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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 1,549 records · Page 86
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Mechanical Behavior and Structure of Advanced Fe-Cr-Al Alloy Weldments

FeCrAl alloys are promising for developing accident tolerant nuclear fuel claddings. These alloys showed good environmental compatibility and oxidation resistance in elevated-temperature water and steam, as well as low radiation-induced swelling. However, FeCrAl alloys may suffer from several degradation mechanisms, one of which may be a susceptibility to cracking during welding. Here, a set of advanced modified FeCrAl alloys were designed and produced by varying Al-content and employing additions of Nb and TiC. Strength, ductility, and deformation hardening behavior of the advanced FeCrAl alloys and their weldments are discussed.

Gussev, Maxim N.↗
DOE OSTI2019

Joining of Lightweight Dissimilar Materials by Friction Self-Piercing Riveting

In this work, we employed a unique solid-state joining process, friction self-piercing riveting (F-SPR), to join carbon fiber composites to the low-ductility magnesium alloy AZ31B. The localized frictional heat generated between the rotating rivet and the underside of the magnesium sheet softened and prevented crack generation in AZ31B. A consumable joining rivet was designed to join the selected material stacks by F-SPR. Lap shear tensile testing was used to assess the joint quality of specimens produced by F-SPR. The joint interface from the cross-sectioned F-SPR specimen was evaluated by optical microscopy.

Lim, Yong Chae↗
DOE OSTI2021

Precipitate Phase Stability and Mechanical Properties of Alloy 263 and Variants in Wrought or Cast Form

Alloy 263 is a candidate Ni-based superalloy for use in advanced ultra-supercritical (AUSC) power plants that are targeted to operate above 700 °C. Exposure times in this type of environment are considerable with target creep properties specified at 100,000 h making phase stability an important parameter in the alloy selection process. In this investigation, the microstructure of alloy 263 and two modified compositions in both cast and cast/wrought forms were investigated after exposure at 800 °C for various times ranging from 1,000 h to 10,000 h. Tension and creep properties were assessed for all alloys in both forms. Modification to the Ti and Al concentrations successfully slowed down the γ' to η transformation while doubling the γ' fraction. Thin elongated η needles or platelets formed in the wrought products while thicker, plate-like, η precipitates were found in the castings. The effect of the various microstructures on the creep properties were determined using isothermally aged specimens aged at 800 °C for 3,000 h and 10,000 h prior to creep screening. Strong precipitation of the η phase was found to considerably decrease creep life and increase minimum creep rate. By modifying the Ti and Al content, the creep life and ductility of the new formulation tested on specimens isothermally aged for 3,000 and 10,000 h were near that of the nominal alloy in its standard aged condition.

Detrois, Martin↗
DOE OSTI2021

Mechanical Behavior of High-Entropy Alloys: A Review

High-entropy alloys (HEAs) are materials that consist of equimolar or near-equimolar multiple principal components but tend to form single phases, which is a new research topic in the field of metallurgy, and have attracted extensive attention in the past decade. The HEAs families contain the face-centered-cubic (fcc), body-centered-cubic (bcc), and hexagonal-close-packed (hcp)-structured HEAs. On the one hand, mechanical properties, e.g., hardness, strength, ductility, fatigue, and elastic moduli, are essential for practical applications of HEAs. Scientists have explored in this direction since the advent of HEAs. On the other hand, the pursuit of high strength and good plasticity is the critical research issue of materials. Hence, strengthening of HEAs is a crucial issue.In this chapter, we reviewed the recent work on the room-temperature elastic properties and mechanical behavior of HEAs, including the mechanisms behind the plastic deformation of HEAs at both low and high temperatures. Furthermore, the present work examined the strengthening strategies of HEAs, e.g., strain hardening, grain-boundary strengthening, solid-solution strengthening, and particle strengthening. The fatigue, creep, and fracture properties were briefly introduced. Lastly, the future scientific issues and challenges of HEAs were discussed.

Shang, Yuanyuan↗
DOE OSTI2022

Effect of post-extrusion heat treatment on mechanical property of aluminum alloy 2024 tube produced using Shear Assisted Processing and Extrusion (ShAPE)

The present work deals with the Shear Assisted Processing and Extrusion (ShAPE) of aluminum alloy 2024 tubes and mechanical property optimization via post extrusion heat treatments (T3510 and T8510). The ShAPE process enables extruding AA2024 at an extrusion speed of 7.4 m/min and extrusion temperature of 480 °C, which is otherwise beyond the extrudability limit of this alloy using conventional extrusion techniques. The ultimate tensile strength reaches 466 MPa for ShAPE+T3510 condition and 503 MPa for ShAPE+T8510 condition, both of which exceed the corresponding ASTM/ASM (minimum/typical) values for the studied tube geometry. The yield strength reaches 382 MPa for ShAPE+T3510 condition and 481 MPa for ShAPE+T8510 condition, both of which surpass any reported values in the literature or the highest industrial values. In addition, the ductility of AA2024 tube fabricated from ShAPE+T3510 or ShAPE+T8510 are evidently improved by the grain size refinement, second phase refinement, and enhanced uniformity in second phase distribution due to the severe plastic deformation of ShAPE process.

Shear Assisted Processing and Extrusions (ShAPE), ↗
DOE OSTI2022

Exploring the Microstructure-Property Relationship of Mg-Al-Mn alloys enhanced via Friction Stir Processing

Friction Stir Processing (FSP) is a solid-state thermomechanical processing technique that enables local grain refinement, densification, and homogenization of microstructure in metallic components. Here, FSP is applied to thin sheets of high-pressure die cast AM60 to address the porosity and heterogeneities inherent to the casting process. In this work, microstructure characterization is correlated to improvements in the static mechanical properties of the Mg-Al-Mn alloy system at various FSP processing conditions. Notably, there is a significant increase in the ductility and ultimate tensile stress of system following FSP. The dominant deformation mechanisms for the as-cast material and the FSP material are investigated. Finally, the fatigue life improvement is correlated to microstructure modifications that may lead to distinct behavior in crack initiation and crack propagation for the as-cast and FSP material.

Garcia, David↗
DOE OSTI2025

Friction Self-piercing Riveting Process for 3T Configuration of AA7075-AA7075-AA6022

Friction self-piercing riveting (F-SPR), as a solid-state joining process that generates frictional heat during the process, was utilized to join a 3 T configuration of low-ductility AA7075-AA7075-AA6022 sheets. A multi-step F-SPR process was employed to precisely control the mechanical interlocking and solid-state joining, ensuring a strong joint formation. With control of the plunge depth when the transition from rivet penetration to rivet flaring, two joining conditions were developed to assess mechanical joint integrity: one bearing deep penetration with a smaller interlock, and the other yielding a shallow penetration with a larger interlock. Both strategies met the criteria for a sound rivet joint. Customized lap shear tensile configurations were designed to assess the joint strength at interface between first and second layers, as well as between second and third layers. Both conditions demonstrated great joint strength between the first and second layers, while deeper penetration approach showed stronger solid-state joint, leading to improved joint strength between the second and third layers.

Wang, Tianzhao [ORNL] (ORCID:0000000315337602)↗
DOE OSTI2016

Highly stretchable miniature strain sensor for large dynamic strain measurement

In this paper, a new type of highly stretchable strain sensor was developed to measure large strains. The sensor was based on the piezo-resistive response of carbon nanotube (CNT)/polydimethylsiloxane (PDMS) composite thin films. The piezo-resistive response of CNT composite gives accurate strain measurement with high frequency response, while the ultra-soft PDMS matrix provides high flexibility and ductility for large strain measurement. Experimental results show that the CNT/PDMS sensor measures large strains (up to 8 %) with an excellent linearity and a fast frequency response. The new miniature strain sensor also exhibits much higher sensitivities than the conventional foil strain gages, as its gauge factor is 500 times of that of the conventional foil strain gages.

47 OTHER INSTRUMENTATION↗
DOE OSTI2016

Preface to the special volume on the second Sandia Fracture Challenge

In this study, ductile failure of structural metals is a pervasive issue for applications such as automotive manufacturing, transportation infrastructures, munitions and armor, and energy generation. Experimental investigation of all relevant failure scenarios is intractable, requiring reliance on computation models. Our confidence in model predictions rests on unbiased assessments of the entire predictive capability, including the mathematical formulation, numerical implementation, calibration, and execution.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Sandia fracture challenge 2: Sandia California's modeling approach

The second Sandia Fracture Challenge illustrates that predicting the ductile fracture of Ti-6Al-4V subjected to moderate and elevated rates of loading requires thermomechanical coupling, elasto-thermo-poro-viscoplastic constitutive models with the physics of anisotropy and regularized numerical methods for crack initiation and propagation. We detail our initial approach with an emphasis on iterative calibration and systematically increasing complexity to accommodate anisotropy in the context of an isotropic material model. Blind predictions illustrate strengths and weaknesses of our initial approach. We then revisit our findings to illustrate the importance of including anisotropy in the failure process. Furthermore, mesh-independent solutions of continuum damage models having both isotropic and anisotropic yields surfaces are obtained through nonlocality and localization elements.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Interfacial toughness: dependence on surface roughness and test temperature

Interfacial toughness quantifies resistance to crack growth along an interface and in this investigation the toughness of an aluminum/epoxy interface was measured as a function of surface roughness and test temperature. The large strain response of the relatively ductile epoxy adhesive used in this study was also characterized. This epoxy adhesive exhibits intrinsic strain-softening after initial compressive yield and then deforms plastically at a roughly constant flow stress until it rapidly hardens at large compressive strains. Here, we find that interface toughness scales as the product of the temperature dependent epoxy yield strength and a length scale that characterizes surface roughness. The proposed scaling is based upon dimensional considerations of a model problem that assumes that the characteristic length scale of both the roughness and the crack-tip yield zone is small relative to the region dominated by the linear elastic asymptotic crack-tip stress field. Furthermore, the model assumes that interfacial failure occurs only after the epoxy begins to harden at large strains. The proposed relationship is validated by our interfacial toughness measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Si–Cu alloy nanowires grown by oblique angle deposition as a stable negative electrode for Li-ion batteries

Thin films having nanocolumnar arrays made of various Si–Cu atomic ratios (90–10, 80–20, 70–30 %) are fabricated by an ion-assisted oblique angle co-deposition technique to produce stable negative electrodes for lithium-ion batteries. Cu is added into the electrode because of its ductility and electron conductivity. Cu plays a crucial role in holding the electrode together, minimizing overall capacity loss and enabling faster electron transfer. Plus, Cu is inactive versus Li?; therefore, Si–Cu variation is expected to affect the electrochemical performances of the electrodes. In this work, the effect of Si–Cu atomic ratios on the morphologies and the structures of the electrodes are studied. Plus, the uses of these nanocolumns with different Cu contents are evaluated as anodes by electrochemical tests. The morphological analyses demonstrate that an increase in Si–Cu atomic ratio affects the width of the nanocolumns and the homogeneity of the thin film morphology. The increase in Cu content dramatically improves the capacity retention of Si–Cu anodes, whereas it decreases the initial discharge capacity.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Analysis of thermal history effects on mechanical anisotropy of 3D-printed polymer matrix composites via in situ X-ray tomography

The tensile behavior of an additively manufactured (AM) polymer matrix composite (PMC) is studied with in situ X-ray computed microtomography (CT) and digital volume correlation (DVC). In this experiment, the effects of recycled material content and print direction on the selective laser-sintered (SLS) material's mechanical response are explored. The PMC samples are printed in a tensile specimen geometry with gage lengths parallel to all three orthogonal, primary sintering directions. In situ tensile-CT experiments are conducted at Argonne National Laboratory's Advanced Photon Source 2-BM beamline. Analysis of the AM PMC's tensile response, failure, and strain evolution is analyzed both from a conventional standpoint, using the load-displacement data recorded by the loading fixture, and from a microstructural standpoint by applying DVC analysis to the reconstructed volumes. Significant variations on both strength and ductility are observed from both vantages with respect to print direction and the recycled material content in the printed parts. As a result, it is found that the addition of recycled source material with a thermal history reduces the tensile strength of the SLS composite for all directions, but the effect is drastic on the strength in the layering direction.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Lightweight TiC–(Fe–Al) ceramic–metal composites made in situ by pressureless melt infiltration

Lightweight ceramic–metal (cermet) composites combine stiffness and hardness with fracture toughness and ductility. TiC and Al are ideal pairs among lightweight cermet composites because of their relatively high strength-to-weight ratios, but these materials are difficult to process in solid state or with Al melt infiltration without making an aluminum carbide phase, which is detrimental to mechanical properties. Here, Fe is added to a TiC powder preform to reduce the activity of Al with TiC during Al melt infiltration and to aid in pressing TiC preforms, making a lightweight TiC–(Fe–Al) composite while avoiding other, unwanted phases. The composites are made by first pressing TiC powder mixed with Fe followed by Al melt infiltration; the result is a composite with high TiC content in a two-phase matrix, both of which are Fe–Al-based. The composite has low density, low porosity, high hardness, no detectable Al 4 C 3 phase with X-ray diffraction and retains shape well during infiltration.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Thermodynamics and kinetics of precipitation and austenite reversion during aging of Ti-free grade 300 maraging steel manufactured by laser powder bed fusion (LPBF)

Austenite reversion and intermetallic precipitation are two key phase transformations in maraging steels which determine the strength and ductility. Usually, an optimum aging temperature/time is determined using trial and error approach with inputs from thermodynamic databases and a-posteriori microscopy/hardness evaluations. In this study, a thermo-kinetic model is developed to predict the precipitation and austenite reversion kinetics during various post-fabrication heat treatments in a Ti-free variant of grade 300 maraging steel manufactured using laser powder bed fusion. The thermo-kinetic model was based on the principles of Scheil solidification and the classical nucleation theory. The predictions from the thermo-kinetic model were verified using suitable microscopy techniques, and the results from the thermo-kinetic model agree well with the experimental measurements. Overall, results highlight the fact that an Integrated Computational Materials Engineering approach can be used to predict the precipitation and austenite reversion kinetics, and be used as an input for an efficient design of heat treatments for achieving optimum mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Microstructural refinement in ultrasonically modified A356 aluminum castings

Two A356 aluminum alloys (Al-Si-Mg), one with 0.09 wt.% Fe and one with 0.91 wt.% Fe, were cast in a graphite mold with the simultaneous application of local ultrasonic intensification to refine the as-cast microstructure. Ultrasonication during casting transformed the morphology of primary Al grains from dendritic (~140-290 microns in size) to globular (~33-36 microns in size). The alloy with high Fe exhibited globular grains at distances up to 45 mm away from the ultrasound probe, while the alloy with low Fe exhibited globular grains at distances only up to 6 mm away from the ultrasound probe. Near the location of the ultrasound probe (< 2 mm away), a second non-dendritic microstructural morphology was observed with fine aluminum grains (~9-25 microns in size). This unique fine-grained morphology has not been previously reported, contains a greater concentration of Si relative to the globular microstructure, and may be a large, fully eutectic region. Ultrasonication during casting also transformed the morphology of the ß-Al 5 FeSi phase particles (which are deleterious to the strength and ductility of the alloy) in the high Fe alloy from needle-like to rectangular, which could enable the greater use of secondary Al alloys. Thermodynamic simulations conducted to calculate the solidification paths of the two alloys studied predict that the ß-Al 5 FeSi phase begins to form earlier in the alloy with high Fe. Finally, data suggest that the ß-Al 5 FeSi phase (which is more abundant in alloys with high Fe content) may enhance ultrasonically-induced grain refinement.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Inhibition of Polyimide Photodegradation by Incorporation of Titanate Nanotubes into a Composite

The effect of UV light exposure on the properties of hexafluoroisopropylidene-diphthalic anhydride–oxydianiline (6FDA–ODA) polyimide (PI) and polyimide–titanate nanotube (TiNT/PI) composites has been studied using Raman spectroscopy, optical microscopy, nanoidentation and TEM. The degree of polymer photodegradation was estimated by measuring the change in affinity to a positively charged dye (methylene blue, MB). The mechanism of photoassisted transformations in polyimides usually involves scission of polymer chains accompanied by appearance of active radicals, which undergo further rapid transformations to more stable phenol, amine, and carboxylic functional groups. The accumulation of these groups can increase the degree of adsorption of charged dyes in the photodegraded polymer. It was found that neat PI showed a significantly increased capacity to adsorb MB after irradiation with UV, reaching a plateau after 1 h. In contrast, TiNT/PI composite demonstrated a much slower rise in concentration of adsorbed MB even after 4 h of UV exposure. Raman spectra indicated cleavage of C=O and C–F bonds in PI while only the C–F bond was damaged in TiNT/PI. Shorter cracks (≈ 40 µm long) appeared in TiNT/PI composites whereas macro cracks (> 100 µm) were visible in neat PI after 3 h of UV exposure. Brittleness was studied by comparing plasticity index which varied from 0 to 1 (0 corresponding to the most brittle material and 1 the most ductile one). Plasticity index reduced by 51% and 2% for PI and TiNT/PI, respectively after 3 h UV irradiation, indicating that TiNT can protect underlying PI from further damage. The hardness of neat PI decreased whereas, for TiNT/PI, it increased under UV, suggesting crosslinking of broken polymer chains with nanotubes. Graphical Abstract: Photodegradation of a titanate nanotubes/polyimide composite can lead to cross-linking of broken polymer chains by nanostructured material, resulting in increased hardness. .

36 MATERIALS SCIENCE↗
DOE OSTI2019

Modification of Poly(L-lactide) via a Pectinate Polymethylphenylsilane-co-poly(ε-caprolactone)

To solve the problem of the hard and brittle mechanical properties of poly(L-lactide) (PLLA), a novel pectinate polymethylphenylsilane-co-poly(ε-caprolactone) (PCL-PMPS-PCL) has been designed to modify PLLA via the hydrolysis polycondensnsation of methylphenyldimethoxysilane and ring-opening polymerization of ε-caprolactone. The triblock copolymer is characterized with {sup 1}HNMR and GPC. It is harmonized with PLLA in chloroform to make smooth blending film. Incorporation of PCL-PMPS-PCL lowers T{sub g} of PLLA, enhances the macromolecular mobility, and facilitates PLLA to form defective crystals. Compared to the brittle PLLA, the cross section of blends is rough and uneven. With the blending amount of PCL-PMPS-PCL going up, the tensile strength curve has a downward glacis, while the elongation at a break climbs upward, and reaches 25% at 10 wt%, exhibiting that the typical characteristics of ductile material. At the same time, the tensile strength for 10 wt% PCL-PMPS-PCL/PLLA reserve about 60 MPa, so PCL-PMPS-PCL can serve as a candidate of plasticizing PLLA.

36 MATERIALS SCIENCE↗