Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 13Citation - Scopus: 16Influence of Recycled Carbon Fiber Addition on the Microstructure and Creep Response of Extruded Az91 Magnesium Alloy(KeAi Communications Co., 2023) Kandemir, Sinan; Bohlen, Jan; Dieringa, HajoIn this study, the recycled short carbon fiber (CF)-reinforced magnesium matrix composites were fabricated using a combination of stir casting and hot extrusion. The objective was to investigate the impact of CF content (2.5 and 5.0 wt.%) and fiber length (100 and 500 µm) on the microstructure, mechanical properties, and creep behavior of AZ91 alloy matrix. The microstructural analysis revealed that the CFs aligned in the extrusion direction resulted in grain and intermetallic refinement within the alloy. In comparison to the unreinforced AZ91 alloy, the composites with 2.5 wt.% CF exhibited an increase in hardness by 16–20% and yield strength by 5–15%, depending on the fiber length, while experiencing a reduction in ductility. When the reinforcement content was increased from 2.5 to 5.0 wt.%, strength values exhibited fluctuations and decline, accompanied by decreased ductility. These divergent outcomes were discussed in relation to fiber length, clustering tendency due to higher reinforcement content, and the presence of interfacial products with micro-cracks at the CF-matrix interface. Tensile creep tests indicated that CFs did not enhance the creep resistance of extruded AZ91 alloy, suggesting that grain boundary sliding is likely the dominant deformation mechanism during creep. © 2023Article 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: 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: 39Citation - Scopus: 41Effect of Post Fabrication Aging Treatment on the Microstructure, Crystallographic Texture and Elevated Temperature Mechanical Properties of In718 Alloy Fabricated by Selective Laser Melting(Elsevier, 2022) Özer, Seren; Bilgin, Güney Mert; Davut, Kemal; Esen, Ziya; Dericioğlu, Arcan.FThe effect of building direction and post fabrication aging treatment on the microstructure, crystallographic texture and high temperature mechanical properties of Inconel 718 (IN718) alloy fabricated by selective laser melting (SLM) method was investigated. After aging, arc-shaped structures seen in as-fabricated samples disappeared and converted into a mixture of columnar and equiaxed grains. Nano-sized γ″ and/or γ′ precipitates were formed upon aging; however, MC type carbides and Laves phase encountered in as-fabricated samples were not dissolved completely after aging. Moreover, aging did not alter the texture ((001)//building direction (BD)) of as-fabricated samples. Mechanical properties of the alloys under tension were influenced by the build direction, aging time and test temperature. As-fabricated samples produced in vertical direction exhibited higher room temperature strengths with lower ductility due to orientation of overlapped prior melt pools. Room temperature tensile test results revealed that peak aging caused a significant improvement in ultimate tensile strength (UTS), from 1066.5 MPa and 998.4 MPa to 1408.5 MPa and 1330.4 MPa whereas elongation values decreased from 27.5% and 32.2% to 19.6% and 23.7% in vertically and horizontally built samples, respectively. Peak-aged samples (aged at 700 °C for 8 h) tested at 600 °C displayed serrated regions in their stress-strain curves due to dynamic strain aging (DSA). Although strength values of the samples displayed an expected decrease by temperature, ductility of the samples reduced to minimum at temperatures around 700–800 °C, which was attributed to intermediate temperature embrittlement.Article Citation - WoS: 41Citation - Scopus: 45High Temperature Tensile, Compression and Creep Behavior of Recycled Short Carbon Fibre Reinforced Az91 Magnesium Alloy Fabricated by a High Shearing Dispersion Technique(National Engineering Research Center for Magnesium Alloys of China, Chongqing University, 2021) Kandemir, Sinan; Gavras, Sarkis; Dieringa, HajoThe present study seeks the feasibility of using short carbon fibres recycled from polymer matrix composites as alternative to virgin carbon fibres in the reinforcement of magnesium alloys. The microstructures, high temperature mechanical and creep properties of AZ91 alloy and its composites with various recycled carbon fibre contents (2.5 and 5 wt.%) and lengths (100 and 500 ?m) were investigated in the temperature range of 25–200 °C. The microstructural characterization showed that the high shear dispersion technique provided the cast composites with finer grains and relatively homogenous distribution of fibres. The materials tested displayed different behaviour depending on the type of loading. In general, while enhancements in the mechanical properties of composites is attributed to the load bearing and grain refinement effects of fibres, the fluctuations in the properties were discussed on the basis of porosity formation, relatively high reinforcement content leading to fibre clustering and interlayer found between the matrix and reinforcement compared to those of AZ91 alloy. The compressive creep tests revealed similar or higher minimum creep rates in the recycled carbon fibre reinforced AZ91 in comparison to the unreinforced AZ91. © 2021Article Citation - WoS: 4Citation - Scopus: 5Effects of Tib2 Nanoparticle Content on the Microstructure and Mechanical Properties of Aluminum Matrix Nanocomposites(Walter de Gruyter GmbH, 2017) Kandemir, SinanThe present work reports the fabrication of A357 alloy matrix nanocomposites reinforced with 0.5, 1.0 and 2.0 wt.-% TiB2 nanoparticles (20-30 nm) by a novel method which is the combination of semi-solid mechanical mixing and ultrasonic dispersion of nanoparticles in liquid state. The microstructural and mechanical properties of the fabricated nanocomposites were investigated. The microstructural studies conducted with optical and advanced electron microscopes indicated that reasonably effective deagglomeration and uniform distribution of TiB2 nanoparticles into the matrix were achieved. Transmission electron microscopy studies also confirmed that the nanoparticles were embedded into the matrix and a good bonding was obtained between the matrix and the reinforcement. Increasing nanoparticle content led to grain refinement and significant enhancement in the mechanical properties of nanocomposites. The addition of 0.5, 1.0, and 2.0 wt.-% TiB2 nanoparticles increased the 0.2 % proof stress of matrix alloy by approximately 31, 48 and 61 %, respectively. The contribution of different mechanisms to the strength enhancement is discussed. It is proposed that the strengthening is mainly due to Orowan mechanism and dislocation generation effect by the coefficient of thermal expansion mismatch between the TiB2 nanoparticles and the matrix.Article Citation - WoS: 187Citation - Scopus: 266Improvement of Barrier and Mechanical Properties of Whey Protein Isolate Based Food Packaging Films by Incorporation of Zein Nanoparticles as a Novel Bionanocomposite(Elsevier Ltd., 2016) Oymacı, Pelin; Alsoy Altınkaya, SacideIn this study, whey protein isolate (WPI) based bio-nanocomposite films embedded with zein nanoparticles (ZNP) were prepared by solution casting. Nanoparticles were coated with sodium caseinate to obtain a uniform distribution in the films. The mechanical, water vapor barrier, surface wetting, morphological and viscoelastic properties of the films were investigated. The addition of ZNP significantly improved the water vapor barrier and mechanical properties of the WPI without adversely affecting the elongation of the films. Dynamical mechanical analysis and contact angle measurements revealed that upon addition of the nanoparticles, the fractional free volume and hydrophilicity of the WPI films decreased. Sodium caseinate containing both hydrophilic and hydrophobic groups created an efficient interface between the hydrophobic ZNP and hydrophilic WPI matrix, allowing for a homogeneous distribution of nanoparticles even at very high loading levels as evidenced by the scanning electron microscope (SEM) and atomic force microscopy (AFM) images. The WPI/ZNP nanocomposite films can potentially become effective food packaging materials.Article Citation - WoS: 55Citation - Scopus: 64High-Early Ductile Cementitious Composites With Characteristics of Low Early-Age Shrinkage for Repair of Infrastructures(Springer Verlag, 2015) Şahmaran, Mustafa; Al-Emam, Muhannad; Yıldırım, Gürkan; Şimşek, Yunus Emre; Erdem, Tahir Kemal; Lachemi, MohamedReduced performance in concrete infrastructures is mainly caused by the formation of cracks, which may arise due to deteriorating mechanisms during service life. In most cases, reduced performance calls for urgent repairs to the degraded section. Therefore, it is highly desirable to develop dimensionally stable, ductile repair materials that can attain adequately high strength in a limited amount of time, compensate for significant deformation due to mechanical and environmental loadings, and prevent early-age shrinkage cracks. In this paper, the performance of such a material (high-early-strength engineered cementitious composites, HES-ECC, with very low early-age shrinkage capacity) was investigated by studying mechanical properties and dimensional stability. Composites were produced with different water to cementitious materials and slag to Portland cement ratios. In order to enhance composite properties in terms of ductility and early-age shrinkage characteristics, saturated lightweight aggregates replaced sand in the mixtures. The experimental results show that the majority of HES-ECC mixtures developed in this study attained compressive strength values of more than 20.0 MPa and minimum flexural strength of 6.0 MPa within 6 h. Moreover, the HES-ECC mixtures exhibited strain-hardening behavior with strain capacities comparable to normal strength ECC, as well as substantially reduced autogenous shrinkage strain, both of which are unlikely to trigger the formation of cracks in tension at early ages. The integration of these conflicting parameters suggests that HES-ECC can easily meet the need for fast and durable repairs.Article Citation - WoS: 62Citation - Scopus: 75Specimen Size Effect on the Residual Properties of Engineered Cementitious Composites Subjected To High Temperatures(Elsevier Ltd., 2014) Erdem, Tahir KemalIn this study, size effect on the residual properties of Engineered Cementitious Composites (ECC) was investigated on the specimens exposed to high temperatures up to 800 C. Cylindrical specimens having different sizes were produced with a standard ECC mixture. Changes in pore structure, residual compressive strength and stress-strain curves due to high temperatures were determined after air cooling. Experimental results indicate that despite the increase of specimen size, no explosive spalling occurred in any of the specimens during the high temperature exposure. Increasing the specimen size and exposure temperature decreased the compressive strength and stiffness. Percent reduction in compressive strength and stiffness due to high temperature was similar for all specimen sizes.Article Citation - WoS: 77Citation - Scopus: 93Improving the Workability and Rheological Properties of Engineered Cementitious Composites Using Factorial Experimental Design(Elsevier Ltd., 2013) Şahmaran, Mustafa; Bilici, Zafer; Özbay, Erdoğan; Erdem, Tahir Kemal; Yücel, Hasan Erhan; Lachemi, MohamedIn the development of Engineered Cementitious Composites (ECC), micromechanics-based design theory is adopted to properly select the matrix constituents, fiber, and fiber-matrix interface properties to exhibit strain hardening and multiple cracking behaviors. Despite the micromechanics design constraints, practical applications show that the workability and rheological properties of matrix can affect the fiber dispersion uniformity, which have also direct concerns on composite mechanical properties. For this reason, in this research, parameters of micromechanics-based optimized ECC mixture design, which most possibly affecting the workability and rheological properties, are investigated. An experimental program that contains 36 different ECC mixtures was undertaken to quantitatively evaluate the combined effects of the following factors on workability and rheological properties: water-binder (w/b), sand-binder (s/b), superplasticizer-binder (SP/b) ratios and maximum aggregate size (Dmax). A mini-slump cone, a Marsh cone and a rotational viscometer were used to evaluate the workability and rheological properties of ECC mixtures. Compressive strength and four point bending tests were used for mechanical characteristics of ECC mixtures at 28 days. The effects of studied parameters (w/b, s/b, SP/b and Dmax) were characterized and analyzed using regression models, which can identify the primary factors and their interactions on the measured properties. Statistically significant regression models were developed for all tested parameters as function of w/b, s/b, SP/b and Dmax. To find out the best possible ECC mixture under the range of parameters investigated for the desired workability and mechanical characteristics, a multi-objective optimization problem was defined and solved based on the developed regression models. Test results indicate that w/b, s/b and SP/b parameters affect the rheological and workability properties. On the other hand, for the range of studied aggregate sizes, Dmax is found to be statistically insignificant on the rheological and workability properties of ECC.