The Experts below are selected from a list of 144 Experts worldwide ranked by ideXlab platform
Konstantinos Georgarakis - One of the best experts on this subject based on the ideXlab platform.
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fabrication of nanoporous copper surface by leaching of Chill Zone cu zr hf alloys
Scripta Materialia, 2015Co-Authors: Daria Barsuk, Konstantinos Georgarakis, Min Zhang, N T Panagiotopoulos, Alberto Moreira Jorge, A R YavariAbstract:In present work we report the synthesis of nanoporous surface using a copper-based alloy via leaching the less noble element-rich phase out of nanostructured ternary Cu–Hf–Zr alloys. The removal of Hf and Zr by mixed acid etchants in the Chill-Zone region of rapidly solidified ingots leads to the formation of a nano-roughened surface layer constituted of copper. The average pore and grain size of the obtained structure were shown to be less than 100 nm and 50 nm respectively.
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AlNiY Chill-Zone alloys with good mechanical properties
Journal of Alloys and Compounds, 2009Co-Authors: Yan Li, Frederic Charlot, Konstantinos Georgarakis, A. Lemoulec, Shujie Pang, J. Antonowicz, Tao Zhang, Alain Reza YavariAbstract:Abstract Using cold graphite mold casting method, Al-based Chill-Zone alloys cylinders of millimeter scale thickness [Y. Li, K. Georgarakis, S.J. Pang, A. LeMoulec, T. Zhang, A.R. Yavari, unpublished research.] were prepared. Using high-resolution scanning electron microscopy (HRSEM), it was found that hard submicron crystalline surface layers of thickness about 200 μm form when the melt can be undercooled. The structure and the thermal properties of the Chill-Zone alloy were examined by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). A metastable phase Al 19 Ni 5 Y 3 nucleated during cooling then transformed to equilibrium intermetallics after annealing. The Chill-Zone alloy shows high mechanical strength in excess of 1 GPa at high ambient temperatures and good plasticity. The combination of high strength and good plasticity will be discussed in relation to the special structure of the Chill-Zone alloy.
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Chill Zone aluminum alloys with gpa strength and good plasticity
Journal of Materials Research, 2009Co-Authors: Yan Li, Frederic Charlot, Konstantinos Georgarakis, A. Lemoulec, Shujie Pang, Tao Zhang, Sandrine Briceprofeta, Alain Reza YavariAbstract:Using a cold graphite mold casting method, bulk AlNiY Chill-Zone alloys were prepared at hypereutectic compositions with Al content from 85 at.% to 94 at.%. It was found that ultra-hard surface layers with a thickness of about 200 μm and submicron grain size form when the melt can be undercooled without heterogeneous nucleation at the mold contact surface. This hard Chill-Zone forming in contact with the mold possesses Vickers microhardness Hv about 350–420 and is thus harder than fully amorphous Al alloys. In compression, ultimate strength more than 1.1 GPa and true strain more than 150% without failure were achieved simultaneously. The combination of high strength and good plasticity will be discussed in relation to the special structure of the Chill-Zone alloy.
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Chill Zone copper with the strength of stainless steel and tailorable color
Acta Materialia, 2008Co-Authors: Alain Reza Yavari, Frederic Charlot, Konstantinos Georgarakis, A. Lemoulec, Gavin Vaughan, A.l. Greer, Akihisa InoueAbstract:Abstract We report here on 90 at.% copper 2–4 mm thick castings with fracture strengths up to 1.9 MPa due to the formation of a thick, scratch-resistant nanocrystalline Chill-Zone next to the copper mold contact surfaces. It is found that the unusually hard nanocrystalline surface layers of thicknesses in the range of 200–300 μm form when the melt can be undercooled: when the alloy composition is such that the contact surface of the copper mold with the liquid alloy does not serve as a preferred site for crystal nucleation, supercooling of the melt in the Chill-Zone is possible. These castings are the hardest coppers ever reported to date in macroscopic specimens. They have mechanical strength superior to those of many stainless steels as well as to Cu–Be alloys and of the order of those of Cu-based bulk metallic glasses (BMGs) of similar dimensions. In addition, and unlike in copper-based BMGs, the color and luster can be tailored by elemental additions to vary from copper-like to gold-like.
A R Yavari - One of the best experts on this subject based on the ideXlab platform.
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fabrication of nanoporous copper surface by leaching of Chill Zone cu zr hf alloys
Scripta Materialia, 2015Co-Authors: Daria Barsuk, Konstantinos Georgarakis, Min Zhang, N T Panagiotopoulos, Alberto Moreira Jorge, A R YavariAbstract:In present work we report the synthesis of nanoporous surface using a copper-based alloy via leaching the less noble element-rich phase out of nanostructured ternary Cu–Hf–Zr alloys. The removal of Hf and Zr by mixed acid etchants in the Chill-Zone region of rapidly solidified ingots leads to the formation of a nano-roughened surface layer constituted of copper. The average pore and grain size of the obtained structure were shown to be less than 100 nm and 50 nm respectively.
S H Jong - One of the best experts on this subject based on the ideXlab platform.
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THE CAST STRUCTURE OF A 7075 ALLOY PRODUCED BY A WATER-COOLING CENTRIFUGAL CASTING METHOD
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 1994Co-Authors: S H JongAbstract:A water-cooling centrifugal casting method was applied to cast the 7075 Al alloy to generate a much finer cast structure than that produced by conventional ingot casting methods. The effects of casting parameters, i.e., rotation speed, pouring temperature, water flow, and grain refiner, on casting structure were systematically studied so that the optimum casting condition and the solidification mechanism could be established. The typical cast structure along the thickness direction of a cast ring could be divided into four equiaxed Zones, including the Chill Zone which is in contact with the mold wall. All Zones have their characteristic grain size, morphology, and relative thickness, which are all dependent on the casting condition. The optimum casting condition yielding the finest structure available was found to be 3000 rpm, 650 °C, and sufficient water cooling. A uniform portion occupying 90 pct of the whole thickness and having a grain size of 17 μm could be achieved under such a casting condition. When a grain refiner was added, the whole ring became further concentrated with grains of fine structure. A mechanism concerning the overall effects of rapid solidification, turbulent flow, and centrifugal force has been proposed for the present casting method and might explain the Zone-structure formation and the effects of the casting parameters on microstructural features.
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The cast structure of a 7075 alloy produced by a water-cooling centrifugal casting method
1994Co-Authors: J.w. Yeh, S H JongAbstract:A water-cooling centrifugal casting method was applied to cast the 7075 Al alloy to generate a much finer cast structure than that produced by conventional ingot casting methods. The effects of casting parameters, i.e., rotation speed, pouring temperature, water flow, and grain refiner, on casting structure were systematically studied so that the optimum casting condition and the solidification mechanism could be established. The typical cast structure along the thickness direction of a cast ring could be divided into four equiaxed Zones, including the Chill Zone which is in contact with the mold wall. All Zones have their characteristic grain size, morphology, and relative thickness, which are all dependent on the casting condition. The optimum casting condition yielding the finest structure available was found to be 3000 rpm, 650-degrees-C, and sufficient water cooling. A uniform portion occupying 90 pct of the whole thickness and having a grain size of 17 mum could be achieved under such a casting condition. When a grain refiner was added, the whole ring became further concentrated with grains of fine structure. A mechanism concerning the overall effects of rapid solidification, turbulent flow, and centrifugal force has been proposed for the present casting method and might explain the Zone-structure formation and the effects of the casting parameters on microstructural features.
Min Zhang - One of the best experts on this subject based on the ideXlab platform.
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fabrication of nanoporous copper surface by leaching of Chill Zone cu zr hf alloys
Scripta Materialia, 2015Co-Authors: Daria Barsuk, Konstantinos Georgarakis, Min Zhang, N T Panagiotopoulos, Alberto Moreira Jorge, A R YavariAbstract:In present work we report the synthesis of nanoporous surface using a copper-based alloy via leaching the less noble element-rich phase out of nanostructured ternary Cu–Hf–Zr alloys. The removal of Hf and Zr by mixed acid etchants in the Chill-Zone region of rapidly solidified ingots leads to the formation of a nano-roughened surface layer constituted of copper. The average pore and grain size of the obtained structure were shown to be less than 100 nm and 50 nm respectively.
Alberto Moreira Jorge - One of the best experts on this subject based on the ideXlab platform.
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fabrication of nanoporous copper surface by leaching of Chill Zone cu zr hf alloys
Scripta Materialia, 2015Co-Authors: Daria Barsuk, Konstantinos Georgarakis, Min Zhang, N T Panagiotopoulos, Alberto Moreira Jorge, A R YavariAbstract:In present work we report the synthesis of nanoporous surface using a copper-based alloy via leaching the less noble element-rich phase out of nanostructured ternary Cu–Hf–Zr alloys. The removal of Hf and Zr by mixed acid etchants in the Chill-Zone region of rapidly solidified ingots leads to the formation of a nano-roughened surface layer constituted of copper. The average pore and grain size of the obtained structure were shown to be less than 100 nm and 50 nm respectively.