Browsing by Author "Gavgali, Mehmet"

Now showing 1 - 10 of 10

Al-5cu/B4cp Composites: the Combined Effect of Artificially Aging (T6) and Particle Volume Fractions on the Corrosion Behaviour
(Elsevier, 2020) Tozkoparan, Burak; Dikici, Burak; Topuz, Mehmet; Bedir, Fevzi; Gavgali, Mehmet
In this study, the Al-5Cu matrix composites reinforced with different boron carbide (B4C) particle volume fractions have been successfully produced by the hot-pressing method. Then, the artificially aging (T6) was applied to the composites for increasing their mechanical properties. The combined effect of the T6 heat treating and the B4C particle volume fraction on the corrosion behaviour of the composites were investigated by potentiodynamic scanning (PDS) technique under aerated and deaerated 3.5% NaCl marine environments. The effect of the T6 treating on the hardness and corrosion susceptibilities of the composites were also evaluated microstructurally to contribute to their industrial use and production processes. The microstructural characterization of the composites was carried out by using a scanning electron microscope (SEM) with an attached energy dispersive spectrum (EDS) and X-ray diffraction (XRD). It was found that the corrosion susceptibilities of the composite have been interestingly decreased with increasing the B4C particle volume fraction in the matrix while the T6 treatment enhances the pitting susceptibility of the composites. The reason of the behaviour has been discussed in details the text. (C) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
Corrosion Susceptibilities of Al-cu/Tic Mmcs Fabricated by Conventional Hot Pressing
(Natl inst Science Communication, 2007) Gavgali, Mehmet; Dikici, Burak; Bedir, Fevzi
The effect of TiC particle volume fraction on the electrochemical behaviours of metal matrix composites (MMCs), which is Al-Cu based reinforced with TiCp has been investigated in both aerated and deaerated 1.0 N H2SO4 aqueous solutions. Composites reinforced with TiC particles at volume fractions of 20, 30 and 40% have been produced by conventional hot pressing method and then, artificially aged (T6). The corrosion susceptibilities of the composites have been analyzed by using the cyclic potentiodynamic polarization technique. The surface morphology of the composites has been determined by scanning electron microscopy (SEM). The results show that the corrosion susceptibilities of the composites increase with increased TiC particle content but decreases with T6 heat treatment pet-formed on the composites.
The Effect of Electroless Ni Coating of Sic Particles on the Corrosion Behavior of A356 Based Squeeze Cast Composite
(Assoc Mechanical Engineers Technicians Slovenia, 2011) Dikici, Burak; Tekmen, Cagri; Gavgali, Mehmet; Cocen, Umit
The corrosion behavior of electroless Ni coated SiC particle reinforced squeeze cast aluminum based composite was investigated by potentiodynamic scanning (PDS) and electrochemical impedance spectroscopy (EIS) techniques in aerated and deaerated chloride solutions. Microstructural and interfacial characterization of the composite was carried out by using an optical microscope, scanning electron microscope (SEM), energy dispersion spectroscopy (EDS) and X-ray diffractometer (XRD). It has been observed that electroless Ni coating of SiC particles is not an effective method to improve its corrosion resistance in structural applications containing halide solution. (C)2011 Journal of Mechanical Engineering. All rights reserved.
Effect of Hydroxyapatite:zirconia Volume Fraction Ratio on Mechanical and Corrosive Properties of Ti-Matrix Composite Scaffolds
(Elsevier, 2022) Topuz, Mehmet; Dikici, Burak; Gavgali, Mehmet; Yilmazer, Yasemin
Ti-based scaffolds reinforced with zirconia and hydroxyapatite were produced successfully by a hybrid method with an eco-friendliness and low cost to obtain low elastic modulus (E) with sufficient physical, electrochemical and biological properties. The effect of simultaneous modification of the volume fraction of hydroxyapatite (HA) and zirconia (ZrO2) on scaffolds was investigated in terms of mechanical, corrosive, and antibacterial properties. Scanning electron microscopy with attached electron dispersive spectroscopy and X-ray diffraction were used for the characterization of scaffolds. Compression and electrochemical tests were performed to determine mechanical properties with detailed fracture mechanism and in-vitro corrosion susceptibility to simulated body fluid at 37 degrees C, respectively. Antibacterial tests were carried out by comparing the inhibition areas of E.coli and S.aureus bacteria. It was observed that the mechanical strength of the scaffolds decreased with increasing HA:ZrO2 volume fraction ratio. The lowest E was achieved (6.61 GPa) in 6:4 HA:ZrO2 composite scaffolds. Corrosion current density (J(corr)) values were calculated to be 21, 337, and 504 mu A/cm(2) for unreinforced Ti, 3:2 and 6:4 HA:ZrO2 reinforced scaffolds, respectively. The inhibition capacity of the 6:4 reinforced composite scaffold was found to be more effective against S.aureus bacteria than other scaffolds.
The Effect of Sintering Time on Synthesis of in Situ Submicron Α-Al2o3 Particles by the Exothermic Reactions of Cuo Particles in Molten Pure Al
(Elsevier Science Sa, 2013) Dikici, Burak; Gavgali, Mehmet
In this study, in situ alpha-Al2O3 reinforcing particles have been successfully synthesised in an Al-Cu matrix alloy by means of the conventional Hot Pressing (HP) method. The effect of sintering time on the forming of the alpha-Al2O3 phase at 1000 degrees C was investigated using Differential Thermal Analysis (DTA), X-ray Diffraction (XRD) and a Scanning Electron Microscope (SEM). The sintered composites contained thermodynamically stable alpha-Al2O3 particles and theta-Al2Cu eutectic phases, which were embedded in the Al-Cu matrix. The in situ alpha-Al2O3 particles were generally spherical and their mean size was observed to be less than 0.5 mu m. The results showed that sintering time influences not only the reaction rate of copper and the formation of Al2O3. Also, an increase in the sintering time accelerates the formation of submicron in situ alpha-Al2O3 particles and decreases the quantity of theta-Al2Cu intermetallic phase in the liquid aluminium. Additionally, sintering of composite for 30 min at 1000 degrees C increased the hardness from 60 to 174 HV. (C) 2012 Elsevier B. V. All rights reserved.
Microstructure and Mechanical Properties of a Novel Tini Particulate Reinforced Az91 Metal Matrix Composite
(Elsevier Science Bv, 2018) Kelen, Fevzi; Gavgali, Mehmet; Aydogmus, Tarik
A new AZ91/TiNi composite has been developed in the present study. The composite containing 20% (vol.) TiNi reinforcement micro-particles was produced by hot pressing of initial prealloyed AZ91D and Ti49.2Ni50.8 powders at 420 degrees C for 1 h. Microstructural analysis revealed that matrix and reinforcement phases did not react each other during processing and a good bonding which is free from porosity, oxide and carbides was attained. Ti49.2Ni50.8 reinforcement increased room temperature yield strength, compressive strength and ductility of AZ91D alloy 5%, 50% and 30%, respectively. Most importantly, yield strength of the composite at 100 degrees C was found to be 267 MPa, 50% higher than that of AZ91D alloy (176 MPa) due to stress-induced martensitic transformation observed in the reinforcing alloy. (C) 2018 Elsevier B.V. All rights reserved.
A Novel Perspective for Lactobacillus Reuteri: Nanoencapsulation To Obtain Functional Fish Fillets
(Elsevier, 2019) Ceylan, Zafer; Uslu, Emin; Ispirli, Humeyra; Meral, Raciye; Gavgali, Mehmet; Yilmaz, Mustafa Tahsin; Dertli, Enes
Enrichment of food products with beneficial Lactic Acid Bacteria (LAB) is an important methodology used to develop functional food products. Lactobacillus reuteri E81 was successfully nanoencapsulated into poly (vinyl alcohol)-based nanofibers for its application to the surface of fish fillets. The Scanning Electron Microscopy analysis confirmed the nanoencapsulation of L. reuteri E81 in electrospun nanofibers (LRNF) that had an average diameter of 381.83 +/- 130.69 nm. LAB growth in rainbow trout fillets and fatty fish (mackerel) and were found to be 2.92 and in the range of 3.27 and 2.66 log CFU/g, respectively. Importantly, the antioxidative characteristics of fish fillets significantly increased following their coating with LRNF. The results revealed a significant increase in the inhibition of free radicals in the samples treated with nanoencapsulated L. reuteri as compared to control group fish fillet samples. DPPH activity significantly increased to 40.24%, 44.96%, 44.97 in mackerel samples treated with nanoencapsulated L. reuteri (MLR) and increased to 19.76%, 20.87%, 21.46% in rainbow samples treated with nanoencapsulated L. reuteri (RLR). MLR samples exhibited the highest ABTS radical-scavenging activity (1631 mu mol TEAC/g). FRAP value of MLR samples was found to be 1.70 times higher than the control group samples.
Processing of Ti/(ha+zro2) Biocomposite and 50% Porous Hybrid Scaffolds With Low Young's Modulus by Powder Metallurgy: Comparing of Structural, Mechanical, and Corrosion Properties
(Elsevier, 2021) Topuz, Mehmet; Dikici, Burak; Gavgali, Mehmet; Kaseem, Mosab
Processing of titanium (Ti)-based implants with improved corrosion resistance and Young's modulus close to that of cortical bone are receiving considerable attention in orthopedic and dental applications. Therefore, Ti matrix, hydroxyapatite (HA) and hydroxyapatite-zirconia (HA+ZrO2) reinforced composites were successfully produced using powder metallurgy as both bulk and 50% in vol. porous scaffold in this study. Microstructure, mechanical and corrosion properties of the bulk and scaffold composites were investigated comparatively. Scanning electron microscopy with attached an energy dispersive spectroscopy (SEM-EDS) and XRD diffraction analysis was used for the characterization of samples. Mechanical properties were determined by using micro Vickers hardness and compressive tests. Besides, the corrosion behaviours of the samples were determined in simulated body fluid (SBF) at 37 degrees C by using potentiodynamic scanning (PDS) tests. Room-temperature compression tests revealed that the bulk samples had higher values of Young's modulus and yield strength in comparison to the scaffold samples where the lowest values of Young's modulus and yield strength of 3 GPa and 6.93 MPa, respectively were obtained in the case of the Ti/(HA+ZrO2) composite scaffold. Moreover, in-vitro corrosion tests in SBF showed that the Ti/(HA+ZrO2) composite scaffold had higher corrosion resistance than the scaffold reinforced with only the HA phase. The corrosion mechanism of the bulk and scaffold samples was also elucidated by taking the microstructural analysis and phase compositional of the samples into account.
Tini Particle-Reinforced Magnesium Matrix Composites: Production, Microstructure, Phase Transformations, and Mechanical Properties
(Wiley-v C H verlag Gmbh, 2025) Kelen, Fevzi; Gavgali, Mehmet; Aydogmus, Tarik
Magnesium matrix composites reinforced with 5-25 vol% Ti49.2Ni50.8 microparticles are produced by uniaxial hot pressing technique. Powder mixtures are hot pressed in cylindrical graphite dies under 50 MPa pressure for 1 h at 600 degrees C. Density measurements show that specimens reach almost full density and do not contain any pores. Microstructural analyses demonstrate that undesired secondary phases or compounds do not form at matrix/reinforcement interface. As a result of aging heat treatment performed simultaneously with the manufacturing process, martensite phase (B19 ') and Ti3Ni4 precipitates are also observed in the microstructure of reinforcing materials in addition to the main austenite (B2) phase. The room-temperature yield strength and compressive strength of the composite materials range between 60 and 86 MPa and 232 and 296 MPa, respectively. Although the ductility values decrease with increasing reinforcement content, the decrease is less than those of ceramic and other metallic reinforced composites. The ductility is determined to be 17.6% for the composite with the highest reinforcement content. In contrast to the reference and conventional materials, the yield strengths of the composite samples produced increase significantly with the increasing temperature up to 100 degrees C. This unusual behavior is attributed to the stress-induced martensitic transformations observed in TiNi alloys.
Titanium-Based Composite Scaffolds Reinforced With Hydroxyapatite-Zirconia: Production, Mechanical and In-Vitro Characterization
(Elsevier, 2021) Topuz, Mehmet; Dikici, Burak; Gavgali, Mehmet
In this study, titanium (Ti)-based composite scaffolds reinforced with hydroxyapatite-zirconia (HA-ZrO2) were successfully produced with powder metallurgy and atmosphere-controlled sintering processes. The scaffolds structures were theoretically selected as 40% and 60% porosity, and fabricated with approximately 1.47 and 4.02 std dev values, respectively. The porosity of the scaffolds was verified by Archimedes? measurements. The scaffolds were characterized by DTA, SEM/EDS, XRD analyses. The mechanical behaviors of the scaffolds were evaluated by compression and hardness tests. Besides, the electrochemical corrosion behaviors of the structures were compared with potentiodynamic scanning (PDS) measurements in simulated body fluids (SBF) at 37 ? 1 ?C. It has been observed that all scaffolds have a bimodal porous structure as they contain varying proportions of micropores as well as macropores in desired dimensions. Biocompatible phases such as TixPy, Ca3(PO4)2 and CaTiO3, respectively, were found in the microstructure after sintering. In compression tests, 40% porous Ti had the highest strength with 37.98 MPa, interestingly, the lowest strength was seen in Ti/HA-ZrO2 scaffold with 60% porosity with 3.80 MPa. Young?s modulus values of all scaffolds vary between 1.67 - 7.20 GPa, due to the bimodal pore structure and composition effect. However, in-vitro corrosion resistance of scaffolds decreased with HA reinforcement, while increased with ZrO2 additive to HA.