Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Al-Ge”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Systematic discovery of new nano-scale metastable intermetallic eutectic phases in laser rapid solidified Aluminum-Germanium alloy

Laser surface remelting of as-cast Al-Ge eutectic alloy is shown to produce ultrafine lamellar eutectic morphology with interlamellar spacing refined up to ∼60 nm and composed of FCC Al solid solution and unusual Al x Ge y intermetallic phases that do not form during near-equilibrium solidification. The microstructures are characterized and analyzed using a combination of selected area electron diffraction, high-resolution scanning transmission electron microscopy, energy dispersive X-ray spectroscopy to obtain high-resolution elemental maps, and atomistic modeling using density functional theory followed by atomic-scale image simulation. Depending on the local solidification conditions, the crystallography of the Al x Ge y intermetallic phases in the eutectic microstructure is either monoclinic (C 2/c) or monoclinic (P 2 1 ), with high densities of defects in both cases. This is in sharp contrast to the as-cast alloys that showed nominally pure Al and Ge phases with significant solute partitioning and equilibrium FCC and diamond cubic crystal structures, respectively. Corresponding kinetic phase diagrams are proposed to interpret the evolution of nano-lamellar eutectic morphologies with equilibrium Al and metastable Al x Ge y phases, and to explain increased solid solubility in the Al phases manifested by precipitation of ultrafine clusters of Ge. Furthermore, the reasons for the formation of these metastable eutectics under laser rapid solidification are discussed from the perspective of the competitive growth criterion.

Al-Ge eutectic↗
NASA NTRS1985

The volume change during solidification

The liquid-solid phase transformation of solidifying metallic melts is accompanied by a volume change Delta-Vm. This volume change produces a gravity-independent microscopic flow near the solidification front. In a ground-based laboratory, solidification processes are also affected by convection due to temperature and concentration gradients. A quantitative evaluation of the effects of these flows on the formation of structure requires reproducible values of Delta-Vm. Alloys with Delta-Vm = 0 would be best suited for such an evaluation, while alloys with a constant value for Delta-Vm are still usable. Another requirement is related to a solidus-liquidus interval which is as small as possible. One-phase alloys, which would be particularly well suited, could not be found. For these reasons, alloys which solidify in two phases, as for example eutectics, have been considered, taking into account the Al-Ge system. Attention is given to the volume change at the melting point, the measurement of this change, the volume change at solidification, and applications to terrestrial technology.

Rittich, M.↗
DOE OSTI2020

Materials Data on Al6Ge5 by Materials Project

Al6Ge5 crystallizes in the trigonal R-3c space group. The structure is three-dimensional. Al is bonded in a 4-coordinate geometry to four Ge atoms. There are a spread of Al–Ge bond distances ranging from 2.51–2.65 Å. There are two inequivalent Ge sites. In the first Ge site, Ge is bonded to three equivalent Al and one Ge atom to form distorted corner-sharing GeAl3Ge tetrahedra. The Ge–Ge bond length is 2.51 Å. In the second Ge site, Ge is bonded to six equivalent Al atoms to form distorted GeAl6 pentagonal pyramids that share corners with four equivalent GeAl6 pentagonal pyramids, corners with six equivalent GeAl3Ge tetrahedra, and edges with four equivalent GeAl6 pentagonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AlGe3 by Materials Project

AlGe3 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Al is bonded to twelve Ge atoms to form AlGe12 cuboctahedra that share corners with four equivalent AlGe12 cuboctahedra, edges with eight equivalent AlGe12 cuboctahedra, edges with sixteen equivalent GeAl4Ge8 cuboctahedra, faces with four equivalent AlGe12 cuboctahedra, and faces with eight equivalent GeAl4Ge8 cuboctahedra. There are four shorter (2.86 Å) and eight longer (3.05 Å) Al–Ge bond lengths. There are two inequivalent Ge sites. In the first Ge site, Ge is bonded to four equivalent Al and eight Ge atoms to form distorted GeAl4Ge8 cuboctahedra that share corners with twelve equivalent GeAl4Ge8 cuboctahedra, edges with eight equivalent AlGe12 cuboctahedra, edges with eight equivalent GeAl4Ge8 cuboctahedra, faces with four equivalent AlGe12 cuboctahedra, and faces with ten equivalent GeAl4Ge8 cuboctahedra. There are four shorter (2.86 Å) and four longer (3.05 Å) Ge–Ge bond lengths. In the second Ge site, Ge is bonded in a square co-planar geometry to four equivalent Al and eight equivalent Ge atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Al3Ge by Materials Project

Al3Ge is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent Al sites. In the first Al site, Al is bonded to eight Al and four equivalent Ge atoms to form distorted AlAl8Ge4 cuboctahedra that share corners with twelve equivalent AlAl8Ge4 cuboctahedra, edges with eight equivalent GeAl12 cuboctahedra, edges with sixteen AlAl8Ge4 cuboctahedra, faces with four equivalent GeAl12 cuboctahedra, and faces with fourteen AlAl8Ge4 cuboctahedra. There are four shorter (2.89 Å) and four longer (2.90 Å) Al–Al bond lengths. All Al–Ge bond lengths are 2.89 Å. In the second Al site, Al is bonded to eight equivalent Al and four equivalent Ge atoms to form AlAl8Ge4 cuboctahedra that share corners with four equivalent AlAl8Ge4 cuboctahedra, corners with eight equivalent GeAl12 cuboctahedra, edges with twenty-four AlAl8Ge4 cuboctahedra, faces with six equivalent GeAl12 cuboctahedra, and faces with twelve AlAl8Ge4 cuboctahedra. All Al–Ge bond lengths are 2.90 Å. Ge is bonded to twelve Al atoms to form GeAl12 cuboctahedra that share corners with four equivalent GeAl12 cuboctahedra, corners with eight equivalent AlAl8Ge4 cuboctahedra, edges with eight equivalent GeAl12 cuboctahedra, edges with sixteen equivalent AlAl8Ge4 cuboctahedra, faces with four equivalent GeAl12 cuboctahedra, and faces with fourteen AlAl8Ge4 cuboctahedra.

36 MATERIALS SCIENCE↗