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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 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

AZ61 and AZ61-La Alloys as Anodes for Mg-Air Battery

AZ61 and AZ61-0.5La (wt.%) alloys are prepared by the conventional casting method and then, AZ61 and AZ61-0.5La alloy sheets are obtained with multi-pass hot rolling. Microstructures and electrochemical properties of four alloys are investigated, and discharge properties are tested by an assembled Mg-air battery using alloy anode sheets with a dimension of 70 × 100 × 2.5 mm. Results show that Al{sub 11}La{sub 3} phases are formed in as-cast AZ61-0.5La alloy and promote the grain refinement and the formation of uniform microstructure in as-rolled AZ61-0.5La alloy. As-rolled AZ61-0.5La alloy exhibits a weak self-corrosion tendency but a strong discharge activity. After discharge test for 5 h, the Mg-air battery based on the as-rolled AZ61-0.5La sheet can provide the maximum power output of 1.625 W, and as-rolled AZ61-0.5La anode can supply the maximum energy density of 1417 mWhg{sup −1}. In addition, the relationship between microstructures and discharge properties is sufficiently described and discussed in this paper.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Microstructure evolution, enhanced aging kinetics, and mechanical properties of AA7075 alloy after friction extrusion

In the present study we utilized Friction Extrusion (FE) a solid phase processing technique to produce fully consolidated dense 5 mm rods of AA7075 alloy. The combination of large shear stresses and temperatures at the tool-billet interface during the FE process resulted in the formation of dynamically recrystallized ~2.0 μm equiaxed grains and fine uniformly distributed stable η (MgZn 2 ) precipitates ~25–100 nm in size. Formation of such a microstructure resulted in lower solutionizing temperature and times (flash annealing) as compared to the conventionally extruded counterparts. Here we demonstrate for the first time that the solutionizing times for the T6 heat treatment of AA7075 can be reduced by three times using this FE process. In addition to being an energy efficient process, FE also serves to improve the performance of AA7075 alloys by retaining their strength while enhancing the ductility of the material. The tensile data for samples that were flash annealed and artificially aged after FE processing showed exceptional increase in ultimate tensile strength by over 19% and yield strength by over 59%, compared with an as-FE-processed sample.

36 MATERIALS SCIENCE↗
DOE OSTI2016

The modification of BaCe{sub 0.5}Zr{sub 0.3}Y{sub 0.2}O{sub 3–δ} with copper oxide: Effect on the structural and transport properties

The effect of the content of CuO additive on the sinterability, phase composition, microstructure, and electrical properties of BaCe{sub 0.5}Zr{sub 0.3}Y{sub 0.2}O{sub 3–δ} proton-conducting material is studied. Ceramic samples were produced by the citrate–nitrate synthesis method with the addition of 0, 0.25, 0.5, and 1% CuO. It is shown that the relative density of the samples containing 0.5 and 1% CuO is higher than 94% at a sintering temperature of 1450°C, whereas the relative density of the material is no higher than 85% at a lower content of the sintering additive. From the data of X-ray diffraction analysis and scanning electron microscopy, it is established that the introduction of a small CuO content (0.25%) is inadequate for single-phase and high-dense ceramics to be formed. The conductivity and scanning electron microscopy data show that the sample with BaCe{sub 0.5}Zr{sub 0.3}Y{sub 0.2}O{sub 3–δ} + 0.5% CuO composition possesses high total and ionic conductivities as well as a high degree of microstructural stability after hydrogen reduction of the ceramics. The citrate–nitrate method modified by the introduction of a small CuO content can be recommended for the production of single-phase, gas-tight, and high-conductivity electrolytes based on both BaCeO{sub 3} and BaZrO{sub 3}.

36 MATERIALS SCIENCE↗
DOE OSTI2024

An approach to combine neutron and ion irradiation data to accelerate material qualification for nuclear reactors

Next-generation nuclear power plants are generally characterized by higher operating temperatures, increased neutron fluences and energies, and distinct corrosive coolant environments versus the existing light water reactor fleet. 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. Ion irradiation has demonstrated success in reproducing material microstructure and select property evolution resulting from neutron irradiation with three to four orders of magnitude reduction in time and cost, making it an ideal candidate for accelerated irradiation testing. Because microstructure has a large impact on bulk material properties, limited neutron irradiation data at lower damage levels can in principle be combined with accelerated ion testing results and modeling and simulation to form an accurate prediction of microstructure evolution and select properties under different neutron irradiation conditions and at higher damage levels. The objective of this work is to present 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. A brief review of the regulatory landscape for materials in nuclear environments is presented, followed by additional overviews to understand the current state of the art for correlation of materials properties across radiation environments using experimental and computational methodologies. Finally, the roles of academia, national laboratories, and industry in the advancement of this accelerated materials qualification framework are discussed as a path forward, with possible case studies presented.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS2003

Cost-Effective TiAl based Materials

Because of their inherent low ductility, TiAl-based materials are difficult to fabricate, especially thin gage titanium gamma aluminide (TiAl) sheet and foil. In this paper, an innovative powder metallurgy approach for producing cost-effective thin gage TiAl sheets (with 356 mm long and 235 mm wide, and a thickness of 0.74, 1.09, 1.55, and 2.34 mm, respectively) is presented. The microstructures and tensile properties at room and elevated temperatures of the thin gage TiAl are studied. Results show that these TiAl sheets have a relatively homogenous chemistry, uniform microstructure, and acceptable mechanical properties. This work demonstrates a cost-effective method for producing both flat products (sheet/foil) and complex chunky parts of TiAl for various advanced applications including aerospace and automotive industries.

Moxson, V. S.↗
DOE OSTI2025

Controlling mechanical properties of laser powder bed fused AlSi10Mg through manipulation of laser scan rotation

The microstructure and mechanical properties of laser powder bed fused (LPBF) AlSi10Mg alloys can be controlled by many processing parameters. This study focuses on the scan rotation angle, α, between adjacent layers, and establishes the relationship between α and tensile behavior of the as-built LPBF-processed AlSi10Mg alloy. Near-full density cubic coupons were manufactured using the same processing parameters but with systematic variation of α from 0° to 90°. Microscopic observations and X-ray diffraction analysis showed that differences among various coupons mainly include orientations of the melt pools with respect to the build direction and development of the crystallographic texture. The α=0° coupon and α=30° coupon showed the highest and lowest texture index, although the overall crystallographic texture was mild. Tensile specimens were manufactured horizontally and vertically using either α=0° or α=30°, but with various first layer laser direction with respect to the build plate. Notably, the α=0° specimen that was tested along the laser scan direction showed the largest yield strength (283 MPa) and highest tensile ductility (10.1 %). Quantitative image analysis and fractography were performed on all specimens. Results showed that the melt pool orientation with respect to the tensile direction affected the tensile behavior across the different specimens. This was closely related to the localized strain distribution within the melt pool and along the melt pool boundary for the different melt pool orientations observed. Further, these results demonstrate that the laser scan rotation angle between layers can be used to fine tune the mechanical properties of LPBF AlSi10Mg alloy.

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 OSTI2018

Effects of thickness and orientation on the small scale fracture behaviour of additively manufactured Ti-6Al-4V

Highlights: • Miniaturized specimens successfully additively manufactured via SLM and SEBM. • Small-scale tensile testing of specimens to capture orientation/thickness effect. • Tomography characterization of defects. • Location dependence of fracture behavior. - Abstract: The effects of sample location, orientation, and thickness on the microstructure and resulting tensile properties of miniature SLM and SEBM AM samples of Ti-6Al-4V has been determined. Microstructure and mechanical property variations in the miniature samples are shown to be related to build orientation and also partly to specimen thickness and position within the build chamber. The present work is our initial attempt to develop a systematic approach for characterization of the microstructure (including defects via tomography) and mechanical properties on miniature AM test specimens that can also be used to reveal issues related to process stability (e.g. fluctuations in build conditions). The discussion is also included regarding their relevance to miniature samples that can be manufactured along with parts, excised from larger samples, and/or excised from actual manufactured components.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Microstructural and nanomechanical studies of PVD Cr coatings on SiC for LWR fuel cladding applications

The microstructure and nanomechanical properties of pure Cr coatings deposited on SiC with various physical vapor deposition (PVD) methods have been investigated for the mitigation of hydrothermal corrosion of SiC-SiC f (SiC fiber-reinforced SiC matrix) composite fuel cladding in light water reactors (LWR). Cr coatings (4–7 μm thick) were deposited on unbiased SiC substrates using six variants of magnetron sputtering processes: (i) standard (S-DCMS), (ii) pulsed (P-DCMS), (iii) ion-assisted (I-DCMS), and (iv) pulsed ion-assisted direct current magnetron sputtering (PI-DCMS), (v) high-power impulse magnetron sputtering (HiPIMS), and (vi) bipolar HiPIMS (B-HiPIMS). Microstructural characterization and nanoindentation testing were used to evaluate effects of deposition technique on coating microstructure and nanomechanical properties. The application of positive reverse pulses to the sputter target induced coarsening of the columnar grain structure, while ion bombardment of substrates during deposition promoted densification of the coating microstructure. Both effects are exemplified in B-HiPIMS deposition, resulting in a high-density microstructure with compressive residual stress. Material pile-up around nano-indents and plastic work during nanoindentation were analyzed to understand deformation behavior of the coatings. Finally, the results suggest the B-HiPIMS process to be among the promising methods for the deposition of Cr coatings on SiC-SiC f for LWR cladding application.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Fabrication of Titanium-Niobium-Zirconium-Tantalium Alloy (TNZT) Bioimplant Components with Controllable Porosity by Spark Plasma Sintering

Spark Plasma Sintering (SPS) is used to fabricate Titanium-Niobium-Zirconium-Tantalum alloy (TNZT) powder—based bioimplant components with controllable porosity. The developed densification maps show the effects of final SPS temperature, pressure, holding time, and initial particle size on final sample relative density. Correlations between the final sample density and mechanical properties of the fabricated TNZT components are also investigated and microstructural analysis of the processed material is conducted. A densification model is proposed and used to calculate the TNZT alloy creep activation energy. The obtained experimental data can be utilized for the optimized fabrication of TNZT components with specific microstructural and mechanical properties suitable for biomedical applications.

36 MATERIALS SCIENCE↗
NASA NTRS1982

Micromechanical model for fibrous ceramic bodies

A micromechanical model is presented to relate the mechanical properties of low-density fibrous ceramic bodies to their microstructures and the properties of the fibers. It is found that properties such as the elastic moduli, fracture toughness, and strength depend on the fiber spacing. In particular, it is shown that the critical stress intensity (Kc) depends on the density of the body with respect to the fiber density, the degree of preferred orientation, the fiber strength, and the fiber radius, suggesting ways of increasing K(c). Furthermore, it is predicted that K(c) will be related to the sonic velocity in the material, reflecting variations in the degree of preferred orientation. The model is found to be consistent with the experimental observations on a silica-based fibrous ceramic, which is being used in the thermal protection system of the Space Shuttle.

Green, D. J.↗
NASA NTRS2001

Directional Solidification of Eutectic Ceramics

Two major problems associated with structural ceramics are lack of damage tolerance and insufficient strength and creep resistance at very high temperatures of interest for aerospace application. This work demonstrated that the directionally solidified eutectics can have unique poly-phase microstructures and mechanical properties superior to either constituent alone. The constraining effect of unique eutectic microstructures result in higher resistance to slow crack growth and creep. Prospect of achieving superior properties through controlled solidification are presented and this technology can also be beneficial to produce new class of materials.

Sayir, Ali↗
DOE OSTI2018

Microstructure evolution, grain morphology variation and mechanical property change of Cu-Sn intermetallic joints subjected to high-temperature aging

Highlights: • The δ-Cu{sub 41}Sn{sub 11} could be formed by reaction of 11Cu{sub 3}Sn + 9Cu → Cu{sub 41}Sn{sub 11} during aging above 350 °C. • The temperature effects on the growth rate and grain morphology of Cu{sub 41}Sn{sub 11} phase were found. • The Cu{sub 41}Sn{sub 11} joints with refined grains exhibited higher hardness and shear strength. • The Cu{sub 41}Sn{sub 11} joints exhibited a combination of transgranular and intergranular fracture during shear test. - Abstract: In this work, the aging treatment was carried out on full Cu{sub 3}Sn joints at different temperatures for various durations, the microstructure evolution, grain morphology variation and mechanical property change of joints were investigated. The temperature effects on the growth rate and grain morphology of Cu{sub 41}Sn{sub 11} phase were found: The complete transformation from Cu{sub 3}Sn phase to Cu{sub 41}Sn{sub 11} phase in joints needed 300 h at 400 °C, but 4 h at 500 °C. The Cu{sub 41}Sn{sub 11} phase formed at 400 °C consisted of columnar grains with an average width of 23.5 μm, while the Cu{sub 41}Sn{sub 11} phase formed at 500 °C consisted columnar grains with an average width of 8.5 μm. The average hardness and shear strength values of the Cu{sub 41}Sn{sub 11} joints formed at 400 °C were 432.5 HV and 62 MPa, while the joints formed at 500 °C exhibited higher hardness and shear strength (451.5 HV and 65 MPa). Besides, the Cu{sub 41}Sn{sub 11} joint was found to exhibit a combination of transgranular and intergranular fracture during shear test.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Gradient process parameter optimization in additive friction stir deposition of aluminum alloys

As one of the most novel additive manufacturing methods, currently selection and optimization of processing parameters in additive friction stir deposition (AFSD) have mainly relied on experiments and subsequent characterization of microstructural and mechanical properties. Such approaches are both time- and resource-consuming. Therefore, an ultrasound elastography enhanced gradient process parameter optimization method was applied in the present work to obtain a window of optimized processing parameters for AFSD processing of aluminum alloy by varying both rotational and linear deposition speeds. Further, the quality of AFSD processed layer was investigated for physical nature of surface, dynamic elastic modulus, and microstructural aspects in cross-sections of the deposited layer. The efficiency in exploring process parameters was significantly enhanced by implementing a high-throughput screening experimental design based on application of gradient process parameters and continuous ultrasound elastographs. In addition, the applied ultrasonic elastography technique assisted in evaluating the homogeneity in microstructure and mechanical properties of AFSD sample over the entire gradients of the process parameters. The techniques adopted in current work can be further extended to identify suitable parameters for AFSD fabrication of components with desired mechanical properties such as hardness, fatigue, etc.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Influence of microstructural heterogeneities on small-scale mechanical properties of an additively manufactured Al-Ce-Ni-Mn alloy

Laser powder bed fusion-based additive manufacturing (AM) is a promising method to fabricate creep-resistant Al-rare earth alloys (Al-Ce-Ni-Mn) with stable microstructures at up to 400°C. However, creep testing of these alloys at high temperatures shows that void coalescence and failure initiation occurs along the melt pool boundaries in the microstructure. Hence it is crucial to understand how the local mechanical behavior of the melt pool boundaries would influence the global properties of the AM produced alloy. In this study, in situ nanoindentation conducted at room temperature and 300°C revealed a reduced hardness at the melt pool boundaries. Similarly, micro-pillar compression showed a slight decline in yield strength at these boundaries, indicating that they are the weak spots in the microstructure. Such multimodal local mechanical property studies are necessary for understanding the influence of melt pool boundaries on the bulk response of fusion-based AM alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Microstructure and water absorption of ancient concrete from Pompeii: An integrated synchrotron microtomography and neutron radiography characterization

There is renewed interest in using advanced techniques to characterize ancient Roman concrete due to its exceptional durability and low-carbon footprint. In the present work, samples were drilled from the “Hospitium” in Pompeii and were analyzed by synchrotron microtomography (μCT) and neutron radiography to study how the microstructure, including the presence of induced cracks, affects their water adsorption. The water distribution and absorptivity were quantified by neutron radiography. The 3D crack propagation, pore size distribution and orientation, tortuosity, and connectivity were analyzed from μCT results using advanced imaging methods. Porosity was also measured by mercury intrusion porosimetry (MIP) as a reference. Ductile fracture patterns were observed once cracks were introduced. Compared to Portland cement mortar/concrete, the Pompeii samples had relatively high porosity, low connectivity, and a similar coefficient of capillary penetration. In addition, permeability was predicted from models based on percolation theory and pore structure data to evaluate the fluid transport properties. Understanding the microstructure of ancient Pompeii concrete is important because it could inspire the development of modern concrete with high durability.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Femtosecond Laser Writing of Waveguide Microstructures in Pb(Zr,Ti)O{sub 3} Films and Their Characterization by the Nonlinear Optical Method

Femtosecond laser writing of ferroelectric one-dimensional microstructures possessing waveguide and nonlinear optical properties in Pb(Zr,Ti)O{sub 3} films is considered, and the passage of light beams via obtained waveguide structures is traced. The optimum speed and power density of the writing laser beam are within 50–500 μm/s and 1–1.5 MW/cm{sup 2}, respectively. A two-stage method of writing is proposed, which provides for improved nonlinear optical properties of obtained waveguide microstructures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Strong photoluminescence emission at low dopant amount in YAG:Ce and YAG:Eu phosphors

Highlights: • YAG:Ce and YAG:Eu materials were prepared by solid state reaction. • Pure YAG phase can be obtained at 1300 °C. • High density materials were synthesized at 1600 °C for 10 h. • The highest PL emission was observed for the YAG:Ce{sub 0.01} and YAG:Eu{sub 0.1} samples. - Abstract: YAG:Ce and YAG:Eu phosphors have been prepared by solid state reaction. The use of submicrometric powders allows preparing pellets with high density, enhancing the photoluminescence (PL) properties. Pellets were prepared by uniaxial pressing and the influence of the thermal treatment on the microstructural and optical properties were also studied. Pure YAG phase was obtained at 1400 °C during 1 h and high density pellets (97%) after sintering at 1600 °C for 10 h. The highest PL emission was achieved for the sintered YAG:Ce and YAG:Eu pellets doped with low dopant concentrations (0.01 mol% for Ce and 0.1 mol% for Eu). Finally, increasing the Ce and Eu concentration the PL intensity decreases and the dopants occupy different positions than the Y one in the YAG lattice.

36 MATERIALS SCIENCE↗