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    Investigation of bio-corrosion behavior, structural and thermal properties of Ni20Ti50Sn30 high-temperature shape memory alloy
    (Springer, 2024) Balci, Esra
    In this study, Ni20Ti50Sn30 (atomic %) sample was prepared using the arc melting method. Some thermodynamic parameters (phase transformation temperatures, PTT; enthalpy, Delta H; and phase transformation hysteresis, H) obtained from the phase transformations of the alloy were determined using differential scanning calorimetry (DSC). The sample exhibited high-temperature shape memory alloy (HTSMA) properties. X-ray (XRD) analysis was performed to determine the crystal structure properties at the alloy. The presence of B2, B19 ', Ti2Ni, beta-Ti, Ni3Sn4, TiNiSn and Ti3Sn phases was identified through X-ray analysis of the alloy. Scanning electron microscopy (SEM) was used to examine the pre- and post-corrosion surface morphologies of the sample, with EDX analysis being performed to reveal chemical structure determinations (matrix phases, precipitates and weathering zones). The presence of dendritic arms was observed, while martensite plates were absent in all SEM images. Particularly in the SEM image taken after corrosion, it was noted that the TiO2 layer placed on the surface of the matrix rich in Ti elements altered the surface morphology of the alloy. The presence of Ti and O elements in the post-corrosion EDX analysis confirmed the existence of this layer. Biocompatibility studies of the alloy were conducted using potentiodynamic corrosion tests and electrochemical impedance spectroscopy (EIS) methods. It was determined that the NiTiSn sample was in the excellent stability class according to corrosion standards.
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    Investigation of Electrochemical and Thermal Properties of Ti50Ni40-xZr10Nbx SMAs
    (Springer, 2024) Abdullah, Shakhawan Salih; Balci, Esra; Qader, Ibrahim Nazem; Dagdelen, Fethi
    Titanium and its alloys have already been widely used as implant materials due to their outstanding mechanical characteristics, thermal properties, and biocompatibility. In this study, Ti50Ni40-xZr10Nbx (x = 1, 3, 5 at.%) shape memory alloys (SMAs) with a constant atomic percentage of Ti and Zr were investigated. For investigation of the structural properties of produced SMAs, scanning electron microscope (SEM-EDX) analysis, optical microscope (OM) images, and x-ray diffraction (XRD) pattern were taken. B2, B19', beta-Nb, and Ti2N phases were detected in all alloys. In SEM-EDX and OM research, it was determined that beta-Nb phase increased in dendritic structure as the Nb ratio increased. For the biocompatibility levels of alloys, the corrosion test method was carried out with the potentiodynamic test, which is one of the electrochemical methods. Tafel test and electrochemical impedance spectroscopy in a simulated body fluid (SBF) showed that the Nb additive increased the corrosion resistance of the alloy. Phase transformation temperatures (PTTs) of these alloys were investigated by using differential scanning calorimetry (DSC) measurements. In DSC research, it was determined that the alloys have a shape memory effect (SME), and the PPTs of the alloys decreased as the Nb ratio increased.
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    Production of V-Doped P2-type Na0.67Mn0.5Fe0.43Al0.07O2 Cathodes and Investigation of Na-Ion Full Cells Performance
    (Wiley-V C H Verlag Gmbh, 2024) Dogan, Ebru; Altundag, Sebahat; Altin, Serdar; Arshad, Muhammad; Balci, Esra; Altin, Emine
    The Na0.67Mn0.5Fe0.43Al0.07O2(x = 0-0.1) samples are successfully produced and their structural properties are investigated by common techniques. The highest surface area is found as 4.94 m(2) g(-1) for x = 0.04 V by the Brunauer-Elmet-Teller analysis. According to X-ray photoelectron spectroscopy of x = 0.04 V-doped sample,V4+, and V5+ ions are formed in the structure. The main phase is observed as P63/mmc symmetry with an impurity phase of V6O13 for x >= 0.06 . According to the CV analysis, while the redox voltage decreases for the Mn3+/Mn4+ , the intensity of the peaks of Fe2+/Fe3+ redox reaction decreases. While the best capacity value of the half cells at C/3-rate is obtained as 171 mAh g(-1) for x = 0.04, the lowest capacity fade is found for x = 0.08 . It is mentioned the V6O13 may contribute to the electrochemical process . The galvanostatic tests are investigated for the voltage windows of 3.5-1.5, 4-1.5, 4-2.5, 4-2, and 4-2.5 V and it is seen that the battery cells for 3.5-1.5 V have the best capacity fade (6%) among the others. The Na0.67Mn0.5Fe0.43Al0.07O2/ hard carbon is used for the full cells with presodiated anode and the first capacity value of the full cell is obtained as 80.2 mAh g(-1) for C/2-rate.