Browsing by Author "Yalamaç E."
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Item Sintering and microstructural investigation of gamma–alpha alumina powders(Elsevier B.V., 2014) Yalamaç E.; Trapani A.; Akkurt S.Sintering behaviors of commercially available alumina powders were investigated using constant-heating rate dilatometric experiments. Each powder had different proportion of alpha/gamma alumina. Densification behaviors of powders were studied up to 1600 °C with three different heating rates of 1, 3.3 and 6.6 °C/min. Compacts of different gamma content alumina powders exhibited systematic anomalous second peaks in the densification rate curves at certain heating rates and temperatures. At 3.3 °C/min heating rate experiments, densification curves of 10% gamma phase alumina powder compacts reached a plateau after 1450 °C, and did not increase any further at higher temperatures. This phenomenon was double checked to understand powder behavior during sintering. 10% gamma phase alumina powder compacts showed the highest density for each heating rate. It reached 94% theoretical density with 1 °C/min heating rate. But 20% gamma phase alumina powder compacts had the finest grain size of about 1.40 μm. Final density and porosity of compacts were also tested by image analysis and the results were coherent with Archimedes results. © 2014 Karabuk UniversityItem Effect of spinel addition on the sintering behavior and microstructure of alumina-spinel ceramics(Institute of Chemical Technology, 2014) Yalamaç E.Sintering behaviors of alumina-spinel powder mixtures were investigated up to 1600°C using a vertical dilatometer. Final density and microstructure of pure alumina, magnesium aluminate spinel (MgAl2O4) ceramics and ceramic composites with different alumina-spinel ratio were examined. As a result, the densification and final density of alumina-spinel composites were affected by addition of 10 wt. % and 20 wt. % spinel into alumina. Non-stoichiometric alumina-rich spinel phase was detected in the matrix of the composites by EDS. The presence of spinel phase inhibited alumina grain growth, therefore the pure alumina sample had nearly twice the grain size as the multiphase alumina-spinel samples. Vickers hardness of the samples was tested and compared. The hardness of the composite with 10 wt. % spinel was slightly higher than the pure alumina ceramic, due to grain size and density of the samples.Item Mechanical properties of interface layers between cosintered alumina and spinel compacts(Maney Publishing, 2015) Yalamaç E.; Culha O.; Karataş A.The main aim of this study is to investigate the mechanical and structural properties of the interface layer (interlayer) between alumina and spinel materials after high temperature thermal treatment (1600°C). A microstructurally distinct layer with columnar grains of up to 50 μm length was detected by SEM. Mechanical properties, such as indentation hardness and elastic modulus of the interface layer, parent alumina and spinel parts, were measured and compared by nanoindentation method. According to the results, several microstructural factors including initial alumina raw powders, the intrinsic microstructural inhomogeneity of the interlayers, such as presence of porosities, unresolved hard alumina phase in the microstructures, size of columnar grains and position of grain boundaries were proposed to affect the mechanical properties. Different micromechanical results between the regions of the samples were also attributed to generation of residual compressive stress during grinding and polishing of the surfaces. © 2015 Institute of Materials, Minerals and Mining.Item Dielectric properties of polystyrene/alumina composites for microelectronic devices(European Conference on Composite Materials, ECCM, 2016) Baştürk S.B.; Yalamaç E.; Gültekin S.The availability/lightness of electronic equipments in automotive, telecommunication and computer sectors have great importance in terms of the cost decrease and usability in high speed applications. Printed circuit boards (PCBs) are the main components of these systems and composed of two basic elements: substrate and passive electronic devices. Microelectronic segments having low dielectric permittivity (dielectric constant) and loss tangent minimize the capacitive coupling effects and decrease the signal attenuation. Ceramic particle filled polymer composites combine the desired dielectric properties and have been employed in electronic industry. In this study, 5%, 15% and 30% wt. alumina (Al2O3) loaded polystyrene (PS) composites were produced. The size of the PS granules was reduced below 100 microns by ball milling process. The Al2O3 and PS powders were mixed by vibratory disc mill and subjected to injection molding for manufacturing the circular specimens. The dielectric permittivity (real and imaginary parts) and loss tangent parameters of the composites were measured via dielectric analyzer up to 1 MHz at room temperature. Based on dielectric measurements, there was no pronounced difference among the samples' real part permittivities along the frequency variation. As expected, the ceramic content increase led to the increase of permittivity and 30%Al2O3 wt. loaded structure showed the maximum values. This behavior was attributed to the effect of polarization which appears in heterogeneous media consisting of phases with different dielectric constant and conductivity. © 2016, European Conference on Composite Materials, ECCM. All rights reserved.Item Ceramic fibers(Elsevier, 2017) Yalamaç E.; Sutcu M.; Basturk S.B.This chapter mainly focuses on type of ceramic fibers, fabrication methods used to make ceramic fibers, and their application areas. Oxide and nonoxide ceramic fibers are being used as reinforcement materials for composites due to their unique properties of high elastic modulus and high-temperature durability. Their properties make them valuable to use in automotive, aerospace, and heat-resistant structural applications. Ceramic fibers are found in two forms, continuous (long length) and discontinuous (short length). Alumina- and silicate-based continuous oxide fibers are made by sol-gel process but short oxide fibers by melt-spinning route. On the other hand, silicon- and boron-based nonoxide ceramic fibers are currently being developed and produced by thermal conversion of polymer precursor process. © 2017 Elsevier Ltd. All rights reserved.Item Growth of the Fe2B layer on SAE 1020 steel employed a boron source of H3BO3 during the powder-pack boriding method(Elsevier Ltd, 2018) Türkmen İ.; Yalamaç E.In this study, an alternative powder-pack boriding mixture containing H3BO3 as boron source was prepared and used for boriding of SAE 1020 steel. The boriding treatment was carried out in the temperature range of 850–950 °C for a treatment time ranging from 4 to 12 h. The generated boride layers were characterized by different experimental techniques such as optical microscope, SEM, XRD analysis and the Daimler-Benz Rockwell C indentation test. The powder-pack boriding mixture was analyzed by TGA and DTA methods and the possible chemical reactions that may be occurred during boriding were investigated. Furthermore, the growth kinetics of the boride layer forming on SAE 1020 steel substrates was investigated. A regression model based on a full factorial design was used to estimate the boride layers' thicknesses as a function of the boriding parameters. A single phase boride layer with saw-tooth morphology was formed on the steel samples. The value of boron activation energy for SAE 1020 steel was estimated as 183.15 kJ/mol. The comparisons were made between the empirical values of the boride layers' thicknesses with estimated ones. The contour diagrams were plotted for estimating the thickness of boride layer as a function of the temperature and time. © 2018 Elsevier B.V.Item Investigation of tribological behaviour and diffusion model of Fe2B layer formed by pack-boriding on SAE 1020 steel(Elsevier B.V., 2019) Türkmen İ.; Yalamaç E.; Keddam M.In this study, a substitute boriding powder including boric acid as boron source was prepared and employed for boronizing of SAE 1020 steel. The boronizing processes were performed at 850, 900 and 950 °C for 4, 8 and 12 h. The formed boride layers were identified by varied experimental methods such as optical microscope, SEM and WDS analysis. As an outcome of the analyses, the boride layer containing only Fe2B phase with saw-tooth morphology was specified on surface of the samples. A diffusion model was proposed to estimate the coefficients of boron diffusion in the Fe2B layers. The value of boron activation energy for SAE 1020 steel was calculated as 183.14 kJ/mol and the result was contrasted with literature data. As a result of the microhardness measurements, the average hardness value of Fe2B layer was about between 1200 and 2000 HV0.1. The average hardness values of the transition zone and matrix zone were determined to be approximately 160 HV0.1 and 151 HV0.1, respectively. This study mainly concentrates on the tribological properties of borided SAE 1020 steel with using alternative boriding powder. Coefficient of friction graph was drawn for each sample and the wear rates were calculated. It was specified that specific wear rate of borided samples was roughly 47 times lower than that of unborided samples. © 2019 Elsevier B.V.Item Effect of heat treatment parameters on the crystallization of feldspathic-based dental glass-ceramics(Taylor and Francis Ltd., 2020) Yalamaç E.; Sutcu M.; Ergani E.S.The effects of heat treatment time and temperature on the crystallization of the feldspathic glass-ceramics produced from frit powders were investigated. Two-step heat treatment processes (nucleation and crystal growth) were applied to produce glass-ceramics. In both stages, the samples were heated at different soaking temperatures and times. Tetragonal leucite crystal nucleation and growth processes were followed by XRD, SEM and dilatometer techniques. Depending on first step heat treatment temperature and soaking time the crystallization gradually increases with increasing time and temperature. The second step heat treatment soaking times showed significant change in the coefficient of thermal expansion (CTE) of the glass ceramic samples. Biaxial flexural strength (σ) of the samples slightly increases with increasing the 2nd step soak time and all results are above the required standard value of 100 MPa for the monolithic ceramic for single-unit anterior on dental restorations. © 2020 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of The Korean Ceramic Society and The Ceramic Society of Japan.Item Characterization and Kinetic Analysis of Iron Boride Layer Formed on the GGG 70 Ductile Cast Iron(Springer, 2021) Yalamaç E.; Türkmen İ.; Fırtına Ö.An alternative powder-pack boriding powder mixture containing H3BO3 as boron source and commercial boriding powder containing B4C as boronizing agent were used for boriding of GGG 70 type ductile iron. As a result of XRD analysis, while only Fe2B phase was detected on the samples boronized with alternative boriding mixture, besides Fe2B phase, small amount of FeB phase was also determined on the samples boronized with commercial powder. The growth kinetics of the boride layer forming on ductile iron was investigated and compared with literature studies. The value of boron activation energy for ductile iron was calculated as 184.67 kJ/mol. An empirical equation and a regression model were derived to estimate the thicknesses of boride layer as a function of the boriding parameters. The comparisons were made between the experimental boride layer thicknesses with estimated ones and the results were consistent with 99% accuracy. © 2021, The Indian Institute of Metals - IIM.Item Effect of Alternative Boronizing Mixtures on Boride Layer and Tribological Behaviour of Boronized SAE 1020 Steel(Korean Institute of Metals and Materials, 2022) Türkmen İ.; Yalamaç E.Abstract: In this study, SAE 1020 steel samples were boronized at 850 °C for 4 h with different boronizing mixtures by powder-pack boronizing method. H3BO3 or Na2B8O13 was used as the boron source, KBF4 or NaBF4 was used as the activator and SiC was used as the diluent. Thus, 4 different boronizing mixtures (M1-M4) were prepared. Thickness, morphology and phase structure of the formed boride layers were studied by X-ray diffraction and microstructural analyzes. The single phase (Fe2B) boride layer with saw-tooth morphology was formed on surface of the samples. The thickest boride layers were obtained by using M1 and M2 boronizing mixtures. Microhardness measurements were performed to determine hardness of the 3 zones (core, transition zone and boride layer). The means of boride layer hardness of the samples were compared according to 95% Confidence Intervals analysis. It was determined that the average hardness value of the boride layers was about 1475 HV. Wear tests were fulfilled by ball on disc type wear test method under dry sliding condition and at 25 °C. According to the friction coefficient and specific wear rate values of boronized samples, it was identified that the sample SM4 boronized with M4 boronizing mixture has the lowest wear rate (1.64 mm3/N.m) and friction coefficient value (0.63). Graphic Abstract: [Figure not available: see fulltext.] © 2021, The Korean Institute of Metals and Materials.Item Artificial neural network investigation of injectability and percolation of highly filled β -Tricalcium phosphate suspensions(Elsevier Ltd, 2022) Kulakoğlu S.; Yalamaç E.; Şahin E.Over the past few decades, calcium phosphate cement has been used successfully for bone reconstruction applications. As percutaneous surgical methods have developed, there is an increased interest in calcium phosphate cement injection behavior. The aim of this study is to minimize percolation (liquid phase migration under pressure) and maximize injectability (ratio of the extruded part to whole) of highly filled β-tri calcium phosphate (β-TCP) suspensions by varying capillary flow process parameters with an artificial neural network (ANN) approach. The effects of hydroxyethyl cellulose (HEC) and polyethylene glycol (PEG-400) were also studied as binder additives for injectable β-tri calcium phosphate pastes. Prepared suspensions were investigated by capillary and small amplitude oscillatory rheometry. The study predicted experimental input and output data by using Backpropagation Neural networks via the Levenberg-Marquardt algorithm. The ANN model was developed by feed-forward back propagation network and predict percolation (%) and injectability (%). A great agreement was observed between the predicted values by the ANN model and the experimental data for injectability (%) and percolation (regression coefficients) of 0.9984 and 0.9982 respectively. The results depict that ANNs can improve the accuracy of injectability and percolation results which can be used to optimize process and additive parameters for injectable bone cements and pastes. 2 wt% HEC was determined as the most effective factor to improve the rheological properties of highly filled β-TCP pastes which could be injected as much as 99.21 % at a rate of 15 mm/min through dies with L/D ratio of 15. Their percolation value was calculated as 0.82 %. Lubricative effect of PEG-400 additive with 2 wt% HEC to reduce injection force was also demonstrated. © 2022 Elsevier Ltd and Techna Group S.r.l.