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Orientational dependence of recrystallization in an Ni-base single-crystal superalloy
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Scripta Materialia 66 (2012) 378–381 www.elsevier.com/locate/scriptamat
Orientational dependence of recrystallization in an Ni-base single-crystal superalloy G. Xie,a L. Wang,a J. Zhanga,b,⇑ and L.H. Loua a
Superalloys Division, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China b Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China Received 11 November 2011; revised 23 November 2011; accepted 24 November 2011 Available online 2 December 2011
The orientational dependence of deformation and recrystallization in an Ni-base single-crystal superalloy indented on the (1 0 0) and (1 1 0) planes was investigated. The surface topography and distribution of slip bands indicated that the deformation depended on the crystallographic orientation. The anisotropy of recrystallization grain growth was observed on the mid-section below the indentation. The size and shape of the recrystallization region showed good correspondence to that of the deformation zone. The orientational dependence of recrystallization was discussed based on the deformation mechanism. Ó 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Recrystallization; Single-crystal superalloy; Orientation; Indentation
Single-crystal (SX) superalloys have been widely used with high reliability for blades and vanes in gas turbines. However, recrystallization (RX) may occur during heat treatment or long-term service. The occurrence of RX poses one of the major difficulties in post-processing of SX blades of Ni-base superalloys [1]. In previous work, the effect of microstructural features, such as c0 , carbides and c/c0 eutectics [2–6], as well as the heat treatment parameters [5–10] on RX behavior has been studied. However, the orientational dependence of RX in SX superalloy has rarely been reported. Okazaki et al. [8] observed that the nucleation of RX exhibited a significant crystallographic anisotropy on the indented surface: the predominant orientations of RX nucleation included h1 1 0i directions on the (0 0 1) plane indentation, [1 0 0] directions on the (0 1 1) plane and h1 1 2i directions on the (1 1 1) plane. They argued that the change of slip systems may play an intrinsic role for the anisotropy of RX on the indented surface. Unfortunately, no detailed observations were made of the deformed microstructure.
⇑ Corresponding
author at: Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China. Tel.: +86 24 23971196; e-mail: [email protected]
The present paper therefore observed the surface topography and slip bands of a SX superalloy after deformation on different crystallographic planes. The orientational dependence of RX and relationship between the deformed microstructure and anisotropy of RX were subsequently studied. The composition of the alloy studied is 13Cr, 4Co, 8(Al + Ti), 11–13(Ta + W + Mo), with minor C and B, and balance Ni, in weight percent. The SX alloy with h0 0 1i orientation was directionally solidified by the liquid metal cooling technique. Liquid tin was selected as the cooling medium. A withdrawal rate of 7 mm min1 was used. Each casting produced four bars, each 16 mm in diameter and 220 mm in length. The bars were cut into slices of size 12 12 5 mm with an electric discharge machine (EDM). The 12 12 mm plane of these slices was parallel to the (1 0 0) and (1 1 0) crystallographic planes, respectively. (The crystallographic plane was determined by X-ray diffraction.) These slices were ground and indented using a Brinell hardness tester with a load of 14.7 kN on the (1 0 0) and (1 1 0) crystallographic planes and named the (1 0 0) and (1 1 0) indentations, respectively. The surface topography was determined using the MicroXAM-3-D surface profiler system. The indented samples were heat treated at 1250 °C/4 h/air cooling (AC), followed by 1110 °C/5 h/AC + 870 °C/24 h/AC.
1359-6462/$ - see front matter Ó 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.scriptamat.2011.11.037
G. Xie et al. / Scripta Materialia 66 (2012) 378–381
Figure 1. 3-D surface topography of (a) (1 0 0) and (b) (1 1 0) indentation with a load of 14.7 kN.
Indented and heat-treated samples were prepared by the standard metallographic procedure to examine the microstructure below the indentation. Some indented and heat-treated samples were cut along the mid-section perpendicular to the indentation surface by the EDM to observe the morphology of the slip bands and RX below the indentation. Mid-sections of the (1 0 0) indentation were parallel to the [0 1 0] and [0 1 1] directions, and those of the (1 1 0) indentation were parallel to the [ 1 1 0] and [ 1 1 2] directions, respectively. The depth, width and area of RX were measured using Image-pro Plus software. Figure 1 shows the three-dimensional (3-D) surface topography around the indentation. Strong pile-up anisotropy can be seen around the (1 0 0) indentation (Fig. 1a). This reflects the fourfold crystallographic symmetry around the [1 0 0] indentation axis, i.e. almost no bulging out of the material could be observed along the h0 0 1i directions, while strong pile-ups were formed along the h0 1 1i directions. Similar behavior has been observed in earlier studies [11–13]. On the other hand, only small pile-ups were observed along the h 1 1 2i directions around the (1 1 0) indentation (Fig. 1b).
379
Figure 2 shows the morphology of the slip bands on the (0 0 1) section of the (1 0 0) indentation. Only half of the section is shown in the figure because the microstructure is symmetrical. Extremely inhomogeneous slip bands were produced. Slip bands with high density were observed near the centre of the indentation. Slip bands with multiple slip were mainly concentrated within the region about 800 lm from the indentation. Three slip bands were observed in this region. The angle between slip bands I and II was about 10°, while that between slip bands I and III was about 90° (showed as white arrows in Fig. 2b). The slip systems operated in slip bands I and III can be deduced as (1 1 1)[ 1 1 0] and (1 1 1)[ 1 10], respectively. The slip band II was probably composed of another (1 1 1)[ 1 1 0] slip system, but with a small rotation (Fig. 2b). The density of the slip bands decreased rapidly with increasing distance from the indentation. Only a single slip in the [1 1 0] direction can be found in Figure 2c. The slip bands gradually disappeared at 1900 lm below the indentation, which was an indication of the end of the deformation zone. Similarly, slip bands on the (0 0 1) section of the (1 1 0) indentation are shown in Figure 3. The distribution of slip bands on this section was relatively homogeneous compared with that of the (1 0 0) indentation. Meanwhile, a higher density of slip bands was observed in this specimen. Two pairs of slip bands were produced in region A. Slip bands I and II were near the [110] direction (showed as white arrows at the lower left corner of Fig. 3b), and slip bands III and IV were near the [ 1 1 0] direction (upper right corner of Fig. 3b). The angle between slip bands I and II or III and IV was about
Figure 2. Morphology of slip bands on the (0 0 1) section of the (100) indentation along the direction of the indentation depth. (a) Distribution of slip bands on the whole (0 0 1) section. (b) and (c) are the expanded views of areas A and B in (a), respectively.
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G. Xie et al. / Scripta Materialia 66 (2012) 378–381
Figure 3. Morphology of slip bands on the (0 0 1) section of the (110) indentation along the direction of the indentation depth. (a) Distribution of slip bands on the whole (0 0 1) section. (b) and (c) are the expanded views of areas A and B in (a), respectively.
20o. Only one pair of slip bands remained as the distance from the indentation increased, as shown in Figure 3c. The maximum depth of the deformation zone was about 3100 lm. Large RX grains formed after heat treatment. The microstructure of RX below the indentation is shown in Figure 4, and the corresponding RX data is compared in Table 1. The width of the RX region along the [0 1 1] direction was significantly larger than that along the
Figure 4. RX on the mid-section perpendicular to the indented surface below the indentation. (a) (0 0 1) and (b) (0 1 1) sections of the (100) indentation; (c) (0 0 1) and (d) (1 1 1) sections of the (110) indentation.
Table 1. Comparison of RX data on the mid-section perpendicular to the indented surface below the indentation. Indented plane
Mid-section
RX depth (lm)
RX width (lm)
RX area (mm2)
(100)
(0 0 1) (0 1 1) (0 0 1) (1 1 1)
2025 1908 2931 2823
3486 4126 2977 3739
5.26 5.56 7.32 8.42
(110)
[0 1 0] direction under the (1 0 0) indentation, while the depths of RX in different cross-sections were comparable (Fig. 4a and b). The area of RX region on the (01 1) mid-section was therefore much larger than that on the (0 0 1) mid-section. Similar results can be seen under the (1 1 0) indentation, where the width and area of RX region on the (1 1 1) mid-section were obviously larger than those on the (0 0 1) mid-section (Fig. 4c and d). The RX region was found to have a greater depth in the specimens with (1 1 0) indentation. The area of RX region under the (1 1 0) indentation was also larger than that under the (1 0 0) indentation (Table 1). Moreover, the size of the RX grains far from the indentation was always larger than those near the indentation in all specimens. The phenomenon addressed in this paper clearly indicates that the anisotropy of RX in SX superalloy was induced by the anisotropy of deformation. Accompanying the rotation of the crystal and the change in stress direction [14,15], slip systems (11 1)[ 11 0] and (1 1 1)[ 1 1 0]
G. Xie et al. / Scripta Materialia 66 (2012) 378–381
were activated. In this case, [ 1 1 0] slip on the (0 0 1) section of the (1 1 0) indentation was easily activated as it possessed a similar orientation to the direction of the stress. Subsequently, slip systems with the same slip direction and different slip planes, e.g. (1 1 1)[ 1 1 0] and ( 1 1 1)[ 1 1 0], may be activated at different stages of deformation, resulting in a small departure of the slip bands from the original slip directions. Multiple slip (two pairs) can also be observed below the (1 1 0) indentation (Fig. 3a). In contrast, only duplex and single slips were observed below the (1 0 0) indentation. Therefore, the distribution of slip bands on the (0 0 1) section of the (1 1 0) indentation was more homogeneous than that of the (1 0 0) indentation. The depth of the plastic deformation zone on the (0 0 1) section of the (1 1 0) indentation was larger than that of the (1 0 0) indentation. This is in agreement with simulation results of nanoindentation in copper SX [13,16]. The present results indicate that the development of RX was related to the distribution of stored energy, i.e. the profile of the plastic deformation zone. In the region near the indentation, the higher density of slip bands resulted in small RX grains due to the large number of nucleation sites (Fig. 4) [17]. Our present work may also provide a possible method for reducing the RX sensitivity of the SX component by controlling the secondary orientation. The present work shows that the orientational dependence of RX in SX superalloy is induced by the anisotropy of deformation. A relatively large displacement is generated along the h0 1 1i direction of the (1 0 0) indentation, while only small pile-ups are observed around the (1 1 0) indentation. A relatively homogeneous distribution of slip bands is found on the (0 0 1) mid-section of the (1 1 0) indentation compared to that of the (1 0 0) indentation, which results in a larger deformation zone. The overall RX area on the (0 0 1) mid-section of the (1 1 0) indentation is larger than that of the (1 0 0) indentation. The RX depth shows good correspondence to the depth of the deformation zone.
381
This work was financially supported by the National Basic Research Program (973 Program) of China under Grant No. 2010CB631201 and National Natural Science Foundation of China under Grant No. 50901079. The authors are grateful for this support. [1] R. Bu¨rgel, P.D. Portella, J. Preuhs, in: T.M. Pollock, R.D. Kissinger, R.R. Bowman, K.A. Green, M. Mclean, S. Olson, J.J. Schirra (Eds.), Superalloys 2000, TMS, New York, 2000, p. 229. [2] A. Porter, B. Ralph, J. Mater. Sci. 16 (1981) 707. [3] M. Dahle´n, L. Winberg, Acta Metall. 48 (1980) 41. [4] L. Wang, F. Pyczak, J. Zhang, R.F. Singer, Inter. J. Mater. Res. 100 (2009) 1046. [5] L. Wang, G. Xie, J. Zhang, L.H. Lou, Scr. Mater. 55 (2006) 457. [6] U. Paul, P.R. Sahm, Mater. Sci. Eng. A 173 (1993) 49. [7] J.M. Oblak, W.A. Owczarski, Trans. Metall. Soc. AIME. 242 (1968) 1563. [8] M. Okazaki, T. Hiura, T. Suzuki, in: T.M. Pollock, R.D. Kissinger, R.R. Bowman, K.A. Green, M. Mclean, S. Olson, J.J. Schirra (eds.), Superalloys 2000. New York: TMS, 2000, p. 505. [9] C.Y. Yo, H.M. Kim, Mater. Sci. Technol. 19 (2003) 1671. [10] G. Xie, J. Zhang, L.H. Lou, Scr. Mater. 59 (2008) 858. [11] C. Zambaldi, F. Roters, D. Raabe, U. Glatzel, Mater. Sci. Eng. A 454–455 (2006) 433. [12] P. Peralta, R. Ledoux, R. Dickerson, M. Hakik, P. Dickerson, Metall. Mater. Trans. A 35 (2004) 2247. [13] Y. Wang, D. Raabe, C. Klu¨ber, F. Roters, Acta Mater. 52 (2004) 2229. [14] N. Zaafarani, D. Raabe, F. Roters, S. Zaefferer, Acta Mater. 56 (2008) 31. [15] N. Zaafarani, D. Raabe, R.N. Singh, F. Roters, S. Zaefferer, Acta Mater. 54 (2006) 1863. [16] Y. Liu, S. Varghese, J. Ma, M. Yoshino, H. Lu, R. Komanduri, Inter. J. Plasticity 24 (2008) 1990. [17] F.J. Humphreys, M. Hatherly, Recrystallization and Related Annealing Phenomena, Oxford, Elsevier, 2004, p. 259.
Scripta Materialia 66 (2012) 378–381 www.elsevier.com/locate/scriptamat
Orientational dependence of recrystallization in an Ni-base single-crystal superalloy G. Xie,a L. Wang,a J. Zhanga,b,⇑ and L.H. Loua a
Superalloys Division, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China b Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China Received 11 November 2011; revised 23 November 2011; accepted 24 November 2011 Available online 2 December 2011
The orientational dependence of deformation and recrystallization in an Ni-base single-crystal superalloy indented on the (1 0 0) and (1 1 0) planes was investigated. The surface topography and distribution of slip bands indicated that the deformation depended on the crystallographic orientation. The anisotropy of recrystallization grain growth was observed on the mid-section below the indentation. The size and shape of the recrystallization region showed good correspondence to that of the deformation zone. The orientational dependence of recrystallization was discussed based on the deformation mechanism. Ó 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Recrystallization; Single-crystal superalloy; Orientation; Indentation
Single-crystal (SX) superalloys have been widely used with high reliability for blades and vanes in gas turbines. However, recrystallization (RX) may occur during heat treatment or long-term service. The occurrence of RX poses one of the major difficulties in post-processing of SX blades of Ni-base superalloys [1]. In previous work, the effect of microstructural features, such as c0 , carbides and c/c0 eutectics [2–6], as well as the heat treatment parameters [5–10] on RX behavior has been studied. However, the orientational dependence of RX in SX superalloy has rarely been reported. Okazaki et al. [8] observed that the nucleation of RX exhibited a significant crystallographic anisotropy on the indented surface: the predominant orientations of RX nucleation included h1 1 0i directions on the (0 0 1) plane indentation, [1 0 0] directions on the (0 1 1) plane and h1 1 2i directions on the (1 1 1) plane. They argued that the change of slip systems may play an intrinsic role for the anisotropy of RX on the indented surface. Unfortunately, no detailed observations were made of the deformed microstructure.
⇑ Corresponding
author at: Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China. Tel.: +86 24 23971196; e-mail: [email protected]
The present paper therefore observed the surface topography and slip bands of a SX superalloy after deformation on different crystallographic planes. The orientational dependence of RX and relationship between the deformed microstructure and anisotropy of RX were subsequently studied. The composition of the alloy studied is 13Cr, 4Co, 8(Al + Ti), 11–13(Ta + W + Mo), with minor C and B, and balance Ni, in weight percent. The SX alloy with h0 0 1i orientation was directionally solidified by the liquid metal cooling technique. Liquid tin was selected as the cooling medium. A withdrawal rate of 7 mm min1 was used. Each casting produced four bars, each 16 mm in diameter and 220 mm in length. The bars were cut into slices of size 12 12 5 mm with an electric discharge machine (EDM). The 12 12 mm plane of these slices was parallel to the (1 0 0) and (1 1 0) crystallographic planes, respectively. (The crystallographic plane was determined by X-ray diffraction.) These slices were ground and indented using a Brinell hardness tester with a load of 14.7 kN on the (1 0 0) and (1 1 0) crystallographic planes and named the (1 0 0) and (1 1 0) indentations, respectively. The surface topography was determined using the MicroXAM-3-D surface profiler system. The indented samples were heat treated at 1250 °C/4 h/air cooling (AC), followed by 1110 °C/5 h/AC + 870 °C/24 h/AC.
1359-6462/$ - see front matter Ó 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.scriptamat.2011.11.037
G. Xie et al. / Scripta Materialia 66 (2012) 378–381
Figure 1. 3-D surface topography of (a) (1 0 0) and (b) (1 1 0) indentation with a load of 14.7 kN.
Indented and heat-treated samples were prepared by the standard metallographic procedure to examine the microstructure below the indentation. Some indented and heat-treated samples were cut along the mid-section perpendicular to the indentation surface by the EDM to observe the morphology of the slip bands and RX below the indentation. Mid-sections of the (1 0 0) indentation were parallel to the [0 1 0] and [0 1 1] directions, and those of the (1 1 0) indentation were parallel to the [ 1 1 0] and [ 1 1 2] directions, respectively. The depth, width and area of RX were measured using Image-pro Plus software. Figure 1 shows the three-dimensional (3-D) surface topography around the indentation. Strong pile-up anisotropy can be seen around the (1 0 0) indentation (Fig. 1a). This reflects the fourfold crystallographic symmetry around the [1 0 0] indentation axis, i.e. almost no bulging out of the material could be observed along the h0 0 1i directions, while strong pile-ups were formed along the h0 1 1i directions. Similar behavior has been observed in earlier studies [11–13]. On the other hand, only small pile-ups were observed along the h 1 1 2i directions around the (1 1 0) indentation (Fig. 1b).
379
Figure 2 shows the morphology of the slip bands on the (0 0 1) section of the (1 0 0) indentation. Only half of the section is shown in the figure because the microstructure is symmetrical. Extremely inhomogeneous slip bands were produced. Slip bands with high density were observed near the centre of the indentation. Slip bands with multiple slip were mainly concentrated within the region about 800 lm from the indentation. Three slip bands were observed in this region. The angle between slip bands I and II was about 10°, while that between slip bands I and III was about 90° (showed as white arrows in Fig. 2b). The slip systems operated in slip bands I and III can be deduced as (1 1 1)[ 1 1 0] and (1 1 1)[ 1 10], respectively. The slip band II was probably composed of another (1 1 1)[ 1 1 0] slip system, but with a small rotation (Fig. 2b). The density of the slip bands decreased rapidly with increasing distance from the indentation. Only a single slip in the [1 1 0] direction can be found in Figure 2c. The slip bands gradually disappeared at 1900 lm below the indentation, which was an indication of the end of the deformation zone. Similarly, slip bands on the (0 0 1) section of the (1 1 0) indentation are shown in Figure 3. The distribution of slip bands on this section was relatively homogeneous compared with that of the (1 0 0) indentation. Meanwhile, a higher density of slip bands was observed in this specimen. Two pairs of slip bands were produced in region A. Slip bands I and II were near the [110] direction (showed as white arrows at the lower left corner of Fig. 3b), and slip bands III and IV were near the [ 1 1 0] direction (upper right corner of Fig. 3b). The angle between slip bands I and II or III and IV was about
Figure 2. Morphology of slip bands on the (0 0 1) section of the (100) indentation along the direction of the indentation depth. (a) Distribution of slip bands on the whole (0 0 1) section. (b) and (c) are the expanded views of areas A and B in (a), respectively.
380
G. Xie et al. / Scripta Materialia 66 (2012) 378–381
Figure 3. Morphology of slip bands on the (0 0 1) section of the (110) indentation along the direction of the indentation depth. (a) Distribution of slip bands on the whole (0 0 1) section. (b) and (c) are the expanded views of areas A and B in (a), respectively.
20o. Only one pair of slip bands remained as the distance from the indentation increased, as shown in Figure 3c. The maximum depth of the deformation zone was about 3100 lm. Large RX grains formed after heat treatment. The microstructure of RX below the indentation is shown in Figure 4, and the corresponding RX data is compared in Table 1. The width of the RX region along the [0 1 1] direction was significantly larger than that along the
Figure 4. RX on the mid-section perpendicular to the indented surface below the indentation. (a) (0 0 1) and (b) (0 1 1) sections of the (100) indentation; (c) (0 0 1) and (d) (1 1 1) sections of the (110) indentation.
Table 1. Comparison of RX data on the mid-section perpendicular to the indented surface below the indentation. Indented plane
Mid-section
RX depth (lm)
RX width (lm)
RX area (mm2)
(100)
(0 0 1) (0 1 1) (0 0 1) (1 1 1)
2025 1908 2931 2823
3486 4126 2977 3739
5.26 5.56 7.32 8.42
(110)
[0 1 0] direction under the (1 0 0) indentation, while the depths of RX in different cross-sections were comparable (Fig. 4a and b). The area of RX region on the (01 1) mid-section was therefore much larger than that on the (0 0 1) mid-section. Similar results can be seen under the (1 1 0) indentation, where the width and area of RX region on the (1 1 1) mid-section were obviously larger than those on the (0 0 1) mid-section (Fig. 4c and d). The RX region was found to have a greater depth in the specimens with (1 1 0) indentation. The area of RX region under the (1 1 0) indentation was also larger than that under the (1 0 0) indentation (Table 1). Moreover, the size of the RX grains far from the indentation was always larger than those near the indentation in all specimens. The phenomenon addressed in this paper clearly indicates that the anisotropy of RX in SX superalloy was induced by the anisotropy of deformation. Accompanying the rotation of the crystal and the change in stress direction [14,15], slip systems (11 1)[ 11 0] and (1 1 1)[ 1 1 0]
G. Xie et al. / Scripta Materialia 66 (2012) 378–381
were activated. In this case, [ 1 1 0] slip on the (0 0 1) section of the (1 1 0) indentation was easily activated as it possessed a similar orientation to the direction of the stress. Subsequently, slip systems with the same slip direction and different slip planes, e.g. (1 1 1)[ 1 1 0] and ( 1 1 1)[ 1 1 0], may be activated at different stages of deformation, resulting in a small departure of the slip bands from the original slip directions. Multiple slip (two pairs) can also be observed below the (1 1 0) indentation (Fig. 3a). In contrast, only duplex and single slips were observed below the (1 0 0) indentation. Therefore, the distribution of slip bands on the (0 0 1) section of the (1 1 0) indentation was more homogeneous than that of the (1 0 0) indentation. The depth of the plastic deformation zone on the (0 0 1) section of the (1 1 0) indentation was larger than that of the (1 0 0) indentation. This is in agreement with simulation results of nanoindentation in copper SX [13,16]. The present results indicate that the development of RX was related to the distribution of stored energy, i.e. the profile of the plastic deformation zone. In the region near the indentation, the higher density of slip bands resulted in small RX grains due to the large number of nucleation sites (Fig. 4) [17]. Our present work may also provide a possible method for reducing the RX sensitivity of the SX component by controlling the secondary orientation. The present work shows that the orientational dependence of RX in SX superalloy is induced by the anisotropy of deformation. A relatively large displacement is generated along the h0 1 1i direction of the (1 0 0) indentation, while only small pile-ups are observed around the (1 1 0) indentation. A relatively homogeneous distribution of slip bands is found on the (0 0 1) mid-section of the (1 1 0) indentation compared to that of the (1 0 0) indentation, which results in a larger deformation zone. The overall RX area on the (0 0 1) mid-section of the (1 1 0) indentation is larger than that of the (1 0 0) indentation. The RX depth shows good correspondence to the depth of the deformation zone.
381
This work was financially supported by the National Basic Research Program (973 Program) of China under Grant No. 2010CB631201 and National Natural Science Foundation of China under Grant No. 50901079. The authors are grateful for this support. [1] R. Bu¨rgel, P.D. Portella, J. Preuhs, in: T.M. Pollock, R.D. Kissinger, R.R. Bowman, K.A. Green, M. Mclean, S. Olson, J.J. Schirra (Eds.), Superalloys 2000, TMS, New York, 2000, p. 229. [2] A. Porter, B. Ralph, J. Mater. Sci. 16 (1981) 707. [3] M. Dahle´n, L. Winberg, Acta Metall. 48 (1980) 41. [4] L. Wang, F. Pyczak, J. Zhang, R.F. Singer, Inter. J. Mater. Res. 100 (2009) 1046. [5] L. Wang, G. Xie, J. Zhang, L.H. Lou, Scr. Mater. 55 (2006) 457. [6] U. Paul, P.R. Sahm, Mater. Sci. Eng. A 173 (1993) 49. [7] J.M. Oblak, W.A. Owczarski, Trans. Metall. Soc. AIME. 242 (1968) 1563. [8] M. Okazaki, T. Hiura, T. Suzuki, in: T.M. Pollock, R.D. Kissinger, R.R. Bowman, K.A. Green, M. Mclean, S. Olson, J.J. Schirra (eds.), Superalloys 2000. New York: TMS, 2000, p. 505. [9] C.Y. Yo, H.M. Kim, Mater. Sci. Technol. 19 (2003) 1671. [10] G. Xie, J. Zhang, L.H. Lou, Scr. Mater. 59 (2008) 858. [11] C. Zambaldi, F. Roters, D. Raabe, U. Glatzel, Mater. Sci. Eng. A 454–455 (2006) 433. [12] P. Peralta, R. Ledoux, R. Dickerson, M. Hakik, P. Dickerson, Metall. Mater. Trans. A 35 (2004) 2247. [13] Y. Wang, D. Raabe, C. Klu¨ber, F. Roters, Acta Mater. 52 (2004) 2229. [14] N. Zaafarani, D. Raabe, F. Roters, S. Zaefferer, Acta Mater. 56 (2008) 31. [15] N. Zaafarani, D. Raabe, R.N. Singh, F. Roters, S. Zaefferer, Acta Mater. 54 (2006) 1863. [16] Y. Liu, S. Varghese, J. Ma, M. Yoshino, H. Lu, R. Komanduri, Inter. J. Plasticity 24 (2008) 1990. [17] F.J. Humphreys, M. Hatherly, Recrystallization and Related Annealing Phenomena, Oxford, Elsevier, 2004, p. 259.