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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

From Cryogenic to High Temperatures: A Microstructural Evolution of δ-phase Pu-Ga Alloys Investigated by Time-of-Flight High-resolution Neutron Diffraction

Phase stability and phase transformations in binary Pu alloys are critical for multiple applications. Long-term phase stability affects mechanical properties, microstructure, corrosion behavior, and structural integrity. A clear and detailed understanding of phase transformations and phase stability mechanisms is necessary to assess the behavior and response to unexpected stimuli. Gaining advanced knowledge on the behavior of Pu and Pu alloys at a variety of temperatures, pressures, and time will ensure better predictions and control on evolution outside laboratory measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure Evolution and Mechanical Properties of the AZ91 Magnesium Alloy with Sr and Ti Additions in the As-Cast and As-Aged Conditions

Effect of different amounts of Sr and Ti additions with T6 heat treatment on microstructure and mechanical properties of the AZ91 alloy was investigated. The microstructure of the AZ91 alloy is consisted of the α-Mg phase surrounded by the semicontinuous network of β-Mg{sub 17}Al{sub 12} intermetallics. The average grain size and volume fraction of β phase decreased up to 1 wt.% Sr and 0.1 wt.% Ti additions. Exceeding Ti additions led to increase in both grain size and volume fraction. It was found that the grain refinement mechanism of AZ91 alloys with Sr additions was grain restriction factor. Also, 0.1 wt.% Ti addition could refine the grain structure of the AZ91 alloy by the formation of Al{sub 3}Ti particles that act as nucleation sites for the α-Mg phase. Furthermore, adding 1 wt.% Sr and 0.1 wt.% Ti enhanced the hardness values for both cast and aged AZ91 alloy. Moreover, ultimate tensile strength and tensile elongation values reached their maximum amounts with the 0.5 wt.% Sr and 0.1 wt.% Ti additions and more Sr and Ti additions deteriorated the mechanical properties of cast and aged AZ91 alloys. The fracture surface characterizations had good relations with the tensile properties. The fracture modes were cleavage and quasi-cleavage in the cast and aged AZ91 alloys. Furthermore, the optimum levels of Sr and Ti additions altered the fracture modes to more quasi-cleavage fractures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of stored strain energy heterogeneity on microstructure evolution of 90% cold rolled AISI 304L stainless steel during interrupted annealing treatment

Highlights: • Study of usefulness of stored strain energy distribution map of the material for variable temperature range. • Advantage of using stored strain energy distribution map • Variation observed in stored energy between isothermal annealing treatment and interrupted annealing treatment. - Abstract: This research work is an attempt to understand the effect of stored strain energy heterogeneity over macro-scale, induced during interrupted annealing treatment, on the micro structural evolution in a heavily cold rolled AISI 304L austenitic stainless steel. The cold rolled AISI 304L stainless steel (SS) samples were subjected to different annealing treatments. The microstructures obtained after each annealing treatment were characterized using optical and electron microscopy techniques. Further, an attempt was made to estimate the stored strain energy by a novel approach of micro hardness measurement both over small scale (area 3600 μm{sup 2}) and large scale (area ~0.25 mm{sup 2}). The stored strain energy was determined using hardness values. Using these data, spatial stored strain energy distribution contour maps were created. They were, in turn, used to characterize the local softening behavior both at micro and macro-scale levels after each interrupted annealing treatment. The results showed that, interrupted annealing treatment induces increased stored strain energy heterogeneity after each annealing interruptions. Also, it was possible to determine recrystallization kinetics of the material using stored strain energy map, which helps in designing annealing cycles for achieving ultrafine grained microstructure.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Probing the Influence of Thermally Induced Structural Changes on the Microstructural Evolution in Shale using Multiscale X-ray Scattering Measurements

Various pathways to accelerate the recovery of hydrocarbons from unconventional subsurface environments have been proposed, including the use of high-temperature fluids. However, the influence of temperature on the structural and microstructural changes in complex subsurface materials characterized by compositional and morphological heterogeneity are not very well understood. In this study, in operando ultrasmall angle, small angle, and wide-angle X-ray scattering (USAXS/ SAXS/WAXS) measurements were performed to link the structural and morphological changes in shale when heated from 30 to 1150 °C. The structural changes observed from the wide-angle X-ray scattering measurements were complemented by the changes in the porosity, particle size, and surface morphology. Overall, we report the combined USAXS/SAXS measurements showed enhanced smoothness in the pore–solid interface on heating. The dehydroxylation of illite and calcination of calcium carbonate were noted prior to the formation of denser and sintered silicate and alumino-silicate phases such as Mg 2 SiO 4 (forsterite), Fe 0.3 Mg 0.7 (SiO 3 ) (enstatite), and Al 2.35 Si 0.64 O 4.82 (mullite).

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Chemical, Molecular, and Microstructural Evolution of Kerogen during Thermal Maturation: Case Study from the Woodford Shale of Oklahoma

Integrated elemental, spectroscopic (infrared spectroscopy and X-ray absorption near-edge structure), and gas intrusion (helium pycnometry and nitrogen adsorption) analyses are used to characterize the bulk chemical, molecular, and physical microstructures of kerogen spanning a thermal maturity transect (vitrinite reflectance, Ro, from 0.5% to 2.6%) across the Woodford Shale of the Anadarko Basin, Oklahoma. The integration takes advantage of novel procedures to prepare kerogen isolates that preserve both the chemical and physical properties of the organic matter in the bulk shale. The Woodford kerogens follow the expected trends in H/C and O/C coordinates during thermal maturation for type II kerogen. Infrared spectra show that loss of hydrogen from kerogen is related to cracking of hydrogen-rich aliphatic (alkyl) carbon structures from aromatic carbons. Within the range of Ro values < 1.5%, peripheral aromatic carbons remain highly substituted with alkyl (methyl and methylene) and probably heteroatom functional groups. At Ro values > 1.5%, these substitutions are substantially removed and replaced by hydrogen. The evolution of carbon structures inferred from the IR spectra is supported by known carbon bond dissociation energies for carbonaceous materials. Total organic sulfur and sulfur-XANES data show that sulfur in Woodford kerogens is dominated by aromatic sulfur (thiophene) and that reactive, aliphatic sulfur (sulfide) is eliminated at low degrees of thermal stress (Ro ≤ 0.9%). At higher thermal stress, sulfur speciation is stable and dominated by thermally stable thiophene. The physical properties of Woodford kerogens evolve during thermal maturation in a manner consistent with their molecular characteristics. Skeletal density of kerogen increases during maturation in a manner that is linearly correlated to its atomic H/C ratio and inferred aromatic carbon content. The specific surface area of kerogen also increases during maturation, reflecting the development of internal pores within the kerogen skeletal framework as aliphatic carbon structures are preferentially cracked and expelled from solid kerogen. The quantitative chemical and structural changes expressed by the Woodford kerogens during thermal maturation, including their hydrogen and carbon content, carbon speciation, and skeletal density, are shown by comparison to not be measurably different for other type II kerogens from numerous oil- and gas-producing shale plays, indicating that thermal stress acts to drive maturation of type II kerogen in a similar way globally.

58 GEOSCIENCES↗
DOE OSTI2019

Microstructure Evolution and Improved Creep Behavior of Mg-Al-Si Alloy Matrix Composite Reinforced with SiC Nanoparticles

The Mg-9Al-1Si matrix composite reinforced with SiC nanoparticles is fabricated by semisolid stirring-assisted ultrasonic vibration, which contains finer grains and a more uniform microstructure compared to that of the Mg-9Al-1Si alloys. The sizes of the Mg{sub 17}Al{sub 12} and Mg{sub 2}Si phases decreased continuously as the volume fraction of n-SiCp increased from 0 to 1% and then increased apparently when the volume fraction of n-SiCp increased to 1.5%. The steady-creep rates of the 1 vol.% n-SiCp/Mg-9Al-1Si are approximately two times lower than those of the Mg-9Al-1Si matrix alloy at 200 °C under applied stress of 70 MPa due to the strengthening effect of the nanosized SiCp. The reason for the improved creep properties is mainly attributed to the obvious grain boundary strengthening, the Orowan strengthening mechanism, the load transfer effect, and the pinning effect of the n-SiCp and the refined Mg{sub 17}Al{sub 12} and Mg{sub 2}Si phases.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Dynamic recrystallization kinetics and microstructure evolution of an AZ91D magnesium alloy during hot compression

Highlights: • DRX kinetic model is developed for the aged AZ91D magnesium alloy. • The DRX behavior in different strained regions was investigated. • Four morphologies of the second phase were proposed during the hot compression tests. • The nucleation mechanisms of the DRX grains were clarified. - Abstract: The flow behavior of as-cast AZ91D magnesium alloy was evaluated by isothermal compression tests within the temperatures of 220 °C, 260 °C, 300 °C, 340 °C, and 380 °C, and the strain rates of 0.001, 0.01, 0.1, 1 and 10s{sup −1}. Based on the stress-strain curve and hyperbolic sine function, the thermal activation energy and the strain rate sensitivity of the material were determined to be 142.2726 kJ·mol{sup −1} and 0.142, respectively. The S type evolution of the dynamic recrystallization with the increasing strain that dynamic recrystallization (DRX) model obtained from stress and strain data. There was a good consistency between the proposed DRX kinetics model and microstructure observation results. Combining isothermal compression specimens with finite element and scanning electron microscopy (SEM) analysis indicated that the sample can be divided into rarely recrystallized region, partially recrystallized region and completely recrystallized region, which falls within the dense deformation zone, free deformation zone and severe deformation zone, respectively. The different forms of the β-Mg{sub 17}Al{sub 12} phase induced by compression tests were confirmed by SEM. Nucleation mechanisms of the DRX were discussed with reference to the transmission electron microscope (TEM) analysis results.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Elevated temperature microstructure evolution of a medium-entropy CrCoNi superalloy containing Al,Ti

A new medium-entropy superalloy was produced based on the compositions of equiatomic CrCoNi and Ni-base superalloy Inconel 740H. Initial alloy design was performed using Thermo-Calc. The aging response and microstructural stability were assessed following heat treatment at temperatures between 600 and 900 °C and durations up to 100 h. Aging from a fully recrystallized state resulted in negligible grain growth and produced γ’ and σ phases. The same phases were present after aging from a cold-rolled state, but partially recrystallized microstructures resulted in multi-modal size distributions and heterogeneous spatial arrangements. Finally, room temperature hardness measurements were used to correlate aging conditions with quantitative precipitate measurements and mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure Evolution of Ultra-Fine-Grained AZ31 B Magnesium Alloy Produced by Submerged Friction Stir Processing

Ten-millimeter-thick strain-hardened AZ31B-H24 magnesium sheets were subjected to friction stir processing (FSP) in air and submerged friction stir processing (SFSP) under water to investigate their microstructures and microhardness properties. Different rotational speeds of 500, 630, 800, and 1000 rpm and traverse speeds of 50, 100, 200, and 350 mm/min were employed for processing the materials. For SFSPed samples, the rotational speed of 500 rpm and 200 mm/min of traverse speed resulted in an ultra-fine-grained structure with a minimum grain size of about 400-500 nm, which is half compared to that of FSPed. It was found that both processes led to variation of crystallographic orientation, and enhancing the rotational speed and lowering the traverse speed promoted the development of a {0002} basal texture. The microhardness of SFSPed material increased significantly up to 110% (~ 95 Hv), while the microhardness was 45% (~ 65 Hv) higher than the base metal (~ 45 Hv) for FSPed material.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of rapid heating and cooling combined with deformation at ultrahigh strain rates on the microstructure evolution of pure titanium shaped charge liner

Highlights: • A slug prepared from pure titanium SCL was recovered after detonation deformation at an ultrahigh strain rate over 10{sup 5} s{sup −1}. • The α → β → α phase transformation occurred in Ti SCL during the ultrahigh-strain -rate deformation. • The microstructures of the recovered slug included lamellar α grains, equiaxed α grains, and jagged α grains. - Abstract: A slug prepared from pure titanium shaped charge liners was recovered after detonation deformation at an ultrahigh strain rate over 10{sup 5} s{sup −1} and high strain over 500%. Optical microscopy, electron backscattered diffraction (EBSD), and transmission electron microscopy (TEM) were employed to investigate the microstructure of the Ti shaped charged liner before and after the detonation deformation. The microstructures of the recovered slug include lamellar α grains, equiaxed α grains within localized shear bands, and jagged α grains. EBSD results indicated that the grain orientation distribution is random and no texture was observed in the slug. TEM observation revealed that the α → β → α phase transformation occurred owing to the rapid heating and cooling combined with deformation at ultrahigh strain rates in the Ti shaped charge liner. No melting phenomenon was observed during the deformation process. The deformation process consisted of the explosive detonation stage combined with rapid heating and the subsequent penetration stage combined with rapid cooling. In the explosive detonation stage, the α → β phase transformation instantaneously occurred via a martensitic mechanism. In the penetration stage, the high-temperature slug in β state was cooled rapidly and showed different deformation behaviors in three different areas.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Predicting mesoscale microstructural evolution in electron beam welding

Using the kinetic Monte Carlo simulator, Stochastic Parallel PARticle Kinetic Simulator, from Sandia National Laboratories, a user routine has been developed to simulate mesoscale predictions of a grain structure near a moving heat source. Here, we demonstrate the use of this user routine to produce voxelized, synthetic, three-dimensional microstructures for electron-beam welding by comparing them with experimentally produced microstructures. When simulation input parameters are matched to experimental process parameters, qualitative and quantitative agreement for both grain size and grain morphology are achieved. The method is capable of simulating both single- and multipass welds. As a result, the simulations provide an opportunity for not only accelerated design but also the integration of simulation and experiments in design such that simulations can receive parameter bounds from experiments and, in turn, provide predictions of a resultant microstructure.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Retardation of Small Creep–Fatigue Crack in Gr. 91 Steel Through the Combined Effects of Stress Relaxation, Microstructural Evolution, and Oxidation

This investigation reports an unusual effect of hold time (up to 10 seconds) on retardation in the growth of creep–fatigue small cracks at 550 °C in Grade 91 steel. The observed phenomenon was interpreted by elucidating multiple processes that are active in the plastic zone at the crack tip. To this effect, microstructural and mechanical responses of the crack tip plastic zone were compared with the mechanical and microstructural responses during low cycle fatigue/creep–fatigue. It is proposed that the stress relaxation that occurs during the hold time can reduce the stress intensity in the plastic zone of crack tip thus, contributing to retardation in the small crack growth rate. Aside from stress relaxation, stress intensity in the crack tip can be further reduced by the phenomenon of cyclic softening that occurs because of plasticity-induced microstructural coarsening. Separately, the contribution of oxidation-induced crack tip shielding is also considered to explain the observed effects of hold time on crack growth rates. Taken together, a combination of stress relaxation, enhanced rate of cyclic softening, and higher degree of oxidation with the introduction of a hold time is demonstrated to be responsible for reduction in the crack growth under creep–fatigue conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Microstructural evolution in Cu-Nb processed via friction consolidation

Immiscible alloys, whether in well-mixed or layered forms, are of increasing interest based on their novel structural and functional properties, such as enhanced thermal stability against grain growth or radiation-induced defect trapping at the interfaces. To address the need for new approaches to tailor microstructures, the microstructural development of an immiscible Cu-Nb alloy processed via friction consolidation of elemental powders is investigated. Friction consolidation is a solid-phase processing technique that imparts severe plastic strain into a deforming volume resulting in elevated temperatures below the melting temperature of the alloy. Two distinct processing pathways were chosen to understand the effect of thermomechanical conditions on the final microstructure. The microstructure was characterized using scanning electron microscopy, scanning transmission electron microscopy, and X-ray diffraction techniques. Path 1 exhibited larger strain, strain rate, and temperature as compared with path 2. In path 1, agglomerated Nb particles were present in the recrystallized ultrafine-grained Cu matrix, while in path 2 extremely fine and dispersed Nb particles were present in a highly deformed Cu matrix. In both pathways, supersaturation of Cu in Nb lattices was noted, but not vice-versa. The asymmetry in mixing is explained based on deformation-based, thermodynamic and kinetic factors. These findings provide a pathway for creation of novel tailored microstructures and improved properties in any number of binary immiscible alloy systems.

Cu-Nb alloys, Microstructural refinement, Friction↗
DOE OSTI2024

Report on the Integration of Experimental and Modeling Data for Initial Equivalence Study of Microstructural Evolution in Irradiated LPBF 316SS

Advanced materials and manufacturing technologies are poised to improve the safety and design characteristics of nuclear technologies and meet US energy, environmental, and economic needs. In particular, metal additive manufacturing (AM) provides an opportunity to produce novel materials and component geometries, but their use is not without hurdles arising from the inherent microstructure variability that can result from the layer-by-layer build approach. Given the greater possible microstructure variability in AM materials—and the dearth of materials test reactors—it is impractical to rely solely on neutron irradiation studies to produce data for materials qualification for every possibility. This work within the Advanced Materials and Manufacturing Technologies (AMMT) Environmental Effects technical area contributes to the rapid qualification framework by developing a science-driven framework for the accelerated qualification of materials for nuclear environments. A key product of the Environmental Effects technical area of the AMMT program is the Licensing Approach with Ions and Neutrons (LAIN). This approach recognizes that whether using existing materials in new environments, newly developed materials tailored for these environments, or new manufacturing methods, the traditional decades-long approach for materials qualification does not facilitate rapid deployment. In FY 2023, the AMMT program presented a conceptual framework of specific steps to fulfill several technical challenges associated with qualifying materials for performance in radiation environments on an accelerated time frame informed by the state of the art in materials science and a review of the current regulatory landscape. The objective of this section of the Environmental Effects technical area is to critically evaluate and refine the proposed qualification framework presented under AMMT by integrating the research results of the neutron irradiations, the ion irradiations, and modeling efforts. These ongoing efforts span across Argonne National Laboratory (ANL), Idaho National Laboratory (INL), and Oak Ridge National Laboratory (ORNL) and are closely coordinated.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructure evolution during near- T g annealing and its effect on shear banding in model alloys

By performing extensive molecular dynamics simulations, we investigate herein the deformation behavior in A l 90 S m 10 and C u 64.5 Z r 35.5 alloys after elongated isothermal annealing in the vicinity of the glass-transition temperature ( T g ). Different microstructural response to the annealing process was observed: A l 90 S m 10 maintains the glassy structure with improved energetic stability, enhanced short-range order (SRO), and a more pronounced spatial network that extends beyond the first atomic shell, while C u 64.5 Z r 35.5 forms nanocrystalline Laves C u 2 Zr phases. Shear banding occurs in both annealed systems under shear loading. For A l 90 S m 10 , the spatial network formed by the local clusters characterizing the SRO of the system is significantly weakened but remains appreciable in the shear band. In contrast, the crystalline ordering in the C u 64.5 Z r 35.5 is completely destroyed during shear banding. Consequently, while displaying higher yield strength, the annealed C u 64.5 Z r 35.5 sample appears to be less ductile. By carefully examining the effect of microstructures on the structural ordering in the shear band and the consequent mechanical response, our work contributes to a better understanding of the deformation mechanism of amorphous alloys as compared with that in crystalline materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Multi‐scale simulation of rock compaction through breakage models with microstructure evolution

Abstract. Regional subsidence due to fluid depletion includes the interaction among multiple physical processes. Specifically, rock compaction is governed by coupled hydro-mechanical feedbacks involving fluid flow, effective stress change and pore collapse. Although poroelastic models are often used to explain the delay between depletion and subsidence, recent evidence indicates that inelastic effects could alter the rock microstructure, thus exacerbating coupling effects. Here, a constitutive law built within the framework of Breakage Mechanics is proposed to account for the inherent connection between rock microstructure, hydraulic conductivity, and pore compaction. Furthermore, it is embedded into a 1-D hydromechanical coupled finite element analysis (FEA) to explore the effects of micro-structure rearrangement on the development of reservoir compaction. Numerical examples with the proposed model are compared with simulations under constant hydraulic conductivity to illustrate the model capability to capture the non-linear processes of reservoir compaction induced by fluid depletion.

Buscarnera, Giuseppe↗
DOE OSTI2019

A Comparative Study of Constitutive Characteristics and Microstructure Evolution between Uniaxial and Plane Strain Compression of an AA6061 Alloy

The hot deformation behavior of an AA6061 alloy was comparatively studied by uniaxial compression (UC) and plane strain compression (PSC) in the temperature range of 300-450 °C and strain rate range of 0.01-5 s{sup −1}. The processing maps were constructed based on a dynamic materials model, and the associated microstructures were observed. Under the same deformation conditions, the flow stress of the AA6061 alloy during PSC is higher than that during UC, which can be characterized by the Zener–Hollomon (Z) parameter in a hyperbolic sine-type equation with an activation energy Q of 175.2 kJ mol{sup −1} and 201.9 kJ mol{sup −1}, respectively. In addition, the instability domain is narrower under PSC compared to that under UC. The observed microstructures also indicate that as the Z value decreases, the tendency of dynamic recrystallization increases during PSC. The softening mechanisms in the AA6061 alloy after PSC and UC mainly consist of the dynamic recovery that is accompanied by a slight dynamic recrystallization. The optimum parameters are in the temperature range of 360-450 °C and strain rate range of 0.03-0.3 s{sup −1} for UC, and for PSC, the optimum parameters are in the temperature range of 320-400 °C and strain rate range of 0.01-0.05 s{sup −1}.

36 MATERIALS SCIENCE↗