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At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Grain size dependence of dynamic mechanical behavior of AZ31B magnesium alloy sheet under compressive shock loading

The effects of grain size on the dynamic deformation behavior of rolled AZ31B alloy at high strain rates were investigated. Rolled AZ31B alloy samples with grain sizes of 6, 18 and 37 μm, were subjected to shock loading tests using Split Hopkinson Pressure Bar at room temperature and at a strain rate of 1100 s{sup −} {sup 1}. It was found that a double-peak basal texture formed in the shock loaded samples. The strength and ductility of the alloy under the high strain-rate compressive loading increased with decreasing grain size. However, twinning fraction and strain hardening rate were found to decrease with decreasing grain size. In addition, orientation imaging microscopy showed a higher contribution of double and contraction twins in the deformation process of the coarse-grained samples. Using transmission electron microscopy, pyramidal dislocations were detected in the shock loaded sample, proving the activation of pyramidal slip system under dynamic impact loading. - Highlights: • A double-peak basal texture developed in all shock loaded samples. • Both strength and ductility increased with decreasing grain size. • Twinning fraction and strain hardening rate decreased with decreasing grain size. • ‘g.b’ analysis confirmed the presence of dislocations in shock loaded alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Investigation of annealing temperature on microstructure and texture of Fe-19Cr-2Mo-Nb-Ti ferritic stainless steel

Highlights: • Fe-19Cr-2Mo-Nb-Ti ferritic stainless steel was investigated. • Shear bands provided recrystallization nucleation sites. • Annealing temperature can affect microstructure and texture. • r-bar increased to a maximum value (1.69) and then decreased to 1.42. - Abstract: The evolution of microstructure and texture of Fe-19Cr-2Mo-Nb-Ti ferritic stainless steel annealed at different temperatures was investigated using a combination of X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). EBSD investigations confirm that the in-grain shear bands provide more recrystallization nucleation sites to γ-fiber recrystallization grains with high Taylor factor orientations during cold rolling requiring further annealing for a more homogenous equiaxied grain structure. As the annealing temperatures increase, the grains in center layer are oriented towards {110}∥ND, and the recrystallization grains at 1050 °C are dominated by the uniform and equiaxial γ-fiber grains favourable for the improvement of r-values, while the occurrence of {100} <011> texture detrimental to r-values indicates that an exorbitant annealing temperature can reduce the intensity of γ-fiber textures affecting the formability, accordingly, the average plastic strain ratio of ferritic stainless steel increases sharply up to a maximum value (1.69) and then decreases to a certain value (1.42).

36 MATERIALS SCIENCE↗
NASA NTRS2005

Olivine and Ca-Phosphate in the Diogenites Manegaon and Roda

The textural relationships between the different primary minerals in igneous rocks provide one of the most fundamental pieces of evidence available for inferring the crystallization history of their parent magmas. Unfortunately, the high degree of brecciation that characterizes most diogenites, along with the low modal abundance and small grain sizes of minerals other than orthopyroxene, combine to make identifying and interpreting such textural relationships extremely difficult in this class of meteorites. A few descriptions of primary igneous contacts between orthopyroxene and chromite, troilite, and to a lesser extent, olivine in diogenites have been provided in the literature. In addition to these, in previous work, our research group has characterized several types of igneous contacts between Ca-pyroxene, plagioclase and orthopyroxene in the Bilanga diogenite. We have also described primary igneous inclusions of troilite + kamacite + chromite + Ca-pyroxene +/- Ca-phosphate in orthopyroxene (i.e. Metal/Troilite- Ball inclusions) in the diogenites Bilanga, Manegaon, Johnstown, Roda, Shalka, and Tatahouine. However, for the most part, detailed data on igneous textural relations between minerals other than orthopyroxene in diogenites are still sparse. Of the diogenite samples that we have examined,

Domanik, K. J.↗
DOE OSTI2011

Microstructure, mechanical properties and texture evolution of AZ31 alloy containing trace levels of strontium

The effect of low levels of Sr (0.01, 0.03, 0.05 wt.%) on the microstructure, mechanical properties and texture of AZ31 magnesium alloy has been investigated. Thermodynamic modeling has been used to study the effect of Sr on phase precipitation at different temperatures. Cooling curve analysis reveals a decrease in solidification superheat with the addition of 0.03 wt.% Sr to AZ31. The as-cast microstructures of the alloys have been studied using optical microscopy (OM) and electron probe micro analysis (EPMA). Results show the refining effect of Sr on the grain size and on the {beta}-Mg{sub 17}Al{sub 12} precipitates through growth poisoning and inoculation, respectively. To investigate the mechanical properties of the alloys, as-cast samples were compression tested at elevated temperatures. Hot compression peak stress ({sigma}{sub max}) and critical strain before recrystallization ({epsilon}{sub c}) initially drop but then increase. {sigma}{sub max} first decreases due to the depletion of Al from solid solution and then increases when the amount of the Al-Sr precipitates reach a significant amount. {epsilon}{sub c} drops due to the acceleration of dynamic recrystallization kinetics as a result of grain refinement. It increases with increasing Sr when the concentration Sr in solid solution is increased leading to dislocation pinning and retardation of recrystallization. X-ray texture measurements on the hot compressed and extruded samples show a decrease in maximum intensity of the basal pole figures with increasing Sr as a result of reduced twining and the changes in Al and Sr concentrations in solid solution. - Research Highlights: {yields} Microstructures/precipitates of AZ31+trace levels of Sr were examined by OM and EPMA. {yields} Thermodynamic calculations and cooling curve analysis were used to predict ppt formation. {yields} It has been shown that Sr refines the grains and Mg17Al12 precipitates. {yields} Mechanical properties and texture were studied using hot compression and X-ray diffraction. {yields} Different micro-mechanisms were responsible for mechanical and texture changes.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effects of Sn microalloying on cold rolling and recrystallization textures and microstructure of a ferritic stainless steel

Highlights: • Sn microalloying contributes to the enhancement in cold rolling texture intensity and the acceleration in cold rolling texture transformation. • Sn microalloying promotes the recrystallization process, and recrystallization occurs preferentially in steel with Sn compared with Sn-free steel. • Sn microalloying inhibits the growth of recrystallized grains, and the finer grains are obtained in steel with Sn. - Abstract: We investigated the effects of Sn microalloying on cold rolling and recrystallization textures and microstructure of a ferritic stainless steel. The as-received hot rolled sheets were cold rolled at 10%–90% reductions; the sheets cold rolled up to an 80% reduction were annealed at 740–880 °C for 5 min. For comparison, the cold rolling and recrystallization textures of the steel sheets with and without Sn were determined with the conventional X-ray diffraction method. The cold rolling and recrystallization metallographic microstructures were measured by scanning electron microscope and optical microscope, and the crystal orientation maps of the cold rolled and annealed samples were observed by electron backscattered diffraction. The micro-hardness was determined using a digital micro-hardness tester. Our results show that Sn microalloying in a medium chromium ferritic stainless steel plays multiple roles in the cold rolling and recrystallization processes. Sn micrcoalloying contributes to the enhancement in cold rolling texture intensity and the acceleration in cold rolling texture transformation. Sn microalloying is beneficial in promoting the recrystallization process. Recrystallization occurs preferentially in the ferritic stainless steel with Sn. Sn microalloying plays an important role in inhibiting the growth of recrystallized grains. The finer grains are obtained in ferritic stainless steel with Sn when annealing at high temperatures.

36 MATERIALS SCIENCE↗
NASA NTRS2007

Petrology and Geochemistry of New Ureilites and Ureilite Genesis

Ureilites are C-bearing, basalt-depleted olivine+pyroxene achondrites from a differentiated asteroid. The group is heterogeneous, exhibiting ranges in O isotopic composition, Fe/Mg, Fe/Mn, pyx/ol, siderophile and lithophile trace element content, and C content and isotopic composition [1]. Some of these characteristics are nebular in origin; others were strongly overprinted by asteroidal igneous processes. The consensus view is that most ureilites are melt-residues, but some are partial cumulates or have interacted with a melt [1,2]. An "unroofing" event occurred while the parent asteroid was hot that froze in mineral core com-positions and resulted in FeO reduction at olivine grain margins. We have studied several new ureilites, but will focus here on two anomalous stones; LAR 04315 and NWA 1241. LAR 04315 is texturally unusual. It contains olivine with angular subdomains, and low-Ca pyroxene riddled with wormy inclusions of metal+troilite, graphite, and possibly other phases, and irregular inclusions of high-Ca pyroxene. Reduction occurred along olivine grain margins and internal fractures, but not along subdomain boundaries. Although texturally odd, LAR 04351 is a typical ureilite in mineral and bulk composition. The olivine is Fo80.8 and falls on the ureilite Fe/Mn-Fe/Mg trend. Its olivine composition falls within the range of the majority of ureilites, and it is typical of these ureilites in bulk rock lithophile and siderophile element contents.

Mittlefehldt, David W.↗
DOE OSTI2023

Outlook on texture evolution in additively manufactured stainless steels: Prospects for hydrogen embrittlement resistance, overview of mechanical, and solidification behavior

Abstract Realizing application specific manufacture with fusion-based additive manufacturing (F-BAM) processes requires understanding of the physical phenomena that drive evolution of microstructural attributes, such as texture. Current approaches for understanding texture evolution in F-BAM are majorly considerate of the phenomena occurring only during solidification. This hinders the comprehensive understanding and control of texture during F-BAM. In this perspective article, we discuss several physical phenomena occurring during and after solidification that can determine texture in F-BAM processed stainless steels (SS). A crystal plasticity-coupled hydrogen adsorption-diffusion modeling framework is also leveraged to demonstrate the prospects of grain boundary engineering with F-BAM for enhanced hydrogen embrittlement resistance of SS. Implications of varying thermokinetics in F-BAM for solidification behavior of SS are discussed. Additionally, microstructural attributes that are key to high temperature mechanical performance of SS are highlighted. Considerations as outlined in this perspective article will enable grain boundary engineering and application specific microstructural design of SS with F-BAM. Graphical abstract

36 MATERIALS SCIENCE↗
NASA NTRS1973

Apollo 16 exploration of Descartes - A geologic summary.

The Cayley Plains at the Apollo 16 landing site consist of crudely stratified breccias to a depth of at least 200 meters, overlain by a regolith 10 to 15 meters thick. Samples, photographs, and observations by the astronauts indicate that most of the rocks are impact breccias derived from an anorthosite-gabbro complex. The least brecciated members of the suite include coarse-grained anorthosite and finer-grained, more mafic rocks, some with igneous and some with metamorphic textures. Much of the transverse area is covered by ejecta from North Ray and South Ray craters, but the abundance of rock fragments increases to the south toward the younger South Ray crater.

Source record↗
NASA NTRS1973

Sintering and hot pressing of Fra Mauro composition glass and the lithification of lunar breccias.

It is proposed that Apollo 14 type breccias lithify by sintering of particles of matrix glass under stress-free conditions. Meteorite impacts generate the heat necessary for sintering. Compacted angular particles of glass with the composition of an Apollo 14 rock were sintered experimentally. Loose clods of sub 37 micron grains form in several days at 700 C. Synthetic rocks, which texturally resemble the breccias, were produced at 795 C and above in 7.5 hours. Glass devitrified with increasing temperature. At 850 C, devitrification prevents much further densification of the synthetic breccias after 2 hours. Experiments compressing glass at 500 bars at 600 C produced dense vitreous masses which did not resemble lunar breccias. Confining pressure does not play a major role in lithifying the breccias. It is concluded that Apollo 14 type lunar breccias form at shallow depths at 800 C+ in a period of minutes to days.

Simonds, C. H.↗
NASA NTRS1974

TDNiCr (ni-20Cr-2ThO2) forging studies

Elevated temperature tensile and stress rupture properties were evaluated for forged TDNiCr (Ni-20Cr-2ThO2) and related to thermomechanical history and microstructure. Forging temperature and final annealed condition had pronounced influences on grain size which, in turn, was related to high temperature strength. Tensile strength improved by a factor of 8 as grain size changed from 1 to 150 microns. Stress-rupture strength was improved by a factor of 3 to 5 by a grain size increase from 10 to 1000 microns. Some contributions to the elevated temperature strength of very large grain material may also occur from the development of a strong texture and a preponderance of small twins. Other conditions promoting the improvement of high temperature strength were: an increase of total reduction, forging which continued the metal deformation inherent in the starting material, a low forging speed, and prior deformation by extrusion. The mechanical properties of optimally forged TDNiCr compared favorably to those of high strength sheet developed for space shuttle application.

Filippi, A. M.↗
NASA NTRS1984

Petrography and classification of Ca, Al-rich and olivine-rich inclusions in the Allende CV3 chondrite

The results of a detailed, systematic petrographic survey of Ca, Al-rich and olivine-rich inclusions in the Allende CV3 chondrite are reported, and a new classification system based on clearly defined and readily applied petrographic criteria is presented. Most Allende inclusions are aggregates containing one or more of three distinct constituents: (1) rimmed concentric objects enriched in Al- and Ti-rich oxide minerals and various amounts of Ca-rich silicates; (2) porous, 'fine-grained' chaotic material enriched in Ca-rich silicates, especially clinopyroxenes and garnets; and (3) porous, 'fine-grained', mafic inclusion matrix, enriched in olivine, pyroxene, and feldspathoids. Two texturally distinct varieties of inclusions consist primarily of inclusion matrix: unrimmed olivine aggregates and rimmed olivine aggregates. Ca, Al-rich inclusions are classified on the basis of the size and abundance of their constituent concentric objects. Some fundamental relationships among Allende inclusions that previusly have not been emphasized are discussed.

Kormacki, A. S.↗
DOE OSTI2015

On the development of the quantitative texture analysis and its application in solving problems of the Earth sciences

A history of texture analysis (TA) evolution is shown, beginning from the first experimental and theoretical attempts to find and characterize preferred orientations of crystal lattices of grains in real polycrystalline samples. Stages of formation of TA theoretical apparatus, its basic elements, and also application of its capabilities for quantitatively describing anisotropic properties of textured samples are discussed. Attention is also paid to the limitations and difficulties associated with the analysis. The application of the quantitative TA apparatus is demonstrated by example describing elastic properties of textured materials up to multiphase samples containing pores and cracks. A wide scope of TA includes the analysis based on neutron scattering which has been effectively developed at the Frank Laboratory of Neutron Physics. A practical opportunity to determine the bulk crystallographic textures of single-phase and multiphase materials is offered by the use of modern neutron diffractometers, including the SKAT diffractometer at the IBR-2 pulsed reactor. This is especially important for studying samples of natural rocks. The examples given show how the neutron scattering data for the quantitative TA are used in combination with other physical and petrological methods for solving fundamental problems of geology and geophysics based on the analysis of a structure and properties of the Earth’s lithosphere matter. The review includes a detailed list of references of original works concerning the TA elaboration, overview publications and monographs, and also information on the most popular TA-related software.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Direct synthesis of highly textured Ge on flexible polyimide films by metal-induced crystallization

The highly (111)-textured Ge thin film (50-nm thickness) is demonstrated on a flexible polyimide film via the low-temperature crystallization (325 °C) of amorphous Ge using Al as a catalyst. Covering the polyimide with insulators significantly improved the crystal quality of the resulting Ge layer. In particular, SiN covering led to 97% (111)-oriented Ge with grains 200 μm in size, two orders larger than the grain size of polycrystalline Ge directly formed on the polyimide film. This achievement will give a way to realize advanced electronic and optical devices simultaneously allowing for high performance, inexpensiveness, and flexibility.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Phase-field model for diffusion-induced grain boundary migration: An application to battery electrodes

Diffusion-induced grain boundary migration is a phenomenon in which a grain boundary moves in response to the driving forces generated by diffusing solute species. For example, diffusing solute species change the atomic volume in the host material, either by filling a vacancy with a misfitting solute atom or by expanding host lattices through interstitial diffusion. These volume changes are inhomogeneous and are stored as elastic energy in the material that drives grain boundaries. In this paper, we introduce our previously developed Cahn-Hilliard–phase-field-crystal model (CH-PFC) as a computational tool to investigate diffusion-induced grain boundary migration in crystalline materials. This multiscale phase-field model couples the composition field of a diffusing species with the crystallographic texture of a host material. We apply the CH-PFC model to battery electrodes and investigate whether interstitial solute diffusion induces grain growth in FePO 4 /LiFePO 4 electrodes. To this end, we compute grain growth in 60 FePO 4 electrodes by conducting two parallel trials: In the first trial, we cycle the electrode and calculate diffusion-induced grain growth. In the second trial, we do not cycle the electrode and calculate curvature-driven grain growth. We find a statistically significant grain growth in the cycled electrodes and negligible grain growth in the noncycled electrodes. Altogether, we show that the CH-PFC model not only predicts electrode microstructures as a function of the Li composition, but also predicts the crystallographic features of an electrode during battery operation.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Metallic minerals, thermal histories and parent bodies of some xenolithic, ordinary chondrite meteorites

The metal grains were investigated in the hosts and lithic fragments of various petrologic types in four xenolithic chondrites using reflected-light microscopy and electron-probe analysis. The kamacite, taenite, tetrataenite, and troilite in Weston and Fayetteville have many textures; on a Wood plot of the central Ni content vs dimensions, the taenite content shows scatter if metal grains had cooled at rates of 10-1000 and 1-100 K/Myr through 700 K. In contrast, metallic minerals in Bhola and Mezo-Madaras have uniform textures and plot coherently, indicating cooling rates of 0.1 and 1 K/Myr, respectively, in the 700-600 K range. It is concluded that the host and xenoliths in these chondrites were cooled slowly after compaction; their clasts underwent peak metamorphic temperatures and slow cooling through 700 K in different environments.

Scott, E. R. D.↗
DOE OSTI2014

The microstructure and mechanical behaviors of the Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy produced by laser melting deposition

The microstructure and mechanical properties of the Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy produced by laser melting deposition have been investigated. The columnar grains of the Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy due to the layer-by-layer epitaxial growth from the underlying template grains during laser melting deposition, which is roughly parallel to the deposition direction, had been found by optical microscopy; strong [101{sup ¯}2]{sub α} crystallographic texture has been confirmed by X-ray diffraction and electron backscattered diffraction. Depending on the last heating history, the microstructure of the alloy undergoes a continued change opposite to the deposition direction: martensitic α′ (transformed β); coarsened primary α laths with transformed β; coarsened primary α laths; and the fine basketweave microstructure with a few coarsened α laths or annealed martensitic α′. The average Vickers micro-hardness value of the alloy is 364 HV. The alloy parallel to the deposition direction presents lower tensile strength (925 MPa) and better elongation (18.8%), compared with 1025 MPa and 8.2% of that vertical to the deposition direction, which has been discussed using its microstructure characterization. - Highlights: • The columnar grains and strong [101{sup ¯}2]{sub α} crystallographic texture of the Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy due to the epitaxial growth from the underlying template grains • The microstructure evolution of the alloy depends on the last heating history. • The specimen parallel to the deposition direction presents lower ultimate tensile strength and higher elongation than the specimen vertical to the deposition direction.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Nanotwinned alloys under high pressure

Nanotwinned alloys are of interest due to their high strength and ductility, but twin boundaries may not be stable under shear. Computational studies indicate that high hydrostatic pressure may suppress detwinning mechanisms. Here, in this study, we investigate the microstructural changes of nanotwinned-nanocrystalline copper-nickel and Inconel 725 alloys under quasi-hydrostatic pressures up to 50 gigapascals (GPa). The alloys are compressed in a diamond anvil cell. In-situ x-ray diffraction (XRD) and ex-situ transmission electron microscopy (TEM) were employed to monitor microstructural changes. Twin boundary deformation and grain growth occur at 11.4 GPa quasi-hydrostatic pressure in the copper-nickel alloy. Molecular dynamics (MD) simulations reveal that hydrostatic pressure causes elevated local shear stress at grain boundaries, which leads to atomic rearrangements. A superposition of hydrostatic and deviatoric pressures lead to partial dislocation mediated twin boundary migration. In contrast, the Inconel 725 alloy showed stable twin and grain boundaries up to a quasi-hydrostatic pressure of 12.7 GPa. Texture, high solid solution strengthening, and low stacking fault energy are hypothesized to the enhanced microstructural stability in Inconel 725.

36 MATERIALS SCIENCE↗