Browsing by Author "Esen, Ziya"

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Interfacial Behavior and Diffusion Mechanisms of Bni-2 Brazing on Titanium Alloy: Experimental and Molecular Dynamics Insights
(Springer, 2025) Goynuk, Tansu; Esen, Ziya; Karakaya, Ishak
ContextJoining titanium alloys, particularly Ti-6Al-4V, is crucial in aerospace applications where reliable, high-performance joints are needed. Brazing offers an effective solution, enabling the joining of dissimilar materials without melting the base metals. However, optimizing the wetting and diffusion behavior of filler metals remains a challenge. This study investigates the high-temperature interaction between BNi-2 filler alloy and Ti-6Al-4V. Boron, the primary melting point depressant in BNi-2, was examined due to its small atomic size and interstitial diffusion mechanism. Elevated temperatures led to improved wetting, reflected by decreased contact angles. Both wetting angles and boron diffusion coefficients were obtained through molecular dynamics simulations and experimental measurements, showing reasonable correlation. These results provide valuable insight into interfacial mechanisms and support further optimization of brazing parameters.MethodsMolecular dynamics simulations were performed using LAMMPS to analyze the temperature-dependent wetting behavior of molten BNi-2 on Ti-6Al-4V and track atomic-scale diffusion. Initial atomic configurations were modeled and simulated under various conditions. Trajectory data were analyzed using OVITO for structural evolution. Boron diffusion was evaluated by calculating mean square displacement from LAMMPS outputs. These values were used to derive diffusion coefficients and activation energies. Parallel experiments were conducted to assess wetting angles and diffusion behavior, and simulation results were compared with experimental data. The consistency between both approaches highlights the reliability of the modeling framework in capturing essential mechanisms during the brazing process.
Citation - WoS: 32
Citation - Scopus: 36
Optimization of the Mechanical Properties of Ti-6al Alloy Fabricated by Selective Laser Melting Using Thermohydrogen Processes
(Elsevier Science Sa, 2017) Esen, Ziya; Akin, Seniz Kushan; Dericioglu, Arcan F.; Bilgin, Guney Mert
2-step Thermo Hydrogen Process (THP) including hydrogenation and dehydrogenation steps was applied to Ti-6Al-4V alloy fabricated by selective laser melting (SLM) process to refine the microstructure and to increase the ductility of the alloy. It was observed that as-fabricated alloy's surface was composed of oxides of titanium and aluminum, which may alter the hydrogenation kinetics. The hydrogen treatment for 1 hat 650 degrees C, the maximum hydrogen solubility temperature of the alloy, transformed starting non-equilibrium alpha'-martensitic phase to 13 and 8 (TiH2) phases. On the other hand, very fine discontinuous beta-phase was formed along with alpha-phase as a result of dehydrogenation at 700 degrees C for 18 h, which decreased the hydrogen level well below the starting value and caused transformation of delta-phase to fine alpha-phase. In contrast to commonly used THP treatments consisting of betatizing at high temperature, 2-step treatment prevented grain boundary alpha-phase formation as well as excessive grain growth. About 110% and 240% increments were detected in % Elongation (EL) and % Reduction in Area (RA) values, respectively, as a result of 2-step THP, while the strength decrease was limited to 10%. The change in ductility of the alloy was also verified by transformation of flat and shiny fracture surfaces seen in SLM fabricated alloy to a fracture surface containing equiaxed dimples after THP treatment. The hardness drop in the alloy after hydrogenation and dehydrogenation treatments was attributed to relief of residual stress and formation of equilibrium alpha and beta-phases.
Citation - Scopus: 41
Characterization of Loose Powder Sintered Porous Titanium and Ti6al4v Alloy
(2009) Bor, Şakir; Esen, Ziya; Bor, Elif Tarhan
Porous titanium and Ti6Al4V alloy, biomedical candidate materials for use in orthopedic and dental implants, were manufactured by sintering the powders at various temperatures in loose condition. The characteristics of the corresponding powders and utilized sintering temperatures limited the final porosities in the range 30-37.5 vol. %. Similar to wrought alloys, compression stress-strain curves of porous samples exhibited 3 distinct deformation regions containing an elastic region, subsequent to yielding strain hardening region up to a peak stress and fast fracture after small straining. The mechanical properties of porous samples of both types were observed to obey minimum solid area (MSA) models in which the bond regions between particles perpendicular to loading direction are assumed to dominate in transmission of stress. A linear relation was obtained between yield strength and square of neck size ratio, (X/D)2, where X and D represent the average neck and particle diameters, respectively.
Citation - WoS: 23
Citation - Scopus: 24
Microstructural and Texture Evolution During Thermo-Hydrogen Processing of Ti6al4v Alloys Produced by Electron Beam Melting
(Elsevier Science inc, 2020) Esen, Ziya; Davut, Kemal; Tan, Evren; Gumus, Berkay; Dericioglu, Arcan F.; Dogu, Merve Nur
The present study was conducted to reveal the effects of building angles and post heat-treatments (2-step Thermo-Hydrogen Processing (THP) and conventional annealing treatment) on the density, microstructure and texture of Ti6Al4V alloy parts produced by Electron Beam Melting (EBM). The results showed that regardless of the building angle; the density, microstructure and crystallographic texture (defined with respect to building angle) of the as-produced samples were identical; having Widmanstatten a structure and columnar beta-grains which are parallel to building direction. The main texture component for the alpha phase was (10 (1) over bar0)//building direction, and for beta phase (001)//building or heat flow direction. The first step of THP, namely, the hydrogenation step, produced a needle-like microstructure and increased the local misorientations due to lattice distortion. On the other hand, after application of the second step of THP, dehydrogenation step, microstructure was refined, particularly alpha-grains that were larger than 10 mu m and located at grain boundaries. Moreover, THP randomized the crystallographic texture since it involves beta to alpha phase transformation, at which one beta-grain can produce 12 distinct alpha-variants. The grain boundary misorientation distributions also changed in accordance with the microstructural changes during the 2-step THP. On the other hand, annealing coarsened the grain boundary and Widmanstatten alpha phases; moreover, it changed the texture so that the basal planes (0001) rotated 30 degrees around the building direction.
Citation - WoS: 11
Citation - Scopus: 11
Effect of Sn Alloying on the Diffusion Bonding Behavior of Al-Mg Alloys
(Springer, 2017) Esen, Ziya; Dericioglu, Arcan F.; Atabay, Sila Ece
Effect of Sn as an alloying element on the diffusion-bonding behavior of Al-Mg-Si alloy has been studied by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and mechanical testing of the diffusion-bonded joint. XRD results revealed the formation of Mg2Sn and (Sn) phases during solidification following induction casting. DSC results showed local liquid (Sn) formation during the bonding process for Sn-containing alloys, where its amount was found to be increasing with the increasing Sn content. Results revealed that Sn addition leads to an increase in the bond shear strength of the diffusion-bonded joints and elimination of the irregularities formed on the bonded interface. Fractured surfaces showed that formation of (Sn) layer at the bonded interface causes the fracture to transform from the ductile to the mixed fracture mode.
Investigations on the Effect of Secondary Treatments on Ti48Al2Cr2Nb Alloy Manufactured by Electron Beam Powder Bed Fusion Method
(Elsevier Sci Ltd, 2025) Bilgin, Guney Mert; Ozer, Seren; Davut, Kemal; Esen, Ziya; Dericioglu, Arcan F.
As-built Ti48Al2Cr2Nb alloy samples produced by electron beam powder bed fusion (PBF-EB) exhibited notable brittleness. The low ductility was attributed to coarse gamma bands aligned perpendicular to the building and tensile direction. Additionally, variations in aluminum content and hardness between the coarse colonies and fine gamma/alpha(2) lamellae contribute to this phenomenon. Electron backscattered diffraction (EBSD) studies revealed a higher amount of dislocation density and inherent strain after PBF-EB manufacturing. Hence, usage of Ti48Al2Cr2Nb alloy in the as-built condition in aviation applications with high loads and demanding environments is not found to be viable. To eliminate these negative aspects and make PBF-EB produced Ti48Al2Cr2Nb alloy available for demanding applications, two distinct post-processing heat treatments; namely, hot isostatic pressing (HIP) and annealing heat treatment (HT) were employed at 1200 degrees C. A comprehensive characterization covering microstructure analysis, EBSD, fracture surface examination, as well as room and high-temperature tensile tests allowed determination of the effect of post-processes. HIPing altered the banded structure observed in the as-built samples by increasing the amount of alpha(2) phase and grain size. On the other hand, HT made the banded structure more pronounced without significantly increasing the amount of alpha(2) phase. HT also strengthened the <001> texture, while HIPing introduced randomization of grains. On the other hand, complete recrystallization is achieved as a result of HT at 1200 degrees C for 2 h, whereas HIPing at the same temperature for 2 h induced only 80.5 % recrystallization. In both post-processes, dislocation density and inherent strain were reduced. Room temperature and high-temperature tensile tests demonstrated that both HIPing and HT eliminated the extreme brittleness of the as-built samples.
Citation - WoS: 20
Citation - Scopus: 21
The Effect of Processing Routes on the Structure and Properties of Magnesium-Tini Composites
(Elsevier Science Sa, 2012) Esen, Ziya
TiNi particulate-reinforced magnesium matrix composites were fabricated by rotary hot swaging and post-annealing heat treatment. The magnesium matrix of the processed composites was observed to contain elongated grains comprised of equiaxed recrystallised grains. Each elongated grain was surrounded by thin, non-continuous magnesium oxide layers composed of nanometric magnesium oxide particles. The TiNi reinforcement particles preserved their starting spherical shape during processing and testing. However, the hot deformation and annealing heat treatment changed the underlying room temperature microstructures and transformation behaviours of the reinforcements. In contrast to the majority of the ceramic reinforcements, the ductility of the composites was not significantly degraded by the addition of TiNi reinforcements; conversely, an approximately 25% enhancement was recorded in the elongation values for the Mg-5 vol% TiNi alloy. While the yield strengths of the composites changed linearly with increasing reinforcement content, the highest compression peak strength value was obtained with the addition of 5 vol% TiNi, beyond which the strength was slightly decreased. During mechanical testing, the TiNi particles debonded due to insufficient bonding between the matrix and reinforcement, and fracture resulted largely within the oxide layers present in the interfacial region and the magnesium oxide film in the magnesium grain boundaries. (C) 2012 Elsevier B.V. All rights reserved.
Biyomedikal Uygulamalar için Gözenekli Ti6al7nb İmplant Alaşımlarının Hidrotermal Yöntemlerle Yüzey Aktivasyonu ve Karakterizasyonu
(2015) Yılmaz, Emre; Bütev, Ezgi; Yeni, Elif Eda; Bağ, Esra; Esen, Ziya
Biyomedikal malzemeler insan vücudundaki kemik, organ ya da dokuların işlevlerini yerine getirmek veya desteklemek amacıyla vücudun birçok bölgesinde kullanılmaktadır. Son zamanlardaki medikal alanlardaki ilerlemelerle birlikte insanların ortalama ömrü yükselmiş, dolayısıyla uzun ömürlü ve vücuda uyumlu biyomedikal malzeme arayışları artmıştır. Yükselen ortalama insan ömrü ile özellikle vücutta değişik yüklere maruz kalan diz ve kalça gibi eklem bölgelerinde ve yapay diş kökleri ile protezlerinde kullanılan biyomedikal malzeme ihtiyacı ivmelenerek artmaktadır. Kullanılan biyomedikal malzemeler arasında polimerik malzemeler düşük mekanik dayanımlarından, seramik malzemeler de düşük kırılma tokluğuna bağlı olarak kırılgan olmalarından dolayı yüke maruz kalan bu bölgelerde kullanılamamaktadır. Bu tür uygulamarda titanyum, titanyum alaşımları, Co-Cr alaşımları ve paslanmaz çelik gibi metalik esaslı biyomalzemeler tercih edilmektedir. Biyomedikal uygulamalarda kullanılan metalik malzemelerin yüksek aşınma, korozyon ve yorulma dayancına sahip olması, biyouyumluluğun yüksek olması ve vücut kemiğine benzer mekanik özellikler sergilemesi beklenmektedir. Co-Cr alaşımları ve paslanmaz çelikler kemiğe nazaran yüksek elastik modülleri nedeniyle vücutta mekanik uyumsuzluğa neden olmaktadırlar. Bu tür biyomalzemelerin vücutta kullanılmaları durumunda implant ve kemik farklı miktarlarda yük taşımakta, az yük taşıyan kemik zamanla zayıflayarak kemik dokusu kaybı yaşanmaktadır. Bu yüzden elastik modülleri kemiğe (1-40 GPa) daha yakın titanyum ve Ti6Al4V alaşımı (105-110 GPa) gibi titanyum alaşımlarının kullanımı artmıştır. Fakat, klinik deneyler Ti6Al4V alaşımında uzun vadede vanadyum salınımının olabileceğini gösterdiği için bu alaşımın yerine yeni nesil Ti6Al7Nb alaşımları geliştirilmiştir. Her ne kadar titanyum ve titanyum alaşımlarının mekanik özellikleri vücut kemiğine yakınlık gösterse de tam olarak bir uyum sağlanamamaktadır. Son zamanlarda titanyum ve alaşımlarının gözenekli yapıda üretimi ile vücut kemiğinin mekanik değerlerine ulaşılabildiği görülmüştür. Genellikle toz metalurji tekniklerinin kullanıldığı bu çalışmalarda yapıdaki düşük erime noktasına sahip üre veya polimerik tozların uçurulmasıyla gözenekli yapı elde edilmekte ile gözenek miktarı ile de mekanik özellikler ayarlanabilmektedir. Bunun yanında implantta açık hücreli gözenekli yapının varlığı vücut sıvılarının akışına imkan sağlamakta ve kemik hücrelerinin büyümesine olanak sağlamaktadır. Fakat, kemik hücrelerinin yüzeye tutunması ve sıkı bir implant-kemik dokusu oluşumu için tek başına gözenekler yeterli değildir. Bu yüzden gözenekli malzemelerde kemik hücrelerinin yüzeye tutunmasını sağlayan farklı yapılarda ve kalınlıklarda TiO2 fazının veya farklı titanat fazların oluşumunu sağlayan ve sıklıkla gözenekli titanyum numunelerde kullanılan kimyasal yöntemlerle yüzeyler aktive edilmektedir. Bu çalışmada ise vücut kemiği mekanik özelliklerine benzer, kemik büyümesine uygun gözenek büyüklüğü ve miktarına sahip gözenekli Ti6Al7Nb alaşımlarının toz metalurji ile üretimi ve gözenekli yüzeylerin kemik hücrelerinin büyümesine olanak sağlayacak şekilde hidrotermal yöntemlerle aktive edilmesi planmaktadır. Gözenekli Ti6Al7Nb alaşımlarının üretiminde kullanılan lazer şekillendirme veya gevşek toz sinterleme yöntemlerinden farklı olarak boşluk yapıcı toz metalurji tekniği kullanılacaktır. Proje yürütücüsü tarafından patenti alınan, saf titanyum, Ti6Al4V ve TiNi alaşımlarında gözenek oluşturmak için kullanılmış olan bu yöntemin önerilen proje kapsamında gözenekli Ti6Al7Nb alaşımının üretiminde kullanılması bu anlamda bir yenilik olacaktır. Boşluk yapıcı olarak magnezyum tozunun kullanılacağı yöntemde, preslenerek şekil verilen Ti6Al7Nb-magnezyum toz karışımlarından magnezyum tozunun düşük sıcaklıkta sistemden uzaklaştırılmasıyla gözenekli yapı oluşturulacak ve yüksek sıcaklıkta sinterleme işlemi yapılacaktır. Bu aşamada vücut kemiği elastik modüllü değerleri olan 1-40 GPa arasında elastik modülüne sahip numunelerin üretimi hedeflenmektedir. Ayrıca, kemik hücrelerinin büyümesi ve vücut sıvısı transferine olanak sağlayacak şekilde gözenek miktarı ve büyüklüğü sırasıyla %40-70 ve 200-500 μm arasında değişen gözenekli Ti6Al7Nb numunelerinin üretilmesi için çalışmalar yürütülecektir. Üretilen gözenekli malzemelerin yüzeyleri ise kemik hücrelerinin yüzeyde tutunmasını sağlayacak şekilde hidrotermal yöntemler kullanılarak aktive edilecektir. Boşluk yapıcı yöntemle üretilmiş gözenekli Ti6Al7Nb alaşımlarında ilk defa uygulanacak olan yöntemde numuneler değişik sıcaklıklarda sodyum hidroksit ve CaCl2 sulu çözeltilerinde bekletilip ek ısıl işlemlerle gözenekli yüzeyler aktive edilecektir. Bu işlemlerde gözenekli yüzeylerde kemik büyümesine olanak veren sodyum titanat ve kalsiyum titanat fazlarının oluşturulması üzerine çalışılacaktır. Yüzeylerde oluşturulan titanat fazlarının apetit oluşturma potansiyelleri ise yapay vücut sıvısında test edilerek farklı tiatanat tabakalarının kemik büyümesine uygunluğu karşılaştırılacaktır. Hidrotermal işlemlerde genellikle numune iç yapısı dikkate alınmamakta ve iç yapının oksit ve titanat gibi fazların oluşumuna etkisi bilinmemektedir. Bu yüzden önerilen projede literatürden farklı olarak değişik iç yapıların (katmanlı yapı, martensit, vb.) hidrotermal işlemlerde titanat fazlarının oluşumuna etkisi araştırılacak ve bu maksatla gözenek oluşturma işleminden sonra numunelere farklı ısıl işlemler uygulanacak ve ayrıca bu fazların gözenekli numunelerin mekanik özelliklerine etkisi belirlenecektir. Ek olarak yüzeyde oluşturulan titanat tabakalarının kararlılıkları nemli ortamda test edilerek kemik büyümesine en uygun titanat tabakası özellikleri belirlenecektir. Özet olarak proje kapsamında üretilecek ve hidrotermal yöntemle yüzeyi aktive edilecek gözenekli Ti6Al7Nb malzemeler biyomedikal alanda birçok boşluğu dolduracak ve problemleri çözebilecek niteliktedir. Malzemedeki gözenek miktarı ile mekanik özellikler kemiğe benzer şekilde hassas olarak ayarlanabilecek, açık hücreli gözenekler sayesinde de vücut sıvılarının malzeme içinde akışına imkan sağlanabilecektir. Ayrıca, aktive edilmiş yüzeylerde kemik hücrelerinin tutunup büyümesine imkan verilerek çok daha kısa sürede kemik-impant bağı oluşturulabilecektir. Bu kapsamda üretilen gözenekli Ti6Al7Nb alaşımları dişçilikte yapay diş kökü olarak ve kalça, diz protezleri gibi alanlarda implant malzemesi olarak uygulama alanı bulabilecektir.
Citation - WoS: 7
Citation - Scopus: 3
Tini Reinforced Magnesium Composites by Powder Metallurgy
(John Wiley & Sons, 2011) Esen, Ziya; Esen, Ziya
Rod shaped Mg-TiNi composite samples were manufactured bypowder metallurgical route in which the samples were heated and deformed simultaneously using rotary hot swaging technique. Firstly, encapsulated argon filled copper tubes which contained compacts of pure magnesium and pre-alloyed TiNi alloy powder mixtures were deformed about 45% in two steps at 450 degrees C. Pre/post annealing heat treatments were applied at 450 degrees C for 20 mins between the stages of coaxial deformation to enhance the sintering degree and to homogenize the heavily deformed composite structures. Next, copper peeled and machined samples were compression tested under quasi-static conditions to investigate the mechanical properties, i.e. yield and peak strength, and ductility. Transmission and Scanning Electron Microscopy studies were carried out to examine the Mg-TiNi interface and fracture surfaces of the compression tested composites, respectively.
Citation - WoS: 21
Citation - Scopus: 26
Experimental Investigation on Wire Electric Discharge Machining of Biodegradable Az91 Mg Alloy
(Springer, 2021) Cogun, Can; Genc, Asim; Esen, Ziya; Bozkurt, Fatih; Urtekin, Levent; Ozerkan, Haci Bekir
The AZ91 magnesium alloy, used commonly as a biodegradable material in biomedical applications, is generally formed by conventional casting method (CCM) and high-pressure die casting method (HPDCM). The AZ91 alloys exhibit poor machinability with conventional chip removal methods since they degrade at elevated temperatures. In this study, the wire electric discharge machining (WEDM) was presented as a candidate process to machine the AZ91 alloy since no cutting stresses and plastic deformations were applied by the cutting tool to the part causing elevated temperatures. In this context, the WEDM machinability of the AZ91 alloy samples produced by cold chamber HPDCM and CCM at different process parameters, was experimentally investigated. The machining performance outputs (the machining current (I), the machining rate (MR), the average surface roughness (R-a), and surface topography) were found for the varying process parameters [pulse time (t(s)), pulse-off time (t(off)), dielectric flushing pressure (P-d), and wire speed (V-w)]. The present study revealed that the I and the MR were significantly dependent on the density, the porosity, and the micro structure of the samples, and the HPDCM samples gave the higher MR and the smoother surface than that of the CCM.
Effect of alkali treatment parameters on surface structure and mechanical properties of porous Ti6A17NB scaffolds
(2014) Bütev Öcal, Ezgi; Yeni, Elif Eda; Yılmaz, Emre; Esen, Ziya; Bor, Şakir
In the present study, highly porous Ti6Al7Nb alloy scaffolds having 70% pore contents with 200-250 µm average pore size were produced through the spacer holder technique as a result of evaporation of Mg powder from the Ti6Al7Nb-Mg powder mixtures. In order to make the manufactured Ti6Al7Nb foam surfaces more suitable for biomedical applications they were exposed to alkali and heat treatment. Porous samples were immersed in 5M NaOH (aq.) solutions at 60°C for 24 hours then subsequent heat treatment was carried out to obtain crystalline sodium titanate layer. Crystallization heat treatments were also conducted in muffle furnaces to investigate the effect of heat treatment environment on titanate formation. Then, the morphology, structure and chemical composition of the formed titanate layers were characterized by using scanning electron microscopy (SEM) and TF-XRD techniques. According to mechanical testing, produced Ti6Al7Nb alloy foams had elastic moduli and yield strength very close to that of bone which makes them suitable for biomedical application because of the lessened stress shielding problem
Citation - WoS: 44
Citation - Scopus: 43
Corrosion Behaviours of Ti6al4v-mg/Mg-alloy Composites
(Pergamon-elsevier Science Ltd, 2020) Butev Ocal, Ezgi; Akkaya, Asli; Gurcay, Bensu; Ozcan, Ceren; Ozgumus, Burcu Asli; Dericioglu, Arcan F.; Esen, Ziya
The effect of coupling of unalloyed Mg and Mg-alloys (AZ91 and WE43) with Ti6Al4V alloy on corrosion and degradation behaviours of produced composites has been investigated in simulated body fluid (SBF) by hydrogen evolution, and surface and electrochemical characterization techniques. Combining of unalloyed Mg with Ti6Al4V intensified galvanic corrosion and catastrophic failure occurred by initiation of microcracks formed by sudden hydrogen gas evolution. In contrast to other composites, Ti6Al4V-AZ91 composites, containing new TiAl3 interface layer formed during composite production, preserved their mechanical integrities due to lowest corrosion and degradation rate of AZ91 alloy.
Citation - WoS: 2
Citation - Scopus: 2
Wetting Behavior and Reaction Layer Formation in C/Sic Composite-Titanium Alloy Joints
(Taylor & Francis Ltd, 2022) Esen, Ziya; Dericioglu, Arcan F.; Saltik, Simge
The present study investigates the effect of brazing parameters on reaction layer formation, and mechanical properties of C/SiC composite-Ti6Al4V alloy joints produced by brazing technique. The wetting mechanism of the C/SiC composite surface by the Ag-CuTi-based active brazing filler alloy has also been studied and correlated with the reaction layer formation. The strength of C/SiC composite/Ti6Al4V alloy joints increased at first and then decreased with increasing reaction layer thickness. The joints with 1-mu m-thick reaction layer, which were obtained by brazing at 915 degrees C for 15 min, had the highest shear strength of 33 MPa. Brazing filler alloy presented a minimum contact angle of 15 degrees on the C/SiC composite surface at 915 degrees C during the wetting experiments. 915 degrees C and 15 min were determined to be the optimised brazing parameters to ensure almost complete wetting and a uniform reaction layer for effective adhesion of the C/SiC composite surface.
Elektro Eğirme Tekniği ile Elde Edilmiş Tco İnce Filmlerde Nanoparçacık İlavesinin Elektriksel Özelliklere Etkisi
(2024) Çelik, Burak; Esen, Ziya; Duygulu, Nilüfer
Bu çalışmada elektro eğirme yöntemiyle üretilen ve saydam iletken oksit bir cam olan indiyum kalay oksitin (ITO) yüzeyine kaplananan fiberlerde nano parçacık katkılamanın fiberlerin yapısı ve elde edilen ince film elektrik özelliklerine etkisi araştırılmıştır. Bu amaçla, Polivinil Alkol (PVA) sulu çözeltisi hazırlanmış ve manyetik karıştırma yöntemiyle ağırlıkça % 3, 5, 10 and 20 oranında gümüş, çinko oksit ve titanyum oksit katkılaması yapılmıştır. Daha sonra nanoparçacık takviye edilmiş PVA çözeltileri ITO camın üstüne bir saat süreyle elektro eğirme yöntemiyle kaplanlanmıştır. Elde edilen filmlerdeki nanoparçacık takviyeli fiberlerin yapıları taramalı electron mikroskobu ile incelenmiş ve elde edilen ince fimlerin direnç ve özdirençleri değerleri belirlenmiştir. PVA fiberlerin içinde bulunan nano parçacıkların topaklandığı ve topaklanan bölgelerin büyüklüğünün kullanılan çözelti içindeki nanoparçacık miktarının artmasıyla birlikte arttığı görülmüştür. En az topaklanma TiO2 takviyeli fiberlerde görülmüş olup, en düşük topaklanma büyüklüğü olan 643.7 ± 85.5 nm ağırlıkça %3 TiO2 eklenen fiberlerde tespit edilmiştir. Benzer şekilde, en küçük fiber çapı ve homojen fiber büyüklük dağılımı TiO2 katkılı fiberlerde görülmüştür. Örneğin, ağırlıkça %3 TiO2, ZnO ve Ag nanoparçacık içeren fiberlerde fiber çapları sırasıyla 370, 376 and 380 nm olarak ölçülmüştür. TiO2 katkılı fiberlerdeki daha az topaklanma ve homojen fiber büyüklük dağılımı ITO cam üzerinde oluşturulan ince filmin elektriksel iletkenliğini de olumlu yönde etkilemiştir. Farklı miktarda nanoparçacık içeren tüm filmlerde nanoparçacık miktarının düşüşüyle birlikte film direnç ve özdirenci de düşmüştür. TiO2 içeren ince filmlerde, film direnci ITO camın direncine (34 ohm) nanoparçacık takviyesi ağırlıkça %10'a düşürüldüğünde ulaşmıştır ve daha az miktarda TiO2 ince filmler hedeflendiği şekilde ITO cama göre daha düşük direnç sergilemişlerdir. Diğer yandan, ZnO ve Ag takviyeli ince filmlerde ITO cam direncine ancak nanoparçacık miktarı ağırlıkça %5'e düşürüldüğünde ulaşılabilmiştir.
Citation - WoS: 31
Citation - Scopus: 35
Effect of Powder Metallurgy Cu-B4c Electrodes on Workpiece Surface Characteristics and Machining Performance of Electric Discharge Machining
(Sage Publications Ltd, 2016) Cogun, Ferah; Akturk, Nizami; Cogun, Can; Esen, Ziya; Genc, Asim
The main aim of this study is to produce new powder metallurgy (PM) Cu-B4C composite electrode (PM/(Cu-B4C)) capable of alloying the recast workpiece surface layer during electric discharge machining process with boron and other hard intermetallic phases, which eventually yield high hardness and abrasive wear resistance. The surface characteristics of the workpiece machined with a PM/(Cu-B4C) electrode consisted of 20 wt% B4C powders were compared with those of solid electrolytic copper (E/Cu) and powder metallurgy pure copper (PM/Cu) electrodes. The workpiece surface hardness, surface abrasive wear resistance, depth of the alloyed surface layer and composition of alloyed layers were used as key parameters in the comparison. The workpiece materials, which were machined with PM/(Cu-B4C) electrodes, exhibited significantly higher hardness and abrasive wear resistance than those of machined with the E/Cu and PM/Cu. The main reason was the presence of hard intermetallic phases, such as FeB, B4C (formed due to the boron in the electrode) and Fe3C in the surface layer. The improvement of the surface hardness achieved for steel workpiece when using PM/(Cu-B4C) electrodes was significantly higher than that reported in the literature. Moreover, the machining performance outputs (workpiece material removal rate, electrode wear rate and workpiece average surface roughness (Ra)) of the electrodes were also considered in this study.
Citation - WoS: 14
Citation - Scopus: 21
Fabrication, Morphology Analysis, and Mechanical Properties of Ti Foams Manufactured Using the Space Holder Method for Bone Substitute Materials
(Mdpi, 2019) Esen, Ziya; Yildirim, Bora; Cetinel, Oktay
Porous titanium (Ti) offers several key attributes as a biomedical material. Among the known characteristics of Ti relevant to biomedical applications, the mechanical performance and effects of a pore structure on the deformation characteristics under compressive loading were examined. The space holder method was employed to generate Ti foams with target porosities of 60%, 70%, and 80%. A micro-computed to mography analysis and light and scanning electron microscopy were performed to examine the pore morphology and microstructure. The mechanical properties along with the elastic modulus and compressive strength were evaluated via uniaxial compression testing. Ti foam samples with three porosity levels displayed average elastic moduli and compressive strengths comparable with those of human cancellous and cortical bone. All the Ti foam samples had elastic moduli similar to those of cancellous bone with their open porous structures. Although the foam samples with similar to 60% porosity had compressive strength comparable to that of cortical bone, the samples with similar to 80% porosity displayed compressive strength similar to that of cancellous bone. The results indicate that Ti foam scaffolds produced using the space holder method have great potential for applications in hard tissue engineering, as their mechanical properties and pore structures are similar to those of bone.
Citation - WoS: 102
Citation - Scopus: 120
Characterization of Ti-6al Alloy Foams Synthesized by Space Holder Technique
(Elsevier Science Sa, 2011) Bor, Sakir; Esen, Ziya
Ti-6Al-4V foams, biomedical candidate materials, were synthesized by powder metallurgical space holder technique as a result of evaporation of magnesium to achieve desired porosity content. Final products contained porosities in the range similar to 43-64% with an average macropore size between 485 and 572 mu m and a lamellar type Widmanstatten microstructure composed of alpha-platelets and beta-laths. Unlike the case of bulk Ti-6Al-4V alloy tested under compression loading, compression stress-strain curves of manufactured Ti-6Al-4V foams were similar to those of elastic-plastic foams, which contain a linear elastic region; a plateau stage: and a densification stage. In the plateau region deformation bands perpendicular to the compression axis were developed and cell collapsing took place together with the buckling and fracture of some of the cell walls and edges in a ductile manner. Calculated elastic modulus and yield strength were in the range 1.42-14.7 GPa and 28.2-150 MPa, respectively, and the foam mechanical properties were found to be dependent on micro porous cell wall properties, which in turn depends on neck size between powder particles. Around 330 MPa yield strength value was calculated for porous cell walls by the use of Ti-6Al-4V alloy powder samples sintered in loose and compacted conditions, which were utilized to simulate the cell wall structure of foams. In addition, overall mechanical properties of foam s were investigated considering macro porosity fraction, p(macro), and the yield strength of foams exhibited a power law dependence, similar to commonly used minimum solid area models, in the form of A*(1 - p(marco))(n), where the proportionality constant "A" was found to be the yield strength of micro porous cell walls. (C) 2011 Elsevier B.V. All rights reserved.
Tini Reinforced Magnesium Composites By Powder Metallurgy
(John Wiley and Sons LTD., 2011) Esen, Ziya
Rod shaped Mg-TiNi composite samples were manufactured bypowder metallurgical route in which the samples were heated and deformed simultaneously using rotary hot swaging technique. Firstly, encapsulated argon filled copper tubes which contained compacts of pure magnesium and pre-alloyed TiNi alloy powder mixtures were deformed about 45% in two steps at 450 degrees C. Pre/post annealing heat treatments were applied at 450 degrees C for 20 mins between the stages of coaxial deformation to enhance the sintering degree and to homogenize the heavily deformed composite structures. Next, copper peeled and machined samples were compression tested under quasi-static conditions to investigate the mechanical properties, i.e. yield and peak strength, and ductility. Transmission and Scanning Electron Microscopy studies were carried out to examine the Mg-TiNi interface and fracture surfaces of the compression tested composites, respectively.
Citation - WoS: 21
Citation - Scopus: 25
Effect of Electrical Discharge Machining on Dental Y-Tzp Ceramic-Resin Bonding
(Elsevier Ireland Ltd, 2017) Kucukturk, Gokhan; Gurun, Hakan; Cogun, Can; Esen, Ziya; Rona, Nergiz; Yenisey, Murat
Purpose: The study determined (i) the effects of electrical discharge machining (EDM) on the shear-bond strength (SBS) of the bond between luting resin and zirconia ceramic and (ii) zirconia ceramic's flexural strength with the three-point bending (TPB) test. Methods: Sixty 4.8 mm x 4.8 mm x 3.2 mm zirconia specimens were fabricated and divided into four groups (n = 15): SBG: sandblasted + silane, TSCG: tribochemical silica coated + silane, LTG: Er:YAG laser treated + silane, EDMG: EDM + silane. The specimens were then bonded to a composite block with a dual-cure resin cement and thermal cycled (6000 times) prior to SBS testing. The SBS tests were performed in a universal testing machine. The SBS values were statistically analyzed using ANOVA and Tukey's test. To determine flexural strength, sixty zirconia specimens were prepared and assigned to the same groups (n = 15) mentioned earlier. After surface treatment TPB tests were performed in a universal testing machine (ISO 6872). The flexural strength values were statistically analyzed using ANOVA and Tukey's test (a = 0.05). Results: The bond strengths for the four test groups (mean SD; MPa) were as follows: SBG (Control), 12.73 +/- 3.41, TSCG, 14.99 +/- 3.14, LTG, 7.93 +/- 2.07, EDMG, 17.05 +/- 2.71. The bond strength of the EDMG was significantly higher than those of the SBG and LTG (p < 0.01). The average flexural strength values for the groups SBG (Control), TSCG, LTG and EDMG were 809.47, 800.47, 679.19 and 695.71 MPa, respectively (p > 0.05). Conclusions: The EDM process improved the SBS. In addition, there was no significant adverse effect of EDM on the flexural strength of zirconia. (C) 2016 Japan Prosthodontic Society. Published by Elsevier Ltd. All rights reserved.
Citation - WoS: 64
Citation - Scopus: 64
Comparison of the Short and Long-Term Degradation Behaviors of As-Cast Pure Mg, Az91 and We43 Alloys
(Elsevier Science Sa, 2020) Esen, Ziya; Aydinol, Kadri; Dericioglu, Arcan F.; Ocal, Ezgi Butev
The corrosion behaviors of pure magnesium, AZ91, and WE43 alloys have been evaluated by weight loss, hydrogen evolution rate, pH change measurements and potentiodynamic polarization as well as electrochemical impedance spectroscopy (EIS) methods. Main corrosion product formed on the surface of Mg/Mg-alloys after immersion of 24 h was Mg(OH)(2) on the other hand, at the end of the 20 days additional CaCO3 which was found to display a critical role in degradation characteristics of the samples, was found. Examination in the cross section of the polished surfaces revealed that protective layers became thicker and corrosion rate of the samples decreased possibly due to increased protective abilities of the surfaces. Intermetallics in AZ91 and WE43 alloys acted as cathodic centers and induced micro galvanic corrosion. Undermining of intermetallics in WE43 alloy intensified the corrosion rate. AZ91 alloy exhibited the lowest corrosion rate among the samples when tested in simulated body fluid (SBF).