Osman Adiguzel

Firat University, Turkey

Title: Shape Reversibility and Cycling Characteristics of Thermomechanical Processes and Crystallographic Transformations in Shape Memory Alloys

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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 already been working as professor. He published over 60 papers in international and national journals; He joined over 100 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 seven years (2014 - 2020) over 80 conferences as Keynote Speaker and Conference Co-Chair organized by different companies. 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.

Abstract

Shape memory alloys take place in a class of advanced smart materials by exhibiting dual memory characteristics, Shape Memory Effect and Superelasticity. Shape Memory Effect is initiated with thermomechanical treatments on cooling and deformation and performed thermally on heating and cooling, with which shape of the material cycles between original and deformed shapes in reversible way. Therefore, this behavior can be called Thermoelasticity. This phenomenon is governed by two crystallographic transformations, thermal and stress induced martensitic transformations. Thermal induced martensitic transformations occur on cooling with cooperative movement of atoms in <110 > -type directions on a {110} - type plane of austenite matrix, along with lattice twinning reaction and ordered parent phase structures turn into the twinned martensite structures. The twinned structures turn into detwinned martensite structures with deformation in the low temperature condition by means of stress induced martensitic transformation. Moreover, detwinned structures turn into ordered parent phase structure on heating by means of reverse austenitic transformation, and crystal structure of the materials cycles between detwinned martensite structure and ordered parent phase structures in reversible way, after first cooling and deformation processes. Superelasticity is performed with mechanically stressing and releasing the material in elasticity limit at a constant temperature in the parent austenite phase region, and shape recovery occurs instantly upon releasing, by exhibiting elastic material behavior. However, shape of the materials cycles between deformed and original shapes on stressing and releasing in the bulk level. Superelasticity is also result of stress induced martensitic transformation and ordered parent phase structures turn into the detwinned martensite structures with stressing in the parent phase region. Also, crystal structures of the materials cycle detwinned martensite and ordered parent phase structures on stressing and releasing. Lattice twinning and detwinning reactions play important role at the transformations and driven by internal and external forces, by means of inhomogeneous lattice invariant shears. Noble metal copper- based alloys exhibit this property in metastable ?-phase region. Lattice twinning and lattice invariant shear is not uniform in these alloys and cause the formation of complex layered structures, The 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.