Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “ZONES”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Type IV failure in weldment of creep resistant ferritic alloys: I. Micromechanical origin of creep strain localization in the heat affected zone

Creep strength enhanced ferritic (CSEF) steels containing 9-12wt% chromium have been extensively used in fossil-fuel-fired power plants. Despite their excellent creep resistance at high temperatures, premature failures (especially Type IV cracking) are often found in the fine-grained heat affected zone (HAZ) or intercritical HAZ of the welded components. This failure mode is preceded by the strain localization in the HAZ, as measured by the Digital Image Correlation (DIC) technique. The present work aims to develop a finite-element based computational method to determine the micromechanical and microstructural origin of the strain localization phenomenon. We construct a two-dimensional digital microstructure based on the actual microstructure of ferritic steel weldments by using the Voronoi-tessellation method, to account for the effects of its large grain-size gradients. A mechanism-based finite element method is developed for modeling the high temperature deformation resulting from a synergy of thermally activated dislocation movements, diffusional flow and grain boundary sliding. The numerical results agree well with the strain measurements by our DIC technique, particularly revealing the effect of pre-welding tempering on the evolution of strain localization in HAZ of creep resistant steel weldments. It is found that the diffusional creep with dependence on grain sizes, dislocation creep with dependence on material strength, and more importantly, grain boundary sliding, contribute synergistically to the creep strain accumulation in the HAZ, and their relative degree of significance is quantified. The creep rupture life will be investigated in the companion paper.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Microstructural analysis of laser weld fusion zone in Haynes 282 superalloy

Analytical electron microscopy and spectroscopy analyses of the fusion zone (FZ) microstructure in autogenous laser beam welded Haynes 282 (HY 282) superalloy were performed. The micro-segregation patterns observed in the FZ indicate that Co, Cr and Al exhibited a nearly uniform distribution between the dendrite core and interdendritic regions while Ti and Mo were rejected into the interdendritic liquid during the weld solidification. Transmission electron diffraction analysis and energy dispersive X-ray microanalysis revealed the second phase particles formed along the FZ interdendritic region to be Ti-Mo rich MC-type carbide particles. Weld FZ solidification cracking, which is sometimes associated with the formation of {gamma}-{gamma}' eutectic in {gamma}' precipitation strengthened nickel-base superalloys, was not observed in the HY 282 superalloy. Modified primary solidification path due to carbon addition in the newly developed superalloy is used to explain preclusion of weld FZ solidification cracking in the material. - Highlights: Black-Right-Pointing-Pointer A newly developed superalloy was welded by CO{sub 2} laser beam joining technique. Black-Right-Pointing-Pointer Electron microscopy characterization of the weld microstructure was performed. Black-Right-Pointing-Pointer Identified interdendritic microconstituents consist of MC-type carbides. Black-Right-Pointing-Pointer Modification of primary solidification path is used to explain cracking resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Microstructure characterization of laser welded Ti-6Al-4V fusion zones

The as-welded microstructure of laser-welded Ti-6Al-4V is characterized as a function of CO2 key-hole mode laser welding speed. Martensitic α′ is the predominant phase, with some α and retained β. Phase transformation is affected by the cooling rate through laser welding speed. A higher welding speed of 1.6 to 2.0 m/min produced more martensite α′ and less retained β in the welds. 1.4 m/min welding speed produced small amounts of α, besides the martensite α′. A trace of δ titanium hydride phase seems to have formed in the weld fusion zone. Moiré fringes are a common feature in the TEM microstructure, due to abundance of multi-phase interfaces. Tensile twins and clusters of dislocations indicate that plastic deformation has happened in the as-welded microstructure, indicating the local stress levels to be approaching the yield stress on-cooling during laser welding.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Characterisation of weld zone reactions in dissimilar glass-to-aluminium pulsed picosecond laser welds

Precision welded joints, produced between fused silica glass and aluminium by a newly-developed picosecond-pulse laser technique, have been analysed for the first time using a full range of electron microscopy methods. The welds were produced as lap joints by focusing a 1.2 μm diameter laser beam through the transparent glass top sheet, slightly below the surface of the metal bottom sheet. Despite the extremely short interaction time, extensive reaction was observed in the weld zone, which involved the formation of nanocrystalline silicon and at least two transitional alumina phases, γ- and δ-Al{sub 2}O{sub 3}. The weld formation process was found to be complex and involved: the formation of a constrained plasma cavity at the joint interface, non-linear absorption in the glass, and the creation of multiple secondary keyholes in the metal substrate by beam scattering. The joint area was found to expand outside of the main interaction volume, as the energy absorbed into the low conductivity and higher melting point silica glass sheet melted the aluminium surface across a wider contact area. The reasons for the appearance of nanocrystalline Si and transitional alumina reaction products within the welds are discussed. - Highlights: •Pulsed laser welding of dissimilar materials causes extensive chemical reactivity. •Metastable Al{sub 2}O{sub 3} phases form due to laser-induced highly-transient thermal regime. •Fused silica is reduced by Al to form nanocrystalline Si. •Mechanism of joint formation is discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Mechanism of heat affected zone cracking in Ni-based superalloy DZ125L fabricated by laser 3D printing technique

Laser 3D printing is a promising technique to repair damaged Ni-based superalloy components. However, the occurrence of heat affected zone (HAZ) cracking severely limits its applicability. In this paper, we unravel the cracking mechanism by studying the element, phase, defect, and strain distribution around an intergranular crack that initiated from the primary HAZ. Using synchrotron X-ray Laue microdiffraction, we measured high tensile strain/stress transverse to the building direction in both the primary HAZ and the cladding layers, as well as high-density dislocations, which resulted from the thermal contraction and rapid precipitation of γ' phase. The crack initiated because the transverse tensile strain/stress tore up the liquid film formed by the low-melting point preexisting phases in the primary HAZ, such as γ/γ' eutectics and coarse γ' precipitates. The incoherent carbide particles were frequently observed near the crack root as local strain concentrators. In the cladding layers, micro-segregation could not be completely avoided, thus the hot crack continued to propagate over several layers with the assistance of the transverse tensile stress. Finally, our investigations provide a useful guideline for the optimization of the 3D printing process to repair Ni-based superalloys with high susceptibility to hot cracking.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Strain age cracking in a simulated heat affected zone of Inconel 740H laser-powder bed fusion components

Inconel® 740H components produced via laser-powder-bed fusion (L-PBF) additive manufacturing are ideal for supercritical CO2 primary heat exchangers. Arc welding is often needed, and subsequent post-weld heat treatment aging at 790–840 °C is required to improve strength via gamma prime (γ’) precipitation; however, strain age cracking (SAC) can occur in the heat affected zone (HAZ) during this process. This study uses stress relaxation testing at 800 °C on simulated HAZ specimens from vertically and horizontally built L-PBF IN740H to assess SAC susceptibility across heating rates of 40–3480 °C/h and weld-induced strains of 3–10 %. Vertical builds require greater mechanical energy input and exhibit longer times to fracture than horizontal builds, and time to fracture occurs sooner at slower heating rates. Creep voids were observed in γ’-denuded regions along grain boundaries, and cracking propagated along migrated grain boundaries and at interfaces between elongated secondary phases (γ’ or carbides) and the γ-matrix.

14 SOLAR ENERGY↗
DOE OSTI2018

Above zone pressure interpretation for leaky well characterization and its identification from leaky caprock/fault

Pressure transient analysis has long been used for reservoir characterization. Above-zone (AZ) pressure has been recently investigated for inferring leakage pathway characteristics in leakage events from subsurface injection operations. The recorded pressure in the AZ should be purely related to leakage and therefore it can be safely inverted to deduce leakage characteristics. It is crucial to evaluate fluid leakage through abandoned wells to plan for further measurements of leakage prevention. However, the recorded AZ leakage signal may not be related to leaky well(s). Therefore, identification and spatial investigation of well leakage is required for leakage evaluation. Here in this paper, we propose a pressure interpretation method for early detection of leaky pathways, applying two observation points in the AZ. We distinguish leaky well, fault and caprock based on their corresponding flow regime identification. We show that the pressure difference of the two observation wells can be applied as a proxy for unknown leakage rate, which is crucial for leakage identification as well as characterization. Results show that the estimated location of the leaky well, leakage coefficient, and the leakage rate are in good agreement with the actual values. The estimated leakage coefficient of the leaky well can be used to evaluate well leakage in multiphase systems such as carbon dioxide leakage in deep saline aquifers.

02 PETROLEUM↗
DOE OSTI2019

Capacity assessment and co-optimization of CO 2 storage and enhanced oil recovery in residual oil zones

Residual oil zones (ROZs) are increasingly being commercially exploited using CO 2 -enhanced oil recovery (CO 2 -EOR) method. In this study, CO 2 storage potential, long-term CO 2 fate and oil recovery potential in ROZs are characterized based on a reservoir model for Goldsmith-Landreth San Andres Unit in the Permian Basin. The effects of CO 2 injection rates, well patterns (five-spot and line-drive), well spacings, injection modes (continuous CO 2 injection and water-alternatinggas injection) on the CO 2 retention in the reservoir and the oil production are investigated. After the preliminary assessment of CO 2 storage and EOR potentials in ROZs, we next develop a novel approach based on a newly developed optimization algorithm-Stochastic Simplex Approximate Gradient (StoSAG) and predictive empirical models constructed using machine learning technique to co-optimize CO 2 storage and oil recovery in ROZs. The performance of co-optimization of CO 2 storage and oil recovery is compared with the performance of optimization of only CO 2 storage.

58 GEOSCIENCES↗
DOE OSTI2011

Poly(dimethylsiloxane) microchip-based immunoassay with multiple reaction zones: Toward on-chip multiplex detection platform

In this work, a poly(dimethylsiloxane) (PDMS) microchip-based immuno-sensing platform with integrated pneumatic micro valves is described. The microchip was fabricated with multiple layer soft lithography technology. By controlling the activation status of corresponding valves, reagent flows in the microchannel network can be well manipulated so that immuno-reactions only take place at designated reaction zones (DRZs). Four DRZs are included in the prototype microchip. Since these DRZs are all isolated from each other by micro valves, cross contamination is prevented. Using the inner surface of the all-PDMS microchannel as immunoassay substrate, on-chip sandwich format solid phase immunoassay was performed to demonstrate the feasibility of this immuno-sensing platform. Mouse IgG and fluorescein isothiocyanate (FITC) were used as the model analyte and the signal reporter respectively. Only 10 ul sample is needed for the assay and low detection limit of 5 ng/ml (≈33 pM) was achieved though low-cost polyclonal antibodies were used in our experiment for feasibility study only. The encouraging results from mouse IgG immunoassay proved the feasibility of our microchip design. With slight modification of the assay protocol, the same chip design can be used for multi-target detection and can provide a simple, cost-effective and integrated microchip solution for multiplex immunoassay applications.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

High-pressure floating-zone growth of perovskite nickelate LaNiO 3 single crystals

We report the first single crystal growth of the correlated metal LaNiO 3 using a high-pressure optical-image floating zone furnace. The crystals were studied using single crystal/powder X-ray diffraction, resistivity, specific heat, and magnetic susceptibility. The availability of bulk LaNiO 3 crystals will (i) promote deep understanding in this correlated material, including the mechanism of enhanced paramagnetic susceptibility, and (ii) provide rich opportunities as a substrate for thin film growth such as important ferroelectric and/or multiferroic materials. As a result, this study demonstrates the power of high pO 2 single crystal growth of nickelate perovskites and correlated electron oxides more generally.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Effect of Water Chemistry and Hydrodynamics on Nitrogen Transformation Activity and Microbial Community Functional Potential in Hyporheic Zone Sediment Columns

Nitrogen (N) transformation in hyporheic zone (HZ) is an important component in N-cycling in ecosystems. A column study was conducted to investigate N transformation in a HZ sediment with a focus on how characteristic HZ properties including water chemistry, fluid residence time, and dynamic groundwater and surface water exchange affect on N transformation. Metagenomic and quantitative polymerase chain reaction (qPCR) analyses were performed to evaluate the dynamic changes in microbial community structure and its function in response to N transformation. The results indicated that N transformation in the HZ sediment was collectively controlled by microbial community functions including: denitrification, dissimilatory nitrate reduction to ammonium (DNRA), nitrification, and anaerobic ammonium oxidation (anammox). However, the spatial distribution of the microbial community functions and associated biogeochemical reaction rates and products changed quickly in response to experimental perturbation, and was influenced by various factors including water chemistry (dissolved O2 and N species), desorption of sediment associated organic carbon, ion exchange reactions of NH4+, and fluid residence time. The results of this study implied that the microbial community in the HZ would exhibit strong function zonation along N and O gradients, which in turn would control the rates and products of N transformation.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Tc(VII) and Cr(VI) Interaction with Naturally Reduced Ferruginous Smectite from a Redox Transition Zone

Fe(II)-rich clay minerals found in subsurface redox transition zones (RTZs) can serve as important source of electron equivalents limiting the transport of redox active contaminants. While most laboratory reactivity studies are based on reduced model clays, the reactivity of naturally reduced clays in field samples remains poorly explored. Characterization of the clay size fraction of a fine-grained unit from RTZ interface at the Hanford site, Washington, including mineralogy, crystal chemistry, and Fe(II)/(III) content, indicates that ferruginous montmorillonite is the dominant mineralogical component. Oxic and anoxic fractions differ significantly in Fe(II) concentration, but FeTOTAL remains constant demonstrating no Fe loss during reduction-oxidation cycling. At its native pH of 8.6, the anoxic fraction despite its significant Fe(II) (~23% of FeTOTAL), exhibits minimal reactivity with TcO4- and CrO42- and much slower reaction kinetics than that measured in studies with biologically/chemically reduced model clays. Reduction capacity is enhanced by added Fe(II) (if Fe(II)SORBED >8% clay Fe(II)LABILE), however the kinetics of this conceptually surface-mediated reaction remain sluggish. Surface-sensitive Fe L-edge X-ray absorption spectroscopy shows that Fe(II)SORBED and the resulting reducing equivalents are not available in the outermost few nanometers of clay surfaces. Slow kinetics thus appear related to diffusion-limited access to electron equivalents retained within clay mineral.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2013

Transport of Europium Colloids in Vadose Zone Lysimeters at the Semiarid Hanford Site

The objective of this study was to quantify transport of Eu colloids in the vadose zone at the semiarid Hanford site. Eu-hydroxy-carbonate colloids, Eu(OH)-(CO 3 ), were applied to the surface of field lysimeters, and migration of the colloids through the sediments was monitored using wick samplers. The lysimeters were exposed to natural precipitation (145-231 mm/year) or artificial irrigation (124-348 mm/year). Wick outflow was analyzed for Eu concentrations, supplemented by electron microscopy and energy-dispersive X-ray analysis. Small amounts of Eu colloids (<1%) were detected in the deepest wick sampler (2.14 m depth) 2.5 months after application and cumulative precipitation of only 20 mm. We observed rapid transport of Eu colloids under both natural precipitation and artificial irrigation; that is, the leading edge of the Eu colloids moved at a velocity of 3 cm/day within the first 2 months after application. Episodic infiltration (e.g., Chinook snowmelt events) caused peaks of Eu in the wick outflow. While a fraction of Eu moved consistent with long-term recharge estimates at the site, the main mass of Eu remained in the top 30 cm of the sediments. This study illustrates that, under field conditions, near-surface colloid mobilization and transport occurred in Hanford sediments.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2012

Conventional and Stuffed Bergman-Type Phases in the Na-Au-T (T = Ga, Ge, Sn) Systems: Syntheses, Structures, Coloring of Cluster Centers, and Fermi Sphere–Brillouin Zone Interactions

Bergman-type phases in the Na-Au-T (T = Ga, Ge, and Sn) systems were synthesized by solid-state means and structurally characterized by single-crystal X-ray diffraction studies. Two structurally related (1:1) Bergman phases were found in the Na-Au-Ga system: (a) a conventional Bergman-type (CB) structure, Na 26 Au x Ga 54-x , which features empty innermost icosahedra, as refined with x = 18.1 (3), Im$\overline{3}$ a = 14.512(2) Å, and Z = 2; (b) a stuffed Bergman-type (SB) structure, Na 26 Au y Ga 55-y , which contains Gacentered innermost icosahedra, as refined with y = 36.0 (1), Im$\overline{3}$, a = 14.597(2) Å, and Z = 2. Although these two subtypes have considerable phase widths along with respective tie lines at Na ≈ 32.5 and 32.1 atom %, they do not merge into a continuous solid solution. Rather, a quasicrystalline phase close to the Au-poor CB phase and an orthorhombic derivative near the Au-rich SB phase lie between them. In contrast, only Au-rich SB phases exist in the Ge and Sn systems, in which the innermost icosahedra are centered by Au rather than Ge or Sn. These were refined for Na26Au40.93(5)Ge14.07(5) (Im$\overline{3}$, a = 14.581(2) Å, and Z = 2) and Na 26 Au 39.83(6) Sn 15.17(6) (Im$\overline{3}$, a = 15.009(2) Å, and Z = 2), respectively. Occupations of the centers of Bergman clusters are rare. Such centering and coloring correlate with the sizes of the neighboring icosahedra, the size ratios between electropositive and electronegative components, and the values of the average valence electron count per atom (e/a). Theoretical calculations revealed that all of these phases are Hume-Rothery phases, with evident pseudogaps in the density of states curves that arise from the interactions between Fermi surface and Brillouin zone boundaries corresponding to a strong diffraction intensity.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Experimental Investigation of Gas Flow and Hydrate Formation Within the Hydrate Stability Zone

Here, we form methane hydrate by injecting methane gas into a brine-saturated, coarse-grained sample under hydrate-stable thermodynamic conditions. Hydrate forms to a saturation of 11%, which is much lower than that predicted assuming three-phase (gas-hydrate-brine) thermodynamic equilibrium (67%). During hydrate formation, there are temporary flow blockages. We interpret that a hydrate skin forms a physical barrier at the gas-brine interface. The skin fails periodically when the pressure differential exceeds the skin strength. Once the skin is present, further hydrate formation is limited by the rate that methane can diffuse through the solid skin. This process produces distinct thermodynamic states on either side of the skin that allows gas to flow through the sample. This study illuminates how gas can be transported through the hydrate stability zone and thus provides a mechanism for the formation of concentrated hydrate deposits in sand reservoirs. It also illustrates that models that assume local equilibrium at the core-scale and larger may not capture the fundamental behaviors of these gas flow and hydrate formation processes.

58 GEOSCIENCES↗
DOE OSTI2018

High‐Pressure/Temperature Behavior of the Alkali/Calcium Carbonate Shortite (Na 2 Ca 2 (CO 3 ) 3 ): Implications for Carbon Sequestration in Earth's Transition Zone

Abstract The behavior of shortite (Na 2 Ca 2 (CO 3 ) 3 ) has been probed using synchrotron‐based single crystal X‐ray diffraction and Raman spectroscopy at high pressures and following laser heating to illuminate carbon retention within the deep earth, and phase equilibria of alkali/calcium carbonate‐rich systems. Above 15 GPa, a transition to the shortite‐II structure occurs at 300 K. This phase is novel as it involves a large distortion of the carbonates, with an onset of 3 + 1 coordination and near‐dimerization of carbonate groups. Above 22 GPa, shortite‐II amorphizes. Samples laser heated at pressures between 12 and 30 GPa crystallize in a new structure, shortite‐III. Below 12 GPa, this phase appears to decompose into a mixture of shortite, nyerereite (Na 2 Ca(CO 3 ) 2 ), and aragonite (CaCO 3 ) in accord with prior phase equilibria results. The high‐pressure behavior of nyerereite using Raman spectroscopy was also investigated to 25 GPa. The structural response of shortite to pressure is modulated by the sodium cations in the structure; hence, the behavior of alkali‐rich carbonates within kimberlitic systems at depth is likely dependent on the bonding and local geometry of alkali cations. Our results show that complex, dense high‐pressure structures are generated in the shortite system, and phase equilibria of the protoliths of carbonatites and kimberlites at deep upper mantle and transition zone pressures will involve intermediate alkali‐calcium carbonate phases, including the high‐pressure phases of shortite. Moreover, 3 + 1 coordination of carbon is observed at far lower pressures than other systems: this coordination could become important in complex carbonates and possibly liquids at substantially shallower depths than previously anticipated.

Vennari, Cara E.↗
DOE OSTI2018

Drought Conditions Maximize the Impact of High-Frequency Flow Variations on Thermal Regimes and Biogeochemical Function in the Hyporheic Zone

Anthropogenic activities, such as dam operations, often induce larger and more frequent stage fluctuations than those occurring in natural rivers. However, the long-term impact of such flow variations on thermal and biogeochemical dynamics of the associated hyporheic zone (HZ) is poorly understood. A heterogeneous, two-dimensional thermo-hydro-biogeochemical model revealed an important interaction between high-frequency flow variations and watershed-scale hydrology. High-frequency stage fluctuations had their strongest thermal and biogeochemical impacts when the mean river stage was low during fall and winter. An abnormally thin snowpack in 2015, however, created a low river stage during summer and early fall, whereby high-frequency stage fluctuations caused the HZ to be warmer than usual. Furthermore, this study provided the scientific basis to assess the potential ecological consequences of the high-frequency flow variations in a regulated river, as well as guidance on how to maximize the potential benefits—or minimize the drawbacks—of river regulation to river ecosystems.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Model‐Based Analysis of the Effects of Dam‐Induced River Water and Groundwater Interactions on Hydro‐Biogeochemical Transformation of Redox Sensitive Contaminants in a Hyporheic Zone

Abstract Biogeochemical processes in the hyporheic zone (HZ) may retard the contaminants migration from groundwater to the river and vice versa. Anthropogenic activities may further complicate such processes. This study investigated the effects of dam‐induced hydrodynamics on biogeochemical transformation of contaminants using Cr as an example in the HZ of the Columbia River at the U.S. Department of Energy's Hanford Site. The flow velocities in the HZ were first simulated using the measured or averaged groundwater level and river stage at hourly, daily, weekly, and monthly time scales. The flow velocities were then incorporated into a reactive transport model with independently characterized biogeochemical reactions and kinetics. Simulation results indicated that hydrodynamics can significantly influence the rate and extent of Cr (VI) biogeochemical transformation, which was mainly controlled by the kinetic reduction of Cr (VI) to sparely soluble Cr (III) by sediment‐associated Fe (II) that can be regenerated by microorganisms with organic carbon as electron donor. The frequent flow direction reversals in the HZ induced by dam operations enhanced the rate of microbial consumption of bioavailable OC, which, if there was no organic carbon supply, can eventually terminate the Fe (II) regeneration mechanism and exhaust the HZ's redox capacity in reducing Cr (VI) to Cr (III). This study demonstrated the importance of hydrodynamics on biogeochemical transformation of contaminants in the HZ and of the time scales used in assessing the reactive transport of chemicals and contaminants in the HZ as the net supply of redox sensitive chemicals such as dissolved oxygen into the HZ is a function of the frequency of flow direction reversal.

Yang, Chen↗