Yazar "Simsek, Telem" seçeneğine göre listele

Listeleniyor 1 - 8 / 8
  • [ X ]
    Öğe
    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.
  • [ X ]
    Öğe
    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.
  • [ X ]
    Öğe
    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.
  • [ X ]
    Öğe
    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]
  • [ X ]
    Öğe
    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.
  • [ X ]
    Öğe
    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.
  • [ X ]
    Öğe
    Synthesis and characterization of amorphous-nanocrystalline Fe70Cr10Nb10B10 powders by mechanical alloying
    (Springer Heidelberg, 2022) Avar, Baris; Chattopadhyay, Arun K.; Simsek, Tuncay; Simsek, Telem; Ozcan, Sadan; Kalkan, Bora
    In this study, structural, morphological, thermal and magnetic properties of amorphous-nanocrystalline Fe70Cr10Nb10B10 (at.%) alloy are discussed. The formation and evaluation of amorphous-nanocrystalline structures of the alloy were followed by XRD, SEM-EDX, TEM, DTA, and VSM techniques. After 50 h of milling Cr, Nb, and B were completely dissolved into the Fe lattice forming 82% of the amorphous phase of the alloy. A gradual dissolution of the alloying elements also increased the lattice parameters concurrently. The lattice parameters reached a maximum value of 2.908 angstrom after 20 h of milling and then leveled off to a value of 2.891 angstrom at the end of 50 h of milling. Based on the XRD data, crystallite size and lattice strain of the alloy were calculated as 3.2 nm and 3.34% respectively. TEM analyses revealed that the alloy particulates comprised needle-shaped nanoparticles of an average size of 21 nm. The room temperature magnetic hysteresis loops showed that the increased duration of milling decreased the saturation magnetization from 91 to 24 emu/g. This was mainly due to the upsurge on the amorphous phase content in the alloy as the milling progressed. The increase in amorphous phase content and the subsequent reduction of the saturation magnetization were due to the inter-diffusion of the non-ferromagnetic Cr and B atoms into the Fe lattice. Thermal studies revealed that around 350 degrees C the amorphous phase of the alloy began crystallizing. The magnetic saturation of the heat-treated alloy also increased with the growth in the crystalline phases. The 50 h milled sample annealed at 700 degrees C was found to have the highest magnetic anisotropy as observed from the temperature-dependent zero-field cooled and field cooled magnetization measurements. The high-pressure X-ray diffraction measurements revealed that the amorphous state of the alloy remained stable up to 11.3 MPa. It also revealed the structural similarities of the Fe70Cr10Nb10B10 alloy with those of the Fe70M10B20 (M = Nb and Cr) types. For all practical purposes, the microstructural stability under high compressive pressure represents the consolidation properties of the nanostructured magnetic materials since both pressure and temperature-induced phase transformations are the primary controlling factors for the specific magnetization properties of the alloy.
  • [ X ]
    Öğe
    The effect of Cr and Nb addition on the structural, morphological, and magnetic properties of the mechanically alloyed high entropy FeCoNi alloys
    (Springer Heidelberg, 2022) Yakin, Alican; Simsek, Telem; Avar, Baris; Chattopadhyay, Arun K.; Ozcan, Sadan; Simsek, Tuncay
    In this study, four different equimolar compositions of FeCoNi, FeCoNiNb, FeCoNiCr, and FeCoNiNbCr were synthesized by the mechanical alloying method. The effects of Cr and Nb addition on the structural, morphological, and magnetic properties of FeCoNi alloy were investigated in detail. The structural aspects of the samples were analyzed by X-ray diffractometer and scanning electron microscope equipped with an energy dispersive X-ray spectrometer. High and low-temperature magnetic properties were evaluated by a vibrating sample magnetometer. It was noticed that the addition of Nb caused amorphization, while Cr promoted crystallization in the alloys. The crystallite sizes were calculated as 9.7, 3.1, 8.3, and 4.4 nm for the FeCoNi, FeCoNiNb, FeCoNiCr, and FeCoNiCrNb alloys, respectively, after 20 h of milling. The SEM images of the as-milled alloys revealed irregular and layered structures for FeCoNi and FeCoNiCr alloys of mean particle sizes around 140 and 120 mu m. In contrast, the addition of Nb in these alloys, viz. FeCoNiNb and FeCoNiNbCr alloys, formed mostly spherical with irregular morphologies of particle sizes ranging between 55 and 80 mu m. It was noticed that the low solubility of Cr caused precipitation at the grain boundaries of the alloy particles, and it contributed to the formation of hard structures of irregular and layered morphologies. The observed increase in the lattice parameters and lattice strain in the solid solution phases of all-alloy systems studied was mainly due to the lattice distortion and intense plastic deformations. The maximum saturation magnetization obtained from the room temperature hysteresis loops was 150.4 emu/g for the FeCoNi alloy after 10 h of milling. The additions of non-magnetic Cr, Nb, and both into FeCoNi, caused a significant decrease in the saturation magnetization. The coercivity of the as-milled alloys was also found to decrease with the reduction in the nano-crystallite sizes, which elucidated that the crystallite sizes of the alloys were smaller than the magnetic exchange length. The high-temperature magnetization curves revealed that all alloys studied had Curie temperature higher than 700 K.