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    A comparative study on mechanical and ballistic performance of functionally graded Al6061 composites reinforced with B4C, SiC, and Al2O3
    (Elsevier, 2023) Karabulut, Sener; Karakoc, Halil; Bilgin, Musa; Canpolat, Hakan; Krolczyk, Grzegorz M.; Sarikaya, Murat
    In the present study, functionally graded Al6061 composites reinforced with boron carbide (B4C), silicon carbide (SiC), and alumina (Al2O3) were prepared using the stir and centrifugal casting techniques. Arc-shaped functionally graded metal (FGM) specimens were treated with a hot-rolling process to enhance their mechanical properties and obtain laminated plates. Then, the impacts of ceramic reinforcements on the density, microhardness, tensile strength, and ballistic resistance of FGMs were studied. Moreover, the microstructural properties of the specimens were analyzed to elucidate the particle gradient from the inner to the outer surface. As a result, the microstructure observations revealed that the ceramic particles are dispersed from the inner to the outer periphery of the FGMs with centrifugal acceleration. A more homogeneous particle distribution was obtained in B4C-reinforced FGM compared to those of SiC and Al2O3. The hot-rolled FGM specimen reinforced with B4C offered the lowest density. The microhardness was improved by 32% and 30.4% in the inner to outer regions of the SiC-and Al2O3-reinforced FGMs, respectively, while it was improved by 22.6% in B4C-reinforced FGM. On the other hand, the tensile strength and elongation of the B4C-reinforced FGM specimen were better than those of the SiC-and Al2O3-reinforced FGMs. In addition, the highest ballistic protection was achieved with B4C-reinforced laminated FGM at an impact speed of 664.25 m/s with a penetration depth of 14 mm, while the impact speeds of SiC-and Al2O3-reinforced FGMs were 500.88 and 435.23 m/s, respectively.(c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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    A study on the influence of thermally assisted novel hybrid methods on the drilling behavior of Ti6Al4V alloy
    (Elsevier Sci Ltd, 2022) Karabulut, Sener; Bilgin, Musa; Karakoc, Halil; Khanna, Navneet; Sarikaya, Murat
    The paper focuses on the drilling behavior of Ti6Al4V alloy under dry, MQL, hot (also expressed as heat-assisted machining), and hybrid (hot+MQL) environments. The surface roughness and morphologies, power consumption, drilling force, microhardness, and microstructural behavior using electron backscatter diffraction (EBSD) analysis were studied. As a result, the lowest roughness value was obtained in the MQL, followed by dry, hot and hybrid drilling environments. Based on SEM investigation on machined surfaces, the defects i.e., smearing, chip debris and side flow were found to be the main causes of poor surface quality, especially under hot and hybrid -assisted drilling environments. According to the Euler color distribution, the hot working affected the machined surface up to the bulk material with a length of 98 mu m. The hot drilling process led to the recrystallization of the grain structure, and the distribution, sizes, and characteristics of the phases were affected by the temperatures. A partially recrystallized grain structure was observed in the IPF maps of the hybrid drilling environment at a distance of 10 mu m from the machined surface. The crystal orientation of machined Ti6Al4V under hybrid-assisted environment was very similar to dry machined crystal orientation indicating stability in the microstructure.
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    An experimental investigation on machining-induced surface/subsurface characteristics of nickel based Inc-718 alloy: A novel hybrid approach in milling process
    (Elsevier Sci Ltd, 2024) Bilgin, Musa; Karabulut, Sener; Karakoc, Halil; Kayir, Yunus; Sarikaya, Murat
    Nickel-based superalloy Inc-718 has become an indispensable alloy in critical sectors, especially in the aerospace industry, thanks to its unique characteristics. However, some properties of the alloy (especially low thermal conductivity and hot hardness) cause difficulties in its machinability. For this reason, comprehensive studies to improve the machinability of Inc-718 alloy by considering the microstructural properties are guiding. In this context, the present study uses various methods to increase the machinability efficiency of Inc-718, while also investigating their effect on microstructural properties. Firstly, the effect of the pre-heating process (hot), pureMQL (PMQL), nanofluid-MQL (NMQL), and hybrid methods (hot+PMQL and hot-NMQL) on the surface roughness, cutting forces, tool wear, vibration, and temperature was investigated while milling Inc-718 surfaces. Then the utilization of Electron Backscatter Diffraction (EBSD) facilitated a comprehensive examination of microstructural behavior, with a specific focus on Euler-colored maps and phase distribution maps, providing valuable insights into the material's behavior under distinct milling conditions. As a result, hot+PMQL, hot+SiCNMQL, and hot+Al2O3-NMQL provided an important contribution to the improvement of machinability characteristics. Also, it was seen that in EBSD analysis, a limited area is affected by heat in the hot machining environment. The crystal orientations of the pre-heated and hybrid machined Inc-718 alloy are highly similar to that of the dry-machined alloy. This similarity indicates that the removal of the heated layer from the workpiece during the milling process contributes to the preservation of the microstructure.