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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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    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, Bora
    Herein, 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.
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    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, Bora
    Nanostructured (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.
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    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.