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Absorbing properties and structural design of PVB/Fe3O4 nanocomposite
(Elsevier Science Sa, 2019) Akinay, Yuksel; Hayat, Fatih; Colak, Bektas
Recently, a wide range of studies has been carried out on microwave absorber composites for use in telecommunications, electromagnetic pollution, stealth technology, and other applications. In this study, the microwave absorption properties of polyvinyl butyral (PVB)/polyaniline (PAM) coated-Fe3O4 (COM1) and PVB/Fe3O4 (COM2) nanocomposites with single and double layer were investigated in the 1-14 GHz for different thickness (t(m)) of composites. XRD, FT-IR, TEM, and SEM were used to determine the structure properties of the composites. The Coaxial transmission line method was used to obtain permittivity (epsilon', epsilon '') and permeability (mu', mu '')parameters of the composites. The reflection loss of the single and multilayers of different thicknesses was calculated. It was figured out that the higher value of reflection loss (R-L) (-51.5 dB at 11.9 GHz) was obtained with COM2 composite. However, using PANI has provided a wider absorption range in COM1 composites. It was found that multilayer composites (COM4) provide broadband absorption compared to COM2 and double-layer design (COM3).
Comparison of microwave absorption properties between BaTiO3/Epoxy and NiFe2O4/Epoxy composites
(Wiley, 2018) Akinay, Yuksel; Hayat, Fatih; Kanbur, Yasin; Gokkaya, Hasan; Polat, Safa
Microwave absorption properties of Epoxy/Nickel Ferrite (NiFe2O4) and Epoxy/Barium Titanate (BaTiO3) composites were investigated and compared in the 1-14 GHz. Epoxy/filler particles (NiFe2O4 and BaTiO3) composites were prepared with 85/15 mixture ratios via Ultrasonic Probe Sonicator method in solution. The complex permittivity (e '-e '') and permeability (mu '-mu '') of the composites have been measured at different microwave frequencies in 1-14 GHz via vector network analyzer (Keysight N9926A). The reflection loss (R-L) of composites was calculated and evaluated from camplex permitivity and permeability. The obtained results show that both composites exhibit the large R-L and broadband within the frequency range from 1 to 14 GHz for different thickness. Epoxy/BaTiO3 showed a better microwave absorption at the range of 6-7.2 GHz for 7 and 6 mm, at the range of 7.4-9.1 GHz for 5 mm. However, the Epoxy/NiFe2O4 exhibits the largest R-L and the widest bandwidth than those obtained from Epoxy/BaTiO3 composite. POLYM. COMPOS., 39:E2143-E2148, 2018. (c) 2017 Society of Plastics Engineers
Effect of Heat Treatment on Microstructure, Mechanical Properties and Fracture Behaviour of Ship and Dual Phase Steels
(Journal Iron Steel Research Editorial Board, 2011) Hayat, Fatih; Uzun, Huseyin
Grade A (GA) and high strength steel DH36 ship steels possessing different chemical compositions were used, and strength properties of GA steel and DH36 steel were compared. Additionally, 4 types of dual phase (DP) steels with different martensite volume fractions (MVFs) were produced from GA steel by means of heat treatment and they were compared with other steels through conducting microstructure, microhardness, tensile and impact tests. The fracture surfaces of specimens (DH36, GA and DP steels) exposed to tensile and Charpy impact tests were investigated by scanning electron microscope. Furthermore, it was found that the specimens quenched from 800 and 900 degrees C had better strength than DH36 steel. The tensile test results indicated that the tensile strength of DP steel water quenched from 900 degrees C was 3 times that of GA steel and twice that of DH36 steel.
Effect of Ni on the mechanical behavior of a high-Mn austenitic TWIP steel
(Carl Hanser Verlag, 2016) Akinay, Yuksel; Hayat, Fatih
The effect of Ni on the mechanical properties and microstructure of twinning induced plasticity (TWIP) steels were investigated in this study. TWIP 1 (0.6 C, 24 Mn) and TWIP 2 (0.6 C, 24 Mn, 1 Ni) steels were fabricated and annealed at 700, 800 and 900 degrees C for 150 minutes and then air-cooled. The results revealed that the Ni containing steel (TWIP 2) exhibits a higher yield strength and tensile strength than the steel TWIP 1. Carbide precipitations have been detected in the microstructure of TWIP 1 and TWIP 2 specimens annealed at 700 degrees C. However, the microstructure of the steel TWIP 1 annealed at 800 and 900 degrees C was fully austenitic and some grains included twins. It turned out that with the addition of Ni, the formation of twinning decreased in consequence of the annealing at 800 and 900 degrees C.
The effect of welding current on nugget geometry, microstructure and mechanical properties of TWIP steels in resistance spot welding
(Springer Heidelberg, 2021) Sahin, Sadettin; Hayat, Fatih; Colgecen, Onur Cem
In this study, two twinning induced plasticity (TWIP) steels with different chemical compositions were produced by casting-hot rolling-cold rolling processes. A total of four groups of samples were formed by obtaining cold-rolled and heat-treated samples giving optimum mechanical properties. Welding parameters of resistance spot welding (RSW) of all samples were determined, and weldability at different welding current values was examined. Button shapes, microstructures, microhardness, and tensile shearing tests of welded joints were investigated. In addition, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analyses of broken samples were examined as a result of tensile testing. It has been concluded that non-heat-treated samples have higher tensile strength than heat-treated samples. In heat-treated steels; a marked increase in ductility was observed. It has been observed that RSWs of non-heat-treated steels have higher tensile load bearing capacity (TLBC) value.
The effect of welding parameters on fracture toughness of resistance spot-welded galvanized DP600 automotive steel sheets
(Springer London Ltd, 2012) Hayat, Fatih; Sevim, Ibrahim
The aim of this study was to evaluate the fracture toughness of resistance spot welded (RSW) lap joints of galvanized DP600 steels. RSW lap joints galvanized DP600 steel sheets were performed on spot welded in a pneumatic, phase-shift-controlled, and 0-9 kA effective weld current capable AC spot welding machine. Defect-free RSW lap joints were produced on galvanized DP600 steel sheets. Fracture toughness of RSW lap joints were calculated from the results of shearing tensile tests: the dependence of fracture toughness to welding current, welding time, and hardness of welding zone for galvanized DP600 steel sheets. According to the experimental data, the fracture toughness increases as welding current and welding time increase up to a certain value, then the fracture toughness starts to decrease. Also, it was seen that the fracture toughness varies with the hardness of the welding zone. This variation is related to welding current.
The effects of boriding process on tribological properties and corrosive behavior of a novel high manganese steel
(Elsevier Science Sa, 2022) Sezgin, Cihangir Tevfik; Hayat, Fatih
In this study, wear and corrosion behavior of a novel borided high manganese steel (HMS) produced by the researchers was investigated. After the sheets were cold-rolled, they were annealed. HMS was borided at 850, 900, and 950 degrees C for 2, 4, and 6 h through the pack-boriding process. Borided HMS uncommonly exhibited a sawtooth morphology like low alloy steels due to similar crystal structures of MnB and FeB. XRD analysis showed the existence of SiC, FeB, MnB and Fe2B phases. The present study indicated a silicon-rich zone by EDX mapping. The formation mechanism of silicon-rich zones was explained and expressed with the term compact transfer of silicones. The boriding time and temperature increased the thickness of the boride layer from 26.13 mu m to 109.04 mu m. The highest hardness value was observed in sample 5 (1757 HV0.05). The activation energy of borided HMS was quite low compared to several high alloy steels in the literature. Daimler-Benz Rockwell-C adhesion test showed that adhesions of borided HMS surfaces were sufficient. The egg-shell effect that emerge due to the high silicon rate did not occur. In the wear tests applied under 5, 10, and 15 N loads, the borided HMSs exhibited a better wear resistance compared to the base metal (BM). However, the wear test was applied under 5 N load and BM had a better performance than several borided HMSs because of the phase transformations. In general, the borided samples had lower corrosion rates compared to the unborided ones.
The effects of the welding current on heat input, nugget geometry, and the mechanical and fractural properties of resistance spot welding on Mg/Al dissimilar materials
(Elsevier Sci Ltd, 2011) Hayat, Fatih
Investigating the joining capability of magnesium AZ31 alloy sheets and aluminium 1350 alloy sheets with the application of resistance spot welding was the objective of this study. The weld current values used in the welding process of Al-Mg sheets were 22, 23, 25, 27, 29, 31, and 33 kA. The studies examined the nugget geometries of joined specimens, recorded the scanning electron microscopy (SEM) images of the welded zone and the fracture surface, and recorded the energy-dispersive spectroscopy (EDS, semi-quantitative) analyses. The results of the experiment confirmed that nugget geometry was different for the Al and Mg sides. Tensile shear tests carried out on the welded joints determined their strength and failure mode. The increase in the weld current and duration resulted in an increase in the nugget size and the weld strength. According to observations, the tensile load bearing capacity (TLBC) increased up to 29 kA of the weld current value. It was also found that tearing during fracture occurred in two different ways. (C) 2010 Elsevier Ltd. All rights reserved.
Electron beam welding of 7075 aluminum alloy: Microstructure and fracture properties
(Elsevier - Division Reed Elsevier India Pvt Ltd, 2022) Hayat, Fatih
Aluminum alloys have widespread use due to their superior properties. However, it exhibits complex effects with its various intermetallic compounds formed by clustering of other elements in its welded joints. In this study, electron beam welding (EBW) of the 7075 aluminum alloys (Al-alloys) was examined. Two different welding current values are used in the welding process (20 and 25 mA). The welded specimens were subjected to tensile testing to determine their mechanical properties. In addition, the fractured surfaces were examined. The microhardness, scanning electron microscopy (SEM) and energy-dispersive spectroscopy analysis (EDS), EDS line analysis and EDS mapping were conducted. The microstructural evolution of EB welded plates investigated in the base metal (BM), heat affected zone (HAZ), and fusion zone (FZ), using SEM. Results indicated that after EBW, microhardness increment was observed in the FZ as compared to the BM and HAZ. The lowest hardness was observed in HAZ. The inter metallic formations in the FZ, and the effects of the elements on fracture were tried to be identified. At parameters 20 mA and 25 mA, 7075 alloys weld joints were brittlely broken. It was observed that the amount of Cu element increased at a high rate in the fracture zones of 7075 alloys (25 mA), it was clumped and active in fracture. Furthermore, it is estimated that a new formation is observed in the FZ of the welded joint made at 20 mA current in this study. As a result of the literature review, it is predicted that a natural structure similar to the one found in our study was not encountered for 7075 alloys or other welded Al-alloys. This formation was named, and the theory was put forward about the formation. The size, shape, chemistry and how this new formation came about were analysed. (c) 2022 Karabuk University. Publishing services by Elsevier B.V.
Investigation of corrosion behaviour of boronised cold rolled high manganese steel
(Inderscience Enterprises Ltd, 2023) Sezgin, Cihangir Tevfik; Hayat, Fatih
Corrosion behaviour of boronised high manganese steels (HMS) was investigated in this study. Pack-boronising was processed at 950 degrees C, 900 degrees C and 850 degrees C for 2 h, 4 h, and 6 h. Boride layers of HMS unpredictably exhibited saw-tooth morphology. FeB, Fe2B, MnB and SiC phases were determined by XRD analyses. The increase in boronising temperature and time caused an increase in boride layer thickness. Although the corrosion rates were lower in boriding processes at 850 degrees C, the corrosion rate of most of the samples boronised at 900 and 950 degrees C was higher than the un-boronised HMS due to micro-cracks and pores formed in the boride layers.
Investigation of resistance spot welds between DP450 steel and aluminum alloys
(Walter De Gruyter Gmbh, 2016) Akinay, Yuksel; Hayat, Fatih
In this study, the resistance spot weldability of DP450 steel and aluminum alloys (AA1050, AA6061 and AA7075) was investigated and the interfacial characteristics of fracture zones was examined via microanalysis, scanning electron microscopy and energy dispersive spectroscopy (EDX). In addition, tensile shear load tests and hardness tests were performed to determine the mechanical properties and fracture behavior of welded joints. These results suggest that the tensile shear strength of the DP450/AA1050 and DP450/AA7075 joints was not affected by the reaction layer formed at the welding interface. This indicates that the spot weldability of DP450/AA6061 is better than DP450/AA1050 and DP450/AA7075 Al alloys.
THE INVESTIGATION OF THE USE OF TRIP STEELS IN AUTOMOTIVE INDUSTRY
(Gazi Univ, Fac Engineering Architecture, 2010) Hayat, Fatih
Turkey has started the integrated steel production with the foundation of Karabuk Iron-Steel Factory which is the first heavy industry attempt of the country. Even though Turkish Iron-Steel industry has been exposed to various crises until the 21(st) century, it took an important step into a growth process starting from the year 2001. However, to keep up with the sectoral changes developing in the global economy and to direct the production in accordance with such developments have become a requirement. For this purpose, it might be an important objective to produce steel for the automotive industry that has come into prominence in our country with a high level of added value and income. Production of light and advanced high-strength steel for Turkish and World industries is a very critical technology. In developed countries, the steel industry is based on integrated plants and has been directed to products such as advanced high-strength steel, stainless steel, etc. that have a very high added value. In spite of that different kinds of steel sheet are being produced in our country, the dual phase steel which has been intensively utilized especially in recent years is being produced in low quantities whereas TRIP steel, which shall be used more with the purpose of reducing the weight of the vehicles in future, is not being produced. The literature study has done considering most recent research shaped within the frame of original studies conducted in recent years. In this study, TRIP steels have been introduced in comparison with other steels used in automobiles based on certain criteria such as microstructure, tensile strength, crash (impact), formability and fatigue. Furthermore, a study has also been conducted about the utilization of the TRIP steel in automotive industry and manufacturability in Turkey.
Magnetic and microwave absorption properties of PVB/Fe3O4 and PVB/NiFe2O4 composites
(Wiley, 2018) Akinay, Yuksel; Hayat, Fatih; Cakir, Mustafa; Akin, Emre
Electromagnetic and microwave absorbing properties of Polyvinylbutyral (PVB)/Fe3O4 and PVB/NiFe2O4 composites were investigated in the 1-14 GHz. PVB/filler particles (Fe3O4 and NiFe2O4) composites were prepared with 90/10 mixture ratios via Ultrasonic Probe Sonicator method in solution. The complex permittivity (epsilon-j epsilon) and permeability (- j) of the composites have been measured at different microwave frequencies in 1-14 GHz employing vector network analyzer (Keysight N9926A). The reflection loss (R-L) of composites was calculated and evaluated using theory of the absorbing wall. It was found that, both composites exhibit the large reflection loss and broadband within the frequency range from 1 to 14 GHz for 3, 5, and 7 mm. However, the R-L results show that, when the thickness is 7 mm, the minimum R-L was found to be -22.9 dB (99% power absorption) at the frequency of 13.93 GHz. The Fe3O4/PVB and NiFe2O4/PVB composites have potential application for microwave and radar absorptions. POLYM. COMPOS., 39:3418-3423, 2018. (c) 2017 Society of Plastics Engineers
Microstructural and mechanical properties of dual-phase steels welded using GMAW with solid and flux-cored welding wires
(Carl Hanser Verlag, 2012) Hayat, Fatih; Uzun, Huseyin
The aim of this study is to demonstrate the transformation of grade-A steel into dual-phase steel by heat treatment, and the joint performance of dual-phase steels welded by means of the gas metal arc welding process using both solid and flux-cored welding wires. Dual-phase steels with different contents of martensite were obtained by intercritical annealing in different temperature ranges of a grade-A shipbuilding steel, followed by water quenching. The experimental results revealed that the tensile strength of the dual-phase steels joined by solid wire is higher than that of the flux-cored wire joints. The microstructure of grade-A steel consists of ferrite and pearlite, while the dual-phase steels consist of ferrite and martensite. On the other hand, while the martensitic phase is especially encountered in the weld metal of the dual-phase steels joined with the solid wire, the ferrite phase is more common in the weld metal of the flux-cored wire joints.
The Microstructure and Mechanical Behavior of TRIP 800 and DP 1000 Steels Welded by Electron Beam Welding Method
(Assoc Brasil Soldagem, 2020) Sezgin, Cihangir Tevfik; Hayat, Fatih
TRIP 800 steel and DP 1000 steel welded by using the electron beam welding (EBW) method were investigated in this study. Martensite was a dominant phase at the fusion zone (FZ) of both steels. In addition, bainite and austenite were observed in the FZ of TRIP 800. The hardness of FZ and heat affected zone (HAZ) of both steels were higher than their base metals. The hardness of FZ of the TRIP 800 joinings was higher than the FZ of DP 1000. Ductility and tensile strength decreased at both of the joinings. However, this decrease became higher at the DP 1000 steel joinings compared to the TRIP 800 joinings. It was observed that the TRIP 800 joining absorbed more energy than the DP 1000 joining at impact notch test for each temperature.
Resistance Spot Weldability of Dissimilar Materials: BH180-AISI304L Steels and BH180-IF7123 Steels
(Journal Mater Sci Technol, 2011) Hayat, Fatih
In this study, resistance spot weldability of 180 grade bake hardening steel (BH180), 7123 grade interstitial free steel (IF7123) and 304 grade austenitic stainless steel (AISI304L) with each other was investigated. In the joining process, electrode pressure and weld current were kept constant and six different weld time were chosen. Microstructure, microhardness, tensile-shear properties and fracture types of resistance spot welded joints were examined. In order to characterize the metallurgical structure of the welded joint, the microstructural profile was developed, and the relationship between mechanical properties and microstructure was determined. The change of weld time, nugget diameter, the HAZ (heat affected zone) width and the electrode immersion depth were also investigated. Welded joints were examined by SEM (scanning electron microscopy) images of fracture surface. As a result of the experiment, it was determined that with increasing weld time, tensile shear load bearing capacity (TLBC) increased with weld time up to 25 cycle and two types of tearing occurred. It was also determined that while the failure occurred from IF side at the BH180+IF7123 joint, it occurred from the BH180 side at the BH180+AISI304L joint.
The study of MIG weldability of heat-treated aluminum alloys
(Springer London Ltd, 2013) Sevim, Ibrahim; Hayat, Fatih; Kaya, Yakup; Kahraman, Nizamettin; Sahin, Sadettin
In this article, Metal Inert Gas (MIG) weldability of commercially received and aged samples of 6061-T-6 and 7075-T-651 aluminum alloys was investigated. The welding joints were prepared in ten different combinations. Microstructure, microhardness, EDX, energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analyses were used in order to evaluate the effect of aged heat treatment on the performance of welded joints. In addition, the mechanical properties of welding joints were characterized using the tensile and microhardness tests. In conclusion, it was shown that prewelding aging heat treatment improves the mechanical properties of welding joints.
Synthesis and microwave absorption enhancement of BaTiO3 nanoparticle/polyvinylbutyral composites
(Sage Publications Ltd, 2019) Akinay, Yuksel; Hayat, Fatih
Barium titanate (BaTiO3)-polyvinyl butyral (PVB) composites at various weight concentrations were prepared via ultrasonic probe sonicator. The sonication was carried out at 20 kHz and 70% amplitude for about 2 h and BaTiO3 nanoparticles were dispersed well in the mixture of PVB/ethanol under probe sonication. As a microwave absorbent, the microwave absorbing properties of the BaTiO3 nanoparticle-PVB composites with different mixture ratios of 5 wt.% (RAM1), 10 wt.% (RAM2) and 15 wt.% (RAM3) BaTiO3 were investigated based on transmission line theory in the frequency range from 1 GHz to 14 GHz. The minimum reflection loss (R-L) of the RAM1 reaches -3.47 dB at 5.57 GHz with a matching thickness of only 7.0 mm. For RAM2 with 4 mm and 4.2 mm thickness (t(m)), the R-L values are less than -10 dB obtained in the frequency 10.3-13.4 GHz. The RAM3 composite with 15 wt.% BaTiO3 mixture ratio shows a minimum reflection loss of -43.8 dB at 11.01 GHz with a -15 dB bandwidth over the extended frequency range of 10.2-13.2 GHz for a thickness of 2.8 mm and -44.2 dB at 4.77 GHz for a thickness of 6.5 mm.
Trip çeliklerinin otomotiv endüstrisinde kullanımının incelenmesi
(2010) Hayat, Fatih
Türkiye ilk ağır sanayi hamlesi olan Karabük Demir-Çelik Fabrikasının kuruluşuyla birlikte entegre çeliküretimine başlamıştır. Türk Demir-Çelik endüstrisi, 21. Yüzyıla kadar olan süreçte farklı krizlere maruzkalmakla birlikte 2001 yılından itibaren hızlı bir büyüme sürecine girmiştir. Fakat küresel ekonomide gelişensektörel değişimlere ayak uydurmak ve üretimi o yönlere çevirmek gereksinim haline gelmiştir. Bu amaçlaülkemizde önemli bir sektör olarak kendini gösteren, katma değeri ve kazanımı yüksek olan otomotivendüstrisine çelik üretmek önemli bir amaç olabilir. Türkiye ve Dünya endüstrileri için gelişmiş hafif yüksekmukavemetli çelik üretimi kritik bir teknolojidir. Gelişmiş ülkelerde çelik endüstrisi entegre tesislere dayalı olup,katma değeri yüksek; gelişmiş yüksek mukavemetli çelik, paslanmaz çelik v.b. gibi ürünlere yönelmiştir.Ülkemizde farklı çelik sac türleri üretilmekle beraber özellikle son yıllarda yoğun bir şekilde kullanılan çift fazlıçelik düşük miktarlarda üretilmekte, ilerleyen yıllarda otomobil ağırlığını azaltmak amacıyla kullanımı artacakolan TRIP çeliği ise üretilmemektedir. Literatür çalışması son yıllarda yapılan özgün çalışmalar çerçevesindebiçimlendirilmiştir. Çalışmada TRIP çeliklerinin otomobillerde kullanılan diğer çeliklerle mikroyapı, çekmedayanımı, çarpma (darbe), şekillendirilebilme ve yorulma özellikleri gibi kriterlere bağlı olarak karşılaştırmalıbir biçimde sunulmuştur. Ayrıca TRIP çeliğinin otomotiv endüstrisinde kullanımı ve Türkiye’de üretilebilirliğihakkında da bir çalışma gerçekleştirilmiştir.
Twip çeliklerinin nokta direnç kaynak kırılma tokluğunun incelenmesi
(2016) Hayat, Fatih; Sevım, İbrahim; Şahin, Sadettin
Proje konusu olan ikizlenme yoluyla plastisite kazanan çelikler (TWIP) son yıllarda geliştirilmiş ultra yüksek mukavemetli çelik sınıfının öncüsü ve mekanik özellikleri nedeniyle en gelişmiş çelik durumundadır. TÜBİTAK tarafından desteklenen projede ülkemizde ticari olarak üretilmeyen, Dünyadaki mevcut TWIP (ikizlenme yoluyla plastisite kazanan) çeliklerinden farklı kimyasal kompozisyonlarda iki adet TWIP çeliğinin üretimi yapılmış ve üretilen çeliklerin nokta direnç kaynaklı bağlantı parametreleri belirlenmiş ve kırılma toklukları incelenmiştir. Bu amaçla özgün kimyasal bileşime sahip iki TWIP çeliğinin, mekanik ve mikroyapı incelemeleri yapılmıştır. En yüksek mekanik özellikleri veren numunelerin ısıl işlem süresi belirlenmiştir. Isıl işlemsiz ve optimum özellikleri veren sıcaklıkta tavlanmış numunelerin nokta direnç kaynakları değişken akımlarda yapılmış ve en yüksek mekanik özellikleri veren parametre seçilerek tekrar kaynaklı bağlantılar elde edilerek kırılma toklukları incelenmiştir. Kırılmış numunelerin SEM ve EDS analizleri yapılmıştır.

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