in the initial sample, the more cube orientation remained after heavy cold rolling and the more cube recrystallization texture developed upon annealing. However, there are still some differences in recrystallization between low and high temperature
70
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fraction of initial cube texture make for stronger cube recrystallization texture. In the case of low-temperature annealing, fraction of initial cube texture has a pronounced effect on the cube recrystallization texture, but for high-temperature annealing, this effect is less.
Acknowledgment This project was supported by the National Natural Science Foundation of China (51171215). References [1] [2] [3] [4] Fig. 5. Fractions of cube texture of different state specimens.
annealing. When annealed at low temperatures, higher initial cube fraction is of more benefit to nucleation of cube grains, thus oriented nucleation is dominated. While annealed at high temperatures, the rates of recovery and growth are very fast and cube oriented grains grow faster as temperature increased [18]. Sample A developed a large number of cube nucleus within the cube bands at first, and more recrystallized grains were in these areas. Consequently, the grain growth will restrict due to the impingement of gains in these areas. Sample B developed less amount of nucleus, and the inhibition of each grain was small, so most grains could grow normally. Hence it presented a little difference in cube fractions after high temperature annealing. Some researchers thought that the structure and local misorientation environment surrounding of the cube bands in deformed matrix are more important for the formation of recrystallization cube texture [7,19]. Nonetheless, the present work indicates that large cube-oriented regions in the deformed microstructure make for the formation of recrystallization cube texture. 4. Conclusions In summary, we report the effects of the initial cube texture on the cube texture of cold rolling and subsequent annealing samples. In both deformed and recrystallized states, fractions of cube textures are commensurate with fractions of initial cube textures, higher
[5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
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