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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Nb5Si3 by Materials Project

Nb5Si3 crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. there are two inequivalent Nb+2.40+ sites. In the first Nb+2.40+ site, Nb+2.40+ is bonded to six Si4- atoms to form NbSi6 octahedra that share corners with six equivalent NbSi6 octahedra, corners with sixteen equivalent NbSi5 trigonal bipyramids, and faces with eight equivalent NbSi5 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 0–52°. There are four shorter (2.60 Å) and two longer (2.99 Å) Nb–Si bond lengths. In the second Nb+2.40+ site, Nb+2.40+ is bonded to five Si4- atoms to form NbSi5 trigonal bipyramids that share corners with four equivalent NbSi6 octahedra, corners with twelve equivalent NbSi5 trigonal bipyramids, edges with seven equivalent NbSi5 trigonal bipyramids, faces with two equivalent NbSi6 octahedra, and a faceface with one NbSi5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 43–64°. There are a spread of Nb–Si bond distances ranging from 2.61–2.74 Å. There are two inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 10-coordinate geometry to ten Nb+2.40+ atoms. In the second Si4- site, Si4- is bonded in a 9-coordinate geometry to eight Nb+2.40+ and one Si4- atom. The Si–Si bond length is 2.41 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb5Si3 by Materials Project

Nb5Si3 crystallizes in the hexagonal P6_3/mcm space group. The structure is three-dimensional. there are two inequivalent Nb+2.40+ sites. In the first Nb+2.40+ site, Nb+2.40+ is bonded to five equivalent Si4- atoms to form distorted NbSi5 trigonal bipyramids that share corners with eight equivalent NbSi6 octahedra, corners with eight equivalent NbSi5 trigonal bipyramids, edges with six equivalent NbSi5 trigonal bipyramids, and faces with four equivalent NbSi6 octahedra. The corner-sharing octahedra tilt angles range from 41–55°. There are a spread of Nb–Si bond distances ranging from 2.61–2.86 Å. In the second Nb+2.40+ site, Nb+2.40+ is bonded to six equivalent Si4- atoms to form distorted NbSi6 octahedra that share corners with six equivalent NbSi6 octahedra, corners with twelve equivalent NbSi5 trigonal bipyramids, edges with three equivalent NbSi6 octahedra, faces with two equivalent NbSi6 octahedra, and faces with six equivalent NbSi5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 35°. All Nb–Si bond lengths are 2.69 Å. Si4- is bonded in a 9-coordinate geometry to nine Nb+2.40+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb5Si3 by Materials Project

Nb5Si3 crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. there are two inequivalent Nb+2.40+ sites. In the first Nb+2.40+ site, Nb+2.40+ is bonded to six Si4- atoms to form distorted NbSi6 pentagonal pyramids that share corners with fifteen equivalent NbSi6 pentagonal pyramids, corners with four equivalent NbSi4 tetrahedra, edges with three equivalent NbSi6 pentagonal pyramids, edges with two equivalent NbSi4 tetrahedra, and faces with seven equivalent NbSi6 pentagonal pyramids. There are a spread of Nb–Si bond distances ranging from 2.66–2.95 Å. In the second Nb+2.40+ site, Nb+2.40+ is bonded to four equivalent Si4- atoms to form NbSi4 tetrahedra that share corners with sixteen equivalent NbSi6 pentagonal pyramids, edges with eight equivalent NbSi6 pentagonal pyramids, and edges with two equivalent NbSi4 tetrahedra. All Nb–Si bond lengths are 2.67 Å. There are two inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 10-coordinate geometry to ten Nb+2.40+ atoms. In the second Si4- site, Si4- is bonded in a 10-coordinate geometry to eight equivalent Nb+2.40+ and two equivalent Si4- atoms. Both Si–Si bond lengths are 2.56 Å.

36 MATERIALS SCIENCE↗
NASA NTRS1991

Containerless processing and rapid solidification of Nb-Si alloys of hypereutectic composition

A combination of bulk undercooling in an electromagnetic levitation apparatus and splat quenching between two copper plates is used to process Nb-Si alloys in order to maximize rapid solidification conditions and minimize the effects of recalescence, with emphasis on the solidification of characteristics of alloys in the 21 to 27 at. pct Si range of composition. SEM and TEM as well as X-ray diffraction are used to characterize the microstructures of the processed samples. In the range of compositions studied, the splat-quenched drops always formed the tetragonal Nb3Si phase directly from the liquid. Drops solidified in the coil were characterized by the presence of the primary intermetallic Nb5Si3 and the absence of both peritectic Nb3Si and the equilibrium eutectic. In these cases, a metastable alpha-Nb + beta-Nb5Si3 eutectic formed. The results are discussed in terms of possible metastable configurations of the Nb-Si phase diagram as well as concepts of nucleation and growth kinetics applied to the Nb3Si and Nb5Si3 intermetallics.

Hofmeister, W. H.↗
NASA NTRS1988

Supercooling effects in faceted eutectic Nb-Si alloys

The effect of melt supercooling on the microstructure of an Nb-58 at. pct Si alloy is investigated experimentally using an electromagnetic levitation apparatus. It is found that, starting with an alloy nominally of eutectic composition, nucleation of Nb5Si3 occurs in the supercooled liquid first. Upon further cooling, the remaining liquid continues to supercool until the second phase, NbSi2 is nucleated, which is commonly accompanied by rapid recalescence. The primary phase exibits a eutectoid-type decomposition. The observations are discussed with reference to the results of quantitative microstructural measurements, compositional and thermal analysis, and preliminary thermodynamic modeling of the phase diagram.

Gokhale, A. B.↗