Malzeme Bilimi ve Mühendisliği Bölümü

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Citation - WoS: 34
Citation - Scopus: 43
Clinoptilolite/Pcl-peg-pcl Composite Scaffolds for Bone Tissue Engineering Applications
(Sage Publications Ltd, 2017) Pazarceviren, Engin; Erdemli, Ozge; Keskin, Dilek; Tezcaner, Aysen
The aim of this study was to prepare and characterize highly porous clinoptilolite/poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) composite scaffolds. Scaffolds with different clinoptilolite contents (10% and 20%) were fabricated with reproducible solvent-free powder compression/particulate leaching technique. The scaffolds had interconnective porosity in the range of 55-76%. Clinoptilolite/poly(epsilon-caprolactone)-poly(ethylene glycol)poly(epsilon-caprolactone) scaffolds showed negligible degradation within eight weeks and displayed less water uptake and higher bioactivity than poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) scaffolds. The presence of clinoptilolite improved the mechanical properties. Highest compressive strength (5.6 MPa) and modulus (114.84 MPa) were reached with scaffold group containing 20% clinoptilolite. In vitro protein adsorption capacity of the scaffolds was also higher for clinoptilolite/poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) scaffolds. These scaffolds had 0.95 mg protein/g scaffold adsorption capacity and also higher osteoinductivity in terms of enhanced ALP, OSP activities and intracellular calcium deposition. Stoichiometric apatite deposition (Ca/P = 1.686) was observed during cellular proliferation analysis with human fetal osteoblasts cells. Thus, it can be suggested that clinoptilolite/poly(epsilon-caprolactone)poly(ethylene glycol)-poly(epsilon-caprolactone) composite scaffolds could be promising carriers for enhancement of bone regeneration in bone tissue engineering applications.
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.
Citation - WoS: 25
Citation - Scopus: 27
Crystallization Kinetics and Phase Transformation Mechanisms in Cu56zr44 Glassy Alloy
(Springer, 2015) Kramer, Matthew J.; Napolitano, Ralph E.; Kalay, Ilkay
The kinetics and phase selection mechanisms involved in the crystallization of an amorphous Cu-Zr alloy of eutectic composition (Cu56Zr44) were investigated using in situ high-energy X-ray diffraction (HEXRD), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) under isothermal and constant heating rate conditions. In situ HEXRD results for 10 K/min (10 A degrees C/min) heating indicate that the amorphous alloy devitrifies into CuZr2 and mainly Cu10Zr7 at the crystallization temperature of 725 K (452 A degrees C). The sequence continues with the precipitation of CuZr (B2) at 1004 K (731 A degrees C), where these three phases coexist until the decomposition of CuZr2 is observed at 1030 K (757 A degrees C). The two equilibrium phases Cu10Zr7 and CuZr (B2) remain present on further heating until melting at the eutectic temperature for the Cu56Zr44 alloy. TEM investigation of the isothermal [705 K (432 A degrees C)] crystallization sequence reveals primary nucleation and growth of the Cu10Zr7 phase, where growth of the Cu10Zr7 crystals is initially planar with a transition to a cellular morphology, associated with partitioning of Zr at the growth front. Related cellular structures and composition profiles are quantified. (C) The Minerals, Metals & Materials Society and ASM International 2015
Citation - WoS: 31
Citation - Scopus: 30
Ionization Energies, Coulomb Explosion, Fragmentation, Geometric, and Electronic Structures of Multicharged Boron Clusters Bn (n=2-13)
(Amer Physical Soc, 2011) Tas, Murat; Ozdogan, Cem; Boustani, Ihsan; Akman, Nurten
Based on the ab initio quantum chemical methods, we have determined fragmentation channels, ionization energies, and the Coulomb explosion of multicharged boron clusters B-n (n = 2-13), where n is the cluster size. The electron-deficient boron clusters sustain more stability and hardly fragment when they are negatively charged. Stability of boron clusters decreases with increasing ionization. Only by the first ionization the odd-size clusters are more stable than the even-size clusters. Further ionizations cause the repulsive Coulomb force between the constituent atoms to get stronger, and lead first to metastable states, then to the Coulomb explosion of clusters. None of the cationic boron clusters studied remain stable after six times ionization. The critical charge for metastability is estimated as Q(m) <= n/2 for even-size clusters, and Q(m) <= 1/2 (n - 1) for odd-size clusters. In addition, the critical charge for the Coulomb explosion is found to be Q(c) = n/2 + 1 for even-size clusters, and Q(c) = 1/2(n + 1) for odd-size clusters. Relative stability of clusters with respect to their nearest neighbors is determined from the analysis of their second energy difference data. Several dissociation channels of B-n(+) and B-13(Q) isomers with the lowest fragmentation energies are presented. All of the vibrational frequencies are found positive indicating that no transition state is possible for the clusters studied. Reliability of our data is verified with a good agreement with experimental results.
Citation - WoS: 11
Citation - Scopus: 13
Nanocrystallization in Cu-Zr Bulk Metallic Glasses
(Springer, 2018) Yasar, Bengisu; Kalay, Ilkay; Sikan, Fatih
The effect of rare-earth element (Sm) microalloying on the thermal stability and crystallization kinetics of melt-spun ribbons and suction-cast rods of Zr48Cu38.4Al9.6Sm4 alloy were investigated using differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), and atom probe tomography (APT). The XRD results of constant heating rate annealing indicated that amorphous Zr48Cu38.4Al9.6Sm4 melt-spun ribbons devitrifies into Cu2Sm at 673 K (400 A degrees C). The sequence continues with the precipitation of Cu10Zr7 and then these two phases coexist. XRD and TEM studies on 1 mm diameter as suction-cast rods indicated the precipitation of 30-nm-mean size Cu2Sm crystals during solidification. TEM investigation of the isothermal crystallization sequence of melt-spun ribbons and 1-mm-diameter suction-cast rods revealed the precipitation of Cu2Sm nanocrystals at the onset of crystallization and the restriction of the growth of these nanocrystals up to 10 nm diameter with further annealing. APT analysis of 1-mm-diameter suction-cast rods showed that the limited growth of Cu2Sm nanocrystals is due to sluggish diffusion of Sm and Al-Zr pile up at the interface.
Kinetics and mechanisms of isothermal devitrification inamorphous cu50zr50
(Springer, 2015) Cullinan, Tim; Kalay, İlkay; Kalay, Y. Eren; Kramer, Matt; Napolitano, Ralph
The crystallization kinetics and microstructural dynamics associated with devitrifying a melt-spun Cu50Zr50 metallic glass were investigated using isothermal treatments, in situ high-energy synchrotron X-ray diffraction, conventional and high-resolution transmission electron microscopy, and differential scanning calorimetry. The analysis of isothermal transformations allows us to more clearly unravel the complex interplay between nucleation and growth of competing stable and metastable phases. The isothermal devitrification response was found to involve the Cu10Zr7, CuZr2, and CuZr phases, consistent with previously reported constant heating rate experiments, but here we have resolved the phase evolution and structural characteristics of the transformation, including the very early stages of crystallization. At 671 K (398 A degrees C), the isothermal transformation starts with the formation of the Cu10Zr7 phase, which grows in a generally equiaxed morphology. At a size of approximately 100 nm, the growth of the Cu10Zr7 particles is interrupted by the precipitation of a thin layer of the CuZr2 phase, upon which the metastable CuZr (B2) grows epitaxially. Crystallization kinetics are quantified here though in situ measurements (HEXRD, DSC) and ex situ microstructural analysis (TEM, HRTEM). Finally, the influences of chemical partitioning, diffusion, and crystallographic orientation on this sequence are examined.
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: 15
Citation - Scopus: 17
Characterization of Ti6al7nb Alloy Foams Surface Treated in Aqueous Naoh and Cacl2 Solutions
(Elsevier Science Bv, 2016) Esen, Ziya; Bor, Sakir; Butev, Ezgi
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 - WoS: 7
Citation - Scopus: 7
A Novel Approach for Synthesis of Monticellite Based Bioactive Ceramic Powders From Boron Derivative Waste
(Elsevier Science Bv, 2017) Butev, Ezgi; Esen, Ziya; Ayas, Erhan; Koroglu, Levent
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 - 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.
Citation - WoS: 23
Citation - Scopus: 24
Kinetics and Mechanisms of Isothermal Devitrification in Amorphous Cu50zr50
(Springer, 2015) Kalay, Ilkay; Kalay, Y. Eren; Kramer, Matt; Napolitano, Ralph; Cullinan, Tim
The crystallization kinetics and microstructural dynamics associated with devitrifying a melt-spun Cu50Zr50 metallic glass were investigated using isothermal treatments, in situ high-energy synchrotron X-ray diffraction, conventional and high-resolution transmission electron microscopy, and differential scanning calorimetry. The analysis of isothermal transformations allows us to more clearly unravel the complex interplay between nucleation and growth of competing stable and metastable phases. The isothermal devitrification response was found to involve the Cu10Zr7, CuZr2, and CuZr phases, consistent with previously reported constant heating rate experiments, but here we have resolved the phase evolution and structural characteristics of the transformation, including the very early stages of crystallization. At 671 K (398 A degrees C), the isothermal transformation starts with the formation of the Cu10Zr7 phase, which grows in a generally equiaxed morphology. At a size of approximately 100 nm, the growth of the Cu10Zr7 particles is interrupted by the precipitation of a thin layer of the CuZr2 phase, upon which the metastable CuZr (B2) grows epitaxially. Crystallization kinetics are quantified here though in situ measurements (HEXRD, DSC) and ex situ microstructural analysis (TEM, HRTEM). Finally, the influences of chemical partitioning, diffusion, and crystallographic orientation on this sequence are examined.
Citation - WoS: 3
Antibacterial Behavior of Oxynitride Glasses as a Glassy Grain Boundary Phase for Silicon Nitride-Based Ceramics
(Wiley Periodicals, inc, 2021) Kushan Akin, Seniz R.; Dolekcekic, Emrah; Webster, Thomas J.
Silicon nitride-based ceramics have provided significant advantages due to their high chemical resistance, high elastic modulus, and combination of hardness and fracture toughness (depending on self-reinforcement). Over the past two decades, a significant amount of interest has been generated for the bio-applications of these materials. However, the effect of the grain boundary phase on such applications is still not very well understood. In this study, the effect of different cations on biological (such as antibacterial and cytocompatibilty) and material properties (like wetting angles and isoelectric points [IEP]) of oxynitride glasses, mimicking the grain boundary phase in Si3N4 and SiAlON ceramics, were investigated. Results revealed that the antibacterial behavior and mammalian cell viability were inversely correlated in glasses with rare-earth cation additions. Ca was the best cation when the two properties (bacterial response and cell proliferation) were considered together, and, thus should be further studied for a wide range of applications.
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.

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