The 12th Global Conference on Materials Science and Engineering (CMSE 2023)

Abstract: Some materials take place in class of advanced smart materials, by exhibiting a peculiar property called shape memory effect. These alloys have dual characteristics called thermoelasticity and superelasticity, from viewpoint of memory behavior. Shape memory effect is initiated on cooling and deformation processes and performed thermally on heating and cooling, with which shape of materials cycles between original and deformed shapes in reversible way. Therefore, this behavior can be called thermal memory or thermoelasticity. Superelasticity is performed with stressing and releasing the material in elasticity limit at a constant temperature in the parent phase region, and shape recovery occurs instantly upon releasing. These phenomena are result of crystallographic transformations called martensitic transformation.

Thermoelasticity is governed by the thermal and stress induced martensitic transformation. Thermal induced martensite occurs on cooling along with lattice twinning and ordered parent phase structures turn into twinned martensite structures by means of lattice invariant shears, and these structures turn into detwinned martensitic structures with deformation by means of stress induced transformation. Lattice twinning occurs in <110 > -type directions on the {110}-type plane of austenite matrix in self-accommodating manner. Superelasticity is also governed by stress induced martensitic transformation and ordered parent phase structures turn into detwinned martensite structures with stressing.

Copper based alloys exhibit this property in metastable β-phase region, which has bcc-based structures. Lattice invariant shear and twinning is not uniform in these alloys and gives rise to the formation of complex layered structures, 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. The unit cell and periodicity are 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 (TEM) studies were carried out on copper based CuAlMn and CuZnAl alloys. X-ray diffraction profiles and electron diffraction patterns exhibit super lattice reflections. 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, lattice twinning, detwinning.

Abstract: One of the ultimate limit state important for the safe design of structures is failure due to buckling. The origin of buckling, as the sudden change in shape of structural component, may arise from mechanical as well from thermal loading conditions. Apart from the loading conditions, the geometrical imperfections are another parameter important for the overall structural stability. In wish to fulfil the lack of thermo-mechanical stability solutions based on Layer Wise (LW) plate theories, which will be able to include general form of geometrical imperfection, this study presents the LW finite element for thermo-mechanical stability of geometrically imperfect FRP (Fibre reinforced polymer) and FGM (Functionally Graded Material) plates. The mathematical model, based on Layer wise theory of Reddy, assumes layer wise variation of in plane displacements and constant transverse displacement through the thickness, linear strain displacement relations and isotropic/orthotropic material properties. The material properties of FGM plates are assumed to be constant in xy-plane and vary through the thickness by a power law function in terms of the volume fraction of the constituents. The Koiter’s model for initial geometric imperfection is adopted. The principle of virtual displacement (PVD) is utilized to derive Euler-Lagrange differential equation of linearized buckling problem. The weak form is discretized using nine node Lagrangian isoparametric finite element. The original MATLAB computer program is coded for the finite element solution and used to study influence of plate thickness a/h, aspect ratio a/b, power low index, imperfection form and material properties on thermo-mechanical stability of FRP and FGM plates. The results are compared with the one from the literature.

Acknowledgements: The author is thankful for the financial support received by the Ministry for Education, Science and Technology, Republic of Serbia, grant number 200092.

Abstract: The study of intermetallic compounds has a long history. These alloys and compounds consist of billions of microscopic elementary particles: electrons, neutrons, protons, quantized lattice vibrations known as phonons, and many others. The physical properties of macroscopic intermetallic compounds cannot be explained completely only by simple extrapolation of the behaviour of mentioned individual elementary particles, even on the basis of statistical physics. Interesting and new properties emerge from a quantum arrangement of particles. This is what attracts scientists to explore condensed matter physics, which is the most active field related to strongly correlated electron systems. In the early years of the 20th century, the study of physical properties in the low-temperature range started to develop. It is related to the emergent behaviour of matter due to the laws of quantum mechanics. When the temperature approaches zero kelvin, the highly correlated state of the electron system arises. This is usually caused by the enhanced electronic density of electron levels close to the Fermi energy in metals, especially in sharp 4f electronic states in rare earth elements. The emerging field of study is arising due to undergoing quantum phase transitions. A fascinating variety of temperature values and magnetic field properties can be observed in the vicinity of the quantum phase transition. Therefore, new physics has appeared. This is one of the reasons why we decided to study such a system in condensed matter physics. The mentioned phenomena, which can arise at the level of quantum mechanics effects, led our group to study the selected intermetallic systems. These materials belong to a group of advanced materials and potential magnetic actuators. Polycrystalline samples based on Yb were prepared, and their interesting physical properties were studied. All of them were prepared by the same method – the inductive melting process. In all studied samples, attractive physical properties could be found by using different scientific methods. Moreover, rare earth materials may become a possible basis for future applications.

Keywords: Physical Properties, Magnetism, Rare-earth.

Acknowledgements: This research work was supported partially by VEGA 1/0705/20, VEGA 1/0404/21 and VEGA 1/0180/23.

Abstract: During recent several years, hydrogenated-diamond (H-diamond) based metal-oxide-semiconductor field-effect transistors (MOSFETs) have been developed greatly. The MOSFETs with structures of SD-Ta₂O₅/ALD-Al₂O₃/H-diamond and SD-ZrO₂/ALD-Al₂O₃/H-diamond (where SD and ALD refer to atomic layer deposition and sputtering deposition techniques for oxide insulators deposition) showed depletion-mode (D-mode) characteristics. In contrast, SD-LaAlO₃/ALD-Al₂O₃/H-diamond and SD-HfO₂/ALD-HfO₂/H-diamond MOSFETs showed enhancement-mode (E-mode) characteristics. The studies revealed that the D-/E-mode characteristics of the H-diamond MOSFETs were independent of the oxide insulators and device structures, and reproducibly depended on the fabrication processes. By comparing the fabrication process difference, it was found that the oxide/H-diamond interface for the E-mode MOSFETs was annealed at 180 °C during the photoresist baking step. However, that of the D-mode MOSFETs was not annealed. Because holes accumulation in the H-diamond channel layer is thermosensitive, annealing possibly led to the disappearance of holes and the formation of E-mode characteristics. Therefore, annealing effect on the electrical properties of H-diamond-based MOSFETs and guidelines to control the D-/E-mode characteristics of H-diamond MOSFETs were investigated. After clarifying the controlling conditions for the D-/E-mode characteristics of the H-diamond MOSFETs, the logic circuits composed of D-/E-mode H-diamond MOSFETs were fabricated successfully.

In this talk, the controlling conditions for the D-/E-mode characteristics of the H-diamond MOSFETs and the fabrication of D-/E-mode H-diamond MOSFET logic circuits will be discussed.