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    Effect of Boron and its Influence on Mechanically Alloyed FeCo Nanocrystals
    (Springer India, 2024) Simsek, Tuncay; Ozgur, Damla; Simsek, Telem; Avar, Baris; Yildiz, Bugra; Chattopadhyay, Arun K.
    This study investigates the effect of adding boron as a ternary addition to binary FeCo alloys. Fe-Co-B ternary alloys with varying boron concentrations between 0 and 2 wt% were synthesized through mechanical alloying. The study aims to analyze the structural, morphological, and magnetic properties of the Fe-Co alloy matrix with the inclusion of boron. The XRD results showed a single solid solution phase of Fe-bcc structure for all alloys, regardless of the boron concentration. It was seen that the low solubility of boron in Fe-Co caused the formation of hard structures at the grain boundaries, resulting in an increase in hardness with an increase in boron concentration. On the other hand, a decreasing trend was observed in coercivity, which is ascribed to the formation of FeB at the grain boundaries, as proved from XRD analysis. An increase in boron concentration did not seem to significantly affect the saturation magnetization, which remained in the range of 190 +/- 10 emu/g for all Fe-Co-B alloys. The experimental data was cross checked and further insights were gained; DFT calculations were performed using Vienna Ab Initio Simulation Package.
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    Effect of Cu, Sn and Sb addition on the structural, thermal and magnetic properties of body-centered cubic structured CoNiMnGaSi high entropy alloy
    (Springer Heidelberg, 2022) Simsek, Telem; Ozkul, Iskender; Canbay, Canan Aksu; Avar, Baris; Simsek, Tuncay; Guler, Seval Hale; Ozcan, Sadan
    In this study structural, morphological, thermal and magnetic properties of equiatomic CoNiMnGaSi (base), CoNiMnGaSiCu, CoNiMnGaSiSn and CoNiMnGaSiSb alloys are discussed. The formation of solid-solution nanocrystalline bcc structure of the alloys was determined by XRD and DTA techniques. SEM-EDS analyses also revealed the homogeneous distribution of the elements. The room temperature magnetic hysteresis loops showed that as-casted alloys reached saturation easily with coercivity less than or equal to 35 Oe. As the Cu and Sn were added to the alloy, the saturation magnetization was decreased from 112 emu/g to 50 emu/g, which was mainly due to the substitution of non-magnetic atoms to the magnetic Co in the base CoNiMnGaSi alloy, whereas the addition of Sb to the base alloy did not have a significant effect on the M-s. The CoNiMnGaSiSb was found to have the highest Curie Temperature of 670 K, which makes the alloy a promising candidate for power industry-related applications.
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    Effects of Cr and W in TiMoNb Refractory High Entropy Alloys
    (Springer India, 2024) Simsek, Tuncay; Kurtulus, Altug; Avar, Baris; Guler, Seval Hale; Dag, Ilker Emin; Chattopadhyay, Arun K.
    This study focuses on synthesizing and characterizing mechanically alloyed refractory high entropy alloys (RHEA) containing TiMoNb, Cr, W, and Cr + W. Analytical techniques including XRD, SEM, EDX, DTA, and TGA were employed to explore the influence of Cr and W on the alloys' structure, morphology, and thermal stability towards oxidation. XRD analysis confirmed the formation of a single-phase bcc solid solution in TiMoNbCr, TiMoNbW, and TiMoNbCrW alloys. Crystallite size decreased as milling progressed, yielding average sizes of approximately 7.2 nm, 7.4 nm, and 9.7 nm, with lattice strains of 1.143%, 1.148%, and 1.15%, respectively. Both experimental and calculated values of lattice parameters converged to around 3.1685 +/- 0.002 and 3.1791 +/- 0.010 angstrom for all three alloys. The synergy of Cr and W in TiMoNb was observed for the first time, impacting dislocation density, hardness, and oxidation stability. TiMoNbCrW exhibited reduced dislocation density and the highest hardness (502 HV). TGA indicated enhanced oxidation resistance up to 400 degrees C for TiMoNbCrW compared to the most vulnerable TiMoNbCr alloy.
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    Experimental investigation of the effects of different quaternary elements (Ti, V, Nb, Ga, and Hf) on the thermal and magnetic properties of CuAlNi shape memory alloy
    (Springer Heidelberg, 2022) Ozkul, Iskender; Karaduman, Oktay; Simsek, Telem; Simsek, Tuncay; Canbay, Canan Aksu; Ibrahim, Pshdar Ahmed; Arpa, Ipek A. K.
    To discover cheaper and functional species of shape memory alloys (SMAs) is one of the main objectives for interested researchers. In this work, five different alloys were produced by adding different quaternary alloying elements (Ti, Ga, V, Hf, and Nb) into the ternary CuAlNi-base (C-) alloy.The thermal and structural properties of the produced alloys were investigated. The phases of Al7Cu23Ni, AlNi, CuNi2Ti, Al80V20, AlNbNi2, Cu3Ga, and NiSHf were observed by X-ray powder diffraction (XRD) analyses after arc melting processes. The average crystallite sizes of the produced alloys were calculated as 17.1, 18.9, 19.4, 20.8, and 23.7 nm for CV, CNb, CHf, CTi, and CGa alloys, respectively. The highest lattice strain was found at about % 0.572 for CGa alloy. Measuring the magnetic properties of the produced alloys revealed the paramagnetic behavior of the alloys at room temperature.
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    Experimental investigation of the effects of different quaternary elements (Ti, V, Nb, Ga, and Hf) on the thermal and magnetic properties of CuAlNi shape memory alloy (Jun, 10.1557/s43578-022-00625-y, 2022)
    (Springer Heidelberg, 2022) Ozkul, Iskender; Karaduman, Oktay; Simsek, Telem; Simsek, Tuncay; Canbay, Canan Aksu; Ibrahim, Pshdar Ahmed; Arpa, Ipek Ak
    [Abstract No tAvailable]
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    FeCoNiMnCr high-entropy alloys (HEAs): Synthesis, structural, magnetic and nuclear radiation absorption properties
    (Elsevier Sci Ltd, 2023) Simsek, Telem; Kavaz, Esra; Guler, Omer; Simsek, Tuncay; Avar, Baris; Aslan, Naim; Almisned, Ghada
    We report the synthesis and structural, magnetic and Radiation shielding properties of High Entropy Alloy (HEA) produced through mechanical alloying method. Using an X-Ray Diffractometer (PanalyticalEmpryan) with CuK radiation at 45 kV and 40 mA, the phase identification starting elements and as-milled powders are identified. Scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDX), morphological and microstructural investigations were conducted (FEI Quanta FEG 450). EDX and elemental mapping analyses are conducted to assess the purity and elemental distributions of the synthesized alloys. Using the Quantum Design Physical Characteristics Measurement System (PPMS) with vibrating sample magnetometer (VSM) and a magnetic field of 30 kOe at room temperature, magnetic properties are examined. Using Cs-137 radioisotope and mathematical methods, gamma-ray and neutron shielding properties of HEA are investigated in a conventional transmission setup using experimental and theoretical approaches. In the presence of a 3 T applied field, the sample exhibits a low magnetization of 5.30 emu/g at 300 K. Moreover, Ms is raised to 22 emu/g at 10 K owing to decreased thermal effects. The temperature dependence of the magnetization is recorded in the presence of a 1 T applied field. HEA exhibits superior neutron attenuation properties than conventional absorption materials such as B4C, graphite, and water. Our results showed that the synthesized HEA has superiority over other alloys and conventional neutron absorption materials. It can be concluded that the proposed novel HEA might be investigated further in terms of broadening its characterization and clarifying its other crucial properties to extend the scope of the current investigation.
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    High Entropy Materials for CO2 Conversion
    (CRC Press, 2024) Simsek, Telem; Guler, Seval H.; Guler, Omer; Simsek, Tuncay
    Metal-based oxides, ceramics, and composite catalysts are commonly used for CO2 conversion. To increase the efficiency of these catalysts, strategies such as heterostructure, defect engineering, nanolayers, mesoporous structure development, and oxygen vacancy engineering are used. In recent years, highly stable high entropy alloys (HEAs), which include at least five different elements in equimolar or nearly equimolar ratios, have recently come to be recognized as promising CO2 conversion catalysts. Their unique properties enable enhanced reactivity and selectivity, making them highly valuable in addressing CO2 emissions and climate change challenges. When several elements are included in a catalyst, surface microstructures with different atomic configurations and active catalytic sites are produced. As a result, different adsorption modes arise for reactants and intermediates. In addition, the mixing of metal elements in varying atomic ratios causes changes in the electronic structure of metals. The distinct catalytic characteristics of HEAs are a result of modifications to their electronic structure brought on by lattice stretching, distortion, and compositional alterations. © 2024 Anuj Kumar and Ram K. Gupta.
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    Investigation of shape memory characteristics and production of HfZrTiFeMnSi high entropy alloy by mechanical alloying method
    (Elsevier, 2022) Guler, Omer; Simsek, Tuncay; Ozkul, Iskender; Avar, Baris; Canbay, Canan A.; Chattopadhyay, Arun K.; Guler, Seval H.
    High entropy alloy (HEA) with shape memory effect (SME) has been the subject of great interest for the past few decades. However, with the increased demands for new materials for high thermal applications, the research activities on the multi elemental high entropy shape memory alloys (HESMA) have been increased by many folds recently. The nano crystalline HEA powder with shape memory effect developed in this study, HfZrTiFeMnSi, was produced by mechanical alloying (MA) for the first time. In this method equiatomic ratio of Hf, Zr, Ti, Fe, Mn, and Si were mixed together and milled by MA process for 100 h. The powder formed was of amorphous in nature. Elemental mapping of the powder from SEM-EDS revealed homogeneity of the alloying elements confirming successful fabrication of HfZrTiFeMnSi HEA powder. The DSC studies from ambient to 500 degrees C of the annealed alloy powders showed reversible austenitic to martensitic (A <-> M) transformations. The A <-> M transformation hysteresis seemed to vary with the milling time and annealing temperature. The enthalpy values, Delta H, for the transformation were calculated from the DSC plots using tangent method for peak area calculation. Regardless of the annealing temperature, the thermal analysis revealed that the Delta H, equilibrium temperature (T0), and crystallization temperature values decreased with the increasing milling time.
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    Local atomic configurations in mechanically alloyed amorphous (FeCoNi)70Ti10B20 powders
    (Elsevier Science Sa, 2023) Kalkan, Bora; Simsek, Tuncay; Avar, Baris
    The atomic structure of amorphous (FeCoNi)70Ti10B20 alloy synthesized by mechanical alloying was in-vestigated using high energy synchrotron X-ray diffraction and inverse Monte Carlo simulations of pair distribution functions. Empirical potential structure refinement indicates a chemical short-range order at the length scales of 2.1-2.5 & ANGS; via local atomic arrangements forming deformed bcc-like clusters. The structural model obtained was described by bond lengths, coordination numbers, and bond angle dis-tribution functions determined for the first neighbor atoms by x-ray scattering supplemented with 3D Monte Carlo simulations. & COPY; 2023 Elsevier B.V. All rights reserved.
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    Nanocrystalline NiTiB reinforced aluminum matrix composites: Synthesis, structural, mechanical and corrosion properties
    (Sage Publications Ltd, 2024) Pul, Muharrem; Dag, Ilker Emin; Simsek, Tuncay; Avar, Baris; Chattopadhyay, Arun K.
    In this study, aluminum composites were developed using a powder metallurgy route by incorporating varying amounts of nanocrystalline NiTiB into the Al2024 alloy. The effects of nanocrystalline NiTiB on the structural, morphological, corrosion, and mechanical properties of the aluminum composites were thoroughly investigated. The results showed that the base alloy and composites with 2% and 4% NiTiB exhibited the highest relative density. The composite with 4% NiTiB achieved the maximum hardness of 87.4 HV. Additionally, the inclusion of nanocrystalline NiTiB significantly improved the compressive strength, corrosion resistance, and wear resistance of the composites. Specifically, the compressive strength increased by approximately 2% with 2% NiTiB and by around 13% with 12% NiTiB. Corrosion resistance was highest in the composite with 4% NiTiB, as confirmed by electrochemical impedance spectroscopy. In the wear-loss study, the wear loss of the composites was found to be reduced by 244% and 457% for those reinforced with 2% and 12% NiTiB, respectively. These findings underscore the potential of nanocrystalline NiTiB to enhance the performance of Al2024 composites in applications demanding superior corrosion resistance, mechanical strength, and wear resistance.
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    Possible Interaction of PVC with Micro-and Nano-fillers
    (Springer Science and Business Media Deutschland GmbH, 2024) Guler, Seval Hale; Simsek, Tuncay; Guler, Omer; Dikici, Burak
    Undoubtedly, polyvinyl chloride (PVC) is one of the most produced synthetic polymers globally and is used in all areas of life. Its general structure consists of hydrocarbon and chloride as well known. The main reasons for its widespread use in our life are low production cost, high mechanical strength, and chemical stability. The PVCs have significant problems such as low thermal resistance or weak impact strength. Thus, nowadays, the current studies are noteworthy on the PVC-matrix composites reinforced with micro-/nano-based fillers. The primary purpose of this studies improves the mechanical, physical, or chemical properties of PVC. Of course, the essential feature of a composite structure is the matrix/reinforcement interface and its interactions. In addition to the production method, the selection of matric and reinforcement fillers is the main factor affecting the adhesion and interactions between the interface. In this chapter, an overview of the possible interaction of PVC with micro- and nano-fillers is presented. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.
  • Küçük Resim
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    Preparation of single-phase YbB(6)by low-temperature solid-state reaction method using iodine
    (SPRINGER, 2020) Simsek, Tuncay
    In this study, low-temperature solid-state synthesis of pure nanocrystalline ytterbium hexaboride (YbB6) employing iodine-based reduction method has been discussed. For the reduction reaction, the mechanically activated powder mixture of ytterbium oxide, boron oxide, magnesium, and iodine was heated up under Ar in a quartz tube to 85 degrees C. All reaction byproducts, viz. MgO, Mg-3(BO3)(2), and YbI2, were removed by hot acid leaching with 3 M HCl solution to form pure YbB6. The morphological and phase structure of the synthesized YbB(6)powder were analyzed by X-ray diffractometry (XRD), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. The crystalline phases obtained were refined by multi-phase Rietveld refinement. XRD and Raman spectroscopy showed a contrast between the nano-YbB(6)formed by the present low-temperature iodine-based reduction method versus mechanochemical method. The YbB(6)produced by the low-temperature iodine reduction method is highly crystalline in nature, whereas YbB(6)produced by mechanochemical method is less crystalline or conversely more amorphous in nature. The iodine-based reduction method indeed played a definitive role to allow the reaction to take place at a lower temperature enabling the formation of nanocrystalline YbB6.