Journal of Physical Chemistry & Biophysics
Open Access
ISSN: 2161-0398
+44 1478 350008
ISSN: 2161-0398
+44 1478 350008
Adiguzel O
Firat University, Turkey
Scientific Tracks Abstracts: J Phys Chem Biophys
Shape memory effect is a peculiar property exhibited by certain alloy system in the β-phase fields. These alloys exhibit thermoelasticity and superelasticity in reversible way, and they are governed by thermomechanical reactions, thermal and stress induced martensitic transformations, and performed thermally and mechanically, respectively. Shape memory effect is initiated by thermomechanical processes on cooling and deformation and performed thermally on heating and cooling. Therefore, this behavior can be called thermoelasticity. Deformation in low temperature condition is plastic deformation; the strain energy is stored by keeping the deformed shape after releasing external stress and released on heating by recovering the original shape. Thermoelasticity is governed by thermal and stress inducing martensitic transformations. Thermal induced transformation occurs with the cooperative movement of atoms in <110 > - type directions on {110}-type planes of austenite matrix, by means of shear-like mechanism, along with lattice twinning on cooling and ordered parent phase structures turn into twinned martensite structures. Twinned martensite structures turn into detwinned martensite structures by means of stress induced transformation by deforming plastically in martensitic condition. Strain energy is stored in the material with deformation and released upon heating, by recovering the original shape in bulk level, and cycles between original and deformed shapes on heating and cooling, respectively. In the superelasticity, the materials are stressed mechanically just over austenite finish temperature, and shape recovery is performed simultaneously upon releasing the applied stress. Superelasticity is also a result of stress induced martensitic transformation and the ordered parent phase structures turn into the detwinned structures by means of stress induced martensitic transformation with stressing, like the deformation step in shape memory. Superelasticity is performed in nonlinear way, unlike normal elastic materials, loading and unloading paths in stress-strain diagram are different, and hysteresis loop reveals energy dissipation. Copper based alloys exhibit this property in metastable β-phase region, which has bcc-based structures. Lattice invariant shears and twinning are not uniform in these alloys, and the ordered parent phase structures martensitically undergo the nonconventional complex layered structures. 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 unit cell and periodicity is 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 microscopy studies were carried out on two copper- based cuznal and cualmn alloys. X-ray diffraction profiles and electron diffraction patterns 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. This result refers to a new transformation in diffusive manner. Keywords: Shape memory effect, martensitic transformation, thermoelasticity, superelasticity, lattice twinning and detwinning.
Adiguzel graduated from Department of Physics, Ankara University, Turkey in 1974 and received phd- degree from Dicle University, Diyarbakir-Turkey. He has studied at Surrey University, Guildford, UK, as a post-doctoral research scientist in 1986-1987, and studied on shape memory alloys. He worked as research assistant, 1975-80, at Dicle University and shifted to Firat University, Elazig, Turkey in 1980. He became professor in 1996, and he has been retired on November 28, 2019, due to the age limit of 67, following academic life of 45 years. He published over 80 papers in international and national journals; He joined over 120 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 particular, he joined in last six years (2014 - 2019) over 60 conferences as Keynote Speaker and Conference Co-Chair organized by different companies. Also, he joined over 70 online conferences in the same way in pandemic period of 2020-2022. The ICDD (International Centre for Diffraction Data) also appreciates cooperation of his group and interest in Powder Diffraction File.