Sürdürülebilir Kalkınma Amaçları

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• MakaleYalnız künye2025/r/gumushane/14101
  Remanent magnetization and magnetic relaxation in Bi:2223/ag tapes fabricated by the Powder-in-Tube (PIT) method at 30 K

  Düzgün, İbrahim; Çelebi, Selahattin

  In this study, the remanent magnetization and magnetic relaxation behaviour of Bi-2223/Ag superconducting tapes fabricated using the Powder-In-Tube (PIT) method were investigated. Measurements were conducted at a fixed temperature of 30 K, both under various field cycling amplitudes and in constant magnetic field conditions to analyse time-dependent magnetization. The remanent magnetization values obtained after full magnetic cycles were normalized and compared with theoretical predictions based on the extended critical state model. Additionally, magnetic relaxation curves were recorded at 30 K to evaluate flux creep characteristics. A clear logarithmic decay in magnetization was observed, indicating the coexistence of at least two distinct pinning regimes. These results contribute to a deeper understanding of flux dynamics and magnetic stability in Bi-2223/Ag PIT tapes for practical superconducting applications.

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• MakaleYalnız künye2021/r/gumushane/13294
  Effect of working pressure and post-annealing on structural, optical and electrical properties of p-type NiO thin films produced by RF magnetron sputtering technique

  Şenaslan, Fatih; Taşdemir, Muharrem; Çelik, Ayhan

  Nickel oxide (NiO) films were deposited on glass and silicon substrates using a Ni target by radio-frequency (RF) sputtering at various working pressure ranging from 5 to 20 mTorr. The films were annealed for 2 h at 400 °C in the air ambient. The effect of working pressure on structural, optical and electrical properties of NiO films was investigated in detail. The deposition rate of the films gradually increased with decreasing working pressure. The X-ray diffraction (XRD) presented that the crystal quality and the average crystallite size of annealed films increased with decreasing working pressure. The X-ray photoelectron spectroscopy (XPS) confirmed the presence of Ni2+ and Ni3+ ions along with the main peak and satellite peaks in the NiO films. Raman spectroscopy exhibited the one-phonon and two-phonon vibrations modes corresponding to Ni–O bond. UV–Visible analyses showed that annealed NiO thin films have higher transmittance than deposited ones. The band gap of the films increased from 3.33 to 3.52 eV with decreasing working pressure and further increased after the annealing process. The electrical properties were affected by the varying crystallinity and lattice defects depending on the deposition condition. All annealed NiO films exhibited p-type conductivity. The lowest resistivity (4.2 Ω.cm) was obtained from the annealed film after deposition at 5 mTorr.

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• MakaleYalnız künye2020/r/gumushane/11508
  Effect of indentation loading type on the mechanical properties of advanced high strength steel grade DP 800

  Ekmekci, Dursun; Cora, Ömer Necati

  The goal of this study was to acquire mechanical properties of a dual-phase grade advanced high strength steel (AHSS) by means of different microindentation loading conditions. Conventional, cyclic, and multi-step indentations were performed on DP 800 sample; and Young’s modulus, hardness values were obtained by the depth-sensing indentation technique. Effects of different load levels (50–300 mN) and type of indentation on the results were also analyzed through ANOVA. The load levels experimented yielded overall material response rather than its constituents (e.g., martensite and ferrite). Both hardness and Young’s modulus tend to decrease with increasing maximum indentation load level, especially from 50 to 100 mN, which is regarded as indentation size effect.

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• MakaleYalnız künye2019/r/gumushane/15016
  Production of silicone-based composite doped with waste NdFeB magnet and determination of mechanical properties by transforming experimental results into images

  Çelik, İlhan; Akben, Selahaddin Batuhan; Mazlum, Uğur

  Waste neodymium–iron–boron (NdFeB)-doped silicon-based magnetic polymer composites are obtained by mixing the double-doped mixtures with a 70–30% ratio. In this study, composite materials were produced by adding NdFeB magnetic particles with sizes between 0–45, 45–63, 63–125, and over 125 (µm), and compression experiments were carried out to determine the mechanical properties of them. Experimental results were transformed into images and then analysed using image processing methods. According to the analysis of images representing the results of compression experiments, the strength values of NdFeB–RTV (vulcanized at room temperature) silicone rubber have increased by increasing the magnetic powder ratio. In addition, it was observed that there is a decrease in the elongation at break values due to weakening of polymer chain bonds. Considering the sensitivity of the successfully produced composite materials to the magnetic field, significant improvements in strength values were obtained. It is hoped that these results will lead to an increase in the recycling rate of waste magnets and will prevent environmental damage.

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• MakaleYalnız künye2018/r/gumushane/12973
  Differential scanning calorimetry (DSC) and Ni+2 release analysis of NiTi-shape-memory dental alloys coated by micro-arc oxidation (MAO) method

  Yeşildal, Ruhi; Karabudak, Filiz; Şüküroğlu, Ebru Emine; Şüküroğlu, Süleyman; Zamanlou, Hamid; Bayındır, Funda; Şen, Sadri; Totik, Yaşar

  This study aims to prevent the release of Ni+2 and increase the biocompatibility of NiTi-shape-memory dental alloys with the micro-arc oxidation (MAO) coating by preserving the shape-memory feature in the oral environment. The TiO2-ceramic coating and Ag-doped TiO2 coating have been grown on shape-memory, co-atoms’ dental NiTi alloys with the MAO method. Biocompatibility properties of the coating were determined by in-vitro tests. In-vitro tests have been made as retention tests in a simulated body fluid (SBF). Whether the grown surface coating impacts the shape-memory properties of the base material or not has been determined by differential scanning calorimetry (DSC) analysis. It was observed as a result of retention tests that bone-like apatite form occurred on the surface of TiO2-coated NiTi and Ag-doped TiO2-coated NiTi coating. It was determined as a result of retention tests in SBF that the Ni+2 release rate from the base material was below the limit of detection in coated samples. As a result of DSC analysis, it was not observed any significant changes in transformation temperature with the MAO coating. It was concluded that the thin-film coatings formed by MAO technique prevent the release of Ni in the oral environment and increase the biocompatibility by preserving shape memory properties of NiTi dental alloys.

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• MakaleYalnız künye2017/r/gumushane/10267
  Microindentation on the porous copper surface modulations

  Ekmekci, Dursun; Yilmaz, Fikret; Kölemen, Ugur; Cora, Omer Necati

  This study aimed to investigate the mechanical properties of a surface modulation which was realized through compaction, and then sintering of copper powders. To this goal, Berkovich type of indenter and depth-sensing indentation technique were used in microindentation to measure the hardness and modulus of elasticity values at different features of compact. Indentations were performed with a peak force of 50 mN. Hardness values were obtained in 0.88-1.12 GPa range while the modulus of elasticity was recorded in the 70-111 GPa interval. Even though both modulus of elasticity and hardness values were noted to be different for copper powders and substrate, one-way ANOVA analyses showed that the differences in both modulus of elasticity and hardness values are insignificant. FE modeling of microindentation was also performed and validated. It was shown that the force-displacement values obtained from FE analyses are quite well in agreement with the experimental data.

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• MakaleYalnız künye2017/r/gumushane/15025
  Improving by postoxidation of corrosion resistance of plasma nitrocarburized AISI 316 stainless steels

  Yenilmez, A.; Karakan, M.; Çelik, I.

  Austenitic stainless steels are widely used in several industries such as chemistry, food, health and space due to their perfect corrosion resistance. However, in addition to corrosion resistance, the mechanic and tribological features such as wear resistance and friction are required to be good in the production and engineering of this type of machines, equipment and mechanic parts. In this study, ferritic (FNC) and austenitic (ANC) nitrocarburizing were applied on AISI 316 stainless steel specimens with perfect corrosion resistance in the plasma environment at the definite time (4 h) and constant gas mixture atmosphere. In order to recover corrosion resistance which was deteriorated after nitrocarburizing again, plasma postoxidation process (45 min) was applied. After the duplex treatment, the specimens’ structural analyses with XRD and SEM methods, corrosion analysis with polarization method and surface hardness with microhardness method were examined. At the end of the studies, AISI 316 surface hardness of stainless steel increased with nitrocarburizing process, but the corrosion resistance was deteriorated with FNC (570 °C) and ANC (670 °C) nitrocarburizing. With the following of the postoxidation treatment, it was detected that the corrosion resistance became better and it approached its value before the process.

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