Professor Jun Peng
University of Lincoln, Lincoln, UK
Areas of Expertise: Sustainable energy technology, sustainable vehicle powertrains and vehicle energy efficiency technology, with both experimental investigation and numerical simulations including CFD modeling
Professor Xin Chen
School of Materials Science and Engineering, East China University of Science and Technology, China
Areas of Expertise: New energy materials; New nano materials and devices with advanced microscope technology
Prof. Kun Liang
Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, China
Areas of Expertise: Synthesis and Characterization of Novel Nanomaterials for Electrochemical Energy Storage and Conversion
Professor Guohua Xie
College of Chemistry and Molecular Sciences, Wuhan University, China
Areas of Expertise: Organic optoelectronic materials and devices, organic semiconductors
Prof. Dr Sadek Khalifa Mohammed Shakshooki
Department of Chemistry, Faculty of Science, Tripoli University, Tripoli, Libya.
Areas of Expertise: Novel Nanomaterials, proton conductance, complex compounds of transition metals, metal complexes.
Prof. Dr. Osman ADIGUZEL
Firat University, Turkey
Areas of Expertise: Shape memory effect and displacive phase transformations in shape memory alloys and other alloys, molecular dynamics simulations, alloy modeling, electron microscopy, electron diffraction, x-ray diffraction and crystallography
Speech Title: Exothermic and endothermic reactions and Energy Storage in Reversible Behavior of Shape Memory Alloys
Abstract: A series of ally systems called shape memory alloys exhibit a peculiar property called shape memory effect with special chemical compositions in the β-phase fields. This phenomenon is initiated with thermomechanical processes 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 is plastic deformation, due to the soft character of materials in low temperature condition, deformation energy is stored, and release on heating by recovering the original shape, by means of reverse endothermic austenitic transformation. This behavior is governed by thermal, and stress induced martensitic transformations.
Thermal induced transformations are exothermic reactions and occur on cooling with cooperative movement of atoms in <110 > -type directions on {110}-type planes of austenite matrix along with lattice twinning reaction and ordered parent phase structures turn into twinned martensitic structure. Twinned structures turn into detwinned martensite by means of stress induced martensitic transformation with stressing. The {110}-type planes of austenite matrix represent six certain planes, and possible 24 martensite variants occur.
These alloys exhibit another property called superelasticity. This behavior is performed in mechanical manner with stressing and releasing the material in elasticity limit at a constant temperature in parent phase region, and shape recovery occurs instantly and simultaneously upon releasing, by exhibiting elastic material behavior. Superelasticity is performed in non-linear way; stressing and releasing paths are different in the stress-strain diagram, and hysteresis loop refers to energy dissipation. The strain energy is stored after releasing, and these alloys are mainly used as strain absorbent materials in building industry against the seismic events. Superelasticity is also result of the stress induced martensitic transformation and ordered parent phase structures turn into the detwinned martensitic structure with stressing in parent phase region. Therefore, lattice twinning and detwinning reactions play important role at the structural transformations.
Copper based alloys exhibit this property in metastable β-phase region. Lattice twinning is not uniform in these alloys and cause to the formation of the complex layered structures with martensitic transformation, like 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) and X-Ray diffraction studies were carried out on two copper- based CuZnAl and CuAlMn alloys. Electron diffraction patterns and x-ray diffractograms exhibit superlattice reactions. X-ray diffractograms taken in a long-time interval show that locations and intensities of diffraction peaks change with the aging time at room temperature, and this result refers to the rearrangement of atoms in diffusive manner.
Keywords: Shape memory effect, martensitic transformation, thermoelasticity, superelasticity, lattice twinning, detwinning.
Assoc. Prof Sajid Hussain Siyal
Dawood University of Engineering and Technology, Pakistan
Areas of Expertise: The development of Energy storage material and their application in Lithium metal batteries/ energy storage devices.Synthesis, Development and Characterization of nanostructured materials.