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15 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Comparison of structures of gas atomized and of emulsified highly undercooled Ni-Sn alloy droplets

A comparison is made of microstructures of droplets of Ni-Sn alloys rapidly solidified by gas atomization and in a glass emulsifying medium. Cooling rate of the gas atomized particles ranged from 10 to the 3rd to 10 to the 6th K/s depending on droplet diameter (20-230 microns). In the hypoeutectic alloy studied, /Ni-(25 wt pct Sn)/, most particles showed a dendritic structure. These same particles, melted and resolidified in a glass medium using DTA (Differential Thermal Analysis), showed undercoolings up to 280 K: the structures were dendritic at low undercoolings and nondendritic at undercoolings above 220 K. It is concluded that the gas atomized particles exhibited little or no undercooling before nucleation; the solidification time of the undercooled emulsified droplets is substantially less than that of gas atomized droplets, and the undercooling required to achieve nondendritic structure depends on sample size.

Yamamoto, M.↗
NASA NTRS1985

Rapid solidification of levitation melted Ni-Sn alloy droplets with high undercooling

Experimental results obtained by high-speed optical temperature sensing for the rapid solidification of highly undercooled, levitation-melted Ni-Sn alloy droplets are presented. These data suggest a solidification model proceeding according to overlapping steps: (1) dendritic growth within the bulk undercooled melt, (2) continued recalescence as supersaturation of the interdendritic liquid dissipates, (3) fine-scale remelting within the dendrites, (4) ripening of the fine structure, and (5) solidification of remaining liquid at the end of recalescence.

Shiohara, Yuh↗
NASA NTRS1987

Solidification of undercooled Ni-Sn eutectic alloy under microgravity conditions in the Space Shuttle

The Space Shuttle Columbia carried an Alloy Undercooling Experiment on its STS 61-C mission in January, 1986. The experiment was performed in an electromagnetic levitator. A sample of Ni-32.5 wt pct Sn eutectic was melted and solidified under microgravity conditions in the Space Shuttle. The specimen achieved only a fairly small undercooling, probably less than 30 K. The specimen was examined by optical and scanning electron microscopy. The surface and cross-sectional microstructures were primarily composed of normal lamellar eutectic, but showed several interesting features, including an apparent surface nucleation site, curved dendrites with nonorthogonal secondary arms, dendrite fragments with extremely fine arm spacing, submicron precipitates, and faceted crystals. The results of the space experiment are presented and compared with ground-based results obtained with the same alloy.

Piccone, T. J.↗
DOE OSTI2020

In situ and ex situ studies of anomalous eutectic formation in undercooled Ni–Sn alloys

Anomalous eutectic formation in undercooled Ni-Sn alloys was investigated by in situ X-ray diffraction and ex situ remelting and annealing experiments. Dynamic recrystallization and partial remelting of primary solids followed by repeated nucleation and growth of eutectic grains in the mushy zone were revealed by time-resolved X-ray diffraction. Ex situ experiments demonstrated that partial remelting of near-equilibrium solidified alloys of eutectic or near-eutectic composition can convert regular lamellar eutectic into anomalous eutectic, whereas high-temperature annealing of splat-quenched alloys of similar composition can convert eutectic or two-phase dendrites into anomalous eutectic. It is concluded that compared to ripening in solid-states, partial remelting of eutectic or two-phase dendrites in a mushy zone provides a more realistic mechanism for anomalous eutectic formation in undercooled solidification of Ni-Sn eutectic alloys. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Crystal growth↗
NASA NTRS1984

Structure and recalescence behavior of undercooled nickel-tin alloys

The effects of undercooling on the thermal behavior and structure of Ni-Sn alloys are investigated. Hypoeutectic (Ni-25 wt pct Sn) and eutectic (Ni-32.5 wt pct Sn) compositions of the Ni-Sn alloy were undercooled using a levitation melting with glass encasement technique, and the recalescence of these alloys was measured using a high speed temperature sensing device and a digital oscilloscope. It is observed that in both samples the total solidification and recalescence times decrease with increasing undercooling; the volume fraction of normal lamellar eutectic decreases with increasing undercooling; and in the hypoeutectic sample, the morphology of the primary phase changes from dendritic to spherical with increasing undercooling.

Wu, Yanzhong↗
NASA NTRS1984

Bulk undercooling

Bulk undercooling methods and procedures will first be reviewed. Measurement of various parameters which are necessary to understand the solidification mechanism during and after recalescence will be discussed. During recalescence of levitated, glass-encased large droplets (5 to 8 mm diam) high speed temperature sensing devices coupled with a rapid response oscilloscope are now being used at MIT to measure local thermal behavior in hypoeutectic and eutectic binary Ni-Sn alloys. Dendrite tip velocities were measured by various investigators using thermal sensors or high speed cinematography. The confirmation of the validity of solidification models of bulk-undercooled melts is made difficult by the fineness of the final microstructure, the ultra-rapid evolution of the solidifying system which makes measurements very awkward, and the continuous modification of the microstructure which formed during recalescence because of precipitation, remelting and rapid coarsening.

Kattamis, T. Z.↗
NASA NTRS1987

Dendritic growth of undercooled nickel-tin. I, II

A comparison is made between high speed cinematography and optical temperature measurements of the solidification of an undercooled Ni-25 wt pct Sn alloy. The first part of this study notes that solidification during the recalescence period at all undercoolings studied occurred in the form of a dendritelike front moving across the sample surface, and that the growth velocities observed agree with calculation results for the dendrite growth model of Lipton et al. (1986); it is concluded that the coarse structure observed comprises an array of much finer, solute-controlled dendrites. In the second part, attention is given to the solidification of levitated metal samples within a transparent glass medium for the cases of two undercooled Ni-Sn alloys, one of which is eutectic and another hypoeutectic. The data obtained suggest a solidification model involving dendrites of very fine structure growing into the melt at temperatures near the bulk undercooling temperature.

Wu, Y.↗
NASA NTRS1988

Dendritic growth and structure of undercooled nickel base alloys

The principal objectives of this overall investigation are to: study means for obtaining high undercooling in levitation melted droplets, and study structures produced upon the solidification of these undercooled specimens. Thermal measurements are made of the undercooling, and of the rapid recalescence, to develop an understanding of the solidification mechanism. Comparison of results is made with the modeling studies. Characterization and metallographic work is done to gain an understanding of the relationship between rapid solidification variables and the structures so produced. In ground based work to date, solidification of undercooled Ni-25 wt percent Sn alloy was observed by high-speed cinematography and the results compared with optical temperature measurements. Also in ground based work, high-speed optical temperature measurements were made of the solidification behavior of levitated metal samples within a transparent glass medium. Two undercooled Ni-Sn alloys were examined. Measurements were carried out on samples at undercoolings up to 330 K. Microstructures of samples produced in ground based work were determined by optical metallography and by SEM, and microsegregation by electron microprobe measurements. A series of flight tests were planned to conduct experiments similar to the ground based experiments. The Space Shuttle Columbia carried an alloy undercooled experiment in the STS 61-C mission in January 1986. A sample of Ni-32.5 wt percent Sn eutectic was melted and solidified under microgravity conditions.

Flemings, M. C.↗
DOE OSTI2020

Materials Data on Ni3Sn by Materials Project

Ni3Sn crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ni is bonded to eight equivalent Ni and four equivalent Sn atoms to form NiNi8Sn4 cuboctahedra that share corners with four equivalent SnNi12 cuboctahedra, corners with fourteen equivalent NiNi8Sn4 cuboctahedra, edges with six equivalent SnNi12 cuboctahedra, edges with twelve equivalent NiNi8Sn4 cuboctahedra, faces with four equivalent SnNi12 cuboctahedra, and faces with sixteen equivalent NiNi8Sn4 cuboctahedra. There are a spread of Ni–Ni bond distances ranging from 2.54–2.76 Å. All Ni–Sn bond lengths are 2.65 Å. Sn is bonded to twelve equivalent Ni atoms to form SnNi12 cuboctahedra that share corners with six equivalent SnNi12 cuboctahedra, corners with twelve equivalent NiNi8Sn4 cuboctahedra, edges with eighteen equivalent NiNi8Sn4 cuboctahedra, faces with eight equivalent SnNi12 cuboctahedra, and faces with twelve equivalent NiNi8Sn4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ni3Sn by Materials Project

Ni3Sn is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Ni is bonded to eight equivalent Ni and four equivalent Sn atoms to form NiNi8Sn4 cuboctahedra that share corners with twelve equivalent NiNi8Sn4 cuboctahedra, edges with eight equivalent SnNi12 cuboctahedra, edges with sixteen equivalent NiNi8Sn4 cuboctahedra, faces with four equivalent SnNi12 cuboctahedra, and faces with fourteen equivalent NiNi8Sn4 cuboctahedra. All Ni–Ni bond lengths are 2.63 Å. All Ni–Sn bond lengths are 2.63 Å. Sn is bonded to twelve equivalent Ni atoms to form SnNi12 cuboctahedra that share corners with twelve equivalent SnNi12 cuboctahedra, edges with twenty-four equivalent NiNi8Sn4 cuboctahedra, faces with six equivalent SnNi12 cuboctahedra, and faces with twelve equivalent NiNi8Sn4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ni3Sn by Materials Project

Ni3Sn is alpha bismuth trifluoride structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. there are two inequivalent Ni sites. In the first Ni site, Ni is bonded in a distorted body-centered cubic geometry to eight equivalent Ni and six equivalent Sn atoms. All Ni–Ni bond lengths are 2.56 Å. All Ni–Sn bond lengths are 2.96 Å. In the second Ni site, Ni is bonded in a distorted body-centered cubic geometry to four equivalent Ni and four equivalent Sn atoms. All Ni–Sn bond lengths are 2.56 Å. Sn is bonded in a distorted body-centered cubic geometry to fourteen Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ni3Sn4 by Materials Project

Ni3Sn4 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Ni sites. In the first Ni site, Ni is bonded in a 6-coordinate geometry to two equivalent Ni and six Sn atoms. Both Ni–Ni bond lengths are 2.78 Å. There are two shorter (2.55 Å) and four longer (2.63 Å) Ni–Sn bond lengths. In the second Ni site, Ni is bonded in a 10-coordinate geometry to three Ni and seven Sn atoms. Both Ni–Ni bond lengths are 2.67 Å. There are a spread of Ni–Sn bond distances ranging from 2.67–2.77 Å. There are two inequivalent Sn sites. In the first Sn site, Sn is bonded in a 6-coordinate geometry to five Ni and one Sn atom. The Sn–Sn bond length is 2.97 Å. In the second Sn site, Sn is bonded in a 5-coordinate geometry to five Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ni3Sn2 by Materials Project

Ni3Sn2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Ni sites. In the first Ni site, Ni is bonded in a 5-coordinate geometry to six equivalent Ni and five Sn atoms. There are four shorter (2.65 Å) and two longer (2.72 Å) Ni–Ni bond lengths. There are a spread of Ni–Sn bond distances ranging from 2.50–2.61 Å. In the second Ni site, Ni is bonded in a 11-coordinate geometry to five Ni and six Sn atoms. There are one shorter (2.56 Å) and one longer (2.66 Å) Ni–Ni bond lengths. There are a spread of Ni–Sn bond distances ranging from 2.61–2.91 Å. There are two inequivalent Sn sites. In the first Sn site, Sn is bonded in a 10-coordinate geometry to eight Ni and two equivalent Sn atoms. Both Sn–Sn bond lengths are 3.18 Å. In the second Sn site, Sn is bonded in a 9-coordinate geometry to nine Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NiSn by Materials Project

NiSn crystallizes in the orthorhombic Pbam space group. The structure is three-dimensional. there are five inequivalent Ni sites. In the first Ni site, Ni is bonded in a 11-coordinate geometry to four Ni and seven Sn atoms. There are a spread of Ni–Ni bond distances ranging from 2.68–3.03 Å. There are a spread of Ni–Sn bond distances ranging from 2.62–2.86 Å. In the second Ni site, Ni is bonded in a 9-coordinate geometry to three Ni and six Sn atoms. There are two shorter (2.63 Å) and one longer (2.82 Å) Ni–Ni bond lengths. There are a spread of Ni–Sn bond distances ranging from 2.57–2.66 Å. In the third Ni site, Ni is bonded in a 10-coordinate geometry to three Ni and seven Sn atoms. There are a spread of Ni–Sn bond distances ranging from 2.65–2.84 Å. In the fourth Ni site, Ni is bonded in a 8-coordinate geometry to four Ni and six Sn atoms. Both Ni–Ni bond lengths are 2.61 Å. There are two shorter (2.54 Å) and four longer (2.62 Å) Ni–Sn bond lengths. In the fifth Ni site, Ni is bonded in a 10-coordinate geometry to four Ni and six Sn atoms. There are four shorter (2.65 Å) and two longer (2.68 Å) Ni–Sn bond lengths. There are four inequivalent Sn sites. In the first Sn site, Sn is bonded in a 7-coordinate geometry to seven Ni atoms. In the second Sn site, Sn is bonded in a 6-coordinate geometry to six Ni atoms. In the third Sn site, Sn is bonded in a 6-coordinate geometry to six Ni atoms. In the fourth Sn site, Sn is bonded in a 7-coordinate geometry to seven Ni atoms.

36 MATERIALS SCIENCE↗