Yazar "Baydogan, Murat" seçeneğine göre listele

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    Indentation creep behavior of Fe-8Ni-xZr oxide dispersion strengthened alloys
    (Walter De Gruyter Gmbh, 2023) Tekin, Mustafa; Muhaffel, Faiz; Kotan, Hasan; Baydogan, Murat
    This study was conducted to understand the creep behavior of two oxide dispersion strengthened alloys containing Zr as the alloying addition by performing indentation creep tests at room temperature. The oxide dispersion strengthened alloys were Fe-8Ni-xZr (x = 1 and 4 at.%, i.e., Zr-1 and Zr-4 alloys, respectively), which had been previously fabricated by mechanical alloying; followed by consolidation via equal channel angular extrusion at 1000?. The indentation tests were conducted under a maximum load of 100 mN with the loading rates at 300 and 400 mN min(-1). The hardness was calculated by the Oliver-Pharr method, and the creep properties, such as the creep displacement, creep strain rate, creep stress, and stress exponent n, were determined. The results showed that the Zr-4 alloy was harder than the Zr-1 alloy. However, the creep resistance of the Zr-1 alloy was better than that of the Zr-4 alloy. It was further demonstrated that both the hardness and creep resistance depended on the loading rate. Moreover, a possible creep mechanism was proposed. Although the tests were performed at room temperature, they can provide insight into the effect of an oxide dispersion strengthened alloys microstructure on creep at higher temperatures.
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    Influence of Electrolyte Compositions and Electrical Parameters on Thermal Properties of Micro-Arc Oxidized AZ91 Alloy
    (Springer, 2021) Selvi, Ekin; Muhaffel, Faiz; Yürektürk, Yakup; Vanli, Ali Serdar; Baydogan, Murat
    In this study, AZ91 Mg alloy was micro-arc oxidized using different voltages in silicate- and aluminate/phosphate-based (dual) electrolytes that included K2ZrF6 or Na2ZrO3 as the Zr source for synthesizing ZrO2 in the micro-arc oxidation (MAO) coatings. Structural characterizations were done by using scanning electron microscopy and x-ray diffraction techniques. MAO coating characteristics of different samples were compared by measuring coating thickness, surface roughness, average pore size, and total pore fraction. Both hardness and pull-off tests were conducted to characterize the mechanical properties of the coatings. Thermal conductivity measurements and thermal shock tests were also carried out to evaluate the effect of the electrolyte composition and the type of Zr containing compound. It was found that the equivalent thermal conductivity of the MAOed samples can be reduced up to 30% compared to the bare AZ91 alloy. The decrease of the thermal conductivity was mainly attributed to formation of a thicker and denser MAO coating, and the incorporation of ZrO2 phase into the fabricated MAO coating. Finally, increased thermal shock resistance was strongly correlated with a lower hardness and higher cohesive strength of the MAO coating, which also leads to smaller crack formation and spallation-free surface characteristics.
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    Investigation of indentation and dry sliding wear behaviour of Al-12.6 wt.% Si-10 wt.% TiB2 composites produced by sequential milling and pressureless sintering
    (Carl Hanser Verlag, 2019) Tekoglu, Emre; Yürektürk, Yakup; Agaogullari, Duygu; Dilawary, Shaikh Asad Ali; Baydogan, Murat; Ovecoglu, M. Lutfi
    The main purpose of this study is to comprehend the effects of cryomilling (CM) time on dry sliding wear behaviour of 10 wt.% TiB2 reinforced Al-12.6 wt.% Si metal matrix composites (MMCs). The MMCs were synthesised via sequential milling (mechanical alloying + cryomilling) and pressureless sintering. Indentation tests performed at a maximum load of 200 g showed that the Young's modulus and hardness of the composites increased up to 20 min of CM time. The effects of CM time and load on the composites were examined based on their tribological properties. Based on the results, the 4 h mechanical alloyed (MA'd) and 30 min CM'd sample showed the lowest wear rate under the normal load of 1 N, with its wear mechanism being predominantly oxidative. However, for the normal load of 4 N, the lowest wear rate was found in the 4 h MA'd composite, in which the dominant wear mechanism was abrasion.
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    Microstructural evolution, nanoindentation creep response, and wear properties of Y2O3-modified CoCrFeNi high entropy alloys
    (Elsevier Science Inc, 2026) Tekin, Mustafa; Kotan, Hasan; Balci, Erdem; Kaba, Mertcan; Baydogan, Murat; Bayrak, Kubra Gurcan; Ayas, Erhan
    The combined effects of wear and creep largely determine the long-term reliability of alloys in demanding thermal and mechanical environments, but conventional structural materials show limited resistance to these degradation mechanisms. High-entropy alloys (HEAs), though inherently robust, have gained attention as potential candidates for such environments, particularly when reinforced with stable oxide dispersions. In this study, oxide-dispersion-strengthened Co-Cr-Fe-Ni HEAs containing 1 and 4 wt% Y2O3 were synthesized through mechanical alloying and spark plasma sintering to evaluate this approach. Microstructural characterization using X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the retention of the fcc crystal lattice. Pronounced grain refinement was achieved, decreasing from 360 +/- 70 nm in the unreinforced HEA to 95 +/- 15 nm in the 4 wt% ODS composition, accompanied by a substantial increase in hardness to 685 +/- 30 HV. Wear experiments revealed a fourfold reduction in specific wear rate. This improvement was accompanied by a transition in wear mode from extensive surface damage in the unreinforced HEA to predominantly oxidative and fatigue-assisted mechanisms in the ODS HEAs, facilitated by the formation of protective tribo-oxide layers. Nanoindentation creep analysis revealed a decrease in stress exponent from 16.05 to 5.72 with increasing Y2O3 content. This change signifies a transition toward dislocation-controlled creep and tunable creep resistance. Collectively, these findings establish that rare-earth oxide dispersion is an effective strategy for simultaneously enhancing surface durability and controlling time-dependent deformation in HEAs, thereby extending their potential for demanding structural and tribological applications.
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    Unveiling the creep mechanisms of rare earth element yttrium added and SPS consolidated CoCrFeNi high entropy alloys
    (Walter De Gruyter Gmbh, 2025) Tekin, Mustafa; Kotan, Hasan; Baydogan, Murat; Kaba, Mertcan; Balci, Erdem; Bayrak, Kubra Gurcan; Ayas, Erhan
    As high entropy alloys (HEAs) continue to be increasingly studied for next-generation structural materials, gaining a comprehensive understanding of their mechanical properties, including their creep behaviors, remains essential. In this work, rare earth element yttrium (Y) added CoCrFeNi HEAs are produced by mechanical alloying, followed by consolidation via spark plasma sintering (SPS) with ultrafine grain sizes. The microstructures after SPS consolidation are examined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The creep properties, including creep displacement, creep strain rate, creep stress, and stress exponent, are evaluated using a nanoindentation test with a Berkovich tip indenter. The results reveal that the average grain size of CoCrFeNi HEA is determined to be 385 +/- 65 nm after SPS consolidation, which reduces to 190 +/- 30 nm and 155 +/- 55 nm with 1 and 4 at.% Y additions, respectively. Accordingly, HEA with the addition of 4 at.% Y exhibits increased hardness, attributed to the presence of additional Y-based oxides and the reduced grain size in its microstructure. Furthermore, the creep mechanisms for the investigated CoCrFeNi HEAs are primarily dominated by dislocation-precipitation interaction based on the calculated stress exponent values.