- Email: [email protected]
Study of microstructure of nickel-based superalloys at high temperatures
Scripta Materialia 126 (2017) 55–57
Contents lists available at ScienceDirect
Scripta Materialia journal homepage: www.elsevier.com/locate/scriptamat
Study of microstructure of nickel-based superalloys at high temperatures Qinghua Zhang a, Yunjie Chang a, Lin Gu a, Yushi Luo b, Binghui Ge a,⁎ a b
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China National Key Laboratory of Science and Technology on Advanced High Temperature Structural Materials, Beijing Institute of Aeronautical Materials, Beijing 100095, People's Republic of China
a r t i c l e
i n f o
Article history: Received 28 June 2016 Received in revised form 12 August 2016 Accepted 15 August 2016 Available online xxxx Keywords: Superalloys In-situ heating TEM Surface reconstruction Interface
a b s t r a c t Nickel-based superalloys are widely used as high temperature materials for turbine blades in aerospace industry and land-based applications. Their structural characterization, however, is mostly carried out at the room temperature. Here, the microstructure of the superalloys was studied at high temperature, 1000 °C, through aberration-corrected scanning transmission electron microscope imaging. It is the first time that both evaporation and reconstruction of alloying elements were observed with the atomic resolution at the high temperature. © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Superalloys are unique high temperature materials used in gas turbine engines, which display excellent resistance to mechanical and chemical degradation [1]. To improve the performance, numerous researchers and technologists have worked on the microstructure of superalloys to develop the basic understanding of their physical behaviors. For example, rhenium plays a critical role in single-crystal superalloys —its addition to first generation alloys improves creep life by a factor of at least two, with further benefits for fatigue performance, which is the so-called “rhenium effect” [2–17], so that single-crystal superalloys are commonly grouped into generations based on their Re content. To study this effect and to understand the strengthening mechanism of Re, the technique of the atom probe and scanning transmission electron microscopy (STEM) as well as the theoretical calculation were utilized to study the distribution of rhenium, although up to now, some postulations such as Re clusters [3–8,11,13,16,18] and enrichment of Re at the γ/γʹ interfaces [16,18,19] are still under debate. To further understand the structural evolution when superalloys are in the service, in-situ transmission electron microscope (TEM) were carried out recently. Through in-situ environmental TEM, Qingqing etc. [20] found that the ordered γʹ phase gradually transformed to the disordered γ phase during oxidization with the appearance of oxidation product consisted of γ-Al2O3 crystallites, which proves the γ-γʹ phase transformation induced by aluminum oxidation with aluminum depleted in γʹ phases. Besides, through in-situ heating experiments, effects of platinum group metals additions on topologically closed packed (TCP) precipitates were studied by Shuang etc. TCP precipitations are found to be inhibited by adding element Pt, Ir and Ru at both 950 and 1050 °C [21]. In the present work, microstructure of one kind of ⁎ Corresponding author. E-mail address: [email protected] (B. Ge).
http://dx.doi.org/10.1016/j.scriptamat.2016.08.013 1359-6462/© 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
superalloys was studied by in-situ heating STEM at 1000 °C. Under the effect of high temperature and high vacuum, alloying elements were vaporized and reconstructed, which were observed with atomic resolution for the first time. The material tested was a typical second-generation single crystal superalloy DD6 and the nominal composition in wt.% is: 5.6Al, 4.3Cr, 9Co, 2Mo, 7.5Ta, 8W, 2Re and balance Ni. The heat treatments were performed according to the following regime: 1290 °C/1 h + 1300 °C/ 2 h + 1315 °C/4 h/AC + 1120 °C/4 h/AC + 870 °C/32 h/AC. Details of DD6 preparation have been described previously [22]. The lamellae of the superalloy was prepared by a focus ion beam system (FEI Helios 600i), and the samples for in situ TEM heating experiments were created using EM heater chips (DENSsolutions) fitting to the MEMS-based Double Tilt Sample Heating System (DENSsolutions) [23]. In-situ heating experiments were carried out at 1000 °C in a double corrected TEM (JEOL ARM 200). Fig. 1(a) is a typical high-angle annular dark field (HAADF) image of γʹ phase at the room temperature, in which bright dots indicate the heavy elements [24] for the HAADF imaging follows almost Z2 dependency with respect to the atomic number Z [25–27]. At 1000 °C, some vacancies can be observed in the HAADF image with black contrast as shown in Fig. 1(b), indicated by an arrow in the enlarged image shown in Fig. 1(c). For heavy elements in single crystal nickel-based superalloys are usually located at the Al sites in γʹ phase (Ni3Al) [24,28,29], Al sites can be determined according to the image show as Fig. 1(c) with the [001] projected model of Ni3Al inset on the right, in which red columns denote Al sites and white columns denote Ni sites. Thus, the vacancies should also be at the Al sites according to Figs. 1(b) and (c). As reported [30], the vapor pressure of Al, almost 2.5 ∗ 10−2 Pa, at 1000 °C, is much higher than the vacuum of the chamber in the ARM microscope, almost 2 ∗ 10−5 Pa, as well as that of Cr, Co and Ni, so these
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Q. Zhang et al. / Scripta Materialia 126 (2017) 55–57
Fig. 1. (a) and (b) HAADF images of the γʹ phase at the room temperature and 1000 °C, respectively. (c) Enlarged image with the projected model of Ni3Al inset on the right, and red disks denote Al sites and white disks Ni sites. (d) HAADF image of the γ/γʹ interface indicated by a white dashed line. Vacancies are denoted by white arrows. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
four alloying elements should be volatile under this condition, among which Al is the most one. In addition, Al is basic constitution of the γʹ phase, so most of the vacancies shown in Figs. 1(b) and (c) should be Al. For there is no site preference of Al in the γ phase, along the direction of electron beam fewer vacancies exist in one atomic column in the γ phase comparing with that in γʹ phase, which makes contrast of vacancies in the γ phase as shown in Fig. 1(d) not obvious as shown in the γʹ phase. In the following, cavities caused by evaporation will be shown in both the γ and γʹ phases. Just as the γʹ phase can be transformed into the γ phase after oxidation because Al is taken out [20], the evaporation of Al of the γʹ phase at the high temperature can also lead to the phase transformation, from the γʹ phase into the γ phase. Indicated by white arrows in Fig. 2, disordered phases are formed at the edge of the sample. In reality, the disordered phase is not transformed directly from the γʹ phase, but an
amount of alloying elements move to the surface and a clusters with the disorder structure are reconstructed. Moreover, as mentioned by Luo etc. [31], heavy elements prefer to form an short range of ordering along 〈100〉 and 〈110〉 directions at the room temperature. In our heating experiment, at the edge of samples 〈100〉 and 〈110〉 heavy atom ordering can be observed clearly as shown in Fig. 2. Besides, the exposed crystal facet, under most of the circumstances, is also {100}and {110} plane, indicating the evaporation can be hindered by the 〈100〉 and 〈110〉 heavy atom ordering to some extent, which confirms the stronger bond between refractory elements such as Re, W and Ta with Ni atoms than the bond between Al, Cr and Co with Ni atoms [32]. Similar as in Figs. 2 (a) and (b), clusters can be observed away from the edge of the sample as shown in Figs. 3 (a) and (b). To be precise, clusters may adhere to the upper/lower surface of the sample. These clusters enhance the contrast of the image but the crystal lattice is not distorted, so these clusters may be similar with the one at the edge of the sample, with the face-centered cubic structure. With the help of EDS analysis as shown in Fig. 3(c), the clusters are enriched with Cr. These clusters are not stable, and can be broken with the irradiation of electrons. Moreover, as we know, the γ/γʹ interface plays an import role in the single crystal nickel-based superalloys, say impeding the slip of the dislocations. In the heating experiment, some interesting features about the interface were observed. With the increase of heating time, size of the clusters becomes bigger and bigger, but when the clusters are close to the interface, they seem to be impeded by the interface, then elongated along the interface as shown in Fig. 4(a). Similar things happened during the evaporation. When more atoms are vaporized in high temperature, some cavities are formed with dark contrast shown in Figs. 4(b) and (c), which is confirmed according to the variation of the local sample thickness determined by the electron energy loss spectroscopy. When cavities are close to the interface, it also expands along the interface, and seems to be hindered by the interface. However, it is still an open question to understand the role of interface of the superalloys at the high temperature. In conclusion, in-situ heating experiments were carried out on one type of single crystal nickel-based superalloys at 1000 °C, and structural evolution with atomic resolution was obtained at the high temperature for the first time. Conclusions are obtained as following: 1) Due to the high vacuum samples were vaporized, and with the evaporation of light atoms especially Al, disordered phases were found to be reconstructed from ordered phases. Meanwhile, heavy atom ordering along the 〈100〉 and 〈110〉 direction was observed at the edge of the sample and {100} and {110} plane are the usually exposed facets.
Fig. 2. HAADF images of superalloys at 1000 °C. In (a) and (b) the disordered phases are indicated by white arrows, and the enlarged area denoted by a rectangle in (a) is inset top right.
Q. Zhang et al. / Scripta Materialia 126 (2017) 55–57
57
Fig. 3. (a) HAADF image of clusters at the temperature of 1000 °C and the area indicated by an ellipse are shown in (b). (c) EDS mapping of clusters.
Fig. 4. (a) HAADF image of clusters, (b) HAADF image of cavities with the area indicated by a white ellipse enlarged and shown in (c).
2) Clusters were found to be formed throughout the sample enriched with Cr. 3) γ/γʹ interface plays an import role even at the high temperature, which seems to not only hinder the expansion of Cr-enriched clusters but also the cavities caused by evaporation, but its mechanism is still an open question
Acknowledgement This work was supported by the National Natural Science Foundation of China (Grant number: 11374332, 11474329). Reference [1] R.C. Reed, The Superalloys Fundamentals and Applications, Cambridge University Press, Cambridge, 2006. [2] K. Harris, G.L. Eickson, R.E. Schwer, Conference on High Temperature Alloys for Gas Turbines and Other Application, 1986 709. [3] M.K. Miller, R.C. Reed, in: J.M. Howe, D.E. Laughlin, J.K. Lee, U. Dahmen, W.A. Soffa (Eds.), Proceedings of an International Conference on Solid–Solid Phase Transformations in Inorganic Materials TMS (Minerals, Metals & Materials Society), Phoenix, AZ 2005, p. 537. [4] D. Blavette, P. Caron, T. Khan, Superalloys TMS, Pennsylvania, 1988 305. [5] N. Wanderka, U. Glatzel, Mater. Sci. Eng. A 203 (1995) 69–74. [6] J. Rusing, N. Wanderka, U. Czubayko, V. Naundorf, D. Mukherji, J. Rosler, Scr. Mater. 46 (2002) 235–240. [7] T. Zhu, C.Y. Wang, Y. Gan, Acta Mater. 58 (2010) 2045–2055. [8] A. Mottura, R.T. Wu, M.W. Finnis, R.C. Reed, Acta Mater. 56 (2008) 2669–2675.
[9] A. Mottura, M.K. Miller, in: R.C. Reed, R.C. Reed, K.A. Green, P. Caron, T.P. Gabb, M.G. Fahrmann, E.S. Huron (Eds.),11th International Symposium on Superalloys, Minerals, Metals & Materials Soc, Champion, PA 2008, pp. 891–900. [10] A. Mottura, N. Warnken, M.K. Miller, M.W. Finnis, R.C. Reed, Acta Mater. 58 (2010) 931–942. [11] A. Mottura, M.W. Finnis, R.C. Reed, Acta Mater. 60 (2012) 2866–2872. [12] S.B. Maisel, N. Schindzielorz, A. Mottura, R.C. Reed, S. Müller, Phys. Rev. B 90 (2014) 094110. [13] J.Y. Guédou, A. Mottura, R.C. Reed, J. Choné, MATEC Web Conf. 14 (2014) 01001. [14] M. Huang, Z. Cheng, J. Xiong, J. Li, J. Hu, Z. Liu, J. Zhu, Acta Mater. 76 (2014) 294–305. [15] M. Huang, J. Zhu, Rare Metals 35 (2016) 127–139. [16] B.H. Ge, Y.S. Luo, J.R. Li, J. Zhu, Scr. Mater. 63 (2010) 969–972. [17] B. Ge, Y. Luo, J. Li, J. Zhu, Metall. Mater. Trans. A 42 (2011) 548–552. [18] P.J. Warren, A. Cerezo, G.D.W. Smith, Mater. Sci. Eng. A 250 (1998) 88–92. [19] K.E. Yoon, D. Isheim, R.D. Noebe, Interface Sci. 9 (2001) 249–255. [20] Q. Ding, Z. Shen, S. Xiang, H. Tian, J. Li, Z. Zhang, JAllC 651 (2015) 255–258. [21] S. Gao, Y. Zhou, C.-F. Li, Z.-Q. Liu, T. Jin, JAllC 671 (2016) 458–464. [22] J.R. Li, Z.G. Zhong, D.Z. Tang, S.Z. Liu, P. Wei, P.Y. Wei, Z.T. Wu, D. Huang, in: T.M. Pollock, R.D. Kissinger, R.R. Bowman, K.A. Green, M. McLean, S.L. Olson, J.J. Schirra (Eds.),Superalloys TMS 2000, pp. 777–783. [23] http://denssolutions.com. [24] B. Ge, Y. Luo, J. Li, J. Zhu, D. Tang, Z. Gui, Philos. Mag. Lett. 92 (2012) 541–546. [25] S.J. Pennycook, L.A. Boatner, Nature 336 (1988) 565–567. [26] S.J. Pennycook, D.E. Jesson, Phys. Rev. Lett. 64 (1990) 938–941. [27] S.J. Pennycook, D.E. Jesson, Ultramicroscopy 37 (1991) 14–38. [28] D. Blavette, E. Cadel, C. Pareige, B. Deconihout, P. Caron, Microsc. Microanal. 13 (2007) 464–483. [29] D. Blavette, E. Cadel, B. Deconihout, Mater. Charact. 44 (2000) 133–157. [30] Y.S.a.D. Lichtman, in: G.L.W., a.R.W. Carlson (Eds.), Vacuum Physics and Technology, MExP, Academic Press 1962, pp. 347–348. [31] Y. Luo, L. Zhang, Y. Wang, B. Ge, W. Guo, J. Zhan, J. Zhang, J. Zhu, Short range ordering of heavy element columns in nickel based superalloys, http://arxiv.org/abs/1601. 017672016. [32] S.-L. Liu, C.-Y. Wang, T. Yu, RSC Adv. 5 (2015) 52473–52480.
Contents lists available at ScienceDirect
Scripta Materialia journal homepage: www.elsevier.com/locate/scriptamat
Study of microstructure of nickel-based superalloys at high temperatures Qinghua Zhang a, Yunjie Chang a, Lin Gu a, Yushi Luo b, Binghui Ge a,⁎ a b
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China National Key Laboratory of Science and Technology on Advanced High Temperature Structural Materials, Beijing Institute of Aeronautical Materials, Beijing 100095, People's Republic of China
a r t i c l e
i n f o
Article history: Received 28 June 2016 Received in revised form 12 August 2016 Accepted 15 August 2016 Available online xxxx Keywords: Superalloys In-situ heating TEM Surface reconstruction Interface
a b s t r a c t Nickel-based superalloys are widely used as high temperature materials for turbine blades in aerospace industry and land-based applications. Their structural characterization, however, is mostly carried out at the room temperature. Here, the microstructure of the superalloys was studied at high temperature, 1000 °C, through aberration-corrected scanning transmission electron microscope imaging. It is the first time that both evaporation and reconstruction of alloying elements were observed with the atomic resolution at the high temperature. © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Superalloys are unique high temperature materials used in gas turbine engines, which display excellent resistance to mechanical and chemical degradation [1]. To improve the performance, numerous researchers and technologists have worked on the microstructure of superalloys to develop the basic understanding of their physical behaviors. For example, rhenium plays a critical role in single-crystal superalloys —its addition to first generation alloys improves creep life by a factor of at least two, with further benefits for fatigue performance, which is the so-called “rhenium effect” [2–17], so that single-crystal superalloys are commonly grouped into generations based on their Re content. To study this effect and to understand the strengthening mechanism of Re, the technique of the atom probe and scanning transmission electron microscopy (STEM) as well as the theoretical calculation were utilized to study the distribution of rhenium, although up to now, some postulations such as Re clusters [3–8,11,13,16,18] and enrichment of Re at the γ/γʹ interfaces [16,18,19] are still under debate. To further understand the structural evolution when superalloys are in the service, in-situ transmission electron microscope (TEM) were carried out recently. Through in-situ environmental TEM, Qingqing etc. [20] found that the ordered γʹ phase gradually transformed to the disordered γ phase during oxidization with the appearance of oxidation product consisted of γ-Al2O3 crystallites, which proves the γ-γʹ phase transformation induced by aluminum oxidation with aluminum depleted in γʹ phases. Besides, through in-situ heating experiments, effects of platinum group metals additions on topologically closed packed (TCP) precipitates were studied by Shuang etc. TCP precipitations are found to be inhibited by adding element Pt, Ir and Ru at both 950 and 1050 °C [21]. In the present work, microstructure of one kind of ⁎ Corresponding author. E-mail address: [email protected] (B. Ge).
http://dx.doi.org/10.1016/j.scriptamat.2016.08.013 1359-6462/© 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
superalloys was studied by in-situ heating STEM at 1000 °C. Under the effect of high temperature and high vacuum, alloying elements were vaporized and reconstructed, which were observed with atomic resolution for the first time. The material tested was a typical second-generation single crystal superalloy DD6 and the nominal composition in wt.% is: 5.6Al, 4.3Cr, 9Co, 2Mo, 7.5Ta, 8W, 2Re and balance Ni. The heat treatments were performed according to the following regime: 1290 °C/1 h + 1300 °C/ 2 h + 1315 °C/4 h/AC + 1120 °C/4 h/AC + 870 °C/32 h/AC. Details of DD6 preparation have been described previously [22]. The lamellae of the superalloy was prepared by a focus ion beam system (FEI Helios 600i), and the samples for in situ TEM heating experiments were created using EM heater chips (DENSsolutions) fitting to the MEMS-based Double Tilt Sample Heating System (DENSsolutions) [23]. In-situ heating experiments were carried out at 1000 °C in a double corrected TEM (JEOL ARM 200). Fig. 1(a) is a typical high-angle annular dark field (HAADF) image of γʹ phase at the room temperature, in which bright dots indicate the heavy elements [24] for the HAADF imaging follows almost Z2 dependency with respect to the atomic number Z [25–27]. At 1000 °C, some vacancies can be observed in the HAADF image with black contrast as shown in Fig. 1(b), indicated by an arrow in the enlarged image shown in Fig. 1(c). For heavy elements in single crystal nickel-based superalloys are usually located at the Al sites in γʹ phase (Ni3Al) [24,28,29], Al sites can be determined according to the image show as Fig. 1(c) with the [001] projected model of Ni3Al inset on the right, in which red columns denote Al sites and white columns denote Ni sites. Thus, the vacancies should also be at the Al sites according to Figs. 1(b) and (c). As reported [30], the vapor pressure of Al, almost 2.5 ∗ 10−2 Pa, at 1000 °C, is much higher than the vacuum of the chamber in the ARM microscope, almost 2 ∗ 10−5 Pa, as well as that of Cr, Co and Ni, so these
56
Q. Zhang et al. / Scripta Materialia 126 (2017) 55–57
Fig. 1. (a) and (b) HAADF images of the γʹ phase at the room temperature and 1000 °C, respectively. (c) Enlarged image with the projected model of Ni3Al inset on the right, and red disks denote Al sites and white disks Ni sites. (d) HAADF image of the γ/γʹ interface indicated by a white dashed line. Vacancies are denoted by white arrows. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
four alloying elements should be volatile under this condition, among which Al is the most one. In addition, Al is basic constitution of the γʹ phase, so most of the vacancies shown in Figs. 1(b) and (c) should be Al. For there is no site preference of Al in the γ phase, along the direction of electron beam fewer vacancies exist in one atomic column in the γ phase comparing with that in γʹ phase, which makes contrast of vacancies in the γ phase as shown in Fig. 1(d) not obvious as shown in the γʹ phase. In the following, cavities caused by evaporation will be shown in both the γ and γʹ phases. Just as the γʹ phase can be transformed into the γ phase after oxidation because Al is taken out [20], the evaporation of Al of the γʹ phase at the high temperature can also lead to the phase transformation, from the γʹ phase into the γ phase. Indicated by white arrows in Fig. 2, disordered phases are formed at the edge of the sample. In reality, the disordered phase is not transformed directly from the γʹ phase, but an
amount of alloying elements move to the surface and a clusters with the disorder structure are reconstructed. Moreover, as mentioned by Luo etc. [31], heavy elements prefer to form an short range of ordering along 〈100〉 and 〈110〉 directions at the room temperature. In our heating experiment, at the edge of samples 〈100〉 and 〈110〉 heavy atom ordering can be observed clearly as shown in Fig. 2. Besides, the exposed crystal facet, under most of the circumstances, is also {100}and {110} plane, indicating the evaporation can be hindered by the 〈100〉 and 〈110〉 heavy atom ordering to some extent, which confirms the stronger bond between refractory elements such as Re, W and Ta with Ni atoms than the bond between Al, Cr and Co with Ni atoms [32]. Similar as in Figs. 2 (a) and (b), clusters can be observed away from the edge of the sample as shown in Figs. 3 (a) and (b). To be precise, clusters may adhere to the upper/lower surface of the sample. These clusters enhance the contrast of the image but the crystal lattice is not distorted, so these clusters may be similar with the one at the edge of the sample, with the face-centered cubic structure. With the help of EDS analysis as shown in Fig. 3(c), the clusters are enriched with Cr. These clusters are not stable, and can be broken with the irradiation of electrons. Moreover, as we know, the γ/γʹ interface plays an import role in the single crystal nickel-based superalloys, say impeding the slip of the dislocations. In the heating experiment, some interesting features about the interface were observed. With the increase of heating time, size of the clusters becomes bigger and bigger, but when the clusters are close to the interface, they seem to be impeded by the interface, then elongated along the interface as shown in Fig. 4(a). Similar things happened during the evaporation. When more atoms are vaporized in high temperature, some cavities are formed with dark contrast shown in Figs. 4(b) and (c), which is confirmed according to the variation of the local sample thickness determined by the electron energy loss spectroscopy. When cavities are close to the interface, it also expands along the interface, and seems to be hindered by the interface. However, it is still an open question to understand the role of interface of the superalloys at the high temperature. In conclusion, in-situ heating experiments were carried out on one type of single crystal nickel-based superalloys at 1000 °C, and structural evolution with atomic resolution was obtained at the high temperature for the first time. Conclusions are obtained as following: 1) Due to the high vacuum samples were vaporized, and with the evaporation of light atoms especially Al, disordered phases were found to be reconstructed from ordered phases. Meanwhile, heavy atom ordering along the 〈100〉 and 〈110〉 direction was observed at the edge of the sample and {100} and {110} plane are the usually exposed facets.
Fig. 2. HAADF images of superalloys at 1000 °C. In (a) and (b) the disordered phases are indicated by white arrows, and the enlarged area denoted by a rectangle in (a) is inset top right.
Q. Zhang et al. / Scripta Materialia 126 (2017) 55–57
57
Fig. 3. (a) HAADF image of clusters at the temperature of 1000 °C and the area indicated by an ellipse are shown in (b). (c) EDS mapping of clusters.
Fig. 4. (a) HAADF image of clusters, (b) HAADF image of cavities with the area indicated by a white ellipse enlarged and shown in (c).
2) Clusters were found to be formed throughout the sample enriched with Cr. 3) γ/γʹ interface plays an import role even at the high temperature, which seems to not only hinder the expansion of Cr-enriched clusters but also the cavities caused by evaporation, but its mechanism is still an open question
Acknowledgement This work was supported by the National Natural Science Foundation of China (Grant number: 11374332, 11474329). Reference [1] R.C. Reed, The Superalloys Fundamentals and Applications, Cambridge University Press, Cambridge, 2006. [2] K. Harris, G.L. Eickson, R.E. Schwer, Conference on High Temperature Alloys for Gas Turbines and Other Application, 1986 709. [3] M.K. Miller, R.C. Reed, in: J.M. Howe, D.E. Laughlin, J.K. Lee, U. Dahmen, W.A. Soffa (Eds.), Proceedings of an International Conference on Solid–Solid Phase Transformations in Inorganic Materials TMS (Minerals, Metals & Materials Society), Phoenix, AZ 2005, p. 537. [4] D. Blavette, P. Caron, T. Khan, Superalloys TMS, Pennsylvania, 1988 305. [5] N. Wanderka, U. Glatzel, Mater. Sci. Eng. A 203 (1995) 69–74. [6] J. Rusing, N. Wanderka, U. Czubayko, V. Naundorf, D. Mukherji, J. Rosler, Scr. Mater. 46 (2002) 235–240. [7] T. Zhu, C.Y. Wang, Y. Gan, Acta Mater. 58 (2010) 2045–2055. [8] A. Mottura, R.T. Wu, M.W. Finnis, R.C. Reed, Acta Mater. 56 (2008) 2669–2675.
[9] A. Mottura, M.K. Miller, in: R.C. Reed, R.C. Reed, K.A. Green, P. Caron, T.P. Gabb, M.G. Fahrmann, E.S. Huron (Eds.),11th International Symposium on Superalloys, Minerals, Metals & Materials Soc, Champion, PA 2008, pp. 891–900. [10] A. Mottura, N. Warnken, M.K. Miller, M.W. Finnis, R.C. Reed, Acta Mater. 58 (2010) 931–942. [11] A. Mottura, M.W. Finnis, R.C. Reed, Acta Mater. 60 (2012) 2866–2872. [12] S.B. Maisel, N. Schindzielorz, A. Mottura, R.C. Reed, S. Müller, Phys. Rev. B 90 (2014) 094110. [13] J.Y. Guédou, A. Mottura, R.C. Reed, J. Choné, MATEC Web Conf. 14 (2014) 01001. [14] M. Huang, Z. Cheng, J. Xiong, J. Li, J. Hu, Z. Liu, J. Zhu, Acta Mater. 76 (2014) 294–305. [15] M. Huang, J. Zhu, Rare Metals 35 (2016) 127–139. [16] B.H. Ge, Y.S. Luo, J.R. Li, J. Zhu, Scr. Mater. 63 (2010) 969–972. [17] B. Ge, Y. Luo, J. Li, J. Zhu, Metall. Mater. Trans. A 42 (2011) 548–552. [18] P.J. Warren, A. Cerezo, G.D.W. Smith, Mater. Sci. Eng. A 250 (1998) 88–92. [19] K.E. Yoon, D. Isheim, R.D. Noebe, Interface Sci. 9 (2001) 249–255. [20] Q. Ding, Z. Shen, S. Xiang, H. Tian, J. Li, Z. Zhang, JAllC 651 (2015) 255–258. [21] S. Gao, Y. Zhou, C.-F. Li, Z.-Q. Liu, T. Jin, JAllC 671 (2016) 458–464. [22] J.R. Li, Z.G. Zhong, D.Z. Tang, S.Z. Liu, P. Wei, P.Y. Wei, Z.T. Wu, D. Huang, in: T.M. Pollock, R.D. Kissinger, R.R. Bowman, K.A. Green, M. McLean, S.L. Olson, J.J. Schirra (Eds.),Superalloys TMS 2000, pp. 777–783. [23] http://denssolutions.com. [24] B. Ge, Y. Luo, J. Li, J. Zhu, D. Tang, Z. Gui, Philos. Mag. Lett. 92 (2012) 541–546. [25] S.J. Pennycook, L.A. Boatner, Nature 336 (1988) 565–567. [26] S.J. Pennycook, D.E. Jesson, Phys. Rev. Lett. 64 (1990) 938–941. [27] S.J. Pennycook, D.E. Jesson, Ultramicroscopy 37 (1991) 14–38. [28] D. Blavette, E. Cadel, C. Pareige, B. Deconihout, P. Caron, Microsc. Microanal. 13 (2007) 464–483. [29] D. Blavette, E. Cadel, B. Deconihout, Mater. Charact. 44 (2000) 133–157. [30] Y.S.a.D. Lichtman, in: G.L.W., a.R.W. Carlson (Eds.), Vacuum Physics and Technology, MExP, Academic Press 1962, pp. 347–348. [31] Y. Luo, L. Zhang, Y. Wang, B. Ge, W. Guo, J. Zhan, J. Zhang, J. Zhu, Short range ordering of heavy element columns in nickel based superalloys, http://arxiv.org/abs/1601. 017672016. [32] S.-L. Liu, C.-Y. Wang, T. Yu, RSC Adv. 5 (2015) 52473–52480.