- Email: [email protected]
In situ TEM observation of heavy-ion-irradiation-induced amorphization in a TiNiCu shape memory alloy
Materials Science and Engineering A363 (2003) 352–355
Short communication
In situ TEM observation of heavy-ion-irradiation-induced amorphization in a TiNiCu shape memory alloy X.T. Zu a,b,∗ , S. Zhu c , X. Xiang a , L.P. You c , Y. Huo d , L.M. Wang c a c
Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, PR China b International Center for Material Physics, Chinese Academy of Sciences, Shengyang 110015, PR China Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI 48109-2014, USA d Department of Mechanics, Fudan University, Shanghai 200433, PR China Received 17 May 2003; received in revised form 18 July 2003
Abstract TiNiCu shape memory alloy samples were irradiated by 400 keV Xe+ ions at room temperature. The in situ TEM observation showed that samples were amorphized at ∼0.4 dpa and the recrystallization after amorphization started when annealing at 550 K and basically finished at 1023 K. © 2003 Elsevier B.V. All rights reserved. Keywords: TiNiCu shape memory alloy; Heavy-ion-irradiation; Amorphization; Recrystallization; In situ TEM
1. Introduction TiNi-based shape memory alloys (SMAs) have potential applications for fission and fusion engineering and space technology because of their unique shape memory effect, superelasticity and high stress relaxation resistance [1,2]. The radiation effect of SMAs is interesting and perplexing. Some researches have been concentrated on the two interesting behaviors. One is the shift of the martensitic and its inverse phase transformation temperatures. SMAs under neutron and electron irradiations were found to cause a strong decrease (from 280 to 210 K and from 302 to 256 K, respectively) of the martensitic transformation start temperature (Ms) [3,4]. The decrease is believed to be due to the chemical disordering of the crystal structure [3–6]. The electron irradiation to about 1.7 × 1021 e/m2 (10−5 dpa), leading to a higher equilibrium temperature (from 327 to 333 K) and martensitic stabilization, had little effect on martensitic transformation temperature in a ternary TiNiCu shape memory alloy [7].
∗ Corresponding author. Tel.: +86-28-83201939; fax: +86-28-83201939. E-mail address: [email protected] (X.T. Zu).
0921-5093/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0921-5093(03)00635-X
The other behavior is the irradiation-induced amorphization, very important problem for the use of the shape memory effect and the mechanical behavior. Since these unique properties depend on the phase transformation from a cubic parent phase B2 to a monoclinic martensitic phase, the irradiation-induced amorphization would destroy the transformation. On the other hand, from the viewpoint of the irradiation damage process in materials, this is an interesting phenomenon. There are some reports on the amorphization of TiNi SMAs induced by neutron, swift ions, proton and electron irradiation [3,8–13]. Comparing with TiNi-base SMAs, the ternary TiNiCu shape memory alloy has a much smaller hysteresis in transformation temperatures and pseudoelasticity and a much lower flow stress for martensitic reorientation. It is also much less sensitive to aging effects [2]. Therefore, TiNiCu is a better candidate for many applications such as electrical connectors, sensors and actuators. However, as far as the authors’ knowledge is concerned, the irradiation-induced amorphization of TiNiCu SMA has not been reported. In the present work, we have investigated the radiation response of TiNiCu SMAs under a 400 keV Xe+ irradiation using in situ TEM observation. Furthermore, The recovery process was observed by post-irradiation annealing experiment from room temperature to 1023 K.
X.T. Zu et al. / Materials Science and Engineering A363 (2003) 352–355
353
2. Experimental
Heating
Heat Flow
Ti–43 at.% Ni–7 at.% Cu SMA samples with a thickness of 0.30 mm, provided by the Northwest Institute of Non-Ferrous Metal of China, were annealed at 773 K for 30 min in an evacuated silica tube and then cooled in the air. The transformation temperatures were measured using Seiko Exstar6000 Differential Scanning Calorimeter (DSC) between 200 and 400 K at a rate of 10 K/min. Disks for TEM samples were cut using a slurry drill core-cutter to minimize mechanical damage. These samples were wet polished using grit SiC paper. A solution of (10% sulfuric acid + 90% methanol) was used for jet electrochemical polishing. A single jet polisher was used at the solution temperature of 283 K and polishing voltage 45 V. The 400 keV Xe+ ion irradiation and in situ TEM observation were performed using the IVEM-Tandem Facility at the Argonne National Laboratory at the room temperature, and the ion flux was 1.25×1011 ions/(cm2 s). The measured ion fluence was converted to a displacement dose (1.25 × 10−3 dpa/s) based on the damage profile calculated by SRIM-2000 using a displacement energy (Ed ) of 25 eV. Xe ion range in the TiNiCu sample was about 68 nm calculated by SRIM-2000 [14]. Xe ions stopped in the foils probably. The concentration of Xe
Mf
290
300
Af
As
Cooling
Ms
310
320
330
340
350
Temperature (K) Fig. 1. The DSC results of TiNiCu specimens showing the martensitic transformation characteristic temperatures (Ms , Mf and As , Af ) before irradiation.
ions is about 20 ppm at 0.5 dpa calculated by SRIM-2000 [14]. Xe ions have little effect because they are inert matter. The observed electron beam was not switched off so that the structural damage upon irradiation could be monitored by the selected area electron diffraction patterns (SAED) under in situ TEM observations. The critical amorphization dose was determined as the ion dose at which complete
Fig. 2. A sequence of bright field TEM images of the TiNiCu SMA samples and SAD pattern before and after irradiation by 400 keV Xe+ (A). The amorphous ring was present while the superlattice reflections were still fairly strong (B). The TiNiCu alloy sample becomes amorphous to a dose of 0.4 dpa (C).
354
X.T. Zu et al. / Materials Science and Engineering A363 (2003) 352–355
amorphization occurs, as manifested by the disappearance of all diffraction maxima in the SAED patterns. The recovery process was observed by post-irradiation annealing experiment from room temperature to 1023 K using in situ TEM observations.
3. Results and discussion The phase transformation characteristic of the sample before irradiation was shown in Fig. 1, measured by DSC. The transformation temperatures, Ms , Mf and As , Af (Ms , Mf and As , Af are corresponding to the martensitic transformation start, finish temperature, and austenite transformation start, finish temperature, respectively) are 318, 305, and 322, 336 K. The irradiation temperature was maintained at about 298 K, well below the martensitic transformation finish temperature Mf (305 K). Thus, the samples have been kept in the martensitic phase state during the irradiation. This is also certified to the results from TEM micrograph (Fig. 2(A)). A sequence of microstructural evolution of the TiNiCu SMA samples and the corresponding selected area electron diffraction (SAD) pattern before and after irradiation was shown in Fig. 2. With increasing fluence, the contrast and bend contour indicating crystalline structure of the irradiated area gradually disappeared, the correspond-
ing electron diffraction maxima were gradually replaced by a diffuse diffraction halo as evident in Fig. 2(C)). Irradiation-induced chemical disordering was concomitant with irradiation-induced amorphization. The ion fluence was converted to an equivalent displacement dose using SRIM-2000 calculations (full cascade calculation) with displacement energy Ed of 25 eV. The critical amorphization dose at room temperature was 0.4 dpa in Fig. 2(C)). The amorphized specimen by Xe+ irradiation was heated between 298 and 1023 K and held at these temperatures for 10 min. A sequence of the bright field images and SAD patterns documented the recrystallization process in the amorphized TiNiCu alloy, as shown in Fig. 3. The recrystallization started when annealing at 550 K for 10 min and the diffraction spots appeared on the amorphous rings (Fig. 3(A)). The polycrystalline nanocrystals grew gradually with increasing temperature. The polycrystalline rings in SAD patterns (Fig. 3(B)) began to form at 820 K and recrystallization basically finished at 1023 K in Fig. 3(C). The polycrystalline rings in Fig. 3(C) are indexed to TiNiCu SMAs (the martensitic phase). Some spots are not in the rings (shown in Fig. 3(C)). These spots should be the diffraction spots of TiNiCu martensitic plates grown up with increasing annealing temperature by comparing the bright image of Fig. 3(B) and (C). The microstructure after the recrystallization is different from that of the unirradiated sample (see Figs. 2(A) and 3(C)), because they experienced
Fig. 3. A sequence of the bright field images and SAD patterns documenting the recrystallization process in the amorphized TiNiCu alloy. The recrystallization started when annealing at 550 K for 10 min and the diffraction spots appeared around the amorphous rings (A). The polycrystalline rings (B) started to form at 820 K and the recrystallization basically finished at 1023 K (C). The polycrystalline rings in C are indexed to TiNiCu SMAs.
X.T. Zu et al. / Materials Science and Engineering A363 (2003) 352–355
the different phase transformation: the former transformed from the amorphous phase and the latter came from the diffusionless martensitic transformation. The amorphous phase was found to nucleate preferentially along dislocation lines and grain boundaries, producing broad amorphous cylinders that grew into the matrix and eventually coalesced and a significant amount of chemical disordering is required before the crystallineamorphous transition starts under electron irradiation [11]. The present results found that amorphization transition induced by Xe+ ion irradiation occurred homogeneously throughout the crystalline matrix, which was similar to proton-irradiation-induced crystalline to amorphous transition in a TiNi SMAs [9]. In the case of heavy-ion (including proton) irradiation, displacement cascades are produced during irradiation. The amorphous transition of TiNiCu SMAs attributed to chemical disordering produced by displacement cascades.
4. Conclusions 400 keV Xe ion-irradiation-induced amorphization in a TiNiCu shape memory alloy has been observed by means of the in situ transmission electron microscopy. The in situ TEM observation showed that TiNiCu samples were amorphized after a peak damage level of ∼0.4 dpa. The recovery process was observed after the amorphization from room temperature to 1023 K at a rate of 10 K/min by in situ TEM. The recrystallization started when annealing at 550 K and basically finished at 1023 K. The microstructure after recrystallization is different from that of the unirradiated sample.
355
Acknowledgements This study was supported financially by the National Natural Science Foundation of China (10175042), by the Sichuan Young Scientists Foundation (03ZQ026-059) and by the Project-sponsored by SRF for ROCS, SEM. The authors thank also the staff of IVEM-Tandem Facility at Argonne National Laboratory for assistance during ion irradiation experiments.
References [1] T. Hoshiya, H. Sekino, Y. Matsui, F. Sakurai, K. Enami, J. Nucl. Mater. 233–237 (1996) 599. [2] K. Otsuka, C.M. Wayman (Eds.), Shape Memory Materials, Cambridge University Press, Cambridge, 1998, pp. 49–87. [3] T. Hoshiya, S. Den, H. Ito, S. Takamura, Y. Ichihashi, J. Jpn. Inst. Met. 55 (1991) 1054. [4] X.T. Zu, L.B. Lin, Z.G. Wang, S. Zhu, L.P. You, L.M. Wang, Y. Huo, J. Alloys Compounds 351 (1–2) (2003) 87–90. [5] R.F. Konopleva, I.V. Nazarkin, V.L. Solovei, V.A. Chekanov, S.P. Belyaev, A.E. Volkov, A.I. Razov, Phys. Solid State 40 (1998) 1550. [6] S.F. Dubinin, S.G. Teploukho, V.D. Parkhomenko, Fiz. Met. Metalloved. 82 (1996) 297. [7] X.T. Zu, L.M. Wang, Y. Huo, L.B. Lin, Z.G. Wang, App. Phys. Lett. 80 (1) (2002) 31. [8] A. Barbu, A. Dunlop, A.H. Duparc, G. Jaskierowicz, N. Lorenzelli, Nucl. Instr. Meth. B 145 (1998) 354. [9] J. Cheng, A.J. Ardell, Nucl. Instr. Meth. B 44 (1990) 336. [10] Y. Matsukawa, S. Ohnuki, J. Nucl. Mater. 239 (1996) 261. [11] H. Mori, H. Fujita, Jpn. J. Appl. Phys. 21 (1982) L494. [12] S. Watanbe, T. Koike, T. Suda, S. Ohnuki, H. Takahashi, N.Q. Lam, Phil. Mag. Lett. 81 (2001) 789. [13] G. Wei, R. Sandstrom, S. Miyazaki, J. Mater. Sci. 33 (1998) 3743. [14] J.F. Zirgler, The Stopping and Range of Ions in Matter IBM-Research, York Town, NY, 2000.
Short communication
In situ TEM observation of heavy-ion-irradiation-induced amorphization in a TiNiCu shape memory alloy X.T. Zu a,b,∗ , S. Zhu c , X. Xiang a , L.P. You c , Y. Huo d , L.M. Wang c a c
Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, PR China b International Center for Material Physics, Chinese Academy of Sciences, Shengyang 110015, PR China Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI 48109-2014, USA d Department of Mechanics, Fudan University, Shanghai 200433, PR China Received 17 May 2003; received in revised form 18 July 2003
Abstract TiNiCu shape memory alloy samples were irradiated by 400 keV Xe+ ions at room temperature. The in situ TEM observation showed that samples were amorphized at ∼0.4 dpa and the recrystallization after amorphization started when annealing at 550 K and basically finished at 1023 K. © 2003 Elsevier B.V. All rights reserved. Keywords: TiNiCu shape memory alloy; Heavy-ion-irradiation; Amorphization; Recrystallization; In situ TEM
1. Introduction TiNi-based shape memory alloys (SMAs) have potential applications for fission and fusion engineering and space technology because of their unique shape memory effect, superelasticity and high stress relaxation resistance [1,2]. The radiation effect of SMAs is interesting and perplexing. Some researches have been concentrated on the two interesting behaviors. One is the shift of the martensitic and its inverse phase transformation temperatures. SMAs under neutron and electron irradiations were found to cause a strong decrease (from 280 to 210 K and from 302 to 256 K, respectively) of the martensitic transformation start temperature (Ms) [3,4]. The decrease is believed to be due to the chemical disordering of the crystal structure [3–6]. The electron irradiation to about 1.7 × 1021 e/m2 (10−5 dpa), leading to a higher equilibrium temperature (from 327 to 333 K) and martensitic stabilization, had little effect on martensitic transformation temperature in a ternary TiNiCu shape memory alloy [7].
∗ Corresponding author. Tel.: +86-28-83201939; fax: +86-28-83201939. E-mail address: [email protected] (X.T. Zu).
0921-5093/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0921-5093(03)00635-X
The other behavior is the irradiation-induced amorphization, very important problem for the use of the shape memory effect and the mechanical behavior. Since these unique properties depend on the phase transformation from a cubic parent phase B2 to a monoclinic martensitic phase, the irradiation-induced amorphization would destroy the transformation. On the other hand, from the viewpoint of the irradiation damage process in materials, this is an interesting phenomenon. There are some reports on the amorphization of TiNi SMAs induced by neutron, swift ions, proton and electron irradiation [3,8–13]. Comparing with TiNi-base SMAs, the ternary TiNiCu shape memory alloy has a much smaller hysteresis in transformation temperatures and pseudoelasticity and a much lower flow stress for martensitic reorientation. It is also much less sensitive to aging effects [2]. Therefore, TiNiCu is a better candidate for many applications such as electrical connectors, sensors and actuators. However, as far as the authors’ knowledge is concerned, the irradiation-induced amorphization of TiNiCu SMA has not been reported. In the present work, we have investigated the radiation response of TiNiCu SMAs under a 400 keV Xe+ irradiation using in situ TEM observation. Furthermore, The recovery process was observed by post-irradiation annealing experiment from room temperature to 1023 K.
X.T. Zu et al. / Materials Science and Engineering A363 (2003) 352–355
353
2. Experimental
Heating
Heat Flow
Ti–43 at.% Ni–7 at.% Cu SMA samples with a thickness of 0.30 mm, provided by the Northwest Institute of Non-Ferrous Metal of China, were annealed at 773 K for 30 min in an evacuated silica tube and then cooled in the air. The transformation temperatures were measured using Seiko Exstar6000 Differential Scanning Calorimeter (DSC) between 200 and 400 K at a rate of 10 K/min. Disks for TEM samples were cut using a slurry drill core-cutter to minimize mechanical damage. These samples were wet polished using grit SiC paper. A solution of (10% sulfuric acid + 90% methanol) was used for jet electrochemical polishing. A single jet polisher was used at the solution temperature of 283 K and polishing voltage 45 V. The 400 keV Xe+ ion irradiation and in situ TEM observation were performed using the IVEM-Tandem Facility at the Argonne National Laboratory at the room temperature, and the ion flux was 1.25×1011 ions/(cm2 s). The measured ion fluence was converted to a displacement dose (1.25 × 10−3 dpa/s) based on the damage profile calculated by SRIM-2000 using a displacement energy (Ed ) of 25 eV. Xe ion range in the TiNiCu sample was about 68 nm calculated by SRIM-2000 [14]. Xe ions stopped in the foils probably. The concentration of Xe
Mf
290
300
Af
As
Cooling
Ms
310
320
330
340
350
Temperature (K) Fig. 1. The DSC results of TiNiCu specimens showing the martensitic transformation characteristic temperatures (Ms , Mf and As , Af ) before irradiation.
ions is about 20 ppm at 0.5 dpa calculated by SRIM-2000 [14]. Xe ions have little effect because they are inert matter. The observed electron beam was not switched off so that the structural damage upon irradiation could be monitored by the selected area electron diffraction patterns (SAED) under in situ TEM observations. The critical amorphization dose was determined as the ion dose at which complete
Fig. 2. A sequence of bright field TEM images of the TiNiCu SMA samples and SAD pattern before and after irradiation by 400 keV Xe+ (A). The amorphous ring was present while the superlattice reflections were still fairly strong (B). The TiNiCu alloy sample becomes amorphous to a dose of 0.4 dpa (C).
354
X.T. Zu et al. / Materials Science and Engineering A363 (2003) 352–355
amorphization occurs, as manifested by the disappearance of all diffraction maxima in the SAED patterns. The recovery process was observed by post-irradiation annealing experiment from room temperature to 1023 K using in situ TEM observations.
3. Results and discussion The phase transformation characteristic of the sample before irradiation was shown in Fig. 1, measured by DSC. The transformation temperatures, Ms , Mf and As , Af (Ms , Mf and As , Af are corresponding to the martensitic transformation start, finish temperature, and austenite transformation start, finish temperature, respectively) are 318, 305, and 322, 336 K. The irradiation temperature was maintained at about 298 K, well below the martensitic transformation finish temperature Mf (305 K). Thus, the samples have been kept in the martensitic phase state during the irradiation. This is also certified to the results from TEM micrograph (Fig. 2(A)). A sequence of microstructural evolution of the TiNiCu SMA samples and the corresponding selected area electron diffraction (SAD) pattern before and after irradiation was shown in Fig. 2. With increasing fluence, the contrast and bend contour indicating crystalline structure of the irradiated area gradually disappeared, the correspond-
ing electron diffraction maxima were gradually replaced by a diffuse diffraction halo as evident in Fig. 2(C)). Irradiation-induced chemical disordering was concomitant with irradiation-induced amorphization. The ion fluence was converted to an equivalent displacement dose using SRIM-2000 calculations (full cascade calculation) with displacement energy Ed of 25 eV. The critical amorphization dose at room temperature was 0.4 dpa in Fig. 2(C)). The amorphized specimen by Xe+ irradiation was heated between 298 and 1023 K and held at these temperatures for 10 min. A sequence of the bright field images and SAD patterns documented the recrystallization process in the amorphized TiNiCu alloy, as shown in Fig. 3. The recrystallization started when annealing at 550 K for 10 min and the diffraction spots appeared on the amorphous rings (Fig. 3(A)). The polycrystalline nanocrystals grew gradually with increasing temperature. The polycrystalline rings in SAD patterns (Fig. 3(B)) began to form at 820 K and recrystallization basically finished at 1023 K in Fig. 3(C). The polycrystalline rings in Fig. 3(C) are indexed to TiNiCu SMAs (the martensitic phase). Some spots are not in the rings (shown in Fig. 3(C)). These spots should be the diffraction spots of TiNiCu martensitic plates grown up with increasing annealing temperature by comparing the bright image of Fig. 3(B) and (C). The microstructure after the recrystallization is different from that of the unirradiated sample (see Figs. 2(A) and 3(C)), because they experienced
Fig. 3. A sequence of the bright field images and SAD patterns documenting the recrystallization process in the amorphized TiNiCu alloy. The recrystallization started when annealing at 550 K for 10 min and the diffraction spots appeared around the amorphous rings (A). The polycrystalline rings (B) started to form at 820 K and the recrystallization basically finished at 1023 K (C). The polycrystalline rings in C are indexed to TiNiCu SMAs.
X.T. Zu et al. / Materials Science and Engineering A363 (2003) 352–355
the different phase transformation: the former transformed from the amorphous phase and the latter came from the diffusionless martensitic transformation. The amorphous phase was found to nucleate preferentially along dislocation lines and grain boundaries, producing broad amorphous cylinders that grew into the matrix and eventually coalesced and a significant amount of chemical disordering is required before the crystallineamorphous transition starts under electron irradiation [11]. The present results found that amorphization transition induced by Xe+ ion irradiation occurred homogeneously throughout the crystalline matrix, which was similar to proton-irradiation-induced crystalline to amorphous transition in a TiNi SMAs [9]. In the case of heavy-ion (including proton) irradiation, displacement cascades are produced during irradiation. The amorphous transition of TiNiCu SMAs attributed to chemical disordering produced by displacement cascades.
4. Conclusions 400 keV Xe ion-irradiation-induced amorphization in a TiNiCu shape memory alloy has been observed by means of the in situ transmission electron microscopy. The in situ TEM observation showed that TiNiCu samples were amorphized after a peak damage level of ∼0.4 dpa. The recovery process was observed after the amorphization from room temperature to 1023 K at a rate of 10 K/min by in situ TEM. The recrystallization started when annealing at 550 K and basically finished at 1023 K. The microstructure after recrystallization is different from that of the unirradiated sample.
355
Acknowledgements This study was supported financially by the National Natural Science Foundation of China (10175042), by the Sichuan Young Scientists Foundation (03ZQ026-059) and by the Project-sponsored by SRF for ROCS, SEM. The authors thank also the staff of IVEM-Tandem Facility at Argonne National Laboratory for assistance during ion irradiation experiments.
References [1] T. Hoshiya, H. Sekino, Y. Matsui, F. Sakurai, K. Enami, J. Nucl. Mater. 233–237 (1996) 599. [2] K. Otsuka, C.M. Wayman (Eds.), Shape Memory Materials, Cambridge University Press, Cambridge, 1998, pp. 49–87. [3] T. Hoshiya, S. Den, H. Ito, S. Takamura, Y. Ichihashi, J. Jpn. Inst. Met. 55 (1991) 1054. [4] X.T. Zu, L.B. Lin, Z.G. Wang, S. Zhu, L.P. You, L.M. Wang, Y. Huo, J. Alloys Compounds 351 (1–2) (2003) 87–90. [5] R.F. Konopleva, I.V. Nazarkin, V.L. Solovei, V.A. Chekanov, S.P. Belyaev, A.E. Volkov, A.I. Razov, Phys. Solid State 40 (1998) 1550. [6] S.F. Dubinin, S.G. Teploukho, V.D. Parkhomenko, Fiz. Met. Metalloved. 82 (1996) 297. [7] X.T. Zu, L.M. Wang, Y. Huo, L.B. Lin, Z.G. Wang, App. Phys. Lett. 80 (1) (2002) 31. [8] A. Barbu, A. Dunlop, A.H. Duparc, G. Jaskierowicz, N. Lorenzelli, Nucl. Instr. Meth. B 145 (1998) 354. [9] J. Cheng, A.J. Ardell, Nucl. Instr. Meth. B 44 (1990) 336. [10] Y. Matsukawa, S. Ohnuki, J. Nucl. Mater. 239 (1996) 261. [11] H. Mori, H. Fujita, Jpn. J. Appl. Phys. 21 (1982) L494. [12] S. Watanbe, T. Koike, T. Suda, S. Ohnuki, H. Takahashi, N.Q. Lam, Phil. Mag. Lett. 81 (2001) 789. [13] G. Wei, R. Sandstrom, S. Miyazaki, J. Mater. Sci. 33 (1998) 3743. [14] J.F. Zirgler, The Stopping and Range of Ions in Matter IBM-Research, York Town, NY, 2000.