Materials Science and Engineering / Malzeme Bilimi ve Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4719
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Article Citation - WoS: 5Citation - Scopus: 6Formation of Monolithic Srtio3-Tio2 Ceramic Heterostructures by Reactive Hydrothermal Sintering(Elsevier, 2023) Karacasulu, Levent; Kartal, Uğur; İçin, Öykü; Bortolotti, Mauro; Biesuz, Mattia; Ahmetoğlu, Çekdar VakıfIn a one-pot approach, monolithic SrTiO3-TiO2 ceramic heterostructures were obtained using the reactive hydrothermal liquid phase densification (rHLPD). Structural, morphological, and photocatalytic properties of the obtained ceramics were analyzed. The relative density of the formed components reached about 80% with reaction time, temperature, and NaOH concentration variation. It was observed via Rietveld refinement that there was no XRD detectable phase other than TiO2 and SrTiO3 in the final structure. The monolithic SrTiO3-TiO2 ceramics obtained by hydrothermal reaction at 120 °C for 24 h in 1 M NaOH concentration showed a dielectric constant being around 500, and the dielectric loss was below 0.25 at frequencies higher than 10 kHz. The SrTiO3-TiO2 heterostructured monoliths having only 20 vol% total porosity and low specific surface area, demonstrated ∼60% efficiency (in 5 h) in degrading Methylene Blue photo-catalytically. © 2023 Elsevier LtdArticle Citation - WoS: 14Citation - Scopus: 20Influence of Al2o3 Reinforcements and Ti-Al Intermetallics on Corrosion and Tribocorrosion Behavior of Titanium(Elsevier, 2023) Sousa, Luis; Antunes, Rui D. M.; Fernandes, Joao C. S.; Alves, Alexandra Cruz; Toptan, FatihTi-Al2O3 composites have demonstrated favorable characteristics for use in load-bearing biomedical implant applications; however, the influence of Al2O3 reinforcement particles and Ti-Al intermetallics on the electrochemical and tribo-electrochemical responses of Ti are not well-understood. This study explored the corrosion and tribocorrosion characteristics of powder metallurgy-manufactured Ti-Al2O3 composites in a simple physiological saline solution at body temperature. Electrochemical analysis was performed by electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization and tribo-electrochemical mechanisms were explored under open circuit potential (OCP) against a 10 mm diameter alumina ball in a ball-on-plate tribometer with reciprocating configuration. Results revealed that the corrosion behavior of Ti was adversely affected by the development of a heterogeneous oxide film on the Ti matrix and the Ti-Al intermetallic phases formed by the interaction of Ti and Al2O3 particles. However, there was a drastic improvement in tribocorrosion behavior, evidenced by decreased corrosion tendency under sliding and a marked reduction in wear volume, primarily as a result of the decreased wear damage resulting from the load-bearing reinforcements.Article Citation - WoS: 8Citation - Scopus: 8Crystallization and Additional Oxide Interlayers Improve the Tribocorrosion Resistance of Tio2 Nanotubular Surfaces Formed on Ti6al4v(Elsevier, 2023) Çaha, İhsan; Türü, İrem Cemre; Erdoğan, Ece; Pinto, Ana Maria Pires; Cansever, Nurhan; Deepak, Francis Leonard; Toptan, Fatih; Alves, Alexandra C.TiO2-based nanotubular surfaces have promising properties for various industrial applications, such as solar cells, fuel cells, photocatalysis, energy storage, gas sensors, and biomedical applications. However, they have very limited use in real applications, and one of the major limiting factors is the weak adhesion of nanotubular surfaces to the substrate. In this study, nanotubular surfaces are formed on Ti6Al4V alloy by anodic treatment followed by a heat treatment at 500 °C for 3 h under an open atmosphere. Microstructural investigations revealed self-organized nanotubes grown on both ? and ? phases. High-resolution TEM/STEM analysis showed crystallization of the nanotubular layer and formation of additional oxide interlayers resulting in a drastic improvement in tribocorrosion resistance. These findings indicated that a simple heat treatment can significantly alter the properties of nanotubular layers and can widen their usage mainly for load-bearing implant applications in corrosive environments. © 2023 Elsevier B.V.Article Citation - WoS: 22Citation - Scopus: 25Effect of Solution Heat Treatment on the Microstructure and Crystallographic Texture of In939 Fabricated by Powder Bed Fusion-Laser Beam(Elsevier, 2023) Doğu, Merve Nur; Özer, Seren; Yalçın, Mustafa Alp; Davut, Kemal; Bilgin, Guney Mert; Obeidi, Muhannad Ahmed; Brodin, Hakan; Gu, Hengfeng; Brabazon, DermotThe effect of various solution heat treatment temperatures (i.e., 1120, 1160, 1200 and 1240 & DEG;C) on the microstructure, grain morphology and crystallographic texture of IN939 fabricated by powder bed fusion-laser beam (PBF-LB) was investigated. Microstructural analyses showed that the high-temperature gradient and rapid solidification of the PBF-LB processing caused different resulting microstructures compared to conventionally pro-duced counterparts. The melt pool morphologies and laser scanning paths were examined in the as-fabricated samples in the XZ-and XY-planes, respectively. After the application of solution heat treatment at 1120 & DEG;C, the as-fabricated PBF-LB initial microstructure was still apparent. For solution heat treatments of 1200 & DEG;C and above, the melt pool and scanning path morphologies disappeared and converted into a mixture of columnar grains in the XZ-plane and equiaxed grains in the XY-plane. On the other hand, large equiaxed grains were observed when the samples were solutionized at 1240 & DEG;C. Additionally, g' phase precipitated within the matrix after all solution heat treatment conditions, which led to increase in the microhardness values. According to electron backscatter diffraction (EBSD) analyses, both as-fabricated and solution heat-treated samples had intense texture with {001} plane normal parallel to the building direction. The first recrystallized grains began to appear when the samples were subjected to the solution heat treatment at 1160 & DEG;C and the fraction of the recrystallized grains increased with increasing temperature, as supported by kernel average misorientation (KAM) and grain spread orientation (GOS) analyses.& COPY; 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Article Citation - WoS: 29Citation - Scopus: 31Effect of Heat Input on Haz Softening in Fiber Laser Welding of 22mnb5 Steel(Elsevier, 2023) Tuncel, Oğuz; Aydın, Hakan; Davut, KemalThis study investigates the effects of heat input on the heat-affected zone (HAZ) softening in fiber laser welding of quenched 1.1 mm thick 22MnB5 steel. Laser power (1500-2500 W) and welding speed (40-120 mm/s) parameters are considered as the input process variables. Depending on the input parameters, the applied heat input varied between 12.5 and 62.5 J/mm. The results indicate that a minimum heat input of 50 J/mm is required for full weld penetration. Microhardness findings revealed that the drop in hardness in the HAZ region relative to the base material (BM) reached 39% due to grain coarsening caused by an increase in heat input under the welding conditions. Grain coarsening (prior austenite grains) is also detected in SEM analysis. In addition, grain coarsening at high heat input was also determined quantitatively in EBSD analyses. The proportion of 8.91 mu m grain size in the sample with high heat input is 4.2%, while it is 1.2% in the sample with low heat input. When the heat input increased from 12.5 to 62.5 J/mm, the width of the softened zone with the lowest hardnesses in the HAZ grew from 0.2 mm to 2.2 mm.Article Citation - WoS: 14Citation - Scopus: 13An Experimental Study on the Ballistic Performance of Ultra-High Hardness Armor Steel (armox 600t) Against 7.62 Mm × 51 M61 Ap Projectile in the Multi-Hit Condition(Elsevier, 2023) Göde, Engin; Teoman, Atanur; Çetin, Barış; Tonbul, Kürşat; Davut, Kemal; Kuşhan, Melih CemalIn this study, Armox 600T armor steel was ballistically tested against 7.62 mm × 51 M61 AP projectile. The experimental design was constructed on the basis of the worst-case scenario which is the highest possible impact velocity in the multi-hit condition. The ballistic tests revealed that Armox 600T could defeat the worst-case scenario with a thickness of 12 mm. Furthermore, the damaged and undamaged regions were inspected microstructurally in a detail manner aiming to observe the possible fractographic modes of the studied material. Finally, high resolution optical scanning efforts were also added to the experimental work whose results uncovers the possible improvement areas regarding the quantification of the results of ballistic testing.Article Citation - WoS: 24Citation - Scopus: 27Atomic–scale Investigations of Passive Film Formation on Ti-Nb Alloys(Elsevier, 2023) Çaha, İhsan; Alves, Alexandra C.; Chirico, Caterina; Maria Pinto, Ana; Tsipas, Sophia; Gordo, Elena; Bondarchuk, Oleksandr; Leonard Deepak, Francis; Toptan, FatihThis study extensively investigates the passive film formation mechanisms on Ti-xNb alloys by using several electrochemical techniques, including electrochemical impedance spectroscopy (EIS) before and after potentiostatic polarization at the passive zone, and Mott-Schottky (MS) measurements in 9 g/l NaCl electrolyte at 37 °C, together with X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analysis. Overall, the Ti40Nb presented lower corrosion resistance due to a thinner passive film as compared to commercial pure Ti (grade 2) and Ti12Nb. The passive film formed on Ti12Nb and Ti40Nb alloys at a steady-state condition (+0.5 VAg/AgCl for 60 min) is composed of amorphous phases of TiO, Ti2O3, TiO2, Nb2O5 and crystalline phases of TiO2 (anatase) and Nb2O5. © 2022 Elsevier B.V.Article Citation - WoS: 11Citation - Scopus: 11Enhanced Electrocaloric Effect of P(vdf-Trfe) Nanocomposites With Ca and Sn Co-Doped Batio3 Particles(Elsevier, 2023) Tokkan, Melike; Demir, Mustafa M.; Adem, UmutWe report on the enhancemenent of electrocaloric effect in solution cast polymer nanocomposites based on Poly (vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE) 55-45] with Ca and Sn co-substituted BaTiO3 ceramic fillers (Ba0.94Ca0.06Ti0.925Sn0.075O3, BCST). Saturated hysteresis loops and normal ferroelectric behaviour of the copolymer-based nanocomposites-as opposed to the relaxor ferroelectric nature of the terpolymer-based ones-allow the utilization of the indirect method to estimate the electrocaloric properties. Both the dielectric constant and electrocaloric temperature change (AT) increases as the particle content increases. Maximum adiabatic temperature change was obtained as 6.96 K under 900 kV/cm for the 10 vol % BCST containing polymer composite around the Curie temperature of the copolymer (70 degrees C). This relatively large electrocaloric strength is slightly lower than those obtained for terpolymer-based nanocomposites.Article Citation - WoS: 13Citation - Scopus: 14Synthesis of Albumin Nanoparticles in a Water-Miscible Ionic Liquid System, and Their Applications for Chlorambucil Delivery To Cancer Cells(Elsevier, 2022) Akdoğan, Yaşar; Sözer, Sümeyra Çiğdem; Akyol, Cansu; Başol, Merve; Karakoyun, Çiğdem; Çakan Akdoğan, GülçinSerum albumin has been a preferred protein to generate biodegradable and non-toxic nanoparticles (NPs) for drug delivery applications. Different methods applied for the preparation of serum albumin NPs mostly used organic solvents. Here, we prepared serum albumin NPs in an ionic liquid (IL) system. ILs are considered to be green and designer solvents with unique properties that can replace organic solvents in the synthesis of albumin NPs. Bovine serum albumin (BSA) proteins dissolved in water were transformed into BSA NPs in a water/ Triton™X (TX-100), 1-butanol/1-butyl-3-methylimidazolium trifluoromethanesulfonate (BmimCF3SO3) microemulsion-like system by using a high-speed homogenizer and crosslinker glutaraldehyde. The obtained BSA NPs have been used in drug loading and release studies with a hydrophobic anticancer drug chlorambucil (Chl). Drug loading increased as increasing the ratio of Chl incubated with BSA NPs. Monitoring the drug release by UV–Vis spectroscopy revealed a burst release at first 4 h, but two-thirds of drugs stayed with NPs upon diffusion method. On the other hand, cellular uptake of Chl loaded BSA NPs caused a significant MCF7 breast cancer cell death, whereas free Chl and unloaded BSA NPs did not have a significant effect on the cell viability. Furthermore, in vivo toxicity assessment of BSA NPs obtained in the IL system was conducted in the zebrafish animal model. It showed that zebrafish body is able to eliminate BSA NPs without any toxic side effects and encapsulation of Chl into NPs reduced the toxicity of free Chl. In summary, we showed that BSA NPs with size smaller than 200 nm could be prepared in BmimCF3SO3 mediated system. They can be used for Chl loading (up to 6.9 wt%) with a sustainable release and they induce significant cell death in Chl sensitive cancer cells up to 45% in 24 h. These results indicate that BSA NPs could be prepared alternatively in IL systems and used in drug delivery studies.Article Citation - WoS: 45Citation - Scopus: 48Recrystallization and Grain Growth Kinetics of In718 Manufactured by Laser Powder Bed Fusion(Elsevier, 2022) Doğu, Merve Nur; Davut, Kemal; Obeidi, Muhannad Ahmed; Yalçın, Mustafa Alp; Gu, Hengfeng; Low, Thaddeus Song En; Ginn, Jon; Brabazon, DermotThe recrystallization and grain growth behaviour of IN718 alloy additively manufactured by laser powder bed fusion (L-PBF) is presented herein. The effects of three different temperatures (1050, 1150 and 1250 °C) and holding times (15, 45 and 90 min) were investigated. The texture evolution of the samples was recorded via electron backscatter diffraction (EBSD). The as-built sample is composed of bowl-shaped melt pools, a chessboard-like grain pattern and has a cube texture {100}<001>. Recrystallized grains were observed in the samples treated at 1150 °C for 15 min, as well as the samples treated for longer periods and at higher temperatures. Recrystallization was observed to start from high dislocation density regions, including the overlapping melt pools and the borders of the chessboard-like pattern. The initial cube texture transforms into a first-generation cube-twin texture {122}<212> via a twinning-assisted recrystallization mechanism. Then, those recrystallization nuclei sweep through the high defect density matrix; during which almost no new twins are formed. The samples treated at 1250 °C are almost completely recrystallized, which forms a weaker cube texture and a stronger P-orientation {011}<112>. However, the growth of recrystallized grains is very limited due to the presence of non-coherent precipitates.