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9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Al3Ni by Materials Project

Al3Ni is Cementite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ni is bonded in a 9-coordinate geometry to nine Al atoms. There are a spread of Ni–Al bond distances ranging from 2.43–2.70 Å. There are two inequivalent Al sites. In the first Al site, Al is bonded in a 2-coordinate geometry to three equivalent Ni atoms. In the second Al site, Al is bonded in a 3-coordinate geometry to three equivalent Ni atoms.

36 MATERIALS SCIENCE↗
NASA NTRS1976

The influence of growth rate and temperature on high cycle fatigue of Al-Al3Ni

High-cycle fatigue tests have been conducted on specimens of an Al-Al3Ni eutectic alloy, unidirectionally solidified at selected rates from 0.000139 to 0.3 cm/sec. Tests were conducted in air at 298, 458 and 683 K. Room temperature fatigue lives were independent of growth rate at low solidification rates but were markedly improved in samples grown at 0.3 cm/sec. Materials grown at 0.00833 cm/sec exhibited fatigue lives similar to those of the lower growth rates, despite gross misalignment due to cellular growth. The dependence of fatigue life on growth rate at elevated temperatures appears to be due primarily to differences in cyclic creep rates as a result of varying interfiber spacings. Crack initiation and propagation mechanisms were established by metallographic and fractographic examination. Dislocation substructure-fiber interactions were studied by transmission electron microscopy.

Maurer, G. E.↗
DOE OSTI2020

Materials Data on Gd(Al3Ni)3 by Materials Project

GdNi3Al9 crystallizes in the trigonal R32 space group. The structure is three-dimensional. Gd is bonded in a 11-coordinate geometry to six equivalent Ni and eleven Al atoms. There are three shorter (3.29 Å) and three longer (3.30 Å) Gd–Ni bond lengths. There are a spread of Gd–Al bond distances ranging from 3.00–3.17 Å. Ni is bonded in a 8-coordinate geometry to two equivalent Gd and eight Al atoms. There are a spread of Ni–Al bond distances ranging from 2.33–2.63 Å. There are six inequivalent Al sites. In the first Al site, Al is bonded in a distorted trigonal non-coplanar geometry to one Gd, three equivalent Ni, and seven Al atoms. There are a spread of Al–Al bond distances ranging from 2.77–2.84 Å. In the second Al site, Al is bonded in a 2-coordinate geometry to two equivalent Gd, two equivalent Ni, and six Al atoms. There are two shorter (2.63 Å) and four longer (2.81 Å) Al–Al bond lengths. In the third Al site, Al is bonded in a linear geometry to two equivalent Ni and six Al atoms. There are two shorter (2.81 Å) and two longer (2.84 Å) Al–Al bond lengths. In the fourth Al site, Al is bonded in a 3-coordinate geometry to two equivalent Gd, three equivalent Ni, and five Al atoms. There are one shorter (2.71 Å) and one longer (2.78 Å) Al–Al bond lengths. In the fifth Al site, Al is bonded in a distorted trigonal non-coplanar geometry to three equivalent Ni and seven Al atoms. The Al–Al bond length is 2.87 Å. In the sixth Al site, Al is bonded in a distorted trigonal non-coplanar geometry to one Gd, three equivalent Ni, and seven Al atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Er(Al3Ni)3 by Materials Project

ErNi3Al9 crystallizes in the trigonal R32 space group. The structure is three-dimensional. Er is bonded in a 11-coordinate geometry to six equivalent Ni and eleven Al atoms. There are three shorter (3.27 Å) and three longer (3.28 Å) Er–Ni bond lengths. There are a spread of Er–Al bond distances ranging from 2.98–3.15 Å. Ni is bonded in a 8-coordinate geometry to two equivalent Er and eight Al atoms. There are a spread of Ni–Al bond distances ranging from 2.33–2.62 Å. There are six inequivalent Al sites. In the first Al site, Al is bonded in a 3-coordinate geometry to two equivalent Er, three equivalent Ni, and five Al atoms. There are a spread of Al–Al bond distances ranging from 2.71–2.79 Å. In the second Al site, Al is bonded in a distorted trigonal non-coplanar geometry to one Er, three equivalent Ni, and seven Al atoms. There are three shorter (2.81 Å) and one longer (2.84 Å) Al–Al bond lengths. In the third Al site, Al is bonded in a 2-coordinate geometry to two equivalent Er, two equivalent Ni, and six Al atoms. Both Al–Al bond lengths are 2.64 Å. In the fourth Al site, Al is bonded in a distorted trigonal non-coplanar geometry to three equivalent Ni and seven Al atoms. There are three shorter (2.83 Å) and one longer (2.87 Å) Al–Al bond lengths. In the fifth Al site, Al is bonded in a distorted trigonal non-coplanar geometry to one Er, three equivalent Ni, and seven Al atoms. All Al–Al bond lengths are 2.80 Å. In the sixth Al site, Al is bonded in a linear geometry to two equivalent Ni and six Al atoms.

36 MATERIALS SCIENCE↗
NASA NTRS1975

Processing eutectics in space

The investigations of directional solidification have indicated the necessity of establishing a secure foundation in earth-based laboratory processing in order to properly assess low-gravity processing. Emphasis was placed on evaluating the regularity of microstructure of the rod-like eutectic Al-Al3Ni obtained under different conditions of growth involving the parameters of thermal gradient, solidification rate, and interfacial curvature. In the case of Al-Al3Ni, where the Al3Ni phase appears as facets rods, solidification rate was determined to be a controlling parameter. Zone melting of thin eutectic films showed that for films of the order of 10 to 20 micrometers thick, the extra surface energy appears to act to stabilize a regular microstructure. The results suggest that the role of low-gravity as provided in space-laboratory processing of materials is to be sought in the possibility of generating a higher thermal gradient in the solidifying ingot for a given power input-output arrangement than can be obtained under normal one-g processes.

Douglas, F. C.↗
DOE OSTI2021

Microstructure and creep properties of cast near-eutectic Al–Ce–Ni alloys

This study investigates the as-cast and aged microstructures, thermal stability, ambient temperature strengthening, and creep resistance of three ternary Al–Ce–Ni alloys (wt%): near-eutectic Al–10Ce–5Ni (with both eutectic and hypoeutectic regions), hypoeutectic Al-7.5Ce-3.75Ni (with numerous primary Al dendrites), and hypereutectic Al-12.5Ce-6.25Ni (with coarse, blocky primary Al3Ni and Al11Ce3 precipitates and some primary Al dendrites). Depending on the alloy composition and local solidification conditions, the following eutectic morphologies are found: (i) coarse Al–Ce eutectic colonies where Al 11 Ce 3 is in the form of “Chinese script”, (ii) intermingled regions of binary Al–Ce and Al–Ni eutectic colonies, with finer Al 3 Ni and Al 11 Ce 3 fibers, (iii) large ternary eutectic colonies, where the binary Al 3 Ni and Al 11 Ce 3 phases are alternating or intertwining within the individual, fine fibers (diameters of ~60–170 nm, depending on solidification rates), and (iv) ternary eutectic zones (between primary Al dendrites), where fine Al 3 Ni and Al 11 Ce 3 build up a 3D-interconnected network. The high volume fraction of intermetallic phases and extremely fine eutectic spacing/fiber diameter both contribute to high ambient strengthening (higher as-cast microhardness than binary Al–Ce or Al–Ni), and also provide enhanced creep resistance at 300 and 350 °C. Additionally, the alloys are coarsening-resistant up to 425 °C for extended periods, with a gradual decrease in microhardness. The alloys aged at 400 °C to 1050 h show fiber fragmentation and coarsening of the resulting particles, with the faster-diffusing Ni driving more rapid coarsening of the Al 3 Ni particles which engulf finer, more stable Al 11 Ce 3 particles. Severe overaging (performed at 590 °C for 24 h) leads to Al 3 Ni and Al 11 Ce 3 spheroids which remain submicron-sized in eutectic colonies, but micron-sized at colony boundary and at Al dendrite-eutectic interface. Creep resistance at 300 °C of overaged Al–10Ce–5Ni remains substantial, consistent with load-transfer based composite strengthening being an important strengthening mechanism in these alloys, making them excellent candidates for replacement of heavier steel or titanium parts operating under stress up to 300 °C.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Detection of fiber cracking by acoustic emission.

A theoretical model is presented that relates acoustic emission to fiber cracking which occurs during a rising load tension test on a fiber reinforced composite. The percentage of broken fibers in an Al3Ni fiber reinforced aluminum was measured as a function of tensile strain by optical inspection of the polished surface of strained specimens. This information was used in conjunction with the proposed model to predict the acoustic emission response of the composite material. These predictions were compared with experimental observations, and a good agreement was obtained between the two sets of results. These results indicate that it is possible to relate acoustic emission quantitatively to the micromechanics of the deformation processes occurring within fiber reinforced composites, thereby demonstrating the applicability of acoustic emission to materials studies and also to nondestructive evaluation of the integrity of composite materials.

Harris, D. O.↗
NASA NTRS1998

Use of Microgravity to Control the Microstructure of Eutectics

This grant began in June of 1996. Its long term goal is to be able to control the microstructure of directionally solidified eutectic alloys, through an improved understanding of the influence of convection. The primary objective of the present projects is to test hypotheses for the reported influence of microgravity on the microstructure of three fibrous eutectics (MnBi-Bi, InSb-NiSb, Al3Ni-Al). A secondary objective is to determine the influence of convection on the microstructure of other eutectic alloys. Two doctoral students and a masters student supported as a teaching assistant were recruited for this research. Techniques were developed for directional solidification of MnBi-Bi eutectics with periodic application of current pulses to produce an oscillatory freezing rate. Image analysis techniques were developed to obtain the variation in MnBi fiber spacing, which was found to be normally distributed. The mean and standard deviation of fiber spacing were obtained for several freezing conditions. Eighteen ampoules were prepared for use in the gradient freeze furnace QUELD developed at Queen's University for use in microgravity. Nine of these ampoules will be solidified soon at Queen's in a ground-based model. We hope to solidify the other nine in the QUELD that is mounted on the Canadian Microgravity Isolation Mount on MIR. Techniques are being developed for directional solidification of the Al-Si eutectic at different freezing rates, with and without application of accelerated crucible rotation to induce convection. For the first time, theoretical methods are being developed to analyze eutectic solidification with an oscillatory freezing rate. In a classical sharp-interface model, we found that an oscillatory freezing rate increases the deviation of the average interfacial composition from the eutectic, and increases the undercooling of the two phases by different amounts. This would be expected to change the volume fraction solidifying and the fiber spacing. Because of difficulties in tracking the freezing interfaces of the two solid phases, a phase-field model is also being developed. A paper demonstrating application of phase field methods to periodic structures has been submitted for publication.

Wilcox, William R.↗