Invited Speaker

Dr. Osman Adiguzel

Dr. Osman Adiguzel

Department of Physics, Firat University, Turkey
Speech Title: Thermomechanical Processes and Reactions in Thermal and Mechanical Memory in Shape Memory Alloys

Abstract: A series of alloy systems called shape memory alloys exhibit a peculiar property called shape memory effect. This phenomenon is initiated by thermomechanical processes on cooling and deformation and performed on heating and cooling. Therefore, this behavior can be called thermal memory or thermoelasticity. Strain energy is stored in the materials due to the plastic deformation and released on heating by recovering the original shape. These alloys exhibit another property, superelasticity, which is performed mechanically by stressing and releasing the material at a constant temperature at the parent phase region, and this behavior can be called mechanical memory. Superelasticity exhibits ordinary elastic material behavior, but it is performed in non-linear way; loading and unloading paths are different at the stress-strain diagram, and hysteresis loop reveals energy dissipation Thermoelasticity is governed by the thermal and stress induced martensitic transformations, and reverse austenitic transformation. Thermal induced martensitic transformation occurs on cooling with cooperative movement of atoms along with lattice twinning in <110 > -type directions on the {110}-type plane of austenite matrix, by means of lattice invariant shear, and ordered parent phase structures turn into twinned martensite structures. The twinned structures turn into detwinned martensite structure with deformation, by means of stress induced martensitic transformation. Detwinned structures also turn into ordered parent phase structure on heating, by means of reverse austenitic transformation. Superelasticity is governed by stress induced martensitic transformations by stressing and releasing materials and ordered parent phase structures turn into detwinned martensitic structure with stressing.

Copper based alloys exhibit this property in metastable beta-phase region, which has bcc-based structures at high temperature parent phase field. Lattice invariant shear and lattice twinning is not uniform in these alloys and cause the formation of complex layered structures, depending on the stacking sequences on the close-packed planes of the ordered lattice.

In the present contribution, x-ray and electron diffraction studies were carried out on two solution treated copper based CuZnAl and CuAlMn alloys. Electron and x-ray diffraction exhibit super lattice reflections. Specimens of these alloys were aged at room temperature, at which both alloys are in martensitic state. A series of x-ray diffractions were taken at different stages of aging in a long-term interval, and reached results are interpreted.

Keywords: Shape memory effect, Martensitic transformation, Thermal memory, Mechanical memory, Twinning and detwinning

Biography: Dr. 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 2020-2021.

He supervised 5 PhD- theses and 3 M. Sc- theses.

Dr. Adiguzel served his directorate of Graduate School of Natural and Applied Sciences, Firat University, in 1999-2004. He received a certificate 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.