Browsing by Author "Esen, Ziya"

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Citation Count: Saltık, S.; Esen Ziya; Dericioğlu, Arcan F. (2023). "A Comparative Study of Effects of Additive Particle Size and Content on Wetting Behavior and Brazing Performance of C/SiC Composite". Journal Of Materıals Engineering And Performance, Vol. 32, No. 13, pp. 5946-5955.
A Comparative Study of Effects of Additive Particle Size and Content on Wetting Behavior and Brazing Performance of C/SiC Composite
(2023) Saltık, Simge; Esen, Ziya; Dericioğlu, Arcan F.; 52373
This study has focused on the influence of size and content of SiC particle incorporation on the wetting behavior of the Ticusil brazing filler alloy and on its brazing performance in C/SiC composite/Ti6Al4V alloy joints. The effect of the size and content of additive SiC particles on the variation of molten brazing filler alloy contact angle was recorded at various brazing time and temperatures. Moreover, the microstructural evolution and mechanical properties of the additive containing C/SiC composite/Ti6Al4V alloy joints produced by the brazing method were investigated. The contact angles in both brazing filler alloys containing nano- and micro-sized SiC particles exhibited a sudden decrease with time during isothermal holding as observed in as-received brazing filler alloys. As the quantity of the SiC particles increased in the brazing alloy, the recorded contact angle values including the final, stable contact angle increased, while the time for the drastic contact angle change also increased remarkably. Compared to as-received counterparts, the addition of 2 wt.% nano-sized SiC and 1 wt.% micro-sized SiC particles improved the shear strength of the joints by 35 and 8%, respectively. Although the recorded contact angle values were close to each other in brazing alloys containing SiC particles with different sizes (37 and 42 degrees for 1 wt.% micro-sized and 2 wt.% nano-sized additions), higher increment was achieved in the mechanical performance of the joints with nano-sized SiC additive due to more homogeneous reinforcement effect of the nanoparticles. The results indicated that the optimum brazing filler alloy contact angle for the highest shear strength is similar to 40 degrees for both nano- and micron-sized additive containing Ticusil filler alloy.
Citation Count: Esen, Ziya; Butev, Ezgi; Karakas, M. Serdar, "A comparative study on biodegradation and mechanical properties of pressureless infiltrated Ti/Ti6Al4V-Mg composites", Journal of the Mechanical Behavior of Biomedical Materials, Vol. 63, pp. 273-283,(2016).
A comparative study on biodegradation and mechanical properties of pressureless infiltrated Ti/Ti6Al4V-Mg composites
(Elsevier Science BV, 2016) Esen, Ziya; Bütev, Ezgi; Karakaş, Mustafa Serdar; 52373; 47423
The mechanical response and biodegradation behavior of pressureless Mg-infiltrated Ti-Mg and Ti6Al4V-Mg composites were investigated by compression and simulated body fluid immersion tests, respectively. Prior porous preforms were surrounded uniformly with magnesium as a result of infiltration and the resultant composites were free of secondary phases and intermetallics. Although the composites' compressive strengths were superior compared to bone, both displayed elastic moduli similar to that of cortical bone and had higher ductility with respect to their starting porous forms. However, Ti-Mg composites were unable to preserve their mechanical stabilities during in-vitro tests such that they fractured in multiple locations within 15 days of immersion. The pressure generated by H-2 due to rapid corrosion of magnesium caused failure of the Ti-Mg composites through sintering necks. On the other hand, the galvanic effect seen in Ti6Al4V-Mg was less severe compared to that of Ti-Mg. The degradation rate of magnesium in Ti6Al4V-Mg was slower, and the composites were observed to be mechanically stable and preserved their integrities over the entire 25-day immersion test. Both composites showed bioinert and biodegradable characteristics during immersion tests and magnesium preferentially corroded leaving porosity behind while Ti/Ti6Al4V remained as a permanent scaffold. The porosity created by degradation of magnesium was refilled by new globular agglomerates. Mg(OH)(2) and CaHPO4 phases were encountered during immersion tests while MgCl2 was detected during only the first 5 days. Both composites were classified as bioactive since the precipitation of CaHPO4 phase is known to be precursor of hydroxyapatite formation, an essential requirement for an artificial material to bond to living bone. (C) 2016 Elsevier Ltd. All rights reserved.
A novel approach for synthesis of monticellite based bioactive ceramic powders from boron derivative waste
(Elsevier Science BV, 2017) Köroğlu, Levent; Bütev, Ezgi; Esen, Ziya; Ayaş, Erhan; 47423
Monticellite bioactive ceramics have a high usage potential as bone graft substitutes due to their superior mechanical properties compared to hydroxyapatite and excellent bioactivity. Turkey has almost 72% of the global boron reserves and the fairly high amount of emerged boron derivative waste causes storage problems and environmental pollutions. The aim of this study was the solid state synthesis of monticellite based ceramic powders from boron derivative waste and the evaluation of bioactivity characteristic of produced powders. The monticellite based ceramic powders were synthesized at low temperature (800 degrees C). The powders were incubated in Simulated Body Fluid and their surfaces were examined using a scanning electron microscope. The surfaces of synthesized powders were bioactive and allowed formation of bone-like apatite layer within 15 days. Results of the study confirmed that cost-effective and ecofriendly monticellite based bioactive ceramic powders can be synthesized from boron derivative waste. (C) 2017 Elsevier B.V. All rights reserved.
Citation Count: Esen, Ziya; Tarhan Bor, Elif; Bor, Şakir (2009). "Characterization of loose powder sintered porous titanium and TI6Al4V alloy", Turkish Journal of Engineering and Environmental Sciences, Vol. 33, No. 3, pp. 207-219.
Characterization of loose powder sintered porous titanium and TI6Al4V alloy
(2009) Esen, Ziya; Tarhan Bor, Elif; Bor, Şakir; 52373
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 Count: Esen, Z., Bor, Ş. (2011). Characterization of Ti-6Al-4V alloy foams synthesized by space holder technique. Materials science and engineering a-structural materials properties microstructure and processing, 528(7-8), 3200-3209. http://dx.doi.org/10.1016/j.msea.2011.01.008
Characterization of Ti-6Al-4V alloy foams synthesized by space holder technique
(Elsevier Science S A, 2011) Esen, Ziya; Bor, Şakir; 52373
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
Citation Count: Butev, Ezgi; Esen, Ziya; Bor, Sakir, "Characterization of Ti6Al7Nb alloy foams surface treated in aqueous NaOH and CaCl2 solutions", Journal of the Mechanical Behavior of Biomedical Materials, Vol. 60, pp. 127-138, (2016).
Characterization of Ti6Al7Nb alloy foams surface treated in aqueous NaOH and CaCl2 solutions
(Elsevier Science BV, 2016) Bütev, Ezgi; Esen, Ziya; Bor, Şakir; 47423; 52373
Ti6Al7Nb alloy foams having 53-73% porosity were manufactured via evaporation of magnesium space holders. A bioactive 1 mu m thick sodium hydrogel titanate layer, NaxH2-xTiyO2y+1., formed after 5 M NaOH treatment, was converted to crystalline sodium titanate, Na2TiyO2y+1, as a result of post-heat treatment. On the other hand, subsequent CaCl2 treatment of NaOH treated specimens induced calcium titanate formation. However, heat treatment of NaOH-CaCl2 treated specimens led to the loss of calcium and disappearance of the titanate phase. All of the aforementioned surface treatments reduced yield strengths due to the oxidation of the cell walls of the foams, while elastic moduli remained mostly unchanged. Accordingly, equiaxed dimples seen on the fracture surfaces of as-manufactured foams turned into relatively flat and featureless fracture surfaces after surface treatments. On the other hand, Ca- and Na-rich coating preserved their mechanical stabilities and did not spall during fracture. The relation between mechanical properties of foams and macro-porosity fraction were found to obey a power law. The foams with 63 and 73% porosity met the desired biocompatibility requirements with fully open pore structures and elastic moduli similar to that of bone. In vitro tests conducted in simulated body fluid (SBF) showed that NaOH-heat treated surfaces exhibit the highest bioactivity and allow the formation of Ca-P rich phases having Ca/P ratio of 1.3 to form within 5 days. Although Ca-P rich phases formed only after 15 days on NaOH-CaCl2 treated specimens, the Ca/P ratio was closer to that of apatite found in bone. (C) 2016 Elsevier Ltd. All rights reserved.
Citation Count: Bütev Öcal, Ezgi...et al."Comparison of the Short and Long-Term Degradation Behaviors of As-Cast Pure Mg, Az91 and We43 Alloys",Materials Chemistry and Physics, Vol. 241, (2020).
Comparison of the Short and Long-Term Degradation Behaviors of As-Cast Pure Mg, Az91 and We43 Alloys
(Elsevier LTD., 2020) Bütev Öcal, Ezgi; Esen, Ziya; Aydınol, Kadri; Dericioğlu, Arcan F.; 52373
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).
Citation Count: Esen, Z...et al. "Corrosion Behaviours of Ti6Al4V-Mg/Mg-Alloy Composites", Corrosion Science, Vol. 166, (2020).
Corrosion Behaviours of Ti6Al4V-Mg/Mg-Alloy Composites
(Elsevier LTD., 2020) Esen, Ziya; Öcal, Ezgi Bütev; Akkaya, Aslı; Gürçay, Bensu; Özcan, Ceren; Özgümüş, Burcu Aslı; Duygulu, Özgür; Dericioğlu, Arcan F.; 52373
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.
Corrosion of Metallic Biomaterials
(Springer Verlag, 2015) Dikici, Burak; Esen, Ziya; Duygulu, Özgür; Güngör, Serap; 52373
Metallic materials have been used as biomedical implants for various parts of the human body for many decades. The physiological environment (body fluid) is considered to be extremely corrosive to metallic surfaces; and corrosion is one of the major problems to the widespread use of the metals in the human body since the corrosion products can cause infections, local pain, swelling, and loosening of the implants. Recently, the most common corrosion-resistant metallic biomaterials are made of stainless steels and titanium and its alloys along with cobalt chromium molybdenum alloys. It is well known that protective surface films of the alloys play a key role in corrosion of the metallic implants. Key documents on the corrosion behavior of the metallic biomaterials in human body have been compiled under this chapter as a review.
Citation Count: Esen, Ziya...et al. "Designing thermochemical processes for ti-alloys produced by additive manufacturing techniques", 4th INTERNATIONAL CONGRESS ON 3D PRINTING (ADDITIVE MANUFACTURING) TECHNOLOGIES AND DIGITAL INDUSTRY, pp. 1383-1387, 2019.
Designing thermochemical processes for ti-alloys produced by additive manufacturing techniques
(2019) Esen, Ziya; Doğu, Merve Nur; Bilgin, Güney Mert; Tan, Evren; Berkay Gümüş, Berkay; Dericioğlu, Arcan F.; 52373
Ti-6Al-4V alloys are extensively used in biomedical, aerospace and petro-chemical applications mainly due to their high specific strength, excellent corrosion resistance and high fatigue strength. In contrast to conventional techniques, additive manufacturing techniques make possible production of parts with complex geometries in one step by minimizing the usage of raw materials. However, post heat treatment processes need to be applied to reduce residual stresses created and to get uniform controllable microstructure so as to obtain desired mechanical properties. Conventional annealing heat treatments are effective in eliminating the residual stress and increasing the ductility. But, they usually degrade the strength and result in coarsening the microstructure. In this study, thermochemical process, called thermo-hydrogen process (THP), was applied to Ti-6Al-4V alloy parts produced by selective laser melting (SLM) and electron beam melting (EBM) with the aim of increasing ductility without degrading the alloy strength. Additively manufactured parts initially hydrogenated at 650oC for 1 h under H2+Ar gas mixture and then, dehyrogenated at 700oC for 18 h under high vacuum. As a result of alloying with hydrogen and dealloying turned martensitic microstructure in SLM parts into fine + lamellar phase mixture. On the other hand, microstructural refinement in EBM parts were limited since as-manufactured parts were already composed of fine lamellar microstructure. THP prevented grain growth and grain boundary α-phase formation in SLM parts. Ductility of the alloys increased by 110 %, while the strength decreased slightly only by 10 %. However, the effect of the THP on mechanical properties of EBM samples couldn’t be observed due to their high surface roughness which induced notch effect.
Citation Count: Bütev Öcal, Ezgi...et al. "Effect of alkali treatment parameters on surface structure and mechanical properties of porous Ti6A17NB scaffolds", IMMC 2014, Istanbul, TURKEY.
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; 52373
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 Count: Tülbez, Simge; Esen, Ziya; Dericioğlu, Arcan F. (2020). "Effect of CNT impregnation on the mechanical and thermal properties of C/C-SiC composites", Advanced Composites and Hybrid Materials, Vol. 3, No. 2, pp. 177-186.
Effect of CNT impregnation on the mechanical and thermal properties of C/C-SiC composites
(2020) Tülbez, Simge; Esen, Ziya; Dericioğlu, Arcan F.; 52373
The present study investigates the effect of additional carbon source, in the form of carbon nanotubes (CNTs), on mechanical and thermal properties of carbon fiber reinforced silicon carbide (C/C-SiC) ceramic matrix composites (CMC) produced by liquid silicon infiltration (LSI) technique. The CNTs used in this study were impregnated into the C/C preforms before the liquid silicon infiltration stage. The results showed that the addition of excess carbon to the C/C preforms in the form of CNTs enhanced Si infiltration efficiency significantly resulting in C/C-SiC composites with higher density and microstructural uniformity. Accordingly, the addition of CNTs improved the flexural strength of the composites by 40% with respect to no-CNT-containing composites due to a lower amount of residual porosity and additional reinforcement effect of the unreacted CNTs. The thermal conductivity of the resulting C/C-SiC composites has been also increased by 31% and 18% parallel and perpendicular to the carbon fiber-woven fabric surface, respectively, by CNT addition.Graphical abstract
Citation Count: Rona, Nergiz...et.al. (2017). "Effect of electrical discharge machining on dental Y-TZP ceramic-resin bonding", Journal Of Prosthodontic Research, Vol.61, No.2, pp.158-167.
Effect of electrical discharge machining on dental Y-TZP ceramic-resin bonding
(Elsevier Ireland LTD, 2017) Rona, Nergiz; Yenisey, Murat; Küçüktürk, Gökhan; Gürün, Hakan; Çoğun, Can; Esen, Ziya; 3837; 52373
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.
Citation Count: Ozer, Seren;...et.al. (2022). "Effect of post fabrication aging treatment on the microstructure, crystallographic texture and elevated temperature mechanical properties of IN718 alloy fabricated by selective laser melting", Journal of Materials Processing Technology, Vol.306.
Effect of post fabrication aging treatment on the microstructure, crystallographic texture and elevated temperature mechanical properties of IN718 alloy fabricated by selective laser melting
(2022) Ozer, Seren; Bilgin, Güney Mert; Davut, Kemal; Esen, Ziya; Dericioglu, Arcan F.; 52373
The 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.
Citation Count: Cogun, Can; Esen, Ziya; Genc, Asim; et al. "Effect of powder metallurgy Cu-B4C electrodes on workpiece surface characteristics and machining performance of electric discharge machining", Proceedings of the Institution of Mechanical Engineers Part B-Journal of Engineering Manufacture, Vol. 230, No. 12, pp. 2190-2203, (2016).
Effect of powder metallurgy Cu-B4C electrodes on workpiece surface characteristics and machining performance of electric discharge machining
(Sage Publications LTD, 2016) Çoğun, Can; Esen, Ziya; Çoğun, Ferah; 3837; 52373
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 Count: Atabay, Sila Ece; Esen, Ziya; Dericioğlu, Arcan F., "Effect of sn alloying on the diffusion bonding behavior of al-mg-si alloys", Metallurgical And Materials Transactions A-Physical Metallurgy And Materials Science, Vol.48A, No.7, pp.3181-3187, (2017).
Effect of sn alloying on the diffusion bonding behavior of al-mg-si alloys
(Springer, 2017) Atabay, Sıla Ece; Esen, Ziya; Dericioğlu, Arcan F.; 52373
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.
Citation Count: Şimşek, Ülke; Çoğun, Can; Esen, Z. (2022). "Effects of electrolytic copper and copper alloy electrodes on machining performance in electrical discharge machining (EDM)", Machining Science and Technology, Vol.26, No.2, pp.229-244.
Effects of electrolytic copper and copper alloy electrodes on machining performance in electrical discharge machining (EDM)
(2022) Şimşek, Ülke; Çoğun, Can; Esen, Ziya; 52373; 3837
The most important cost element of electric discharge machining (EDM) is the production of tool electrode (shortly electrode). In the EDM process, copper and its alloys are often used as electrode materials. The machining with EDM without increasing the costs can be achieved by selecting the proper electrode with low production and material costs as well as high workpiece material removal rate (MRR), low electrode wear rate (EWR), and relative wear (RW ¼ MRR/EWR). In this study, the EDM performance outputs, namely, MRR and RW were experimentally investigated for electrolytic copper, CuCr1Zr (with and without aging treatment) and CuCo2Be alloy electrode materials for varying machining parameters. The performance outputs were affected by the electrode material and the applied aging treatment. The aged CuCr1Zr alloy electrodes had higher electrical conductivity and better machining performance than the as-received alloy. The CuCo2Be alloy electrodes exhibited moderate to high MRR; however, their RW was the highest. Although the electrolytic copper has moderate MRR performance compared to the investigated alloys, its low cost increased its performance index, making it a more suitable electrode material for EDM applications.
Citation Count: Ürtekin, Levent...et al. (2021). "Experimental Investigation on Wire Electric Discharge Machining of Biodegradable AZ91 Mg Alloy", Journal of Materials Engineering and Performance, Vol. 30, No. 10, pp. 7752-7761.
Experimental Investigation on Wire Electric Discharge Machining of Biodegradable AZ91 Mg Alloy
(2021) Ürtekin, Levent; Özerkan, Hacı Bekir; Çoğun, Can; Genç, Asım; Esen, Ziya; Bozkurt, Fatih; 3837; 52373
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 (Ra), and surface topography) were found for the varying process parameters [pulse time (ts), pulse-off time (toff), dielectric flushing pressure (Pd), and wire speed (Vw)]. 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. © 2021, ASM International.
Citation Count: Cetinel, Oktay; Esen, Ziya; Yildirim, Bora, "Fabrication, Morphology Analysis, and Mechanical Properties of Ti Foams Manufactured Using the Space Holder Method for Bone Substitute Materials", Metals, Vol. 9, No. 3, (March 2019)
Fabrication, Morphology Analysis, and Mechanical Properties of Ti Foams Manufactured Using the Space Holder Method for Bone Substitute Materials
(MDPI, 2019) Çetinel, Oktay; Esen, Ziya; Yıldırım, Bora; 52373
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 Count: Butev, Ezgi; Esen, Ziya; Bor, Sakir, "In Vitro Bioactivity Investigation of Alkali Treated Ti6al7nb Alloy Foams", Applied Surface Science, 327, pp. 437-443, (2015).
In Vitro Bioactivity Investigation of Alkali Treated Ti6al7nb Alloy Foams
(Elsevier, 2015) Bütev, Ezgi; Esen, Ziya; Bor, Şakir; 47423
Biocompatible Ti6Al7Nb alloy foams with 70% porosity manufactured by space holder method were activated via alkali treatment using 5 M NaOH solution at 60 degrees C. The interconnected pore structures enabled formation of homogenous sodium rich coating on the foam surfaces by allowing penetration of alkali solution throughout the pores which had average size of 200 mu m. The resulted coating layer having 500 nm thickness exhibited porous network morphology with 100 nm pore size. On the other hand, heat treatment conducted subsequent to alkali treatment at 600 degrees C in air transformed sodium rich coating into crystalline bioactive sodium titanate phases. Although the coatings obtained by additional heat treatment were mechanically stable and preserved their morphology, oxidation of the samples deteriorated the compressive strength significantly without affecting the elastic modulus. However, heat treated samples revealed better hydroxyapatite formation when soaked in simulated body fluid (SBF) compared to alkali treated foams. On the other hand, untreated surfaces containing bioactive TiO2 layer were observed to comprise of Ca and P rich precipitates only rather than hydroxyapatite within 15 days. The apatite formed on the treated porous surfaces was observed to have flower-like structure with Ca/P ratio around 1.5 close to that of natural bone. (C) 2014 Elsevier B.V. All rights reserved.