Materials Science and Engineering / Malzeme Bilimi ve Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4719
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Article Citation - WoS: 5Citation - Scopus: 4Influence of Partitioning Treatment on Microstructure and Mechanical Properties of an Alloyed Ductile Iron Austempered at Different Temperatures(Walter de Gruyter GmbH, 2023) Neite, Maximilian; Münstermann, Sebastian; Nalçacı, Burak; Davut, Kemal; Erdoğan, MehmetThe present study was conducted to uncover effects of partitioning treatment on Cu-Ni-Mo alloyed ductile iron (DI) austempered at different temperatures. For this purpose, the DI samples, produced via sand casting, were austenitized at 900 °C for 60 min, followed by austempering at the temperatures of 275-325-375 °C for 120 min and afterwards a partitioning treatment was applied at 200 °C for 15 min. In the characterization studies, dilatometer, image analysis, JMat-Pro, mechanical tests, XRD, optical microscope, and scanning electron microscope (SEM) equipped with EBSD detector were utilized. Characterization studies showed that the effects of partitioning treatment were directly correlated with austempering temperature and high carbon austenite volume fraction changed in the range of 19.48-35.45%. That redistribution of carbon (C) between bainitic ferrite and high carbon austenite occurred, in turn, the carbon content of high carbon austenite increased with the partitioning treatment irrespective of austempering temperature were uncovered. Furthermore, the partitioning treatment considerably changed the grain morphologies of both high carbon austenite and banitic ferrite. As a consequence of these microstructural differences, the highest tensile strength of 1489.2 MPa was established in the sample austempered at 275 °C and partitioned at 200 °C, whereas the highest ductility of 5.61% acquired at the austempering temperature of 375 °C. © 2023 Walter de Gruyter GmbH, Berlin/Boston.Article Citation - WoS: 22Citation - Scopus: 25Effect of Solution Heat Treatment on the Microstructure and Crystallographic Texture of In939 Fabricated by Powder Bed Fusion-Laser Beam(Elsevier, 2023) Doğu, Merve Nur; Özer, Seren; Yalçın, Mustafa Alp; Davut, Kemal; Bilgin, Guney Mert; Obeidi, Muhannad Ahmed; Brodin, Hakan; Gu, Hengfeng; Brabazon, DermotThe effect of various solution heat treatment temperatures (i.e., 1120, 1160, 1200 and 1240 & DEG;C) on the microstructure, grain morphology and crystallographic texture of IN939 fabricated by powder bed fusion-laser beam (PBF-LB) was investigated. Microstructural analyses showed that the high-temperature gradient and rapid solidification of the PBF-LB processing caused different resulting microstructures compared to conventionally pro-duced counterparts. The melt pool morphologies and laser scanning paths were examined in the as-fabricated samples in the XZ-and XY-planes, respectively. After the application of solution heat treatment at 1120 & DEG;C, the as-fabricated PBF-LB initial microstructure was still apparent. For solution heat treatments of 1200 & DEG;C and above, the melt pool and scanning path morphologies disappeared and converted into a mixture of columnar grains in the XZ-plane and equiaxed grains in the XY-plane. On the other hand, large equiaxed grains were observed when the samples were solutionized at 1240 & DEG;C. Additionally, g' phase precipitated within the matrix after all solution heat treatment conditions, which led to increase in the microhardness values. According to electron backscatter diffraction (EBSD) analyses, both as-fabricated and solution heat-treated samples had intense texture with {001} plane normal parallel to the building direction. The first recrystallized grains began to appear when the samples were subjected to the solution heat treatment at 1160 & DEG;C and the fraction of the recrystallized grains increased with increasing temperature, as supported by kernel average misorientation (KAM) and grain spread orientation (GOS) analyses.& COPY; 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Article Citation - WoS: 29Citation - Scopus: 31Effect of Heat Input on Haz Softening in Fiber Laser Welding of 22mnb5 Steel(Elsevier, 2023) Tuncel, Oğuz; Aydın, Hakan; Davut, KemalThis study investigates the effects of heat input on the heat-affected zone (HAZ) softening in fiber laser welding of quenched 1.1 mm thick 22MnB5 steel. Laser power (1500-2500 W) and welding speed (40-120 mm/s) parameters are considered as the input process variables. Depending on the input parameters, the applied heat input varied between 12.5 and 62.5 J/mm. The results indicate that a minimum heat input of 50 J/mm is required for full weld penetration. Microhardness findings revealed that the drop in hardness in the HAZ region relative to the base material (BM) reached 39% due to grain coarsening caused by an increase in heat input under the welding conditions. Grain coarsening (prior austenite grains) is also detected in SEM analysis. In addition, grain coarsening at high heat input was also determined quantitatively in EBSD analyses. The proportion of 8.91 mu m grain size in the sample with high heat input is 4.2%, while it is 1.2% in the sample with low heat input. When the heat input increased from 12.5 to 62.5 J/mm, the width of the softened zone with the lowest hardnesses in the HAZ grew from 0.2 mm to 2.2 mm.Article Citation - WoS: 5Citation - Scopus: 6Effect of Coiling Temperature on the Structure and Properties of Thermo-Mechanically Rolled S700mc Steel(Technical Faculty in Bor, 2022) Di Nunzio, P. E.; Cesile, M. C.; Oktay, S.; Davut, Kemal; Şeşen, M. K.The boron-free S700MC steel is usually produced by exploiting the properties of a ferrite-bainite mixed microstructure formed by coiling the strips at a temperature of about 450 degrees C, i.e.below the bainite starting temperature. With the aim of further enhancing the mechanical properties of 6 to 10 mm thick strips, industrial tests were carried out at a coiling temperature of 600 degrees C to promote the formation of a structure of ferrite and carbides, which is also acceptable for this type of steel. Unexpectedly, a microstructure composed of ferrite and martensite was obtained. Compared to the ferritic-bainitic grade, the new structure is characterized by a slight decrease of the yield point but by an increase of the ultimate tensile strength by no less than 80 MPa, with a transition from a quasi-discontinuous to a clearly continuous yielding behaviour. Accordingly, the ratio of yield strength to tensile strength decreases from 0.90 to 0.75 and the impact energy decreases by 35 J and 60 J for the two gauge levels, respectively. The mechanical behaviour of the strips coiled at high temperature is explained as a direct consequence of the dual phase structure with a hard phase interspersed in a soft ferrite matrix. The presence of martensite is explained by the so-called incomplete bainite reaction. The partial transformation into ferrite after coiling and the long time required for the coil to cool down stabilize the untransformed austenite due to the carbon enrichment making bainite formation at lower temperatures impossible.Article Citation - WoS: 3Citation - Scopus: 3Nondestructive Microstructural Characterization of Austempered Ductile Iron(Walter de Gruyter GmbH, 2023) Tüzün, Mert Yağız; Yalçın, Mustafa Alp; Davut, Kemal; Kılıçlı, VolkanAustempered ductile iron (ADI) has been preferred in a wide range of applications due its unique combination of high strength, good ductility, wear resistance and fracture toughness together with lower cost and lower density compared to steels. Magnetic Barkhausen noise (MBN) measurement offers a better alternative to traditional characterization techniques by being fast and non-destructive. A simple linear regression using only one single independent variable cannot correlate the MBN with the microstructure of ADI, since its microstructure is multi component. Multiple linear regression analysis (MLRA) was used to build a model that uses the characteristic features of microstructural constituents as input parameters to predict the MBN. For that purpose, Cu-Ni-Mo alloyed ductile iron samples austempered between 325 and 400 degrees C and for 45-180 min duration were used. The results show that MBN is most sensitive to the size and shape of acicular ferrite and retained austenite. Moreover, MBN is almost insensitive to the size, morphology and volume fraction of graphite particles. This indicates that retained austenite pins the domain walls more effectively than the graphite particles. Considering the results MLRA, MBN technique can be used to characterize the ausferritic microstructure of ADI.Article Citation - WoS: 14Citation - Scopus: 13An Experimental Study on the Ballistic Performance of Ultra-High Hardness Armor Steel (armox 600t) Against 7.62 Mm × 51 M61 Ap Projectile in the Multi-Hit Condition(Elsevier, 2023) Göde, Engin; Teoman, Atanur; Çetin, Barış; Tonbul, Kürşat; Davut, Kemal; Kuşhan, Melih CemalIn this study, Armox 600T armor steel was ballistically tested against 7.62 mm × 51 M61 AP projectile. The experimental design was constructed on the basis of the worst-case scenario which is the highest possible impact velocity in the multi-hit condition. The ballistic tests revealed that Armox 600T could defeat the worst-case scenario with a thickness of 12 mm. Furthermore, the damaged and undamaged regions were inspected microstructurally in a detail manner aiming to observe the possible fractographic modes of the studied material. Finally, high resolution optical scanning efforts were also added to the experimental work whose results uncovers the possible improvement areas regarding the quantification of the results of ballistic testing.Article Citation - WoS: 45Citation - Scopus: 48Recrystallization and Grain Growth Kinetics of In718 Manufactured by Laser Powder Bed Fusion(Elsevier, 2022) Doğu, Merve Nur; Davut, Kemal; Obeidi, Muhannad Ahmed; Yalçın, Mustafa Alp; Gu, Hengfeng; Low, Thaddeus Song En; Ginn, Jon; Brabazon, DermotThe recrystallization and grain growth behaviour of IN718 alloy additively manufactured by laser powder bed fusion (L-PBF) is presented herein. The effects of three different temperatures (1050, 1150 and 1250 °C) and holding times (15, 45 and 90 min) were investigated. The texture evolution of the samples was recorded via electron backscatter diffraction (EBSD). The as-built sample is composed of bowl-shaped melt pools, a chessboard-like grain pattern and has a cube texture {100}<001>. Recrystallized grains were observed in the samples treated at 1150 °C for 15 min, as well as the samples treated for longer periods and at higher temperatures. Recrystallization was observed to start from high dislocation density regions, including the overlapping melt pools and the borders of the chessboard-like pattern. The initial cube texture transforms into a first-generation cube-twin texture {122}<212> via a twinning-assisted recrystallization mechanism. Then, those recrystallization nuclei sweep through the high defect density matrix; during which almost no new twins are formed. The samples treated at 1250 °C are almost completely recrystallized, which forms a weaker cube texture and a stronger P-orientation {011}<112>. However, the growth of recrystallized grains is very limited due to the presence of non-coherent precipitates.Article Citation - WoS: 3Citation - Scopus: 4Partial Austenitisation and Tbf Steel Composed of Ferrite, Bainitic Ferrite, and Austenite(Taylor & Francis, 2022) Erişir, Ersoy; Bilir, Oğuz Gürkan; Sözer, Yunus Emre; Ararat, Özge; Davut, KemalA TRIP-aided bainitic-ferritic (TBF) steel with a chemical composition of Fe-0.19C-1.7Mn-1.09Si-0.51Al-0.05Nb (wt-%) was partially austenitised from a hot-rolled martensitic initial microstructure. After the hot rolling, the martensitic specimens were reheated to different intercritical temperatures and then austempered at 350 degrees C. Thus, the effect of the initial microstructure of TBF steel on intercritical austenite formation during partial austenitisation was studied. The microstructures were investigated by scanning electron microscopy and electron backscatter diffraction (EBSD), and the tensile properties were tested. Microstructural observations revealed that a final microstructure of fine ferrite, bainitic ferrite, and retained austenite can be obtained. The steel partial austenitised at 770 degrees C showed a good combination of ultimate tensile strength and total elongation.Article Citation - WoS: 8Citation - Scopus: 8Design and Fabrication of Polymer Micro/Nano Composites With Two-Level Mechanical Reinforcing Procedure(Wiley, 2022) Kandemir, Ayşe Çağıl; Dönmez, Fatma; Davut, Kemal; Kaplan Can, HaticeBiocompatible composite production was accomplished by utilizing two-level hierarchical approach for mechanical reinforcement. A well-known commodity polymer; low-density polyethylene (LDPE), which has high-fracture toughness, yet low strength and modulus was used as the main matrix material. As the first step of hierarchy, ductile LDPE was blended with brittle polyvinylpyrrolidone (PVP), which is an eco-friendly, nontoxic and biocompatible polymer. This resulted in slight decrease of strength and drastic reduction of toughness (%70), yet modulus was increased by 78%. As the second level of hierarchy, PVP composites were introduced in LDPE. Nano-scaled Halloysite clay and micro-scaled spherical Silica particles were utilized as additives in the aforementioned PVP composites. The reason for the choice of these particles is that they are nontoxic, low-cost and in the case of Halloysite; abundant in nature. Owing to the implementation of the second level; modulus improvement was further enhanced to 150%, with additional benefits of strength increase up to 17% and less reduction in fracture toughness (minimum 51% reduction). Dynamic mechanical analysis also supported these outcomes that storage modulus of composites are higher than both LDPE and LDPE-PVP blend. The proposed biocompatible composites in the end of this study would be utilized in biomedical applications necessitating mechanical improvements.Article Citation - WoS: 6Citation - Scopus: 6A Numerical Methodology for Monitoring Stress Distributions and Experimental Proof of the Concept on Metal Embedded Thin Polymer-Matrix Composites Using X-Ray Diffraction(Elsevier, 2022) Demir, Eralp; Sas, Hatice S.; Işık, Murat; Aydoğan Güngör, Eda; Davut, KemalIn this study, a numerical methodology is developed to monitor stress distributions and an experimental technique is investigated to measure stresses on metal embedded polymer matrix fiber-reinforced composite materials using X-ray diffraction (XRD) method. The numerical method successfully predicts the stress distributions using only a few data points with an average accuracies of 11.6% and 11.8%, respectively for tapered and open hole tensile sample geometries. Experimental part of this study investigates different methodologies to measure stresses on surfaces of polymer composites materials of thin walled structures by XRD. For this reason, metallic materials were integrated onto the surface and near-surface of polymer matrix composites in three different configurations as in the forms of metal foil, metal powder, and metal wire mesh. In-situ experiments of measured and applied stresses revealed metal powder embedded composite materials as a promising material configuration for reliable monitoring of stresses.