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Martensite microstructure transformed from ultra-fine-grained Fe–32%Ni alloy austenite
Materials Science and Engineering A 487 (2008) 64–67
Martensite microstructure transformed from ultra-fine-grained Fe–32%Ni alloy austenite Baojun Han ∗ , Zhou Xu Key Laboratory for High Temperature Materials and Tests of Ministry of Education, Shanghai Jiao Tong University, Shanghai 200030, PR China Received 26 April 2007; accepted 26 September 2007
Abstract The martensite microstructure transformed from the ultra-fine-grained Fe–32%Ni alloy austenite produced by severe plastic deformation was examined by the SEM and TEM observations. The Fe–32%Ni alloy was multi-axially forged with cumulative strain up to 9.0 at the temperature of 773 K and a strain rate of 10−2 s−1 . Then the large strain deformed specimen was quenched in liquid nitrogen to cause martensitic transformation. The results indicate that the severe plastic deformed microstructure was characterized by equilaxed grains with non-equilibrium high-angle boundaries, high-level internal stresses and elastic distortions in crystal lattice. The lenticular martensite plates transformed from the severe plastic deformed austenite are not integral but are broken and fragmental. Twins and high-density dislocations act as martensite substructure. The formation of broken and fragmental martensite is resulted from the strengthening of parent phase austenite, the high-level distortions in crystal lattice and the large fraction non-equilibrium curved grain boundaries formed during SPD. © 2007 Elsevier B.V. All rights reserved. Keywords: Martensitic transformation; Severe plastic deformation (SPD); Fe–32%Ni alloy; Transmission electron microscopy (TEM)
1. Introduction Grain refinement by various processing techniques has attracted significant attention in the last decade. Severe plastic deformation (SPD), involving processes such as equal channel angular processing (ECAP) [1,2], accumulative roll bonding (ARB) [3,4] and high-pressure torsion (HPT) [5,6], has been used successfully to produce ultra-fine-grained materials with mean size smaller than 1 m. It has been shown that these ultrafine-grained materials possess excellent mechanical properties, such as high-strength and superplasticity, as well as novel physical properties compared with corresponding coarse-grained materials [7,8]. For example, Akhmadeev et al. [9] studied the elastic and dissipative properties of submicron-grained copper with size of about 0.2 m produced by ECAP. Valiev et al. [10] confirmed the existence of a specific state of atoms in a submicron-grained metal by Mossbauer analysis of iron with mean sizes ranging from 0.12 to 0.65 m. Mulyukov et al. [11] examined the microstructure and magnetic properties of submicron-grained cobalt after large plastic deformation, and
∗
Corresponding author. Tel.: +86 21 54742618; fax: +86 21 62829641. E-mail address: [email protected] (B. Han).
0921-5093/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2007.09.056
established a correlation between the hysteretic properties and microstructure. The transformation from austenite to ferrite is also beneficial to the properties of metallic materials. Therefore, it is expected that the combination of austenite grain refinement by SPD and subsequent phase transformation would greatly improve the properties of steels. However, no investigation to date but Kitahara et al. [12] investigated the martensitic transformation of ultra-fine-grained austenite fabricated by SPD. Multi-axial forging (MF) is one more SPD method to produce ultra-fine-grained metallic materials [13,14]. The aim of the present work is to investigate the martensite microstructure transformed from the ultra-fine-grained austenite produced by MF. 2. Materials and experimental procedures The material used in the present experiment was a Fe–32%Ni alloy, whose chemical composition was shown in Table 1. The Fe–32%Ni alloy has a single metastable austenite phase with FCC structure at room temperature, and its martensite transformation starting (Ms) temperature is lower than room temperature. So there is no phase transformation during deformation at elevated temperatures and the martensitic transformation can be realized by subzero treatment.
B. Han, Z. Xu / Materials Science and Engineering A 487 (2008) 64–67 Table 1 Chemical composition of Fe–32%Ni alloy in wt.% C Si Mn P S Ni Al N O Fe
0.007 0.01 0.04 0.005 0.0006 32.4 0.022 0.00074 0.020 Balance
The samples were machined into cubic in dimensions of 16 mm × 16 mm × 16 mm with initial grain size of about 200 m. Preheated at 773 K for 600 s, the samples were alternately forged at a strain rate of 10−2 s−1 with loading direction changed through 90◦ from pass to pass, i.e. x–y–z–x. . .. The graphite was used as lubricant to make the specimens deformed homogeneously. The strain achieved in each forging was about 0.5, and the curved surfaces were cut down after each stage of forging. After 6 cycles MF (ε = 9.0), a slice about 1 mm in thickness was cut down from the deformed sample, and in order to avoid the machining effects, a layer of about 0.1 mm was removed from the slice by chemical etching. Then the slice was quenched in liquid nitrogen to cause martensitic transformation. Microstructure observations were carried out using JEM6460 SEM and Hitachi H-800 TEM. Samples for the SEM observation was etched in a solution of 10 ml HNO3 and 30 ml HCl3 . Thin foils for the TEM investigations were twin-jet polished in a solution of 5% perchloric acid and 95% ethanol at 243 K. 3. Results and discussions Fig. 1 shows the TEM microstructure and corresponding selected area diffraction (SAD) pattern of multi-axially forged Fe–32%Ni alloy with cumulative strain of 9.0. It can be seen that
Fig. 1. The typical TEM microstructure and corresponding selected area diffraction (SAD) pattern of multi-axially forged Fe–32%Ni alloy (ε = 9.0).
65
the severe plastic deformed microstructure consisted of homogeneously distributed ultra-fine grains with mean size of about 300 nm. There were high-density dislocations accommodated in the non-equilibrium curved grain boundaries. Inspection of the SAD pattern indicates that numerous diffraction spots were arranged along the circles in the SAD pattern, which means that the misorientations between the grains were high ones. The diffraction spots morphology observation shows that some diffraction spots were elongated, which indicates there were high-level internal stresses and elastic distortions in crystal lattice. Therefore, it was apparent that ultra-fine grains with high-angle boundaries, high-level internal stresses and crystal lattice distortions had been produced by MF. Several investigations have been conducted on the inspection of grain refinement mechanism during such a deformation technique [15,16]. It has been shown that the new grains formation is resulted from a strain-induced continuous reaction during deformation, i.e. the subgrains separated by high-density dislocations subboundaries with low misorientations are formed by the original grains subdivision, then followed by the transformation from these subgrains to ultra-fine ones. The martensite morphology from the severe plastic deformed Fe–32%Ni alloy observed by SEM is shown in Fig. 2. Although the martensite generally showed lenticular morphology after subzero treatment, the martensite plates were not integral but are broken in midribs and serrated at martensite plate edges. It could be found that there was large fraction remained austenite in Fig. 2. Fig. 3 shows the typical TEM martensite microstructure transformed from severe plastic deformed Fe–32%Ni alloy. It reveals that martensite variants with different orientations lay in the parent grains, which had been found by conventional SEM observation (Fig. 2). Morphology inspection indicates that the martensite plates were not integral and most of them were broken and fragmental. Fig. 3b indicates that the main substructures of martensite were still twins, whereas high-density dislocation also existed near the martensite plate edges. Intensive observation reveals that some martensite twins became crooked and
Fig. 2. The SEM martensite morphology of large strain deformed Fe–32%Ni alloy (ε = 9.0).
66
B. Han, Z. Xu / Materials Science and Engineering A 487 (2008) 64–67
site crystal elongated to the rolling direction, and the other was the martensite crystal inclined by about 50◦ to the rolling direction. The emergence of the present broken and fragmental martensite plates should be attributed to the parent phase characteristic microstructure produced by SPD. First, the considerable work hardening of the parent phase will increase the phase transformation strain and the shear resistance that is necessary to overcome during martensitic transformation [17,20]. So the grain refinement and high-level crystal lattice distortions in parent phase hinder the martensite nucleation and growth. That is also the reason that there were large amounts of remained austenite after phase transformation (Fig. 2). Secondly, although the martensite nucleation is considered to be heterogeneous and martensite is prior to nucleate at the austenite grain boundaries, the high-density dislocations accommodated in the ultra-fine grain boundaries impose constraints on the martensite growth [21–23]. Therefore, the large amounts of nonequilibrium curved grain boundaries formed during SPD impede the martensite continuous growth. 4. Conclusions The martensite microstructure transformed from the ultrafine-grained Fe–32%Ni alloy austenite produced by large strain MF was investigated by the SEM and the TEM observations. The following conclusions could be obtained:
Fig. 3. The TEM martensite (a) microstructure and (b) substructure transformed from large strain deformed Fe–32%Ni alloy (ε = 9.0).
serrated too. Such kind of martensite morphology also had been found in the hot deformed Fe–32%Ni alloy [17]. The present experiment results indicate that the martensite morphology transformed from ultra-fine-grained austenite processed by MF was characterized by irregular shape, i.e. the martensite plates are not integral but are broken and fragmental. Twins and high-density dislocations act as martensite substructures. Few works to date have been conducted to investigate the martensitic transformation of ultra-fine-grained austenite. Umemoto et al. [18] studied the martensitic transformation of polycrystalline austenite with various mean sizes ranging from 4 to 450 m in Fe–31%Ni and Fe–31%Ni–0.28%C alloy. The results indicated that the austenite grain size had great effect on martensitic transformation behavior, such as Ms temperature, etc. Kitahara et al. [12,19] reported the martensitic transformation of the ultra-fine-grained austenite in Fe-28.5%Ni alloy fabricated by ARB. It was shown in the paper that the martensite transformed from the large strain ARB processed austenite showed two kinds of morphology. One was the marten-
(1) Ultra-fine grains with mean size of about 300 nm were achieved in Fe–32%Ni alloy by large strain MF. The severe plastic deformed microstructure was characterized by equilaxed grains with non-equilibrium high-angle boundaries, high-level internal stresses and distortions in crystal lattices. (2) The martensite plates transformed from the ultra-fine grains are not integral but are broken and fragmental in morphology, which is resulted from the parent phase strengthening by grain refinement, elastic distortions in crystal lattice and the large fraction non-equilibrium curved grain boundaries formed during SPD. Acknowledgement The authors would like to acknowledge the financial support of the National Natural Science Foundation of China under granted number 50471017. References [1] Y. Iwahashi, Z.J. Horita, M. Nemoto, Acta Mater. 46 (1998) 3317. [2] O. Sitdikov, T. Sakai, E. Avtokratova, R. Kaibyshev, Y. Kimura, K. Tsuzaki, Mater. Sci. Eng. A 444 (2007) 18. [3] Y. Saito, N. Tsuji, H. Utsunomiya, T. Sakai, Scr. Mater. 39 (1998) 1221. [4] N. Tsuji, R. Ueji, Y. Minamino, Scr. Mater. 47 (2002) 69. [5] R.Z. Valiev, Y.V. Ivansenko, E.F. Rauch, B. Baudelet, Acta Mater. 44 (1996) 4705. [6] G. Azevedo, R. Barbosa, E.V. Pereloma, D.B. Santos, Mater. Sci. Eng. A 402 (2005) 98. [7] N. Ridley, E. Cullen, F.J. Humphreys, Mater. Sci. Technol. 16 (2000) 117. [8] I. Nikulin, R. Kaibyshe, T. Sakai, F. Musin, Mater. Sci. Forum 447/448 (2004) 453.
B. Han, Z. Xu / Materials Science and Engineering A 487 (2008) 64–67 [9] N.A. Akhmadeev, N.P. Kobelev, R.R. Mulyukov, Y.M. Soifer, R.Z. Valiev, Acta Metall. Mater. 41 (1993) 1041. [10] R.Z. Valiev, R.R. Mulyukov, V.V. Ovchinnikov, V.A. Shabashov, Scr. Metall. Mater. 25 (1991) 2717. [11] K.Y. Mulyukov, S.B. Khaphizov, R.Z. Valiev, Phys. Status Solid A 125 (1991) 609. [12] H. Kitahara, N. Tsuji, Y. Minamino, Mater. Sci. Eng. A 438/440 (2006) 233. [13] A. Belyakov, K. Tsuzaki, H. Miura, T. Sakai, Acta Mater. 51 (2003) 847. [14] S.Y. Mironov, G.A. Salishchev, M.M. Myshlyaev, Mater. Sci. Eng. A 418 (2006) 257.
[15] [16] [17] [18] [19] [20] [21] [22] [23]
67
J. Huang, Z. Xu, Mater. Lett. 60 (2006) 1854. Q. Guo, H.G. Yan, Z.H. Chen, H. Zhang, Mater. Char. 58 (2007) 162. Z. Xu, J. Huang, Mater. Sci. Eng. A 438/440 (2006) 258. M. Umemoto, W.S. Owen, Metall. Trans. 5 (1974) 2041. H. Kitahara, N. Tsuji, Y. Minamino, Mater. Sci. Forum 503/504 (2006) 913. J. Huang, Z. Xu, Mater. Sci. Eng. A 438/440 (2006) 254. S. Kajiwara, Metal. Trans. A 17 (1986) 1693. T. Waitz, V. Kazykhanov, H.P. Karnthaler, Acta Mater. 52 (2004) 137. T. Waitz, A. Antretter, F.D. Fischer, J. Mech. Phys. Solids 55 (2007) 419.
Martensite microstructure transformed from ultra-fine-grained Fe–32%Ni alloy austenite Baojun Han ∗ , Zhou Xu Key Laboratory for High Temperature Materials and Tests of Ministry of Education, Shanghai Jiao Tong University, Shanghai 200030, PR China Received 26 April 2007; accepted 26 September 2007
Abstract The martensite microstructure transformed from the ultra-fine-grained Fe–32%Ni alloy austenite produced by severe plastic deformation was examined by the SEM and TEM observations. The Fe–32%Ni alloy was multi-axially forged with cumulative strain up to 9.0 at the temperature of 773 K and a strain rate of 10−2 s−1 . Then the large strain deformed specimen was quenched in liquid nitrogen to cause martensitic transformation. The results indicate that the severe plastic deformed microstructure was characterized by equilaxed grains with non-equilibrium high-angle boundaries, high-level internal stresses and elastic distortions in crystal lattice. The lenticular martensite plates transformed from the severe plastic deformed austenite are not integral but are broken and fragmental. Twins and high-density dislocations act as martensite substructure. The formation of broken and fragmental martensite is resulted from the strengthening of parent phase austenite, the high-level distortions in crystal lattice and the large fraction non-equilibrium curved grain boundaries formed during SPD. © 2007 Elsevier B.V. All rights reserved. Keywords: Martensitic transformation; Severe plastic deformation (SPD); Fe–32%Ni alloy; Transmission electron microscopy (TEM)
1. Introduction Grain refinement by various processing techniques has attracted significant attention in the last decade. Severe plastic deformation (SPD), involving processes such as equal channel angular processing (ECAP) [1,2], accumulative roll bonding (ARB) [3,4] and high-pressure torsion (HPT) [5,6], has been used successfully to produce ultra-fine-grained materials with mean size smaller than 1 m. It has been shown that these ultrafine-grained materials possess excellent mechanical properties, such as high-strength and superplasticity, as well as novel physical properties compared with corresponding coarse-grained materials [7,8]. For example, Akhmadeev et al. [9] studied the elastic and dissipative properties of submicron-grained copper with size of about 0.2 m produced by ECAP. Valiev et al. [10] confirmed the existence of a specific state of atoms in a submicron-grained metal by Mossbauer analysis of iron with mean sizes ranging from 0.12 to 0.65 m. Mulyukov et al. [11] examined the microstructure and magnetic properties of submicron-grained cobalt after large plastic deformation, and
∗
Corresponding author. Tel.: +86 21 54742618; fax: +86 21 62829641. E-mail address: [email protected] (B. Han).
0921-5093/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2007.09.056
established a correlation between the hysteretic properties and microstructure. The transformation from austenite to ferrite is also beneficial to the properties of metallic materials. Therefore, it is expected that the combination of austenite grain refinement by SPD and subsequent phase transformation would greatly improve the properties of steels. However, no investigation to date but Kitahara et al. [12] investigated the martensitic transformation of ultra-fine-grained austenite fabricated by SPD. Multi-axial forging (MF) is one more SPD method to produce ultra-fine-grained metallic materials [13,14]. The aim of the present work is to investigate the martensite microstructure transformed from the ultra-fine-grained austenite produced by MF. 2. Materials and experimental procedures The material used in the present experiment was a Fe–32%Ni alloy, whose chemical composition was shown in Table 1. The Fe–32%Ni alloy has a single metastable austenite phase with FCC structure at room temperature, and its martensite transformation starting (Ms) temperature is lower than room temperature. So there is no phase transformation during deformation at elevated temperatures and the martensitic transformation can be realized by subzero treatment.
B. Han, Z. Xu / Materials Science and Engineering A 487 (2008) 64–67 Table 1 Chemical composition of Fe–32%Ni alloy in wt.% C Si Mn P S Ni Al N O Fe
0.007 0.01 0.04 0.005 0.0006 32.4 0.022 0.00074 0.020 Balance
The samples were machined into cubic in dimensions of 16 mm × 16 mm × 16 mm with initial grain size of about 200 m. Preheated at 773 K for 600 s, the samples were alternately forged at a strain rate of 10−2 s−1 with loading direction changed through 90◦ from pass to pass, i.e. x–y–z–x. . .. The graphite was used as lubricant to make the specimens deformed homogeneously. The strain achieved in each forging was about 0.5, and the curved surfaces were cut down after each stage of forging. After 6 cycles MF (ε = 9.0), a slice about 1 mm in thickness was cut down from the deformed sample, and in order to avoid the machining effects, a layer of about 0.1 mm was removed from the slice by chemical etching. Then the slice was quenched in liquid nitrogen to cause martensitic transformation. Microstructure observations were carried out using JEM6460 SEM and Hitachi H-800 TEM. Samples for the SEM observation was etched in a solution of 10 ml HNO3 and 30 ml HCl3 . Thin foils for the TEM investigations were twin-jet polished in a solution of 5% perchloric acid and 95% ethanol at 243 K. 3. Results and discussions Fig. 1 shows the TEM microstructure and corresponding selected area diffraction (SAD) pattern of multi-axially forged Fe–32%Ni alloy with cumulative strain of 9.0. It can be seen that
Fig. 1. The typical TEM microstructure and corresponding selected area diffraction (SAD) pattern of multi-axially forged Fe–32%Ni alloy (ε = 9.0).
65
the severe plastic deformed microstructure consisted of homogeneously distributed ultra-fine grains with mean size of about 300 nm. There were high-density dislocations accommodated in the non-equilibrium curved grain boundaries. Inspection of the SAD pattern indicates that numerous diffraction spots were arranged along the circles in the SAD pattern, which means that the misorientations between the grains were high ones. The diffraction spots morphology observation shows that some diffraction spots were elongated, which indicates there were high-level internal stresses and elastic distortions in crystal lattice. Therefore, it was apparent that ultra-fine grains with high-angle boundaries, high-level internal stresses and crystal lattice distortions had been produced by MF. Several investigations have been conducted on the inspection of grain refinement mechanism during such a deformation technique [15,16]. It has been shown that the new grains formation is resulted from a strain-induced continuous reaction during deformation, i.e. the subgrains separated by high-density dislocations subboundaries with low misorientations are formed by the original grains subdivision, then followed by the transformation from these subgrains to ultra-fine ones. The martensite morphology from the severe plastic deformed Fe–32%Ni alloy observed by SEM is shown in Fig. 2. Although the martensite generally showed lenticular morphology after subzero treatment, the martensite plates were not integral but are broken in midribs and serrated at martensite plate edges. It could be found that there was large fraction remained austenite in Fig. 2. Fig. 3 shows the typical TEM martensite microstructure transformed from severe plastic deformed Fe–32%Ni alloy. It reveals that martensite variants with different orientations lay in the parent grains, which had been found by conventional SEM observation (Fig. 2). Morphology inspection indicates that the martensite plates were not integral and most of them were broken and fragmental. Fig. 3b indicates that the main substructures of martensite were still twins, whereas high-density dislocation also existed near the martensite plate edges. Intensive observation reveals that some martensite twins became crooked and
Fig. 2. The SEM martensite morphology of large strain deformed Fe–32%Ni alloy (ε = 9.0).
66
B. Han, Z. Xu / Materials Science and Engineering A 487 (2008) 64–67
site crystal elongated to the rolling direction, and the other was the martensite crystal inclined by about 50◦ to the rolling direction. The emergence of the present broken and fragmental martensite plates should be attributed to the parent phase characteristic microstructure produced by SPD. First, the considerable work hardening of the parent phase will increase the phase transformation strain and the shear resistance that is necessary to overcome during martensitic transformation [17,20]. So the grain refinement and high-level crystal lattice distortions in parent phase hinder the martensite nucleation and growth. That is also the reason that there were large amounts of remained austenite after phase transformation (Fig. 2). Secondly, although the martensite nucleation is considered to be heterogeneous and martensite is prior to nucleate at the austenite grain boundaries, the high-density dislocations accommodated in the ultra-fine grain boundaries impose constraints on the martensite growth [21–23]. Therefore, the large amounts of nonequilibrium curved grain boundaries formed during SPD impede the martensite continuous growth. 4. Conclusions The martensite microstructure transformed from the ultrafine-grained Fe–32%Ni alloy austenite produced by large strain MF was investigated by the SEM and the TEM observations. The following conclusions could be obtained:
Fig. 3. The TEM martensite (a) microstructure and (b) substructure transformed from large strain deformed Fe–32%Ni alloy (ε = 9.0).
serrated too. Such kind of martensite morphology also had been found in the hot deformed Fe–32%Ni alloy [17]. The present experiment results indicate that the martensite morphology transformed from ultra-fine-grained austenite processed by MF was characterized by irregular shape, i.e. the martensite plates are not integral but are broken and fragmental. Twins and high-density dislocations act as martensite substructures. Few works to date have been conducted to investigate the martensitic transformation of ultra-fine-grained austenite. Umemoto et al. [18] studied the martensitic transformation of polycrystalline austenite with various mean sizes ranging from 4 to 450 m in Fe–31%Ni and Fe–31%Ni–0.28%C alloy. The results indicated that the austenite grain size had great effect on martensitic transformation behavior, such as Ms temperature, etc. Kitahara et al. [12,19] reported the martensitic transformation of the ultra-fine-grained austenite in Fe-28.5%Ni alloy fabricated by ARB. It was shown in the paper that the martensite transformed from the large strain ARB processed austenite showed two kinds of morphology. One was the marten-
(1) Ultra-fine grains with mean size of about 300 nm were achieved in Fe–32%Ni alloy by large strain MF. The severe plastic deformed microstructure was characterized by equilaxed grains with non-equilibrium high-angle boundaries, high-level internal stresses and distortions in crystal lattices. (2) The martensite plates transformed from the ultra-fine grains are not integral but are broken and fragmental in morphology, which is resulted from the parent phase strengthening by grain refinement, elastic distortions in crystal lattice and the large fraction non-equilibrium curved grain boundaries formed during SPD. Acknowledgement The authors would like to acknowledge the financial support of the National Natural Science Foundation of China under granted number 50471017. References [1] Y. Iwahashi, Z.J. Horita, M. Nemoto, Acta Mater. 46 (1998) 3317. [2] O. Sitdikov, T. Sakai, E. Avtokratova, R. Kaibyshev, Y. Kimura, K. Tsuzaki, Mater. Sci. Eng. A 444 (2007) 18. [3] Y. Saito, N. Tsuji, H. Utsunomiya, T. Sakai, Scr. Mater. 39 (1998) 1221. [4] N. Tsuji, R. Ueji, Y. Minamino, Scr. Mater. 47 (2002) 69. [5] R.Z. Valiev, Y.V. Ivansenko, E.F. Rauch, B. Baudelet, Acta Mater. 44 (1996) 4705. [6] G. Azevedo, R. Barbosa, E.V. Pereloma, D.B. Santos, Mater. Sci. Eng. A 402 (2005) 98. [7] N. Ridley, E. Cullen, F.J. Humphreys, Mater. Sci. Technol. 16 (2000) 117. [8] I. Nikulin, R. Kaibyshe, T. Sakai, F. Musin, Mater. Sci. Forum 447/448 (2004) 453.
B. Han, Z. Xu / Materials Science and Engineering A 487 (2008) 64–67 [9] N.A. Akhmadeev, N.P. Kobelev, R.R. Mulyukov, Y.M. Soifer, R.Z. Valiev, Acta Metall. Mater. 41 (1993) 1041. [10] R.Z. Valiev, R.R. Mulyukov, V.V. Ovchinnikov, V.A. Shabashov, Scr. Metall. Mater. 25 (1991) 2717. [11] K.Y. Mulyukov, S.B. Khaphizov, R.Z. Valiev, Phys. Status Solid A 125 (1991) 609. [12] H. Kitahara, N. Tsuji, Y. Minamino, Mater. Sci. Eng. A 438/440 (2006) 233. [13] A. Belyakov, K. Tsuzaki, H. Miura, T. Sakai, Acta Mater. 51 (2003) 847. [14] S.Y. Mironov, G.A. Salishchev, M.M. Myshlyaev, Mater. Sci. Eng. A 418 (2006) 257.
[15] [16] [17] [18] [19] [20] [21] [22] [23]
67
J. Huang, Z. Xu, Mater. Lett. 60 (2006) 1854. Q. Guo, H.G. Yan, Z.H. Chen, H. Zhang, Mater. Char. 58 (2007) 162. Z. Xu, J. Huang, Mater. Sci. Eng. A 438/440 (2006) 258. M. Umemoto, W.S. Owen, Metall. Trans. 5 (1974) 2041. H. Kitahara, N. Tsuji, Y. Minamino, Mater. Sci. Forum 503/504 (2006) 913. J. Huang, Z. Xu, Mater. Sci. Eng. A 438/440 (2006) 254. S. Kajiwara, Metal. Trans. A 17 (1986) 1693. T. Waitz, V. Kazykhanov, H.P. Karnthaler, Acta Mater. 52 (2004) 137. T. Waitz, A. Antretter, F.D. Fischer, J. Mech. Phys. Solids 55 (2007) 419.