Malzeme Bilimi ve Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/396
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Article Citation - WoS: 41Citation - Scopus: 44Effect of Post Fabrication Aging Treatment on the Microstructure, Crystallographic Texture and Elevated Temperature Mechanical Properties of In718 Alloy Fabricated by Selective Laser Melting(Elsevier Science Sa, 2022) Bilgin, Guney Mert; Davut, Kemal; Esen, Ziya; Dericioglu, Arcan F.; Ozer, SerenThe 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 dis-appeared and converted into a mixture of columnar and equiaxed grains. Nano-sized gamma '' and/or gamma' 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 degrees C for 8 h) tested at 600 degrees 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 degrees C, which was attributed to intermediate temperature embrittlement.Article Citation - Scopus: 185Nanoscale Structure and Structural Relaxation in Zr 50cu 45al 5 Bulk Metallic Glass(2012) Melgarejo, Z.H.; Kalay, Y.E.; Kalay, I.; Kramer, M.J.; Stone, D.S.; Voyles, P.M.; Hwang, J.Hybrid reverse Monte Carlo simulations of the structure of Zr 50Cu 45Al 5 bulk metallic glass incorporating medium-range structure from fluctuation electron microscopy data and short-range structure from an embedded atom potential produce structures with significant fractions of icosahedral- and crystal-like atomic clusters. Similar clusters group together into nanometer-scale regions, and relaxation transforms crystal-like clusters into icosahedral clusters. A model refined against only the potential does not agree with the fluctuation microscopy data and contains few crystal-like clusters. © 2012 American Physical Society.Article Citation - WoS: 25Citation - Scopus: 27Microstructural 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 NurThe 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.Article Citation - WoS: 5Citation - Scopus: 5Effect of Nitrogen on the Antibacterial Behavior of Oxynitride Glasses(Elsevier Sci Ltd, 2021) Akin, Seniz R. Kushan; Dolekcekic, Emrah; Webster, Thomas J.; Kushan Akin, Seniz R.The main drawback of bioglasses is their restricted use in load bearing applications and the consequent need to develop stronger glassy materials. This has led to the consideration of oxynitride glasses for numerous biomedical applications. This paper investigated two different types of glasses at a constant cationic ratio, with and without nitrogen (a N containing and a N-free glass composition) to better understand the effect of N on the biological properties of glasses. The results revealed that the addition of N increased the glass transition temperature, isoelectric point (IEP) and slightly increased wettability. Moreover, compared to N including glass, N-free glass exhibited better anti-bacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), two key bacteria that infect implants. In summary, these in vitro results indicated that amine functional groups existing in N containing glasses which are missing in N-free glasses, caused a slight difference in wetting behavior and a more obvious change in isoelectric point and in bacterial response. N-free glasses exhibited better inhibitory results both against E. coli and S. aureus compared to N including glass suggesting that oxygen rich glasses should be further studied for their novel antibacterial properties.Article Citation - WoS: 7Citation - Scopus: 7Investigation of Phase Selection Hierarchy in Mn-Al Alloys(Elsevier Sci Ltd, 2019) Acar, Ozgun; Turan, Servet; Kalay, Ilkay; Savaci, Umut; Kalay, Yunus Eren; Genc, Ayse MervePrimarily attributed to the formation of the ferromagnetic tau-phase, near equiatomic composition of Mn-Al have recently received much attention in permanent magnet industry. Several mechanisms have been proposed in literature for the tau-phase formation but controversy still arises regarding the dominating mode. In the current work, MnAl-based alloys having different compositions in a range between Mn50.5Al49.5 and Mn57Al43 have been studied by means of in-situ high energy X-ray diffraction, differential scanning calorimetry (DSC) and magnetic measurements. Synchrotron and DSC experiments showed the dependence of the tau-MnAl on the intermediate disordered epsilon'-phase. Alloys having 53.4 at% or less Mn (S1, S2) followed a transformation route of epsilon+epsilon'-> tau ->beta+gamma(2) upon annealing. Alloys having more than 53.4 at% of Mn had only epsilon-phase. High energy X-ray diffraction patterns showed that epsilon-phase directly transformed into stable phases in the absence of epsilon'-phase. It is observed that epsilon' not only promoted the ferromagnetic tau-phase but also stabilized it by delaying the nucleation of stable phases.Article Citation - WoS: 32Citation - Scopus: 33Effect of Cnt Impregnation on the Mechanical and Thermal Properties of C/C-sic Composites(Springernature, 2020) Esen, Ziya; Dericioglu, Arcan F.; Tulbez, SimgeThe 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 abstractArticle Citation - WoS: 62Citation - Scopus: 69Titanium-Magnesium Based Composites: Mechanical Properties and In-Vitro Corrosion Response in Ringer's Solution(Elsevier Science Sa, 2013) Esen, Ziya; Dikici, Burak; Duygulu, Ozgur; Dericioglu, Arcan F.Ti-Mg composite rods exhibiting both bioinert and biodegradable characteristics have been manufactured by hot rotary swaging from elemental powders of titanium and magnesium. As a result of processing, spherical magnesium powders elongated in the direction of deformation and the dendritic structure in starting magnesium powders transformed into highly equiaxed grains. Magnesium particles in the outer layer of the composites were decorated by thin layer of MgO while the interior parts were free from oxides. As expected, Young's moduli, yield and peak strengths of the composites were observed to decrease with an increase in the magnesium content, while ductility of composites was enhanced by decreasing the amount of titanium. Composites fractured at an angle 45 to the loading axis along the titanium particle boundaries and through the magnesium particles via transgranular type of fracture with the accumulation of twins near the fracture surface of magnesium. Mechanical properties of the composites were observed to be comparable to that of bone and the composites exhibited biodegradable and bioinert character upon testing in Ringer's solution such that magnesium was selectively corroded and pores were formed at prior magnesium powder sites while titanium preserved its starting skeleton structure. In addition, it was found that volume ratio of titanium and magnesium, and continuous MgO layer are the most important parameters which should be considered in designing biodegradable magnesium alloys with an appropriate corrosion rate. (C) 2013 Elsevier B.V. All rights reserved.Article Citation - WoS: 44Citation - Scopus: 44Corrosion 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; Öcal, Ezgi BütevThe 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.Article Citation - WoS: 66Citation - Scopus: 66Comparison 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; Bütev Öcal, EzgiThe 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).Article Citation - WoS: 23Citation - Scopus: 26In Vitro Bioactivity Investigation of Alkali Treated Ti6al7nb Alloy Foams(Elsevier, 2015) Esen, Ziya; Bor, Sakir; Butev, EzgiBiocompatible 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.