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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Harnessing metastability for grain size control in multiprincipal element alloys during additive manufacturing

Abstract Controlling microstructure in fusion-based metal additive manufacturing (AM) remains a significant challenge due to the many parameters that directly impact solidification condition. Multiprincipal element alloys (MPEAs), also known as high entropy alloys, offer a vast compositional space to design for microstructural engineering due to their chemical complexity and exceptional properties. Here, we use the FeMnCoCr system as a model platform for exploring alloy design in MPEAs for AM. By exploiting the decreasing stability of the face-centered cubic phase with increasing Mn content, we achieve notable grain refinement and breakdown of epitaxial columnar grain growth. We employ a multifaceted approach encompassing thermodynamic modeling, operando synchrotron X-ray diffraction, multiscale microstructural characterization, and mechanical testing to gain insight into the solidification physics and its ramifications on the resulting microstructure of FeMnCoCr MPEAs. This work aims toward tailoring desirable grain sizes and morphology through targeted manipulation of phase stability, thereby advancing microstructure control in AM applications.

Wakai, Akane↗
NASA NTRS2020

Dust from Mars-Analog Plains (Iceland): Physico-Compositional Properties as a Function of Grain-Size Fraction

Dust is a key component of the geological and climatic systems of Earth and Mars. On Mars, dust is ubiquitous. It coats rocks and soils, and, in the atmosphere, it interacts strongly with solar and thermal radiation. Yet, key questions remain about the genesis and fate of martian dust, as well as its sources, composition, and properties. We collected wind-blown dust from basaltic plains in SW Iceland at Skjaldbreiðauhraun that represent a geologic Mars-analog environment. Icelandic dust differs from the typical continental sources (e.g. Sahara, Asia) because of its basaltic volcanogenic origin, which is similar to Mars. Dust collection took place in July of 2019 as a complementary project to the SAND-E: Semi-Autonomous Navigation for Detrital Environments project. Here we report preliminary analyses of this Mars-analog dust material, with the goal of understanding the processes that control the physico-chemical proper-ties of the different grain-size fractions.

Nachon, Marion↗
NASA NTRS1987

Effect of composition and grain size on slow plastic flow properties of NiAl between 1200 and 1400 K

A series of about 15-micron diameter polycrystalline B2 crystal structure NiAl alloys ranging in composition from 43.9 to 52.7 Al (at. pct) have been compression tested at constant velocities in air between 1200 and 1400 K. All materials were fabricated via powder metallurgy techniques with hot extrusion as the densification process. Seven intermediate compositions were produced by blending various amounts of two master heats of prealloyed powder; in addition, a tenth alloy of identical composition, 48.25 Al, as one of the blended materials, was produced from a third master heat. Comparison of the flow stress-strain rate behavior for the two 48.25 Al alloys revealed that their properties were identical. The creep strength of materials for Al/Ni not above 1.03 was essentially equal, and deformation could be described by a single stress exponent and activation energy. Creep at low temperatures and faster strain rates is independent of grain sizes and appears to be controlled by a subgrain mechanism. However, at higher temperatures and slower strain rates, diffusional creep seems to contribute to the overall deformation rate.

Whittenberger, J. Daniel↗
NASA NTRS1987

Effect of grain size on the high temperature properties of B2 aluminides

Measurements of the slow plastic flow behavior of cobalt, iron and nickel B2 crystal structure aluminides were conducted on materials fabricated by metallurical techniques. Due to this processing, the aluminides invariably had small equiaxed grains, ranging in size from about 3 to 60 microns in diameter. Grain size was dependent on the extrusion temperature used for powder consolidation, and it proved to be remarkably stable at elevated temperatures. Mechanical properties of all three aluminides were determined via constant velocity compression testing in air between 1000 and 1400 K at strain rates ranging from approx. 10 to the minus 3 power to 10 to the minus 7 power s (-1).

Whittenberger, J. Daniel↗
NASA NTRS1977

C-14 in lunar soil - Temperature-release and grain-size dependence

C-14 is released from surface soils by heatings between 600 and 1000 C. The amounts of 600-1000-C C-14 obtained increase inversely with grain diameter for the 10-30 and 74-125-micron size fractions. The inverse relation shows that the 600-1000-C C-14 is located on the surface of grains and probably is of solar-wind origin. The amount released at these temperatures gives 0.002 C-14 ions per sq cm/sec for the implantation rate and corresponds to a C-14/H ratio of the order of 4 hundred-billionths for the solar wind. This result from the grain-size dependence is in accord with C-14 depth-variation studies. The C-14 released above melting temperatures can be attributed to spallation production.

Fireman, E. L.↗
NASA NTRS2023

Investigating Abrasion Effects of Lunar Simulant Grain Sizes on Candidate Spacesuit Fabric

Lunar dust is identified as one of the most significant challenges during the Apollo exploration missions due to its extremely abrasive and electrostatic characteristics. As NASA and the space industry prepare for the upcoming Artemis missions, researching and testing with lunar simulant is quintessential to understanding the effects of lunar dust on the systems and equipment that will be deployed on the lunar surface. Testing will also provide paths that lead to developing technologies and cleaning tools that could be used for dust mitigation. Additionally, it is expected that any hardware that will be exposed to the dusty environment should undergo rigorous testing to ensure it will maintain long-term performance and operate on the lunar surface. For this study, exterior spacesuit fabric was observed. Abrasion is one of the main concerns of lunar dust exposure for spacesuit fabric. Three different abrasion methods were chosen: a rotary tumbler, the Martindale method, and Accelerotor. These abrasion methods were tested on coated and uncoated spacesuit material, Orthofabric, to understand the abrasion rates of sieved lunar simulant and investigate if the addition of ceramic coating mitigated dust abrasion. To summarize, the testing results provided that larger grains are more abrasive than smaller grains, and the selected ceramic coatings did not minimize abrasion during the controlled abrasion tests. It is important to note that the selected ceramic coatings were not designed or intended to provide protection from the abrasive lunar environment. It is recommended to select additional ceramic coatings with an elevated TRL of 5 or greater for testing with Orthofabric and lunar simulant. As an additional note, contact angle measurements were not accounted for in coating selection and should be a factor when selecting adhesion resistant coatings for lunar dust.

grain size↗
NASA NTRS1974

Provenance of KREEP and the exotic component - Elemental and isotopic studies of grain size fractions in lunar soils

Sieve fraction analyses of lunar soils reveal the presence of a fine-grained exotic component enriched in K, Rb, Sr, Ba, and in radiogenic Sr in all soils. The probable source of this exotic component is the areas of high-surficial radioactivity observed by orbital gamma ray spectrometry, such as those at Fra Mauro and Archimedes. If the exotic component is fine-grained KREEP, the origin and distribution of KREEP fragments in the soils are identified. It is suggested that the exotic component represents trace element enriched material located at some depth in the Imbrium area which was surficially deposited during Imbrium excavation.

Evensen, N. M.↗
NASA NTRS2011

Light Scattering by Wavelength-Sized Particles "Dusted" with Subwavelength-Sized Grains

The numerically exact superposition T-matrix method is used to compute the scattering cross sections and the Stokes scattering matrix for polydisperse spherical particles covered with a large number of much smaller grains. We show that the optical effect of the presence of microscopic dust on the surfaces of wavelength-sized, weakly absorbing particles is much less significant than that of a major overall asphericity of the particle shape.

Mishchenko, Michael I.↗
NASA NTRS1972

The role of grain size and shape in the strengthening of dispersion hardened nickel alloys

Thermomechanical processing was used to develop various microsstructures in Ni, Ni-2ThO2, Ni-20Cr, Ni-20CR-2ThO2, Ni-20Cr-10W-and Ni-20Cr-10W-2ThO2. The yield strength at 25 C increased with substructure refinement according to the Hall-Petch relation, and substructure refinement was a much more potent means of strengthening than was dispersion hardening. At elevated temperature (1093 C), the most important microstructural feature affecting strength was the grain aspect ratio (grain length, L, divided by grain width, 1. The yield strength and creep strength increased linearly with increasing L/1.

Wilcox, B. A.↗
NASA NTRS1972

The role of grain size and shape in strengthening of dispersion hardened nickel alloys.

Thermomechanical processing was used to develop various microstructures in Ni, Ni-2ThO2, Ni-20Cr, Ni-20Cr-2ThO2, Ni-20Cr-10W and Ni-20Cr-10W-2ThO2, and the influence of microstructure on room temperature and elevated temperature strength was investigated. The yield strength at 25 C increased with substructure refinement according to the Hall-Petch relation. It was found that substructure refinement was a much more potent means of strengthening at room temperature than was dispersion hardening. At elevated temperature (1093 C), the most important microstructural feature affecting strength of dispersion hardened nickel alloys was the grain aspect ratio, i.e. grain length, L, divided by grain width,l. The yield strength and creep strength increased linearly with increasing L/l.

Wilcox, B. A.↗
NASA NTRS2003

A Microphysically-based Approach to Inferring Porosity, Grain Size, and Dust Abundance in the Seasonal Caps from Atmospherically-corrected TES Spectra

One of the highlights of the TES observations in the polar regions has been the identification of a "cryptic" region in the south where CO2 appears to be in the form of a solid slab rather than a fluffy frost. While the exact mechanism(s) by which the cryptic region is formed are still subject of some debate, it appears certain that a type of rapid metamorphism related to the high volatility of CO2 ice is involved. The high volatility of CO2 ice under martian conditions has several Solar System analogs (N2 on Triton and Pluto, SO2 on Io), thus making the martian cryptic region somewhat less cryptic and certainly non-unique among planetary objects. In an endmember scenario, both the formation and the spectral properties of the cryptic region (and of other areas in the seasonal caps) can be quantitatively modeled by considering sintering of an ensemble of quasi-spherical CO2 grains. This model includes the special case of instanteneous slab formation, which occurs when the grains are sufficiently small (in the submicron range) so that their sintering timescale is short relative to the deposition timescale (a situation analogous to the "sintering" of water droplets falling into a pond).

Eluszkiewicz, J.↗
NASA NTRS1976

Closure and ratio correlation analysis of lunar chemical and grain size data

Major element and major element plus trace element analyses were selected from the lunar data base for Apollo 11, 12 and 15 basalt and regolith samples. Summary statistics for each of the six data sets were compiled, and the effects of closure on the Pearson product moment correlation coefficient were investigated using the Chayes and Kruskal approximation procedure. In general, there are two types of closure effects evident in these data sets: negative correlations of intermediate size which are solely the result of closure, and correlations of small absolute value which depart significantly from their expected closure correlations which are of intermediate size. It is shown that a positive closure correlation will arise only when the product of the coefficients of variation is very small (less than 0.01 for most data sets) and, in general, trace elements in the lunar data sets exhibit relatively large coefficients of variation.

Butler, J. C.↗