Browsing by Author "Hong S."

Now showing 1 - 7 of 7

Densification behaviour analysis of ZrO2 nanopowders for dental applications compacted by magnetic pulsed compaction
(2013-08-15) Park H.; Kilicaslan M.; Hong S.
Sintered bulks of commercial ZrO2 nanopowders were produced by combined application of magnetic pulsed compaction (MPC) and subsequent two-step sintering, and finally, their density, hardness, shrinkage and formability were analyzed. The formability tests were conducted by a CAD/CAM system. Nearly fully dense (∼98%) commercial ZrO2 bulks were successfully obtained. With increasing MPC pressure, there was a decrease in the grain size of zirconia block. The ratio of PVA did not have a remarkable effect on the grain size. The optimum compaction pressure during MPC was 1 GPa and mixing conditions included using 1.0 wt. % PVA. The optimum processing condition included MPC process, followed by two-step sintering (first at 1000 and then at 1450 C). The bulk under these conditions was found to have good formability, ∼97% density, reasonable hardness (1150 Hv) and ∼19% shrinkage© 2013 Elsevier B.V. All rights reserved.
Effect of Co on Si and Fe-containing intermetallic compounds (IMCs) in Al-20Si-5Fe alloys
(2012-10-30) Fatih Kilicaslan M.; Yilmaz F.; Hong S.; Uzun O.
The effects of cobalt addition on microstructure and mechanical properties of Al-20Si-5Fe-XCo (X=0, 1, 3, and 5) alloys were reported in this study. The alloys were produced by both conventional sand casting and melt-spinning at 20. m/s disk velocity. Microstructures of the samples were investigated using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Vickers micro-hardness tester was used for hardness measurements. Results showed that Co addition can alter morphology of Fe-bearing intermetallic compounds (IMCs) from long rod/needle-like structures to short rod-like ones, and lead to a more homogenous distribution in the microstructure. Addition of 5. wt% Co leads to a decrease in average size of the primary silicon phases in as-cast Al-Si alloys. In melt-spun alloys, with the addition of Co, the microstructure became finer and more homogenously distributed, while thickness of the featureless zone has seen great increase. The optimum Fe to Co ratio was found to be 1 for suppressing the undesirable effect of Fe-bearing acicular/needle-like intermetallic compounds. © 2012 Elsevier B.V.
Effect of multiple pressures by magnetic pulsed compaction (MPC) on the density of gas-atomized Al-20Si powder
(2012-07-01) Park H.; Kilicaslan M.; Hong S.
Rapidly solidified Al-20. wt.%Si alloy powders with particle size of ~. 106. μm in diameter were fabricated by gas atomization, and the powder compaction was performed by using magnetic pulsed compaction. Multiple way experiments were carried out on Al-Si powders with varying pressing time, weight and intensity of initial and final pressures. Effects of process parameters during multiple pressing such as, number of repeated pressing, initial pressure, and final pressure, on the density were investigated. It was found that density decreases with increasing weight of powder poured to the die, but it enhances with increasing pressure. The last compaction pressure has a more dominant effect on the density than the initial compaction pressure in magnetic pulsed compaction process. With increasing the number of repeated pressing, the density of the compacted product increases. © 2012 Elsevier B.V..
Effect of Sc addition on the microstructure and mechanical properties of as-atomized and extruded Al-20Si alloys
(2012-03-15) Kilicaslan M.; Lee W.; Lee T.; Sohn Y.; Hong S.
The microstructure evolution and mechanical properties of Al-20Si alloy with Sc addition were investigated after as-atomized and hot-extruded conditions. Microstructural and spectroscopic analyses demonstrate that Sc is enriched at the Si/Al interface. It could be observed that the presence of Sc refined the size of the primary and eutectic Si, without significantly affecting the shape. A considerable improvement in tensile strength, compressive strength, and elongation was observed due to addition in Sc percentage into the composition. The correlation between the microstructure and mechanical behavior strongly indicates that the addition of Sc modifies the Si particles by impurity induced twinning (IIT) mechanisms. © 2011 Elsevier B.V. All rights reserved.
Effects of Substitution of Al and Bi for Ni on Structure and Hydrogen Storage Properties of LaNi 4.7-xAl 0.3Bi x (x = 0:1; 0:2; 0:3) Alloy
(2012-09-01) Yilmaz F.; Kilicaslan M.; Atanur O.; Hong S.; Uzun O.
In this research, the effects of Al and Bi substitution for Ni on the microstructure and hydrogen absorption/desorption properties of LaNi 4.7-xAl 0.3Bi x (x = 0:1; 0:2; 0:3) alloys were investigated. The results showed that substituting Ni with Al led to a desirable decrease in absorption/desorption plateau pressure as well as to hysteresis without a reduction in hydrogen capacity. However, Bi substitution reduced the hydrogen capacity and increased the absorption/desorption plateau pressure of the samples. The formation of the (Al,Ni) intermetallic and Bi phases at grain boundaries was found to be the main reason for the changes in hydrogen storage properties. © 2012 The Japan Society of Applied Physics.
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.
Thermoelectric properties of n-type Bi2Te3 alloys produced by a combined process of magnetic pulsed compaction (MPC) and spark plasma sintering (SPS)
(2014-01-01) Lee C.; Fatih Kilicaslan M.; Madavali B.; Hong S.
In this study, n-type 95 %Bi2Te3-5 %Bi 2Se3 thermoelectric materials have been produced by a combined process of gas atomization with subsequent magnetic pulsed compaction and spark plasma sintering, and then we investigated the behavior of transport properties with sintering temperature. The microstructural observation was performed by optical microscopy and scanning electron microscopy. The crystal structures were analyzed by X-ray diffractometer. The mechanical properties were calculated by measuring the density and micro-Vickers hardness of the samples. It was found that with increasing sintering temperature the gaps between powder particles decreases and the grain sizes were coarsened. The mechanical properties shows higher values along the parallel direction compared to the perpendicular direction to the pressing. The transport properties of the thermoelectric material were investigated with variation of the sintering temperatures. The maximum power factor 1.7 × 10-3 Wm -1 K-2 was measured at the sintering temperature of 450 °C. © 2014 Springer Science+Business Media Dordrecht.