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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Fabrication and Characterization of Brazed Joints for SiC-Metallic Systems Utilizing Refractory Metals

Metal to ceramic joining plays a key role for the integration of ceramics into many nuclear, ground and aero based technologies. In order to facilitate these technologies, the active metal brazing of silicon carbide (CVD beta-SiC, 1.1 mm thick, and hot-pressed alpha-SiC, 3 mm thick) to the refractory metals molybdenum and tungsten using active braze alloys was studied. The joint microstructure, composition, and microhardness were evaluated by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Knoop hardness testing. The braze alloys, Cusil-ABA, Ticusil and Copper-ABA, all formed sound joints with excellent wetting and chemical bonding with the SiC substrate. Despite the close thermal expansion match between the metal substrates and SiC, hairline cracks formed in alpha-SiC while beta-SiC showed no signs of residual stress cracking. The use of ductile interlayers to reduce the effect from residual stresses was investigated and joints formed with copper as an interlayer produced crack free systems utilizing both CVD and hot-pressed SiC.

Coddington, Bryan↗
NASA NTRSDate not supplied

Geometric Sensitivity of Residual Fields in Metal Additive Manufacturing

The sensitivity of geometrical parameters on the residual stress and distortion as computed by a metal additive manufacturing simulation is presented. A nozzle-like geometry was chosen with its length, wall thickness, and outer radius varied. A Latin hypercube sampling of 300 specimens produced the combinations of the geometrical parameters. Full thermomechanical simulations predicted the residual fields. Statistical analysis including regression curves shows that there is a strong correlation between these residual fields and the geometry, hinting that it may be possible to predictably influence the residual displacements and residual stresses by varying the overall geometry.

Multiscale Modeling↗
NASA NTRSDate not supplied

A Novel Ultrasonic Fully Reversible Bending Fatigue Test Specimen for Simulated Gear Tooth Bending Fatigue

Gears in vertical lift applications will typically experience greater than 107bending fatigue cycles over their design lifetime. Currently, fatigue life prediction of gears exceeding 107cycles are based on empirical correlations, since collection of fatigue data beyond 107 cycles is impractical with traditional fatigue testing methods. Ultrasonic fatigue testing enables fatigue testing in excess of 109cycles in as few as 14 hours. In this paper, a novel specimen design for ultrasonic fatigue testing to accurately represent the geometry, stress profile, and residual stress of gear teeth in reversible bending fatigue is presented. The specimen design is discussed in detail, testing is performed to validate operating principles, and an initial fatigue data set of 8 specimens is presented.

Single Tooth Bending Fatigue↗
NASA NTRSDate not supplied

A Novel Ultrasonic Fully Reversible Bending Fatigue Test Specimen for Simulated Gear Tooth Bending Fatigue

Gears in vertical lift applications will typically experience greater than 107bending fatigue cycles over their design lifetime. Currently, fatigue life prediction of gears exceeding 107cycles are based on empirical correlations, since collection of fatigue data beyond 107 cycles is impractical with traditional fatigue testing methods. Ultrasonic fatigue testing enables fatigue testing in excess of 109cycles in as few as 14 hours. In this paper, a novel specimen design for ultrasonic fatigue testing to accurately represent the geometry, stress profile, and residual stress of gear teeth in reversible bending fatigue is presented. The specimen design is discussed in detail, testing is performed to validate operating principles, and an initial fatigue data set of 8 specimens is presented.

Single Tooth Bending Fatigue↗
DOE OSTI2019

Electrochemical Corrosion Behavior of 5083 Aluminum Alloy Subjected to Laser Shock Peening

This paper investigates the effect of ablative coating used during laser shock peening (LSP) on corrosion behavior of 5083 aluminum alloy in artificial seawater. Micro-hardness, residual stress, and surface morphology of the specimens were measured. The corrosion behavior was investigated by electrochemical test. Surface corrosion morphologies after electrochemical tests were examined by SEM and EDS. The results show that surface roughness and surface compressive residual stress of the specimen treated by LSP without ablative coating (LSPwC) are lower than that of the specimen treated by LSP with ablative coating under the same laser energy. The open-circuit potentials and self-corrosion potentials of the specimens treated by LSP and LSPwC both shift positively, and the diameters of the capacitor arcs were larger after LSP and LSPwC. The corrosion resistance of 5083 aluminum alloy is improved by LSP and LSPwC. Moreover, superior corrosion resistance is achieved without using the ablative coating during LSP.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Surface Integrity Analysis of Ti6Al4V After Semi-finishing Turning Under Different Low-Temperature Cooling Strategies

During machining of difficult-to-cut alloys, the rapid tool wear as a consequence of the high values of cutting forces and temperatures significantly affects the surface integrity of the machined surfaces reducing the product in-service performances. The use of conventional cutting fluids limits the tool deterioration, but provides several environmental issues to deal with, such as the exhausted fluid disposal, cleaning of the parts after machining, health hazards for the machines operators. In recent years, several researches have proposed to use environmental-friendly cryogenic coolants, whose very low operating temperatures have demonstrated to be able to inhibit the thermally activated tool wear mechanisms leaving the machined surface almost free from pollutants. In this framework, the aim of this research work is to analyze the surface integrity of the machined surfaces produced in semi-finishing turning of the Ti6Al4V titanium alloy under different low-temperature cooling techniques, namely liquid nitrogen (LN{sub 2}), carbon dioxide (CO{sub 2}) and gaseous nitrogen (N{sub 2}) cooled at different temperatures, using the dry and wet cutting conditions as baseline. The surface integrity was evaluated considering both the surface finish (surface defects, roughness and topography) and the surface microstructural and mechanical alterations (altered layer, nano-hardness and residual stresses). The results showed that the best performances were obtained using N{sub 2} cooled at − 150 °C, which determined both the absence of surface defects, as wrinkles or feed marks irregularities typical of the surface generated under LN{sub 2}, and high compressive residual stresses that made the surface suitable for biomedical and aerospace applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Characterization of texture and grain boundary character distributions of selective laser melted Inconel 625 alloy

Highlights: • <110> texture along layer build direction was generated in as-SLMed Inconel 625. • The stress relief process dominates texture and GBCD evolution. • SLMed IN 625 alloy can be GBEed via suitable post annealing. - Abstract: Select laser melting (SLM) is one of the practical metal additive manufacturing processes to fabricate complex structures. The inhomogeneous microstructure and high residual stress are typically resulted from a non-uniform melting and rapid solidification during a SLM process, which has the significant impact on part dimensional instability, corrosion resistance, and mechanical properties. The bulk of current research is limited to the general characterization of grain size, texture, and mechanical properties. However, grain boundary character distribution (GBCD) and its relationship with texture are yet to be understood. This study has shown that the preferred <110> along building direction and <100> along laser scanning direction were produced. The high density of low angle grain boundary (LAGB) can be an indicator of residual stress levels in the as-SLMed samples. The newly-developed ∑3, ∑9 and ∑27 grain boundaries were heavily populated, and the cluster of grains interfaced by ∑3{sup n} (n = 0, 1, 2…) was introduced at the expense of LAGB only at high recrystallization annealing (1150°C or over). The research results suggest that GBCD optimization be possible in the SLMed Inconel 625 alloy via suitable post annealing, which allows improving intergranular corrosion resistance and enhancing mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of Fine Particle Shot Peening Treatment on Fatigue Properties of Al-7Si-0.3Mg Alloy

In this study, two different fine particle shot peening (FPSP) treatments were performed on Al-7Si-0.3Mg alloy specimens to evaluate their effects on fatigue properties. After the treatment, the microstructure morphology of the specimens was observed, and the surface roughness and residual stress distribution were measured. Rotating bending fatigue tests were conducted, and the fatigue fracture surfaces were observed using scanning electron microscopy (SEM). The crack initiation and propagation behavior were investigated using the replica method. The results indicate that FPSP can introduce residual stress on the surface layer of the material and refine the surface microstructure, and also change the surface roughness. At low stress amplitude levels, FPSP can improve fatigue life significantly. At 5 × 10{sup 7} cycles, the fatigue strength of shot-peened specimens increased by 33% compared to unpeened specimens. In unpeened and steel shot-peened (SSP) specimens, both crystal slip and casting defects can induce fatigue failure, while only casting defects can cause failure in the case of ceramic shot-peened (CSP) specimens. Moreover, FPSP can move the crack initiation site to the subsurface from the surface. The range of threshold stress intensity factor of the material can be improved significantly by this treatment. Casting defects have a significant influence on fatigue strength; the effect on fatigue strength can be well evaluated by the modified Murakami equation.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Cu Interlayer on the Microstructure and Strength for Brazing of Tungsten/316L Steel

Brazing is an effective technique for joining tungsten and steel. However, the high residual stresses are produced due to the different coefficients of thermal expansions between tungsten and steel. Compared with the direct brazing with BNi-2 foil filler, BNi-2/Cu/ BNi-2 multiple interlayer was used as filler to minimize the residual stresses between tungsten and 316L steel. The brazing experiments were conducted at 1050 °C for 25 min using Cu foils with different thickness. The results show that tungsten and 316L steel have been successfully joined by brazing. The intermetallic compound of NiW formed at the W/BNi-2 interface, which was detrimental to the strength of the joint. The microhardness of different diffusion zones is higher than that of the substrates owing to the formation of intermetallic compound and solid solution. All specimens of shear testing fractured at the W/BNi-2 interface close to W substrate, and the average strength of joints was 197, 275 and 268 MPa with multiple interlayer thickness of 0.2 , 0.1 and 0.05 mm copper foil, respectively, while the average strength of joints was 143 MPa with BNi-2 foil filler. The significant increase in the joint shear strength can be ascribed to the Cu foil in the multiple interlayer because of with excellent plasticity and toughness.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Stress compensation for arbitrary curvature control in vanadium dioxide phase transition actuators

Due to its thermally driven structural phase transition, vanadium dioxide (VO{sub 2}) has emerged as a promising material for micro/nano-actuators with superior volumetric work density, actuation amplitude, and repetition frequency. However, the high initial curvature of VO{sub 2} actuators severely obstructs the actuation performance and application. Here, we introduce a “seesaw” method of fabricating tri-layer cantilevers to compensate for the residual stress and realize nearly arbitrary curvature control of VO{sub 2} actuators. By simply adjusting the thicknesses of the individual layers, cantilevers with positive, zero, or negative curvatures can be engineered. The actuation amplitude can be decoupled from the curvature and controlled independently as well. Based on the experimentally measured residual stresses, we demonstrate sub-micron thick VO{sub 2} actuators with nearly zero final curvature and a high actuation amplitude simultaneously. This “seesaw” method can be further extended to the curvature engineering of other microelectromechanical system multi-layer structures where large stress-mismatch between layers are inevitable.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Measurement of probability distributions for internal stresses in dislocated crystals

Here, we analyse residual stress distributions obtained from various crystal systems using high resolution electron backscatter diffraction (EBSD) measurements. Histograms showing stress probability distributions exhibit tails extending to very high stress levels. We demonstrate that these extreme stress values are consistent with the functional form that should be expected for dislocated crystals. Analysis initially developed by Groma and co-workers for X-ray line profile analysis and based on the so-called “restricted second moment of the probability distribution” can be used to estimate the total dislocation density. The generality of the results are illustrated by application to three quite different systems, namely, face centred cubic Cu deformed in uniaxial tension, a body centred cubic steel deformed to larger strain by cold rolling, and hexagonal InAlN layers grown on misfitting sapphire and silicon carbide substrates.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Calculated efficiencies of three-material low stress coatings for diffractive x-ray transmission optics

Diffractive X-ray optical elements made by thin film coating techniques such as multilayer Laue lenses (MLL) and multilayer zone plates (MZP) are promising approaches to achieve resolutions in hard X-ray microscopy applications of less than 10 nm. The challenge is to make a lens with a large numerical aperture on the one hand and a decent working distance on the other hand. One of the limiting factors with the coated structures is the internal stress in the films, which can lead to significant bending of the substrate and various types of unwanted diffraction effects. Several approaches have been discussed to overcome this challenge. One of these is a three-material combination such as Mo/MoSi{sub 2}/Si, where four single layers per period are deposited. Mo and Si represent the absorber and spacer in this case while MoSi{sub 2} forms a diffusion barrier; in addition the thicknesses of absorber and spacer are chosen to minimize residual stress of the overall coating. Here the diffraction efficiency as well as the profile of the beam in the focal plane are discussed in order to find a tradeoff between lowest residual stress and best diffraction properties.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

In-situ TOF neutron diffraction studies of cyclic softening in superelasticity of a NiFeGaCo shape memory alloy

Real-time in-situ neutron diffraction was conducted during uniaxial cycling compression of a Ni 49.3 Fe 18 Ga 27 Co 5.7 shape memory alloy to explore the mechanism on its superelasticity at room temperature, which was manifested by the almost recoverable large strains and the apparent cyclic softening. Based on the Rietveld refinements, the real-time evolution of volume fraction of martensite was in-situ monitored, indicating the incremental amount of residual martensite with increasing load cycles. Real-time changes in intensities and lattice strains of { hkl } reflections for individual phase were obtained through fitting individual peaks, which reveal the quantitative information on phase transformation kinetics as a function of grain orientation and stress/strain partitioning. Moreover, a large compressive residual stress was evidenced in the parent phase, which should be balanced by the residual martensite after the second unloading cycle. As a result, the large compressive residual stress found in the parent austenite phase may account for the cyclic effect on critical stress required for triggering the martensitic transformation in the subsequent loading.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Metallurgical Analysis and Forward Modeling of Weld Distortion in SMR Containment Vessels

This work aimed to apply Sandia’s expertise in metallurgy and modeling to enable the use of hybrid laser arc welding for building nuclear reactor containment structures, via a collaboration with Holtec International. Experimental observations were coupled with finite element analysis to resolve microstructure development, mechanical properties, distortion, and residual stress in welds relevant to the production of the Holtec SMR-160. High residual stresses were observed in welds that were not subjected to preheat. Meanwhile, the microstructure of the welds generally exhibited a narrow heat affected zone relative to conventional arc welds. FEA appeared to be effective in simulating the thermal/mechanical conditions that occur during hybrid laser arc welding of simplified and instrumented test welds. Subsequently, FEA was used to perform sensitivity analyses for various weld geometries that would be prohibitively costly to assess with physical experiments. Insights from the study were used to inform Holtec’s welding process, and successful production welds were performed in 2025.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2022

Mechanisms of Mitigating Chloride-Induced Stress Corrosion Cracking of Austenitic Steels by Laser Shock Peening

This study investigates the effect of laser shock peening (LSP) on the chloride-induced stress corrosion cracking (SCC) of 304 austenitic steels. LSP can induce a high compressive residual stress to a depth of 700 µm and plastic deformation structures of dislocations, deformation twins, and stacking faults. Constant-load SCC tests in MgCl2 solution suggested that LSP can retard the crack initiation and slow the crack growth. LSP-treated subsurface layers experience ductile fracture while the central regions exhibit intergranular SCC. The LSP-induced deformation structures may impede dislocation slips, while the LSP-induced compressive residual stress can lessen the stress intensity factor of crack tips and decrease the local stress for film rupture.

Materials Science↗
DOE OSTI2018

Microstructure, texture and tensile behavior of pulsed electrodeposited Ni–Al composites produced using organic additive-free sulfamate bath loaded with Al nanoparticles

Highlights: • Foils of fine grained Ni with Al nanoparticles reinforcement are produced by pulsed electro-codeposition. • Ni–Al composite foils exhibit increased compressive residual stresses with increasing Al content. • Well-dispersed Al nanoparticles refine Ni matrix microstructure and induces significant texture changes. • Ultrafine grained Ni-Al composites exhibit improved hardness and tensile strength. - Abstract: Nickel and Ni–Al composites with varying Al nanoparticle content were produced by pulsed electrodeposition using an organic additive-free sulfamate bath. The as-deposited Ni–Al composites exhibited increased compressive residual stresses with increasing Al nanoparticles. Detailed microstructural investigation revealed that Al codeposition led to significant refinement of the columnar morphology and grain structure of Ni matrix along with a texture change from strong <001> to <011> fiber texture parallel to the growth direction. The as-deposited Ni with bimodal grain structure displayed good tensile strength and ductility. The microhardness and tensile strength of the Ni deposits were increased initially with Al content and then decreased at higher particle content. Particle induced grain refinement and texture changes could be related to change in the growth of upcoming Ni nuclei on to the surface of well-dispersed Al nanoparticles. Significant grain refinement and lesser internal stresses along with good particle distribution and relatively harder <011> fiber texture at lower particles concentration collectively contributed to the observed higher strengths in Ni–Al composites as compared to Ni deposits. There was substantial change in fracture morphology from spherical dimples to flat regions with increasing Al content due to agglomeration of nanoparticles at higher particle loading.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Deposition of high permeability FeCoN films on mica substrates

In this study, sheet mica was explored as an alternative substrate for thin film deposition due to its unique layered structure and atomically flat surface. Static magnetic properties and microwave permeability of sputtered FeCoN films on mica with and without SiO{sub 2} under-layer were examined. In-plane isotropy and a large coercivity of 70 Oe were observed for the film directly deposited on mica substrate. With the insertion of 40 nm SiO{sub 2} under-layer between the film and mica substrate, well-defined in-plane anisotropy is formed due to the significant reduce in film residual stress, associated with a 3 Oe coercive force along easy axis. As a result, excellent microwave properties have been achieved and are comparable with the same film on Si substrate. Moreover, the permeability spectra are surprisingly stable from room temperature up to 390 K. Mica is proved as a promising substrate for magnetic films with high microwave performance, which is a great advantage for practical applications. Furthermore, our results provide an effective way to reduce the residual stress in sputtered films.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Stress Birth and Death: Disruptive Computational Mechanics and Novel Diagnostics for Fluid-to-Solid Transitions

Many materials of interest to Sandia transition from fluid to solid or have regions of both phases coexisting simultaneously. Currently there are, unfortunately, no material models that can accurately predict this material response. This is relevant to applications that "birth stress" related to geoscience, nuclear safety, manufacturing, energy production and bioscience. Accurately capturing solidification and residual stress enables fully predictive simulations of the evolving front shape or final product. Accurately resolving flow of proppants or blood could reduce environmental impact or lead to better treatments for heart attacks, thrombosis, or aneurism. We will address a science question in this proposal: When does residual stress develop during the critical transition from liquid to solid and how does it affect material deformation? Our hypothesis is that these early phases of stress development are critical to predictive simulation of material performance, net shape, and aging. In this project, we use advanced constitutive models with yield stress to represent both fluid and solid behavior simultaneously. The report provides an abbreviated description of the results from our LDRD "Stress Birth and Death: Disruptive Computational Mechanics and Novel Diagnostics for Fluid-to-Solid Transitions," since we have written four papers that document the work in detail and which we reference. We give highlights of the work and describe the gravitationally driven flow visualization experiment on a model yield stress fluid, Carbopol, at various concentrations and flow rates. We were able to collapse the data on a single master curve by showing it was self-similar. We also describe the Carbopol rheology and the constitutive equations of interest including the Bingham-Carreau-Yasuda model, the Saramito model, and the HB-Saramito model including parameter estimation for the shear and oscillatory rheology. We present several computational models including the 3D moving mesh simulations of both the Saramito models and Bingham-Carreau-Yasuda (BCY) model. We also show results from the BCY model using a 3D level set method and two different ways of handling reduced order Hele-Shaw modeling for generalized Newtonian fluids. We present some first ever two-dimensional results for the modified Jeffries Kamani-Donley-Rogers constitutive equation developed during this project. We include some recent results with a successful Saramito-level set coupling that allows us to tackle problems with complex geometries like mold filling in a thin gap with an obstacle, without the need for remeshing or remapping. We report on some experiments for curing systems where fluorescent particles are used to track material flow. These experiments were carried out in an oven on Sylgard 184 as a model polymerizing system. We conclude the report with a summary of accomplishments and some thoughts on follow-on work.

36 MATERIALS SCIENCE↗