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At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Thermal Exposure Effects on Properties of Al-Li Alloy Plate Products

Aluminum-Lithium (AL-Li) alloys offer significant performance benefits for aerospace structural applications due to their higher specific properties compared with conventional aluminum alloys. For example, the application of an Al-Li alloy to the space shuttle external cryogenic fuel tank contributed to the weight savings that enabled successful deployment of International Space Station components. The composition and heat treatment of this alloy were optimized specifically for strength-toughness considerations for an expendable cryogenic tank. Time dependent properties related to reliability, such as thermal stability, fatigue, and corrosion, will be of significant interest when materials are evaluated for a reusable cryotank structure. As most aerospace structural hardware is weight sensitive, a reusable cryotank will be designed to the limits of the materials mechanical properties. Therefore, this effort was designed to establish the effects of thermal exposure on the mechanical properties and microstructure of one relatively production mature alloy and two developmental alloys C458 and L277. Tensile and fracture toughness behavior was evaluated after exposure to temperatures as high as 3oooF for up to IO00 hrs. Microstructural changes were also evaluated to correlate with the observed data trends. The ambient temperature parent metal data showed an increase in strength and reduction in elongation after exposure at lower temperatures. Strength reached a peak with intermediate temperature exposure followed by a decrease at highest exposure temperature. Characterizing the effect of thermal exposure on the properties of Al-Li alloys is important to defining a service limiting temperature, exposure time, and end-of-life properties.

Shah, Sandeep↗
NASA NTRS2003

Thermal Exposure Effects on Properties of Al-Li Alloy Plate Products

The objective of this viewgraph representation is to evaluate the effects of thermal exposure on the mechanical properties of both production mature and developmental Al-Li alloys. The researchers find for these alloys, the data clearly shows that there is no deficit in mechanical properties at lower exposure temperatures in some cases, and a signficant deficit in mechanical properties at higher exposure temperatures in all cases. Topics considered include: Al-Li alloys composition, key characteristics of Al-Li alloys and thermal exposure matrix.

Shah, Sandeep↗
NASA NTRS1994

(abstract) Transmission Electron Microscopy of Al(sub x)Ga(sub 1-x)N/SiC Multilayer Structures

The potential of wide-band-gap III-V nitrides as solar-blind ultraviolet sensors and light emitters has prompted an increasing amount of work recently, including the fabrication of the first UV sensors from as-deposited single crystal GaN. We have used high resolution transmission electron microscopy (TEM) to study the microstructure of two novel developments of wide-band-gap III-V nitrides: the growth of ultra-short period GaN/AlN super lattices (digital alloys); and the incorporation of SiC layers into Al(sub x)Ga(sub 1-x)N structures. By varying the relative periods in a GaN/AlN superlattice, it should be possible to tailor the band gap of the composite to lie between the elemental values of 365 nm for GaN and 200 nm for AlN. The group IV semiconductor, SiC, has a close lattice match (< 3%) to Al(sub x)Ga(sub 1-x)N for growth on the basal plane. Demonstration of epitaxial growth for Al(sub x)Ga(sub 1-x)N/SiC multilayers could enable an extension of direct band-gap material towards the visible.

microscopy GaN AlN semiconductor SiC↗
NASA NTRS2007

Stardust in STARDUST - the C, N, and O Isotopic Compositions of Wild 2 Cometary Matter in Al foil Impacts

In January 2006, the STARDUST mission successfully returned dust samples from the tail of comet 81P/Wild 2 in two principal collection media, low density silica aerogel and Al foil. While hypervelocity impacts at 6.1 km/s, the encounter velocity of STARDUST, into Al foils are generally highly disruptive for natural, silicate-dominated impactors, previous studies have shown that many craters retain sufficient residue to allow a determination of the elemental and isotopic compositions of the original projectile. We have used the NanoSIMS to perform C, N, and O isotope imaging measurements on four large (59-370 microns diameter) and on 47 small (0.32-1.9 microns diameter) Al foil impact craters as part of the STARDUST Preliminary Examination. Most analyzed residues in and around these craters are isotopically normal (solar) in their C, N, and O isotopic compositions. However, the debris in one large crater shows an average 15N enrichment of approx. 450 %, which is similar to the bulk composition of some isotopically primitive interplanetary dust particles. A 250 nm grain in another large crater has an O-17 enrichment with approx. 2.65 times the solar O-17/O-16 ratio. Such an O isotopic composition is typical for circumstellar oxide or silicate grains from red giant or asymptotic giant branch stars. The discovery of this circumstellar grain clearly establishes that there is authentic stardust in the cometary samples returned by the STARDUST mission. However, the low apparent abundance of circumstellar grains in Wild 2 samples and the preponderance of isotopically normal material indicates that the cometary matter is a diverse assemblage of presolar and solar system materials.

Stadermann, Frank J.↗
NASA NTRS2007

Stardust in STARDUST - the C, N, and O Isotopic Compositions of Wild 2 Cometary Matter in Al Foil Impacts

In January 2006, the Stardust mission successfully returned dust samples from the tail of comet 81P/Wild 2 in two principal collection media, low density silica aerogel and Al foil. While hypervelocity impacts at the Stardust encounter velocity of 6.1 kilometers per second into Al foils are generally highly disruptive for natural, silicate-dominated impactors, previous studies have shown that many craters retain sufficient residue to allow a determination of the elemental and isotopic compositions of the original projectile. We have used two NanoSIMS ion microprobes to perform C, N, and O isotope imaging measurements on four large (59-295 micrometer diameter) and on 47 small (0.32-1.9 micrometer diameter) Al foil impact craters as part of the Stardust Preliminary Examination. Most analyzed residues in and around these craters are isotopically normal (solar) in their C, N, and O isotopic compositions. However, the debris in one large crater shows an average N-15 enrichment of approx. 450%o, which is similar to the bulk composition of some isotopically primitive interplanetary dust particles and to components of some primitive meteorites. A 250 nm grain in another large crater has an O-17 enrichment with approx. 2.65 times the solar O-17/O-16 ratio. Such an O isotopic composition is typical for circumstellar oxide or silicate grains from red giant or asymptotic giant branch stars. The discovery of this circumstellar grain clearly establishes that there is authentic stardust in the cometary samples returned by the Stardust mission. However, the low apparent abundance of circumstellar grains in Wild 2 samples and the preponderance of isotopically normal material indicates that the cometary matter is a diverse assemblage of presolar and solar system materials.

Stadermann, Frank J.↗
NASA NTRS2008

Effects of Solute Concentrations on Kinetic Pathways in Ni-Al-Cr Alloys

The kinetic pathways resulting from the formation of coherent gamma'-precipitates from the gamma-matrix are studied for two Ni-Al-Cr alloys with similar gamma'-precipitate volume fractions at 873 K. The details of the phase decompositions of Ni-7.5Al-8.5Cr at.% and Ni-5.2Al-14.2Cr at.% for aging times from 1/6 to 1024 h are investigated by atom-probe tomography, and are found to differ significantly from a mean-field description of coarsening. The morphologies of the gamma'-precipitates of the alloys are similar, though the degrees of gamma'-precipitate coagulation and coalescence differ. Quantification within the framework of classical nucleation theory reveals that differences in the chemical driving forces for phase decomposition result in differences in the nucleation behavior of the two alloys. The temporal evolution of the gamma'-precipitate average radii and the gamma-matrix supersaturations follow the predictions of classical coarsening models. The compositional trajectories of the gamma-matrix phases of the alloys are found to follow approximately the equilibrium tie-lines, while the trajectories of the gamma'-precipitates do not, resulting in significant differences in the partitioning ratios of the solute elements.

Booth-Morrison, Christopher↗
NASA NTRS2009

Effects of Tantalum on the Temporal Evolution of a Model Ni-Al-Cr Superalloy During Phase Decomposition

The effects of a 2.0 at.% addition of Ta to a model Ni-10.0Al-8.5Cr (at.%) superalloy aged at 1073 K are assessed using scanning electron microscopy and atom-probe tomography. The gamma'(Ll2)-precipitate morphology that develops as a result of gamma-(fcc)matrix phase decomposition is found to evolve from a bimodal distribution of spheroidal precipitates, to {001}-faceted cuboids and parallelepipeds aligned along the elastically soft {001}-type directions. The phase compositions and the widths of the gamma'-precipitate/gamma-matrix heterophase interfaces evolve temporally as the Ni-Al-Cr-Ta alloy undergoes quasi-stationary state coarsening after 1 h of aging. Tantalum is observed to partition preferentially to the gamma'-precipitate phase, and suppresses the mobility of Ni in the gamma-matrix sufficiently to cause an accumulation of Ni on the gamma-matrix side of the gamma'/gamma interface. Additionally, computational modeling, employing Thermo-Calc, Dictra and PrecipiCalc, is employed to elucidate the kinetic pathways that lead to phase decomposition in this concentrated Ni-Al-Cr-Ta alloy.

Booth, Morrison, Christopher↗
NASA NTRS2010

Alvin (Al) Sieff: Thoughts About and Lessons from a Great Engineer

Alvin (Al) Seiff was known as a world-class atmospheric scientist during the last three decades of his life. Equally deserving, however, were his prior achievements as an innovative engineer, an exceptional technical manager, and a mentor of young engineers at NASA Ames Research Center. This paper outlines Al's role in developing Ames ballistic range facilities, probably the most advanced in the world at that time, and his seminal 1963 report that contained the concepts used to reconstruct the atmospheres of Mars, Venus, Jupiter and Titan. Also discussed is my affiliation with Al after he hired me in 1962, including our joint work on Mars missions and investigating the feasibility that a Jupiter probe could survive entry, work that eventually led to the development of the Galileo probe. Finally, suggestions are offered for speeding the analysis and design of thermal protection systems based on lessons learned from successful probes and landers.

Tauber, Michael↗
NASA NTRS2016

Cu-Al-Ni Shape Memory Single Crystal Wires with High Transformation Temperature

CN-250X is a new material with higher performance than Nickel-Titanium Shape Memory Alloy (SMA). For space mechanisms, the main disadvantage of Nickel-Titanium Shape Memory Alloy is the limited transformation temperature. The new CN-250X Nimesis alloy is a Cu-Al-Ni single crystal wire available in large quantity because of a new industrial process. The triggering of actuators made with this Cu-Al-Ni single crystal wire can range from ambient temperature to 200 C in cycling and even to 250 C in one-shot mode. Another advantage of CN-250X is a better shape recovery (8 to 10%) than Ni-Ti (6 to 7%). Nimesis is the first company able to produce this type of material with its new special industrial process. A characterization study is presented in this work, including the two main solicitation modes for this material: tensile and torsion. Different tests measure the shape recovery of Cu-Al-Ni single crystals wires during heating from room temperature to a temperature higher than temperature of end of martensitic transformation.

Hautcoeur, Alain↗
NASA NTRS2016

Primary Dendrite Arm Spacing and Trunk Diameter in Al-7-Weight-Percentage Si Alloy Directionally Solidified Aboard the International Space Station

Under a NASA-ESA collaborative research project, three Al-7-weight-percentage Si samples (MICAST-6, MICAST-7 and MICAST 2-12) were directionally solidified aboard the International Space Station to determine the effect of mitigating convection on the primary dendrite array. The samples were approximately 25 centimeters in length with a diameter of 7.8 millimeter-diameter cylinders that were machined from [100] oriented terrestrially grown dendritic Al-7Si samples and inserted into alumina ampoules within the Sample Cartridge Assembly (SCA) inserts of the Low Gradient Furnace (LGF). The feed rods were partially remelted in space and directionally solidified to effect the [100] dendrite-orientation. MICAST-6 was grown at 5 microns per second for 3.75 centimeters and then at 50 microns per second for its remaining 11.2 centimeters of its length. MICAST-7 was grown at 20 microns per second for 8.5 centimeters and then at 10 microns per second for 9 centimeters of its remaining length. MICAST2-12 was grown at 40 microns per second for 11 centimeters. The thermal gradient at the liquidus temperature varied from 22 to 14 degrees Kelvin per centimeter during growth of MICAST-6, from 26 to 24 degrees Kelvin per centimeter for MICAST-7 and from 33 to 31 degrees Kelvin per centimeter for MICAST2-12. Microstructures on the transverse sections along the sample length were analyzed to determine nearest-neighbor spacing of the primary dendrite arms and trunk diameters of the primary dendrite-arrays. This was done along the lengths where steady-state growth prevailed and also during the transients associated with the speed-changes. The observed nearest-neighbor spacings during steady-state growth of the MICAST samples show a very good agreement with predictions from the Hunt-Lu primary spacing model for diffusion controlled growth. The observed primary dendrite trunk diameters during steady-state growth of these samples also agree with predictions from a coarsening-based model. The radial macrosegregation and "steepling" caused by thermosolutal convection during terrestrial growth of the Al-7Si was not observed in the space-grown MICAST samples.

Ghods, M.↗
NASA NTRS2020

Mg Isotopic Compositions of Fine-Grained Ca-Al-Rich Inclusions from Reduced CV3 Chondrites and Implications on the Timescale of Nebular Condensation

Fine-grained Ca-Al-rich inclusions (FGIs) in carbonaceous chondrites are interpreted as aggregates of nebular gas-solid condensates that escaped significant melting [1]. Recent Al-Mg isotopic studies of small FGIs (<200 µm in size) from pristine CO3 chondrites have revealed significant variations in initial 26Al/27Al ratio, (26Al/27Al)(sub 0), spanning from 5.73×10(exp ˗5) to 8×10(exp ˗6) [2,3]. Importantly, [3] found a main CAI population characterized by (26Al/27Al)(sub 0) = 5.4×10(exp ˗5) that likely record the onset of dust condensation and initial coagulation events, followed by multiple thermal events over an extended time period. Thus far, a small number of large FGIs from CV3 chondrites have been analyzed, showing a narrower range of ( 26Al/27Al)(sub 0) = 5.27×10(exp ˗5) to 3.35×10(exp ˗5) [4-6], similar to those inferred from coarse-grained, igneous CAIs (CGIs) from CV3 chondrites [7]. These observed different ratios may raise a question if large FGIs in CV3 chondrites record a time interval from primary direct condensation of refractory solids to their aggregation and growth into larger inclusions. In this study, we present Al-Mg isotopic compositions of FGIs from reduced CV3 chondrites to better constrain their formation timescale relative to smaller FGIs in CO3 chondrites, as well as to CGIs in CV3 chondrites. This isotopic study is coordinated with a microstructural study to elucidate the origin and nature of FGIs in the petrologic and mineralogical context.

Han, J.↗
NASA NTRS2018

Adrianite, Ca12(Al4Mg3Si7)O32Cl6, a New Cl-rich Silicate Mineral From the Allende Meteorite: An Alteration Phase in a Ca-Al-rich Inclusion

Adrianite (IMA 2014-028), Ca12(Al4Mg3Si7)O32Cl6, is a new Cl-rich silicate mineral and the Si,Mg analog of wadalite. It occurs with monticellite, grossular, wadalite, and hutcheonite in altered areas along some veins between primary melilite, spinel, and Ti,Al-diopside in a Type B1 FUN (Fractionation and Unidentified Nuclear effects) Ca-Al-rich inclusion (CAI), Egg-3, from the Allende CV3 carbona-ceous chondrite. The mean chemical composition of type adrianite by electron probe microanalysis is (wt%) CaO 41.5, SiO2 27.5, Al2O3 12.4, MgO 7.3, Na2O 0.41, Cl 13.0, O=Cl –2.94, total 99.2, giving rise to an empirical formula of (Ca11.69Na0.21)(Al3.85Mg2.88Si7.23)O32Cl5.80. The end-member formula is Ca12(Mg5Si9)O32Cl6. Adrianite has the I43d wadalite structure with a = 11.981 Å, V = 1719.8 Å3, and Z = 2, as revealed by electron backscatter diffraction. The calculated density using the measured composition is 3.03 g/cm3. Adrianite is a new secondary mineral in Allende, apparently formed by alkali-halogen metasomatic alteration of primary CAI minerals such as melilite, anorthite, perovskite, and Ti,Al-diopside on the CV chondrite parent asteroid. Formation of secondary Cl-rich minerals sodalite, adrianite, and wadalite during metasomatic alteration of the Allende CAIs suggests that the metasomatic fluids had Cl-rich compositions. The mineral name is in honor of Adrian J. Brearley, mineralogist at the University of New Mexico, U.S.A., in recognition of his many contributions to the understanding of secondary mineralization in chondritic meteorites.

Chi Ma↗
NASA NTRSDate not supplied

Mineral composition of Al-rich float rocks in Jezero crater as seen by Super-Cam

During its traverse across the Jezero crater floor and western fan, the Perseverance rover encountered > 4000 float rocks – of variable size (up to ~ 50 cm) scattered on the ground without apparent connection to the surrounding stratigraphy [1]. Analysis performed using the SuperCam instrument’s [2,3,4], Laser Induced Breakdown Spectroscopy (LIBS) revealed a high concentration of Al 2 O 3 , Cr, Ti and Ni [5], and very low of Fe, Mg, Ca and Na [5, 1]. SuperCam’s infrared reflectance spectroscopy (IRS, between 1.3 and 2.6 μm) showed the presence of Al-rich aqueous alteration minerals (characteristic absorption bands of kaolinite and Al-smectites at 1.4 and 2.2 μm) as well as some (likely Cr-) spinels, identified uthrough their broad asymmetric 2 μm band, responsible for the concavity of IR spectra. These mineral species alone do not fully account for the spectral shapes; hence, the objective is to further investigate spectral modeling to determine the most probable mineral assemblages. Here, we present the results of modeling 17 light-toned float rocks, up to Sol 924, complementary to [1].

C. Royer↗
NASA NTRSDate not supplied

Utilizing Strain Rate Jump Testing to Predict Flow Formability of Al Alloys Sensitive to Portevin-Le Chatelier Instabilities

Predicting the flow formability of Al alloys is challenging due to the incremental deformation, complex loading path, and wide range of strain rates characteristic of the process. State-of-the-art research efforts have primarily focused on formability metrics derived from ambient temperature, constant strain rate uniaxial tensile testing. However, Al alloys in formable tempers tend to exhibit serrated Portevin-Le Chatelier (PLC) flow. The appearance of PLC instabilities implies a negative strain rate sensitivity, loss of tensile area reduction capacity, and decreased formability. Elevated temperature and interrupted strain rate tensile tests of relevant Al alloys were conducted to investigate the effects of rapid changes in strain rate (analogous to a forming increment by a passing roller) on common formability metrics. Emphasis was placed on the character/extent of PLC instabilities using digital image correlation strain measurements. The outcome of this work highlights the possibility of predicting flow formability using strain rate jump testing.

flow forming↗
DOE OSTI2020

Materials Data on Al(CoSi)2 by Materials Project

Al(CoSi)2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Co+2.50+ is bonded in a 5-coordinate geometry to five equivalent Si4- atoms. There are a spread of Co–Si bond distances ranging from 2.27–2.43 Å. Al3+ is bonded in a 6-coordinate geometry to six equivalent Si4- atoms. All Al–Si bond lengths are 2.78 Å. Si4- is bonded in a 11-coordinate geometry to five equivalent Co+2.50+, three equivalent Al3+, and three equivalent Si4- atoms. All Si–Si bond lengths are 2.67 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Al(PO3)3 by Materials Project

Al(PO3)3 crystallizes in the cubic I-43d space group. The structure is three-dimensional. Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six equivalent PO4 tetrahedra. All Al–O bond lengths are 1.89 Å. P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent AlO6 octahedra and corners with two equivalent PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 13–33°. There are a spread of P–O bond distances ranging from 1.48–1.62 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to one Al3+ and one P5+ atom. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent P5+ atoms. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to one Al3+ and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Al(MoS2)4 by Materials Project

Al(MoS2)4 crystallizes in the cubic F-43m space group. The structure is three-dimensional. Mo+3.25+ is bonded to six S2- atoms to form distorted MoS6 octahedra that share corners with three equivalent AlS4 tetrahedra and edges with six equivalent MoS6 octahedra. There are three shorter (2.35 Å) and three longer (2.62 Å) Mo–S bond lengths. Al3+ is bonded to four equivalent S2- atoms to form AlS4 tetrahedra that share corners with twelve equivalent MoS6 octahedra. The corner-sharing octahedral tilt angles are 65°. All Al–S bond lengths are 2.29 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded to three equivalent Mo+3.25+ and one Al3+ atom to form a mixture of distorted edge and corner-sharing SAlMo3 tetrahedra. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three equivalent Mo+3.25+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Al(MoS2)4 by Materials Project

Al(MoS2)4 crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are two inequivalent Mo+3.25+ sites. In the first Mo+3.25+ site, Mo+3.25+ is bonded to six S2- atoms to form distorted MoS6 octahedra that share corners with three equivalent AlS4 tetrahedra, edges with four equivalent MoS6 octahedra, and edges with two equivalent MoS6 pentagonal pyramids. There are a spread of Mo–S bond distances ranging from 2.34–2.63 Å. In the second Mo+3.25+ site, Mo+3.25+ is bonded to six S2- atoms to form distorted MoS6 pentagonal pyramids that share corners with three equivalent AlS4 tetrahedra and edges with six equivalent MoS6 octahedra. There are three shorter (2.37 Å) and three longer (2.64 Å) Mo–S bond lengths. Al3+ is bonded to four S2- atoms to form AlS4 tetrahedra that share corners with nine equivalent MoS6 octahedra and corners with three equivalent MoS6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 65°. All Al–S bond lengths are 2.29 Å. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded in a 3-coordinate geometry to three equivalent Mo+3.25+ atoms. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three Mo+3.25+ atoms. In the third S2- site, S2- is bonded to three Mo+3.25+ and one Al3+ atom to form a mixture of distorted edge and corner-sharing SAlMo3 tetrahedra. In the fourth S2- site, S2- is bonded to three equivalent Mo+3.25+ and one Al3+ atom to form a mixture of distorted edge and corner-sharing SAlMo3 tetrahedra.

36 MATERIALS SCIENCE↗