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Processing of TiPd shape memory alloy reinforced Ti-matrix composites and their mechanical properties
Materials Science and Engineering A316 (2001) 93 – 101 www.elsevier.com/locate/msea
Processing of TiPd shape memory alloy reinforced Ti-matrix composites and their mechanical properties K. Mizuuchi a,*, K. Inoue b, K. Yamauchi c, K. Enami d, M. Itami a, Y. Okanda a a
Osaka Municipal Technical Research Institute, 1 -6 -50, Morinomiya Joto-ku, Osaka 536 -8553, Japan b Materials Science and Engineering, Uni6ersity of Washington, Seattle, WA 98195 -2120, USA c Tokin Corporation, Sendai 982 -8512, Japan d Department of Mechanical and System Engineering, Ryukoku Uni6ersity, Otsu 520 -2123, Japan Received 19 November 1999; received in revised form 16 February 2001
Abstract Ti and Ti-2Cu matrix composites reinforced by TiPd-based shape memory alloys (SMAs) were fabricated by sheath rolling of Ti or Ti-2Cu plates with TiPd fiber. Fibers of three TiPd SMAs were used as reinforcements. The Young’s modulus of TiPd fiber increased with increasing temperature above austenite start temperature, As. Good bonding between the fiber and matrix was obtained by heat treatment at 1123 K for 3.6 ks following sheath rolling at the same temperature. A multi-layered reaction region was formed in the vicinity of the interface between Ti or Ti-2Cu matrix and TiPd-based SMA fiber. Tensile tests were performed at various temperatures for Ti-2Cu matrix composites containing Ti– 22Pd– 27Ni– 1W and Ti/Ti– 25Pd– 24Ni– 1W fiber. It was found that the 0.5% offset stress of these composites increased with increasing temperature. This stress increase is mainly caused by residual compressive stresses generated in association with shape memory effects of the TiPd-based SMAs. Surface observations of fractured specimens showed that interfacial layers were fractured in a ductile fracture mode. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Ti– Pd alloy; Shape memory effect; Smart; Metal– matrix-composite; Sheath-rolling; Martensitic transformation
1. Introduction Smart materials are a class of emerging materials whose concept was introduced in 1989 [1]. According to the concept [2], the smart material should have multiple, unique functions. Because no monolithic materials are classified as smart materials except for shape memory alloys (SMAs), materials are needed to fabricate in innovative design concepts. One way to make a material smart is to fabricate a composite consisting of two different functional materials. They are, for example, a material with structural superiority and another with sensing and/or actuating capabilities. Such composites can be metal- and polymer – matrix composites reinforced with SMA fibers. Here, the SMA fiber behaves as a sensor and actuator in response to a change in * Corresponding author. Tel.: + 81-6-69638155; fax: + 81-669638145. E-mail address: [email protected] (K. Mizuuchi).
external stimuli, such as temperature and stress. Because of some technically unsolved problems, however, metal –matrix composite reinforced with SMA fiber has not yet demonstrated multi-functional properties, although it has shown some improvement of mechanical properties [2–8]. In a previous study [4], the design concept of a SMA-fiber-reinforced smart composite has been shown, which is described here in brief. The SMA fiber is loaded in tension at room temperature to transform its austenite phase to a martensite phase. Then they are heated so as to induce reverse transformation. The SMA fiber in a composite becomes shorter during this reverse transformation, which creates tensile stresses in fiber and compressive stresses in the matrix. Formation of such compressive stresses in the matrix is the main origin of the yield stress enhancement for this kind of smart composite [2–8]. Recently, we have carried out a series of research in an attempt to develop composites containing TiNi
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Table 1 Nominal compositions of Ti–Pd-based shape memory alloy fibers (at.%) Elements
Ti
Pd
Ni
W
SMA fiber Ti–22Pd–27Ni–1W Ti–24Pd–25Ni–1W Ti–25Pd–24Ni–1W
50 50 50
22 24 25
27 25 24
1 1 1
SMA fiber as reinforcement using various processing methods. Then, we have successfully demonstrated enhancement of the yield stress of Al– matrix composites [5– 7]. In previous studies [2,4– 12], pure Al and an Al alloy were used as matrix material, while TiNi fiber was used as reinforcement. In these cases, however, there are rather serious technical problems in terms of applications. That is, TiNi has low transformation temperatures (e.g. Af being 330 K) and the matrix materials have a low melting point (933 K). This indicates potential problems if such composites are to be used at high temperatures. In an attempt to overcome this problem, high-temperature TiPd-based SMA fiber and commercially pure Ti and Ti alloy have been used in the present study as reinforcement and matrix materials, respectively. In this material selection, the Af point of TiPd is between 413 and 473 K, and the melting point of the matrix is about 1700K. Using these materials, Ti- and Ti alloy–matrix composite containing TiPd fiber have been fabricated by sheath rolling. The processing condition of fabricating these composites are examined microscopically, and mechanical properties of thus fabricated composites have been investigated in a temperature range between
298 and 473 K. Microstructural observations and compositional analyses have been carried out by means of scanning electron microscopy (SEM) and EPMA (Electron Probe Micro Analysis) techniques.
2. Experimental procedures Three TiPd-based SMA alloys containing different Pd and Ni content were prepared as reinforcement materials from high purity Ti, Pd, Ni and W metals by arc melting in an argon atmosphere (0.1 MPa) using a copper crucible. The alloy ingot made was in the shape of buttons 20 mm in diameter and high. Using each alloy button, continuous alloy filaments were produced by an in-rotating-water spinning method [13]. Each filament was wiredrawn at 773 K to a fiber shape 400 mm in diameter. Table 1 shows the nominal compositions of the three SMAs produced, which are Ti –22Pd–27Ni–1W, Ti –24Pd–25Ni– 1W and Ti– 25Pd–24Ni–1W (in at.%). As matrix materials, both pure Ti and a Ti alloy containing 2 at.% Cu (hereafter called Ti–2Cu) were prepared by arc melting followed by hot rolling to a plate shape 1 mm thick. Schematic illustration of the fabrication process is shown in Fig. 1. Each SMA fiber was alternatively laminated with matrix plate and inserted in a SUS304 stainless steel pipe of 20 mm inside diameter with 1mm of wall thickness. Then, cold rolling was carried out to flatten the pipe to 5 mm thick so as to form a roughly 3 mm thick composite inside the pipe. Both ends of the pipe were then spot-welded in a vacuum of 0.1 Pa. The pipe was then heated to a temperature between 1123 and 1223 K and sheath-rolled to 4.1 mm thick, leading
Fig. 1. Schematic illustration of sheath-rolling process.
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Fig. 2. Microstructure of Ti-matrix composite containing Ti – 22Pd – 27Ni– 1W made by sheath rolling at various temperatures, followed by reheating to and holding at the same temperatures.
to a roughly 2.1 mm thick composite contained in the 3 mm-thick pipe. After sheath rolling, the pipe was heated up again to sheath rolling temperatures selected between 1123 and 1223 K, keeping it in a furnace for various times in a range between 0.6 and 3.6 ks. Then, the pipe was opened to take out the composite. Using the process described above, four kinds of TiPd fiberreinforced composites were fabricated. They are Ti– matrix composites with Ti22Pd– 27Ni – 1W and Ti24Pd– 25Ni–1W, and Ti – 2Cu – matrix composites with Ti –22Pd–27Ni – 1W and Ti/Ti – 25Pd – 24Ni–1W. The composites fabricated were cut with a SiC wheel cutter to make tensile specimens with a gauge size of 5×2 ×20 mm and then polished mechanically using emery paper and alumina powders. Tensile tests were carried out in air on an Instron testing machine at various temperatures between 298 and 473 K. Young’s modulus of TiPd fibers was measured at a strain rate of 1.0× 10 − 4 s − 1 in a stress range between 0 and 60 MPa. A JOEL JSM 5800LV microscope was used for microstructural observations before and after mechanical testing. 3. Results and discussion
3.1. Optimum processing condition The Ti –matrix composite containing Ti–22Pd–
27Ni–1W fabricated at various processing parameters was observed by SEM, and the microstructures are shown in Fig. 2. As indicated by an arrow in Fig. 2(a), local melting of TiPd fibers had taken place when fabricated at 1223 K. When fabricated at 1173 K, as seen in Fig. 2(b), most part of fiber was consumed to form interfacial layer through a reaction between fiber and matrix. In this case, it seems that reinforcement by fiber is ineffective. When fabrication temperature was 1123 K and the holding time was 1.8 ks, the interfacial reaction between the matrix and fiber appears poor. In some regions, fibers were not reacted with matrix. When fabricated at the same temperature but for a longer holding time (3.6 ks), however, a uniform interfacial reaction layer 30 mm thick is formed, as seen in Fig. 2(d). Among sheath-rolling conditions employed in the present study, this condition seems the best in terms of microstructure.
3.2. EPMA analyses Chemical analyses were carried out using an EPMA method for Ti –matrix composite containing Ti–22Pd– 27Ni–1W fabricated under the condition (1123 K, 3.6 ks) used in Fig. 2(d). The results obtained are shown in Fig. 3. As seen in Fig. 3(a), an SEM micrograph of an area at and near the interface between the matrix and a fiber clearly reveals that there is an interfacial reaction
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Fig. 3. Scanning electron micrograph and X-ray images in the vicinity of interface between Ti matrix and Ti – 22Pd– 27Ni – 1W SMA fiber. Table 2 EPMA results obtained from regions in Fig. 3(a) for Ti-matrix composite reinforced by Ti–22Pd–27Ni–1W SMA fiber (at.%) Region
1
2
3
4
5
6
7
8
9
10
Elements Ti Pd Ni W
47.69 21.64 29.56 1.11
51.61 20.95 26.65 0.79
71.50 7.63 20.62 0.25
83.24 10.93 4.93 0.90
85.23 6.32 8.31 0.14
89.99 4.54 5.31 0.16
90.48 3.41 5.75 0.36
94.28 0.93 4.55 0.24
99.82 0.00 0.08 0.11
45.21 19.72 34.40 0.68
layer. In order to get some insight into compositional alterations at various positions as a function of distance from the SMA fiber, EPMA analyses were performed on 10 regions, indicated by numbers in Fig. 3(a), and the results obtained are tabulated in Table 2. A set of micrographs shown in Fig. 3(b–e) is X-ray images of the alloying elements, Ti, Pd, Ni and W. As seen in Fig. 3 and Table 3, the interfacial layer is found to be composed of a triple-layered structure: Pd, poor; Ni, poor; and Ti, rich layers. Here, the Pd-poor layer was
Table 3 Martensite and reverse transformation temperatures of Ti–Pd-based shape memory alloy fibers (K) SMA fiber
Ms
Mf
As
Af
Ti–22Pd–27Ni–1W Ti–24Pd–25Ni–1W Ti–25Pd–24Ni–1W
405.3 K 411.8 K 450.0 K
371.6 K 362.6 K 425.5 K
403.8 K 387.7 K 440.5 K
421.8 K 429.1 K 465.2 K
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Fig. 4. DSC curve for Ti –22Pd –27Ni– 1W SMA, obtained during cooling and heating at a rate of 0.217 K s − 1.
formed next to the TiPd SMA fiber and Ti-rich layer was formed next to the Ti matrix. From X-ray images of Pd and Ni (Fig. 3(c– d), respectively) and the compositional alternations of Pd and Ni near the interface, the formation of these three interfacial layers can be explained by considering the diffusion of Pd and Ni from the fiber into the matrix. Microstructural observations were also carried out for the other three kinds of composites and the results obtained were almost same as those obtained by EPMA analyses for the Ti/Ti – 22Pd –27Ni–1W composite.
3.3. DSC analyses Differential scanning calorimetric (DSC) experiments were carried out to examine the martensite and reverse transformation temperatures of TiPd SMAs. Specimens 10 mg of fibers with the length of 2– 3 mm were heated up and cooled down at a rate of 0.217 K s − 1 during testing. Fig. 4 shows a DSC curve of Ti –22Pd– 27Ni–1W alloy. All alloys show similar exothermic and endothermic behaviors upon cooling and heating, respectively. That is, only one peak was observed in each processing. From these DSC curves, the transformation temperatures of the SMAs can be obtained and the results are tabulated in Table 3. Table 3 indicates that Ti –22Pd –27Ni– 1W would be slightly better in terms of actuation response, if measured, than Ti–24Pd–
25Ni–1W. It is because the former has a narrower peak than the latter. As shown in Table 3, Af temperature of Ti –25Pd–24Ni–1W was 465 K, which is much higher than those of Ti–22Pd–27Ni–1W and Ti–24Pd– 25Ni–1W. This indicates that Ti–25Pd–24Ni–1W seems more suitable for higher temperature use.
3.4. Young’s modulus Young’s moduli of three TiPd-based SMA fibers used in the present study were obtained from the slant of stress–strain curves loaded to 60 MPa in a temperature range between 393 and 473 K, and the results obtained were plotted as a function of temperature, as shown in Fig. 5. The Young’s modulus of each fiber decreases with increasing temperature at a temperature range between 298 K and As, and becomes minimum at around As. At temperatures \ As, Young’s modulus increases with increasing temperature. It should be noted that in the test temperature range shown in Fig. 5, Young’s modulus of Ti–22Pd–27Ni–1W is higher than that of Ti–24Pd–25Ni–1W. Thus, it is considered that Ti –22Pd–27Ni–1W may be better than Ti–24Pd– 25Ni–1W if used as reinforcement of metal–matrix composites, especially for use in the temperature range mentioned above. In the case of Ti–25Pd–24Ni–1W, the gradient of Young’s modulus at temperatures \As is the highest among the three SMA fibers used. This
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indicates that Ti– 25Pd – 24Ni – 1W may most effectively create compressive stress in matrix when pre-strain is given at temperatures higher than Af.
3.5. Mechanical properties 3.5.1. Tensile properties of matrix materials and Ti-Pd-based SMA fibers Pure Ti and a Ti – 2Cu alloy were deformed in tension at 298 K and temperatures between 373 and 473 K. From stress–strain curves of these matrix materials, 0.5% off-set stress (called yield stress hereafter) was obtained and they were plotted as a function of test temperature, as shown in Fig. 6, which also shows stress –strain curves obtained at 298 K. As seen, these
Fig. 5. Temperature dependence of Young’s moduli of Ti– Pd-based SMAs.
Fig. 6. Tensile stress –strain curves for pure Ti and Ti – 2Cu alloy deformed at 298 K, and the temperature dependence of 0.5%-offset stress obtained by successively loading and unloading at various temperatures after deformation at 298 K.
Fig. 7. Temperature dependence of 0.5%-offset stress for fibers of three Ti – Pd-based shape memory alloys.
matrix materials show the normal, negative temperature dependence of yield stress. Tensile tests were also carried out for fibers of the three Ti–Pd-based SMAs. That is, tensile loading was made first at 298 K, followed by unloading. Immediate after that, temperature was changed to a higher temperature (e.g. 393 K in the case of Ti–22Pd–27Ni–1W), which is slightly lower than As and then tensile loading was made again at the temperature. Similar processing was repeated again but test temperature was changed to a further higher temperature (e.g. 433 K in the case of Ti –22Pd–27Ni–1W). This time, the temperature was set to be slightly higher than Af. In this way, tensile stress–strain curves were obtained for the three composites, Ti–22Pd–27Ni–1W, Ti –24Pd–25Ni–1W and Ti –25Pd–24Ni–1W. From the stress–strain curves thus obtained, 0.5% off-set stress was obtained and it was plotted as a function of temperature. The result is depicted in Fig. 7. As seen in Fig. 7, the yield stress of all the three SMAs initially decreases from room temperature with increasing temperature up to a temperature slightly BAs. Then it decreases drastically at a temperature \Af, except for Ti–25Pd–24Ni–1W. In the case of this SMA, the yield stress increases even at temperatures \Af. At temperatures \Af, all the alloys show partial superelasticity. That is, stress–strain curves of these SMAs shift toward the stress axis upon unloading, resulting in smaller ‘apparent plastic’ strains, compared with those normally obtained for materials when plastic deformation takes place. In other wards, no perfect shape recovery takes place when deformed at temperatures between As and Md (above which plastic deformation occurs). It should be pointed out that, while these three SMAs all shows similar yield strength, Ti –25Pd–24Ni–1W shows the highest strength at higher temperatures.
K. Mizuuchi et al. / Materials Science and Engineering A316 (2001) 93–101
3.5.2. Tensile properties of Ti–Pd-based SMA reinforced composites Four kinds of composites fabricated were deformed in tension at the same temperatures used for fibers of SMAs to investigate the temperature dependence of the yield stress of these composites. It is found that the yield stress is lower at temperatures around Af than at or B As for Ti-matrix composites containing Ti–22Pd– 27Ni– 1W and Ti– 24Pd – 25Ni – 1W fibers. This can be attributed primarily to lower yield stress of pure Ti at higher temperatures in a temperature range between 373 and 473 K (Fig. 6) and/or by lower yield stress of Ti –22Pd–27Ni– 1W and Ti– 24Pd – 25Ni – 1W fibers near Af than near As (Fig. 7). Different mechanical properties can be seen in the case of Ti– matrix composite containing Ti– 25Pd – 24Ni – 1W fiber and Ti– 2Cu –matrix composite containing Ti– 22Pd – 27Ni–1W fiber. The results will be described below.
Fig. 8. Tensile stress –strain curves of Ti-matrix composite containing Ti– 25Pd –24Ni – 1W SMA fiber. Curves obtained at 298, 433 and then at 473 K. Volume fraction of the shape memory alloy fiber is 28.4%.
Fig. 9. Tensile stress –strain curves of Ti –2Cu-matrix composite containing Ti – 22Pd –27Ni –1W SMA fiber. Curves obtained at 298, 393 and then at 433 K. Volume fraction of the shape memory alloy fiber is 29.3%.
99
3.5.2.1. Ti –matrix composite containing Ti– 25Pd – 24Ni – 1W SMA fiber. The Ti –matrix composite containing Ti–25Pd–24Ni–1W was deformed in tension under similar conditions used above and the tensile stress–strain curves were obtained, which are shown in Fig. 8. As seen, the yield stress of the composite is 285 MPa at 433 K and 335 MPa at 473 K. The yield stress is higher by 50 MPa at 473 K than at 433 K. The yield stress of pure Ti decreases monotonically from 373 to 473 K, and thus the stress increase of the composite with temperature is clearly caused by shape memory effects of the SMA fiber embedded in the composite. In addition to this stress increase with temperature, it is also evident that the composite becomes strong compared with the pure Ti at intermediate temperature. That is, the yield stress of the composite is 285 MPa at 473 K, while that of pure Ti is 180 MPa at 433 K. 3.5.2.2. Ti – 2Cu-matrix composite containing Ti– 22Pd – 27Ni – 1W SMA fiber. Tensile stress–strain curves were obtained from the composite when tested in a similar way to that described above, and they are shown in Fig. 9. In this case, strengthening can be expected higher than the above case. It is because the matrix of Ti –2Cu is twice stronger than pure Ti. Similarly to the Ti-matrix composite described above, the yield stress is higher at 433 K (\Af) than 393 K ( B As), which is caused by a similar mechanism related to shape memory effects of the SMA fiber embedded in the matrix. In this case, the yield stress is 500–550 MPa at 393 and 433K, 80% stronger than that for the Ti-matrix composite (Fig. 8). This suggests that the Ti-2Cu matrix composite may be a better candidate than the pure Ti-matrix composite for intermediate temperature use. 3.6. Fracture surface Some specimens of the Ti–2Cu-matrix composite containing Ti–22Pd–27Ni–1W SMA fiber and the Timatrix composite containing Ti–25Pd–24Ni– 1W SMA fiber were fractured in tensile deformation and the fracture surfaces were observed by scanning electron microscopy. SEM micrographs taken from such fracture surfaces are shown in Fig. 10. As seen, no apparent de-bonding has been observed between the matrix and the SMA fiber in both composites after an elongation of several percent. It seems that composites fabricated by sheath rolling have good bonding between matrix and fiber (Fig. 10 (a, c). Such good bonding can also readily be seen by closer looks at higher magnification micrographs, as shown in Fig. 10(b, d). These higher magnification micrographs clearly show typical ductile dimples on fracture surfaces near the interfacial areas of these composites. Because of such good bonding between the matrix and the SMA fiber, stresses gener-
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Fig. 10. SEM micrographs of Ti-matrix and Ti –2Cu– matrix composites, showing ductile, dimple fracture modes at and near interface between the matrix materials and fibers of high-temperature TiPd-based shape memory alloys. (a – b) for Ti – 2Cu-matrix composite containing Ti –22Pd– 27Ni – 1W SMA fiber; and (c –d) for Ti-matrix composite containing Ti – 25Pd – 24Ni – 1W SMA fiber. Note no de-bonding between the matrix materials and the shape memory alloys.
ated between matrix and SMA fiber are expected to effectively transfer to each other, resulting in increase in yield stress from room temperature to 473 K.
4. Summary Pure Ti-matrix and Ti-2 at.% Cu alloy– matrix composites reinforced by fibers of high-temperature TiPdbased shape memory alloys were fabricated by sheath rolling. The fabricated composites were Ti-matrix composites with fibers of Ti – 22Pd – 27Ni – 1W (by at.%), Ti –24Pd–25Ni–1W, and Ti-matrix composite with Ti– 25Pd –24NI–1W, and a Ti – 2Cu-matrix composite with Ti –22Pd–27Ni–1%W SMA fiber. Microstructural observations and chemical analyses revealed that all composites have interfacial regions homogeneously reacted between the matrix and the SMA fibers when heated at 1123 K for 3.6 ks after sheath rolling at 1123 K. The interfacial region consists of a triple layered structure 30 mmm thick: Pd-poor layer (next to SMA fiber), Ni-poor layer, and Ti-rich layer (next to Ti matrix). The 0.5% offset stress of the Ti– 2Cu-matrix composite containing Ti–22Pd – 27Ni – 1W SMA fiber and the Timatrix composite containing Ti– 25Pd – 24NI–1W SMA fiber increased with increasing temperature up to Af. In the case of the Ti– 2Cu-matrix composite, the 0.5% offset stress at 433 K became as high as 530
MPa, 30% higher than that (410 MPa) for the Ti–2Cu alloy. On the other hand, in the case of the pure Ti-matrix composite, the 0.5% offset stress at 433 K became 285 MPa, 50% higher than that (190 MPa) of pure Ti. In both cases, the stress increase is associated with shape memory effects of the high-temperature TiPd-based SMAs. Interfacial regions between the Tior Ti-2Cu-matrix materials and the TiPd-based fibers in these composites fractured in a ductile, dimple fracture mode, suggesting good bonding between the matrix and TiPd fibers.
References [1] J. Shimamura, Proceedings of the International Workshop on Intelligent Materials, Tsukuba Science City, Japan, March 1989, Technomic Publishing Co., Inc., Pennsylvania, USA, 1989, p. 1. [2] M. Taya, Y. Furuya, Y. Yamada, R. Watanabe, S. Shibata, T. Mori, in: V.K. Varadon (Ed.), Proc. Smart Materials, SPIE, Bellingham, WA, USA, 1993, p. 373. [3] A. Shimamoto, Y. Furuya, M. Taya, in: J. Tani (Ed.), Proc. Intl. Symp. Microsystems, Intelligent Materials and Robots, JIM, Sendai, Japan, 1995, p. 463. [4] Y. Furuya, A. Sasaki, M. Taya, Mater. Trans. JIM 34 (1993) 224. [5] K. Mizuuchi, K. Hamada, M. Taya, K. Inoue, in: K. Inoue, S.I.Y. Shen, M. Taya (Eds.), US – Japan Workshop on Smart Materials and Structures, The Minerals, Metals and Materials Society, Warrendale, PA, USA, 1997, p. 75.
K. Mizuuchi et al. / Materials Science and Engineering A316 (2001) 93–101 [6] K. Hamada, J.H. Lee, K. Mizuuchi, M. Taya, K. Inoue, Mater. Smart Syst. 459 (1997) 143. [7] J.H. Lee, K. Hamada, K. Mizuuchi, M. Taya, K. Inoue, Mater. Smart Syst. 459 (1997) 419. [8] K. Mizuuchi, M. Sugioka, M. Itami, Kagaku to Kogyo 71 (1997) 362. [9] A. Venkatesh, J. Hilborn, J.E. Bidaux, R. Gotthardt, in: B. Culshaw, P.T. Gardiner, T. McDonach (Eds.), Proceedings of the First European Conference on Smart Structure and Materials, IOP, Bristol, UK, 1992, p. 185.
.
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[10] J.G. Boyd, D.C. Lagoudas, J. Intell. Mater. Syst. Struct. 5 (1994) 333. [11] W.D. Armstrong, J. Intell. Mater. Syst. Struct. 7 (1996) 448. [12] M. Taya, A. Shimamoto, Y. Furuya, in: A. Poursatrip, K. Street (Eds.), Proceedings of the Tenth International Conference on Composite Materials, V, Woodhead, Cambridge, UK, 1996, p. 275. [13] I. Ohnaka, T. Fukusako, T. Ohmichi, J. Japan Inst. Metals 45 (1981) 751.
Processing of TiPd shape memory alloy reinforced Ti-matrix composites and their mechanical properties K. Mizuuchi a,*, K. Inoue b, K. Yamauchi c, K. Enami d, M. Itami a, Y. Okanda a a
Osaka Municipal Technical Research Institute, 1 -6 -50, Morinomiya Joto-ku, Osaka 536 -8553, Japan b Materials Science and Engineering, Uni6ersity of Washington, Seattle, WA 98195 -2120, USA c Tokin Corporation, Sendai 982 -8512, Japan d Department of Mechanical and System Engineering, Ryukoku Uni6ersity, Otsu 520 -2123, Japan Received 19 November 1999; received in revised form 16 February 2001
Abstract Ti and Ti-2Cu matrix composites reinforced by TiPd-based shape memory alloys (SMAs) were fabricated by sheath rolling of Ti or Ti-2Cu plates with TiPd fiber. Fibers of three TiPd SMAs were used as reinforcements. The Young’s modulus of TiPd fiber increased with increasing temperature above austenite start temperature, As. Good bonding between the fiber and matrix was obtained by heat treatment at 1123 K for 3.6 ks following sheath rolling at the same temperature. A multi-layered reaction region was formed in the vicinity of the interface between Ti or Ti-2Cu matrix and TiPd-based SMA fiber. Tensile tests were performed at various temperatures for Ti-2Cu matrix composites containing Ti– 22Pd– 27Ni– 1W and Ti/Ti– 25Pd– 24Ni– 1W fiber. It was found that the 0.5% offset stress of these composites increased with increasing temperature. This stress increase is mainly caused by residual compressive stresses generated in association with shape memory effects of the TiPd-based SMAs. Surface observations of fractured specimens showed that interfacial layers were fractured in a ductile fracture mode. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Ti– Pd alloy; Shape memory effect; Smart; Metal– matrix-composite; Sheath-rolling; Martensitic transformation
1. Introduction Smart materials are a class of emerging materials whose concept was introduced in 1989 [1]. According to the concept [2], the smart material should have multiple, unique functions. Because no monolithic materials are classified as smart materials except for shape memory alloys (SMAs), materials are needed to fabricate in innovative design concepts. One way to make a material smart is to fabricate a composite consisting of two different functional materials. They are, for example, a material with structural superiority and another with sensing and/or actuating capabilities. Such composites can be metal- and polymer – matrix composites reinforced with SMA fibers. Here, the SMA fiber behaves as a sensor and actuator in response to a change in * Corresponding author. Tel.: + 81-6-69638155; fax: + 81-669638145. E-mail address: [email protected] (K. Mizuuchi).
external stimuli, such as temperature and stress. Because of some technically unsolved problems, however, metal –matrix composite reinforced with SMA fiber has not yet demonstrated multi-functional properties, although it has shown some improvement of mechanical properties [2–8]. In a previous study [4], the design concept of a SMA-fiber-reinforced smart composite has been shown, which is described here in brief. The SMA fiber is loaded in tension at room temperature to transform its austenite phase to a martensite phase. Then they are heated so as to induce reverse transformation. The SMA fiber in a composite becomes shorter during this reverse transformation, which creates tensile stresses in fiber and compressive stresses in the matrix. Formation of such compressive stresses in the matrix is the main origin of the yield stress enhancement for this kind of smart composite [2–8]. Recently, we have carried out a series of research in an attempt to develop composites containing TiNi
0921-5093/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 5 0 9 3 ( 0 1 ) 0 1 2 3 7 - 0
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Table 1 Nominal compositions of Ti–Pd-based shape memory alloy fibers (at.%) Elements
Ti
Pd
Ni
W
SMA fiber Ti–22Pd–27Ni–1W Ti–24Pd–25Ni–1W Ti–25Pd–24Ni–1W
50 50 50
22 24 25
27 25 24
1 1 1
SMA fiber as reinforcement using various processing methods. Then, we have successfully demonstrated enhancement of the yield stress of Al– matrix composites [5– 7]. In previous studies [2,4– 12], pure Al and an Al alloy were used as matrix material, while TiNi fiber was used as reinforcement. In these cases, however, there are rather serious technical problems in terms of applications. That is, TiNi has low transformation temperatures (e.g. Af being 330 K) and the matrix materials have a low melting point (933 K). This indicates potential problems if such composites are to be used at high temperatures. In an attempt to overcome this problem, high-temperature TiPd-based SMA fiber and commercially pure Ti and Ti alloy have been used in the present study as reinforcement and matrix materials, respectively. In this material selection, the Af point of TiPd is between 413 and 473 K, and the melting point of the matrix is about 1700K. Using these materials, Ti- and Ti alloy–matrix composite containing TiPd fiber have been fabricated by sheath rolling. The processing condition of fabricating these composites are examined microscopically, and mechanical properties of thus fabricated composites have been investigated in a temperature range between
298 and 473 K. Microstructural observations and compositional analyses have been carried out by means of scanning electron microscopy (SEM) and EPMA (Electron Probe Micro Analysis) techniques.
2. Experimental procedures Three TiPd-based SMA alloys containing different Pd and Ni content were prepared as reinforcement materials from high purity Ti, Pd, Ni and W metals by arc melting in an argon atmosphere (0.1 MPa) using a copper crucible. The alloy ingot made was in the shape of buttons 20 mm in diameter and high. Using each alloy button, continuous alloy filaments were produced by an in-rotating-water spinning method [13]. Each filament was wiredrawn at 773 K to a fiber shape 400 mm in diameter. Table 1 shows the nominal compositions of the three SMAs produced, which are Ti –22Pd–27Ni–1W, Ti –24Pd–25Ni– 1W and Ti– 25Pd–24Ni–1W (in at.%). As matrix materials, both pure Ti and a Ti alloy containing 2 at.% Cu (hereafter called Ti–2Cu) were prepared by arc melting followed by hot rolling to a plate shape 1 mm thick. Schematic illustration of the fabrication process is shown in Fig. 1. Each SMA fiber was alternatively laminated with matrix plate and inserted in a SUS304 stainless steel pipe of 20 mm inside diameter with 1mm of wall thickness. Then, cold rolling was carried out to flatten the pipe to 5 mm thick so as to form a roughly 3 mm thick composite inside the pipe. Both ends of the pipe were then spot-welded in a vacuum of 0.1 Pa. The pipe was then heated to a temperature between 1123 and 1223 K and sheath-rolled to 4.1 mm thick, leading
Fig. 1. Schematic illustration of sheath-rolling process.
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Fig. 2. Microstructure of Ti-matrix composite containing Ti – 22Pd – 27Ni– 1W made by sheath rolling at various temperatures, followed by reheating to and holding at the same temperatures.
to a roughly 2.1 mm thick composite contained in the 3 mm-thick pipe. After sheath rolling, the pipe was heated up again to sheath rolling temperatures selected between 1123 and 1223 K, keeping it in a furnace for various times in a range between 0.6 and 3.6 ks. Then, the pipe was opened to take out the composite. Using the process described above, four kinds of TiPd fiberreinforced composites were fabricated. They are Ti– matrix composites with Ti22Pd– 27Ni – 1W and Ti24Pd– 25Ni–1W, and Ti – 2Cu – matrix composites with Ti –22Pd–27Ni – 1W and Ti/Ti – 25Pd – 24Ni–1W. The composites fabricated were cut with a SiC wheel cutter to make tensile specimens with a gauge size of 5×2 ×20 mm and then polished mechanically using emery paper and alumina powders. Tensile tests were carried out in air on an Instron testing machine at various temperatures between 298 and 473 K. Young’s modulus of TiPd fibers was measured at a strain rate of 1.0× 10 − 4 s − 1 in a stress range between 0 and 60 MPa. A JOEL JSM 5800LV microscope was used for microstructural observations before and after mechanical testing. 3. Results and discussion
3.1. Optimum processing condition The Ti –matrix composite containing Ti–22Pd–
27Ni–1W fabricated at various processing parameters was observed by SEM, and the microstructures are shown in Fig. 2. As indicated by an arrow in Fig. 2(a), local melting of TiPd fibers had taken place when fabricated at 1223 K. When fabricated at 1173 K, as seen in Fig. 2(b), most part of fiber was consumed to form interfacial layer through a reaction between fiber and matrix. In this case, it seems that reinforcement by fiber is ineffective. When fabrication temperature was 1123 K and the holding time was 1.8 ks, the interfacial reaction between the matrix and fiber appears poor. In some regions, fibers were not reacted with matrix. When fabricated at the same temperature but for a longer holding time (3.6 ks), however, a uniform interfacial reaction layer 30 mm thick is formed, as seen in Fig. 2(d). Among sheath-rolling conditions employed in the present study, this condition seems the best in terms of microstructure.
3.2. EPMA analyses Chemical analyses were carried out using an EPMA method for Ti –matrix composite containing Ti–22Pd– 27Ni–1W fabricated under the condition (1123 K, 3.6 ks) used in Fig. 2(d). The results obtained are shown in Fig. 3. As seen in Fig. 3(a), an SEM micrograph of an area at and near the interface between the matrix and a fiber clearly reveals that there is an interfacial reaction
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Fig. 3. Scanning electron micrograph and X-ray images in the vicinity of interface between Ti matrix and Ti – 22Pd– 27Ni – 1W SMA fiber. Table 2 EPMA results obtained from regions in Fig. 3(a) for Ti-matrix composite reinforced by Ti–22Pd–27Ni–1W SMA fiber (at.%) Region
1
2
3
4
5
6
7
8
9
10
Elements Ti Pd Ni W
47.69 21.64 29.56 1.11
51.61 20.95 26.65 0.79
71.50 7.63 20.62 0.25
83.24 10.93 4.93 0.90
85.23 6.32 8.31 0.14
89.99 4.54 5.31 0.16
90.48 3.41 5.75 0.36
94.28 0.93 4.55 0.24
99.82 0.00 0.08 0.11
45.21 19.72 34.40 0.68
layer. In order to get some insight into compositional alterations at various positions as a function of distance from the SMA fiber, EPMA analyses were performed on 10 regions, indicated by numbers in Fig. 3(a), and the results obtained are tabulated in Table 2. A set of micrographs shown in Fig. 3(b–e) is X-ray images of the alloying elements, Ti, Pd, Ni and W. As seen in Fig. 3 and Table 3, the interfacial layer is found to be composed of a triple-layered structure: Pd, poor; Ni, poor; and Ti, rich layers. Here, the Pd-poor layer was
Table 3 Martensite and reverse transformation temperatures of Ti–Pd-based shape memory alloy fibers (K) SMA fiber
Ms
Mf
As
Af
Ti–22Pd–27Ni–1W Ti–24Pd–25Ni–1W Ti–25Pd–24Ni–1W
405.3 K 411.8 K 450.0 K
371.6 K 362.6 K 425.5 K
403.8 K 387.7 K 440.5 K
421.8 K 429.1 K 465.2 K
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Fig. 4. DSC curve for Ti –22Pd –27Ni– 1W SMA, obtained during cooling and heating at a rate of 0.217 K s − 1.
formed next to the TiPd SMA fiber and Ti-rich layer was formed next to the Ti matrix. From X-ray images of Pd and Ni (Fig. 3(c– d), respectively) and the compositional alternations of Pd and Ni near the interface, the formation of these three interfacial layers can be explained by considering the diffusion of Pd and Ni from the fiber into the matrix. Microstructural observations were also carried out for the other three kinds of composites and the results obtained were almost same as those obtained by EPMA analyses for the Ti/Ti – 22Pd –27Ni–1W composite.
3.3. DSC analyses Differential scanning calorimetric (DSC) experiments were carried out to examine the martensite and reverse transformation temperatures of TiPd SMAs. Specimens 10 mg of fibers with the length of 2– 3 mm were heated up and cooled down at a rate of 0.217 K s − 1 during testing. Fig. 4 shows a DSC curve of Ti –22Pd– 27Ni–1W alloy. All alloys show similar exothermic and endothermic behaviors upon cooling and heating, respectively. That is, only one peak was observed in each processing. From these DSC curves, the transformation temperatures of the SMAs can be obtained and the results are tabulated in Table 3. Table 3 indicates that Ti –22Pd –27Ni– 1W would be slightly better in terms of actuation response, if measured, than Ti–24Pd–
25Ni–1W. It is because the former has a narrower peak than the latter. As shown in Table 3, Af temperature of Ti –25Pd–24Ni–1W was 465 K, which is much higher than those of Ti–22Pd–27Ni–1W and Ti–24Pd– 25Ni–1W. This indicates that Ti–25Pd–24Ni–1W seems more suitable for higher temperature use.
3.4. Young’s modulus Young’s moduli of three TiPd-based SMA fibers used in the present study were obtained from the slant of stress–strain curves loaded to 60 MPa in a temperature range between 393 and 473 K, and the results obtained were plotted as a function of temperature, as shown in Fig. 5. The Young’s modulus of each fiber decreases with increasing temperature at a temperature range between 298 K and As, and becomes minimum at around As. At temperatures \ As, Young’s modulus increases with increasing temperature. It should be noted that in the test temperature range shown in Fig. 5, Young’s modulus of Ti–22Pd–27Ni–1W is higher than that of Ti–24Pd–25Ni–1W. Thus, it is considered that Ti –22Pd–27Ni–1W may be better than Ti–24Pd– 25Ni–1W if used as reinforcement of metal–matrix composites, especially for use in the temperature range mentioned above. In the case of Ti–25Pd–24Ni–1W, the gradient of Young’s modulus at temperatures \As is the highest among the three SMA fibers used. This
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indicates that Ti– 25Pd – 24Ni – 1W may most effectively create compressive stress in matrix when pre-strain is given at temperatures higher than Af.
3.5. Mechanical properties 3.5.1. Tensile properties of matrix materials and Ti-Pd-based SMA fibers Pure Ti and a Ti – 2Cu alloy were deformed in tension at 298 K and temperatures between 373 and 473 K. From stress–strain curves of these matrix materials, 0.5% off-set stress (called yield stress hereafter) was obtained and they were plotted as a function of test temperature, as shown in Fig. 6, which also shows stress –strain curves obtained at 298 K. As seen, these
Fig. 5. Temperature dependence of Young’s moduli of Ti– Pd-based SMAs.
Fig. 6. Tensile stress –strain curves for pure Ti and Ti – 2Cu alloy deformed at 298 K, and the temperature dependence of 0.5%-offset stress obtained by successively loading and unloading at various temperatures after deformation at 298 K.
Fig. 7. Temperature dependence of 0.5%-offset stress for fibers of three Ti – Pd-based shape memory alloys.
matrix materials show the normal, negative temperature dependence of yield stress. Tensile tests were also carried out for fibers of the three Ti–Pd-based SMAs. That is, tensile loading was made first at 298 K, followed by unloading. Immediate after that, temperature was changed to a higher temperature (e.g. 393 K in the case of Ti–22Pd–27Ni–1W), which is slightly lower than As and then tensile loading was made again at the temperature. Similar processing was repeated again but test temperature was changed to a further higher temperature (e.g. 433 K in the case of Ti –22Pd–27Ni–1W). This time, the temperature was set to be slightly higher than Af. In this way, tensile stress–strain curves were obtained for the three composites, Ti–22Pd–27Ni–1W, Ti –24Pd–25Ni–1W and Ti –25Pd–24Ni–1W. From the stress–strain curves thus obtained, 0.5% off-set stress was obtained and it was plotted as a function of temperature. The result is depicted in Fig. 7. As seen in Fig. 7, the yield stress of all the three SMAs initially decreases from room temperature with increasing temperature up to a temperature slightly BAs. Then it decreases drastically at a temperature \Af, except for Ti–25Pd–24Ni–1W. In the case of this SMA, the yield stress increases even at temperatures \Af. At temperatures \Af, all the alloys show partial superelasticity. That is, stress–strain curves of these SMAs shift toward the stress axis upon unloading, resulting in smaller ‘apparent plastic’ strains, compared with those normally obtained for materials when plastic deformation takes place. In other wards, no perfect shape recovery takes place when deformed at temperatures between As and Md (above which plastic deformation occurs). It should be pointed out that, while these three SMAs all shows similar yield strength, Ti –25Pd–24Ni–1W shows the highest strength at higher temperatures.
K. Mizuuchi et al. / Materials Science and Engineering A316 (2001) 93–101
3.5.2. Tensile properties of Ti–Pd-based SMA reinforced composites Four kinds of composites fabricated were deformed in tension at the same temperatures used for fibers of SMAs to investigate the temperature dependence of the yield stress of these composites. It is found that the yield stress is lower at temperatures around Af than at or B As for Ti-matrix composites containing Ti–22Pd– 27Ni– 1W and Ti– 24Pd – 25Ni – 1W fibers. This can be attributed primarily to lower yield stress of pure Ti at higher temperatures in a temperature range between 373 and 473 K (Fig. 6) and/or by lower yield stress of Ti –22Pd–27Ni– 1W and Ti– 24Pd – 25Ni – 1W fibers near Af than near As (Fig. 7). Different mechanical properties can be seen in the case of Ti– matrix composite containing Ti– 25Pd – 24Ni – 1W fiber and Ti– 2Cu –matrix composite containing Ti– 22Pd – 27Ni–1W fiber. The results will be described below.
Fig. 8. Tensile stress –strain curves of Ti-matrix composite containing Ti– 25Pd –24Ni – 1W SMA fiber. Curves obtained at 298, 433 and then at 473 K. Volume fraction of the shape memory alloy fiber is 28.4%.
Fig. 9. Tensile stress –strain curves of Ti –2Cu-matrix composite containing Ti – 22Pd –27Ni –1W SMA fiber. Curves obtained at 298, 393 and then at 433 K. Volume fraction of the shape memory alloy fiber is 29.3%.
99
3.5.2.1. Ti –matrix composite containing Ti– 25Pd – 24Ni – 1W SMA fiber. The Ti –matrix composite containing Ti–25Pd–24Ni–1W was deformed in tension under similar conditions used above and the tensile stress–strain curves were obtained, which are shown in Fig. 8. As seen, the yield stress of the composite is 285 MPa at 433 K and 335 MPa at 473 K. The yield stress is higher by 50 MPa at 473 K than at 433 K. The yield stress of pure Ti decreases monotonically from 373 to 473 K, and thus the stress increase of the composite with temperature is clearly caused by shape memory effects of the SMA fiber embedded in the composite. In addition to this stress increase with temperature, it is also evident that the composite becomes strong compared with the pure Ti at intermediate temperature. That is, the yield stress of the composite is 285 MPa at 473 K, while that of pure Ti is 180 MPa at 433 K. 3.5.2.2. Ti – 2Cu-matrix composite containing Ti– 22Pd – 27Ni – 1W SMA fiber. Tensile stress–strain curves were obtained from the composite when tested in a similar way to that described above, and they are shown in Fig. 9. In this case, strengthening can be expected higher than the above case. It is because the matrix of Ti –2Cu is twice stronger than pure Ti. Similarly to the Ti-matrix composite described above, the yield stress is higher at 433 K (\Af) than 393 K ( B As), which is caused by a similar mechanism related to shape memory effects of the SMA fiber embedded in the matrix. In this case, the yield stress is 500–550 MPa at 393 and 433K, 80% stronger than that for the Ti-matrix composite (Fig. 8). This suggests that the Ti-2Cu matrix composite may be a better candidate than the pure Ti-matrix composite for intermediate temperature use. 3.6. Fracture surface Some specimens of the Ti–2Cu-matrix composite containing Ti–22Pd–27Ni–1W SMA fiber and the Timatrix composite containing Ti–25Pd–24Ni– 1W SMA fiber were fractured in tensile deformation and the fracture surfaces were observed by scanning electron microscopy. SEM micrographs taken from such fracture surfaces are shown in Fig. 10. As seen, no apparent de-bonding has been observed between the matrix and the SMA fiber in both composites after an elongation of several percent. It seems that composites fabricated by sheath rolling have good bonding between matrix and fiber (Fig. 10 (a, c). Such good bonding can also readily be seen by closer looks at higher magnification micrographs, as shown in Fig. 10(b, d). These higher magnification micrographs clearly show typical ductile dimples on fracture surfaces near the interfacial areas of these composites. Because of such good bonding between the matrix and the SMA fiber, stresses gener-
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Fig. 10. SEM micrographs of Ti-matrix and Ti –2Cu– matrix composites, showing ductile, dimple fracture modes at and near interface between the matrix materials and fibers of high-temperature TiPd-based shape memory alloys. (a – b) for Ti – 2Cu-matrix composite containing Ti –22Pd– 27Ni – 1W SMA fiber; and (c –d) for Ti-matrix composite containing Ti – 25Pd – 24Ni – 1W SMA fiber. Note no de-bonding between the matrix materials and the shape memory alloys.
ated between matrix and SMA fiber are expected to effectively transfer to each other, resulting in increase in yield stress from room temperature to 473 K.
4. Summary Pure Ti-matrix and Ti-2 at.% Cu alloy– matrix composites reinforced by fibers of high-temperature TiPdbased shape memory alloys were fabricated by sheath rolling. The fabricated composites were Ti-matrix composites with fibers of Ti – 22Pd – 27Ni – 1W (by at.%), Ti –24Pd–25Ni–1W, and Ti-matrix composite with Ti– 25Pd –24NI–1W, and a Ti – 2Cu-matrix composite with Ti –22Pd–27Ni–1%W SMA fiber. Microstructural observations and chemical analyses revealed that all composites have interfacial regions homogeneously reacted between the matrix and the SMA fibers when heated at 1123 K for 3.6 ks after sheath rolling at 1123 K. The interfacial region consists of a triple layered structure 30 mmm thick: Pd-poor layer (next to SMA fiber), Ni-poor layer, and Ti-rich layer (next to Ti matrix). The 0.5% offset stress of the Ti– 2Cu-matrix composite containing Ti–22Pd – 27Ni – 1W SMA fiber and the Timatrix composite containing Ti– 25Pd – 24NI–1W SMA fiber increased with increasing temperature up to Af. In the case of the Ti– 2Cu-matrix composite, the 0.5% offset stress at 433 K became as high as 530
MPa, 30% higher than that (410 MPa) for the Ti–2Cu alloy. On the other hand, in the case of the pure Ti-matrix composite, the 0.5% offset stress at 433 K became 285 MPa, 50% higher than that (190 MPa) of pure Ti. In both cases, the stress increase is associated with shape memory effects of the high-temperature TiPd-based SMAs. Interfacial regions between the Tior Ti-2Cu-matrix materials and the TiPd-based fibers in these composites fractured in a ductile, dimple fracture mode, suggesting good bonding between the matrix and TiPd fibers.
References [1] J. Shimamura, Proceedings of the International Workshop on Intelligent Materials, Tsukuba Science City, Japan, March 1989, Technomic Publishing Co., Inc., Pennsylvania, USA, 1989, p. 1. [2] M. Taya, Y. Furuya, Y. Yamada, R. Watanabe, S. Shibata, T. Mori, in: V.K. Varadon (Ed.), Proc. Smart Materials, SPIE, Bellingham, WA, USA, 1993, p. 373. [3] A. Shimamoto, Y. Furuya, M. Taya, in: J. Tani (Ed.), Proc. Intl. Symp. Microsystems, Intelligent Materials and Robots, JIM, Sendai, Japan, 1995, p. 463. [4] Y. Furuya, A. Sasaki, M. Taya, Mater. Trans. JIM 34 (1993) 224. [5] K. Mizuuchi, K. Hamada, M. Taya, K. Inoue, in: K. Inoue, S.I.Y. Shen, M. Taya (Eds.), US – Japan Workshop on Smart Materials and Structures, The Minerals, Metals and Materials Society, Warrendale, PA, USA, 1997, p. 75.
K. Mizuuchi et al. / Materials Science and Engineering A316 (2001) 93–101 [6] K. Hamada, J.H. Lee, K. Mizuuchi, M. Taya, K. Inoue, Mater. Smart Syst. 459 (1997) 143. [7] J.H. Lee, K. Hamada, K. Mizuuchi, M. Taya, K. Inoue, Mater. Smart Syst. 459 (1997) 419. [8] K. Mizuuchi, M. Sugioka, M. Itami, Kagaku to Kogyo 71 (1997) 362. [9] A. Venkatesh, J. Hilborn, J.E. Bidaux, R. Gotthardt, in: B. Culshaw, P.T. Gardiner, T. McDonach (Eds.), Proceedings of the First European Conference on Smart Structure and Materials, IOP, Bristol, UK, 1992, p. 185.
.
101
[10] J.G. Boyd, D.C. Lagoudas, J. Intell. Mater. Syst. Struct. 5 (1994) 333. [11] W.D. Armstrong, J. Intell. Mater. Syst. Struct. 7 (1996) 448. [12] M. Taya, A. Shimamoto, Y. Furuya, in: A. Poursatrip, K. Street (Eds.), Proceedings of the Tenth International Conference on Composite Materials, V, Woodhead, Cambridge, UK, 1996, p. 275. [13] I. Ohnaka, T. Fukusako, T. Ohmichi, J. Japan Inst. Metals 45 (1981) 751.