Damping characteristics of as-spun and annealed Ti51Ni49 ribbons measured by dynamic mechanical analysis

Journal of Alloys and Compounds 577S (2013) S175–S178

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Damping characteristics of as-spun and annealed Ti51 Ni49 ribbons measured by dynamic mechanical analysis S.H. Chang a , S.K. Wu b,∗ a b

Department of Chemical and Materials Engineering, National I-Lan University, I-Lan 260, Taiwan Department of Materials Science and Engineering, National Taiwan University, Taipei 106, Taiwan

a r t i c l e

i n f o

Article history: Received 21 September 2011 Received in revised form 31 October 2011 Accepted 29 December 2011 Available online 5 January 2012 Keywords: Shape memory alloys Melt-spun ribbon Internal friction Dynamic mechanical analysis

a b s t r a c t This study investigates the annealing effect on the damping properties of melt-spun Ti51 Ni49 ribbon by dynamic mechanical analysis (DMA). Both as-spun and 200 ◦ C annealed Ti51 Ni49 ribbons with abundant nano-sized Guinier–Preston (GP) zones exhibit conspicuous martensitic transformation internal friction (IF) peaks in DMA tests. The damping capacity of as-spun Ti51 Ni49 ribbon measured by a thin film tension clamp is better than that of the bulk Ti51 Ni49 specimen measured by a single cantilever clamp. The Ti51 Ni49 ribbons annealed at ≥400 ◦ C with disc-like Ti2 Ni precipitates possess lower damping capacity than as-spun Ti51 Ni49 ribbon and Ti51 Ni49 ribbon annealed at 200 ◦ C with plate-like GP zones. © 2012 Elsevier B.V. All rights reserved.

1. Introduction TiNi-based alloys are known as the most important shape memory alloys (SMAs) because they exhibit thermalelastic martensitic transformation and show unique property of shape memory effect/superelasticity and have quite good damping capacity [1]. Many studies revealed that TiNi-based SMAs possess better mechanical damping than many other metals or alloys because their abundant moveable parent/martensite interfaces and twin boundaries in transformed martensite can dissipate energy more easily during damping [2–4]. TiNi-based SMAs typically exhibit an obvious internal friction (IF) peak during martensitic transformation when they are examined by a traditional inverted torsion pendulum [2–8]. Damping capacity of the martensitic transformation IF peak is closely related to the experimental parameters such as heating/cooling rate (T˙ ), frequency () and applied strain amplitude (ε). Recently, TiNi-based sputtered thin films and melt-spun ribbons have attracted much attention because of their potential applications on microactuators [9–15]. However, the damping characteristics of SMAs thin films and ribbons cannot be determined by inverted torsion pendulum since the thickness of the films and ribbons (typically below 20 ␮m) is much less than that of normal bulk SMAs (typically above 1 mm).

∗ Corresponding author. Tel.: +886 2 2363 7846; fax: +886 2 2363 4562. E-mail address: [email protected] (S.K. Wu). 0925-8388/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2011.12.165

Besides of inverted torsion pendulum, dynamic mechanical analysis (DMA) is another instrument suitable for investigating the damping properties of SMAs [16–19]. Except of the most widely used single/dual cantilever, DMA can also configure other different types of clamps, such as fiber tension clamp or thin film tension clamp. Therefore, damping capacity of the specimens in the shapes of thin film, fiber, or ribbon can eventually be determined appropriately. Chang et al. [20] reported that amorphous Ti50 Ni25 Cu25 melt-spun ribbons only exhibit an extremely low damping capacity before crystallization, but these ribbons’ damping capacity increases significantly when they are annealed under appropriate conditions to acquire abundant crystallized grains. Chang et al. also investigated the damping properties of as-spun Ti51 Ni49 ribbon which is essentially crystalline with abundant plate-like nano-size Guinier–Preston (GP) zones [21], and found that Ti50 Ni49 ribbon exhibits a higher martensitic transformation IF peak than crystallized Ti50 Ni25 Cu25 ribbon [22]. Nevertheless, the size of the GP zones in Ti50 Ni49 ribbon gradually increases with increasing the annealing temperature and finally, at annealing temperature ≥400 ◦ C, the GP zones convert to larger disc-like Ti2 Ni precipitates [23]. It has been reported that Ti51 Ni49 ribbon with GP zones behaves a larger recoverable strain and a lower permanent strain than that with Ti2 Ni precipitates [22,23]. However, how these GP zones and Ti2 Ni precipitates influence the damping properties of Ti51 Ni49 ribbon has never been investigated. The main purpose of this study is therefore to focus on the annealing effect on the damping properties of melt-spun Ti51 Ni49 ribbon. The damping characteristics of Ti51 Ni49 ribbon and bulk Ti51 Ni49 SMA determined

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0.25

a

b 0.20

R B2 47.9 C

0.8

Ti51Ni49 ribbon

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B19' R 23.1 C

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cooling

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35000

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Temperature (ºC)

45000

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Ti51Ni49 bulk

0.05

20000 150

Temperature (ºC) Fig. 1. (a) DSC cooling curves for as-spun Ti51 Ni49 ribbon measured at T˙ = 10 ◦ C/min. (b) DMA tan ı and storage modulus cooling curves for as-spun Ti51 Ni49 ribbon measured at T˙ = 3 ◦ C/min,  = 1 Hz and ε = 8.5 × 10−4 .

by DMA tests configured with thin film tension clamp and single cantilever clamp, respectively, are also compared in this study. 2. Experimental procedures Ti51 Ni49 melt-spun ribbons used in this study were prepared by the Institute for Materials Research of Tohoku University, Japan, using a single-roller melt-spinning technique. A Ti51 Ni49 ingot was first prepared by conventional vacuum arc melting. Then the ingot was remelted in a quartz crucible using an induction furnace filled with argon. The melted Ti–Ni alloy was subsequently ejected with pressurized argon gas onto a water-cooled copper roller with a surface velocity of 42 m/s. The final dimensions of the ribbons were 14 ␮m in thickness and 1.05 mm in width. Some of the as-spun Ti51 Ni49 ribbons were placed in Ar-purged quartz tubes and further annealed at 200 ◦ C, 400 ◦ C and 600 ◦ C for 1 h. Martensitic transformation temperatures and transformation enthalpies of Ti51 Ni49 ribbons were determined using TA Q10 differential scanning calorimeter (DSC) with a constant cooling rate of 10 ◦ C/min. Damping capacity (tan ı) of Ti51 Ni49 ribbons was measured by TA 2980 DMA configured with a thin film tension clamp and a liquid nitrogen cooling apparatus. The dimension of the DMA specimens was 10 mm in gauge length, 14 ␮m in thickness and 1.05 mm in width. Bulk Ti51 Ni49 SMA was fabricated by vacuum arc remelter from raw materials of Ti (purity 99.7 wt.%) and Ni (purity 99.9 wt.%). The Ti51 Ni49 ingot was homogenized at 950 ◦ C for 24 h and then cut to dimensions of 20.0 mm × 5.9 mm × 1.5 mm using a low-speed diamond saw. Damping capacity of bulk Ti51 Ni49 SMA was also determined by TA 2980 DMA but configured with a single cantilever clamp.

Fig. 2. DMA tan ı cooling curves for as-spun Ti51 Ni49 ribbon and bulk Ti51 Ni49 SMA measured at T˙ = 3 ◦ C/min,  = 1 Hz and ε = 8.5 × 10−4 .

determined as 24.1 J/g. Fig. 1(b) shows DMA tan ı and storage modulus cooling curves for as-spun Ti51 Ni49 ribbon measured at T˙ = 3 ◦ C/min,  = 1 Hz and strain ε = 8.5 × 10−4 (amplitude  0 = 20 ␮m). In Fig. 1(b), there are two internal friction peaks corresponding to B2 → R and R → B19 martensitic transformation appearing at 48.4 ◦ C (tan ı = 0.15) and 41.7 ◦ C (tan ı = 0.18), respectively. The different martensitic transformation temperatures determined by DSC and DMA in Fig. 1(a) and (b) are due to the cooing rate effect, which has been described in detail elsewhere [24]. Fig. 1(b) also shows that the storage modulus value of as-spun Ti51 Ni49 ribbon decreases significantly during B2 → R and R → B19 martensitic transformation to a minimum (about 22,200 MPa) and then increases with further decreasing temperature. This behavior is similar to that of normal bulk TiNi SMAs but the storage modulus minimum of Ti51 Ni49 ribbon is lower than that of normal bulk TiNi SMAs (about 30,000 MPa) [16,25–27]. Fig. 2 shows DMA tan ı cooling curve for bulk Ti51 Ni49 SMA measured at the same experimental parameters as Fig. 1(b), i.e., T˙

= 3 ◦ C/min,  = 1 Hz and ε = 8.5 × 10−4 (amplitude  0 = 65 ␮m), but using a single cantilever clamp. The tan ı cooling curve for as-spun Ti51 Ni49 ribbon shown in Fig. 1 is also plotted in Fig. 2 for comparison. As shown in Fig. 2, the bulk Ti51 Ni49 specimen exhibits a single B2 → B19 martensitic transformation IF peak but possesses a lower damping capacity of tan ı = 0.09. Fig. 2 also reveals that the damping capacity of B2 parent phase for bulk Ti51 Ni49 SMA is higher than that for as-spun Ti51 Ni49 ribbon. However, the damping capacity of B19 martensite for bulk Ti51 Ni49 SMA and as-spun Ti51 Ni49 ribbon does not show conspicuous distinction. Fig. 2 indicates that the damping characteristics of Ti51 Ni49 bulk and ribbon are different even they have identical chemical composition and are determined at the same experimental parameters. This feature is due to their different specimen geometries and tension clamps used in DMA tests. 3.2. Damping characteristics comparison between as-pun Ti51 Ni49 and crystallized Ti50 Ni25 Cu25 ribbons

3. Results and discussion 3.1. Damping capacity of as-spun Ti51 Ni49 ribbon and bulk Ti51 Ni49 SMAs Fig. 1(a) shows the DSC cooling curve for as-spun Ti51 Ni49 ribbon. As shown in Fig. 1(a), there are B2 → R and R → B19 martensitic transformation peaks appearing at about 47.9 ◦ C and 23.1 ◦ C, respectively. Besides, the transformation enthalpy of both B2 → R and R → B19 martensitic transformation peaks is

Fig. 3 shows DMA tan ı curves for as-spun Ti51 Ni49 ribbon, as-spun Ti50 Ni25 Cu25 ribbon and Ti50 Ni25 Cu25 ribbon annealed at 500 ◦ C for 3 min and 60 min [20]. Each specimen in Fig. 3 is conducted at identical cooling rate (T˙ = 3 ◦ C/min) and frequency ( = 10 Hz) while the applied strain on as-spun Ti51 Ni49 ribbon (ε = 1.5 × 10−3 ) is slightly larger than that on annealed Ti50 Ni25 Cu25 ribbons (ε = 1.2 × 10−3 ). Note that as-spun Ti51 Ni49 ribbon used in this study is essential crystalline while as-spun Ti50 Ni25 Cu25 ribbon is completely amorphous and, for the latter, it only exhibits

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Ti Ni Cu ribbon annealed at 500 Cx3min

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annealed at 500 Cx60min as-spun Ti Ni Cu ribbon

0.00 -150

-100

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0

50

100

Temperature (ºC) Fig. 3. DMA tan ı cooling curves for as-spun Ti51 Ni49 and Ti50 Ni25 Cu25 ribbons measured at T˙ = 3 ◦ C/min and  = 10 Hz while the applied strain on Ti51 Ni49 ribbon (ε = 1.5 × 10−3 ) is slightly larger than that on Ti50 Ni25 Cu25 ribbons (ε = 1.2 × 10−3 ).

an extremely low damping capacity, as shown in Fig. 3. Fig. 3 also reveals that the Ti50 Ni25 Cu25 ribbon annealed at 500 ◦ C for 3 min shows a B2 → B19 martensitic transformation IF peak at about −20 ◦ C and a broad relaxation peak at about −75 ◦ C. With further prolonging annealing time to 60 min, both the IF and relaxation peaks of Ti50 Ni25 Cu25 ribbon shift to higher temperatures but their damping capacities decrease simultaneously because of the increasing Cu content in the crystallized grains [20]. Fig. 3 shows that the damping capacity of the martensitic transformation IF peak for as-spun Ti51 Ni49 ribbon is much higher than that for crystallized Ti50 Ni25 Cu25 ribbon. This feature can be explained by the fact that there are more abundant martensite transformed in as-spun Ti51 Ni49 ribbon during martensitic transformation since the transformation enthalpy (H) of as-spun Ti51 Ni49 ribbon (about 24 J/g) is much larger than that of crystallized Ti50 Ni25 Cu25 ribbon (only about 8 J/g) [20,22]. As-spun Ti51 Ni49 ribbon also possesses an IF peak with higher peak temperature (at about 50 ◦ C) than that of crystallized Ti50 Ni25 Cu25 ribbon (at below room temperature). Besides, Ti51 Ni49 ribbon also exhibits an advantage of not becoming fragile after annealing, which is different from Ti50 Ni25 Cu25 ribbon. The above characteristics indicate that as-spun Ti51 Ni49 ribbon is more suitable for practical damping applications than Ti50 Ni25 Cu25 ribbon. 3.3. Annealing effect on damping characteristics of Ti51 Ni49 ribbon Fig. 4(a)–(c) show the DSC cooling curves of Ti51 Ni49 ribbons annealed at 200 ◦ C, 400 ◦ C and 600 ◦ C, respectively, for 1 h. Fig. 4(a)–(c) reveal that Ti51 Ni49 ribbons annealed at different temperatures also possess B2 → R and R → B19 martensitic transformation peaks in cooling as as-spun Ti51 Ni49 ribbon does (Fig. 1(a)). However, as shown in Fig. 4, both the peak temperatures of B2 → R and R → B19 martensitic transformation peaks increases with the increase of annealing temperature. This feature is attributed from the facts that higher annealing temperatures can eliminate the residual stress and defects in the ribbons which depress the martensitic transformation. Fig. 4(a)–(c) also show that the H values of annealed Ti51 Ni49 ribbons are slightly larger than that of the as-spun ribbon. Besides, the H value of the annealed ribbon only increases gently with the increase of annealing temperature. This phenomenon demonstrates that the as-spun Ti51 Ni49 ribbon is almost fully crystallized. Fig. 5 shows DMA tan ı cooling curves of as-spun Ti51 Ni49 ribbon and the ribbon annealed at 200 ◦ C, 400 ◦ C and 600 ◦ C for 1 h measured at identical experimental parameters, i.e., T˙ = 3 ◦ C/min,

Fig. 4. DSC cooling curves for Ti51 Ni49 ribbon annealed at (a) 200 ◦ C, (b) 400 ◦ C and (c) 600 ◦ C for 1 h.

 = 1 Hz and ε = 8.5 × 10−4 . From Fig. 5, both as-spun Ti51 Ni49 rib-

bon and Ti51 Ni49 ribbon annealed at 200 ◦ C for 1 h exhibit a high martensitic transformation IF peak with tan ı values above 0.15. However, Ti51 Ni49 ribbons annealed at 400 ◦ C and 600 ◦ C for 1 h only possess a low IF peak of B2 → B19 martensitic transformation with tan ı values below 0.10. Since the H values of as-spun and annealed ribbons are comparable, as shown in Fig. 1(a) and Fig. 4, the significant deviation of the tan ı values cannot be explained by the different transformation enthalpy values as crystallized

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4. Conclusions

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As-spun Ti51 Ni49 ribbon possesses abundant nano-sized GP zones and exhibits conspicuous martensitic transformation IF peaks in DMA tan ı cooling curve. For damping capacity of transformation IF peak determined by DMA tests, as-spun Ti51 Ni49 ribbon with a thin film tension clamp is higher than bulk Ti51 Ni49 specimen with a single cantilever clamp. Experimental results show that as-spun Ti51 Ni49 ribbon is more suitable for practical damping applications than crystallized Ti50 Ni25 Cu25 ribbon because the former exhibits the advantages of higher martensitic transformation temperature, better damping capacity and not apt to be fragile after annealing. Both as-spun Ti51 Ni49 ribbon and Ti51 Ni49 ribbon annealed at 200 ◦ C with plate-like GP zones show a larger transformation IF peak than Ti51 Ni49 ribbon annealed at 400 ◦ C and 600 ◦ C with disc-like Ti2 Ni precipitates.

Temperature (ºC) Fig. 5. DMA tan ı cooling curves for the as-spun Ti51 Ni49 ribbon and the ribbons annealed at different temperatures for 1 h measured at T˙ = 3 ◦ C/min,  = 1 Hz and ε = 8.5 × 10−4 .

Ti50 Ni25 Cu25 ribbons discussed above. On the other hand, this feature is corresponding to the different microstructures appearing in as-spun and annealed Ti51 Ni49 ribbons. According to our previous studies [21,23], as-spun Ti51 Ni49 ribbon has abundant nano size plate-like Guinier–Preston (GP) zones, which possess a coherent stress field around them and induce the transformed R-phase plates along <1 0 0>B2 directions. Meanwhile, both the length of these GP zones and that of transformed R-phase plates increase after Ti51 Ni49 ribbon is annealed at 200 ◦ C and 300 ◦ C for 1 h. On the other hand, larger disc-like Ti2 Ni precipitates, rather than GP zones, can be observed when Ti51 Ni49 ribbon is annealed at 400 ◦ C and 600 ◦ C for 1 h. These disk-like Ti2 Ni plates also induce transformed R-phase plates along <1 0 0>B2 directions but develop a semicoherent stress field around them. It has been reported that the parent/martensite interfaces and the twin boundaries in transformed martensite can pass through the coherent stress field around GP zones, but are impeded by the semicoherent interfaces around Ti2 Ni precipitates [10]. Consequently, the ribbon with abundant nano-sized GP zones can dissipate more energy during damping and exhibit higher IF peaks than those with Ti2 Ni precipitates. Fig. 5 also reveals that only the ribbon annealed at 600 ◦ C for 1 h shows an extra IF peak at temperature about −75 ◦ C. This extra IF peak is usually observed in damping measurement of normal bulk TiNi-based SMAs and is known as the relaxation peak [3]. Fan et al. [17] reported that the formation of the relaxation peak is related to the interaction of hydrogen with the motion of high-density twin boundaries in martensite. In this study, the origination of hydrogen atoms may come from the chemical reaction of the residual trace H2 O with the ribbon in Ar-purged quartz tube during the annealing procedure. However, more investigation is needed to illuminate why the hydrogen doping effect is more dominating when Ti51 Ni49 ribbon is annealed at 600 ◦ C.

Acknowledgements The authors gratefully acknowledge the financial support from National Science Council (NSC), Taiwan, Republic of China, under grants No. NSC100-2221-E002-100-MY3 and No. NSC-99-2221E197-010. We also highly appreciate Professor H. Kimura, Institute for Materials Research, Tohoku University, Japan, for his assistance in ribbon preparation. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27]

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