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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Neutron transmission simulation of texture in polycrystalline materials

The application Sinpol, a novel tool for neutron transmission data analysis, is used to simulate the effect of deformation and recrystallization crystallographic textures in fcc materials. The texture is characterized using an orientation distribution function (ODF), which describes the distribution of crystal orientations over the three-dimensional orientation space. The Sinpol code combines the transmission contribution of each single crystal grain in the ODF to generate neutron transmission patterns through a polycrystalline aggregate. A series of texture components, commonly found in fcc materials, are considered and their neutron transmission calculated for further analysis of experimental data. The effect of grain statistics is investigated and the simulation results on more complex ODF textures are also presented. Finally, the neutron transmission simulations are successfully benchmarked on experimental data recorded on an additive manufactured Inconel 718 specimen.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Microstructure study of pinning sites of highly (0001) textured Sm(Co,Cu){sub 5} thin films grown on Ru underlayer

In this paper, microstructure study of pinning sites of highly (0001) textured Sm(Co,Cu){sub 5} thin films was presented. Various types of pinning sites were identified, such as voids, grain/matrix boundaries (or crystalline/amorphous boundaries), grain boundaries between crystalline grains, and composition inhomogeneity in grains. One key finding of TEM elemental mapping was that Cu atoms were rich in the inner part of Sm(Co,Cu){sub 5} grains (defined by Sm and Co concentrations), instead of the outer part of grains, such as grain boundaries. Cu served as an alloying element in Sm(Co,Cu){sub 5} grains, not as a doping element to form Cu-rich grain boundaries. A model of Sm(Co,Cu){sub 5} films with lateral graded anisotropy due to composition/crystallization variation can explain the huge difference between the H{sub C} and H{sub K}.

36 MATERIALS SCIENCE↗
NASA NTRS1974

A general model for the textural evolution of lunar soil

The investigation reported is concerned with the qualitative expansion of an earlier model developed by Lindsay (1971, 1972, 1973). Questions regarding the maturity of lunar soils are examined. A multivariate model related to textural maturity is considered, taking into account mean and standard deviations, the asymmetry of the grain size curve, the kurtosis anomaly, and pyroclastic materials. It is concluded that the mean grain size and the standard deviation of the lunar soil can be used as general indicators of the textural maturity of the soil anywhere on the lunar surface.

Lindsay, J. F.↗
NASA NTRS1996

Search for Past Life on Mars: Possible Relict Biogenic Activity in Martian Meteorite ALH84001

Fresh fracture surfaces of the martian meteorite ALH84001 contain abundant polycyclic aromatic hydrocarbons (PAHs). These fresh fracture surfaces also display carbonate globules. Contamination studies suggest the PAHs are indigenous to the meteorite. High resolution scanning and transmission electron microscopy study of surface textures and internal structures of selected carbonate globules show that the globules contain fine-grained, secondary phases of single-domain magnetite and Fe-monosulfides. The carbonate globules are similar in texture and size to some terrestrial bacterially induced carbonate precipitates. Although inorganic formation is possible, formation of the globules by biogenic processes could explain many of the observed features including the PAHs. The PAHs, the carbonate globules, and their associated secondary mineral phases and textures could thus be fossil remains of a past martian biota.

McKay, David S.↗
NASA NTRS1996

Search for past life on Mars: possible relic biogenic activity in martian meteorite ALH84001

Fresh fracture surfaces of the martian meteorite ALH84001 contain abundant polycyclic aromatic hydrocarbons (PAHs). These fresh fracture surfaces also display carbonate globules. Contamination studies suggest that the PAHs are indigenous to the meteorite. High-resolution scanning and transmission electron microscopy study of surface textures and internal structures of selected carbonate globules show that the globules contain fine-grained, secondary phases of single-domain magnetite and Fe-sulfides. The carbonate globules are similar in texture and size to some terrestrial bacterially induced carbonate precipitates. Although inorganic formation is possible, formation of the globules by biogenic processes could explain many of the observed features, including the PAHs. The PAHs, the carbonate globules, and their associated secondary mineral phases and textures could thus be fossil remains of a past martian biota.

NASA Discipline Number 52-10↗
DOE OSTI2013

Microstructural and textural evolution of AZ61 magnesium alloy sheet during bidirectional cyclic bending

In this work, the microstructural and textural evolution in the sheets of AZ61 magnesium alloy was studied by means of bidirectional cyclic bending for 8 passes at 623 K. The bended samples were examined by optical microscopy and electron backscatter diffraction analysis. The results showed that a gradient structure with fine grains about 3 μm in the regions near two surfaces and, in contrast, coarse grains in the middle of the sheet were formed. The evident grain refinement was attributed to twin-assisted dynamic recrystallization and continuous dynamic recrystallization induced by kink bands. The texture intensity was clearly reduced, resulting in a negative gradient distribution, with the texture intensity decreases from the center of the sheet to two surfaces. The weakened texture greatly facilitated the reduction of the yield strength. A higher fracture elongation and a slightly improved ultimate tensile strength were achieved concurrently. - Highlights: • The AZ61 Mg alloy is deformed at 623 K by bidirectional cyclic bending. • A symmetric gradient distribution of fine grains along the thickness is formed. • The basal texture in the regions near two surfaces is weakened significantly.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Annealing-induced microstructural evolution and mechanical anisotropy improvement of the Mg-Gd-Y-Zr alloy processed by hot ring rolling

Highlights: • Growth of SRX grains in GBR is random, while that of TBR is anisotropic. • The new texture component in annealed MR weakens the anisotropy obviously. • T6 treatment leads to an excellent comprehensive mechanical property. - Abstract: Hot ring rolling (HRR) is widely used to fabricate large-size seamless ring-shape components. However, this process produces a severe mechanical anisotropy, which is not acceptable in practical industrial application and should be avoided. This paper reports the annealing-induced microstructural evolution and mechanical anisotropy improvement of HRRed Mg-8.12Gd-1.82Y-0.35Zr alloy ring. Results show that annealing treatment could improve the microstructural homogeneity of the ring owing to the occurrence of static recrystallization (SRX). SRX grains are preferentially formed at twin boundaries and initial grain boundaries due to high dislocation density, high level of stored energy, and stress concentration. Twin boundaries, to some extent, can suppress the migration of SRX grain boundaries. In addition, occurrence of SRX weakens the texture intensity and basal pole inclination, leading to a decrease in the mechanical anisotropy of the ring. Considering the weakened anisotropy, comparable strength, and improved ductility, annealing + aging (T6), compared with direct aging (T5), is a more suitable heat treatment schedule for the HRRed Mg-8.12Gd-1.82Y-0.35Zr alloy ring.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Influence of Rolling Temperature on the Mechanical Properties and Microstructure of Variable-Plane-Rolled Mg-3Al-1Zn Alloy

AZ31 magnesium alloy was produced via variable-plane rolling (VPR) under different temperatures. The effects of rolling temperature on the microstructure, texture and mechanical properties were investigated. A double-peak basal texture was formed during VPR treatment. Dynamic recrystallization (DRX) was observed during the VPR treatment, and it can reduce the texture intensity owing to the coalescence of sub-grains. Four types of twins were observed in the VPR treatment: {10-12} extension twins, {10-13}, {10-11} contraction twins and {10-11}-{10-12} double twins. The suitable temperature of AZ31 magnesium alloy for VPR treatment is determined as 623 K through experiments with tensile yield strength of 240 MPa, compressive yield strength of 162 MPa and elongation of 13%. Owing to the important impact of temperature on mechanical properties, the alloy was further VPRed with a decrease in temperature pass-by-pass. The high temperature of 623 K at the initial passes randomized the texture, which led to notably high ductility.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Coincidence site lattice boundary mechanism for the preferred growth of Goss and Cube grains during annealing in an Al-Cu-Mg alloy

Highlights: • Both Goss and Cube grains are recrystallized out of Brass matrix. • Boundary character between Brass and Goss grains was Σ9, and that between Brass and Cube was Σ5. • Σ9 and Σ5 boundaries only transitionally appeared during recrystallization. • Temperature had decisive effect on the formation and mobility of CSL boundaries. • Σ9 and Σ5 boundaries with high index planes were highly mobile. - Abstract: The formation mechanism of recrystallized textures in an Al-Cu-Mg alloy was investigated by means of three dimensional orientation distribution functions (ODFs) and in-situ electron back-scattered diffraction (EBSD). The results showed that in the hot-rolled alloy with a very sharp Brass texture but weak Copper and S orientations, both Goss and Cube grains were recrystallized out of parent Brass matrix. In-situ EBSD analysis revealed that characteristic boundary between Brass and Goss grains to be Σ9, while that between Brass and Cube grains to be Σ5. Frequency of Σ9 and Σ5 boundaries increased quickly at early stage and then reduced gradually with the process of recrystallization. Annealing at a higher temperature (320 °C) was found to be beneficial for the formation of Σ9 boundary, while at lower one (300 °C), Σ5 boundary became dominant. Besides, with temperature decreasing from 320 to 300 °C, the mobility of Σ9 boundaries was greatly degraded, but relatively, Σ5 boundaries still behaved highly mobile. Principally, the preferred growth of recrystallized Goss and Cube grains was respectively attributed to the high mobility of Σ9 and Σ5 boundaries with high index planes that the square sum of plane index was larger than 3.

36 MATERIALS SCIENCE↗
NASA NTRS2009

Late Reduction Textures in Almahata Sitta Ureilite

The Almahata Sitta ureilite, derived from asteroid 2008 TC3, consists of many individual fragments recovered from the Nubian dessert strewn field [1]. Like most ureilites, it contains abundant carbon and exhibits examples of disequilibrium textures that record a late reduction event accompanied by rapid cooling (tens of degC/h) from high temperatures (1150-1300 C). Variations in Fe/Mg of silicate minerals are accompanied by variations in Fe/Mn, indicating loss of Fe into metal [2]. In coarser-grained fragments of Almahata Sitta, olivine exhibits irregular high mg# rims in contact with networks of interstitial metal 5- 20 microns in typical thickness. This is a common ureilite texture thought to be driven by the reaction of graphite to a CO gas phase and the concurrent reduction of FeO in olivine to Fe metal, with excess silica going primarily into pyroxene (2MgFeSiO4 + C approaches MgSiO4 + MgSiO3 + 2Fe + CO) [3, see also 4,5,6]. Other fragments of Almahata Sitta exhibit anomalous textures such as fine grain size, high porosity, and abundant graphite. Within these fragments pyroxene locally exhibits high-mg# rims in contact with metal and a discreet silica phase, suggesting that the reduction mechanism MgFeSi2O6 + C approaches MgSiO3 + Fe + SiO2 + CO. Metals in Almahata Sitta are particularly unaltered in comparison to ureilite finds. Variations in minor and trace element composition of this metal might partly result from localized dilution as iron is supplied by reduction of silicates.

Herrin, J. S.↗
DOE OSTI2025

Production of Creep-Resistant FeCrAl-ODS

Four ODS FeCrAl alloys with base alloy composition Fe-16Cr-4Al-2Mo-0.2Y (wt.%) were mechanically alloyed with minor additions of CeO 2 and Y 2 O 3 additions and were successfully extruded into rectangular-shaped bars. Two oxide compositions were explored, which were designated NC with oxide addition of 0.5CeO 2 plus 0.2Yin solution of the base alloy powder and PC with additions of 0.5CeO 2 and 0.7Y 2 O 3 to elevate the O level. The microstructure of both alloys revealed by SEM and EBSD to consist of very small grains with sizes of ~450-520 nm and weak texture components. Sub-size tensile specimens fabricated from both alloys were tensile tested from room temperature to 800ºC. The results for both alloys from room temperature to 400ºC showed very high strengths, but low ductilities, especially uniform strain. From 500ºC to 800ºC, the strengths decreased rapidly, and the ductilities increased significantly. The reason for the rapid decreases in tensile strengths above 500ºC for both alloys is not clear, but will require advanced characterization techniques including atom probe tomography, to determine the size and number density of the nano-size oxide particles, and TEM/EFTEM, for investigating the dispersion of nano-size oxide particles on grain boundaries to assess the Zener grain boundary pinning effect, which will hinder grain coarsening at high temperatures that may enhance the Hall Petch strengthening mechanism.

36 MATERIALS SCIENCE↗
NASA NTRS1982

Intergrown mica and montmorillonite in the Allende carbonaceous chondrite

High resolution transmission electron microscopy (HRTEM) observations were made of a mixture of mica and montmorillonite from fine-grained calcium, aluminum inclusions (CAI) in the Allende C3(V) meteorite. A petrographic thin section having a diameter of 4 mm contained CAI fragments ranging from less than 1 to 50 microns. The observed textural and chemical characteristics placed the inclusion in the fine-grained alkali-rich spinel aggregate category of Warks' (1979) classifications of CAIs and as type 3 in Kornacki's classifications of fine grains in Allende. Chemical analyses were performed on the phyllosilicate grains observed in the TEM scan by means of an X ray observed, and the proximity to the matrix boundary suggests a metamorphism which included aqueous alteration at a relatively low temperature.

Tomeoka, K.↗
DOE OSTI2015

An EBSD investigation of cryogenically-rolled Cu–30%Zn brass

Electron backscatter diffraction was used to study grain structure development in heavily cryogenically-rolled Cu–30%Zn brass. The produced microstructure was found to be very inhomogeneous. At a relatively coarse scale, it consisted of texture bands having crystallographic orientations close to the α- and γ-fibers. The texture bands contained internal structure comprising shear bands, mechanical twins, and low-angle boundaries. Such features were more pronounced within the γ-fiber, and this resulted in a heterogeneous ultrafine grain structure. The cryogenic rolling was concluded to be not straightforward for production of nanocrystalline grain structure in Cu–30%Zn brass. - Highlights: • Cryogenic rolling produced an inhomogeneous ultrafine-grained microstructure. • Grain refinement was mainly related with twinning and shear banding. • Grain refinement preferentially occurred in (111) fiber texture.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Structure of Ultrathin Polycrystalline Iron Films Grown on SiO{sub 2}/Si(001)

The structure of polycrystalline Fe films grown on an oxidized Si(001) surface at room temperature has been studied by the technique of high-energy electron diffraction. It has been found that the grain orientation in the films depends of the amount of deposited iron. In Fe films less than 5 nm thick, grains have been found to be randomly oriented. Fe films more than 5 nm in thickness exhibit the (111) texture with an axis coinciding with the surface normal. The angular dispersion of the [111] direction in the Fe lattice from the surface normal is ±25°. It has been found that as the Fe films become thicker, the (111) texture changes to the (110) texture.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Grain detachment and transport clogging during mineral dissolution in carbonate rocks with permeable grain boundaries

In this paper, we explore the effect of permeable grain boundaries on carbonate rock dissolution in order to improve our understanding of grain detachment and migration during reactive flow. To do so we investigated the effects of grain size and enhanced reactivity along grain boundaries on global dissolution kinetics. Variations of permeability and porosity were calculated, and exponential relationships were observed in fractured rocks. Our model employed a reactive transport framework based on the Darcy-Brinkman equation to simulate calcite dissolution in carbonate rocks composed of microporous grains and, included fluid transport along grain boundaries. The model includes fluid flow, solute transport by advection–diffusion, heterogeneous reaction between fluid and minerals and grain detachment with subsequent grain transport in macropores. The migration of solid particles due to dissolution was based on cluster analysis and local movement, and the results show that grain detachment can lead to significant decreases in permeability due to the clogging of transport pathways. Microporous media with smaller grain sizes (fine grains in this study) showed a higher average reaction rate than those with coarser grains. In addition, as the overall rates of geochemical processes are commonly affected by the presence of texture heterogeneities such as fractures, a single fracture (macropore) introduced into a microporous matrix composed of permeable grains and grain boundaries was modelled as a large channel connecting the inlet and outlet of the simulation domain. It was found that macropore clogging by grain detachment temporary decreased permeability, lowering the long-term global reaction rates. Lastly, we observed that increases in flow rate can reduce detachment and fracture clogging by reducing local dissolution along grain boundaries.

58 GEOSCIENCES↗
DOE OSTI2017

Strategy for Texture Management in Metals Additive Manufacturing

Additive manufacturing (AM) technologies have long been recognized for their ability to fabricate complex geometric components directly from models conceptualized through computers, allowing for complicated designs and assemblies to be fabricated at lower costs, with shorter time to market, and improved function. Lacking behind the design complexity aspect is the ability to fully exploit AM processes for control over texture within AM components. Currently, standard heat-fill strategies utilized in AM processes result in largely columnar grain structures. Here, we propose a point heat source fill for the electron beam melting (EBM) process through which the texture in AM materials can be controlled. Using this point heat source strategy, the ability to form either columnar or equiaxed grain structures upon solidification through changes in the process parameters associated with the point heat source fill is demonstrated for the nickel-base superalloy, Inconel 718. Mechanically, the material is demonstrated to exhibit either anisotropic properties for the columnar-grained material fabricated through using the standard raster scan of the EBM process or isotropic properties for the equiaxed material fabricated using the point heat source fill.

36 MATERIALS SCIENCE↗
DOE OSTI2015

On the pressure effect in energetic deposition of Cu thin films by modulated pulsed power magnetron sputtering: A global plasma model and experiments

The modulated pulsed power magnetron sputtering (MPPMS) discharge processes are numerically modeled and experimentally investigated, in order to explore the effect of the pressure on MPPMS discharges as well as on the microstructure of the deposited thin films. A global plasma model has been developed based on a volume-averaged global description of the ionization region, considering the loss of electrons by cross-B diffusion. The temporal variations of internal plasma parameters at different pressures from 0.1 to 0.7 Pa are obtained by fitting the model to duplicate the experimental discharge data, and Cu thin films are deposited by MPPMS at the corresponding pressures. The surface morphology, grain size and orientation, and microstructure of the deposited thin films are investigated by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. By increasing the pressure from 0.1 to 0.7 Pa, both the ion bombardment energy and substrate temperature which are estimated by the modeled plasma parameters decrease, corresponding to the observed transition of the deposited thin films from a void free structure with a wide distribution of grain size (zone T) into an underdense structure with a fine fiber texture (zone 1) in the extended structure zone diagram (SZD). The microstructure and texture transition of Cu thin films are well-explained by the extended SZD, suggesting that the primary plasma processes are properly incorporated in the model. The results contribute to the understanding of the characteristics of MPPMS discharges, as well as its correlation with the microstructure and texture of deposited Cu thin films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Microstructure and texture evolution of Cu–Nb composite wires

The evolution of microstructure and texture in Cu–Nb composite wires fabricated by an accumulative drawing and bundling process was investigated by backscattered electron (BSE), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Results indicate the onset of severe curling and shape changing occurred at the size of Nb ∼ 400 nm with a surface increase of about 6.91 μm{sup 2}/μm{sup 3} (the area per unit volume). Two kinds of grain boundaries in Nb are suggested: one is 20°–50° boundary with a rotate/tilt axis around <110> parallel to drawing direction (DD), and another is > 50° boundary with the axis perpendicular to DD. The curling phenomenon occurred at the Cu–Nb interface and is related not only to the deformation mechanism of Nb but also to the presence of interface. This result is distinct from reported works showing that curling takes place when BCC metals are heavily drawn (Area reduction > 73%). The variation in microstructure and texture evolution between Cu and Nb filaments was discussed based on the differences in deformation mechanisms of these two metals. - Highlights: • Microstructure and texture evolution were studied systematically by EBSD. • In Nb, grain boundaries of 20°–50° have a rotate/tile axis around <110>//DD. • The rotation axes of above 50° boundaries are concentrated around <111> ⊥ DD in Nb. • Curling is related to not only deformation mode of BCC but also Cu–Nb interface.

36 MATERIALS SCIENCE↗