Effects of grain orientation and precipitates on the superelasticity in directionally solidified FeNiCoAlTaB shape memory alloy

Accepted Manuscript Effects of grain orientation and precipitates on the superelasticity in directionally solidified FeNiCoAlTaB shape memory alloy Huadong Fu, Wei Li, Shilei Song, Yanbin Jiang, Jianxin Xie PII:

S0925-8388(16)31557-2

DOI:

10.1016/j.jallcom.2016.05.209

Reference:

JALCOM 37729

To appear in:

Journal of Alloys and Compounds

Received Date: 7 April 2016 Revised Date:

18 May 2016

Accepted Date: 19 May 2016

Please cite this article as: H. Fu, W. Li, S. Song, Y. Jiang, J. Xie, Effects of grain orientation and precipitates on the superelasticity in directionally solidified FeNiCoAlTaB shape memory alloy, Journal of Alloys and Compounds (2016), doi: 10.1016/j.jallcom.2016.05.209. 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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Graphical Abstract

ACCEPTED MANUSCRIPT Effects of grain orientation and precipitates on the superelasticity in directionally solidified FeNiCoAlTaB shape memory alloy Huadong Fu a,*, Wei Li a, Shilei Song a, Yanbin Jiang a, Jianxin Xie a, b,∗ Institute for Advanced Materials and Technology, University of Science and

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a

Technology Beijing, Beijing 100083, People’s Republic of China b

Beijing Laboratory of Metallic Materials and Processing for Modern Transportation,

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Beijing 100083, People’s Republic of China

Abstract：FeNiCoAlTaB alloy with good superelasticity was fabricated by using the

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directional solidification technology to control grain orientation and solution-aging treatment to change the morphology and distribution of precipitates, and the superelasticity improving mechanism of the alloy was investigated in this study. The

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results indicated that with the melt zone temperature of 1420±5

and withdrawing

velocity of 0.5 mm/min, the columnar-grained FeNiCoAlTaB alloy with strong <100> fiber texture was obtained. After solution treatment at 1315

for 6 h, the columnar-grained FeNiCoAlTaB alloy exhibited the superelasticity

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700

for 20 min and aging at

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strain of 1.7%, residual strain of 0.5% and tensile strength of 860MPa. Compared with the non-superelastic equiaxed-grained alloy fabricated by vacuum melting and forging, the desired grain orientation, the size and distribution of the precipitates resulted in the good superelasticity of the columnar-grained FeNiCoAlTaB alloy. Keywords：Directional solidification, Grain orientation, Precipitates, Superelasticity, Shape memory alloy * Corresponding author. Tel.: +86 10 6233 2253; Fax: +86 10 6233 2254; E-mail: [email protected] (H. D. Fu), [email protected] (J. X. Xie)

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ACCEPTED MANUSCRIPT 1 Introduction Shape memory alloys (SMAs), as one of intelligent functional materials with both shape memory effect (SME) and superelasticity (SE), are widely used in electronic

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communications, biomedicine, aerospace, robotics, civil construction and many other fields [1-3]. Researches on the shape memory alloy are mainly focused on NiTi SMAs [4]

, Cu-based SMAs

[5]

and Fe-based SMAs

[6]

. Fe-based shape memory alloys have

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the advantages of high strength, excellent cold workability and low cost, etc.,

In

recent

years,

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enjoying broad application prospect in industry [7]. thermoelastic

martensitic

transformation

obtained

in

Fe-Ni-Co-based alloy with excellent superelasticity[8] has been reported by Tanaka et al, and it is believed that these alloy may be the best alternative material for Ni-Ti

continuously [9-12].

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alloy in some engineering fields, and the further researches were carried out

The keys to get good shape memory properties of Fe-Ni-Co-based alloy were to

[14,15]

. Tanaka et al

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L12 structure

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obtain the specific grain orientation [8,13] and appropriate amount of γ precipitates with [8]

found that strong {035}<100> textured

FeNiCoAlTaB alloy showing huge superelasticity could be obtained through cold rolling with a reduction of over 98%, and solution-treated at 1300 aged at 600

for 72 h. Krooβ et al

alloy after 1300

[13]

for 18 h, then

discovered that single crystal FeNiCoAlTa

, 24 h solution and 700

, 1 h aging received excellent

superelasticity of up to 5.2%. In addition, Ma et al[14] indicated that the influence of the precipitates in Fe-Ni-Co-based alloy on superelasticity was related to the 2

ACCEPTED MANUSCRIPT martensite variants structure. When the twinning inside occured easily, increasing size of precipitate and decreasing quantity of precipitates contributed to the formation of more coarse martensite variants and less energy consumption during transformation.

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When the twinning inside was not easy to occur, increasing precipitates size caused the formation of self-cooperating martensite variants become difficult, thus to hinder the martensitic transformation. Geng et al [15] showed that the growth of γ precipitates

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in FeNiCoAlTaB alloy happened with an increase of aging time in line with the

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Ostwald ripening model at the early stage of aging, as the size of precipitates increased, the martensitic transformation changed from the thermoelastic type to the non-thermoelastic one.

The preparation methods of Fe-Ni-Co-based shape memory alloy were mainly

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divided into two kinds of large deformation rolling + recrystallization and single crystal preparation. The efficiency of single crystal preparation was low, and adding grain boundary strengthening element B into the alloy system for improving the

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mechanical properties was difficult. Meanwhile, the process of large deformation

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rolling + recrystallization was a little more complicated and it was difficult to control the desired texture accurately. Through directional solidification technology, the grain orientation of solidified structure was effectively controlled, the casting defects were reduced, the transverse grain boundaries of the alloy were decreased and even eliminated, and large size plates or bars can be manufactured

[16-19]

. In this study,

therefore, the grain orientation and precipitates of FeNiCoAlTaB alloy were controlled by directional solidification technology and appropriate solution-aging 3

ACCEPTED MANUSCRIPT process, respectively. For the purpose of improving the shape memory properties of FeNiCoAlTaB alloys and clarifying the relevant mechanism, the present work mainly focuses on the effects of grain orientation and precipitates on shape memory

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properties of the alloy. It is expected that this work may offer a guideline for exploring efficient methods for the preparation of high performance Fe-Ni-Co-based shape memory alloys.

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2 Experimental procedures

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Pure iron (99.9wt%), pure nickel (99.9wt%), pure cobalt (99.9wt%), pure aluminum (99.9wt%), pure tantalum (99.9wt%) and ferroboron (20.0wt% boron content, iron and boron content 99.95wt%) were used as raw materials. Referring to the research result given by Tanaka et al [8], the alloy was first induction melted and

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cast in a vacuum furnace. Its chemical composition is shown in Table 1. The as-cast ingot was then homogenized and forged in the temperature range of 1100~1200

to

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both reduce the casting defects and improve the homogeneity of microstructure. Table 1

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A part of the as-forged samples with the size of Φ8mm×100mm were polished, cleaned, dried and directionally solidified to control the grain orientation using directional solidification equipment. According to our previous study[20], directional solidification rates (withdrawing velocities) were 0.5, 1 and 2 mm/min, the melt zone temperature were 1420±5

and 1450±5

cooling with the temperature of 25

, the cooling mode was circulating water

. Another part of the forged specimen was used

to make comparative tests. 4

ACCEPTED MANUSCRIPT The scanning electron microscope (SEM) was used to test the microstructure and grain orientation of the as-forged and directionally solidified FeNiCoAlTaB alloy with electron backscatter diffraction (EBSD). In order to determine the phase

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transformation temperatures of FeNiCoAlTaB alloy, magnetization changes under applied magnetic field as a function of temperature between -265

to 125

were

measured under 7T magnetic field level using a Quantum Design Superconducting

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Quantum Interference Device (SQUID) magnetometer. The morphology and

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distribution of precipitates in the alloy were observed by F30 Tecnai field emission high resolution transmission electron microscope (HRTEM). 3 Results and discussion

3.1 Effects of directional solidification parameters on grain orientation of

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FeNiCoAlTaB alloy

In order to investigate the effects of directional solidification on the grain growth of the FeNiCoAlTaB alloy, the microstructure of the as-forged and directionally

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solidified alloys were tested and analyzed by EBSD technology. Fig. 1 shows the

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microstructure, grain orientation and grain boundary misorientation of the FeNiCoAlTaB alloy. For the as-forged alloy, the equiaxed grains with an average grain size of about 200 µm is observed as shown in Fig. 1(a). A large number of annealing twins exist inside the grains. The alloy mainly exhibits high angle grain boundaries (HAGB), random distribution of grain orientation and grain boundary misorientation except the twin boundaries. The microstructure of the alloy fabricated at withdrawing velocity of 0.5 mm/min 5

ACCEPTED MANUSCRIPT is shown in Fig. 1(b) and (c). With the melt zone temperature of 1420±5

, the alloy

consists of coarse columnar grains with a width of 200-500 µm. Grain boundaries are almost parallel to the specimen withdrawing direction with few transverse boundaries.

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The grain orientation of the specimen withdrawing direction concentrates in <100> fiber texture and the low angle grain boundaries (LAGB) account for about 26.7%.

Fig.1(b), (d) and (e) exhibit microstructure, grain orientation and grain boundary

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misorientation of the FeNiCoAlTaB alloy with the withdrawing velocities of 0.5, 1 , respectively. Under the

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and 2 min/min and the melt zone temperature of 1420±5

same melt zone temperature, with the increase of withdrawing velocity, grain boundary density of the FeNiCoAlTaB alloy increases, grain boundary type gradually transforms into high angle grain boundary, and the grain orientation changes from

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<100> fiber texture to random.

Under the experimental conditions of this study, with the melt zone temperature of 1420±5

, solidification rate of 0.5 mm/min and circulating water cooling

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be fabricated.

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conditions, columnar-grained FeNiCoAlTaB alloy with strong <100> fiber texture can

Fig. 1.

Generally speaking, the grain growth rate is closely related to its orientation. For

cubic metals, due to the difference in atomic arrangement, <100> is a priority direction of grain growth and grain growth rate in the <111> direction is the slowest [21-23]

. As a result, if the <001> orientation of the grains is consistent with the

temperature gradient axial, the growth rate is the fastest. During the directional 6

ACCEPTED MANUSCRIPT solidification of the alloy, grains are competing to grow and most grains are inhibited. At last, columnar grains with the similar orientation which is generally parallel to the heat flux direction are retained.

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During the growth of the columnar grains, the actual growth direction of the columnar grains is closer to the theoretical growing direction only in high G/R (temperature gradient/solidification rate) value condition. Otherwise, the grain will be

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deviated from the direction, resulting in the dispersion of grain orientation. When the

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grain growth rate is consistent with the withdrawing velocity, the heat loss caused by the lateral heat radiation does not form a large transverse temperature gradient, the columnar grains formed under these conditions has minimum orientation dispersion, such as melt temperature of 1420±5

and withdrawing velocity of 0.5 mm/min in

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this study. When the withdrawing velocity is larger than the grain growth rate or the melt zone temperature rises, both of them will cause downward movement of the solid-liquid interface of the alloy. Thus, the increase of heat loss caused by lateral

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thermal radiation results in the increase of transverse temperature gradient and

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inclined growth of columnar grains. Therefore, the grain orientation dispersion degree of the columnar grains increases, such as other directional solidification processes in this study, the definite heat transfer rules are shown in Fig. 2. Fig. 2.

In addition, the value of G×R (temperature gradient × solidification rate) determines the solidification grain size of the alloy, and the grain size decreases with the increase of G×R value. The increases of the melt zone temperature and the 7

ACCEPTED MANUSCRIPT withdrawing velocity lead to the increase of G×R value, which results in the decrease of the grain size. 3.2 Effect of solution-aging process on the superelasticity of columnar-grained

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FeNiCoAlTaB alloy The columnar-grained FeNiCoAlTaB alloy with <100> fiber texture was chosen as the research object, which was prepared under the melt zone temperature of , withdrawing velocity of 0.5 mm/min and circulating water cooling

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1420±5

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conditions. In order to prevent oxidation, the FeNiCoAlTaB alloy specimens were enclosed in quartz tubes, which were filled with argon for protection, and then treated by solid solution at 1315

for 20 min and quenching in order to remain the austenite

parent phase. The sealed specimens in quartz tubes were aged at 700

for 1 h, 3 h, 6

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h, 9 h, 12 h and 24 h. The microstructure of the FeNiCoAlTaB alloy after aging was observed, and no significant changes were found after the aging treatment for 1~24h. Tensile cyclic cumulative deformation method was chosen for testing the

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superelasticity. Each cycle of deformation value is 1%, and the results are shown in

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Fig. 3 (εt is the total strain, εse is superelastic strain, εr is residual strain, εe is the elastic strain).

Fig. 3.

As shown in Fig. 3, the as-forged FeNiCoAlTaB alloy has the total tensile plastic

deformation of about 5.0%, however, the tensile plastic deformation of directionally solidified alloy are up to 22.0% which increases by over 3 times. Unfortunately, both the as-forged and directionally solidified alloys were non-superelastic before aging. 8

ACCEPTED MANUSCRIPT The specimen aged for 1h is broken after three cycles of tension, the tensile deformation is 3.2%, and the superelasticity is not observed. The specimen aged for 3h fractures in the second cycle of tension, the tensile deformation is 1.0%, it has

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certain superelasticity and the recoverable strain is about 0.2%. The specimen aged for 6 h finishes three tensile cycles, and then fractures in the fourth tensile cycle with obvious superelasticity. The recoverable strain and maximum tensile strain are 1.7%

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and 3%, respectively. The specimen aged for 9 h fractures in the second tensile cycle,

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and the recovery strain is only about 1.0%. The specimen aged for 12 h fractures in the third tensile cycle when the tensile strain is up to about 3.3%, the recoverable strain is about 1.2%. The specimen aged for 24 h fractures in the third tensile cycle when the tensile strain is up to about 2.9% without recoverable strain.

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The total strain, recovery strain and critical stress value of the FeNiCoAlTaB alloy after different aging time are shown in Fig. 4. For the alloys aging for 1 h and 24 h, no obvious recoverable strain are observed. When the aging time was 6 h, the alloy

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had the largest superelasticity and the recoverable strain was 1.7%. Compared with

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the specimens aging for 6 h with the same four times tensile cycles, less recoverable strain and larger residual strain are obtained in the alloy aging for 12 h. Meanwhile, the critical stress of directionally solidified alloy after aging for 1h is 1060 MPa, and the plateau stress of the specimens is about 1150 MPa, which reaches the maximum after aging for 3 h. With the aging time prolonging, plateau stress decreases, and drops to 510 MPa when aging for 24 h. The specific reasons for the above characteristics will be discussed in Section 3.4. 9

ACCEPTED MANUSCRIPT Fig. 4. Compared the superelasticity of the FeNiCoAlTaB alloy in different aging times, for 20 min and aging at 700

the alloy by soluting-treatment at 1315

for 6 h has

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the best superelasticity with the superelastic strain of 1.7%, residual strain of 0.5% and tensile strength of 860 MPa. Admittedly, there still exists a certain gap with the performances of FeNiCoAlTaB alloy reported by Tanaka et al[8]. The main reason is

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possibly associated with the precise control of the composition and the structure of the

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alloy. The relevant contents need to be further studied.

3.3 Influence mechanism of solution-aging on the superelasticity of the alloy In order to explore the influence rules of different solution-aging heat treatments on superelasticity of the FeNiCoAlTaB alloy, SQUID method was used to measure

as shown in Fig. 5.

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the martensitic transformation temperatures of the alloy treated by different processes,

Fig. 5.

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When aging for 1 h, M-T cooling and heating curves almost coincide, and

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magnetic mutational site does not appear, which indicates that no martensitic transformation occurs. When aging for 6 h and 12 h, the martensitic transformation temperature (Ms) are -117.0

and -72.9

by the M-T curves, respectively.

However, the temperature hysteresis (Th) of the alloy aging for 12 h is larger when martensitic transformation occurs. When the aging lasts for 24 h, the austenite-martensite transformation of the alloy occurs during cooling at -43.7

, and

the martensite-austenite transformation occurs during the heating. However, the phase 10

ACCEPTED MANUSCRIPT transformation has not completed until 125

, which illustrates that the austenitic

transformation temperature (Af) is above 125

. Otherwise, the M-T curve shape of

the FeNiCoAlTaB alloy aging for 6 h is closed, which indicates that the alloy has a

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thermalelastic martensitic transformation. When the aging time is 12 h, the M-T curve has a small gap, which explains that the alloy has partial thermalelastic martensitic transformation. With aging for 24 h, the M-T curve of the alloy isn’t closed and the

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temperature curve at the gap get close to the parallel state, which indicates that the

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martensitic transformation of the alloy is non-thermalelastic.

In order to ascertain the causes of the effect of solution-aging treatment on transformation temperature of the alloy, the precipitation phase of the FeNiCoAlTaB alloy prepared by different solution-aging treatments were detected by JEM-200CXII

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transmission electron microscope (TEM), as shown in Fig. 6.

As the precipitates in the FeNiCoAlTaB alloy shown in Fig. 6, the size and density of the precipitates increase with the increase of aging time. Aging for 1 h, only

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small amounts of precipitates with the smaller size of ~3nm are obtained. When the

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aging time is prolonged to 6 h, the precipitate phases grow significantly with the size of ~ 13 nm. When the aging time increases to more than 12 h, the precipitate phases further grow up. Aging for more than 24 h, the size of the precipitate phase is about 20 nm and the distribution also tends to be more intensive. Fig. 6.

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ACCEPTED MANUSCRIPT 3.4 Influences of grain orientation and precipitates on mechanical properties of FeNiCoAlTaB alloy According to the above experimental results, it is indicated that the plastic

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deformation behavior of the FeNiCoAlTaB alloy prepared by directional solidification was improved significantly compared with that of the as-forged alloy. This is due to that the directionally solidified alloy has uniform columnar grains with straight grain

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boundaries, which can reduce the number of stress components needed to be

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coordinated during deformation. Thus, the deforming coordinate ability of the grain boundary is increased and the stress concentration in the alloy is reduced, which can suppress the cracks caused by local stress concentration. In addition, compared with the superelasticity of the as-forged FeNiCoAlTaB alloy, the superelasticity of the

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columnar-grained alloy are obviously higher. This is because the plasticity of the equiaxed-grained alloy is poor and random orientation of the alloy leads to very little superelasticity. Nevertheless, after directional solidification, the plasticity of the

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columnar-grained alloy is improved greatly and the grain orientation concentrates in

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<100> orientation, thus the superelasticity is significantly enhanced. The reason for excellent phase transformation plasticity of <100> orientation has been discussed by Tanaka et al [8].

Meanwhile, the as-forged and directional solidified FeNiCoAlTaB alloys differ

greatly in microstructure of grain boundary, as shown in Fig. 7. The as-forged alloy with a random orientation distribution, where most of the grain boundaries are composed of high-angle boundaries covered by the β phase, often fractures before 12

ACCEPTED MANUSCRIPT showing superelasticity. However, more low-angle boundaries with low-energy could be obtained by directional solidification, which can improve the mechanical properties by suppression of the grain boundary precipitation of the brittle β phase.

Fig. 7

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The results are in agreement with the related research presented by Tanaka et al [8].

Based on the comparison of superelasticity curves of the directionally solidified

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FeNiCoAlTaB alloy with different aging durations, it is found that the alloy aged for

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short term or long term has poor superelasticity. Precipitate has a decisive influence on the superelasticity of the alloy. With a relatively short aging time (1 h), insufficient precipitates can be used to improve the alloy’s lattice tetragonality and to support γ/α’ thermoelastic martensitic transformation of the alloy. While aging for a long time (24

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h), a great number of precipitates exist in the alloy, which prevents the martensitic transformation. In addition, the precipitates lead to the change of matrix composition. It is indicated in previous study[6] that the martensitic transformation temperature of

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Fe-Ni-Co-based alloys was very sensitive to the content of Ni. The Ms rose up when

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the content of Ni in the matrix decreased. In Fig. 5(d), with the aging time increasing to 24 h, the Ms temperature increases to -43.7

, and Af temperature cannot be found

in the M-H curve, which illustrates that the martensite cannot be fully recovered to austenite after the martensitic transformation. Therefore, the alloy is mostly in the martensite phase at room temperature. As a result, the alloy mainly has plastic deformation on martensite phase, and consequently it is hard to exhibit the superelasticity. From the above analysis, after proper aging the alloy exhibits 13

ACCEPTED MANUSCRIPT excellent superelasticity since the precipitates has optimum size and quantity. The critical stress of martensitic transformation decreases as Ms temperature increases. The above phenomenon can be explained by the Clausius-Clapeyron

dσ ∆s ∆H =− =− dT ε εT

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equation and the relationship is expressed as Equation (1).

(1)

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where σ is the uniaxial stress, ε is the transformation strain, ∆s represents transformation entropy per unit volume, ∆H is the enthalpy per unit volume.

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The Eq. (1) indicates that the lower martensitic transformation temperature Ms is, the smaller ∆H gets, and the higher critical stress σ becomes. The changes of the plateau stress of the alloy aging for 3~24 h during the transformation is shown in Fig.

4 Conclusions

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4.

(1) Under directional solidification conditions of melt zone temperature of , withdrawing velocity of 0.5 mm/min and circulated water cooling, the

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1420±5

columnar-grained FeNiCoAlTaB alloy with strong <100> fiber texture can be

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fabricated. After solution treatment at 1315

for 20 min and aging at 700

for 6 h,

the superelastic strain of the alloy reaches 1.7%, residual strain is 0.5% and tensile strength is about 860 MPa. (2) Compared with the non-superelastic equiaxed-grained alloy prepared by vacuum melting and forging, the columnar-grained FeNiCoAlTaB alloy prepared by directional solidification exhibits good superelasticity, which is caused by specific grain orientation, appropriate size and distribution of precipitates. 14

ACCEPTED MANUSCRIPT Acknowledgements This work was supported by the Major States Basic Research Development Program (973 Program) of China under contract number 2011CB606300, National

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Natural Science Foundation of China (No. 51504023), State Key Lab of Advanced Metals and Materials Foundation (2014-Z06) and Fundamental Research Funds for the Central Universities (No. FRF-TP-15-051A2).

Otsuka K, Wayman C M (Eds.), Shape Memory Materials, Cambridge University Press, 1998.

[2]

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[1]

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ACCEPTED MANUSCRIPT Figure Captions Fig. 1. Microstructure, grain orientation and grain boundary misorientation of the , 0.5 mm/min (c) 1450±5

mm/min (d) 1420±5

, 2 mm/min WD: Withdrawing

, 1 mm/min (e) 1420±5

Direction

, 0.5

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FeNiCoAlTaB alloy. (a) as-forged (b) 1420±5

Fig. 2. Heat flux model on directional solidification processes of the FeNiCoAlTaB , 0.5 mm/min (b) 1450±5

, 0.5 mm/min

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alloy (a) 1420±5

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Fig. 3. Cyclic tensile stress - strain curves of the FeNiCoAlTaB alloy (a) before aging (b) aging for 1h (c) aging for 3 h (d)as-forged, aging for 6 h (e) aging for 6 h (f) aging for 9 h (g) aging for 12 h (h) aging for 24 h

Fig. 4 Mechanical properties of the FeNiCoAlTaB alloy after different aging time

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Fig. 5. M-T curves of the FeNiCoAlTaB alloy fabricated by directional solidification with different aging times (a) 1 h (b) 6 h (c) 12 h (d) 24 h Fig. 6. Precipitates of the FeNiCoAlTaB alloy for different aging time (a) 1 h (b) 6 h

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(c) 12 h (d) 24 h

Fig. 7. Precipitates of FeNiCoAlTaB alloy (a) as-forged specimen (b) directionally

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solidified specimen with 1420±5

, 0.5 mm/min (arrow pointing to β phase)

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Ni

Co

40.57

28.22

17.97

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Al

Ta

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Fe

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（wt%） ） Table 1 Chemical composition of the FeNiCoAlTaB alloy（

5.22

8.01

B 0.01

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SC

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Fig. 1. Microstructure, grain orientation and grain boundary misorientation of the FeNiCoAlTaB alloy. (a) as-forged (b) 1420±5℃ ℃, 0.5 mm/min (c) 1450±5℃ ℃, 0.5 mm/min (d) 1420±5℃ ℃, 1 mm/min (e) 1420±5℃ ℃, 2 mm/min WD: Withdrawing Direction

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Fig. 2. Heat flux model on directional solidification processes of the

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FeNiCoAlTaB alloy (a) 1420±5℃ ℃, 0.5 mm/min (b) 1450±5℃ ℃, 0.5 mm/min

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Fig. 3. Cyclic tensile stress - strain curves of the FeNiCoAlTaB alloy (a) before aging (b) aging for 1h (c) aging for 3 h (d)as-forged, aging for 6 h (e) aging for 6 h (f) aging for 9 h (g) aging for 12 h (h) aging for 24 h 3

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time

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Fig. 4. Mechanical properties of the FeNiCoAlTaB alloy after different aging

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Fig. 5. M-T curves of the FeNiCoAlTaB alloy fabricated by directional

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solidification with different aging times (a) 1 h (b) 6 h (c) 12 h (d) 24 h

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h (c) 12 h (d) 24 h

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EP

Fig. 6. Precipitates of the FeNiCoAlTaB alloy for different aging time (a) 1 h (b) 6

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Fig. 7. Precipitates of FeNiCoAlTaB alloy (a) as-forged specimen (b) directionally

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solidified specimen with 1420±5℃ ℃, 0.5 mm/min (arrow pointing to β phase)

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Research Highlights：

FeNiCoAlTaB alloy with good superelasticity was fabricated by a new

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method


Alloy grain orientation was controlled by directional solidification

Precipitates morphology and distribution were controlled by solution-aging

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technology

treatment


Parameters of directional solidification and solution-aging were firstly

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confirmed