Browsing by Author "Yalamaç, E"

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    Investigation of tribological behaviour and diffusion model of Fe2B layer formed by Pack-boriding on SAE 1020 steel
    (ELSEVIER SCIENCE SA) Türkmen, I; Yalamaç, E; Keddam, M
    In this study, a substitute boriding poWder including boric acid as boron source was Prepired and employed for boronizing of SAE 1020 steel. The boronizing processes were performed at 850, 900 and 950 degrees 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 rnicrohardness measure- . ments, 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.
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    Ceramic fibers
    (WOODHEAD PUBL LTD) Yalamaç, E; Sutcu, M; Basturk, SB
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    Effect of Alternative Boronizing Mixtures on Boride Layer and Tribological Behaviour of Boronized SAE 1020 Steel
    (KOREAN INST METALS MATERIALS) Türkmen, I; Yalamaç, E
    In this study, SAE 1020 steel samples were boronized at 850 degrees 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 degrees C. According to the friction coefficient and specific wear rate values of boronized samples, it was identified that the sample S-M4 boronized with M4 boronizing mixture has the lowest wear rate (1.64 mm(3)/N.m) and friction coefficient value (0.63). Graphic
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    Effect of heat treatment parameters on the crystallization of feldspathic-based dental glass-ceramics
    (TAYLOR & FRANCIS LTD) Yalamaç, E; Sutcu, M; Ergani, ES
    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 (sigma) of the samples slightly increases with increasing the 2(nd)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.
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    Mechanical properties of interface layers between cosintered alumina and spinel compacts
    (TAYLOR & FRANCIS LTD) Yalamaç, E; Culha, O; Karatas, 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 degrees C). A microstructurally distinct layer with columnar grains of up to 50 mu m 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.
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    EFFECT OF SPINEL ADDITION ON THE SINTERING BEHAVIOR AND MICROSTRUCTURE OF ALUMINA-SPINEL CERAMICS
    (INST CHEMICAL TECHNOLOGY, DEPT GLASS CERAMICS) Yalamaç, E
    Sintering behaviors of alumina-spinel powder mixtures were investigated up to 1600 degrees 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.
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    Artificial neural network investigation of injectability and percolation of highly filled β -Tricalcium phosphate suspensions
    (ELSEVIER SCI LTD) Kulakoglu, S; Yalamaç, E; Sahin, 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 beta-tri calcium phosphate (beta-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 beta-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 beta-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.
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    Characterization and Kinetic Analysis of Iron Boride Layer Formed on the GGG 70 Ductile Cast Iron
    (SPRINGER INDIA) Yalamaç, E; Türkmen, I; Firtina, 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.
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    English
    (2215-0986) Yalamaç, E; Trapani, A; Akkurt, S
    ELSEVIER - DIVISION REED ELSEVIER INDIA PVT LTD