Malzeme Bilimi ve Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/396

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Citation Count: Karataş, Mustafa Serdar...et al. "A Comparison of Radiation Shielding of Stainless Steel With Different Magnetic Properties", Nuclear Technology and Radiation Protection, Vol. 29, No. 3, pp. 186-189, (2014).
A Comparison of Radiation Shielding of Stainless Steel With Different Magnetic Properties
(Vinca Inst Nuclear Sci, 2014) Çalık, Adnan; Akbunar, Şahin; Uçar, Nazim; Yılmaz, Nihat; Karakaş, Mustafa Serdar; Akkurt, İskender; 48915
The radiation shielding properties of three different stainless steels have been investigated. For this purpose, linear attenuation coefficients at photon energy levels of 662 keV and 1250 keV have been mea sured. The obtained results showed that ferritic stainless steel was more capable in stopping the high energy photons than its non-magnetic counterpart. © 2014 Vinca Inst Nuclear Sci. All rights reserved.
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: 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.
Citation Count: Akman, N...et al. (2011). Ionization energies, Coulomb explosion, fragmentation, geometric, and electronic structures of multicharged boron clusters B-n (n=2-13). Physical Review B , 84(7). http://dx.doi.org/10.1103/PhysRevB.84.075463
Ionization energies, Coulomb explosion, fragmentation, geometric, and electronic structures of multicharged boron clusters B-n (n=2-13)
(Amer Physical Soc, 2011) Akman, Nurten; Taş, Murat; Özdoğan, Cem; Boustani, Ihsan; 27617
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 Count: Kuntsmann, J...et al. (2011). Stability of edge states and edge magnetism in graphene nanoribbons. Physical Review B, 83(4). http://dx.doi.org/10.1103/PhysRevB.83.045414
Stability of edge states and edge magnetism in graphene nanoribbons
(Amer Physical Soc, 2011) Kuntsmann, Jens; Özdoğan, Cem; Quandt, Alexander; Fehske, Holger
We critically discuss the stability of edge states and edge magnetism in zigzag edge graphene nanoribbons (ZGNRs). We point out that magnetic edge states might not exist in real systems and show that there are at least three very natural mechanisms-edge reconstruction, edge passivation, and edge closure-which dramatically reduce the effect of edge states in ZGNRs or even totally eliminate them. Even if systems with magnetic edge states could be made, the intrinsic magnetism would not be stable at room temperature. Charge doping and the presence of edge defects further destabilize the intrinsic magnetism of such systems
Citation Count: Esen, Ziya, "TiNi Reinforced Magnesium Composites by Powder Metallurgy", Magnesium Technology 2011, pp. 457-462, (2011)
Tini Reinforced Magnesium Composites By Powder Metallurgy
(John Wiley and Sons LTD., 2011) Esen, Ziya; 52373
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.

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Browsing Malzeme Bilimi ve Mühendisliği Bölümü Yayın Koleksiyonu by Department "Çankaya Üniversitesi, Mühendislik Fakültesi, Malzeme Birimi ve Mühendisliği Bölümü"