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A K Dahle - One of the best experts on this subject based on the ideXlab platform.
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determination of strontium segregation in modified hypoeutectic al si alloy by micro x ray fluorescence analysis
Scripta Materialia, 2006Co-Authors: Kazuhiro Nogita, Hideyuki Yasuda, Kazuki Yoshida, Kentaro Uesugi, Akihisa Takeuchi, Yoshio Suzuki, A K DahleAbstract:Analysis of intra- and inter-phase distribution of modifying elements in aluminium-Silicon Alloys is difficult due to the low concentrations used. This research utilises a mu-XRF (X-ray fluorescence) technique at the SPring-8 synchrotron radiation facility X-ray source and reveals that the modifying element strontium segregates exclusively to the eutectic Silicon phase and the distribution of strontium within this phase is relatively homogeneous. This has important implications for the fundamental mechanisms of eutectic modification in hypoeutectic aluminium-Silicon Alloys. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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eutectic nucleation in al si Alloys
Acta Materialia, 2004Co-Authors: S D Mcdonald, Kazuhiro Nogita, A K DahleAbstract:In addition to a change in Silicon morphology, modification of aluminium-Silicon Alloys with strontium or sodium increases the size of the eutectic grains. To determine the mechanism responsible, eutectic solidification in commercial purity and ultra-high purity aluminium-Silicon Alloys, with and without strontium additions, was examined by a quenching technique. In the commercial unmodified alloy, nucleation was prolific while in the high-purity unmodified alloy few eutectic grains nucleated. The addition of strontium to the commercial alloy reduced the number of eutectic grains that nucleated. Addition of strontium to the high-purity alloy did not significantly alter nucleation. It is concluded that commercial purity Alloys contain a large number of potent nuclei that are susceptible to poisoning by impurity modification. The flake-to-fibre transition that occurs with impurity modification is shown to be independent of any change in eutectic nucleation mode and frequency.
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eutectic grains in unmodified and strontium modified hypoeutectic aluminum Silicon Alloys
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2004Co-Authors: S D Mcdonald, A K Dahle, J A Taylor, D H StjohnAbstract:Additions of strontium to hypoeutectic aluminum-Silicon Alloys modify the morphology of the eutectic Silicon phase from a coarse platelike structure to a fine fibrous structure. Thermal analysis, interrupted solidification, and microstructural examination of sand castings in this work revealed that, in addition to a change in Silicon morphology, modification with strontium also causes an increase in the size of eutectic grains. The eutectic grain size increases because fewer grains nucleate, possibly due to poisoning of the phosphorus-based nucleants, that are active in the unmodified alloy. A simple growth model is developed to estimate the interface velocity during solidification of a eutectic grain. The model confirms, independent of microstructural observations, that the addition of 100 ppm strontium increases the eutectic grain size by at least an order of magnitude compared with the equivalent unmodified alloy. The model predicts that the growth velocity varies significantly during eutectic growth. At low strontium levels, these variations may be sufficient to cause transitions between flake and fibrous Silicon morphologies depending on the casting conditions. The model can be used to rationally interpret the eutectic grain structure and Silicon morphology of fully solidified aluminum-Silicon castings and, when coupled with reliable thermal data, can be used to estimate the eutectic grain size.
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columnar to equiaxed transition of eutectic in hypoeutectic aluminium Silicon Alloys
Acta Materialia, 2002Co-Authors: G Heiberg, Kazuhiro Nogita, A K Dahle, Lars ArnbergAbstract:Directional solidification of unmodified and strontium modified binary, high-purity aluminium-7 wt% Silicon and commercial A356 Alloys has been carried out to investigate the mechanism of eutectic solidification. The microstructure of the eutectic growth inter-face was investigated with optical microscopy and Electron Backscattering Diffraction (EBSD). In the commercial Alloys, the eutectic solidification inter-face extends in the growth direction and creates a eutectic mushy zone. A planar eutectic growth front is observed in the high-purity Alloys. The eutectic aluminium has mainly the same crystallographic orientation as the dendrites in the unmodified Alloys and the strontium modified high-purity alloy. A more complex eutectic grain structure is found in the strontium modified commercial alloy. A mechanism involving constitutional undercooling and a columnar to equiaxed transition explains the differences between pure and commercial Alloys. It is probably caused by the segregation of iron and magnesium and the activation of nucleants in the commercial alloy. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
D K Dwivedi - One of the best experts on this subject based on the ideXlab platform.
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adhesive wear behaviour of cast aluminium Silicon Alloys overview
Materials & Design, 2010Co-Authors: D K DwivediAbstract:Abstract This paper describes the various technological aspects related to adhesive wear of cast aluminium–Silicon (Al–Si) Alloys. Number of hypothesis and theories proposed in the last two decades in order to explain the different phenomenon related with wear and friction, and influence of test parameters (such as load, sliding speed, counter-surface) and work material properties (like mechanical and metallurgical) on tribological behaviour of aluminium–Silicon Alloys have been presented and discussed.
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adhesive wear of stir cast hypereutectic al si mg alloy under reciprocating sliding conditions
Wear, 2009Co-Authors: T V S Reddy, D K Dwivedi, N K JainAbstract:Abstract This paper describes an attempt to enhance the wear properties of hypereutectic cast aluminium–Silicon Alloys produced by semi-solid metal (SSM) processing technique. The rheological experiments on SSM slurries were performed under continuous cooling condition from liquidus temperature. Wear characteristics of alloy under investigation were studied using pin on flat wear system over a range of normal load (10–40 N) at constant average sliding speed (0.2 m/s) against cast iron and stainless steel counter surface. Stir cast alloy showed lesser weight loss compared to conventional cast alloy. Stir cast and conventional cast Alloys showed higher weight loss against the stainless steel as compared to that against cast iron counter surface. Optical microscopy of the conventional cast and stir cast hypereutectic alloy has shown that stir casting causes refinement of primary Silicon particles and modification of eutectic Silicon compared to conventional cast alloy. The scanning electron microscopy of wear surfaces was carried out to investigate the mode of wear.
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wear behaviour of cast hypereutectic aluminium Silicon Alloys
Materials & Design, 2006Co-Authors: D K DwivediAbstract:Abstract In the present paper, influence of alloying elements on wear behaviour of binary (Al–17%Si) and multi-component (Al–17Si–0.8Ni–0.6Mg–1.2Cu–0.6Fe) cast hypereutectic aluminium Alloys has been reported. Experimental Alloys were prepared via foundry technique. Wear behaviour of Al–17Si and Al–17Si–X {X = Ni, Cu, Mg, Fe} Alloys was studied using pin on disc (ASTM: G99) type of friction and wear testing machine. Dry sliding wear tests were performed at various sliding speeds (0.2–4.0 m/s) and contact loads (10–30 N) against hardened ground steel disc (hardness 60 HRC). It was observed that the addition of alloying element not only reduces the wear rate in mild oxidative wear condition but also increases the transition load. Temperature of wear pin near the sliding surface was measured and it was related to wear and friction behaviour of experimental Alloys. Increase in hardness was also noticed due to alloying. SEM study of wear surface and wear debris was conducted to analyse the mode of wear and wear mechanism.
Kazuhiro Nogita - One of the best experts on this subject based on the ideXlab platform.
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determination of strontium segregation in modified hypoeutectic al si alloy by micro x ray fluorescence analysis
Scripta Materialia, 2006Co-Authors: Kazuhiro Nogita, Hideyuki Yasuda, Kazuki Yoshida, Kentaro Uesugi, Akihisa Takeuchi, Yoshio Suzuki, A K DahleAbstract:Analysis of intra- and inter-phase distribution of modifying elements in aluminium-Silicon Alloys is difficult due to the low concentrations used. This research utilises a mu-XRF (X-ray fluorescence) technique at the SPring-8 synchrotron radiation facility X-ray source and reveals that the modifying element strontium segregates exclusively to the eutectic Silicon phase and the distribution of strontium within this phase is relatively homogeneous. This has important implications for the fundamental mechanisms of eutectic modification in hypoeutectic aluminium-Silicon Alloys. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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eutectic nucleation in al si Alloys
Acta Materialia, 2004Co-Authors: S D Mcdonald, Kazuhiro Nogita, A K DahleAbstract:In addition to a change in Silicon morphology, modification of aluminium-Silicon Alloys with strontium or sodium increases the size of the eutectic grains. To determine the mechanism responsible, eutectic solidification in commercial purity and ultra-high purity aluminium-Silicon Alloys, with and without strontium additions, was examined by a quenching technique. In the commercial unmodified alloy, nucleation was prolific while in the high-purity unmodified alloy few eutectic grains nucleated. The addition of strontium to the commercial alloy reduced the number of eutectic grains that nucleated. Addition of strontium to the high-purity alloy did not significantly alter nucleation. It is concluded that commercial purity Alloys contain a large number of potent nuclei that are susceptible to poisoning by impurity modification. The flake-to-fibre transition that occurs with impurity modification is shown to be independent of any change in eutectic nucleation mode and frequency.
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columnar to equiaxed transition of eutectic in hypoeutectic aluminium Silicon Alloys
Acta Materialia, 2002Co-Authors: G Heiberg, Kazuhiro Nogita, A K Dahle, Lars ArnbergAbstract:Directional solidification of unmodified and strontium modified binary, high-purity aluminium-7 wt% Silicon and commercial A356 Alloys has been carried out to investigate the mechanism of eutectic solidification. The microstructure of the eutectic growth inter-face was investigated with optical microscopy and Electron Backscattering Diffraction (EBSD). In the commercial Alloys, the eutectic solidification inter-face extends in the growth direction and creates a eutectic mushy zone. A planar eutectic growth front is observed in the high-purity Alloys. The eutectic aluminium has mainly the same crystallographic orientation as the dendrites in the unmodified Alloys and the strontium modified high-purity alloy. A more complex eutectic grain structure is found in the strontium modified commercial alloy. A mechanism involving constitutional undercooling and a columnar to equiaxed transition explains the differences between pure and commercial Alloys. It is probably caused by the segregation of iron and magnesium and the activation of nucleants in the commercial alloy. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
Thomas Graule - One of the best experts on this subject based on the ideXlab platform.
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studying the wettability of si and eutectic si zr alloy on carbon and Silicon carbide by sessile drop experiments
Journal of The European Ceramic Society, 2019Co-Authors: Manoj Naikade, Beate Fankhanel, Ludger Weber, Alberto Ortona, M Stelter, Thomas GrauleAbstract:Abstract The contact angles of two different systems, molten Silicon and a eutectic Si-8 at. pct Zr alloy and their evolution over timeon vitreous carbon and polycrystalline Silicon carbide (SiC) substrates were investigated at 1500°C under vacuum, as well as in argon using the sessile drop technique. The contact angle and microstructure of the liquid droplet/solid substrate interface were studied to understand fundamental features of reactive wetting as it pertains to the infiltration process of Silicon and Silicon Alloys into carbon or C/SiC preforms. Both pure Si and theeutectic alloy showed good wettability onvitreous carbon and SiC characterized by equilibrium contact angles between 29° and 39°. Theeutectic alloy showed a higher initial contact angle and slower spreading as compared to that of pure Si. On vitreous carbon bothSilicon and the eutecticalloy formed SiC at the interface, while no reaction was observed on the SiC substrates.
Guillaume Morard - One of the best experts on this subject based on the ideXlab platform.
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high pressure deformation of iron nickel Silicon Alloys and implications for earth s inner core
Journal of Geophysical Research, 2021Co-Authors: Matthew C Brennan, Rebecca A Fischer, Samantha Couper, Lowell Miyagi, Daniele Antonangeli, Guillaume MorardAbstract:Earth’s inner core exhibits strong seismic anisotropy, often attributed to the alignment of hexagonal close-packed iron (hcp-Fe) alloy crystallites with the Earth’s poles. How this alignment developed depends on material properties of the alloy and is important to our understanding of the core’s crystallization history and active geodynamical forcing. Previous studies suggested that hcp-Fe is weak under deep Earth conditions but did not investigate the effects of the lighter elements known to be part of the inner core alloy. Here, we present results from radial X-ray diffraction experiments in a diamond anvil cell that constrain the strength and deformation properties of iron–nickel–Silicon (Fe–Ni–Si) Alloys up to 60 GPa. We also show the results of laser heating to 1650 K to evaluate the effect of temperature. Observed alloy textures suggest different relative activities of the various hcp deformation mechanisms compared to pure Fe, but these textures could still account for the theorized polar alignment. Fe–Ni–Si Alloys are mechanically stronger than Fe and Fe–Ni; extrapolated to inner core conditions, Si-bearing Alloys may be more than an order of magnitude stronger. This enhanced strength proportionally reduces the effectivity of dislocation creep as a deformation mechanism, which may suggest that texture developed during crystallization rather than as the result of post-solidification plastic flow.
