Shape reversibility and temperature deformation relations in shape memory alloys

Title : Shape reversibility and temperature deformation relations in shape memory alloys

Abstract:

Shape memory alloys take place in a class of adaptive structural materials called intelligent or smart materials by exhibiting a peculiar property called shape memory effect and superelasticity with the recoverability of two shapes at different conditions.  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. Deformation in low temperature condition is plastic deformation, with which strain energy is stored in the materials and released on heating by recovering the original shape. This phenomenon is governed by the thermal and mechanical reactions, 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 by means of stress induced martensitic transformations.  Superelasticity is performed in only mechanical manner with stressing the material and releasing in the parent austenite phase region, and shape recovery occurs instantly upon releasing, by exhibiting elastic material behavior. Superelasticity is performed in non-linear way, loading, and releasing paths are different at the stress-strain diagram, and hysteresis loop refers to the energy dissipation. Superelasticity is also result of stress induced martensitic transformation and ordered parent phase structures turn into the detwinned martensite structures with stressing. Shape memory alloys are deformed in the low temperature condition for thermoelasticity, and they are stressed and released in parent phase region for superelasticity. Stressing or deformation at different temperatures exhibit different characteristics at stress-strain diagrams, beyond shape memory effect and superelasticity.
Copper based alloys exhibit this property in metastable beta-phase region. Lattice twinning is not uniform in these alloys and cause the formation of unusual complex layered structures, depending on the stacking sequences on the close-packed planes of the ordered parent phase lattice, depending on the stacking sequences on the close-packed planes of the ordered parent phase lattice. 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.
In the present contribution, x-ray diffraction and transmission electron microscopy (TEM) studies were carried out on copper based CuZnAl and CuAlMn alloys. X-ray diffraction profiles and electron diffraction patterns exhibit super lattice reflection. X-ray diffractograms taken in a long-time interval show that diffraction angles and intensities of diffraction peaks change with the aging duration at room temperature.  This result refers to the rearrangement of atoms in diffusive manner.
Keywords: Shape memory effect, martensitic transformation, thermoelasticity, superelasticity, twinning, detwinning. 

Audience Take Away:

• Shape memory alloys are functional materials and used in many fields from biomedical to the building industry. This is a multidisciplinary conference, and I will introduce the basic terms and definition at the beginning of my talk and continue with experimental results.

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 120 virtual conferences in the same way in pandemic period of 2020-2022. 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.