Shape memory effect is a peculiar property exhibited by certain alloy system, and shape memory behavior
is evaluated by the structural changes in microscopic scale. Shape-memory effect is based on martensitic
transformation, which occurs on cooling from high-temperature parent phase region with the cooperative
movements of atoms on {110}-type close-packet planes of parent austenite phase by means of
shear-like mechanism. The material changes its internal crystalline structure with martensitic transition,
and the ordered structure or super lattice structure is essential for the shape memory quality of the material.
Copper based alloys exhibit this property in metastable B-phase field which has bcc-based high symmetric
structure at high temperature parent state. These structures turn into non-conventional stacking
ordered structure with low symmetry following two ordered reactions on cooling from high temperatures.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3543

Adiguzel, O.

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 2 No 2, 02NNPA01(4pp) (2013)   2304-1862/2013/2(2)02NNPA01(4) 02NNPA01-1  2013 Sumy State University Martensitic Transition and the Role of Ordering in Copper Based Shape Memory Alloys  O. Adiguzel  Firat University, Department of Physics, 23169 Elazig, Turkey  (Received 29 December 2012; published online 29 August 2013)  Shape memory effect is a peculiar property exhibited by certain alloy system, and shape memory be-havior is evaluated by the structural changes in microscopic scale. Shape-memory effect is based on mar-tensitic transformation, which occurs on cooling from high-temperature parent phase region with the coop-erative movements of atoms on 110-type close-packet planes of parent austenite phase by means of shear-like mechanism. The material changes its internal crystalline structure with martensitic transition, and the ordered structure or super lattice structure is essential for the shape memory quality of the mate-rial. Copper based alloys exhibit this property in metastable -phase field which has bcc-based high sym-metric structure at high temperature parent state. These structures turn into non-conventional stacking ordered structure with low symmetry following two ordered reactions on cooling from high temperatures.   Keywords: Martensitic transition, Shape memory effect, Ordered structures, Layered structures.   PACS numbers: 64.70.K –, 81.30.Kf   1. INTRODUCTION  A series of alloy systems exhibit a peculiar proper-ty which involves which repeated recovery of macro-scopic shape of material at different temperatures. The origin of this phenomenon lies in the fact that the material changes its internal crystalline structure with changing temperature. The basis of this phe-nomenon is   the stimulus-induced phase transfor-mations, martensitic transitions, which govern the remarkable changes in internal crystalline structure of the materials [1-5].  In the shape memory alloys, the austenite lattice has a higher order of symmetry than that of marten-site.  Martensite variants have identical crystal lat-tice, but are oriented in different directions [2]. Shape memory alloys are easily deformed at low tempera-ture martensitic phase, and recover the original shape on heating over the reverse transformation tempera-ture. On the other hand, martensitic transformations have diffusionless character, and product martesite inherits the order of the parent phase [3, 4].  The martensitic transformation is a shear-dominant solid-state phase transformation, and, shape memory materials transform from the parent phase to one or more of the different variants of the martensitic phase in thermal induced manner [6, 7]. The variants of the martensite usually arrange themselves in a self-accommodating manner through twinning [6, 7]. The shape memory effect is based on martensitic transfor-mation, and shape memory properties are intimately related to the microstructures of the material, especial-ly orientation relationship between the various mar-tensite variants [6, 7]. Twinning and detwinning processes can be consid-ered as elementary processes activated during the transformation. These processes are responsible for shape memory effect, as well as martensitic transfor-mation. In particular, the detwinning is essential as well as martensitic transformation in reversible shape memory effect [6, 7]. By applying external stress, the martensitic variants are forced to reorient into a single variant leading inelastic strains.  Deformation of shape memory alloys in martensitic state proceeds through a martensite variant reorienta-tion or detwinning of twins. The basic mechanism of shape memory effect is schematically illustrated in Fig. 1 [6]. As seen from this figure; the ordered parent phase turns into twinned martensite in thermal man-ner on cooling from high temperature, and the twinned martensites turn into the detwinned martensites or oriented martensites in stress-induced manner by ap-plying external forces.                                              (a)                        (b)                                 (c)  Fig. 1 – Schematic illustration of the mechanism of the shape-memory effect: (a) atomic configuration on {110}- type planes of parent austenite phase, (b) twinned martensite phase oc-curring thermally on cooling, (c) detwinned martensite occur-ring with deformation [6]   Copper-based alloys exhibit shape memory effect in metastable beta-phase region. Beta phases of copper-based alloys have the A2-type disordered structures at high temperatures and undergo the ordered structure with B2 or DO3 - type superlattice with disorder-order transition on cooling, and these ordered structures also transform into martensite with further cooling. The basic ordered -phase structures are schematically  illustrated in Fig. 2. Martensitic transformations occur in a few steps in Copper-based alloys. The first one is Bain distortion and the second one is lattice invariant shear. Bain distortion consists of an expansion of 26 % parallel to the [001] axis and a compression of 11 % parallel to the [110] and [110]  directions. Lattice in-variant shear occurs on a {110}-type plane of austenite matrix, which is basal plane of martensite. With these distortions, 9R (or 18R)-type layered structures occur in the material. cool →      deform   → cool →  O. ADIGUZEL PROC. NAP 2, 02NNPA01 (2013)   02NNPA01-2   Fig. 2 – Basic ordered beta-phase structures; CsCl-type unit cell (B2) and Cu3Al- (DO3)- type unit cell  The -type martensites have the layered structures which consist of an array of close-packed planes. For-mation of the layered structures and sequence of  to 8R martensite transformation is shown in Fig. 3. The layered structures are characterized by the stacking sequences depending on the order in parent phase.                   (a)                            (b)  Fig. 3 – a) Stacking of [110] planes viewed from [001] direc-tion, b) inhomogeneous shear and formation of layered struc-tures  Internally faulted martensites in Cu-Zn-Al alloys are characterized by a long period stacking order such as the 9R or 18R type structures, depending on the number of close-packed layers in the unit cell.  Copper based ternary alloys have the DO3 (or B2)-type superlattice prior to the transformation, and stacking sequence is AB’CB’CA’CA’BA’ BC’BC’AC’AB’ (18R) in martensitic case. Monoclinic distortion takes place in some cases and 18R structure is modified as M18R [4, 8]. It has been reported that the basal plane of 18R martensites originates from one of the [110] planes of the matrix and the inhomogeneous shear occurs on the basal plane in two opposite directions (a 110  -type direction and its opposite) [8-10].  2. EXPERIMENTAL  Two copper based ternary shape memory alloys were selected for investigation; Cu-26.1 %Zn 4 %Al and Cu-11 %Al-6 %Mn (in weight). The martensitic trans-formation temperature of these alloys is over the room temperature and both alloys are entirely martensitic at room temperature. Specimens obtained from these al-loys were solution treated for homogenisation in the -phase field (15 minutes at 830 C for the Alloy 1 and 20 minutes at 700 C for the Alloy 2), then quenched in iced-brine to retain the -phase and  aged at room tem-perature after quenching (both alloys). Powder specimens for X-ray examination were pre-pared by filling the alloys. These specimens were then heated in evacuated quartz tubes at 830 C for 15 minutes and immediately quenched into iced-brine for homogenisation. X-ray diffraction profiles were tak-en from the quenched specimens using Cu-K radiation with wavelength 1.5418 Å. The scanning speed of the Geiger counter was chosen as 2, 2 / min for the dif-fractograms. Specimens for TEM examination were prepared from 3 mm diameter discs and thinned down mechani-cally to 0.3 mm thickness. These specimens were heat-treated for homogenization at 830 C for 15 minutes and quenched into iced-brine to obtain -type marten-site. The quenched disc-shaped specimens were elec-tropolished in a Struers Tenupol-2 instrument at – 20 C in a solution of 20 % nitric acid in methanol, and examined in a JEOL 200CX electron microscope oper-ated at 160 kV.  3. RESULTS AND DISCUSSION  When the copper based beta-phase alloys are cooled below a critical temperature called martensite start temperature, Ms, the martensitic transformation occurs and martensite forms as plates in groups of variants. It enables the shape memory alloys to deform under low stresses by variant coalescence because the total shape change on transformation becomes nearly zero for the group [6]. Product martensite phase including 24 vari-ants undergoes the single crystal of martensite by means of reorientation mechanism on stressing in mar-tensitic condition, and deformed single crystal of mar-tensite undergoes the single crystal of parent phase as a reverse transformation on heating over the austenite finish temperature. This single crystal retransform to the 24 martensite variants on cooling below Ms. The mechanism of this formation has been given elsewhere [9, 10]. On the other hand, a single variant cannot have a coherent interface with the austenite. However a re-gion consisting of fine twins of two martensitic variants can form a coherent interface with the parent austenite [11].  It has been reported that some copper based ter-nary alloys (cubic → monoclinic transformation) exhibit an undeformed interface between austenite and a sin-gle variant of martensite [12].  A typical X-ray powder diffraction profile taken from CuZnAl alloy specimen in as-quenched case is shown in Fig. 4. This diffractograms which exhibits superlattice reflection has been indexed on the mono- MARTENSITIC TRANSITION AND THE ROLE OF ORDERING… PROC. NAP 2, 02NNPA01 (2013)   02NNPA01-3 clinic M18R basis. Two electron diffraction patterns taken from the quenched samples of Alloy 1 and 2 are also shown in Fig. 5 (a and b). Both X-ray diffractogram and electron diffraction patterns reveal that both alloys exhibit superlattice reflections.  Many X-ray diffractograms have been taken from both of the alloy samples in a long time interval, and some changes in peak characteristics on the diffracto-gram with aging duration have been observed. Alt-hough all of the diffractograms exhibit similar proper-ties, it was observed that peak locations of some dif-fraction planes have changed. In particular, some of the neighbour peak pairs have moved toward each oth-er.  It is interesting that miller indices of these plane pairs provide a special relation:    2 2 2 21 2 2 1/ 3 /h h k k n    where n  4 for 18R marten-site [4]. These plane pairs can be listed as follow; (122)-(202), (128)-(208), (12 10)-(20 10), (040)-(320). This ob-servation can be attributed to a relation between inter-plane distances of these plane pairs. When the martensite is transformed from the par-ent phase with differently ordered states such as B2 or DO3, the close-packed plane may consist of atomic sites with different sizes due to the ordering arrangement. The different sizes of atomic sites lead to a distortion of the close-packed plane from an exact hexagon and thus a more close-packed layered structure may be expected. The martensitic phase in copper-based -phase  alloys is based on one of the {110} planes of parent phase called basal plane for martensite. The lattice invariant shears occurs, in two opposite directions, 110-type directions on the {110}-type planes of aus-tenite matrix. {110}-plane group has the following planes; (110), (110 ), (101), (101 ), (011) and ( 011 ). With the lattice invariant shears in two opposite directions on both sides of these planes, 24 martensite variants occur.  050010001500200038 42 46 50→ 2→INTENSITY      Fig. 4 – A X-ray powder diffractogram  of CuZnAl alloy  On the other hand, (110)- type planes of the parent phase are rectangular in original case, and it trans-forms to a hexagon with hexagonal distortion. The de-tailed explanation and illustration related to these dis-tortions has been given elsewhere [4]. Structural ordering is one of the important factors   Fig. 5 – Electron diffraction patterns taken from CuZnAl and CuAlMn alloy samples  for the formation of martensite, and atom sizes have an important effect on formation of ordered structures [9, 10]. The martensite basal plane (110) has an ideal hexagonal form in case atom sizes of alloying elements are equal, and it undergoes a hexagonal distortion in case atom sizes are different. In the disordered case, lattice sites are occupied randomly by different atoms, and the basal plane be-comes ideal hexagon taking the atomic sizes approxi-mately equal. In the ordered case, sub-lattices are oc-cupied regularly by certain atoms which have different atomic sizes, and basal plane undergoes a hexagonal distortion owing to the differences in atom sizes. Metastable phases of copper-based shape memory alloys are very sensitive to the ageing effects, and any heat treatment can change the relative stability of both martensite and parent phases. Martensite stabilization is closely related to the disordering in martensitic state. Although martensitic transformations are diffu-sionless, the transitions occurring during the ageing in the martensitic condition have a diffusive character because this transition requires a structural change and this also gives rise to a change in the configura-tional order.  4. CONCLUSIONS  On the basis of austenite-martensite relation, the basal plane of 9R (or 18R) martensite originates from one of the {110 planes of the parent phase, which have six different planes, and inhomogeneous shears occur in two opposite directions. The basal plane of martensite is subjected to the hexagonal distortion by means of Bain distortion with martensite formation on which atom sizes have important effect. In case the atoms occupying the lattice sites have the same size, the basal plane of martensite becomes regular hexagon. Otherwise the deviations occur from the hexagon ar-rangement of the atoms in case atom sizes are differ-ent. In the light of this knowledge, the atom sizes can be taken approximately equal, in the disordered lattice case, and basal plane becomes nearly ideal hexagon.  In the superlattice case, the sizes of atoms occupying the hexagonal lattice sites are different, and the hexagon deviates from regular one.  In conclusion, the changes in the location of the  O. ADIGUZEL PROC. NAP 2, 02NNPA01 (2013)   02NNPA01-4 above mentioned plane pairs reveal the rearrange-ments of the atom in displacive manner; and this result provides us information on the degree of ordering in the martensitic state of the material.  REFERENCES  1. R.D. James, K.F. Hane, Acta Mater. 48, 197 (2000). 2.  J.J. Zhu, K.M. Liew, Acta Mater. 51, 2443 (2003). 3. J. Pons, et al., Acta Mater. 48, 3027 (2000). 4. O. Adiguzel, J. Mater. Proc. Tech. 185, 120 (2007). 5. Y. Sutou, et al., Acta Mater. 53, 4121 (2005). 6. J. Ma, I. Karaman, R.D. Noebe, Int. Mater. Rev. 55, 257 (2010). 7. Y. Liu, Proc. SPIE 4234, 82 (2001). 8. T. Uhera, T. Tamai, Mech. Adv. Mater. Struc. 13, 197 (2006). 9. Y.F. Guo, et al., Acta Mater. 55, 6634 (2007). 10. A. Aydogdu, Y. Aydogdu, O. Adiguzel, J. Mater. Proc. Tech. 153-154, 164 (2004). 11. C. Lexcellent, P. Blanc, Acta Mater. 52, 2317 (2004). 12. K.F. Hane, J Mech. Phys. Solids 47, 1917 (1999).  

Martensitic Transition and the Role of Ordering in Copper Based Shape Memory Alloys

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  
NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 2 No 2, 02NNPA01(4pp) (2013) 
 
 
2304-1862/2013/2(2)02NNPA01(4) 02NNPA01-1  2013 Sumy State University 
Martensitic Transition and the Role of Ordering in Copper Based Shape Memory Alloys 
 
O. Adiguzel 
 
Firat University, Department of Physics, 23169 Elazig, Turkey 
 
(Received 29 December 2012; published online 29 August 2013) 
 
Shape memory effect is a peculiar property exhibited by certain alloy system, and shape memory be-
havior is evaluated by the structural changes in microscopic scale. Shape-memory effect is based on mar-
tensitic transformation, which occurs on cooling from high-temperature parent phase region with the coop-
erative movements of atoms on 110-type close-packet planes of parent austenite phase by means of 
shear-like mechanism. The material changes its internal crystalline structure with martensitic transition, 
and the ordered structure or super lattice structure is essential for the shape memory quality of the mate-
rial. Copper based alloys exhibit this property in metastable -phase field which has bcc-based high sym-
metric structure at high temperature parent state. These structures turn into non-conventional stacking 
ordered structure with low symmetry following two ordered reactions on cooling from high temperatures.  
 
Keywords: Martensitic transition, Shape memory effect, Ordered structures, Layered structures. 
 
 PACS numbers: 64.70.K –, 81.30.Kf 
 
 
1. INTRODUCTION 
 
A series of alloy systems exhibit a peculiar proper-
ty which involves which repeated recovery of macro-
scopic shape of material at different temperatures. 
The origin of this phenomenon lies in the fact that the 
material changes its internal crystalline structure 
with changing temperature. The basis of this phe-
nomenon is   the stimulus-induced phase transfor-
mations, martensitic transitions, which govern the 
remarkable changes in internal crystalline structure 
of the materials [1-5].  
In the shape memory alloys, the austenite lattice 
has a higher order of symmetry than that of marten-
site.  Martensite variants have identical crystal lat-
tice, but are oriented in different directions [2]. Shape 
memory alloys are easily deformed at low tempera-
ture martensitic phase, and recover the original shape 
on heating over the reverse transformation tempera-
ture. 
On the other hand, martensitic transformations 
have diffusionless character, and product martesite 
inherits the order of the parent phase [3, 4].  
The martensitic transformation is a shear-dominant 
solid-state phase transformation, and, shape memory 
materials transform from the parent phase to one or 
more of the different variants of the martensitic phase 
in thermal induced manner [6, 7]. The variants of the 
martensite usually arrange themselves in a self-
accommodating manner through twinning [6, 7]. The 
shape memory effect is based on martensitic transfor-
mation, and shape memory properties are intimately 
related to the microstructures of the material, especial-
ly orientation relationship between the various mar-
tensite variants [6, 7]. 
Twinning and detwinning processes can be consid-
ered as elementary processes activated during the 
transformation. These processes are responsible for 
shape memory effect, as well as martensitic transfor-
mation. In particular, the detwinning is essential as 
well as martensitic transformation in reversible shape 
memory effect [6, 7]. By applying external stress, the 
martensitic variants are forced to reorient into a single 
variant leading inelastic strains.  
Deformation of shape memory alloys in martensitic 
state proceeds through a martensite variant reorienta-
tion or detwinning of twins. The basic mechanism of 
shape memory effect is schematically illustrated in 
Fig. 1 [6]. As seen from this figure; the ordered parent 
phase turns into twinned martensite in thermal man-
ner on cooling from high temperature, and the twinned 
martensites turn into the detwinned martensites or 
oriented martensites in stress-induced manner by ap-
plying external forces.  
 
                                          
 
(a)                        (b)                                 (c) 
 
Fig. 1 – Schematic illustration of the mechanism of the shape-
memory effect: (a) atomic configuration on {110}- type planes 
of parent austenite phase, (b) twinned martensite phase oc-
curring thermally on cooling, (c) detwinned martensite occur-
ring with deformation [6]  
 
Copper-based alloys exhibit shape memory effect in 
metastable beta-phase region. Beta phases of copper-
based alloys have the A2-type disordered structures at 
high temperatures and undergo the ordered structure 
with B2 or DO3 - type superlattice with disorder-order 
transition on cooling, and these ordered structures also 
transform into martensite with further cooling. The 
basic ordered -phase structures are schematically  
illustrated in Fig. 2. Martensitic transformations occur 
in a few steps in Copper-based alloys. The first one is 
Bain distortion and the second one is lattice invariant 
shear. Bain distortion consists of an expansion of 26 % 
parallel to the [001] axis and a compression of 11 % 
parallel to the [110] and [110]  directions. Lattice in-
variant shear occurs on a {110}-type plane of austenite 
matrix, which is basal plane of martensite. With these 
distortions, 9R (or 18R)-type layered structures occur 
in the material. 
cool 
→     
 deform 
  → 
cool 
→ 
 O. ADIGUZEL PROC. NAP 2, 02NNPA01 (2013) 
 
 
02NNPA01-2 
 
 
Fig. 2 – Basic ordered beta-phase structures; CsCl-type unit 
cell (B2) and Cu3Al- (DO3)- type unit cell 
 
The -type martensites have the layered structures 
which consist of an array of close-packed planes. For-
mation of the layered structures and sequence of  to 
8R martensite transformation is shown in Fig. 3. The 
layered structures are characterized by the stacking 
sequences depending on the order in parent phase. 
 
  
 
              (a)                            (b) 
 
Fig. 3 – a) Stacking of [110] planes viewed from [001] direc-
tion, b) inhomogeneous shear and formation of layered struc-
tures 
 
Internally faulted martensites in Cu-Zn-Al alloys 
are characterized by a long period stacking order such 
as the 9R or 18R type structures, depending on the 
number of close-packed layers in the unit cell.  
Copper based ternary alloys have the DO3 (or B2)-
type superlattice prior to the transformation, and 
stacking sequence is AB’CB’CA’CA’BA’ BC’BC’AC’AB’ 
(18R) in martensitic case. Monoclinic distortion takes 
place in some cases and 18R structure is modified as 
M18R [4, 8]. It has been reported that the basal plane 
of 18R martensites originates from one of the [110] 
planes of the matrix and the inhomogeneous shear 
occurs on the basal plane in two opposite directions 
(a 110  -type direction and its opposite) [8-10]. 
 
2. EXPERIMENTAL 
 
Two copper based ternary shape memory alloys 
were selected for investigation; Cu-26.1 %Zn 4 %Al and 
Cu-11 %Al-6 %Mn (in weight). The martensitic trans-
formation temperature of these alloys is over the room 
temperature and both alloys are entirely martensitic at 
room temperature. Specimens obtained from these al-
loys were solution treated for homogenisation in the -
phase field (15 minutes at 830 C for the Alloy 1 and 
20 minutes at 700 C for the Alloy 2), then quenched in 
iced-brine to retain the -phase and  aged at room tem-
perature after quenching (both alloys). 
Powder specimens for X-ray examination were pre-
pared by filling the alloys. These specimens were then 
heated in evacuated quartz tubes at 830 C for 
15 minutes and immediately quenched into iced-brine 
for homogenisation. X-ray diffraction profiles were tak-
en from the quenched specimens using Cu-K radiation 
with wavelength 1.5418 Å. The scanning speed of the 
Geiger counter was chosen as 2, 2 / min for the dif-
fractograms. 
Specimens for TEM examination were prepared 
from 3 mm diameter discs and thinned down mechani-
cally to 0.3 mm thickness. These specimens were heat-
treated for homogenization at 830 C for 15 minutes 
and quenched into iced-brine to obtain -type marten-
site. The quenched disc-shaped specimens were elec-
tropolished in a Struers Tenupol-2 instrument at –
 20 C in a solution of 20 % nitric acid in methanol, and 
examined in a JEOL 200CX electron microscope oper-
ated at 160 kV. 
 
3. RESULTS AND DISCUSSION 
 
When the copper based beta-phase alloys are cooled 
below a critical temperature called martensite start 
temperature, Ms, the martensitic transformation occurs 
and martensite forms as plates in groups of variants. It 
enables the shape memory alloys to deform under low 
stresses by variant coalescence because the total shape 
change on transformation becomes nearly zero for the 
group [6]. Product martensite phase including 24 vari-
ants undergoes the single crystal of martensite by 
means of reorientation mechanism on stressing in mar-
tensitic condition, and deformed single crystal of mar-
tensite undergoes the single crystal of parent phase as 
a reverse transformation on heating over the austenite 
finish temperature. This single crystal retransform to 
the 24 martensite variants on cooling below Ms. The 
mechanism of this formation has been given elsewhere 
[9, 10]. On the other hand, a single variant cannot have 
a coherent interface with the austenite. However a re-
gion consisting of fine twins of two martensitic variants 
can form a coherent interface with the parent austenite 
[11]. 
 It has been reported that some copper based ter-
nary alloys (cubic → monoclinic transformation) exhibit 
an undeformed interface between austenite and a sin-
gle variant of martensite [12].  
A typical X-ray powder diffraction profile taken 
from CuZnAl alloy specimen in as-quenched case is 
shown in Fig. 4. This diffractograms which exhibits 
superlattice reflection has been indexed on the mono-
 MARTENSITIC TRANSITION AND THE ROLE OF ORDERING… PROC. NAP 2, 02NNPA01 (2013) 
 
 
02NNPA01-3 
clinic M18R basis. Two electron diffraction patterns 
taken from the quenched samples of Alloy 1 and 2 are 
also shown in Fig. 5 (a and b). Both X-ray diffractogram 
and electron diffraction patterns reveal that both alloys 
exhibit superlattice reflections.  
Many X-ray diffractograms have been taken from 
both of the alloy samples in a long time interval, and 
some changes in peak characteristics on the diffracto-
gram with aging duration have been observed. Alt-
hough all of the diffractograms exhibit similar proper-
ties, it was observed that peak locations of some dif-
fraction planes have changed. In particular, some of 
the neighbour peak pairs have moved toward each oth-
er.  
It is interesting that miller indices of these plane 
pairs provide a special relation: 
   2 2 2 21 2 2 1/ 3 /h h k k n    where n  4 for 18R marten-
site [4]. These plane pairs can be listed as follow; (122)-
(202), (128)-(208), (12 10)-(20 10), (040)-(320). This ob-
servation can be attributed to a relation between inter-
plane distances of these plane pairs. 
When the martensite is transformed from the par-
ent phase with differently ordered states such as B2 or 
DO3, the close-packed plane may consist of atomic sites 
with different sizes due to the ordering arrangement. 
The different sizes of atomic sites lead to a distortion of 
the close-packed plane from an exact hexagon and thus 
a more close-packed layered structure may be expected. 
The martensitic phase in copper-based -phase  
alloys is based on one of the {110} planes of parent 
phase called basal plane for martensite. The lattice 
invariant shears occurs, in two opposite directions, 
110-type directions on the {110}-type planes of aus-
tenite matrix. {110}-plane group has the following 
planes; (110), (110 ), (101), (101 ), (011) and ( 011 ). With 
the lattice invariant shears in two opposite directions 
on both sides of these planes, 24 martensite variants 
occur. 
 
0
500
1000
1500
2000
38 42 46 50→ 2
→
IN
T
E
N
S
IT
Y
  
  
 
 
Fig. 4 – A X-ray powder diffractogram  of CuZnAl alloy 
 
On the other hand, (110)- type planes of the parent 
phase are rectangular in original case, and it trans-
forms to a hexagon with hexagonal distortion. The de-
tailed explanation and illustration related to these dis-
tortions has been given elsewhere [4]. 
Structural ordering is one of the important factors 
 
 
Fig. 5 – Electron diffraction patterns taken from CuZnAl and 
CuAlMn alloy samples 
 
for the formation of martensite, and atom sizes have an 
important effect on formation of ordered structures 
[9, 10]. The martensite basal plane (110) has an ideal 
hexagonal form in case atom sizes of alloying elements 
are equal, and it undergoes a hexagonal distortion in 
case atom sizes are different. 
In the disordered case, lattice sites are occupied 
randomly by different atoms, and the basal plane be-
comes ideal hexagon taking the atomic sizes approxi-
mately equal. In the ordered case, sub-lattices are oc-
cupied regularly by certain atoms which have different 
atomic sizes, and basal plane undergoes a hexagonal 
distortion owing to the differences in atom sizes. 
Metastable phases of copper-based shape memory 
alloys are very sensitive to the ageing effects, and any 
heat treatment can change the relative stability of both 
martensite and parent phases. Martensite stabilization 
is closely related to the disordering in martensitic 
state. Although martensitic transformations are diffu-
sionless, the transitions occurring during the ageing in 
the martensitic condition have a diffusive character 
because this transition requires a structural change 
and this also gives rise to a change in the configura-
tional order. 
 
4. CONCLUSIONS 
 
On the basis of austenite-martensite relation, the 
basal plane of 9R (or 18R) martensite originates from 
one of the {110 planes of the parent phase, which 
have six different planes, and inhomogeneous shears 
occur in two opposite directions. The basal plane of 
martensite is subjected to the hexagonal distortion by 
means of Bain distortion with martensite formation on 
which atom sizes have important effect. In case the 
atoms occupying the lattice sites have the same size, 
the basal plane of martensite becomes regular hexagon. 
Otherwise the deviations occur from the hexagon ar-
rangement of the atoms in case atom sizes are differ-
ent. In the light of this knowledge, the atom sizes can 
be taken approximately equal, in the disordered lattice 
case, and basal plane becomes nearly ideal hexagon.  In 
the superlattice case, the sizes of atoms occupying the 
hexagonal lattice sites are different, and the hexagon 
deviates from regular one.  
In conclusion, the changes in the location of the 
 O. ADIGUZEL PROC. NAP 2, 02NNPA01 (2013) 
 
 
02NNPA01-4 
above mentioned plane pairs reveal the rearrange-
ments of the atom in displacive manner; and this result 
provides us information on the degree of ordering in 
the martensitic state of the material. 
 
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Martensitic Transition and the Role of Ordering in Copper Based Shape Memory Alloys

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