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13 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Analysis of X-Ray Microradiographs of Al-Au Interface Quench Profile using Modeling of Solidification Including Double-Diffusion and Convection in the Melt

Experimental data on Al-0.8Au horizontal solidification of a 1 mm thick specimen in a BN crucible shows the effect of growth rate on the solidification interface shape. For translation rates below 0.5 micron/s the interface maintains a plain and flat shape. When the translation rate is 3 to 5 micron/s or more, the interface appearance changes to two planar zones, with the zone closer to the bottom having higher inclination. The interface shapes were measured by first quenching in place during growth. X-ray microscopy shows the interface shape within the quenched sample by viewing through the side of the specimen. In order to provide theoretical explanation of the phenomena, numerical modeling was undertaken using finite element code FIDAP. Double diffusion convection in Al-0.8Au melt and crystal-melt interface curvature during directional solidification was analyzed numerically. Actual thermophysical properties of Al-0.8Au including the binary Al-Au phase diagram were used. Although convection in the sample is weak, for the slower translation rate convection and diffusion is sufficient for the redistribution of initial compositional stratification caused by gravity. When translation rate is raised, neither convection nor diffusion can provide proper mixing so that solidification temperatures differ significantly near the bottom within the bulk of the sample. As a result, the solid-liquid interface appears to have two planar zones with different inclination.

Bune, Andris V.↗
NASA NTRS1997

Real Time Characterization of Solid/Liquid Interfaces During Directional Solidification

A X-Ray Transmission Microscope (XTM) has been developed to observe in real time and in-situ solidification phenomenon at the solid/liquid interface. Recent improvements in the horizontal Bridgman furnace design provides real-time magnification (during solidification) up to 12OX. The increased magnification has enabled for the first time the XTM imaging of real-time growth of fibers and particles with diameters of 3-6 micrometers. Further, morphological transitions from planar to cellular interfaces have also been imaged. Results from recent XTM studies on Al-Bi monotectic system, Al-Au eutectic system and interaction of insoluble particles with s/I interfaces in composite materials will be presented. An important parameter during directional solidification of molten metal is the interfacial undercooling. This parameter controls the morphology and composition at the s/I interface. Conventional probes such as thermocouples, due to their large bead size, do not have sufficient resolution for measuring undercooling at the s/I interface. Further, the intrusive nature of the thermocouples also distorts the thermal field at the s/I interface. To overcome these inherent problems we have recently developed a compact furnace which utilizes a non-intrusive technique (Seebeck) to measure undercooling at the S/I interface. Recent interfacial undercooling measurements obtained for the Pb-Sn system will be presented. The Seebeck measurement furnace in the future will be integrated with the XTM to provide the most comprehensive tool for real time characterization of s/I interfaces during solidification.

Sen, S.↗
NASA NTRS1999

A Real Time Investigation of Morphological Evolution During Solidification of Different Alloy Systems

Solidification phenomenon which occur at the solid/liquid (s/I) interface play a major role in the determination of structure and hence the technologically important properties of a casting. However, metals being opaque, conclusions related to several important phenomenon such as boundary layer thickness, morphological evolution, and eutectic and cell spacing are deduced from quenching experiments and subsequent post solidification metallographic analysis. Consequently, limited information is obtained about the dynamics of the process. This paper will discuss the recent efforts at the Space Science Laboratory, NASA Marshall Space Flight Center, to view and quantify in-situ and in real time the dynamics of the solidification process and to measure interfacial undercooling. First, a high resolution x-ray transmission microscope (XTM) has been developed to monitor fundamental interfacial phenomena during directional solidification of metals and alloys. The XTM operates in the range of 10-100 KeV and through projection is capable of achieving magnification of up to 16OX. Secondly, an innovative collapsible furnace has been designed to quantify interfacial undercooling by measuring the temperature of a moving s/I interface in reference to a fixed s/l interface. This measurement technique is non-intrusive in nature and is based on the Seebeck principle. In this paper real time results obtained to characterize the dynamics of irregular eutectic spacing will be presented. As an example fiber to lamella or plate transition in the Al-Al2Au eutectic system will be discussed. Further, a resolution limit of 25 micron has permitted viewing in real time morphological instability and cellular growth in Al-Au and Al-Ag systems. Simultaneously, a systematic investigation has been carried out to measure interfacial undercooling for Pb-1 wt.% Sn at and near the marginal stability regime. In conjunction with the XTM observations this study attempts to validate existing relationships between undercooling and growth velocity during plane front growth, marginal stability regime, and stable cellular growth.

Sen, S.↗
DOE OSTI2020

Materials Data on AlAu by Materials Project

AuAl is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Au is bonded in a body-centered cubic geometry to eight equivalent Al atoms. All Au–Al bond lengths are 2.79 Å. Al is bonded in a body-centered cubic geometry to eight equivalent Au atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AlAu by Materials Project

AuAl is Modderite structured and crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. there are two inequivalent Au sites. In the first Au site, Au is bonded in a 6-coordinate geometry to six Al atoms. There are a spread of Au–Al bond distances ranging from 2.64–2.76 Å. In the second Au site, Au is bonded in a 6-coordinate geometry to six Al atoms. There are a spread of Au–Al bond distances ranging from 2.62–2.76 Å. There are two inequivalent Al sites. In the first Al site, Al is bonded in a 6-coordinate geometry to six Au atoms. In the second Al site, Al is bonded in a 6-coordinate geometry to six Au atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AlAu4 by Materials Project

Au4Al crystallizes in the cubic P2_13 space group. The structure is three-dimensional. there are two inequivalent Au sites. In the first Au site, Au is bonded in a 12-coordinate geometry to nine Au and three equivalent Al atoms. There are a spread of Au–Au bond distances ranging from 2.90–3.01 Å. There are a spread of Au–Al bond distances ranging from 2.76–3.11 Å. In the second Au site, Au is bonded in a distorted trigonal planar geometry to nine equivalent Au and three equivalent Al atoms. All Au–Al bond lengths are 2.63 Å. Al is bonded to twelve Au atoms to form a mixture of distorted face and corner-sharing AlAu12 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Al2Au by Materials Project

AuAl2 is Fluorite structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Au is bonded in a body-centered cubic geometry to eight equivalent Al atoms. All Au–Al bond lengths are 2.63 Å. Al is bonded to four equivalent Au atoms to form a mixture of corner and edge-sharing AlAu4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AlAu2 by Materials Project

Au2Al crystallizes in the orthorhombic Pnnm space group. The structure is three-dimensional. there are five inequivalent Au sites. In the first Au site, Au is bonded in a 4-coordinate geometry to five Al atoms. There are a spread of Au–Al bond distances ranging from 2.75–3.12 Å. In the second Au site, Au is bonded in a 4-coordinate geometry to four Al atoms. There are two shorter (2.70 Å) and two longer (2.74 Å) Au–Al bond lengths. In the third Au site, Au is bonded in a 5-coordinate geometry to five Al atoms. There are a spread of Au–Al bond distances ranging from 2.69–2.82 Å. In the fourth Au site, Au is bonded in a 4-coordinate geometry to four Al atoms. All Au–Al bond lengths are 2.73 Å. In the fifth Au site, Au is bonded in a 5-coordinate geometry to five Al atoms. There are a spread of Au–Al bond distances ranging from 2.79–2.85 Å. There are three inequivalent Al sites. In the first Al site, Al is bonded in a 8-coordinate geometry to ten Au atoms. In the second Al site, Al is bonded in a distorted q6 geometry to nine Au atoms. In the third Al site, Al is bonded in a distorted q6 geometry to nine Au atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AlAu2 by Materials Project

Au2Al crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Au sites. In the first Au site, Au is bonded in a 5-coordinate geometry to five equivalent Al atoms. There are a spread of Au–Al bond distances ranging from 2.71–2.89 Å. In the second Au site, Au is bonded in a 4-coordinate geometry to four equivalent Al atoms. There are two shorter (2.66 Å) and two longer (2.72 Å) Au–Al bond lengths. Al is bonded in a distorted q6 geometry to nine Au atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AlAu2 by Materials Project

Au2Al crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Au is bonded in a 10-coordinate geometry to five equivalent Al atoms. There are four shorter (2.76 Å) and one longer (3.09 Å) Au–Al bond lengths. Al is bonded in a 10-coordinate geometry to ten equivalent Au atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Al3Au by Materials Project

AuAl3 is Uranium Silicide-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Au is bonded to twelve Al atoms to form a mixture of corner, edge, and face-sharing AuAl12 cuboctahedra. There are four shorter (2.86 Å) and eight longer (2.87 Å) Au–Al bond lengths. There are two inequivalent Al sites. In the first Al site, Al is bonded to four equivalent Au atoms to form a mixture of distorted corner and edge-sharing AlAu4 cuboctahedra. In the second Al site, Al is bonded in a distorted square co-planar geometry to four equivalent Au atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AlAu4 by Materials Project

Au4Al crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Au sites. In the first Au site, Au is bonded in a 3-coordinate geometry to three equivalent Au and three equivalent Al atoms. There are one shorter (2.96 Å) and two longer (2.97 Å) Au–Au bond lengths. There are one shorter (2.58 Å) and two longer (2.68 Å) Au–Al bond lengths. In the second Au site, Au is bonded in a distorted q6 geometry to ten Au atoms. There are a spread of Au–Au bond distances ranging from 2.88–2.97 Å. Al is bonded in a 6-coordinate geometry to six equivalent Au atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AlAu3 by Materials Project

Au3Al is Uranium Silicide-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Au1- is bonded in a distorted see-saw-like geometry to four equivalent Al3+ atoms. There are two shorter (2.89 Å) and two longer (2.91 Å) Au–Al bond lengths. Al3+ is bonded to twelve equivalent Au1- atoms to form a mixture of face and corner-sharing AlAu12 cuboctahedra.

36 MATERIALS SCIENCE↗