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Journal of Materials Science and Nanotechnology | Volume: 2
November 22-23, 2018 | Paris, France
Materials Physics and Materials Science
International Conference on
Osman Adiguzel
Firat University, Turkey
Nanoscale characterization of crystallographic phase transformations in shape
memory alloys
Shape memory effect is a peculiar property exhibited a
series alloy system in the β-phase fields. Shape memory
alloys are sensitive to external condition and temperature,
and crystal structure of these alloys change with changing
temperature and stressing, by means of crystallographic
phase transformations, called martensitic transformations.
Shape memory effect is initiated by cooling and stressing,
and by means of thermal and stress induced martensitic
transformation. Thermal induced transformation occurs as
martensite variants with lattice twinning in crystallographic
scale on cooling below martensite finish temperature.
Twinned martensite structures turn into detwinned
martensite structure by means of stress induced martensitic
transformation by stressing material in a strain limit in
martensitic condition. Shape memory alloys are in the
fully martensitic state below martensite finish temperature
with fully twinned structure can be easily deformed
through variant reorientation/detwinning process. Thermal
induced martensitic transformation is lattice-distorting
phase transformation and occurs with the cooperative
movement of atoms by means of shear-like mechanism.
Martensitic transformations occur by two or more lattice
invariant shears on a {110}-type plane of austenite matrix
which is basal plane or stacking plane for martensite, as a
first step, and the transformed region consists of parallel
bands containing alternately two different variants. In the
martensitic transformation, the lattice of high temperature
austenite phase has greater crystallographic symmetry than
that of the low-temperature product phase. Copper based
alloys exhibit this property in metastable β-phase region,
which has bcc-based structures at high temperature parent
phase field and these structures martensitically turn into the
complex stacking ordered structures with lattice twinning
reaction on cooling. Lattice invariant shears are not uniform
in copper-based shape memory alloys, and the ordered
parent phase structures martensitically undergo the non-
conventional complex layered structures on cooling. The
long-period layered structures can be described by different
unit cells as 3R, 9R or 18R depending on the stacking
sequences on the close-packed planes of the ordered lattice.
The close packed planes exhibit high symmetry and short-
range order as parent phase, but other planes do not exhibit
symmetry. The unit cell and periodicity are completed
through 18 layers in direction z, in case of 18R martensite,
and unit cells are not periodic in short range in direction z. In
the present contribution, x-ray diffraction and transmission
electron microscope studies were carried out on two copper
based CuZnAl and CuAlMn alloys. These alloy samples have
been heat treated for homogenization in the β-phase fields.
X-ray diffraction profiles and electron diffraction patterns
reveal that both alloys exhibit super lattice reflections
inherited from parent phase due to the displacive character
of martensitic transformation. X-ray diffractograms taken
in a long time, interval show that diffraction angles and
intensities of diffraction peaks change with the aging time
at room temperature. In particular, some of the successive
peak pairs providing a special relation between Miller
indices come close each other, and this result leads to the
rearrangement of atoms in diffusive manner.
Speaker Biography
Osman Adiguzel graduated from department of physics, Ankara University, Turkey in
1974 and received PhD from Dicle University, Diyarbakir-Turkey in Solid State Physics
with experimental studies on diffusion less phase transformations in Ti-Ta alloys in
1980. He has studied at Surrey University, UK, as a post-doctoral research scientist in
1986-1987, and He studied on shape memory alloys. He worked as research assistant,
1975-80, at Dicle University, Turkey. He moved to Firat University in 1980, and became
professor in 1996, He published over 50 papers in international and national journals.
He joined over 80 conferences and symposia in international and national level as
participant, invited speaker or keynote speaker with contributions of oral or poster.
He served the program chair or conference chair/co-chair in some of these activities.
In last three years he joined (2014 - 2016) over 20 conferences as Keynote Speaker
and Conference Co-Chair organized by different companies. He supervised 5 PhD-
theses and 3 .- theses. He served his directorate of Graduate School of Natural
and Applied Sciences, Firat University, in 1999-2004. He received a certificate which
is being awarded to him and his experimental group in recognition of significant
contribution of 2 patterns to the Powder Diffraction File – Release 2000. The ICDD
(International Centre for Diffraction Data) also appreciates cooperation of his group
and interest in Powder Diffraction File.
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