The paper presents an X ray diffraction study for a cooper based shape memory alloy. The behavior of CuAl13Ni4 alloy, which exhibits a peculiar property, is evaluated by structural changes. On cooling, the martensitic transformation takes place from the ordered structures to the long period two layered structure. The crystalline phase transformations of those alloys are very sensitive to the heat treatments, deformation degrees and also to the undesired aging effects. In particular, the study has been made on the CuAl13Ni4 shape memory alloy samples after being hot extruded, quenched and aged in martensitic state

Carmela GURAU

F. M. Braz FERNANDES

Gheorghe GURAU

The Annals of “Dunarea de Jos” University of Galati Fascicle IX Metallurgy and Materials Science

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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 2 – 2008, ISSN 1453 – 083X 
 
 
 
 
X-RAY DIFFRACTION STUDY OF THE REVERSE MARTENSITIC 
TRANSFORMATION IN Cu-Al-Ni SHAPE MEMORY ALLOY 
 
Carmela GURAU1, Gheorghe GURAU1,  
F. M. Braz FERNANDES2
1”Dunarea de Jos” University of Galati 
2CENIMAT Department of Material Science, FCT/UNL, Campus da Caparica, 2829-516 Caparica, Portugal 
email: carmela.gurau@ugal.ro, gheorghe.gura@ugal.ro  
 
ABSTARCT 
 
The paper presents an X ray diffraction study for a cooper based shape memory 
alloy. The behavior of CuAl13Ni4 alloy, which exhibits a peculiar property, is 
evaluated by structural changes. On cooling, the martensitic transformation takes 
place from the ordered structures to the long period two layered structure. The 
crystalline phase transformations of those alloys are very sensitive to the heat 
treatments, deformation degrees and also to the undesired aging effects. In 
particular, the study has been made on the CuAl13Ni4 shape memory alloy samples 
after being hot extruded, quenched and aged in martensitic state. 
 
KEYWORDS: Shape memory alloy, Shape memory effect; Martensitic 
transformation, XRD 
 
1. Introduction 
 
The shape memory alloys (SMA) are in a so 
called class of smart materials whose properties have 
high performances especially their ability to recover 
the desired shape only by changing temperatures. 
SMAs are a typical smart material fully reversible. 
Martensitic transformation is a first-order 
diffusionless structural phase transformation between 
a high temperature austenite phase and low 
temperature martensite phase [1].  
The shape memory effect is related essential by to 
a thermoelastic martensitic transformation [2]. A 
shape memory alloy plastic deformed at temperature 
below the martensite finish temperature, Mf, by 
heating over the austenite start temperature, As, 
recovers the undeformed original shape. The 
characteristic is called shape memory effect (SME). 
After thermomechanical treatments the change 
reoccurs during heating and cooling processes, the 
characteristic is called two way memory effect 
(TWSME). Due to the shape recoverable properties 
these alloys can be used as devices like sensors and 
actuators. Cooper based alloys exhibit shape memory 
within a certain range of composition. It is known 
that for the particular composition CuAl13Ni4 from 
the metastable beta phase whit DO3 structures, after 
quenching, takes place a martensitic transformation 
with two long period layered structures (18R and 2H) 
[3-5]. 
2. Experiment 
 
The CuAl13Ni4 shape memory alloy was 
obtained by a classic direct melting method using 
high purity for components and precised chemical 
composition. The cast ingots were turned in 
cylindrical shapes Φ35X35 mm. The samples were 
plastic deformed by extrusion in three steps until 
Φ4mm wires. After last extrusion the samples were 
cooled in air. The samples were 9 months hot 
extruded wires 4mm diameter and 145 mm length. 
The samples were machined for following tests. For 
X ray diffraction tests we studied the same sample: in 
extrusion state after nine months aged; a subsequent 
quenched; in quenched state after fourteen months 
aged. The experiments for quenched samples 
comprised heat treatment using a vertical furnace, air 
environment, holding at 8500C during 30 minutes. 
After solubilization, the specimens were immediately 
quenched in ice water. Few samples were deliberately 
kept in martensitic state at room temperature.  
Prior to experiments all samples were submitted 
to the chemical etching in order to remove the layer 
deformed by cutting operation as well as the oxide. 
The XRD analysis was run in a RIGAKU (Cu 
sealed tube) at room temperature using 
20mmX2mmX1mm dimension samples. The 2Θhkl 
was between 100 and 900. The acquisition time was 1s 
per point.  
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 2 – 2008, ISSN 1453 – 083X 
 
 
The goniometer radius is 180 mm. The radiation 
used was Cu-Ka. The widths of divergence, 
dispersion and transmission slots were 10, 10 and 
0.15mm. The XRD analyses were made at 
50kW/30mA. The (h k l) planes related to diffraction 
lines were identified using ICDD data base built in 
computer in EVA program 7.0 version. 
 
3. Results and discussion 
 
The CuAl13Ni4 shape memory alloy was studied 
in different stage of deformation respectively 
extruded and quenched samples. 
The hot extruded sample had in structure: solid 
solution a; a mechanical mixture a and g2 an 
intermetallic compound NiAl and premartensitic 
structure. 
The subsequent quenched samples and after 
fourteen months aging were entirely martensitic 
structure at room temperature. 
Two morphological types of martensite structure 
coexist in CuAl13Ni4. In table 1 are shown the 
crystalline parameter and the diffraction line specific 
to martensitic structures. 
 
Table 1 
Martensite 
type 
Parameters of 
crystal lattice 
Angles of 
crystal lattice 
Diffraction 
planes 
Monoclinic 
Al7Cu23Ni 
a= 4.44 
b = 5.31 
c = 37.86 
a=900 
b=89.360
g=900
(-1 2 5) 
(0 0 18) 
(-1 1 15) 
(3 2 4) 
(-2 1 4) 
Orthorhombic 
AlCu3
a= 4.494 
b = 5.189 
c = 46.61 
a=900 
b=900
g=900
(1 1 1 ) 
(0 1 11) 
(0 2 1 ) 
(2 0 2 ) 
(2 0 12) 
(3 2 13) 
 
The memory properties like SME and TWSME, 
transformation characteristic temperatures, thermal 
hysteresis, recovery deformation, generating 
mechanical work are influenced by heat treatments 
history and aging phenomena in initial state but also 
in martensitic state. The main objective of this work 
was to study the changes in fine internal structure for 
extruded and quenched samples the aging process 
accompanied by martensite stabilization. The XRD 
analyses taken three times, reveal important 
modification in crystallographic lattice. In figure 1 are 
shown the XRD diffractograms taken from alloy in 
extrusion state. 
In figure 2 are shown the XRD diffractograms 
taken from alloy in quenched state. 
In figure 3 are shown the XRD diffractograms 
taken from alloy in quenched state aged fourteen 
months at room temperature. The electron diffraction 
patterns of extruded alloy have a disordered structure. 
In this case it can be observed that the characteristic 
lines have large widths. The maximum line intensity 
is corresponding to the monoclinic martensite    (-1 1 
15) hkl plane. As seen from diffraction patterns from 
figure 2, CuAlNi martensite have the ordered 
structure and exhibit superlattice reflection. After the 
heat treatment they have the ordered structures. It can 
be observed that the maximum intensity of 
monoclinic (-1 1 15) hkl plane was kept. The aspect 
of diffraction lines were really narrow because the 
long period order and the coarse martensite specific 
this alloy. 
The diffraction patterns from figure 3, reveal the 
same ordered structure and exhibit superlattice even 
after martensitic aging.  
Anyway the maximum intensity was kept for the 
same monoclinic (-1 1 15) hkl plane and near that it 
can be observed the pick for the pair plan (-2 1 4) and 
both structures are monoclinic. It can be observed a 
flattening of diffraction picks corresponding to plan 
(2 0 2) and (0 0 18). The (2 0 2) habitus plan is an 
attribute of orthorhombic martensite. 
The (0 0 18) habitus plan is an attribute of 
monoclinic martensite.  
It turns out that the pick accordingly to diffraction 
plan (-1 2 5) was missing. The pick accordingly to 
diffraction plan (2 0 12) was reduced until flattening. 
The structure was partially ordered after martensitic 
aging time. 
In cooper based SMAs as in Ti Ni, Ni Al or Fe Al 
alloy systems there can be observed a lot of aging 
process. Cooper based especially brasses are in 
general predisposition for aging even at room 
temperature [1]. 
The aging at high temperatures is determined for 
the precipitation from austenite phase in Cu9Al4 (γ2) 
and NiAl (B2) phases. In ternary Cu Al Ni alloy 
system the precipitation for γ2 phase is inhibited by 
nickel addition. 
It is considered that the precipitation brakes MT 
throw two mechanisms: 
• Coherence of the fields around precipitations 
and/or destroyed potential germination centers in 
martensite state; 
• Introducing vacations at quenching and 
precipitation process. 
 
 
 
 
 
 
 
 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 2 – 2008, ISSN 1453 – 083X 
 
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Fig. 1. X ray diffractogram of  
hot extruded sample 
Fig. 3. X ray diffractogram of quenched and 
14 months aged sample 
Fig. 2. X ray diffractogram of  
quenched sample 
Li
n 
(c
ou
nt
s)
 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 2 – 2008, ISSN 1453 – 083X 
 
FO N D ATĂ
197 6
 
The increasing precipitates manage to changes in 
chemical composition of initial phase that modify 
transformation temperatures. In these conditions the 
shapes recovery becomes more difficult. Aging effect 
changes the memory characteristics for SMAs. The 
martensitic aging effect is accompanied by martensite 
stabilization process. The aging time in martensitic 
phase influences direct critical temperatures and 
sometimes the reverse martensitic transformation is 
canceled. The origin of the martensitic stabilization 
lies in two different mechanisms. One of them 
consists in internal crystalline structure changes. An 
atomic reorder takes place in martensite and that 
determined a relative stabilization between initial 
phase and martensite. It has been reported that the 
base plane of monoclinic martensite originates from 
one of (0 0 1)b planes of the matrix [3]. 
The reversible transformation occurs as: 
)2()18()( '1
,
,
'
1
,
,3
HRDO
ctT
ctT
ctT
ctT
γββ
σ
σ
σ
σ
=↓
=↑
=↓
=↑
⇔⇔  
The mechanism is crystallographically describable 
by two steps. The transformation involves lattice 
deformation called Bain distortion and the second 
step called lattice invariant deformation when one of 
the close packed     (0 0 1)b planes of matrix becomes 
martensite basal plan[8]. The martensite basal plan is 
distorted in case atom sizes are different and become 
sregular in case atom sizes are equal. Because of this 
deviation, the spacing differences ∆d between the 
adjacent diffraction planes became different from null 
and it can be a measure of martensite order. It was 
observed that alloys from Cu Al Ni system undergo a 
partial order disorder transformation in primary aging 
stages so as in long term aging. 
The second mechanism doesn’t explain aging in 
single crystals but is valid for polycrystalline SMAs. 
One of SMAs properties behavior like rubber is 
determined by martensite stabilization. After 
quenching the alloy has the ordered structure and 
exhibits superlattice reflection. 
 
4. Conclusions 
 
The behavior of CuAl13Ni4 alloy, which exhibits 
shape memory properties, was evaluated by structural 
changes.  
 
The alloy was studied, in different stages of 
deformation respectively extruded and quenched 
samples, using XRD analysis: 
1. The memory characteristics are influenced by 
heat treatments history and aging phenomena in 
initial state but also in martensitic state. 
2. The electron diffraction patterns of extruded 
alloy have a disordered structure with large widths of 
the characteristic lines. The structure was only 
partially premartensitic. 
3. After quenching the alloy has the ordered 
structure and exhibit superlattice reflection. The 
aspect of diffraction lines were narrow because the 
long period order and the coarse martensite specific 
this alloy. In Cu Al13Ni4 SMA coexists two 
martensite types (monoclinic and orthorhombic). 
4. The structure was partiallz ordered after 
martensitic aging time but it can be observed 
modification in accommodation of different habitus 
plans. Near the (-1 1 15) hkl plane it can be observed 
increasing the pick for the pair plan (-2 1 4) the both 
structures are monoclinic. 
 
References 
 
[1]. K.Otsuka and C.M. Wayman - “Shape memory materials” 
1999 
[2]. R. Zengin, S. Ozgen, M. Ceylan, 2004, Oxidation behaviour 
and kinetic properties of shape memory CuAlxNi4 alloys, 
Thermochimica Acta 414 
[3]. G Gurau, C Gurau, D Tanase, 2006, Processing Smart Wires 
Cu Al Ni System authors, Metal, 15th International Metallurgical & 
Material Conference, TANGER Ltd., Ostrava, Czech Society for 
New Materials and Technologies, ASM International, Czech 
Chapter, Czech Metallurgical Society, VSB-Technical University, 
Ostrava 
[4]. H. Morawiec, J. Lelatko, D, Stroz, Gila, 1999, Structure and 
properties of melt-spun Cu-Al-Ni shape memory alloys, Met Sci 
Eng, A273- 275 
[5]. V. Recarte, J.I. Perez-Landazabal, A. Ibarra, M.L. No, J. 
San Juan, 2004, High temperature β phase decomposition process 
in a Cu-Al-Ni shape memory alloy, Mat.Sci.Eng. A378 
[6]. R.Gastien, C.E.Corbellani, M.Sade Thermomechanical 
aspects of martensitic transformations in CuAlNi single crystals”  
[7]. Paula, J.P.H.G. Canejo, R.M.S. Martins, F.M. Braz 
Fernandes, 2004, “Effect of thermal cycling on the transformation 
temperature ranges of Ni-Ti shape memory alloy”- A.S., Mat.Sci. 
Eng., A378  
[8]. A. Aydgdu, Y. Aygdogdu, O. Adiguzel, 2004, Long-term 
ageing behaviour of martensite in shape memory Cu-Al-Ni alloys, 
Journal of materials Processing Technology 153/154. 
 
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X-Ray Diffraction Study of the Reverse Martensitic Transformation In Cu-Al-Ni Shape Memory Alloy

https://www.gup.ugal.ro/ugaljournals/index.php/mms/article/download/3099/2781

X-Ray Diffraction Study of the Reverse Martensitic Transformation In Cu-Al-Ni Shape Memory Alloy

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