Browsing by Author "Ovecoglu, M. Lutfi"

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Nbmovta Refractory High-Entropy Alloy Incorporated Wni Matrix Composite as a Future Plasma-Facing Material: Evaluation of Mechanical Properties and Helium Ion Irradiation Behavior
(Elsevier Sci Ltd, 2025) Boztemur, Burcak; Filiz, Kaan; Karaguney, Zahide; Gokaydin, Eyupcan; Bozkurt, Yasin; Ozbasmaci, Ceren; Ovecoglu, M. Lutfi
Refractory high-entropy alloys (RHEAs) have gained attention in the last decades with their high mechanical strength, self-healing mechanism, and high irradiation resistance. These materials are evaluated to have a high potential as plasma-facing materials for fusion reactors. In this study, helium ion irradiation and mechanical behaviors of the RHEA-reinforced WNi matrix composites were investigated based on this perspective. Equimolar molybdenum, niobium, tantalum and vanadium powders were mechanically alloyed for 6 h to produce NbMoVTa RHEA with a single BCC phase. Then, different amounts (10, 20, 30, and 40 wt%) of RHEA were added into the W1Ni (containing 99 wt% W and 1 wt% Ni) matrix by planetary ball milling for 72 h. Consolidation was conducted by spark plasma sintering technique (1410 degrees C, 1 min). X-ray diffraction, scanning electron microscopy coupled with energy dispersion spectroscopy, and Archimedes' density analyses were performed on the composites. Moreover, wear and hardness properties of the composites were examined, and the lowest specific wear rate (0.59 mm3/N.m x 10- 5) and the highest hardness value (10.10 GPa) were found for the W1Ni-40RHEA composite. Helium irradiation was exposed to the composites to observe their irradiation resistance. It was observed that the lowest increment and the least deformation were obtained with the SPS'ed W1Ni-40RHEA composite. With the analysis of He+ irradiation, it was determined that the effect of radiation on mechanical properties is irrelevant. Also, it was observed that the addition of RHEA into the W matrix can create a high potential for using plasma-facing material. Moreover, it decreased the problems of tungsten against He+ irradiation.
Powder Metallurgical Synthesis, Thermochemical Calculations and Characterization Studies of HfB2 Powders
(Springer India, 2025) Akbari, Amir; Suzer-Cicek, Ilayda; Mertdinc-Ulkuseven, Siddika; Gokce, Hasan; Ovecoglu, M. Lutfi; Agaogullari, Duygu
This study reports on the thermochemical calculations, mechanochemical synthesis, purification process, and characterization studies of the HfB2 powders by using native sources. Firstly, HfO2, native B2O3, and Mg starting powders were prepared with a multi-axial vibratory ball mill (NanoMultimix) in stoichiometric and excess amounts. The milling process was optimized by varying the time (2, 4, 6, 8, 10, 12 h). Then, unwanted by-products (HfO2, MgO) were removed by leaching with 4 and 6 M HCl. Phase and Rietveld analysis, microstructure investigations with scanning electron microscopy/energy dispersion spectroscopy and transmission electron microscopy, and particle size measurement were conducted. The purest HfB2 was obtained in the powders milled for 8 h in stoichiometric ratios and leached with 6 M HCl. The resulting optimum powder has an average particle size of 135 nm. Oxidation kinetics (500, 600, 700, 800, and 900 degrees C) were also investigated. As the temperature increased, the amount of oxidation increased based on the TG result. As a result of the characterization studies, the synthesis of single-phase, high-purity HfB2 was achieved using domestic resources.