Browsing by Author "Ergen S."

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Microstructure and microhardness of melt-spun Al-25Si-5Fe-XCo (X = 0, 1, 3, 5) alloys
(2013-02-01) Kiliçaslan M.; Yilmaz F.; Ergen S.; Hong S.; Uzun O.
The microstructure and microhardness evolution of melt-spun Al-25Si-5Fe alloy with Co addition (1, 3 and 5 wt.%) were investigated. Microstructural and spectroscopic analyses demonstrate that Co could refine primary Si grains and change their morphology because it causes higher constitutional undercooling and has large mixing enthalpy with Si. Especially, 3 wt.% Co addition causes homogeneously distributed fine spherical Si particles in the rapidly solidified Al-25Si-5Fe alloy. The size of the spherical silicon particles was from around 200 to 600 nm near the wheel side region, and it varied from 800 nm to 1.3 μm at the air side. The optimum ratio of Si and Co should be between 6 and 8.3 to form spherical Si grains in Al-25/30Si-5Fe alloys. A considerable improvement in microhardness value (from 211 to 370 HV) was obtained with the addition of Co. © 2013 Elsevier Inc.
Nanoindentation study on Gd-deposited YBaCuO superconductor
(2013-01-01) Yilmaz F.; Uzun O.; Kolemen U.; Kilicaslan M.; Basman N.; Ergen S.; Ozturk K.; Yanmaz E.
Nanoindentation technique was used to characterize the mechanical properties of Gd-deposited bulk YBaCuO superconductors fabricated by solid-state reaction method. In order to determine the hardness and reduced modulus of the samples, load-displacement data were analysed by using the Oliver-Pharr method. The hardness values exhibited significant peak load-dependence especially at lower peak loads, while the reduced modulus values were found to be nearly constant at studied loading range. In order to find true hardness of the samples, the peak load-dependency of hardness was analysed by using Meyer's law,minimum resistance model, elastic/plastic deformation model, energy balance model, Nix-Gao model and Mukhopadhyay approach. Of the aforementioned models, energy balance model and Mukhopadhyay approach were found to be the most effective models to explain the load-dependency of hardness. © Indian Academy of Sciences.
Shape memory properties and microstructural evolution of rapidly solidified CuAlBe alloys
(2013-05-03) Ergen S.; Uzun O.; Yilmaz F.; Kiliçaslan M.
In this work, the effects of Be addition on the microstructure and phase transformation temperatures of Cu-12Al-xBe (x = 0.4, 0.5 and 0.6 wt.%) shape memory alloys fabricated by using the arc-melting and melt-spinning techniques have been investigated. X-ray diffraction analysis revealed that the arc-melted alloys consisted of austenitic β1, martensitic β1′ and γ2 precipitate phases, whereas melt-spun ribbons were composed of a fully martensitic phase. The average grain size of martensitic phases in melt-spun ribbons was determined by electron microscopy images, showing a decrease with increasing Beryllium (Be) amount. Moreover, it was found that the Be addition in the arc-melted alloys had a distinct effect on the morphology of the γ2 precipitate phase. Transmission electron microscopy analysis showed that the thickness of martensitic plates in the melt-spun ribbons reduced with increasing Be addition. In a differential scanning calorimeter analysis, no martensitic transformation (Ms) peak was observed in arc-melted alloys, but it was clearly detected in melt-spun ribbons, in which Ms decreased dramatically with increasing Be addition. The improvement in the shape memory ability of melt-spun ribbons was explained in terms of the refinement in grain size and martensitic plates. © 2013 Elsevier Inc.
Structural and mechanical properties of hypereutectic AlSiFe powders and a new method for determination of sintering temperature
(2018-03-01) Ergen S.; Yılmaz F.; Gul S.; Kolemen U.; Kilicaslan M.; Uzun O.
In this study, the effect of Si amount on the microstructure, crystal structure and some mechanical properties of Al-(20,25,30 wt%)Si–5Fe powder mixtures produced by high energy ball milling method was investigated by determining the sintering temperature. In the X-ray diffraction analysis, no inter-metallic phases were found except for the Al, Si and Fe phases of the powder mixtures. The X-ray diffraction patterns were analyzed by the Rietveld method to determine amounts of the Al, Si and Fe elements in the powder mixtures. From the scanning electron microscopy analysis, it is seen that as the amount of Si increases, there is a marked decrease in the grain size of powders. In the micro-indentation tests performed at room temperature, the hardness and elastic modulus values of the pelletized powders were found to increase with the amount of Si. It was also found that the Al-20Si-5Fe powder mixture with the lowest Si content had the highest damping capability. The high temperature micro-indentation tests showed that the resulting Al-(20,25,30 wt%) Si-5 Fe powder mixtures started to consolidation at 200 °C and completed the consolidation at 400 °C. This method can be used as an alternative method in the determination of the sintering temperature of materials.