- Email: [email protected]
The effects of shape-setting on transformation temperatures of pseudoelastic shape memory alloy springs
Journal Pre-proof The effects of shape-setting on transformation temperatures of pseudoelastic shape memory alloy springs Farideh Jahanbazi Asl, Mahmoud Kadkhodaei, Fathallah Karimzadeh PII:
S2468-2179(19)30235-7
DOI:
https://doi.org/10.1016/j.jsamd.2019.10.005
Reference:
JSAMD 258
To appear in:
Journal of Science: Advanced Materials and Devices
Received Date: 13 April 2019 Revised Date:
21 October 2019
Accepted Date: 24 October 2019
Please cite this article as: F.J. Asl, M. Kadkhodaei, F. Karimzadeh, The effects of shape-setting on transformation temperatures of pseudoelastic shape memory alloy springs, Journal of Science: Advanced Materials and Devices, https://doi.org/10.1016/j.jsamd.2019.10.005. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi.
The effects of shape-setting on transformation temperatures of pseudoelastic shape memory alloy springs Farideh Jahanbazi Asla a.
Department of Mechanical Engineering, Isfahan University of Technology, Isfahan, 8415683111, Iran; [email protected]
Mahmoud Kadkhodaeib b.
Department of Mechanical Engineering, Isfahan University of Technology, Isfahan, 8415683111, Iran; [email protected]
Fathallah Karimzadehc c.
Department of Materials Engineering, Isfahan University of Technology, Isfahan, 8415683111, Iran; [email protected]
Corresponding author:
Mahmoud Kadkhodaei, Department of Mechanical Engineering, Isfahan University of Technology, Isfahan, 84156-83111, Iran. Email: [email protected]
1
The effects of shape-setting on transformation temperatures of pseudoelastic shape memory alloy springs
2
Abstract Since shape memory alloy (SMA) wires can hardly ever be reliably employed under compressive loadings, SMA springs are developed as axial actuators with the ability of withstanding both tension and compression. In this paper, shape memory alloy helical springs are produced by shape-setting two types of wires: one with shape memory effect (SME) and the other with pseudoelasticity (PE) at the ambient temperature. Phase transformation temperatures of the produced springs are measured by differential scanning calorimetry (DSC), and the influences of effective parameters including cold work, heat treatment temperature and duration, and cooling rate are investigated on transformation temperatures of the products. The results show that phase transition temperatures of the fabricated springs can be tuned by performing cold work and by adjusting temperature and duration of the conducted heat treatment as well as the subsequent cooling rate. It is found that transformation temperatures of the springs fabricated using the SME wire increase as the heat treatment temperature increases. However, for samples manufactured using PE wire, transformation temperatures first increase and then decrease with increase in the heat treatment temperature. Increase in the cooling rate leads to decrease in the austenite final temperature (Af), and increase in the extent of cold work leads to increase in transformation temperatures especially Af. Keywords: Shape memory alloy, SMA, Transformation temperature, Heat treatment, Shape-setting. 1.
Introduction
Shape memory alloys (SMAs) are a class of smart materials which exhibit two extraordinary behaviors of shape memory effect (SME) and pseudoelasticity (PE) (or superelasticity) owing to thermoelastic martensitic phase transformation between the two phases of martensite and austenite. The so-called shape memory effect is thermallydriven recovery of the initial configuration of an SMA when residual strains appear after an inelastic loading/unloading cycle. In PE, recovery occurs spontaneously upon unloading once a large deformation is induced during inelastic loadings [1]. Shape memory alloys with several shapes have been widely employed in various fields such as robotics, biomechanics and microelectromechanical systems [2]. In particular, beside SMA wires, spring actuators are vastly used owing to their simplicity of fabrication [3] compared to other shapes such as tubes. Moreover, in contrary to wires, helical springs can be subjected to both tension and compression. Many studies have been so far accomplished to investigate the behaviors of SMA springs both theatrically and experimentally. In theoretical modeling of SMA springs, the main goal is to predict force-displacement response of a helical spring. Toi et al. [4] presented a finite element formulation for analysis of superelasticity in SMA springs using linear Timoshenko beam elements. Aguiar et al. [5] proposed a numerical method based on the operator split technique in this regard. Mirzaeifar et al. [6 and 7] studied pure torsion of SMA bars with circular cross sections to investigate the pseudoelastic response of SMA helical springs under an axial force. Heidari et al. [8] proposed an enhanced one-dimensional constitutive model to describe shear stress-strain response within the coils of an SMA spring. Their model was based on the von-Mises effective stress and strain, and it was further extended to take large deformations into account [9]. To fabricate SMA elements with a desirable shape, specific thermomechanical treatments called "shape-setting" are required [10]. Shape-setting mainly includes annealing but may be accompanied by cold work and quenching on the products. Although several microstructural analyses have been carried out [11, 12, 13, 14, 15 and 16] to investigate detailed mechanisms of various stages in shape-setting, macroscopic studies have gained a great attention in order to directly observe the influences of each stage on phase transition and other features of an SMA specimen after shapesetting. Wang et al. [17] investigated the effect of annealing on transformation characteristics of TiNi shape memory alloys by differential scanning calorimetry (DSC). Their results showed that R-phase transformation appeared at low annealing temperatures. The R-phase disappeared and austenite directly transformed to martensite as the annealing temperature exceeded 550oC. When R-phase appends to austenite and martensite, several thermomechanical behaviors of an SMA may be affected [18, 19, 20, 21, 22 and 23]. Yeung et al. [24] found that phase transition temperatures can be manipulated by adjusting heat treatment parameters including duration, temperature and cooling rate. Liu et al. [25] showed that the austenite final temperature (Af) mostly increases after ageing. Eggeler et al. [26]
3
realized that, in general, the transformation temperatures increase as the aging time increases. Sadiq et al. [27] investigated the effect of annealing temperature on the transformation temperatures. They found that, after annealing NiTi alloy above the recrystallization temperature, the R-phase disappears so that direct transformation from austenite to martensite takes place. The transformation temperatures increase as the annealing temperature increases; however, the R-phase transforms at lower temperatures. Wang et al. [28] investigated the microstructure, martensitic transformation, shape memory effect and superelastic property of Ti49.6Ni45.1Cu5Cr0.3 alloy. They concluded that, in the course of elevating the annealing temperature, the transformation temperatures increased for annealing temperatures in the range of 623 K to 873 K. Then, they decreased for the temperature range of 873 K to 1023 K and did not considerably vary after 1023 K until 1273 K. Heidari et al. [8] fabricated SMA helical springs by shapesetting NiTi wires and evaluated thermomechanical characteristics of their products. They found that transformation temperatures of the fabricated springs increase as the annealing temperature increases; however, the start and final temperatures of the R-phase transition decrease so that the R-phase eventually disappears at the annealing temperature of 600°C. Motemani et al. [29] studied the effect of cooling rate on the phase transformation and mechanical properties of Nirich NiTi shape memory alloy. They realized that austenite final temperature Af increases as cooling rate decreases while the martensite final temperature Mf reduces. Consequently, a furnace-cooled sample has the highest phase transformation hysteresis (Af–Mf) compared to samples with lower cooling rates. Mitwally and Farag [30] studied the effect of cold work on superelasticity, shape memory effect and hardness of NiTi alloy. They found that the shape memory recovery is diminished by cold rolling as well as bending. Lin and Wu [31] observed that, by augmenting the extent of applied cold work, the products would show lower residual strains upon unloading. Grossmann et al. [32] proposed a procedure to fabricate an SMA spring and to characterize its microstructural evolution during the production. Costanza et al. [33] investigated shape memory effect in Ni-Ti springs and presented a technique to design a linear actuator made of SMAs. Follador et al. [3] fabricated an SMA spring actuator. They further described the mechanical characteristics of the SMA spring by a simple linear-elastic model whose parameters depend on the crystalline characteristics. In most of the available works on fabrication of SMA springs, the products are martensitic at the ambient temperature. Moreover, the influences of all shape-setting parameters on transformation temperatures of the fabricated springs are not thoroughly investigated. Since pseudoelastic SMA springs at the ambient temperatures are vastly required, in this paper, the main purpose is to fabricate austenitic springs using shape memory alloy wires. Two types of NiTi (Ti-55.87 at % Ni) wires (one of which is martensitic at ambient temperature and the other is austenitic) are utilized. The wires are wound and locked on a screw and are then heat treated at temperatures within the range of 300 to 1000oC for 5 to 1260 minutes. The effects of various production parameters such as cold work, heat treatment temperature and duration, and the subsequent cooling rate on transformation temperatures of the fabricated springs are further investigated. 2.
Materials and Methods
The present investigation is carried out on commercial SMA wires provided by Memry Co. with the nominal composition of Ti-55.87%Ni and the diameter of 1.5 mm. Two types of wires, one with shape memory effect (SME) and the other with pseudoelasticity (PE) at the ambient temperature, were utilized. Fig. 1 and Fig. 2 illustrate results of Differential scanning calorimetry (DSC), and Table 1 shows the transformation temperatures of these wires. To fabricate springs using SME and PE wires, according to Fig. 3, each wire was first wound and locked on a screw. Once temperature of the furnace has reached a desired number, the specimen was placed in the furnace for the required time interval. Then, the specimen was cooled down. To prevent oxidation of the specimens, the whole wound wire together with the fastening components were covered by a stainless steel foil. Heat treatments were performed on the fabricated springs at different conditions so that various combinations of the influential parameters were examined. For instance, the springs S-11, S-12 and S-13 were made using SME wire by heat treating at 750oC for 10 minutes; the samples S-11and S-13 were quenched in water-ice bath, but S-12 was quenched in dry-ice bath. Cold work was performed on S-13, but specimens S-11 and S-12 were fabricated with no cold work. Sample S-14
4
indicates the SME wire which was heat treated at 1000oC for 10 minutes and finally was quenched in water-ice bath. For fabricating the spring S-15, sample S-14 was first wound and locked on the screw; then, it was heat treated at 1000oC for 10 minutes. Eventually, quenching in water-ice bath was performed. This procedure of heat treatment followed by quenching was repeated to fabricate spring S-16 from S-15. A summary of heat treatment temperatures, duration, and cooling method is given in Appendix 1. DSC tests were used to determine the transformation temperatures of the products. DSC samples were cut into 30-50 mg in mass, and the tests were performed at the heating/cooling rate of 5oC/min between -50oC and +150oC.
Fig. 1. Transformation temperatures for SME wire.
Fig. 2. Transformation temperatures for PE wire.
5
Table 1. Transformation temperatures of the utilized wires. Initial wire
Af ( oC)
As ( oC)
Rs ( oC)
Rf ( oC)
Ms ( oC)
Mf ( oC)
SME wire
64.00
43.63
50.00
28.00
8.00
-26.00
PE wire
15.00
-5.00
17.30
-10.00
-45.00
Fig. 3. Constrained SMA wire on a screw. To induce a thermal shock in order to reduce transformation temperatures of samples S-13 and S-16, heat treatment without using stainless steel foil was carried out in three stages as follows: 1. Heat treatment for the initial wire at the required temperature followed by quenching in water-ice bath 2. Wounding the heat-treated wire on the screw followed by quenching in water-ice bath 3. Heat treatment of the fabricated spring followed by quenching in water-ice bath Additionally, cold work was carried out on some of the samples in order to obtain desirable transformation temperatures. To this end, cold rolling was used to reduce thickness by the amounts of 3.5% and 32.1%. A wide range of temperatures from 300oC to 1000oC was chosen for the shape-setting; however, in order to prevent oxidation of the samples, heat treatment at lower temperatures is more preferred. 3.
Results and discussion
In this section, the effects of temperature and duration of the heat treatments, cooling rate, and cold work on the transformation temperatures of the products are investigated. Transformation temperatures of the products are given in Appendix 2. Since the utilized instrument was limited to the minimum temperature of -50oC, determination of Mf and Ms for some specimens was not possible. Fig. 4 shows one of these cases for sample S-09. R-phase transition occurs for most of the specimens (for instance, in Fig. 5 where DSC curve of sample S-13 is shown) while it is not seen for some specimens (for instance, in sample S-24 whose DSC curve is shown in Fig. 6). Samples S-18, S-19, S20, S-21, S-22 and 23 were pseudoelastic springs at the room temperature while the other ones showed shape memory effect. Fig. 7 illustrates one of the fabricated pseudoelastic springs from two different views. As shown in Appendix 2, the austenitic transformation temperatures of specimens S-18, S-19, S-20 and S-22 are lower than the ambient temperature. It should be noted that sample S-21 is similar to S-22 with this difference that sample S-21 was placed into quartz capsule under vacuum to prevent from oxidation as much as possible. The specimen S-23 was heat treated to find the lowest applicable temperature for achieving pseudoelastic spring. Accordingly, 630oC was the minimum temperature to optimize the process of fabricating a pseudoelastic spring with the PE wire. Samples S-21 and S-23 were mechanically shown to be pseudoelastic: they were examined under inelastic stretch followed by inelastic compression and could return to their original configuration after unloading. The samples S24, S-25 and S-26 are 32.1% cold-worked SME wires.
6
Fig. 4. Transformation temperatures for sample S-09.
Fig. 5. Transformation temperatures for sample S-13.
7
Fig. 6. Transformation temperatures for sample S-24.
Fig. 7. A fabricated pseudoelastic helical spring. As formerly indicated, in some specimens, the reverse transformation (during heating cycle) occurs in two stages: from martensite to an intermediate R-phase and then to austenite. Similarly, for some samples, the forward transformation (during cooling cycle) occurs in two stages: from austenite (parent phase) to R-phase and then to martensite. Table 2 shows transformation temperatures of R-phase during heating cycle for such specimens. Table 2. Transformation temperatures of Rhombohedral phase during heating cycle. Specimen Code
Rs ( oC)
Rf ( oC)
S-18
-7
7
S-19
-7
4
S-20
-10
5
S-24
55
66
S-25
53
68
S-26
52
66
8
Since pseudoelastic springs are planned to be manufactured in the present work, Af of the products should be lower than the ambient temperature. Therefore, the effects of various parameters on the austenite transformation temperatures are investigated in the following subsections. 3.1.
Influence of heat treatment on the transformation temperatures
Heat treatment parameters including temperature, cooling rate, and the duration affect transformation temperatures of the fabricated springs. Here, the findings of this work are presented. 3.1.1
Effect of heat treatment temperature
Fig. 8 shows the influence of heat treatment temperature on austenite transformation temperatures of the springs fabricated by using the SME wire. It is seen that transformation temperatures increase with increment in the heat treatment temperature. Moreover, for the manufactured spring at the minimum temperature of 750oC, As and Af are higher than the ambient temperature. The rapid growth of Af with increase in the heat treatment temperature indicates that fabrication of pseudoelastic spring with SME wire is impossible at these conditions.
Fig. 8. Effect of heat treatment temperature on the transformation temperatures for a spring made from SME wire.
Fig. 9. Effect of heat treatment temperature on the transformation temperatures of samples manufactured using PE wire.
9
Variations of the transformation temperatures for the springs made from PE wire with heat treatment temperature are shown in Fig. 9. It is observed that the transformation temperatures strongly depend on the heat treatment temperature. According to this figure, there are three trends for variations in the transformation temperatures: 1- Transformation temperatures are enhanced by elevating the heat treatment temperature until 500oC. 2- Transformation temperatures, except Ms, reduce by increasing the heat treatment temperature between 550oC to 650oC. 3- Transformation temperatures except Rs and Rf are nearly constant with increase in the heat treatment temperature beyond 650oC until 750oC. In fact, with further addition of the heat treatment temperature, transformation temperatures remain fairly constant. This is why heat treatment at temperatures above 650oC results in pseudoelastic products. 3.1.2. Effect of cooling rate According to the provided data in Appendix 2, comparison between the transformation temperatures of specimens S-19 and S-22 and between those of S-10 to S-12 indicates that transformation temperatures of the products mostly decrease when quenching in water-ice bath is done instead of cooling in the furnace for both series of springs made using PE and SME wires. However, by comparing the samples S-11 and S-12, it is seen that Mf increases by increasing the cooling rate. This trend coincides with the findings of investigations carried out by Motemani et al. [29] on Ni-rich Ni-Ti shape memory alloys. In other words, the furnace-cooled specimen has the highest phase transformation hysteresis (Af–Mf) compared to the other samples. Increase in transformation temperatures for the quenched sample in dry ice, compared to the sample quenched in water-ice, is due to the application of the steel foil to prevent oxidation of the parts. When the sample cools in water-ice, since the steel foil is not completely sealed, water may leak during the cooling time. Consequently, cooling using dry ice is performed more gradually. 3.1.3.
Effect of heat treatment duration
Variations of the austenite transformation temperatures with the duration of heat treatment for springs made from the SME wire are shown in Fig. 10. As is seen, As and Af first increase slightly with increase in the heat treatment duration. Then, by more prolonging the heat treatment, their increase is suppressed so that As reduces a little. Fig. 11 shows the effect of heat treatment time on the transformation temperatures for springs made from the PE wire. It is seen that increase in duration of the heat treatment leads to a very negligible rise in As and Af compared to the observed increase for the springs made of the SME wire. Moreover, the effect of heat treatment duration on transformation temperatures is less than that of the other production parameters.
10
Fig. 10. Effect of heat treatment duration on the transformation temperatures of sample springs made from SME wire.
Fig. 11. Effect of heat treatment duration on the transformation temperatures of springs made from PE wire. 3.2. Effect of cold work Using a flat rolling machine, the SME wire with the initial diameter of 1.5 mm was cold-rolled to achieve a 0.75 mm-thick strip. The cold-rolled specimen was further wound and locked on a screw. Then, the prepared spring was heat treated at 750oC for 10 minutes followed by quenching in water-ice bath. Specimen S-13 was manufactured with the use of a 3.5 % cold-worked SME wire. According to Appendix 2, comparison of transformation temperatures for samples S-11 and S-13 indicates that the SME wire becomes austenitic at the room temperature when the cold work percentage increases to 32.1 %. Moreover, transformation temperatures of 32.1 % cold-worked wires S-24 to S-26 are generally higher than those of the as-received wire. This is in agreement with the findings reported by Mitwally and Farag [30].
11
According to the findings of this work, the effects of various shape-setting stages on transformation temperatures for the fabricated samples using PE wire are schematically illustrated in Fig. 12. By elevating the heat treatment temperature, the transformation temperatures increase and then decrease. Consequently, in early stages of annealing when the temperature is not high enough, the possibility of achieving pseudoelastic parts may be lessen even with the use of initially austenitic wires. In other words, if one needs to reduce transformation temperatures after annealing, the set temperature is recommended to be as high as possible. A more pronounced cooling rate gives rise to decrease in transformation temperatures; thus, severe cooling such as quenching is beneficial when pseudoelastic products are desirable. Cold work on the specimens leads to rise in transformation temperatures; therefore, such processes may be useful in achieving martensitic parts and are not recommended when austenitic products are desired.
Fig. 12. Schematic illustration of the effect of various parameters on transformation temperatures for springs sample made of PE wire. 4. Conclusions In this paper, pseudoelastic helical springs were manufactured by shape-setting two types of NiTi wires: one was martensitic at the ambient temperature and the other one was austenitic. The effects of various stages such as cold work, heat treatment temperature and duration, and the subsequent cooling rate on the transformation temperatures of the products were investigated. The main results obtained in this research can be summarized as follows: - Heat treatment duration has the less effect on the transformation temperatures than the other adjustments of a shape-setting process. - Transformation temperatures of the springs fabricated using the SME wire increase as the heat treatment temperature increases. However, for samples manufactured using PE wire, transformation temperatures first increase and then decrease with increase in the heat treatment temperature. - Increase in cooling rate result in decrease in Af which is beneficial to fabricate PE springs at the ambient temperature. - Cold work leads to rise in transformation temperatures especially Af. Depending on the desired type of product with either pseudoelasticity or shape memory effect, the presented
12
findings regarding the effects of various shape-setting stages on transformation temperatures of an SMA spring can be considered as guidelines for a manufacturer who wishes to fabricate SMA springs with a predefined phase (austenite or martensite) at the ambient temperature. Metallurgical investigations will improve the present understanding, and such studies will be planned for further investigations. In addition to the procedures used in current study, various thermomechanical treatments cause a well-developed dislocation sub-structure or nanocrystalline structure and may be used for improving the properties of SMAs in future works.
5. References [1] SH. Youn, YS. Jang, JH. Han. Development of a three-axis hybrid mesh isolator using the pseudoelasticity of a shape memory alloy. Smart Materials and Structures. 20(7) (2011) 075017. https:// doi.org/10.1088/09641726/20/7/075017. [2] KK. Alaneme, S. Umar. Mechanical behaviour and damping properties of Ni modified Cu–Zn–Al shape memory alloys, Journal of Science: Advanced Materials and Devices. 3(3) (2018) 371-379. https:// doi.org/10.1016/j.jsamd.2018.05.002. [3] M. Follador, M. Cianchetti, A. Arienti, C. Laschi. A general method for the design and fabrication of shape memory alloy active spring actuators. Smart Materials and Structures. 21 (2012) 115029-115039. https:// doi.org/ 10.1088/0964-1726/21/11/115029. [4] Y. Toi, JB. Lee, M. Taya. Finite element analysis of superelastic, large deformation behavior of shape memory alloy helical springs. Computers and Structure. 82 (2004) 1685-1693. https://doi.org/10.1016/j.compstruc.2004.03.025. [5] RAA. Aguiar, NA. Savi, PMCL. Pacheco Experimental and numerical investigations of shape memory alloy helical springs. Smart Material and Structures. 19 (2010) 025008-025017. [6] R. Mirzaeifar, R. Desroches, A. Yavari. Exact solution for pure torsion of shape memory alloy circular. Mechanical of Materials. 42 (2010) 797-806. http://doi.org/ 10.1088/0964-1726/19/2/025008. [7] R. Mirzaeifar, R. Desroches, A. Yavari. A combined analytical, numerical, and experimental study of shapememory-alloy helical springs. International Journal of Solids and Structures. 48 (2011) 611-624. https://doi.org/10.1016/j.ijsolstr.2010.10.026. [8] B. Heidari, M. Kadkhodaei, M. Barati, F. Karimzadeh. Fabrication and modeling of shape memory alloy springs. Smart Materials and Structures. 25(12) (2016) 125003. https://doi.org/ 10.1088/0964-1726/25/12/125003. [9] Y. Mohammad Hashemi, M. Kadkhodaei. The Effects of Geometric Parameters under Small and Large Deformations on Dissipative Performance of Shape Memory Alloy Helical Springs, Journal of Stress Analysis. 3 (1) (2018) 69-79. https://doi.org/10.22084/jrstan.2018.17137.1061. [10] SH. Kayani, MI. Khan, FA. Khalid, HY. Kim, S. Miyazaki. Precipitation Behavior of Thermo-Mechanically Treated Ti 50 Ni 20 Au 20 Cu 10 High-Temperature Shape-Memory Alloy. Shape Memory and Superelasticity. 2(1) (2016) 29-36. https://doi.org/10.1007/s40830-015-0048-6. [11] E. Prokofiev, J. Burow, J. Frenzel, D. Gunderov, G. Eggeler, R. Valiev. Phase transformations and functional properties of NiTi alloy with ultrafine-grained structure. Materials Science Forum. (2011) 667–669: 1059-1064. https://doi.org/10.4028/www.scientific.net/MSF.667-669.1059.
13
[12] Sh. Jiang, M. Tang, Y. Zhao, Hu , Y. Zhang, L. Liang. Crystallization of amorphous NiTi shape memory alloy fabricated by severe plastic deformation. Transactions of Nonferrous Metals Society of China. 24 (2014) 1758-1765. https://doi.org/10.1016/S1003-6326(14)63250-7. [13] E. Mohammad Sharifi, A. Kermanpur. Superelastic behavior of nanostructured Ti50Ni48Co2 shape memory alloy with cold rolling processing. Transactions of Nonferrous Metals Society of China. 28 (2018) 1351-1359. https://doi.org/10.1016/S1003-6326(18)64773-9. [14] M. Abbasi, A. Kermanpur, R. Emadi. Effects of Thermo-Mechanical Processing on the Mechanical Properties and Shape Recovery of the Nanostructured Ti50Ni45Cu5 Shape Memory Alloy. Procedia Materials Science. 11 (2015) 61-66. https://doi.org/10.1016/j.mspro.2015.11.089. [15] V. Brailovsky, V. Demers, SD. Prokoshkin, KE. Inaekyan. Functional properties of Nano crystalline, sub microcrystalline and polygonized Ti-Ni alloys processed by cold rolling and post deformation annealing. Journal of Alloys and Compounds. 509 (2011) 2066-2075. https://doi.org/ 10.1016/j.jallcom.2010.10.142. [16] SH. Chang, SK. Wu. Effect of cooling rate on the martensitic transformation of TiNi alloy by differential Scanning Calorimetry and dynamic mechanical analysis. Materials Characterization. 59 (2008) 987-990. https://doi.org/ 10.1016/j.matchar.2007.08.014. [17] ZG. Wang, XT. Zu, XD. Feng, S. Zhu, JM. Zhou, LM. Wang. Annealing-induced evolution of transformation characteristics in TiNi shape memory alloys. Physica B. 353 (2004) 9-14. https://doi.org/ 10.1016/j.physb.2004.08.021. [18] Y. Luo, T. Takagi, S. Maruyama, M. Yamada. A shape memory alloy actuator using Peltier modules and Rphase transition. Journal of Intelligent Material Systems and Structures. 11(7) (2000) 503-511. https://doi.org/10.1106/92YH-9YU9-HVW4-RVKT. [19] M. Tomozawa, HY. Kim, S. Miyazaki. Microactuators using R-phase transformation of sputter-deposited Ti47.3 Ni shape memory alloy thin films. Journal of intelligent material systems and structures. 17(12) (2006) 10491058. https://doi.org/ 10.1177/1045389X06064883. [20] TW. Duerig, K. Bhattacharya. The influence of the R-phase on the superelastic behavior of NiTi. Shape Memory and Superelasticity. 1(2) (2015) 153-161. https://doi.org/ 10.1007/s40830-015-0013-4. [21] D. Chatziathanasiou, Y. Chemisky, F. Meraghni, G. Chatzigeorgiou, E. Patoor. Phase transformation of anisotropic shape memory alloys: Theory and validation in superelasticity. Shape Memory and Superelasticity. 1(3) (2015) 359-374. . https://doi.org/10.1007/s40830-015-0027-y. [22] A. Shamimi, B. Amin-Ahmadi, A. Stebner, T. Duerig. The Effect of Low Temperature Aging and the Evolution of R-Phase in Ni-Rich NiTi. Shape Memory and Superelasticity. 4(4) (2018) 417-427. https://doi.org/10.1007/s40830-018-0193-9. [23] P. Shayanfard, M. Kadkhodaei, S. Safaee. Proposition of R-phase transformation strip in the phase diagram of Ni-Ti shape memory alloy using electromechanical experiments. Journal of Intelligent Material Systems and Structures. 28(19) (2017) 2757-2768. https://doi.org/10.1177/1045389X17698587. [24] KWK. Yeung, KMC. Cheung, WW. Lu, CY. Chung. Optimization of thermal treatment parameters to alter austenitic phase transition temperature of NiTi alloy for medical implant. Materials Science and Engineering A. 383 (2004) 213-218. https://doi.org/10.1016/j.msea.2004.05.063. [25] X. Liu, Y. Wang, D. Yang, M. Qi. The effect of ageing treatment on shape-setting and superelasticity of a nitinol stent. Materials Characterization. 59 (2008) 402-406. https://doi.org/ 10.1016/j.matchar.2007.02.007. [26] G. Eggeler, J. Khalil-Allafi, S. Gollerthan, C. Somsen, W. Schmahl, D. Sheptyakov. On the effect of aging on
14
martensitic transformations in Ni-rich NiTi shape memory alloys. Smart Materials and Structures. 14 (2005) 186– 91. https://doi.org/ 10.1088/0964-1726/14/5/002. [27] H. Sadiq, MB. Wong, R. Al-Maghaidi, XL. Zhao. The effects of heat treatment on the recovery stresses of shape memory alloys. Smart Materials and Structures. 19 (2010) 035021-035028. https://doi.org/ 10.1088/09641726/19/3/035021. [28] QY. Wang, YF. Zheng, Y. Liu. Microstructure, martensitic transformation and superelasticity of Ti49.6Ni45.1Cu5Cr0.3 shape memory alloy. Materials Letters. 65 (2011) 74-77. https://doi.org/10.1016/j.matlet.2010.09.036. [29] Y. Motemani, M. Nili-Ahmadabadi, MJ. Tan, M. Bornapour, Sh. Rayagan. Effect of cooling rate on the phase transformation behavior and mechanical properties of Ni-rich NiTi shape memory alloy. Journal of Alloys and Compounds. 469 (2009) 164-168. https://doi.org/10.1016/j.jallcom.2008.01.153. [30] ME. Mitwally, M. Farag. Effect of cold work on the behavior of NiTi shape memory alloy. In Advances in Biomedical and Biomimetic Materials, Editors .J. Narayan P.N. Kumta W.R. Wagner, The American Ceramic Society. (2009) 59-70. https://doi.org/ 10.1002/9780470538357.ch6. [31] HC. Lin, SK. Wu. The tensile behavior of a cold-rolled and reverse-transformed equitaomic TiNi alloy. Acta Metallurgica et Materialia. 42 (1994) 1623-1630. https://doi.org/10.3390/ma10070704. [32] C. Grossmann, J. Frenzel, V. Sampath, T. Depka, A. Oppenkowski, C. Somsen, K. Neuking, W. Theisen, G. Eggeler. Processing and property assessment of NiTi and NiTiCu shape memory actuator springs. Materialwiss. Werkstofftech. 39 (2008) 499-510. https://doi.org/10.1002/mawe.200800271. [33] G. Costanza, ME. Tata, C. Calisti. Nitinol one-way shape memory springs, Thermomechanical. and actuator design. Sens. Actuators A. 157 (2010) 113-117. https://doi.org/10.1016/j.sna.2009.11.008.
15
Appendix 1. Summary of Heat Transfer Conditions Specimen
Heat Treatment
Heat Treatment
Temperature (oC)
Duration (min)
Material Code Code
Cooling Method
S-01
SME
300
25
Ambient Temperature
S-02
SME
300
180
Ambient Temperature
S-03
SME
300
300
Ambient Temperature
S-04
SME
300
480
Ambient Temperature
S-05
SME
300
780
Ambient Temperature
S-06
SME
300
1260
Ambient Temperature
S-07
SME
400
780
Ambient Temperature
S-08
SME
868
10
Cooled in Furnace
S-09
SME
868
10
Quenched in water-ice bath
S-10
SME
750
10
Cooled in Furnace
S-11
SME
750
10
Quenched in water-ice bath
S-12
SME
750
10
Quenched in dry-ice bath
S-13
SME
750
10
Quenched in water-ice bath
S-14
SME
1000
10
Quenched in water-ice bath
S-15
SME
1000
10
Quenched in water-ice bath
S-16
SME
1000
10
Quenched in water-ice bath
S-17
PE
600
1260
Ambient Temperature
S-18
PE
750
1260
Cooled in Furnace
S-19
PE
750
10
Cooled in Furnace
S-20
PE
650
10
Cooled in Furnace
S-21
PE
750
10
Quenched in water-ice bath (Quartz Capsule) S-22
PE
750
10
Quenched in water-ice bath
S-23
PE
630
10
Quenched in water-ice bath
16
S-24
SME
750
10
Quenched in water-ice bath
S-25
SME
750
10
Quenched in liquid N2 bath
S-26
SME
1000
10
Quenched in liquid N2 bath
17
Appendix 2. Transformation temperatures of selected specimens Specimen Af ( oC)
As ( oC)
Rs ( oC)
Rf ( oC)
Ms ( oC)
Mf ( oC)
S-09
64
44
34
5
S-10
71
47.5
34
10
S-11
57.18
32.50
45
20
14
-20
S-12
58
37.5
48
22.5
17.5
-17
S-13
58
28
45
20
12.5
-25
S-14
69.51
45
33
-4
S-15
70
45.38
27.50
7.50
S-16
72.68
32.50
36
16
S-17
41
17.5
24
3
-1
-27.5
S-18
20
10
39
-7.5
-31
S-19
16
7
22
-6
-39
S-20
14
7
7.5
-1.5
-36
S-22
-7.5
-25
-28
S-24
77.5
74
42.5
28
S-25
77.5
75
42.5
27.5
S-26
77.5
74
42
22.5
code
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
S2468-2179(19)30235-7
DOI:
https://doi.org/10.1016/j.jsamd.2019.10.005
Reference:
JSAMD 258
To appear in:
Journal of Science: Advanced Materials and Devices
Received Date: 13 April 2019 Revised Date:
21 October 2019
Accepted Date: 24 October 2019
Please cite this article as: F.J. Asl, M. Kadkhodaei, F. Karimzadeh, The effects of shape-setting on transformation temperatures of pseudoelastic shape memory alloy springs, Journal of Science: Advanced Materials and Devices, https://doi.org/10.1016/j.jsamd.2019.10.005. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi.
The effects of shape-setting on transformation temperatures of pseudoelastic shape memory alloy springs Farideh Jahanbazi Asla a.
Department of Mechanical Engineering, Isfahan University of Technology, Isfahan, 8415683111, Iran; [email protected]
Mahmoud Kadkhodaeib b.
Department of Mechanical Engineering, Isfahan University of Technology, Isfahan, 8415683111, Iran; [email protected]
Fathallah Karimzadehc c.
Department of Materials Engineering, Isfahan University of Technology, Isfahan, 8415683111, Iran; [email protected]
Corresponding author:
Mahmoud Kadkhodaei, Department of Mechanical Engineering, Isfahan University of Technology, Isfahan, 84156-83111, Iran. Email: [email protected]
1
The effects of shape-setting on transformation temperatures of pseudoelastic shape memory alloy springs
2
Abstract Since shape memory alloy (SMA) wires can hardly ever be reliably employed under compressive loadings, SMA springs are developed as axial actuators with the ability of withstanding both tension and compression. In this paper, shape memory alloy helical springs are produced by shape-setting two types of wires: one with shape memory effect (SME) and the other with pseudoelasticity (PE) at the ambient temperature. Phase transformation temperatures of the produced springs are measured by differential scanning calorimetry (DSC), and the influences of effective parameters including cold work, heat treatment temperature and duration, and cooling rate are investigated on transformation temperatures of the products. The results show that phase transition temperatures of the fabricated springs can be tuned by performing cold work and by adjusting temperature and duration of the conducted heat treatment as well as the subsequent cooling rate. It is found that transformation temperatures of the springs fabricated using the SME wire increase as the heat treatment temperature increases. However, for samples manufactured using PE wire, transformation temperatures first increase and then decrease with increase in the heat treatment temperature. Increase in the cooling rate leads to decrease in the austenite final temperature (Af), and increase in the extent of cold work leads to increase in transformation temperatures especially Af. Keywords: Shape memory alloy, SMA, Transformation temperature, Heat treatment, Shape-setting. 1.
Introduction
Shape memory alloys (SMAs) are a class of smart materials which exhibit two extraordinary behaviors of shape memory effect (SME) and pseudoelasticity (PE) (or superelasticity) owing to thermoelastic martensitic phase transformation between the two phases of martensite and austenite. The so-called shape memory effect is thermallydriven recovery of the initial configuration of an SMA when residual strains appear after an inelastic loading/unloading cycle. In PE, recovery occurs spontaneously upon unloading once a large deformation is induced during inelastic loadings [1]. Shape memory alloys with several shapes have been widely employed in various fields such as robotics, biomechanics and microelectromechanical systems [2]. In particular, beside SMA wires, spring actuators are vastly used owing to their simplicity of fabrication [3] compared to other shapes such as tubes. Moreover, in contrary to wires, helical springs can be subjected to both tension and compression. Many studies have been so far accomplished to investigate the behaviors of SMA springs both theatrically and experimentally. In theoretical modeling of SMA springs, the main goal is to predict force-displacement response of a helical spring. Toi et al. [4] presented a finite element formulation for analysis of superelasticity in SMA springs using linear Timoshenko beam elements. Aguiar et al. [5] proposed a numerical method based on the operator split technique in this regard. Mirzaeifar et al. [6 and 7] studied pure torsion of SMA bars with circular cross sections to investigate the pseudoelastic response of SMA helical springs under an axial force. Heidari et al. [8] proposed an enhanced one-dimensional constitutive model to describe shear stress-strain response within the coils of an SMA spring. Their model was based on the von-Mises effective stress and strain, and it was further extended to take large deformations into account [9]. To fabricate SMA elements with a desirable shape, specific thermomechanical treatments called "shape-setting" are required [10]. Shape-setting mainly includes annealing but may be accompanied by cold work and quenching on the products. Although several microstructural analyses have been carried out [11, 12, 13, 14, 15 and 16] to investigate detailed mechanisms of various stages in shape-setting, macroscopic studies have gained a great attention in order to directly observe the influences of each stage on phase transition and other features of an SMA specimen after shapesetting. Wang et al. [17] investigated the effect of annealing on transformation characteristics of TiNi shape memory alloys by differential scanning calorimetry (DSC). Their results showed that R-phase transformation appeared at low annealing temperatures. The R-phase disappeared and austenite directly transformed to martensite as the annealing temperature exceeded 550oC. When R-phase appends to austenite and martensite, several thermomechanical behaviors of an SMA may be affected [18, 19, 20, 21, 22 and 23]. Yeung et al. [24] found that phase transition temperatures can be manipulated by adjusting heat treatment parameters including duration, temperature and cooling rate. Liu et al. [25] showed that the austenite final temperature (Af) mostly increases after ageing. Eggeler et al. [26]
3
realized that, in general, the transformation temperatures increase as the aging time increases. Sadiq et al. [27] investigated the effect of annealing temperature on the transformation temperatures. They found that, after annealing NiTi alloy above the recrystallization temperature, the R-phase disappears so that direct transformation from austenite to martensite takes place. The transformation temperatures increase as the annealing temperature increases; however, the R-phase transforms at lower temperatures. Wang et al. [28] investigated the microstructure, martensitic transformation, shape memory effect and superelastic property of Ti49.6Ni45.1Cu5Cr0.3 alloy. They concluded that, in the course of elevating the annealing temperature, the transformation temperatures increased for annealing temperatures in the range of 623 K to 873 K. Then, they decreased for the temperature range of 873 K to 1023 K and did not considerably vary after 1023 K until 1273 K. Heidari et al. [8] fabricated SMA helical springs by shapesetting NiTi wires and evaluated thermomechanical characteristics of their products. They found that transformation temperatures of the fabricated springs increase as the annealing temperature increases; however, the start and final temperatures of the R-phase transition decrease so that the R-phase eventually disappears at the annealing temperature of 600°C. Motemani et al. [29] studied the effect of cooling rate on the phase transformation and mechanical properties of Nirich NiTi shape memory alloy. They realized that austenite final temperature Af increases as cooling rate decreases while the martensite final temperature Mf reduces. Consequently, a furnace-cooled sample has the highest phase transformation hysteresis (Af–Mf) compared to samples with lower cooling rates. Mitwally and Farag [30] studied the effect of cold work on superelasticity, shape memory effect and hardness of NiTi alloy. They found that the shape memory recovery is diminished by cold rolling as well as bending. Lin and Wu [31] observed that, by augmenting the extent of applied cold work, the products would show lower residual strains upon unloading. Grossmann et al. [32] proposed a procedure to fabricate an SMA spring and to characterize its microstructural evolution during the production. Costanza et al. [33] investigated shape memory effect in Ni-Ti springs and presented a technique to design a linear actuator made of SMAs. Follador et al. [3] fabricated an SMA spring actuator. They further described the mechanical characteristics of the SMA spring by a simple linear-elastic model whose parameters depend on the crystalline characteristics. In most of the available works on fabrication of SMA springs, the products are martensitic at the ambient temperature. Moreover, the influences of all shape-setting parameters on transformation temperatures of the fabricated springs are not thoroughly investigated. Since pseudoelastic SMA springs at the ambient temperatures are vastly required, in this paper, the main purpose is to fabricate austenitic springs using shape memory alloy wires. Two types of NiTi (Ti-55.87 at % Ni) wires (one of which is martensitic at ambient temperature and the other is austenitic) are utilized. The wires are wound and locked on a screw and are then heat treated at temperatures within the range of 300 to 1000oC for 5 to 1260 minutes. The effects of various production parameters such as cold work, heat treatment temperature and duration, and the subsequent cooling rate on transformation temperatures of the fabricated springs are further investigated. 2.
Materials and Methods
The present investigation is carried out on commercial SMA wires provided by Memry Co. with the nominal composition of Ti-55.87%Ni and the diameter of 1.5 mm. Two types of wires, one with shape memory effect (SME) and the other with pseudoelasticity (PE) at the ambient temperature, were utilized. Fig. 1 and Fig. 2 illustrate results of Differential scanning calorimetry (DSC), and Table 1 shows the transformation temperatures of these wires. To fabricate springs using SME and PE wires, according to Fig. 3, each wire was first wound and locked on a screw. Once temperature of the furnace has reached a desired number, the specimen was placed in the furnace for the required time interval. Then, the specimen was cooled down. To prevent oxidation of the specimens, the whole wound wire together with the fastening components were covered by a stainless steel foil. Heat treatments were performed on the fabricated springs at different conditions so that various combinations of the influential parameters were examined. For instance, the springs S-11, S-12 and S-13 were made using SME wire by heat treating at 750oC for 10 minutes; the samples S-11and S-13 were quenched in water-ice bath, but S-12 was quenched in dry-ice bath. Cold work was performed on S-13, but specimens S-11 and S-12 were fabricated with no cold work. Sample S-14
4
indicates the SME wire which was heat treated at 1000oC for 10 minutes and finally was quenched in water-ice bath. For fabricating the spring S-15, sample S-14 was first wound and locked on the screw; then, it was heat treated at 1000oC for 10 minutes. Eventually, quenching in water-ice bath was performed. This procedure of heat treatment followed by quenching was repeated to fabricate spring S-16 from S-15. A summary of heat treatment temperatures, duration, and cooling method is given in Appendix 1. DSC tests were used to determine the transformation temperatures of the products. DSC samples were cut into 30-50 mg in mass, and the tests were performed at the heating/cooling rate of 5oC/min between -50oC and +150oC.
Fig. 1. Transformation temperatures for SME wire.
Fig. 2. Transformation temperatures for PE wire.
5
Table 1. Transformation temperatures of the utilized wires. Initial wire
Af ( oC)
As ( oC)
Rs ( oC)
Rf ( oC)
Ms ( oC)
Mf ( oC)
SME wire
64.00
43.63
50.00
28.00
8.00
-26.00
PE wire
15.00
-5.00
17.30
-10.00
-45.00
Fig. 3. Constrained SMA wire on a screw. To induce a thermal shock in order to reduce transformation temperatures of samples S-13 and S-16, heat treatment without using stainless steel foil was carried out in three stages as follows: 1. Heat treatment for the initial wire at the required temperature followed by quenching in water-ice bath 2. Wounding the heat-treated wire on the screw followed by quenching in water-ice bath 3. Heat treatment of the fabricated spring followed by quenching in water-ice bath Additionally, cold work was carried out on some of the samples in order to obtain desirable transformation temperatures. To this end, cold rolling was used to reduce thickness by the amounts of 3.5% and 32.1%. A wide range of temperatures from 300oC to 1000oC was chosen for the shape-setting; however, in order to prevent oxidation of the samples, heat treatment at lower temperatures is more preferred. 3.
Results and discussion
In this section, the effects of temperature and duration of the heat treatments, cooling rate, and cold work on the transformation temperatures of the products are investigated. Transformation temperatures of the products are given in Appendix 2. Since the utilized instrument was limited to the minimum temperature of -50oC, determination of Mf and Ms for some specimens was not possible. Fig. 4 shows one of these cases for sample S-09. R-phase transition occurs for most of the specimens (for instance, in Fig. 5 where DSC curve of sample S-13 is shown) while it is not seen for some specimens (for instance, in sample S-24 whose DSC curve is shown in Fig. 6). Samples S-18, S-19, S20, S-21, S-22 and 23 were pseudoelastic springs at the room temperature while the other ones showed shape memory effect. Fig. 7 illustrates one of the fabricated pseudoelastic springs from two different views. As shown in Appendix 2, the austenitic transformation temperatures of specimens S-18, S-19, S-20 and S-22 are lower than the ambient temperature. It should be noted that sample S-21 is similar to S-22 with this difference that sample S-21 was placed into quartz capsule under vacuum to prevent from oxidation as much as possible. The specimen S-23 was heat treated to find the lowest applicable temperature for achieving pseudoelastic spring. Accordingly, 630oC was the minimum temperature to optimize the process of fabricating a pseudoelastic spring with the PE wire. Samples S-21 and S-23 were mechanically shown to be pseudoelastic: they were examined under inelastic stretch followed by inelastic compression and could return to their original configuration after unloading. The samples S24, S-25 and S-26 are 32.1% cold-worked SME wires.
6
Fig. 4. Transformation temperatures for sample S-09.
Fig. 5. Transformation temperatures for sample S-13.
7
Fig. 6. Transformation temperatures for sample S-24.
Fig. 7. A fabricated pseudoelastic helical spring. As formerly indicated, in some specimens, the reverse transformation (during heating cycle) occurs in two stages: from martensite to an intermediate R-phase and then to austenite. Similarly, for some samples, the forward transformation (during cooling cycle) occurs in two stages: from austenite (parent phase) to R-phase and then to martensite. Table 2 shows transformation temperatures of R-phase during heating cycle for such specimens. Table 2. Transformation temperatures of Rhombohedral phase during heating cycle. Specimen Code
Rs ( oC)
Rf ( oC)
S-18
-7
7
S-19
-7
4
S-20
-10
5
S-24
55
66
S-25
53
68
S-26
52
66
8
Since pseudoelastic springs are planned to be manufactured in the present work, Af of the products should be lower than the ambient temperature. Therefore, the effects of various parameters on the austenite transformation temperatures are investigated in the following subsections. 3.1.
Influence of heat treatment on the transformation temperatures
Heat treatment parameters including temperature, cooling rate, and the duration affect transformation temperatures of the fabricated springs. Here, the findings of this work are presented. 3.1.1
Effect of heat treatment temperature
Fig. 8 shows the influence of heat treatment temperature on austenite transformation temperatures of the springs fabricated by using the SME wire. It is seen that transformation temperatures increase with increment in the heat treatment temperature. Moreover, for the manufactured spring at the minimum temperature of 750oC, As and Af are higher than the ambient temperature. The rapid growth of Af with increase in the heat treatment temperature indicates that fabrication of pseudoelastic spring with SME wire is impossible at these conditions.
Fig. 8. Effect of heat treatment temperature on the transformation temperatures for a spring made from SME wire.
Fig. 9. Effect of heat treatment temperature on the transformation temperatures of samples manufactured using PE wire.
9
Variations of the transformation temperatures for the springs made from PE wire with heat treatment temperature are shown in Fig. 9. It is observed that the transformation temperatures strongly depend on the heat treatment temperature. According to this figure, there are three trends for variations in the transformation temperatures: 1- Transformation temperatures are enhanced by elevating the heat treatment temperature until 500oC. 2- Transformation temperatures, except Ms, reduce by increasing the heat treatment temperature between 550oC to 650oC. 3- Transformation temperatures except Rs and Rf are nearly constant with increase in the heat treatment temperature beyond 650oC until 750oC. In fact, with further addition of the heat treatment temperature, transformation temperatures remain fairly constant. This is why heat treatment at temperatures above 650oC results in pseudoelastic products. 3.1.2. Effect of cooling rate According to the provided data in Appendix 2, comparison between the transformation temperatures of specimens S-19 and S-22 and between those of S-10 to S-12 indicates that transformation temperatures of the products mostly decrease when quenching in water-ice bath is done instead of cooling in the furnace for both series of springs made using PE and SME wires. However, by comparing the samples S-11 and S-12, it is seen that Mf increases by increasing the cooling rate. This trend coincides with the findings of investigations carried out by Motemani et al. [29] on Ni-rich Ni-Ti shape memory alloys. In other words, the furnace-cooled specimen has the highest phase transformation hysteresis (Af–Mf) compared to the other samples. Increase in transformation temperatures for the quenched sample in dry ice, compared to the sample quenched in water-ice, is due to the application of the steel foil to prevent oxidation of the parts. When the sample cools in water-ice, since the steel foil is not completely sealed, water may leak during the cooling time. Consequently, cooling using dry ice is performed more gradually. 3.1.3.
Effect of heat treatment duration
Variations of the austenite transformation temperatures with the duration of heat treatment for springs made from the SME wire are shown in Fig. 10. As is seen, As and Af first increase slightly with increase in the heat treatment duration. Then, by more prolonging the heat treatment, their increase is suppressed so that As reduces a little. Fig. 11 shows the effect of heat treatment time on the transformation temperatures for springs made from the PE wire. It is seen that increase in duration of the heat treatment leads to a very negligible rise in As and Af compared to the observed increase for the springs made of the SME wire. Moreover, the effect of heat treatment duration on transformation temperatures is less than that of the other production parameters.
10
Fig. 10. Effect of heat treatment duration on the transformation temperatures of sample springs made from SME wire.
Fig. 11. Effect of heat treatment duration on the transformation temperatures of springs made from PE wire. 3.2. Effect of cold work Using a flat rolling machine, the SME wire with the initial diameter of 1.5 mm was cold-rolled to achieve a 0.75 mm-thick strip. The cold-rolled specimen was further wound and locked on a screw. Then, the prepared spring was heat treated at 750oC for 10 minutes followed by quenching in water-ice bath. Specimen S-13 was manufactured with the use of a 3.5 % cold-worked SME wire. According to Appendix 2, comparison of transformation temperatures for samples S-11 and S-13 indicates that the SME wire becomes austenitic at the room temperature when the cold work percentage increases to 32.1 %. Moreover, transformation temperatures of 32.1 % cold-worked wires S-24 to S-26 are generally higher than those of the as-received wire. This is in agreement with the findings reported by Mitwally and Farag [30].
11
According to the findings of this work, the effects of various shape-setting stages on transformation temperatures for the fabricated samples using PE wire are schematically illustrated in Fig. 12. By elevating the heat treatment temperature, the transformation temperatures increase and then decrease. Consequently, in early stages of annealing when the temperature is not high enough, the possibility of achieving pseudoelastic parts may be lessen even with the use of initially austenitic wires. In other words, if one needs to reduce transformation temperatures after annealing, the set temperature is recommended to be as high as possible. A more pronounced cooling rate gives rise to decrease in transformation temperatures; thus, severe cooling such as quenching is beneficial when pseudoelastic products are desirable. Cold work on the specimens leads to rise in transformation temperatures; therefore, such processes may be useful in achieving martensitic parts and are not recommended when austenitic products are desired.
Fig. 12. Schematic illustration of the effect of various parameters on transformation temperatures for springs sample made of PE wire. 4. Conclusions In this paper, pseudoelastic helical springs were manufactured by shape-setting two types of NiTi wires: one was martensitic at the ambient temperature and the other one was austenitic. The effects of various stages such as cold work, heat treatment temperature and duration, and the subsequent cooling rate on the transformation temperatures of the products were investigated. The main results obtained in this research can be summarized as follows: - Heat treatment duration has the less effect on the transformation temperatures than the other adjustments of a shape-setting process. - Transformation temperatures of the springs fabricated using the SME wire increase as the heat treatment temperature increases. However, for samples manufactured using PE wire, transformation temperatures first increase and then decrease with increase in the heat treatment temperature. - Increase in cooling rate result in decrease in Af which is beneficial to fabricate PE springs at the ambient temperature. - Cold work leads to rise in transformation temperatures especially Af. Depending on the desired type of product with either pseudoelasticity or shape memory effect, the presented
12
findings regarding the effects of various shape-setting stages on transformation temperatures of an SMA spring can be considered as guidelines for a manufacturer who wishes to fabricate SMA springs with a predefined phase (austenite or martensite) at the ambient temperature. Metallurgical investigations will improve the present understanding, and such studies will be planned for further investigations. In addition to the procedures used in current study, various thermomechanical treatments cause a well-developed dislocation sub-structure or nanocrystalline structure and may be used for improving the properties of SMAs in future works.
5. References [1] SH. Youn, YS. Jang, JH. Han. Development of a three-axis hybrid mesh isolator using the pseudoelasticity of a shape memory alloy. Smart Materials and Structures. 20(7) (2011) 075017. https:// doi.org/10.1088/09641726/20/7/075017. [2] KK. Alaneme, S. Umar. Mechanical behaviour and damping properties of Ni modified Cu–Zn–Al shape memory alloys, Journal of Science: Advanced Materials and Devices. 3(3) (2018) 371-379. https:// doi.org/10.1016/j.jsamd.2018.05.002. [3] M. Follador, M. Cianchetti, A. Arienti, C. Laschi. A general method for the design and fabrication of shape memory alloy active spring actuators. Smart Materials and Structures. 21 (2012) 115029-115039. https:// doi.org/ 10.1088/0964-1726/21/11/115029. [4] Y. Toi, JB. Lee, M. Taya. Finite element analysis of superelastic, large deformation behavior of shape memory alloy helical springs. Computers and Structure. 82 (2004) 1685-1693. https://doi.org/10.1016/j.compstruc.2004.03.025. [5] RAA. Aguiar, NA. Savi, PMCL. Pacheco Experimental and numerical investigations of shape memory alloy helical springs. Smart Material and Structures. 19 (2010) 025008-025017. [6] R. Mirzaeifar, R. Desroches, A. Yavari. Exact solution for pure torsion of shape memory alloy circular. Mechanical of Materials. 42 (2010) 797-806. http://doi.org/ 10.1088/0964-1726/19/2/025008. [7] R. Mirzaeifar, R. Desroches, A. Yavari. A combined analytical, numerical, and experimental study of shapememory-alloy helical springs. International Journal of Solids and Structures. 48 (2011) 611-624. https://doi.org/10.1016/j.ijsolstr.2010.10.026. [8] B. Heidari, M. Kadkhodaei, M. Barati, F. Karimzadeh. Fabrication and modeling of shape memory alloy springs. Smart Materials and Structures. 25(12) (2016) 125003. https://doi.org/ 10.1088/0964-1726/25/12/125003. [9] Y. Mohammad Hashemi, M. Kadkhodaei. The Effects of Geometric Parameters under Small and Large Deformations on Dissipative Performance of Shape Memory Alloy Helical Springs, Journal of Stress Analysis. 3 (1) (2018) 69-79. https://doi.org/10.22084/jrstan.2018.17137.1061. [10] SH. Kayani, MI. Khan, FA. Khalid, HY. Kim, S. Miyazaki. Precipitation Behavior of Thermo-Mechanically Treated Ti 50 Ni 20 Au 20 Cu 10 High-Temperature Shape-Memory Alloy. Shape Memory and Superelasticity. 2(1) (2016) 29-36. https://doi.org/10.1007/s40830-015-0048-6. [11] E. Prokofiev, J. Burow, J. Frenzel, D. Gunderov, G. Eggeler, R. Valiev. Phase transformations and functional properties of NiTi alloy with ultrafine-grained structure. Materials Science Forum. (2011) 667–669: 1059-1064. https://doi.org/10.4028/www.scientific.net/MSF.667-669.1059.
13
[12] Sh. Jiang, M. Tang, Y. Zhao, Hu , Y. Zhang, L. Liang. Crystallization of amorphous NiTi shape memory alloy fabricated by severe plastic deformation. Transactions of Nonferrous Metals Society of China. 24 (2014) 1758-1765. https://doi.org/10.1016/S1003-6326(14)63250-7. [13] E. Mohammad Sharifi, A. Kermanpur. Superelastic behavior of nanostructured Ti50Ni48Co2 shape memory alloy with cold rolling processing. Transactions of Nonferrous Metals Society of China. 28 (2018) 1351-1359. https://doi.org/10.1016/S1003-6326(18)64773-9. [14] M. Abbasi, A. Kermanpur, R. Emadi. Effects of Thermo-Mechanical Processing on the Mechanical Properties and Shape Recovery of the Nanostructured Ti50Ni45Cu5 Shape Memory Alloy. Procedia Materials Science. 11 (2015) 61-66. https://doi.org/10.1016/j.mspro.2015.11.089. [15] V. Brailovsky, V. Demers, SD. Prokoshkin, KE. Inaekyan. Functional properties of Nano crystalline, sub microcrystalline and polygonized Ti-Ni alloys processed by cold rolling and post deformation annealing. Journal of Alloys and Compounds. 509 (2011) 2066-2075. https://doi.org/ 10.1016/j.jallcom.2010.10.142. [16] SH. Chang, SK. Wu. Effect of cooling rate on the martensitic transformation of TiNi alloy by differential Scanning Calorimetry and dynamic mechanical analysis. Materials Characterization. 59 (2008) 987-990. https://doi.org/ 10.1016/j.matchar.2007.08.014. [17] ZG. Wang, XT. Zu, XD. Feng, S. Zhu, JM. Zhou, LM. Wang. Annealing-induced evolution of transformation characteristics in TiNi shape memory alloys. Physica B. 353 (2004) 9-14. https://doi.org/ 10.1016/j.physb.2004.08.021. [18] Y. Luo, T. Takagi, S. Maruyama, M. Yamada. A shape memory alloy actuator using Peltier modules and Rphase transition. Journal of Intelligent Material Systems and Structures. 11(7) (2000) 503-511. https://doi.org/10.1106/92YH-9YU9-HVW4-RVKT. [19] M. Tomozawa, HY. Kim, S. Miyazaki. Microactuators using R-phase transformation of sputter-deposited Ti47.3 Ni shape memory alloy thin films. Journal of intelligent material systems and structures. 17(12) (2006) 10491058. https://doi.org/ 10.1177/1045389X06064883. [20] TW. Duerig, K. Bhattacharya. The influence of the R-phase on the superelastic behavior of NiTi. Shape Memory and Superelasticity. 1(2) (2015) 153-161. https://doi.org/ 10.1007/s40830-015-0013-4. [21] D. Chatziathanasiou, Y. Chemisky, F. Meraghni, G. Chatzigeorgiou, E. Patoor. Phase transformation of anisotropic shape memory alloys: Theory and validation in superelasticity. Shape Memory and Superelasticity. 1(3) (2015) 359-374. . https://doi.org/10.1007/s40830-015-0027-y. [22] A. Shamimi, B. Amin-Ahmadi, A. Stebner, T. Duerig. The Effect of Low Temperature Aging and the Evolution of R-Phase in Ni-Rich NiTi. Shape Memory and Superelasticity. 4(4) (2018) 417-427. https://doi.org/10.1007/s40830-018-0193-9. [23] P. Shayanfard, M. Kadkhodaei, S. Safaee. Proposition of R-phase transformation strip in the phase diagram of Ni-Ti shape memory alloy using electromechanical experiments. Journal of Intelligent Material Systems and Structures. 28(19) (2017) 2757-2768. https://doi.org/10.1177/1045389X17698587. [24] KWK. Yeung, KMC. Cheung, WW. Lu, CY. Chung. Optimization of thermal treatment parameters to alter austenitic phase transition temperature of NiTi alloy for medical implant. Materials Science and Engineering A. 383 (2004) 213-218. https://doi.org/10.1016/j.msea.2004.05.063. [25] X. Liu, Y. Wang, D. Yang, M. Qi. The effect of ageing treatment on shape-setting and superelasticity of a nitinol stent. Materials Characterization. 59 (2008) 402-406. https://doi.org/ 10.1016/j.matchar.2007.02.007. [26] G. Eggeler, J. Khalil-Allafi, S. Gollerthan, C. Somsen, W. Schmahl, D. Sheptyakov. On the effect of aging on
14
martensitic transformations in Ni-rich NiTi shape memory alloys. Smart Materials and Structures. 14 (2005) 186– 91. https://doi.org/ 10.1088/0964-1726/14/5/002. [27] H. Sadiq, MB. Wong, R. Al-Maghaidi, XL. Zhao. The effects of heat treatment on the recovery stresses of shape memory alloys. Smart Materials and Structures. 19 (2010) 035021-035028. https://doi.org/ 10.1088/09641726/19/3/035021. [28] QY. Wang, YF. Zheng, Y. Liu. Microstructure, martensitic transformation and superelasticity of Ti49.6Ni45.1Cu5Cr0.3 shape memory alloy. Materials Letters. 65 (2011) 74-77. https://doi.org/10.1016/j.matlet.2010.09.036. [29] Y. Motemani, M. Nili-Ahmadabadi, MJ. Tan, M. Bornapour, Sh. Rayagan. Effect of cooling rate on the phase transformation behavior and mechanical properties of Ni-rich NiTi shape memory alloy. Journal of Alloys and Compounds. 469 (2009) 164-168. https://doi.org/10.1016/j.jallcom.2008.01.153. [30] ME. Mitwally, M. Farag. Effect of cold work on the behavior of NiTi shape memory alloy. In Advances in Biomedical and Biomimetic Materials, Editors .J. Narayan P.N. Kumta W.R. Wagner, The American Ceramic Society. (2009) 59-70. https://doi.org/ 10.1002/9780470538357.ch6. [31] HC. Lin, SK. Wu. The tensile behavior of a cold-rolled and reverse-transformed equitaomic TiNi alloy. Acta Metallurgica et Materialia. 42 (1994) 1623-1630. https://doi.org/10.3390/ma10070704. [32] C. Grossmann, J. Frenzel, V. Sampath, T. Depka, A. Oppenkowski, C. Somsen, K. Neuking, W. Theisen, G. Eggeler. Processing and property assessment of NiTi and NiTiCu shape memory actuator springs. Materialwiss. Werkstofftech. 39 (2008) 499-510. https://doi.org/10.1002/mawe.200800271. [33] G. Costanza, ME. Tata, C. Calisti. Nitinol one-way shape memory springs, Thermomechanical. and actuator design. Sens. Actuators A. 157 (2010) 113-117. https://doi.org/10.1016/j.sna.2009.11.008.
15
Appendix 1. Summary of Heat Transfer Conditions Specimen
Heat Treatment
Heat Treatment
Temperature (oC)
Duration (min)
Material Code Code
Cooling Method
S-01
SME
300
25
Ambient Temperature
S-02
SME
300
180
Ambient Temperature
S-03
SME
300
300
Ambient Temperature
S-04
SME
300
480
Ambient Temperature
S-05
SME
300
780
Ambient Temperature
S-06
SME
300
1260
Ambient Temperature
S-07
SME
400
780
Ambient Temperature
S-08
SME
868
10
Cooled in Furnace
S-09
SME
868
10
Quenched in water-ice bath
S-10
SME
750
10
Cooled in Furnace
S-11
SME
750
10
Quenched in water-ice bath
S-12
SME
750
10
Quenched in dry-ice bath
S-13
SME
750
10
Quenched in water-ice bath
S-14
SME
1000
10
Quenched in water-ice bath
S-15
SME
1000
10
Quenched in water-ice bath
S-16
SME
1000
10
Quenched in water-ice bath
S-17
PE
600
1260
Ambient Temperature
S-18
PE
750
1260
Cooled in Furnace
S-19
PE
750
10
Cooled in Furnace
S-20
PE
650
10
Cooled in Furnace
S-21
PE
750
10
Quenched in water-ice bath (Quartz Capsule) S-22
PE
750
10
Quenched in water-ice bath
S-23
PE
630
10
Quenched in water-ice bath
16
S-24
SME
750
10
Quenched in water-ice bath
S-25
SME
750
10
Quenched in liquid N2 bath
S-26
SME
1000
10
Quenched in liquid N2 bath
17
Appendix 2. Transformation temperatures of selected specimens Specimen Af ( oC)
As ( oC)
Rs ( oC)
Rf ( oC)
Ms ( oC)
Mf ( oC)
S-09
64
44
34
5
S-10
71
47.5
34
10
S-11
57.18
32.50
45
20
14
-20
S-12
58
37.5
48
22.5
17.5
-17
S-13
58
28
45
20
12.5
-25
S-14
69.51
45
33
-4
S-15
70
45.38
27.50
7.50
S-16
72.68
32.50
36
16
S-17
41
17.5
24
3
-1
-27.5
S-18
20
10
39
-7.5
-31
S-19
16
7
22
-6
-39
S-20
14
7
7.5
-1.5
-36
S-22
-7.5
-25
-28
S-24
77.5
74
42.5
28
S-25
77.5
75
42.5
27.5
S-26
77.5
74
42
22.5
code
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: