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Birol Y.,TUBITAK - Marmara Research Center
Tribology International | Year: 2013

The frictional forces arising from sliding contact with aluminium produce considerable shear stresses on the CrN coating that degrade its integrity and its adhesion to the substrate tool steel. The CrN coating suffers the most extensive wear damage. There is a net improvement in the sliding wear performance of the AlCrN coating owing to a multilayered structure and a much higher hardness. However, AlTiN outperforms both CrN and AlCrN in sliding contact against aluminium owing to its exceptionally high chemical resistance against aluminium. The superiority of the AlTiN coating is confirmed by wear rates estimations. © 2012 Elsevier Ltd.

Birol Y.,TUBITAK - Marmara Research Center
Journal of Alloys and Compounds | Year: 2012

The potential of AlB3 master alloy in the grain refinement of AlSi10Mg and AlSi12Cu foundry alloys was investigated and compared with that of the AlTi5B1 master alloy, the standard grain refiner for most aluminium foundries. The latter refines the grain structures of both alloys. However, this performance is not nearly as good as that obtained in wrought aluminium alloys with the same grain refiner. The Ti-free AlSi10Mg and AlSi12Cu alloys, on the other hand, exhibit very small grains for the entire range of holding times when inoculated with AlB3. This implies a remarkable grain refining efficiency, typical of grain refined wrought aluminium alloys, as well as a strong resistance to fading of the grain refinement effect. Lack of Ti in the melt allows the entire B to form AlB 2 particles, the perfect substrates, shortly before α-Al starts to crystallize. Aluminium castings can enjoy grains as small as those of the wrought alloys, well below 200 μm, with an addition of 0.02 wt% B provided that their Ti content is controlled. © 2011 Elsevier B.V. All rights reserved.

Ozkara-Aydnolu S.,TUBITAK - Marmara Research Center
International Journal of Hydrogen Energy | Year: 2010

Thermodynamics equilibrium analysis of carbon dioxide reforming of methane combined with steam reforming to synthesis gas was studied by Gibbs free energy minimization method to understand the effects of process variables such as temperature, pressure and inlet CH4/H2O/CO2 ratios on product distributions. For this purpose, the calculations were carried out at total pressures of 1 and 20 bar, and at ranges of temperature and steam-to-carbon ratios of 200-1200 °C and 0-0.50, respectively. The results revealed that carbon dioxide reforming of methane combined with steam reforming process was controlled by different reactions with regard to the operating temperature, pressure and varying feed compositions. The H2/CO product ratio could be modified by changing the relative concentration of steam and CO2 in the feed, temperature and pressure, depending on the downstream application. © 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Tan O.,TUBITAK - Marmara Research Center
Journal of Geodynamics | Year: 2013

The Aegean coast of Turkey is a transition zone between the Anatolian and the South Aegean microplates. The recent geophysical studies suggest the existence of additional microplates and suggest a modification of the block boundaries; the Karaburun Peninsula is most likely located on one of these boundaries. The earthquake activity in and around the peninsula was very low until the Mw 5.8 Siĝacik Bay earthquake of 17 October 2005. The continuing seismicity in the Karaburun Peninsula has been monitored with the help of the dense seismology network. I re-located more than 5000 earthquakes using the double-difference algorithm and obtained fault plane solutions to understand the seismotectonic properties of the region. It is found that the micro-seismic activity has increased towards the NW of the Siĝacik Bay. These observations imply the existence of a NW-SE-oriented sinistral strike-slip fault. This fault is possibly a conjugate of the dominant NE-SW-oriented dextral strike-slip faults in this transition region occupying the area between western Anatolia and the mainland of Greece, where a dominantly extensional regime prevails. Moreover, it is clear that the micro-earthquake activity is related to the Uzunkuyu Intrusive located in the middle of an approximately 40km strike-slip Karaburun Seismic Zone between the Siĝacik and Gerence bays. © 2012 Elsevier Ltd.

Birol Y.,TUBITAK - Marmara Research Center
Journal of Materials Processing Technology | Year: 2011

EN AW-2014 extruded alloy slugs were thixoformed at 615 °C where the solid fraction is estimated to be 80%. The recrystallization process occurred during heating to the thixoforming temperature, between 550 °C and 600 °C, well above the solidus temperature owing to the pinning of grain boundaries by Al2Cu precipitates. The equiaxed polygonal grains thus obtained have become increasingly globular upon soaking. Si was enriched in the grain boundaries during soaking while the solid solution matrix was gradually depleted off Cu. The grain boundary composition has moved closer to that of the Al-Cu-Si ternary eutectic with a lower melting point than the binary Al-Cu eutectic, facilitating grain boundary melting. The liquid phase has then penetrated between the grains, forming a more or less continous intergranular network. Microstructural features essential for forming in the semi-solid state were obtained after about 10 min at 615 °C. The subsequent forming process has occurred in the semi-solid state with no evidence of grain deformation. The thixoformed EN AW-2014 part was solutionized at 500 °C for 2 h and was subsequently quenched in water. Artificial ageing at 160 °C has produced hardness values as high as 160 HV after only 8 h. It is concluded that the high strength wrought EN AW-2014 alloy feedstock processed by the RAP route respond to a thixoforming operation in a very favorable fashion. © 2011 Elsevier B.V. All rights reserved.

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