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Relationship between transformation temperatures and alloyingelements in Cu–Al–Ni shape memory alloys

Z. Karagoz • C. Aksu Canbay

Received: 4 January 2013 / Accepted: 19 March 2013/ Published online: 6 April 2013 Akademiai Kiado, Budapest, Hungary 2013

Abstract Cu–Al–Ni shape memory alloys are good

candidates for high temperature applications. We haveinvestigated the effects of alloying elements on transfor-

mation temperatures, heat-capacity values, and structural

properties of Cu–13.73Al–4.3Ni and Cu–13Al–4.3Ni

(wt%) shape memory alloys. The evolution of the trans-

formation temperatures was studied by differential scan-

ning calorimetry with different heating/cooling rates. The

heat-capacity measurements of the samples were made. It

was found that the mass percentage of the alloying element

has an important effect on the characteristic transformation

temperatures and thermodynamic parameters. The struc-

tural changes of the samples were studied by X-ray

diffraction measurements and optical microscope obser-

vations at room temperature. It is evaluated that the

transformation parameters of CuAlNi shape memory alloy

can be controlled by the change of the mass percentages of

the alloying elements.

Keywords Shape memory alloy Transformation

temperatures Heat capacity

Introduction

In todays’ technological developments, conventional

materials are not enough for industrial applications. In this

point of view, functional materials become more important

for industrial applications. Functional materials are notinteresting much more for their properties under normal

conditions, but when the conditions change such as

applying stress or increasing/decreasing the temperature

they behave differently and this behavior attracts attention.

Among the others shape memory alloys belong to func-

tional materials [1]. Functional properties of SMAs are

largely related to the thermoelastic martensitic transfor-

mation. It is well known that both the elements and the

composition of the elements in the alloy have noticeable

effect on the transformation temperatures in SMAs [2–5].

Cu-based SMAs are largely studied group of shape

memory alloys due to their easy production and low cost.

Especially, Cu–Al–Ni SMAs have been considered a

potential for high temperature applications owing to its

transformation temperatures which can lie between 300

and -200 C, and depend on the Al and Ni contents in the

alloy. The effect of Al content is much stronger than the

effect of Ni in CuAlNi SMAs [2, 3, 6–9]. The increase in

Al concentration modifies the transformation temperatures

and promotes the formation of c 0 phase [1, 10–12]. SMAs

have two main phases, high temperature phase and low

temperature phase named as austenite and martensite. The

austenite and martensite transformation start and finish

temperatures are As, Af , M s, and M f , respectively [1, 2, 13,

14]. Cu-based SMAs are sensitive to alloying elements and

mass percentages of alloying elements can change both

martensite and austenite phase transformation temperatures

in these alloys.

The aim of this study is to investigate the effect of

alloying elements on transformation temperatures, ther-

modynamic parameters and microstructure of Cu–Al–Ni

shape memory alloys using differential scanning calorim-

etry, X-ray measurements and optical microscope analysis.

Z. Karagoz

Department of Chemistry, Faculty of Science,

University of Firat, 23119 Elazig, Turkey

C. A. Canbay (&)

Department of Physics, Faculty of Science,

University of Firat, 23119 Elazig, Turkey

e-mail: [email protected]

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J Therm Anal Calorim (2013) 114:1069–1074

DOI 10.1007/s10973-013-3145-9

8/12/2019 art%3A10.1007%2Fs10973-013-3145-9


Experimental

Two polycrystalline alloys with a nominal composi-

tions given in Table 1 were produced by arc melting of

pure metals, under an argon atmosphere. Then, the samples

were cut from the cast ingot in dimensions of

3.5 9 2.5 9 1.5 mm3. The specimens were solution-trea-

ted in the b-phase region for 1 h and quenched in iced brine

water. The transformation characteristics of the specimens

were determined by Shimadzu DSC-60A differential

scanning calorimetry (DSC). DSC measurements were

carried out from room temperature to 523 and 623 K with

different heating and cooling rates for Cu–13.73Al–4.3Niand Cu–13Al–4.3Ni (wt%) shape memory alloys, respec-

tively. The heat-capacity measurements of the alloys were

made using differential scanning calorimetry. The chemi-

cal composition of the alloys was determined by LEO evo

40 Model energy dispersive X-ray (EDX). The XRD

measurements were carried out in a Rigaku RadB-DMAX

II diffractometer using CuK a

(k = 1.5405 A) radiation.

After the EDX and X-ray analysis, the surfaces of the

samples were first mechanically polished and afterward the

damaged surface layer was cleaned by etching in a solution

of 10 g (FeCl3–6H2O)–192 ml methanol with 40 ml HCl.

The structure of the specimens was characterized using

Nikon MA200 model optical micrograph.

Results and discussion

Thermal properties of the SMAs

The transformation temperatures of the studied alloys were

determined by differential scanning calorimetry (DSC)

with different heating/cooling rates. Differential scanning

calorimetry measurements of the N1 sample were taken

from room temperature to 523 K and from room temper-

ature to 623 K for the N2 sample. As seen in Figs. 1 and 2,

the endothermic peak refers to reverse transformation

during heating and the exothermic peak refers to forward

transformation during cooling. These reverse and forward

transformations are characterized by As, Af , M s, M f tem-

peratures, where DSC curve deviates from linearity. The

DSC curves of the N1 and N2 samples with a heating/

cooling rate of 25 K min-1 are given in Fig. 3. When we

compare the phase transition temperatures of the studied

alloys with each other, Al content (wt%) affected the

reverse and forward transformation temperatures. In ter-

nary CuAlNi systems, the effective element on forward

transformation ( M s) is aluminum and the Ni addition sup-

presses the diffusion of Al and Cu. This formation helps the

Table 1 Alloys composition/wt%

Alloys Cu Al Ni

N1 81.97 13.73 4.3

N2 82.27 13 4.3

20.00

10.00

15 K min–1

25 K min–1

35 K min–1

45 K min–1

0.00

–10.00

–20.00

–30.00

300.00 400.00

Temperature/K

H e a t

f l o w

/ m W

500.00

Fig. 1 DSC curves obtained for N1 SMA with different heating/

cooling rates

20.00

0.00

–20.00

–40.00

H e a t

f l o w

/ m W

300.00 400.00

Temperature/K

500.00 600.00

15 K min–1

25 K min–1

35 K min–1

45 K min–1

Fig. 2 DSC curves obtained for N2 SMA with different heating/

cooling rates

20.00

0.00

–20.00

–40.00

N1

N2

H e a t f l o w / m W

300.00 400.00Temperature/K

500.00 600.00

Fig. 3 DSC curves obtained for N1 and N2 SMAs with a heating/

cooling rate of 25 K min-1

1070 Z. Karagoz, C. A. Canbay

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SMA to retain a single phase on cooling [2, 12, 15, 16]. It is

well known that the change in Al content (wt%) in the alloy

has noticeable influence on the transformation tempera-

tures [3–5]. The reverse and forward transformation tem-

peratures and maximum peak temperature in reverse

transformation ( Amax) of N1 and N2 samples are given in

Tables 2 and 3, respectively. The obtained DSC peaks and

characteristic transformation temperatures serve as a basis

for determining kinetic parameters, i.e., activation energy

of the process of forward and reverse transformations. The

activation energy can change with the temperature [17]. So

various heating and cooling rates are used for determining

activation energy. The methods of Kissinger and Ozawa

[18, 19] lead to linear relationships for martensitic and

reverse transformations as well. The activation energies of

the N1 and N2 samples were determined for reverse

transformation. The activation energy values of the N1

according to Kissinger and Ozawa methods are 91.70 and

93.79 kJ mol-1, respectively. The calculated activation

energy values of N2 sample according Kissinger and

Ozawa methods are 92.70 and 96.8 kJ mol-1, respectively.

The transformation of the SMAs are related to the

energy which the materials retain in their structure. So this

energy consists of chemical energy and reversible

mechanical energy and T 0 is the temperature at which the

chemical energies of austenite and martensite phases are

equal [2, 3, 5, 20, 21]. The equilibrium temperature

according to Salzbrenner and Cohen [22] is determined by

the following relation:

T 0 ¼ 1

2 M s þ Af ð Þ; ð1Þ

where M s is the martensite start temperature and Af is the

austenite finish temperature. The endothermic and

exothermic peaks recorded during heating and cooling

cycles in DSC measurements were integrated as a function

of temperature. The total area of the endothermic and

exothermic peaks gives the enthalpy changes of D H M?A

and D H A?M. The entropy change during the reverse

transformation can be calculated by the following equation

[10, 23]:

DS M! A ¼ D H M! A

T 0; ð2Þ

where DS is the entropy change, D H is the enthalpy change,

and T 0 is the equilibrium temperature between the mar-

tensite and austenite phases. The equilibrium temperatures,

enthalpy and entropy values of the each alloy are given in

Tables 2 and 3. The change in Al content (wt%) in the

CuAlNi SMA affects the transformation temperatures and

in consequence the enthalpy and entropy [2, 3, 5, 20, 21].

Figures 4 and 5 shows the Af , M s, and T 0 temperatures of

N1 and N2 samples versus heating rate, respectively. The

Af and M s temperature change with the variation of heating

rate. So the variation of Af and M s changes the value of T 0temperature according to the well-known equation deter-

mined by Salzbrenner and Cohen (Eq. 1) [22]. When we

compare Figs. 4 and 5 with each other, the change of Af temperature against heating rate of N1 sample is noticeably

high, so this behavior reflected on the calculation of

equilibrium temperature. As mentioned, the Al percentage

in the alloy affected the transformation temperature, so

high Al concentration decreases the transformation tem-

perature. In these figures, the Af and T 0 curves versus

heating rate are increasing, while the M s curve is

decreasing with the increase in heating rate, as expected.

The specific heat-capacity measurements of the N1 and

N2 SMAs were made in air atmosphere with a heating rate

of 10 K min-1. Figures 6 and 7 are showing these specific

heat values of N1 and N2 SMAs during heating. The

measurement range of N1 sample is between 373–433 and

453–573 K for N2 sample. Alumina was used as standard

Table 2 Transformation temperatures and thermal parameters of N1 SMA with different heating/cooling rates

Heating rate/K min-1 As /K Af /K M s /K M f /K Amax /K T 0 /K D H M?A /J g-1 DS M?A /J g-1 K -1

15 391.6 415.5 382.3 361.8 406.4 398.9 4.73 0.0118

25 390.4 422.8 381.2 363.7 409 402 5.95 0.0148

35 398.5 432.7 380.4 363.2 413.6 406.5 4.75 0.0116

45 405.2 450.8 379.2 362.1 421 415 4.36 0.0105

Table 3 Transformation temperatures and thermal parameters of N2 SMA with different heating/cooling rates

Heating rate/K min-1 As /K Af /K M s /K M f /K Amax /K T 0 /K D H M?A /J g-1 DS M?A /J g-1 K -1

15 529.9 562.5 512.3 450.7 551.8 537.4 6.03 0.0112

25 526.3 557 510 464.4 546.9 533.5 6.58 0.0123

35 524.2 571.4 508 460.7 552.6 539.7 5.45 0.0100

45 531.2 573.5 505.8 444.2 552.7 539.7 4.95 0.0091

Relationship between transformation temperatures and alloying elements 1071

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material for the calculations. Heat-capacity measurements

of the N1 sample were determined according to the fol-

lowing steps:

(i) Isothermal at 373 K for 10 min,

(ii) Increasing the temperature from 373 to 423 K with a

heating rate of 10 K min-1,

(iii) Isothermal at 423 K for 10 min.

And the following steps were carried out for the N2

sample:

(i) Isothermal at 453 K for 10 min,

(ii) Increasing the temperature from 453 to 573 K with a

heating rate of 10 K min-1,

(iii) Isothermal at 573 K for 10 min.

After the measurements, the specific heat capacity val-

ues can be calculated using Shimadzu DSC-60A C p soft-

ware program by the following equation [24]:

C P ¼ 1

m

dQ

dT ¼

1

m

dQ=dt

dT =dt

; ð3Þ

where (dQ /dt ) is the heat flux given by DSC curve, m is the

mass of sample, (dT /dt ) is the heating rate of the sample,

15 20 25 30 35 40 45360

380

400

420

440

460 M s

A f

T 0

Heating rate/K min–1

M

s a n d A

f / K

320

340

360

380

400

420

440

460

T 0

/ K

Fig. 4 Variation in M s, Af , and T 0 temperatures according to heating

rate of N1 SMA

15 20 25 30 35 40 45

480

500

520

540

560

580

600

M s

Af

T 0

500

520

540

560

580

600

M s

a n d A

f / K

Heating rate/K min–1

T 0

/ K

Fig. 5 Variation in M s, Af , and T 0 temperatures according to heating

rate of N2 SMA

Temperature/K

C P

/ J g – 1 K

– 1

370.00

0.10

0.60

1.10

380.00 390.00 400.00 410.00

Fig. 6 Specific heat during heating of N1 SMA

0.00

450.00 500.00 550.00

0.50

1.00

Temperature/K

C P

/ J g – 1 K

– 1

Fig. 7 Specific heat during heating of N2 SMA

35 40 45 50 55 60 65 70 75 80

( 2 0 2 )

( 1 2 2 )

( 3 2 0 )

( 2 0 1 4 )

( 0 4 0 )

( 2 0 1 0 )

( 1 2 8 )

N1

I n t e n s i t y

/ a . u .

2θ /°

N2

( 0 0 1 8 )

( 1 2 8 )

( 0 0 1 8 )

Fig. 8 The X-ray diffraction patterns obtained for N1 and N2 SMAs


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T is the temperature, and t is the time. The peak observed in

C p–T curves (Figs. 6, 7) for each sample refers to the

transformation of samples from martensite phase to aus-

tenite phase. At the same time heat capacity is related to

the entropy change in the sample in consequence of the

energy absorbing by the sample from the environment.Heat capacity values of N1 and N2 samples are 0.545 and

0.517 J g-1K -1, respectively.

Structural properties of CuAlNi alloy

X-ray diffraction profile of the CuAlNi SMAs at room

temperature are shown in Fig. 8. X-ray diffraction patterns

were indexed on monoclinic unit cell with the lattice

parameters of a = 4.443 A, b = 5.169 A, and

c = 37.012 A. The calculated a / b ratio was 0.84 and this

confirms that the parent phase is ordered 18R martensite

and has 18R long period stacking order structure. Thismeans that during the rapid cooling high temperature b-

phase is transformed into a DO3 ordered structure and can

further be transformed into a martensite phase of 18R

microstructure. Although the diffractograms of N1 and N2

samples exhibit similar characteristics, some changes were

observed in the peak intensities as shown in diffraction

patterns. As we compare the diffraction patterns of the

samples N1 and N2, the structure of the N1 sample exhibits

a bi-phase structure formed by the martensitic phase b01

and the a phase. Because of high aluminum concentration

in N1 sample, the homogenization at b phase region lead to

a total martensitic transformation with a mixture of b0

1 ? a. X-ray diffraction measurements indicate that, the

samples exhibit superlattice reflections and have ordered

structure in martensite phase. Generally (0 0 18), (1 2 8),

and (1 2 10) planes belong to b01 martensite in Cu-based

shape memory alloys [15, 20, 25–27].

As seen in Fig. 9, the CuAlNi SMAs exhibit martensite

structures at room temperature. The martensite phase

observed in optical micrographs were identified as b01. In

Fig. 9a, the grain boundries of the N1 sample can be

observed and the grains have V-type and needle-type

variants exhibiting different orientations. Similarly, we can

detect only V-type variants for N2 sample from Fig. 9b.

Conclusions

The effects of alloying elements on transformation tem-

peratures, heat-capacity values, and structural properties of

Cu–13.73Al–4.3Ni and Cu–13Al–4.3Ni (wt%) shape

memory alloys were studied by differential thermal anal-

ysis methods and microstructural observations.

DSC measurement was used to investigate the reverse–

forward transformation temperatures, enthalpy, entropy,

and heat-capacity values upon continuous heating. The

calculated values of the entropy from martensite to aus-

tenite transformation are increased with the increasingheating rates. When we compare the phase transition

temperatures of the studied alloys with each other, Al

content (wt%) effected on reverse and forward transfor-

mation temperatures. N1 sample has high Al concentration

in comparison with N2 and consequently, low transfor-

mation temperature ( As) at about 393 K, while N2 sample

has high transformation temperature ( As) at about 528 K.

The calculated activation energies of each sample are

different and this is mainly due to the effect of Al con-

centration in the alloy. The effective element on transfor-

mation temperatures hence on activation energy is

aluminum. The diffraction patterns taken from the CuAlNiSMAs at room temperature showed b0

1 martensite which

correspond to the 18R structure. Besides this the optical

micrographs taken at room temperature for each sample

supported the XRD results and showed b01 martensite. The

results obtained from the measurements show that CuAlNi

SMAs have two-way shape memory effect and exhibit

varying transformation temperatures which can be used in

high temperature applications.

100 µm 100 µm

(a) (b)Fig. 9 Optical micrographs

obtained for CuAlNi SMAs:

a N1 sample and b N2 sample

Relationship between transformation temperatures and alloying elements 1073

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References

1. Lojen G, Anzel I, Kneissl A, Krizman A, Unterweger E, Kosec B,

Bizjak M. Microstructure of rapidly solidified Cu–Al–Ni shape

memory alloy ribbons. J Mater Process Technol. 2005;162–

163:220–9.

2. Suresh N, Ramamurty U. Aging response and its effect on the

functional properties of Cu–Al–Ni shape memory alloys. J Alloy

Compd. 2008;449:113–8.3. Kannarpady GK, Bhattacharyya A, Pulnev S, Vahni I. The effect

of isothermal mechanical cycling on Cu–13.3Al–4.0Ni (wt%)

shape memory alloy single crystal wires. J Alloy Compd.

2006;425:112–22.

4. Sanchez-Arevalo FM, Aldama-Reyna W, Lara-Rodriguez AG,

Garcia-Fernandez T, Pulos G, Trivi M, Villagram-Muniz M. Use

of time history speckle pattern and pulsed photoacoustic tech-

niques to detect the self-accommodating transformation in a Cu–

Al–Ni shape memory alloy. Mater Charact. 2010;61:518–24.

5. Rodriguez-Aseguinoloaza J, Ruiz-Larrea I, No ML, Lopez-Ec-

harri A, San Juan J. Temperature memory effect in Cu–Al–Ni

shape memory alloys studied by adiabatic calorimetry. Acta

Mater. 2008;58:3711–22.

6. Zarubova N, Gemperlova J, Gemperle A, Dlabacek Z, Sittner P,

Novak V. In situ TEM observation of stress-induced martensitictransformations and twinning process in CuAlNi single crystal.

Acta Mater. 2010;58:5109–19.

7. Vajpai SK, Dube RK, Sangal S. Microstructure and properties of

Cu–Al–Ni shape memory alloy strips prepared via hot densifi-

cation rolling of argon atomized powder preforms. Mat Sci Eng

A. 2011;529:378–87.

8. Lin ZC, Yu W, Zee RH, Chin BA. CuAlPd alloys for sensor and

actuator applications. Intermetallics. 2000;8:605–11.

9. Otsuka K, Wayman CM. Shape memory materials. Cambridge:

Cambridge University Press; 1998.

10. Portier RA, Ochin P, Pasko A, Monastyrsky GE, Gilchuk AV,

Kolomytsev VI, Koval YN. Spark plasma sintering of Cu–Al–Ni

shape memory alloy. J Alloy Compd. 2012. doi:10.1016/

j.jallcom.2012.02.145.

11. Recarte V, Perez-Landazabal JI, Rodriguez PP, Bocanegra EH,No ML, Ssn Juan J. Thermodynamics of thermally induced

martensitic transformations in Cu–Al–Ni shape memory alloys.

Acta Mater. 2004;52:3941–8.

12. Aksu Canbay C, Aydogdu A. Thermal analysis of Cu–14.82 wt%

Al–0.4 wt% Be shape memory alloy. J Therm Anal Calorim.

2012. doi:10.1007/s10973-012-2792-6.

13. Izadinia M, Dehghani K. Structure and properties of nanostruc-

tured Cu–13.2Al–5.1Ni shape memory alloy produced by melt

spinning. Trans Nonferrous Met Soc China. 2011;21:2037–43.

14. Sobrero CE, La Roca P, Roatta A, Bolmaro RE, Malarria J. Shape

memory properties of highly textured Cu–Al–Ni–(Ti) alloys. Mat

Sci Eng A. 2012;536:207–15.

15. Chentouf SM, Bouabdallah M, Gachon J-I, Proor E, Sari A.

Microstructural and thermodynamic study of hypoeutectoidal

Cu–Al–Ni shape memory alloys. J Alloy Compd. 2009;470:

507–14.

16. Colic M, Ruddolf R, Stamenkovic D, Anzel I, Vucevic D, Jenko

M, Lazic V, Lojen G. Relationship between microstructure,

cytotoxicity and corrosion properties of a Cu–Al–Ni shape

memory alloy. Acta Biomater. 2010;6:308–17.

17. Vyazovkin S, Burnham AK, Criado JM, Perez-Maqueda LA,

Popescu C, Sbirrazzuoli N. ICTAC kinetics committee recom-

mendations for performing kinetic computations on thermal

analysis data. Thermochim Acta. 2011;20:1–19.

18. Kissinger HE. Reaction kinetics in differential thermal analysis.

Anal Chem. 1957;29(11):1702–6.

19. Ozawa T. Kinetic analysis of derivative curves in thermal anal-

ysis. Anal Calorim. 1970;2(3):321–4.

20. Aksu Canbay C. The production of Cu-based shape memory

alloys and ınvestigation of microstructural, thermal and electrical

properties of alloys. Ph.D Thesis, Institue of Science, Fırat Uni-

versity, 2010.

21. Kato H, Yasuda Y, Sasaki K. Thermodynamic assesment of the

stabilization effect in deformed shape memory alloy martensite.

Acta Mater. 2011;59:3955–64.

22. Salzbrenner RJ, Cohen M. On the thermodynamics of thermo-

elastic martensitic transformations. Acta Metall. 1979;27(5):

739–48.

23. Prado MO, Decarte PM, Lovey F. Martensitic transformation in

Cu–Mn–Al alloys. Scripta Metall Mater. 1995;33(6):878–83.

24. Sonia D, Rotaru P, Rizescu S, Bizdoaca NG. Thermal study of a

shape memory alloy (SMA) spring actuator designed to insure the

motion of a barrier structure. J Therm Anal Calorim.

2013;111:1255–62. doi:10.1007/s10973-012-2369-4.

25. Ortin J, Planes A. Thermodynamic analysis of thermal mea-

surements in thermoelastic martensitic transformations. Acta

Metall. 1988;37:1873–89.

26. Meng Q, Yang H, Liu Y, Nam T. Transformation intervals and

elastic strain energies of B2–B190 martensitic transformation of

NiTi. Intermetallics. 2010;18:2431–4.

27. Perez-Landazabal I, Recarte V, Sanchez-Alarcos V, No ML, San

Juan J. Study of stability and decomposition of the b phase in Cu–

Al–Ni shape memory alloy. Mat Sci Eng A Struct. 2006;438–

440:734–7.


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