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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Flow Patterns, Microstructure and Mechanical Properties of AZ31/Al6061 Dissimilar Friction Stir-Welded Joints

Dissimilar joints between die-cast AZ31 and extruded Al6061-T6 were joined using friction stir welding technology at a constant transverse speed (50 mm/min) and rotation rate of 800 or 1000 rpm. The flow patterns, microstructure evolution and intermetallic compounds in dissimilar joints were studied by optical and scanning electron microscopy. The relationship between microstructure and tensile properties was analyzed. The microhardness distribution along the horizontal centerline in cross section was investigated. Local flow without obvious mixing existed between Mg and Al metals in the tool shoulder-affected zone. For the tool-pin-affected zone, two typical zones, namely, the “extrusion zone” and “flow zone” existed because of the different flow modes of the plastic metals. The phase analysis showed that intermetallic compounds, including Al{sub 12}Mg{sub 17} and Al{sub 3}Mg{sub 2} formed in banded structures. Phase analysis showed that a joint with welding parameters of 800 rpm and 50 mm/min (Joint-500) had good mechanical properties because of the more uniform microstructure distribution and fewer intermetallic compounds. Fracture analysis indicated some microvoids and lamellate intermetallic compounds in the fracture surface of the joint with welding parameters of 1000 rpm and 50 mm/min (Joint-1000), which deteriorated its tensile strength significantly.

36 MATERIALS SCIENCE↗
DOE OSTI2017

TEM analysis of the deformation microstructure of polycrystalline cobalt plastically strained in tension

Highlights: • Deformation of cobalt was studied by TEM and AE. • Basal dislocation glide is the main deformation mechanism in first straining stage. • Twinning mechanism becomes predominant in the second stage. • Statistical analysis was performed in data set generated by electron diffraction. • Tensile {10 2-bar 1} twins are the most common twins in cobalt. - Abstract: The microstructure evolution of hexagonal close-packed cobalt at different stages of work hardening has been studied. The deformation microstructure of polycrystalline samples upon a tension test was investigated by Transmission Electron Microscopy (TEM). Corresponding straining mechanisms were also identified by acoustic emission measurements. It was shown that dislocation glide is the predominant deformation mechanism during the first stage of plastic deformation, while twinning becomes the prominent strain accommodation mechanism in the later stage. A detailed TEM study using electron diffraction allowed identifying different types of twins activated during tensile testing. Four single twinning modes were identified, from which two types correspond to tensile strain and two types to compressive strain (with respect to the c direction), double twins were also observed. A relative importance of various systems is estimated and it is shown that the vast majority of twins correspond to the {10 1-bar 2} twinning system.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Shear deformation of pure-Cu and Cu/Nb nano-laminates using micromechanical testing

Solid phase processing by introducing shear deformation into materials can result in unique microstructure evolution and enhanced mechanical properties, especially for immiscible systems such as Cu/Nb. To better understand the correlation between microstructure and deformation behavior during shear, a dedicated testing design of stress localization at predicted sites is necessary. In this study, a specialized S-shaped specimen geometry is implemented to apply localized simple-shear loading in pure-Cu and Cu/Nb accumulative roll-bonded nanolaminates. The nanoscale microstructure and proximity of interfaces in Cu/Nb offer a ~2.8-fold increase in shear stresses than pure-Cu. In pure-Cu, the plastic instability causes shear banding and an in-plane lattice rotation. In Cu/Nb, a partial bending of the interfaces occurred, resulting in a localized lattice rotation. The adapted geometry for micro-scale specimens thus successfully captures the shear deformation at predicted sites in two distinct material systems and could potentially be a powerful technique to study the deformation mechanisms.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Age hardening response of Cu-30Ni alloys: The role of Si microalloying additions

Cu-30Ni alloys offer high strength and excellent corrosion resistance for maritime applications. While primarily a solid solution system, industrial alloys typically include microalloying additions of Fe, Mn, Nb and/or Si to enable age hardening. However, an understanding of the microstructural evolution during age hardening remains incomplete. Here, we conduct systematic ageing treatments and report the resulting hardness and microstructures. The Cu-30Ni alloy with Si aged at 650 °C for 6 h demonstrates significantly enhanced Vickers hardness, reaching ∼201 HV 1 compared to 103 HV 1 for the as-homogenised sample. Si-rich clusters and γ′ precipitates are identified, with their composition, size, and volume fraction quantified to determine their strengthening contributions. First-principles atomistic simulations elucidate the underlying formation mechanisms of these clusters and precipitates, highlighting the critical role of Si in driving their nucleation and growth. This study advances the design of high-strength, Cu alloys with the potential for corrosion resistance in demanding maritime environments.

Age hardening↗
DOE OSTI2022

Damage Accumulations Predictions for Boiler Components Via Microstructurally Informed Material Models

The goal of the project was to model material behavior and degradation during cyclic plasticity— with and without hold time—for nickel-based superalloys used in USC (ultra-super-critical) and A-USC (advanced-ultra-super-critical) boiler components. The study provided physically informed models, capturing the microstructural changes taking place in the industrial components under cyclic loading and long duration stress (up to 300,000 hours) and high temperature exposure (1100°F/593°C to 1400°F/760°C). The major developments were: 1) Qualitative and quantitative understanding of microstructure evolution (gamma prime precipitates), deformation (dislocation density), and damage mechanisms of Haynes ® 282 alloy. 2) Qualitative understanding of microstructural features generating local strain variations. 3) A continuum damage mechanics model (CDM) for Haynes ® 282 alloy at 1100°F to 1400°F capturing cyclic behavior with and without hold time. 4) Structural analysis for creep and LCF life predictions of an USC thick-wall Grade 91 superheater steel header and understanding life sensitivity to wall thickness of an AUSC Haynes ® 282 header.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2019

Improvement of Al/Steel Tungsten Inert Gas Welding–Brazing Joint by High-Energy Shot Peening

High-energy shot peening treatment was applied to improve the Al/steel tungsten inert gas welding–brazing lap joint. The mechanical properties and microstructure evolution of the joint were investigated. Results showed that the mechanical properties of weld were evidently reinforced due to microstructure transformation of joint surface layer. The grain structure in the joint surface layer was distorted and refined. Large compressive residual stress was introduced into the joint surface, and its hardness obviously increased due to strain hardening. When the peening pressure was 0.15 MPa, the tensile shear strength of the joint reached the maximum value (199.6 MPa), which was 16.5% higher than that of the as-welded joint.

36 MATERIALS SCIENCE↗
DOE OSTI2017

An EBSD Evaluation of the Microstructure of Crept Nimonic 101 for the Validation of a Polycrystal–Plasticity Model

Nimonic 101 is one of the early nickel-based superalloys developed for the use in gas turbines. In such environments, the material is exposed to a combination of both high temperatures and mechanical loads for a long duration. Hence, thermal creep is of the utmost concern as it often limits service life. This study focuses on creep tests, carried out on Nimonic 101 at different temperatures under a constant tensile load of 735 MPa. To characterize the microstructural evolution, electron backscatter diffraction (EBSD) measurements were employed before and after loading. At higher temperatures, a significant change of the microstructure was observed. The grains elongated and aligned their orientation along the load axis. In parallel, a crystal plasticity material model has been set up in the classical large deformation framework. Modeling results are compared to the acquired EBSD data.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Microstructural Coarsening Kinetics and Mechanical Property Changes in Long-Term Aged Sn–Pb–Sb Solder Joints

Tin-lead-antimony (50Sn–47Pb–3Sb wt.%) soldered assemblies were mechanically tested approximately 30 years after initial production and found to have solder joints of reduced strength. The microstructure of this solder alloy exhibits a ternary eutectic structure with Sn-rich, Pb-rich, and SnSb phases. Accelerated aging was performed to evaluate solder microstructural coarsening and associated strength of laboratory solder joints to correlate these properties to the “naturally aged” solder joints. Isothermal aging was conducted at room temperature, 55, 70, 100, and 135 °C and aging times that ranged from 0.1 to 365 days. The coarsening kinetics of the Pb-rich phase were determined through optical microscopy and image analysis methods established in previous studies on binary Sn–Pb solder. A kinetic equation was developed with time exponent n of 0.43 and activation energy of 24000 J/mol, suggesting grain boundary diffusion or other fast diffusion pathways controlling the microstructural evolution. Compression testing and Vickers microhardness showed significant strength loss within the first 20–30 days after soldering; then, the microstructure and mechanical properties changed more slowly over long periods of time. Further, by combining accelerated aging data and the microstructure-based kinetics, strength predictions were made that match well with the properties of the actual soldered assemblies naturally aged for 30 years. However, aging at the highest temperature of 135 °C produced anomalous behavior suggesting that extraneous aging mechanisms are active. Therefore, data obtained at this temperature or higher should not be used. Overall, the combined microstructural and mechanical property methods used in this study confirmed that the observed reduction in strength of ~ 30-year-old solder joints can be accounted for by the microstructural coarsening that takes place during long-term solid-state aging.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Understanding structure-processing relationships in metal additive manufacturing via featurization of microstructural images

Understanding and predicting accurate property-structure-processing relationships for additively manufactured components is important for both forward and inverse design of robust, reliable parts and assemblies. While direct mapping of process parameters to properties is sometimes plausible, it is often rendered difficult due to poor microstructural control. Exploring the direct relationship between processing conditions and microstructural features can thus provide significant physical insights and aid the overall design process. Here, in this study, we develop an automated high-throughput framework to simulate an uncertainty-aware additive manufacturing (AM) process, characterize microstructural images, and extract meaningful features/descriptors. A kinetic Monte Carlo (KMC) based model of the AM process is used to simulate microstructural evolution for a diverse set of experimentally relevant processing conditions. We perform a parametric study to explore the relationship between microstructural features and processing conditions. Our results indicate that a many-to-one mapping can exist between processing conditions and typical descriptors; therefore, multiple descriptors are thus necessary to unambiguously represent microstructural images. Our work provides crucial quantitative and qualitative in-formation that would aid in the selection of features for microstructural images. Featurized microstructures could then be utilized to build data-driven models for predictive control of microstructures and thereby properties of additively manufactured components.

36 MATERIALS SCIENCE↗
DOE OSTI2021

The subsurface structure of abraded Al–Zn–Mg–Cu alloy

Surface abrasion has been shown to introduce heavy shear stress and produce a few hundred nanometers thick altered surface layer (ASL) on Al alloys. Such ASLs exhibit microstructural changes at room temperature and different corrosion resistance than the underlying substrate. Here, we report how sample dimensions and temperature affect the deformed subsurface microstructure evolution on an abraded Al–Zn–Mg–Cu alloy using transmission electron microscopy (TEM) and atom probe tomography. The ASL microstructure evolves differently in the bulk sample than in the thin TEM specimen. In the freshly abraded ASL, the original η'/η precipitates and grain boundaries were deformed toward the abrasion direction. After 7-day natural aging of the freshly abraded bulk sample, well-defined subgrains formed locally in the ASL, and unusual Al 2 Cu (θ) and Mg x Zn y phases precipitated at the subgrain boundaries. However, during natural aging of this TEM specimen taken from the abraded and aged bulk samples, much faster changes occurred, including the continued formation of subgrains and θ particles in the entire ASL, and the diffusion of Zn atoms out of Mg x Zn y particles to form a Zn particle. On the other hand, no obvious microstructural changes occurred in the ASL during 3-month natural aging of the TEM specimen immediately taken from the freshly abraded sample. Finally, this work advances the understanding of how Al alloy microstructures respond during and following any shear deformation, and complex and unexpected effects of sample dimensions on the behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Multiscale Model for Simulating Fission-Induced Recrystallization in U-Mo Alloy

U-Mo alloy is one of the most promising fuels for the future high performance research and test reactors due to its high uranium loading density and stable irradiation behavior. However, a major concern to its qualification is the fuel swelling at high fission density due to the formation of large fission-gas bubbles. The fission-induced recrystallization further expedites the formation and growth of gas bubbles. So far, the exact mechanism of recrystallization is still unclear. One possible driving force for recrystallization is the production of point defects and interstitial loops due to irradiation. Following this, we developed a multi-scale model by integrating the rate-theory and phase-field models to study microstructural evolutions in irradiated U-Mo alloy, i.e., fission-induced gas bubble evolution and recrystallization. Density function theory (DFT) calculations are utilized to predict the defect formation energies, diffusivities of defects, the interfacial energy of gas bubble, and the elastic constants of U-Mo alloy, etc. The dislocation density evolution is predicted by the rate-theory developed by Jeff. The grain subdivision occurs once the dislocation density is above a critical value. The grain growth coupled with gas bubbles evolution is modeled using a multi-phase phase-field model. The effects of fission rate and initial grain microstructure on the recrystallization process are systematically investigated. The simulated dislocation density, sub-grain size distribution, and volume fraction of the recrystallization grains under different fission density are comparable with experimental data. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

Manufacturing ODS Steels from GARS Powders by Friction Consolidation and Extrusion

Previous research suggested that friction-based processing is a promising method for fabricating oxide dispersion-strengthened (ODS) steel. In this study, we combined friction consolidation and friction extrusion to successfully manufacture ODS steel rods using precursor powder made with gas atomization reaction synthesis. We examined the microstructure evolution from the initial powder to the final extruded rod, which revealed the dispersion process of Y. Additionally, by comparing the microstructures of three rods extruded at different temperatures, we showed that low-temperature friction extrusion effectively enhanced microstructure uniformity and prevented grain coarsening, leading to improved mechanical properties. Furthermore, our findings provide practical guidelines for adjusting processing parameters in the production of ODS steel using friction-based processing.

36 MATERIALS SCIENCE↗
DOE OSTI2023

An efficient instance segmentation approach for studying fission gas bubbles in irradiated metallic nuclear fuel

Abstract Gaseous fission products from nuclear fission reactions tend to form fission gas bubbles of various shapes and sizes inside nuclear fuel. The behavior of fission gas bubbles dictates nuclear fuel performances, such as fission gas release, grain growth, swelling, and fuel cladding mechanical interaction. Although mechanical understanding of the overall evolution behavior of fission gas bubbles is well known, lacking the quantitative data and high-level correlation between burnup/temperature and microstructure evolution blocks the development of predictive models and reduces the possibility of accelerating the qualification for new fuel forms. Historical characterization of fission gas bubbles in irradiated nuclear fuel relied on a simple threshold method working on low-resolution optical microscopy images. Advanced characterization of fission gas bubbles using scanning electron microscopic images reveals unprecedented details and extensive morphological data, which strains the effectiveness of conventional methods. This paper proposes a hybrid framework, based on digital image processing and deep learning models, to efficiently detect and classify fission gas bubbles from scanning electron microscopic images. The developed bubble annotation tool used a multitask deep learning network that integrates U-Net and ResNet to accomplish instance-level bubble segmentation. With limited annotated data, the model achieves a recall ratio of more than 90%, a leap forward compared to the threshold method. The model has the capability to identify fission gas bubbles with and without lanthanides to better understand the movement of lanthanide fission products and fuel cladding chemical interaction. Lastly, the deep learning model is versatile and applicable to the micro-structure segmentation of similar materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Final Cooling Temperature on Microstructure and Mechanical Properties of a Cr-Ni-Mo-V Bainite Steel

The microstructural evolution and mechanical properties of a low-carbon high-strength bainitic steel under different final cooling temperatures were studied. The microstructures of the experimental steel at different final cooling temperatures were composed of acicular ferrite and granular bainite. A decrease in final cooling temperature resulted in an increase in volume fraction of granular bainite and a decrease in volume fraction of acicular ferrite. The specimen with the lowest final cooling temperature (459 °C) exhibited the highest yield strength, tensile strength, and yield ratio, and a lower total elongation than the specimens with the highest final cooling temperatures (501 and 535 °C) because of the higher volume fraction of granular bainite and finer bainitic ferrite lath. The specimen with the lowest final cooling temperature had a lower absorbed energy than that of the highest final cooling temperature, because the strip-like martensite–austenite (M-A) constituents that existed between the bainitic ferrite or in prior austenite grain boundaries reduced its toughness. At an intermediate final cooling temperature of 501 °C, the experimental steel exhibited excellent mechanical properties with a yield strength, tensile strength, and absorbed energy of 825 MPa, 1232 MPa, and 102 J, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Study of retained austenite and nano-scale precipitation and their effects on properties of a low alloyed multi-phase steel by the two-step intercritical treatment

Microstructure evolution and properties were studied in a low carbon low alloyed hot-rolled bainitic steel by annealing and annealing plus tempering. Microstructure of the hot-rolled steel consists of lath bainite and martensite. By annealing at 720 °C for 30 min and water quenching, multi-phase microstructure consisting of intercritical ferrite, tempered bainite/martensite, retained austenite and fresh martensite was obtained. With increasing annealing temperature to 760 °C, microstructure of the steel consisted of intercritical ferrite, fresh martensite without retained austenite. After the second step of tempering at 680 °C for samples annealed both at 720 °C and 760 °C, ~ 8–9% volume fraction of retained austenite was obtained in the multi-phase microstructure. Moreover, fine precipitates of VC with size smaller than 10 nm and copper precipitates with size of ~ 10–50 nm were obtained after tempering. Results from scanning transmission electron microscopy (STEM) give evidence to support that the partitioning of Mn, Ni and Cu is of significance for retained austenite stabilization. Due to the combined contribution of multiphase microstructure, the transformation-induced-plasticity effect of retained austenite and strengthening effect of nanometer-sized precipitates, yield strength greater than 800 MPa, yield to tensile ratio of 0.9, uniform elongation of ~ 9% and good low temperature impact toughness of 147 J at − 40 °C were achieved. - Highlights: • Stable retained austenite was produced in a low alloyed steel. • Partition of Mn, Ni and Cu was confirmed by STEM for austenite stabilization. • Nano-sized VC and Cu precipitates were achieved by second tempering. • High strength–high toughness with low Y/T ratio was obtained.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Salt-Mediated Coarsening in Conversion-Reaction-Synthesized Nanoporous Metals and Nanocomposites Resolved through In Situ Synchrotron Diffraction Studies

High-energy synchrotron X-rays were used to probe the structural and microstructural evolution in Fe, Co, and Cu nanoporous metals (NPMs) and metal/salt nanocomposites (NCs) produced by recently developed conversion reaction synthesis (CRS) methods. Microstructure analysis of as-synthesized samples via whole pattern fitting showed that the NPMs exhibit domain sizes that increase as Co < Fe < Cu, with both Fe and Co having crystallite sizes below 3.0 nm. The as-synthesized metal/salt NCs had similar metal sizes, and additionally, the salt in the composite had unusually large lattice microstrain whose origin is attributed to chemical substitution of metal ions into the salt (e.g., Li $1–3x$ Fe $x$ Cl for Fe 3+ ). When thermal annealing is used to modify crystallite size, pore collapse often occurs in NPMs but NCs can be effectively tuned without this problem. While the NC coarsening occurs slowly at low temperatures, it was found that there is a drastic acceleration of the reaction rate at a specific onset temperature that results in the crystallite size increasing by an order of magnitude in about a minute. Curiously, there was no evidence in the diffraction data for salt melting at this onset temperature. However, there was a sharp reduction in the salt chemical lattice strain at the onset temperature, indicating that rapid metal coarsening is facilitated by the salt. Importantly, this behavior indicates an unexpectedly coupled reaction mechanism by which the metal ions needed for grain growth are supplied by the salt in a rate-limiting fashion.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2026

Irradiation-Induced Structural Disorder and Its Influence on the Mechanical Response of Polycrystalline MoS2

Molybdenum disulfide (MoS2) thin films are widely used as dry-film lubricants and protective coatings in aerospace and other radiation-exposed environments. Conventional synthesis routes produce polycrystalline films whose grain boundaries and other native defects cause their mechanical and tribological behavior to differ substantially from that of ideal single crystals. Under irradiation, these films progressively evolve from polycrystalline structures, composed of layered MoS2 grains, into highly disordered and eventually amorphous structures, altering both their tribological performance and mechanical integrity. Here, we employ reactive atomistic simulations to investigate irradiation-driven structural evolution in bulk polycrystalline MoS2. Using controlled primary knock-on atom (PKA) events, we characterize the progressive transition from a polycrystalline microstructure to an amorphous network by tracking defect accumulation and structural disorder. We then establish how this transition modifies the dominant deformation mechanisms and the temperature-dependent tensile response. Specifically, irradiation suppresses interlayer sliding and delamination, mechanisms which facilitate the deformation of the pristine polycrystal, resulting in defect-induced hardening. Broadly, our results establish direct process–structure–property relationships linking irradiation-induced defect accumulation, microstructural evolution, deformation mechanisms, and mechanical behavior, providing an atomistic framework for understanding the structural integrity and long-term reliability of irradiated MoS2 coatings.

Moore, Daniel [Sandia National Laboratories (SNL)]↗
DOE OSTI2018

Elucidating Lithium Alloying-Induced Degradation Evolution in High-Capacity Electrodes

Alloy electrode materials offer high capacity in lithium ion batteries; however, they exhibit rapid degradation resulting in particle disintegration and electrochemical performance decay. Here in this study, the evolution of lithium alloying induced degradation due to electrochemo-mechanical interactions is examined based on a multi-pronged electrochemical and microstructural analysis. Copper-tin (Cu 6 Sn 5 ) is chosen as an exemplary alloy electrode material. Electrodes with compositional variations were fabricated and electrochemical performance was examined under varying conditions including voltage window, C-rate, and short- and long-term cycling. Morphology and composition analyses of pristine and cycled electrodes were conducted using micrography and spectroscopy techniques. Alloying induced electrode microstructural evolution was probed using X-ray microtomography. The rapid capacity fading was found to be caused by mechanical degradation of the electrode. Driving the electrode to a lower potential (E ≈ 0.2 V vs. Li/Li + ) induced Li-Sn alloy formation and provided the characteristic large capacity; however, this led to a large volume expansion and active particle cracking and disintegration. Copper expulsion was found to be a consequence of the alloy formation; however, it was not the primary contributor to the dramatic electrochemical performance decay.

25 ENERGY STORAGE↗