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Compressive behavior of NiTi-based composites reinforced with alumina nanoparticles
Accepted Manuscript Compressive behavior of NiTi-based composites reinforced with alumina nanoparticles Mohammad Farvizi, Mohammad Reza Akbarpour, Dong-Hyun Ahn, Hyoung Seop Kim PII:
S0925-8388(16)32032-1
DOI:
10.1016/j.jallcom.2016.06.299
Reference:
JALCOM 38168
To appear in:
Journal of Alloys and Compounds
Received Date: 3 April 2016 Revised Date:
30 June 2016
Accepted Date: 30 June 2016
Please cite this article as: M. Farvizi, M.R. Akbarpour, D.-H. Ahn, H.S. Kim, Compressive behavior of NiTi-based composites reinforced with alumina nanoparticles, Journal of Alloys and Compounds (2016), doi: 10.1016/j.jallcom.2016.06.299. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.
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Compressive behavior of NiTi-based composites reinforced with alumina nanoparticles Mohammad Farvizi*a, Mohammad Reza Akbarpour b, Dong-Hyun Ahn c, Hyoung Seop Kim c a
Ceramic Division, Materials and Energy Research Center, Karaj, P.O. Box 31787-316, Iran Department of Materials Engineering, Faculty of Engineering, University of Maragheh, Maragheh, Iran c Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, 790-784, South Korea
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b
*
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Corresponding author: M. Farvizi Email: [email protected], [email protected] Fax: +98-21-88773352; Tel: +98-935 848 5439
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Abstract
NiTi alloys are extensively used in various industrial applications. However, to enhance the performance of this alloy in applications, its mechanical properties should be improved. In previous research, the effect of addition of ceramic microparticles on the mechanical properties of a NiTi matrix has been explored. In this study, to improve the mechanical properties of NiTi,
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small fractions of alumina nanoparticles were used as reinforcement. The compressive stressstrain curves of the NiTi and NiTi-2Al2O3 samples demonstrated well-known four-stage behavior with double yielding. Moreover, it was found that the addition of 2 wt% alumina nanoparticles enhanced the elastic modulus, shortened the first plateau region, and reduced the
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fracture strain, compared to the unreinforced NiTi sample. Increasing alumina nanoparticle contents to 6 wt% completely changed the mechanical behavior of this composite: considerable elasticity, followed by a short plateau region, and fracture. The high resolution transmission
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electron microscopy images showed that, a high fraction of dislocations in the vicinity of nanoparticles can be generated in NiTi, which seems to lock the matrix in the NiTi-6Al2O3 sample. Fracture surface analysis using scanning electron microscopy showed dimple features in the NiTi and NiTi-2Al2O3 samples and a smooth and brittle appearance in the NiTi-6Al2O3 sample. Keywords: NiTi; Nano alumina; Compressive test; HRTEM; Fracture surface.
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1. Introduction Recently, Ti-Ni based alloys have become widely used in various industrial applications due to their unique properties (e.g., shape memory effect (SME), pseudoelasticity (PE),
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biocompatibility, and corrosion and wear resistance) [1-4]. Among the various properties of NiTi, SME and PE have attracted great attention. These properties originate from a reversible thermoelastic martensitic transformation between a high temperature B2-NiTi phase (known as austenite) and a low temperature B19′ NiTi phase (known as martensite). During NiTi cooling
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cycles, martensitic transformation starts at a characteristic temperature, known as Ms, and it is completed at Mf (martensite finish temperature). Reverse martensitic transformation takes place during heating cycles. This transformation starts at a temperature known as As in which the low
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temperature martensite phase starts to transform to the high temperature B2 phase and this transformation completes at Af temperature (austenite finish temperature) [5]. These transformation temperatures are dependent on many factors, including the chemical composition of the NiTi alloy (Ni/Ti ratio) and (internal or external) stresses [5]. The mechanical response of a NiTi alloy is directly related to its phase constituents and test temperature [6].
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Under ideal condition, the stress-strain curves of NiTi during compressive and tensile tests can be divided into four regions: (i) initial linear region which corresponds to the elastic deformations of austenite and martensite phases; (ii) pseudoelastic/pseudoplastic region in which stress induced martensite (SIM) formation occurs in the case of pseudoelasticity effect and
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moving of twin boundaries happens for pseudoplasticity. This region is recognized as a plateaulike feature; (iii) in the third region, SIM martensite phases or detwinned martensite variants are
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elastically deformed; and (iv) finally, in the fourth region, NiTi deforms plastically before it fractures [[7, 8]. At temperatures higher than Md, the highest possible temperature for SIMs formation, the NiTi alloy deforms like normal alloys and does not show any typical plateau. One of the most important issues to resolve to enhance the industrial applicability of NiTi alloys is improvement of their mechanical properties. For example, Ni4Ti3 precipitates are formed using an appropriate aging heat treatment of the Ni-rich NiTi alloy, which can enhance the mechanical properties of the alloy [5]. However, this heat treatment reduces the Ni-content of the matrix and consequently alters the martensitic transformation temperatures [9]. Another approach that can be used to improve the mechanical properties of NiTi alloys is using secondary 2
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hard ceramic particles. The deformation behavior and microstructure of NiTi-based composites reinforced with TiC microparticles, in both austenitic and martensitic states, are well studied by Dunand et al. [10-12] and Vaidyanathan et al. [13, 14]. The effect of carbon nanotubes on the tensile properties of the NiTi-based composites [15], and the effect of nano SiC additives on the
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mechanical properties of porous NiTi [16] have been investigated. In these studies, the reinforcing ceramic particles reacted with the matrix, which can alter the Ni/Ti ratio and affect transformation temperatures. Recently, we demonstrated that using small fractions of alumina nanoparticles can considerably enhance the wear resistance of the NiTi matrix [17, 18]. Also, the
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microstructural aspects of NiTi-nano alumina composites have been studied [19].
In this paper, we report the effects from adding small fractions of alumina nanoparticles on
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the compressive behavior of NiTi-based composites prepared using hot isostatic pressing (HIP).
2. Materials and Methods 2.1 Materials Description
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Previous studies [20-23] have shown that using elemental Ni and Ti powders for the preparation of NiTi can yield to the formation of stable intermetallics (Ni3Ti and NiTi2) of the Ti-Ni system. In order to reduce this side effect, in the current study, prealloyed NiTi powders with the exact composition of Ti (44 wt%)-Ni (56 wt%) were used as the matrix. The
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transformation temperatures of the prealloyed NiTi powders, which were determined using the differential scanning calorimetry (DSC) technique, are as follows: Ms 3°C, Mf -22°C, As 6°C,
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and Af 28°C. For reinforcement, 0 to 6 wt% α-Al2O3 nanoparticles with an average diameter of 80 nm, was used.
2.2 Sample Preparation
NiTi-nano Al2O3 composite powders were prepared using planetary ball milling in a stainless steel vial under argon gas. During all experiments, the rotational speed and ball-topowder weight ratio were 300 rpm and 10:1, respectively [24]. After preparing the composite 3
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powders from the prealloyed NiTi and alumina nanopowders, the consolidation process was performed using the hot isostatic pressing (HIP) method. The HIP process was performed at the temperature of 1065°C and pressure of 100 MPa for 3h [25]. After the HIP process, the samples were carefully mechanically polished using abrasive papers. The relative density of the samples
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measured using the Archimedes method, was about 98% of theoretical density.
2.3 Mechanical tests
Compressive tests were conducted on cylindrical samples (7.2 mm thick, diameter of 6
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mm) using an Instron 8862 machine (INSTRON, Norwood, MA, USA) at room temperature (23°C). The strain rate was 510-4 s-1 during all tests. The ARAMIS 5M optical strain gauge
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system was employed during the compression tests to attain precise strains.
2.4. Characterization
X-ray diffraction (XRD) analysis was performed on all the samples using a D8 Advanced Bruker diffractometer with Cu Ka radiation (λ = 0.154 nm at 20 kV and 30 mA) with a step size
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of 0.016°. The fracture surface of the samples was studied using a scanning electron microscope (SEM: JSPM-5400, JEOL, Japan) to clarify the fracture mechanism. A scanning transmission electron microscope (CS-corrected STEM, JEM-2100F, JEOL, Japan) operated at 200 kV was used to study the structure of the samples. Specimens were prepared for high resolution
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transmission electron microscopy (HRTEM) by mechanical grinding, dimpling, and ion milling.
3. Results and discussion
3.1 Microstructural studies
Figure 1 exhibits the results of XRD analysis of the HIP-consolidated samples. In our
previous investigation [19], the microstructure and transformational behavior of the NiTi-based composites were studied. It was observed that the addition of alumina nanoparticles enhanced the intensity of the B19′ phase and reduced the intensity of the B2 phase in the corresponding XRD patterns. Also, small peaks related to the NiTi2 and Ni3Ti intermetallics appeared in the XRD 4
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pattern of the NiTi-6Al2O3 sample. In the XRD pattern of the NiTi-2Al2O3 sample, NiTi2 /Ni3Ti peaks were not detected, which shows that their content was below the detection limit of XRD (small fractions of stable intermetallics were observed in the SEM studies). A possible explanation for the formation of these intermetallics can be found in Ref. [19]. Investigation of
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the samples using the DSC technique [19] showed that the transformation temperatures increased after addition of nano alumina particles, which could be attributed to alteration of the Ni/Ti ratio due to the formation of NiTi2/Ni3Ti intermetallics and internal stresses originating from mismatch and misfit stresses. Also, the enthalpy of martensitic transformation decreased from 23
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J/g for pure NiTi to about 4.3 J/g for NiTi-6Al2O3 sample which shows that only a small fraction of B2 austenite phase can participate in transformation and a large fraction of B2 phase remains
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in an untransformed condition [19]. So, in the XRD pattern of NiTi-6Al2O3 sample both of untransformed austenite and transformed martensite phases coexists. The phase constituents of the samples indicated by the present XRD and DSC results are summarized in Table 1.
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Fig. 1. Results of XRD analysis of the HIP-consolidated samples
Table 1. Summary of the XRD and DSC results performed on the HIP-consolidated samples. The
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phase contents of the samples were obtained using the Rietveld method (presented in Fig. 1).
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3.2 Mechanical properties
In order to understand the role of addition of alumina nanoparticles on the compressive
stress-strain behavior of NiTi matrix composites, compression tests were conducted on the HIPNiTi (hereafter named NiTi), HIP-NiTi-2 wt% nano alumina (named NiTi-2Al2O3), and HIPNiTi-6 wt% nano alumina (named NiTi-6Al2O3) samples. Figure 2 shows the stress-strain curves of the samples. The results of the mechanical properties of the samples from Fig. 2 are summarized in Table 2. It can be seen that the pure NiTi and NiTi-2Al2O3 samples exhibit typical four-stage stress-strain curves with double yield points on the related curves. According to the data obtained from the DSC and XRD tests, these samples mainly consist of B2-NiTi and B19′5
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NiTi phases. However, because of higher transformation temperatures in the NiTi-2Al2O3 sample, the amount of martensitic B19′ phase in this sample is more than that in the pure NiTi sample. In the case of pure NiTi sample, no other intermetallics were found, but small sample fractions of NiTi2 and Ni3Ti phases were observed in NiTi-2Al2O3 during the microscopy
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studies. Meanwhile, the peaks related to the intermetallics were not found in the XRD pattern of this sample. A comparison between the stress-strain curves of the NiTi and NiTi-2Al2O3 samples shows that there are four differences: (i) the NiTi-2Al2O3 sample shows higher first yield strength (σ
trans)
in comparison with the pure NiTi sample; (ii) elastic modulus of the NiTi-
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2Al2O3 sample was higher than that of the NiTi sample; (iii) the first plateau region in the NiTi2Al2O3 sample is shorter than in the NiTi sample; and (iv) the fracture of the NiTi-2Al2O3
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sample occurred at lower strains. The phase constituents of these two samples mainly consist of B2-B19′ phases at the test temperature. From this, it can be concluded that the stress required for the formation of stress-induced martensite phase from the B2 phase, and martensite reorientation in the NiTi-2Al2O3 composite sample, is higher than that in the pure NiTi sample. In addition, the shorter plateau region in the NiTi-2Al2O3 sample confirms that a smaller fraction of the B2/B19′ phases can participate in the SIM formation/detwinning processes. This phenomenon shows that
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the addition of nanoparticles can produce strong reinforcement against martensite detwinning and formation of SIMs processes. This yielded increase in the elastic modulus and shortening of the plateau region in the corresponding stress-strain curve of the composite samples reinforced with 2 wt% of alumina nanoparticles.
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Interestingly, the NiTi-6Al2O3 composite sample exhibited completely different behavior during the compression test than the two other samples. This sample deformed elastically until
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the stress of 2371 MPa followed by a small plastic deformation, and then it fractured. To figure out the origin of this behavior, the microstructure of the NiTi-6Al2O3 sample was explored using HRTEM analysis (figure 3). It was observed that, a high density of dislocations was generated in the NiTi matrix in the vicinity of the nanoparticles. According to previous investigation [11], the NiTi matrix showed the well-known plateau region with the addition of 20 wt% TiC microparticles (particle size 44-100 µm). However, in this study, the addition of 6 wt% alumina nanoparticles
and
the
formation
of
NiTi2/Ni3Ti
intermetallics
affected
the
NiTi
pseudoelastic/pseudoplastic behavior. As a consequence, a large fraction of austenite and martensite phases cannot participate in the SIM formation and detwinning processes, which 6
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yielded a short plateau region and a premature fracture. In other words, it seems that the reinforcement particle size and weight percentage has considerable influence on the NiTi matrix properties. With the addition of secondary microparticles, the NiTi matrix can accommodate interfacial stresses [11], but, as was observed in this study, using nanoparticles will influence a
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higher volume fraction of NiTi which leads to formation of a high-density of dislocations in the matrix. These dislocations lock NiTi matrix and makes it susceptible to brittle fracture. It should be
noted
that
while
the
NiTi-6Al2O3
sample
did
not
exhibit
considerable
pseudoelastic/pseudoplastic behavior during the compression test, this sample showed a
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satisfactory η ratio during indentation tests, which yielded a high wear resistance for this sample
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[18].
Fig. 2. Stress- strain curves for HIP-consolidated samples under compression.
Fig. 3. HRTEM image taken from NiTi-6Al2O3 composite sample showing high number of
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dislocations in the (110) plane of B2 phase in the vicinity of nano alumina particles.
The SEM microfractography analyses of the fracture surfaces of the NiTi sample are
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presented in Fig. 4 (a, b). It is observed that the fracture surface of the pure NiTi sample contains typical dimple features, which show that this sample deforms plastically during the compression tests. The fracture surface of the NiTi-2Al2O3 samples are shown in Fig. 4(c, d). It is seen that,
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dimples in the fracture surface of this sample became shallower and in some areas, brittle cleavage features appeared. The fracture surface images of the NiTi-6Al2O3 sample represented in Fig.4 (e, f) shows a smooth appearance, which indicates a brittle fracture mode.
Fig. 4. Fracture surface of (a, b) NiTi, (c, d) NiTi-2Al2O3 and (e, f) NiTi-6Al2O3 samples after compression test at room temperature
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4. Conclusions In this study, the stress-strain behavior of NiTi matrix composites reinforced with small fractions of alumina nanoparticles was investigated. The NiTi and NiTi-2Al2O3 samples showed well-known four-stage stress-strain curves. It was observed that the addition of 2 wt% nano alumina to the NiTi matrix enhanced the elastic modulus of the NiTi matrix and shortened the
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first plateau region. Fracture occurred under smaller strains in this sample compared to the unreinforced sample. In the case of NiTi matrix reinforced with 6 wt% alumina nanoparticles,
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the composite behavior was completely different: it deformed elastically, had a short plateau region, and fractured. According to these microstructural studies, a high density of dislocations formed in the vicinity of the nanoparticles locked the NiTi matrix, and affected the stressinduced martensite formation and detwinning processes. Fractography analysis using SEM showed that, the NiTi-6Al2O3 composite samples showed a smooth fracture surface (indicating a
5. Acknowledgements
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tendency to brittle fracture), while the fracture surface of NiTi contained dimple features.
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This work was supported by the National Research Foundation of Korea (NRF) grant funded by
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the Korea government (MSIP) (No. 2014R1A2A1A10051322).
6. References
[1] B.T. Lester, T. Baxevanis, Y. Chemisky, D.C. Lagoudas, Review and perspectives: shape memory alloy composite systems, Acta Mech., 226(12) (2015) 3907-3960. [2] S. Hattori, A. Tainaka, Cavitation erosion of Ti–Ni base shape memory alloys, Wear 262 (2007) 191-197. [3] J. Khalil-Allafi, B. Amin-Ahmadi, M. Zare, Biocompatibility and corrosion behavior of the shape memory NiTi alloy in the physiological environments simulated with body fluids for medical applications, Mater. Sci. Eng. C. 30(2010) 1112-1117.
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[4] M. Farvizi, M. R. Akbarpour, E.Y. Yoon, H.S. Kim, Effect of high-pressure torsion on the microstructure and wear behavior of NiTi alloy, Met. Mater. Int. 21(5)(2015) 891-896. [5] K. Otsuka, X. Ren, Physical metallurgy of Ti-Ni-based shape memory alloys, Prog. Mater. Sci. 50 (2005) 511-
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678. [6] J.M.G. Fuentes, P. Gümpel, J. Strittmatter, Phase Change Behavior of Nitinol Shape Memory Alloys, Adv. Eng. Matter., 4(7) (2002) 437-451.
[7] K. Johansen, H. Voggenreiter, G. Eggeler, On the effect of TiC particles on the tensile properties and on the
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intrinsic two way effect of NiTi shape memory alloys produced by powder metallurgy, Mater. Sci. Eng. A 273– 275(1999) 410–414
[8] L. Krone, E. Schüller, M. Bram, O. Hamed, H.-P. Buchkremer, D. Stöver, Mechanical behaviour of NiTi parts
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prepared by powder metallurgical methods, Mater. Sci. Eng. A 378 (2004) 185-190.
[9] J. Khalil-Allafi, , A. Dlouhy, G. Eggeler, Ni4Ti3-precipitation during aging of NiTi shape memory alloys and its influence on martensitic phase transformations. Acta mater., 50 (2002) 4255–4273. [10] D. Mari, D.C. Dunand, NiTi and NiTi-TiC Composites: Part I. Transformation and Thermal Cycling Behavior, Metal Mater. Trans. A 26A (1995) 2833-2847.
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[11] K.L. Fukami-Ushiro, D. Mari, D.C. Dunand, NiTi and NiTi-TiC Composites: Part II. Compressive Mechanical Properties, Metal Mater. Trans. A 27A (1996) 183-191.
[12] K.L. Fukami-Ushiro, D.C. Dunand, NiTi and NiTi-TiC Composites: Part III. Shape-Memory Recovery, Metal
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Mater. Trans. A 27A (1996) 193-203.
[13] R. Vaidyanathan, M.A.M. Bourke, D.C. Dunand, Stress-induced martensitic transformations in NiTi and NiTiTiC composites investigated by neutron diffraction, Mater. Sci. Eng. A 273-275 (1999) 404-409.
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[14] R. Vaidyanathan, M.A.M. Bourke, D.C. Dunand, Phase fraction, texture and strain evolution in superelastic NiTi and NiTi–TiC composites investigated by neutron diffraction, Acta Mater. 47 (1999) 3353-3363. [15] J. Lee, J Hwang, D. Lee, H.J. Ryu, S.H. Hong, Enhanced mechanical properties of spark plasma sintered NiTi composites reinforced with carbon nanotubes, J. Alloy Comp., 617 (2014) 505–510. [16] H.J. Jiang, S. Cao, C.B. Ke, X. Ma, X.P. Zhang, Nano-sized SiC particle reinforced NiTi alloy matrix shape memory composite, Mater. Letter., 100 (2013) 74 –77. [17] M. Farvizi, T. Ebadzadeh, M.R. Vaezi, H.S. Kim, A. Simchi, Effect of nano Al2O3 addition on mechanical properties and wear behavior of NiTi intermetallic, Mater Design, 51C (2013) 375-382.
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[18] M. Farvizi, T. Ebadzadeh, M.R. Vaezi, E.Y. Yoon, Y-J. Kim, J.Y. Kang, H.S. Kim, A. Simchi, Effect of Starting Materials on the Wear Performance of NiTi-Based Composites, 334-335 (2015) 35-43. [19] M. Farvizi, T. Ebadzadeh, M.R. Vaezi, E.Y. Yoon, Y-J. Kim, H.S. Kim, A. Simchi, Microstructural
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characterization of HIP consolidated NiTi–nano Al2O3 composites, J. Alloy Comp. 606, 21 (2014). [20] A. Ghasemi, S.R. Hosseini, S.K. Sadrnezhaad, Pore control in SMA NiTi scaffolds via space holder usage, Mater. Sci. Eng. C. 32 (2012) 1266-1270.
[21] J. Laeng, Z. Xiu, X. Xu, X. Sun, H.Ru, Y. Liu, Phase formation of Ni-Ti via solid state reaction, Physica
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Scripta, 129 (2007) 250-254.
[22] W. Maziarz, J. Dutkiewicz, J. Van Humbeeck, T. Czeppe, Mechanically alloyed and hot pressed Ni–49.7Ti
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alloy showing martensitic transformation, Mater. Sci. Eng. A.375-377 (2004) 844-848.
[23] S. K. Sadrnezhaad, A. R. Selahi, Effect of Mechanical Alloying and Sintering on Ni-Ti Powders, Mater. Manuf. Process. 19 (3) (2004) 475-486.
[24] M. Farvizi, T. Ebadzadeh, M.R. Vaezi, A. Simchi, H. S. Kim, MECHANICAL-ACTIVATED PHASE FORMATION OF NiTi IN THE PRESENCE OF NANOPARTICLES, NANO, 8 (2013) 1350048. [25] L. Krone, E. Schüller, M. Bram, O. Hamed, H.-P. Buchkremer, D. Stöver, Mechanical behaviour of NiTi parts
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prepared by powder metallurgical methods, Mater. Sci. Eng. A. 378 (2004) 185-190.
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Figures caption
Fig. 1. Results of XRD analysis of the HIP-consolidated samples
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(The XRD patterns of NiTi and NiTi-6Al2O3 samples were obtained from Ref. [19])
Fig. 2. Stress- strain curves for HIP-consolidated samples under compression.
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Fig. 3. HRTEM image taken from NiTi-6Al2O3 composite sample showing high number of dislocations in the (110) plane of B2 phase in the vicinity of nano alumina particles. Fig. 4. Fracture surface of (a, b) NiTi, (c, d) NiTi-2Al2O3 and (e, f) NiTi-6Al2O3 samples after
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compression test at room temperature
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Tables
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Table 1. Summary of the XRD and DSC results performed on HIP-consolidated samples. The
B2
B19′
Ni3Ti
NiTi2
(wt %)
(wt %)
(wt %)
(wt %)
HIP-NiTi
92
8
-
HIP-NiTi-2Al2O3
71
29
-
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phase contents of the samples were obtained by the Rietveld method obtained from Fig. 1.
HIP-NiTi-6Al2O3
40
36
9
Mf
As
Af
-
8
-16
-4
31
-
29
4
23
38
15
82
72
101
112
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Table 2. Results of mechanical properties of HIP-consolidated samples obtained from figure 2.
NiTi NiTi-2Al2O3
Yield Strength
Fracture Strength
Elongation
(GPa)
(MPa)
(MPa)
(%)
48.1
538.4
2408.8
18.5
83.9
960.8
2648
12.8
94.8
2371.9
2498.2
4.3
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NiTi-6Al2O3
Elastic Modulus
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Highlights
Nano Al2O3 particles were added to NiTi matrix to improve mechanical properties.
•
NiTi and NiTi-2Al2O3 samples showed double yielding during compression test.
•
Addition of 2wt% nano-alumina enhanced elastic modulus compared to pure NiTi.
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NiTi-6Al2O3 sample shows a considerable elasticity and short plastic deformation.
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High density of dislocations in the vicinity of nanoparticles restricts PE in NiTi.
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•
S0925-8388(16)32032-1
DOI:
10.1016/j.jallcom.2016.06.299
Reference:
JALCOM 38168
To appear in:
Journal of Alloys and Compounds
Received Date: 3 April 2016 Revised Date:
30 June 2016
Accepted Date: 30 June 2016
Please cite this article as: M. Farvizi, M.R. Akbarpour, D.-H. Ahn, H.S. Kim, Compressive behavior of NiTi-based composites reinforced with alumina nanoparticles, Journal of Alloys and Compounds (2016), doi: 10.1016/j.jallcom.2016.06.299. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.
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Compressive behavior of NiTi-based composites reinforced with alumina nanoparticles Mohammad Farvizi*a, Mohammad Reza Akbarpour b, Dong-Hyun Ahn c, Hyoung Seop Kim c a
Ceramic Division, Materials and Energy Research Center, Karaj, P.O. Box 31787-316, Iran Department of Materials Engineering, Faculty of Engineering, University of Maragheh, Maragheh, Iran c Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, 790-784, South Korea
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b
*
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Corresponding author: M. Farvizi Email: [email protected], [email protected] Fax: +98-21-88773352; Tel: +98-935 848 5439
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Abstract
NiTi alloys are extensively used in various industrial applications. However, to enhance the performance of this alloy in applications, its mechanical properties should be improved. In previous research, the effect of addition of ceramic microparticles on the mechanical properties of a NiTi matrix has been explored. In this study, to improve the mechanical properties of NiTi,
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small fractions of alumina nanoparticles were used as reinforcement. The compressive stressstrain curves of the NiTi and NiTi-2Al2O3 samples demonstrated well-known four-stage behavior with double yielding. Moreover, it was found that the addition of 2 wt% alumina nanoparticles enhanced the elastic modulus, shortened the first plateau region, and reduced the
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fracture strain, compared to the unreinforced NiTi sample. Increasing alumina nanoparticle contents to 6 wt% completely changed the mechanical behavior of this composite: considerable elasticity, followed by a short plateau region, and fracture. The high resolution transmission
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electron microscopy images showed that, a high fraction of dislocations in the vicinity of nanoparticles can be generated in NiTi, which seems to lock the matrix in the NiTi-6Al2O3 sample. Fracture surface analysis using scanning electron microscopy showed dimple features in the NiTi and NiTi-2Al2O3 samples and a smooth and brittle appearance in the NiTi-6Al2O3 sample. Keywords: NiTi; Nano alumina; Compressive test; HRTEM; Fracture surface.
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1. Introduction Recently, Ti-Ni based alloys have become widely used in various industrial applications due to their unique properties (e.g., shape memory effect (SME), pseudoelasticity (PE),
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biocompatibility, and corrosion and wear resistance) [1-4]. Among the various properties of NiTi, SME and PE have attracted great attention. These properties originate from a reversible thermoelastic martensitic transformation between a high temperature B2-NiTi phase (known as austenite) and a low temperature B19′ NiTi phase (known as martensite). During NiTi cooling
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cycles, martensitic transformation starts at a characteristic temperature, known as Ms, and it is completed at Mf (martensite finish temperature). Reverse martensitic transformation takes place during heating cycles. This transformation starts at a temperature known as As in which the low
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temperature martensite phase starts to transform to the high temperature B2 phase and this transformation completes at Af temperature (austenite finish temperature) [5]. These transformation temperatures are dependent on many factors, including the chemical composition of the NiTi alloy (Ni/Ti ratio) and (internal or external) stresses [5]. The mechanical response of a NiTi alloy is directly related to its phase constituents and test temperature [6].
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Under ideal condition, the stress-strain curves of NiTi during compressive and tensile tests can be divided into four regions: (i) initial linear region which corresponds to the elastic deformations of austenite and martensite phases; (ii) pseudoelastic/pseudoplastic region in which stress induced martensite (SIM) formation occurs in the case of pseudoelasticity effect and
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moving of twin boundaries happens for pseudoplasticity. This region is recognized as a plateaulike feature; (iii) in the third region, SIM martensite phases or detwinned martensite variants are
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elastically deformed; and (iv) finally, in the fourth region, NiTi deforms plastically before it fractures [[7, 8]. At temperatures higher than Md, the highest possible temperature for SIMs formation, the NiTi alloy deforms like normal alloys and does not show any typical plateau. One of the most important issues to resolve to enhance the industrial applicability of NiTi alloys is improvement of their mechanical properties. For example, Ni4Ti3 precipitates are formed using an appropriate aging heat treatment of the Ni-rich NiTi alloy, which can enhance the mechanical properties of the alloy [5]. However, this heat treatment reduces the Ni-content of the matrix and consequently alters the martensitic transformation temperatures [9]. Another approach that can be used to improve the mechanical properties of NiTi alloys is using secondary 2
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hard ceramic particles. The deformation behavior and microstructure of NiTi-based composites reinforced with TiC microparticles, in both austenitic and martensitic states, are well studied by Dunand et al. [10-12] and Vaidyanathan et al. [13, 14]. The effect of carbon nanotubes on the tensile properties of the NiTi-based composites [15], and the effect of nano SiC additives on the
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mechanical properties of porous NiTi [16] have been investigated. In these studies, the reinforcing ceramic particles reacted with the matrix, which can alter the Ni/Ti ratio and affect transformation temperatures. Recently, we demonstrated that using small fractions of alumina nanoparticles can considerably enhance the wear resistance of the NiTi matrix [17, 18]. Also, the
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microstructural aspects of NiTi-nano alumina composites have been studied [19].
In this paper, we report the effects from adding small fractions of alumina nanoparticles on
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the compressive behavior of NiTi-based composites prepared using hot isostatic pressing (HIP).
2. Materials and Methods 2.1 Materials Description
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Previous studies [20-23] have shown that using elemental Ni and Ti powders for the preparation of NiTi can yield to the formation of stable intermetallics (Ni3Ti and NiTi2) of the Ti-Ni system. In order to reduce this side effect, in the current study, prealloyed NiTi powders with the exact composition of Ti (44 wt%)-Ni (56 wt%) were used as the matrix. The
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transformation temperatures of the prealloyed NiTi powders, which were determined using the differential scanning calorimetry (DSC) technique, are as follows: Ms 3°C, Mf -22°C, As 6°C,
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and Af 28°C. For reinforcement, 0 to 6 wt% α-Al2O3 nanoparticles with an average diameter of 80 nm, was used.
2.2 Sample Preparation
NiTi-nano Al2O3 composite powders were prepared using planetary ball milling in a stainless steel vial under argon gas. During all experiments, the rotational speed and ball-topowder weight ratio were 300 rpm and 10:1, respectively [24]. After preparing the composite 3
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powders from the prealloyed NiTi and alumina nanopowders, the consolidation process was performed using the hot isostatic pressing (HIP) method. The HIP process was performed at the temperature of 1065°C and pressure of 100 MPa for 3h [25]. After the HIP process, the samples were carefully mechanically polished using abrasive papers. The relative density of the samples
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measured using the Archimedes method, was about 98% of theoretical density.
2.3 Mechanical tests
Compressive tests were conducted on cylindrical samples (7.2 mm thick, diameter of 6
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mm) using an Instron 8862 machine (INSTRON, Norwood, MA, USA) at room temperature (23°C). The strain rate was 510-4 s-1 during all tests. The ARAMIS 5M optical strain gauge
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system was employed during the compression tests to attain precise strains.
2.4. Characterization
X-ray diffraction (XRD) analysis was performed on all the samples using a D8 Advanced Bruker diffractometer with Cu Ka radiation (λ = 0.154 nm at 20 kV and 30 mA) with a step size
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of 0.016°. The fracture surface of the samples was studied using a scanning electron microscope (SEM: JSPM-5400, JEOL, Japan) to clarify the fracture mechanism. A scanning transmission electron microscope (CS-corrected STEM, JEM-2100F, JEOL, Japan) operated at 200 kV was used to study the structure of the samples. Specimens were prepared for high resolution
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transmission electron microscopy (HRTEM) by mechanical grinding, dimpling, and ion milling.
3. Results and discussion
3.1 Microstructural studies
Figure 1 exhibits the results of XRD analysis of the HIP-consolidated samples. In our
previous investigation [19], the microstructure and transformational behavior of the NiTi-based composites were studied. It was observed that the addition of alumina nanoparticles enhanced the intensity of the B19′ phase and reduced the intensity of the B2 phase in the corresponding XRD patterns. Also, small peaks related to the NiTi2 and Ni3Ti intermetallics appeared in the XRD 4
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pattern of the NiTi-6Al2O3 sample. In the XRD pattern of the NiTi-2Al2O3 sample, NiTi2 /Ni3Ti peaks were not detected, which shows that their content was below the detection limit of XRD (small fractions of stable intermetallics were observed in the SEM studies). A possible explanation for the formation of these intermetallics can be found in Ref. [19]. Investigation of
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the samples using the DSC technique [19] showed that the transformation temperatures increased after addition of nano alumina particles, which could be attributed to alteration of the Ni/Ti ratio due to the formation of NiTi2/Ni3Ti intermetallics and internal stresses originating from mismatch and misfit stresses. Also, the enthalpy of martensitic transformation decreased from 23
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J/g for pure NiTi to about 4.3 J/g for NiTi-6Al2O3 sample which shows that only a small fraction of B2 austenite phase can participate in transformation and a large fraction of B2 phase remains
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in an untransformed condition [19]. So, in the XRD pattern of NiTi-6Al2O3 sample both of untransformed austenite and transformed martensite phases coexists. The phase constituents of the samples indicated by the present XRD and DSC results are summarized in Table 1.
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Fig. 1. Results of XRD analysis of the HIP-consolidated samples
Table 1. Summary of the XRD and DSC results performed on the HIP-consolidated samples. The
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phase contents of the samples were obtained using the Rietveld method (presented in Fig. 1).
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3.2 Mechanical properties
In order to understand the role of addition of alumina nanoparticles on the compressive
stress-strain behavior of NiTi matrix composites, compression tests were conducted on the HIPNiTi (hereafter named NiTi), HIP-NiTi-2 wt% nano alumina (named NiTi-2Al2O3), and HIPNiTi-6 wt% nano alumina (named NiTi-6Al2O3) samples. Figure 2 shows the stress-strain curves of the samples. The results of the mechanical properties of the samples from Fig. 2 are summarized in Table 2. It can be seen that the pure NiTi and NiTi-2Al2O3 samples exhibit typical four-stage stress-strain curves with double yield points on the related curves. According to the data obtained from the DSC and XRD tests, these samples mainly consist of B2-NiTi and B19′5
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NiTi phases. However, because of higher transformation temperatures in the NiTi-2Al2O3 sample, the amount of martensitic B19′ phase in this sample is more than that in the pure NiTi sample. In the case of pure NiTi sample, no other intermetallics were found, but small sample fractions of NiTi2 and Ni3Ti phases were observed in NiTi-2Al2O3 during the microscopy
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studies. Meanwhile, the peaks related to the intermetallics were not found in the XRD pattern of this sample. A comparison between the stress-strain curves of the NiTi and NiTi-2Al2O3 samples shows that there are four differences: (i) the NiTi-2Al2O3 sample shows higher first yield strength (σ
trans)
in comparison with the pure NiTi sample; (ii) elastic modulus of the NiTi-
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2Al2O3 sample was higher than that of the NiTi sample; (iii) the first plateau region in the NiTi2Al2O3 sample is shorter than in the NiTi sample; and (iv) the fracture of the NiTi-2Al2O3
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sample occurred at lower strains. The phase constituents of these two samples mainly consist of B2-B19′ phases at the test temperature. From this, it can be concluded that the stress required for the formation of stress-induced martensite phase from the B2 phase, and martensite reorientation in the NiTi-2Al2O3 composite sample, is higher than that in the pure NiTi sample. In addition, the shorter plateau region in the NiTi-2Al2O3 sample confirms that a smaller fraction of the B2/B19′ phases can participate in the SIM formation/detwinning processes. This phenomenon shows that
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the addition of nanoparticles can produce strong reinforcement against martensite detwinning and formation of SIMs processes. This yielded increase in the elastic modulus and shortening of the plateau region in the corresponding stress-strain curve of the composite samples reinforced with 2 wt% of alumina nanoparticles.
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Interestingly, the NiTi-6Al2O3 composite sample exhibited completely different behavior during the compression test than the two other samples. This sample deformed elastically until
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the stress of 2371 MPa followed by a small plastic deformation, and then it fractured. To figure out the origin of this behavior, the microstructure of the NiTi-6Al2O3 sample was explored using HRTEM analysis (figure 3). It was observed that, a high density of dislocations was generated in the NiTi matrix in the vicinity of the nanoparticles. According to previous investigation [11], the NiTi matrix showed the well-known plateau region with the addition of 20 wt% TiC microparticles (particle size 44-100 µm). However, in this study, the addition of 6 wt% alumina nanoparticles
and
the
formation
of
NiTi2/Ni3Ti
intermetallics
affected
the
NiTi
pseudoelastic/pseudoplastic behavior. As a consequence, a large fraction of austenite and martensite phases cannot participate in the SIM formation and detwinning processes, which 6
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yielded a short plateau region and a premature fracture. In other words, it seems that the reinforcement particle size and weight percentage has considerable influence on the NiTi matrix properties. With the addition of secondary microparticles, the NiTi matrix can accommodate interfacial stresses [11], but, as was observed in this study, using nanoparticles will influence a
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higher volume fraction of NiTi which leads to formation of a high-density of dislocations in the matrix. These dislocations lock NiTi matrix and makes it susceptible to brittle fracture. It should be
noted
that
while
the
NiTi-6Al2O3
sample
did
not
exhibit
considerable
pseudoelastic/pseudoplastic behavior during the compression test, this sample showed a
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satisfactory η ratio during indentation tests, which yielded a high wear resistance for this sample
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[18].
Fig. 2. Stress- strain curves for HIP-consolidated samples under compression.
Fig. 3. HRTEM image taken from NiTi-6Al2O3 composite sample showing high number of
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dislocations in the (110) plane of B2 phase in the vicinity of nano alumina particles.
The SEM microfractography analyses of the fracture surfaces of the NiTi sample are
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presented in Fig. 4 (a, b). It is observed that the fracture surface of the pure NiTi sample contains typical dimple features, which show that this sample deforms plastically during the compression tests. The fracture surface of the NiTi-2Al2O3 samples are shown in Fig. 4(c, d). It is seen that,
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dimples in the fracture surface of this sample became shallower and in some areas, brittle cleavage features appeared. The fracture surface images of the NiTi-6Al2O3 sample represented in Fig.4 (e, f) shows a smooth appearance, which indicates a brittle fracture mode.
Fig. 4. Fracture surface of (a, b) NiTi, (c, d) NiTi-2Al2O3 and (e, f) NiTi-6Al2O3 samples after compression test at room temperature
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4. Conclusions In this study, the stress-strain behavior of NiTi matrix composites reinforced with small fractions of alumina nanoparticles was investigated. The NiTi and NiTi-2Al2O3 samples showed well-known four-stage stress-strain curves. It was observed that the addition of 2 wt% nano alumina to the NiTi matrix enhanced the elastic modulus of the NiTi matrix and shortened the
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first plateau region. Fracture occurred under smaller strains in this sample compared to the unreinforced sample. In the case of NiTi matrix reinforced with 6 wt% alumina nanoparticles,
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the composite behavior was completely different: it deformed elastically, had a short plateau region, and fractured. According to these microstructural studies, a high density of dislocations formed in the vicinity of the nanoparticles locked the NiTi matrix, and affected the stressinduced martensite formation and detwinning processes. Fractography analysis using SEM showed that, the NiTi-6Al2O3 composite samples showed a smooth fracture surface (indicating a
5. Acknowledgements
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tendency to brittle fracture), while the fracture surface of NiTi contained dimple features.
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This work was supported by the National Research Foundation of Korea (NRF) grant funded by
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the Korea government (MSIP) (No. 2014R1A2A1A10051322).
6. References
[1] B.T. Lester, T. Baxevanis, Y. Chemisky, D.C. Lagoudas, Review and perspectives: shape memory alloy composite systems, Acta Mech., 226(12) (2015) 3907-3960. [2] S. Hattori, A. Tainaka, Cavitation erosion of Ti–Ni base shape memory alloys, Wear 262 (2007) 191-197. [3] J. Khalil-Allafi, B. Amin-Ahmadi, M. Zare, Biocompatibility and corrosion behavior of the shape memory NiTi alloy in the physiological environments simulated with body fluids for medical applications, Mater. Sci. Eng. C. 30(2010) 1112-1117.
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[4] M. Farvizi, M. R. Akbarpour, E.Y. Yoon, H.S. Kim, Effect of high-pressure torsion on the microstructure and wear behavior of NiTi alloy, Met. Mater. Int. 21(5)(2015) 891-896. [5] K. Otsuka, X. Ren, Physical metallurgy of Ti-Ni-based shape memory alloys, Prog. Mater. Sci. 50 (2005) 511-
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678. [6] J.M.G. Fuentes, P. Gümpel, J. Strittmatter, Phase Change Behavior of Nitinol Shape Memory Alloys, Adv. Eng. Matter., 4(7) (2002) 437-451.
[7] K. Johansen, H. Voggenreiter, G. Eggeler, On the effect of TiC particles on the tensile properties and on the
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intrinsic two way effect of NiTi shape memory alloys produced by powder metallurgy, Mater. Sci. Eng. A 273– 275(1999) 410–414
[8] L. Krone, E. Schüller, M. Bram, O. Hamed, H.-P. Buchkremer, D. Stöver, Mechanical behaviour of NiTi parts
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prepared by powder metallurgical methods, Mater. Sci. Eng. A 378 (2004) 185-190.
[9] J. Khalil-Allafi, , A. Dlouhy, G. Eggeler, Ni4Ti3-precipitation during aging of NiTi shape memory alloys and its influence on martensitic phase transformations. Acta mater., 50 (2002) 4255–4273. [10] D. Mari, D.C. Dunand, NiTi and NiTi-TiC Composites: Part I. Transformation and Thermal Cycling Behavior, Metal Mater. Trans. A 26A (1995) 2833-2847.
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[11] K.L. Fukami-Ushiro, D. Mari, D.C. Dunand, NiTi and NiTi-TiC Composites: Part II. Compressive Mechanical Properties, Metal Mater. Trans. A 27A (1996) 183-191.
[12] K.L. Fukami-Ushiro, D.C. Dunand, NiTi and NiTi-TiC Composites: Part III. Shape-Memory Recovery, Metal
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Mater. Trans. A 27A (1996) 193-203.
[13] R. Vaidyanathan, M.A.M. Bourke, D.C. Dunand, Stress-induced martensitic transformations in NiTi and NiTiTiC composites investigated by neutron diffraction, Mater. Sci. Eng. A 273-275 (1999) 404-409.
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[14] R. Vaidyanathan, M.A.M. Bourke, D.C. Dunand, Phase fraction, texture and strain evolution in superelastic NiTi and NiTi–TiC composites investigated by neutron diffraction, Acta Mater. 47 (1999) 3353-3363. [15] J. Lee, J Hwang, D. Lee, H.J. Ryu, S.H. Hong, Enhanced mechanical properties of spark plasma sintered NiTi composites reinforced with carbon nanotubes, J. Alloy Comp., 617 (2014) 505–510. [16] H.J. Jiang, S. Cao, C.B. Ke, X. Ma, X.P. Zhang, Nano-sized SiC particle reinforced NiTi alloy matrix shape memory composite, Mater. Letter., 100 (2013) 74 –77. [17] M. Farvizi, T. Ebadzadeh, M.R. Vaezi, H.S. Kim, A. Simchi, Effect of nano Al2O3 addition on mechanical properties and wear behavior of NiTi intermetallic, Mater Design, 51C (2013) 375-382.
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[18] M. Farvizi, T. Ebadzadeh, M.R. Vaezi, E.Y. Yoon, Y-J. Kim, J.Y. Kang, H.S. Kim, A. Simchi, Effect of Starting Materials on the Wear Performance of NiTi-Based Composites, 334-335 (2015) 35-43. [19] M. Farvizi, T. Ebadzadeh, M.R. Vaezi, E.Y. Yoon, Y-J. Kim, H.S. Kim, A. Simchi, Microstructural
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characterization of HIP consolidated NiTi–nano Al2O3 composites, J. Alloy Comp. 606, 21 (2014). [20] A. Ghasemi, S.R. Hosseini, S.K. Sadrnezhaad, Pore control in SMA NiTi scaffolds via space holder usage, Mater. Sci. Eng. C. 32 (2012) 1266-1270.
[21] J. Laeng, Z. Xiu, X. Xu, X. Sun, H.Ru, Y. Liu, Phase formation of Ni-Ti via solid state reaction, Physica
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Scripta, 129 (2007) 250-254.
[22] W. Maziarz, J. Dutkiewicz, J. Van Humbeeck, T. Czeppe, Mechanically alloyed and hot pressed Ni–49.7Ti
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alloy showing martensitic transformation, Mater. Sci. Eng. A.375-377 (2004) 844-848.
[23] S. K. Sadrnezhaad, A. R. Selahi, Effect of Mechanical Alloying and Sintering on Ni-Ti Powders, Mater. Manuf. Process. 19 (3) (2004) 475-486.
[24] M. Farvizi, T. Ebadzadeh, M.R. Vaezi, A. Simchi, H. S. Kim, MECHANICAL-ACTIVATED PHASE FORMATION OF NiTi IN THE PRESENCE OF NANOPARTICLES, NANO, 8 (2013) 1350048. [25] L. Krone, E. Schüller, M. Bram, O. Hamed, H.-P. Buchkremer, D. Stöver, Mechanical behaviour of NiTi parts
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prepared by powder metallurgical methods, Mater. Sci. Eng. A. 378 (2004) 185-190.
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Figures caption
Fig. 1. Results of XRD analysis of the HIP-consolidated samples
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(The XRD patterns of NiTi and NiTi-6Al2O3 samples were obtained from Ref. [19])
Fig. 2. Stress- strain curves for HIP-consolidated samples under compression.
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Fig. 3. HRTEM image taken from NiTi-6Al2O3 composite sample showing high number of dislocations in the (110) plane of B2 phase in the vicinity of nano alumina particles. Fig. 4. Fracture surface of (a, b) NiTi, (c, d) NiTi-2Al2O3 and (e, f) NiTi-6Al2O3 samples after
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compression test at room temperature
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Tables
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Table 1. Summary of the XRD and DSC results performed on HIP-consolidated samples. The
B2
B19′
Ni3Ti
NiTi2
(wt %)
(wt %)
(wt %)
(wt %)
HIP-NiTi
92
8
-
HIP-NiTi-2Al2O3
71
29
-
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phase contents of the samples were obtained by the Rietveld method obtained from Fig. 1.
HIP-NiTi-6Al2O3
40
36
9
Mf
As
Af
-
8
-16
-4
31
-
29
4
23
38
15
82
72
101
112
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Table 2. Results of mechanical properties of HIP-consolidated samples obtained from figure 2.
NiTi NiTi-2Al2O3
Yield Strength
Fracture Strength
Elongation
(GPa)
(MPa)
(MPa)
(%)
48.1
538.4
2408.8
18.5
83.9
960.8
2648
12.8
94.8
2371.9
2498.2
4.3
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NiTi-6Al2O3
Elastic Modulus
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Highlights
Nano Al2O3 particles were added to NiTi matrix to improve mechanical properties.
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NiTi and NiTi-2Al2O3 samples showed double yielding during compression test.
•
Addition of 2wt% nano-alumina enhanced elastic modulus compared to pure NiTi.
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NiTi-6Al2O3 sample shows a considerable elasticity and short plastic deformation.
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High density of dislocations in the vicinity of nanoparticles restricts PE in NiTi.
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