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Öğe A comparison of magnetic, structural and thermal properties of NiFeCoMo high entropy alloy produced by sequential mechanical alloying versus the alloy produced by conventional mechanical alloying(Elsevier, 2021) Simsek, Tuncay; Akgul, Saban; Guler, Omer; Ozkul, Iskender; Avar, Baris; Chattopadhyay, Arun K.; Canbay, Canan A.The soft ferromagnetic materials are of great industrial importance for their applications in magnetic cores for transformers, electric motors, inductors, and generators. In recent years, the trend has been to use magnetic high entropy alloys (HEAs) owing to their superior magnetic properties compared to the conventional magnetic materials. In this study, the traditional magnetic materials, (NiFeCo)(95)Mo-5 and (NiFeCo)(90)Mo-10 produced by conventional mechanical alloying method, were compared with the NiFeCoMo high entropy alloy produced by the sequential mechanical alloying method. Unlike conventional mechanical alloying, NiFeCoMo HEA was produced by mechanical alloying using sequential additions of Co and Mo to the preformed Fe-Ni alloy. Besides its magnetic properties, the effect of Co and Mo on the overall characteristics of the alloy was also investigated. In 60 h milled samples of the (NiFeCo)(95)Mo-5 and (NiFeCo)(90)Mo-10 alloys, the crystallite sizes were estimated as 10.5 and 10.8 nm respectively, whereas the crystallite size for the NiFeCoMo HEA was 15 nm. The presence of Mo in the alloy induced the formation of lamellar or layered structures of the particles. During the sequential milling to form NiFeCoMo HEA, it was noticed that the addition of Co into the preformed Fe-Ni alloy increased the magnetic saturation value due to the formation of FeCoNi alloy phase. However, further addition of Mo into the FeCoNi alloy phase reduced the magnetic saturation value of NiFeCoMo alloy significantly. After 60 h of milling the magnetic saturation value was dropped from 102.48 emu/g for the NiFeCo alloy to 60.52 emu/g for the NiFeCoMo alloy.Öğe A review of soft magnetic properties of mechanically alloyed amorphous and nanocrystalline powders(Springernature, 2023) Yakin, Alican; Simsek, Tuncay; Avar, Baris; Simsek, Telem; Chattopadhyay, Arun K.The development of soft magnetic materials is fundamentally important for improving operational efficiencies of the ever-growing field of power electronics, electrical motors, and generators. It requires to meet the challenges of constantly changing fields of modern areas of applications starting from spaceships to day-to-day electronics. Many new materials with soft magnetic properties, viz. ferrous alloys, soft ferrites, amorphous and nanocrystalline magnetic alloys, have been continuously evolving since the inception of electromagnetic induction. The main drive for the continuous improvements of soft magnetic materials is primarily to enhance energy efficiency, to reduce size and weight, and to boost the power of high-frequency power electronics and electrical machines of high rotational speed. Despite some predicaments, the amorphous and nanocrystalline soft magnetic materials have become a field of major research interest since their invention four decades ago. It has been observed that the amorphous and nanocrystalline alloys exhibit better magnetic properties than the conventional soft magnetic alloys. This group of materials is produced adapting various production techniques. In this review, amorphous, nanocrystalline, and high entropy alloys (HEA) are discussed as soft magnetic materials and their electromagnetic properties are assessed. However, this review will particularly focus on the mechanically alloyed amorphous, nanocrystalline, and HEA soft magnetic materials. The soft magnetic alloys of interest for this review are grouped on the basis of Fe, Co, Ni, and FeCoNi. Furthermore, the effect of MA parameters and subsequent annealing processes on the magnetic properties is also assessed. This review brings forth a great promise in the field of soft-core magnets for high-end applications.Öğe A single step synthesis by mechanical alloying and characterization of nanostructured Fe2B of high magnetic moment(Elsevier Sci Ltd, 2021) Simsek, Telem; Avar, Baris; Simsek, Tuncay; Yildiz, Busra; Chattopadhyay, Arun K.; Ozcan, SadanThis paper delineates a single-step production method of nanostructured diiron boride (Fe2B) and its structural, magnetic and magnetothermal properties. Structurally Fe2B resembles the tetragonal copper aluminide, CuAl2. The samples of nanostructured Fe2B were synthesized by milling Fe and B powders without any pre-treatment. Single phase Fe2B nanoparticles were successfully produced with the crystallite sizes of 68 and 46 nm after milling the powders for 10 h and 20 h, respectively. The saturation magnetization of the samples was found to decrease with increased milling time indicating that the surface spin disorder plays a crucial role in the magnetic properties. The highest saturation magnetization (Ms) of 141 emu/g with low coercivity (Hc) of 48 Oe was obtained for the 10 h milled sample of Fe2B, whereas the 20 h milled sample exhibited Ms and Hc as 129 emu/g and 149 Oe. This paper also presents a detailed information on the total and atom projected densities of state functions as well as the magnetic moment contribution of the individual atoms of Fe and B in Fe2B explaining the strong room temperature ferromagnetic properties contributed by the large number of unpaired 3 d electrons in Fe. The magnetothermal properties of the as-made Fe2B nanocrystals of high magnetic moment were investigated by measuring the rise in temperature as a function of time in the presence of AC magnetic fields. The magnetic Fe2B nanocrystals show significant thermal response with the high specific absorption rate of 172 W/g, demonstrating the advantages of using Fe2B nanocrystals for the application in magnetic fluid therapy for hyperthermia.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.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, SadanIn 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.Öğe 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.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, GhadaWe 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.Öğe 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.Öğe Local atomic configurations in mechanically alloyed amorphous (FeCoNi)70Ti10B20 powders(Elsevier Science Sa, 2023) Kalkan, Bora; Simsek, Tuncay; Avar, BarisThe 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.Öğe 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.Öğe Solid-State Synthesis and Characterization of the Stable Nanostructured Ni21Ti2B6 Phase(Wiley-V C H Verlag Gmbh, 2021) Simsek, Tuncay; Avar, Baris; Ozcan, Sadan; Chattopadhyay, Arun K.; Kalkan, BoraHerein, nanostructured ternary Ni-Ti-B alloy synthesized by mechanical alloying from the elemental Ni, Ti, and B powders by high energy ball milling is described. The synthesized alloy of nominal composition of Ni70Ti10B20 results in the formation of a unique stable phase of Ni21Ti2B6, which happens to be stoichiometrically very close to Ni70Ti10B20 in the cubic symmetry. The synthesized alloy samples also show amorphization together with the formation of nanocrystalline phases of Ni21Ti2B6 at both early and later stages of the alloying process. Thermal analysis carried out on Ni70Ti10B20 induces crystallinity and reveals the formation of crystalline Ni-Ti-B ternary alloy, Ni21Ti2B6, above 523 K, confirming the stability of the ternary crystalline phase of the alloy. The magnetic saturation of the alloy is measured as 0.95 emu g(-1) for the starting amorphous phase that increases to 9.05 emu g(-1) for the crystalline phase upon annealing. Correspondingly, the coercivity value for the annealed sample is reduced to 70 Oe from 194 Oe for the amorphous phase. This is the first time that an evidence of the stable crystalline Ni-Ti-B ternary alloy is reported.Öğe Structural stability of mechanically alloyed amorphous (FeCoNi)70Ti10B20 under high-temperature and high-pressure(Elsevier Science Sa, 2021) Avar, Baris; Simsek, Tuncay; Ozcan, Sadan; Chattopadhyay, Arun K.; Kalkan, BoraNanostructured (FeCoNi)(70)Ti10B20 (at%) alloy was synthesized by mechanical alloying from elemental powder mixture of Fe, Co, Ni, Ti and B using ball milling. The effect of ball milling time on the evolution of structure and morphology was investigated by X-ray diffraction, scanning and transmission electron microscopy and differential thermal analysis. It was observed that the formation of solid solution of (FeCoNi)(70)Ti10B20 started from the very onset of the milling process. Crystallite size and lattice strains seemed to be leveled off after 20 h of milling with no further major changes. The milling process for longer periods introduced severe plastic deformations causing formation of amorphous phase of (FeCoNi)(70)Ti10B20. The amorphous alloy composition was confirmed by energy dispersive X-ray spectroscopy analysis that showed an excellent homogeneity of the alloying elements. The phase stability of the mechanically alloyed amorphous sample was further verified by employing high-temperature and high-pressure studies. The alloy samples heat-treated at 700 degrees C revealed crystallization of the amorphous phase. However, synchrotron-based high-pressure ambient temperature X-ray diffraction studies confirmed that the amorphous phase of the alloy remained stable up to the pressure of 30 GPa. The 50 h milled sample after being annealed at 350 degrees C showed improvement in the soft magnetic properties of the alloy, which was due to the probable elimination of the residual stress in the amorphous phase of the alloy powders. (C) 2020 Elsevier B.V. All rights reserved.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, BoraIn 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.Öğe Synthesis of boron-based alloys and compounds by mechanical alloying: A review(Elsevier, 2023) Yakin, Alican; Avar, Baris; Simsek, Tuncay; Chattopadhyay, Arun K.Boron and its derivatives are highly valued in many alloy systems for their ability to enhance material strength, hardness, thermoelectric properties, wear and corrosion resistance, and electromagnetic properties. Incorporating boron-based derivatives like boron nitride (BN), boron carbide (B4C), hexaborides, and metal borides into composites, amorphous alloys, high entropy alloys (HEAs), and magnetic alloys results in materials with superior properties compared to those without boron. As a result, there is growing market interest in advanced material applications of these boron-based alloys, which are utilized in diverse fields from health and automotive to space exploration, smart engineering materials, manufacturing industry, glass and ceramics, cleaning materials, hightech electronics, and modern household appliances. The use of boron and its derivatives has spurred innovation in the production of new materials, with the mechanical alloying (MA) method being a desirable option for synthesizing boron-based alloys with desired properties by adjusting alloying parameters. This review examines the properties of boron-based alloys synthesized by MA methods, providing valuable insights into the potential applications of these materials. Overall, this review provides a comprehensive survey of boron-based alloys and their potential for advanced material applications.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, TuncayIn 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.
