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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

In Situ Observation of Domain Wall Lateral Creeping in a Ferroelectric Capacitor

As a promising candidate for next-generation nonvolatile memory devices, ferroelectric oxide films exhibit many emergent phenomena with functional applications, making understanding polarization switching and domain evolution behaviors of fundamental importance. However, tracking domain wall motion in ferroelectric oxide films with high spatial resolution remains challenging. Here, in this study, an in situ biasing approach for direct atomic-scale observations of domain nucleation and sideways motion is presented. By accurately controlling the applied electric field, the lateral translational speed of the domain wall can decrease to less than 2.2 Å s −1 , which is observable with atomic resolution STEM imaging. In situ observations on a capacitor structured PbZr 0.1 Ti 0.9 O 3 /La 0.7 Sr 0.3 MnO 3 heterojunction demonstrate the unique creeping behavior of a domain wall under a critical electric field, with the atomic structure of the creeping domain wall revealed. Moreover, the evolution of the metastable domain wall forms an elongated morphology, which contains a large proportion of charged segments. Phase-field simulations unveil the competition between gradient, elastic, and electrostatic energies that decide this unique domain wall creeping and morphology variation. This work paves the way toward a complete fundamental understanding of domain wall physics and potential modulations of domain wall properties in real devices.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Creep and oxidation behavior of modified CF8C-plus with W, Cu, Ni, and Cr

Here, the microstructures of modified CF8C-Plus (Fe-19Cr-12Ni-0.4W-3.8Mn-0.2Mo-0.6Nb-0.5Si-0.9C) with W and Cu (CF8CPWCu) and CF8CPWCu enhanced with 21Cr + 15Ni or 22Cr + 17.5Ni were characterized in the as-cast condition and after creep testing. When imaged at lower magnifications, the as-cast microstructure was similar among all three alloys as they all contained a Nb-rich interdendritic phase and Mn-based inclusions. Transmission electron microscopy (TEM) analysis showed the presence of nanoscale Cu-rich nanoprecipitates distributed uniformly throughout the matrix of CF8CPWCu, whereas in CF8CPWCu22/17, Cu precipitates were found primarily at the grain boundaries. The presence of these nanoscale Cu-rich particles, in addition to W-rich Cr 23 C 6 , nanoscale Nb carbides, and Z-phase (Nb 2 Cr 2 N 2 ), improved the creep strength of the CF8CPWCu steel. Modification of CF8CPWCu with Cr and Ni contents slightly decreased the creep strength but significantly improved the oxidation behavior at 1073 K (800 °C). In particular, the addition of 22Cr and 17.5Ni strongly enhanced the oxidation resistance of the stainless steel resulting in a 100 degrees or greater temperature improvement, and this composition provided the best balance between improving both mechanical properties and oxidation resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Mapping Multivariate Influence of Alloying Elements on Creep Behavior for Design of New Martensitic Steels

Here, heritage data for the class of 9 to 12 wt pct Cr steels are studied using data science to quantify the statistically significant relationships among multiple processing/microstructure and performance variables. The effort is undertaken to find new martensitic steels for creep life of 10 5 hours or greater at 650 °C and 100 MPa using machine learning. Linear regression and lasso regression were utilized to identify alloying elements that contribute towards better creep strength. Visualization techniques such as t-distributed stochastic neighbor embedding and pair-wire element specific comparisons were utilized to explore information gaps that exist within the data and are in conflict with existing domain knowledge. Lastly, cfombining all results suggest that the next alloy design to be explored should be 9 wt pct Cr with high W (2 to 3 wt pct) and high Co (2 to 3 wt pct) for creep life of 10 5 hours or greater at 650 °C, 100 MPa.

36 MATERIALS SCIENCE↗
DOE OSTI2020

An Alternative Casting Technique to Improve the Creep Resistance of Cast INCONEL Alloy 740H

The increasing performance requirements of power plant designs, such as advanced-ultra supercritical (A-USC), require the use of Ni-based superalloys to replace high-strength, ferritic-martensitic steels for components subjected to temperatures above 898 K (625 °C) and for austenitic stainless steels components at temperatures above 973 K (700 °C). To date, commercial Ni-based superalloy INCONEL 740H has been shown to be appropriate for use in A-USC power plants as boiler components in a wrought product. However, large complex components in boilers as well as other casings in the turbine and valve chest require castings of a thick-wall nature. Using the alloy in its cast form would be significantly valuable in terms of range of component size, geometry and complexity. Previous investigations revealed short creep lives from cast INCONEL alloy 740H. Here in this investigation, an alternative casting route that utilized a melt procedure resulting in a fine-grain casting, and in conjunction with a computationally optimized homogenization heat treatment, not only controlled the grain size and grain boundary structure but minimized chemistry variability and segregation. A primarily equiaxed and homogenous grain size distribution was obtained from this approach with better repartition of M 23 C 6 carbides along the grain boundaries. Furthermore, better than 38 pct increase was obtained for this material in comparison to the creep life obtained from the best performing conventionally cast material. More importantly, the fine-grain homogenized (FGH) casting route resulted in the Larson–Miller plot for this material that coincided with that of wrought alloy 740. At low creep stresses (with a test still in progress), the FGH casting is resulting in higher values of the LMP than the wrought alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Creep Behavior of a High-$\gamma^{\prime}$ Ni-Based Superalloy Fabricated via Electron Beam Melting

Additive manufacturing enables the fabrication of complex engineering components previously inaccessible through traditional processes. Nickel-base superalloys with large γ' volume fraction are typically considered non-weldable and therefore exhibit a propensity for cracking during the fusion process. These crack-prone materials, however, are of great importance in gas turbine engines due to their excellent high temperature creep resistance. In this study we investigate the creep behavior of IN738LC produced by the electron beam melting process. Here, we find that with appropriate post-build heat treatment the creep response of material oriented in the build direction exhibits deformation and rupture behavior comparable to that of conventionally cast IN738 & IN738LC. In the transverse direction properties fall below the expected cast behavior, however, we argue this is likely due to differences in grain scale and crystallographic texture. It may be possible to coarsen the grain morphology with appropriate process-parameter optimization in order to reduce the severity of intergranular fracture in the transverse direction. These results illustrate that high temperature properties exhibited by additively manufactured IN738LC are suitable for the hot section of gas turbine engines.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Acoustic Emission Responses of Three Typical Metals During Plastic and Creep Deformations

In this paper, the acoustic emission (AE) responses of three typical engineering metals (namely, Q235 carbon steel, H62 brass and 304 stainless steel) during plastic and high-temperature creep deformations were experimentally investigated. To gain insight into the AE response mechanisms, the micro scale mechanical behaviors of these metals were studied with a micro-tensile tester with observation by scanning electron microscopy (SEM). The following observations were found: (1) although the intensities and activities of the AE signals greatly differed under the same configurations, the AE peak values appeared at the transition from elasticity to plasticity for all three metals; (2) compared to the AE signal intensity during plastic deformation, the signal intensity during high-temperature creep was much weaker; (3) slip lines appeared within the crystal grains at the stress level corresponding to the peak AE signal intensity, but the densities of the slip lines and their crossover were not proportional to the AE signals of the metals. From these findings, the following conclusions were drawn about the application of AE: (1) AE is more scientific method to determine the yielding point of a metal without plastic flow than the nominal yield stress; (2) AE can be used to determine the deformation mechanism at high temperature, particularly, to distinguish creep from plastic deformation; (3) the AE response is the result of a sudden energy release by dislocation motion; however, the AE signal intensity is not necessarily proportional to the dislocation activity.

36 MATERIALS SCIENCE↗
DOE OSTI2023

High temperature creep model development using in-situ 3-D DIC techniques during a simulated LOCA transient

In-situ strain measurements of fuel cladding can enable high-throughput data collection and validation to support accelerated qualification of cladding materials. Here, in this work, 3D digital image correlation was used to map strain for both Zircaloy-4 (Zry-4) and Cr-coated Zry-4 during two types of cladding rupture experiments: isobaric temperature ramp tests at 5 °C/s and isothermal pressure jump tests at 600 °C. Zry-4 strain data initially showed a temperature dependence expected for creep deformation, yet a shift to a new plastic deformation mechanism not reported in literature dominated during the finals seconds prior to rupture. Cr-coated Zry-4 did not show the change in deformation mechanism at the end of life and showed a delay in measurable creep deformation. Stress dependences were similar for Zry-4 and Cr/Zry-4 during pressure jump tests. Cr-coatings were found to decrease the strain rate during both testing scenarios. Creep parameters were calculated to support modelling efforts regarding design basis accidents.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Coupled modeling of a directly heated tubular solar receiver for supercritical carbon dioxide Brayton cycle: Structural and creep-fatigue evaluation

A supercritical carbon dioxide (sCO 2 ) Brayton cycle is an emerging high energy-density cycle undergoing extensive research due to the appealing thermo-physical properties of sCO 2 and single phase operation. Development of a solar receiver capable of delivering sCO 2 at 20 MPa and 700 °C is required for implementation of the high efficiency (~50%) solar powered sCO 2 Brayton cycle. In this work, extensive candidate materials are review along with tube size optimization using the ASME Boiler and Pressure Vessel Code. Moreover, temperature and pressure distribution obtained from the thermal-fluid modeling (presented in a complementary publication) are used to evaluate the thermal and mechanical stresses along with detailed creep-fatigue analysis of the tubes. For resulting body stresses were used to approximate the lifetime performance of the receiver tubes. A cyclic loading analysis is performed by coupling the Strain-Life approach and the Larson-Miller creep model. The structural integrity of the receiver was examined and it was found that the stresses can be withstood by specific tubes, determined by a parametric geometric analysis. The creep-fatigue analysis display the damage accumulation due to cycling and the permanent deformation on the tubes showed that the tubes can operate for the full lifetime of the receiver.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Crystal viscoplasticity model for the creep-fatigue interactions in single-crystal Ni-base superalloy CMSX-8

A crystal viscoplasticity (CVP) model for the creep-fatigue interactions of nickel-base superalloy CMSX-8 is proposed. At the microstructure scale of relevance, the superalloys are a composite material comprised of a γ phase and a γ' strengthening phase with unique deformation mechanisms that are highly dependent on temperature. Considering the differences in the deformation of the individual material phases is paramount to predicting the deformation behavior of superalloys at a wide range of temperatures. In this work, we account for the relevant deformation mechanisms that take place in both material phases by utilizing two additive strain rates to model the deformation on each material phase. The model is capable of representing the creep-fatigue interactions in single-crystal superalloys for realistic 3-dimensional components in an Abaqus User Material Subroutine (UMAT). Using a set of material parameters calibrated to superalloy CMSX-8, the model predicts creep-fatigue, fatigue and thermomechanical fatigue behavior of this single-crystal superalloy. In conclusion, a sensitivity study of the material parameters is done to explore the effect on the deformation due to changes in the material parameters relevant to the microstructure.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Partitioning of tramp elements Cu and Si in a Ni-based superalloy and their effect on creep properties

An alloy's processing history, including melting, remelting or the choice of stock material, affects its purity and eventually involves tramp element pickup or retention. Herein, variants of a novel Ni-based superalloy were manufactured with different levels of purity. The so-called low purity alloys contained 0.138 wt. % Cu and 0.019 wt. % Si while the Cu and Si levels were below x-ray fluorescence (XRF) detection limits of 0.003 and 0.010 wt. %, respectively, in the high purity ingots. Atom-probe tomography (APT) was carried out and revealed Si partitioning at the following interfaces: grain boundaries, MC carbide/γ, M 3 B 2 boride/$γ$ and M 3 B 2 boride/$γ$'. Copper was found to primarily segregate to the $γ$' precipitates. An average of 2.4 × decrease in creep life and 4.3 × decrease in creep ductility was measured in the low purity alloys, which was attributed to the embrittlement caused by Si segregation to grain boundaries. Furthermore, the positive effect of B on the creep properties was mitigated by the presence of Si. Thermodynamic predictions for the matrix and γ' precipitate compositions represented the trends observed experimentally although the extent of preferential partitioning lacks accuracy. Monte Carlo simulations were performed to describe the partitioning of Cu and Si atoms to either $γ$ or $γ$' phases.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Universal lower limit on vortex creep in superconductors

Superconductors are excellent testbeds for studying vortices, topological excitations that also appear in superfluids, liquid crystals and Bose–Einstein condensates. Vortex motion can be disruptive; it can cause phase transitions, glitches in pulsars, and losses in superconducting microwave circuits, and it limits the current-carrying capacity of superconductors4. Understanding vortex dynamics is fundamentally and technologically important, and the competition between thermal energy and energy barriers defined by material disorder is not completely understood. Specifically, early measurements of thermally activated vortex motion (creep) in iron-based superconductors unveiled fast rates (S) comparable to measurements of YBa 2 Cu 3 O 7–δ . This was puzzling because S is thought to somehow correlate with the Ginzburg number (Gi), and Gi is significantly lower in most iron-based superconductors than in YBa 2 Cu 3 O 7–δ . Here, we report very slow creep in BaFe 2 (As 0.67 P 0.33 ) 2 films, and propose the existence of a universal minimum realizable S ~ Gi 1/2 (T/T c ) (T c is the superconducting transition temperature) that has been achieved in our films and few other materials, and is violated by none. Furthermore, this limitation provides new clues about designing materials with slow creep and the interplay between material parameters and vortex dynamics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

The role of diffusion-driven pure climb creep on the rheology of bridgmanite under lower mantle conditions

The viscosity of Earth’s lower mantle is poorly constrained due to the lack of knowledge on some fundamental variables that affect the deformation behaviour of its main mineral phases. This study focuses on bridgmanite, the main lower mantle constituent, and assesses its rheology by developing an approach based on mineral physics. Following and revising the recent advances in this field, pure climb creep controlled by diffusion is identified as the key mechanism driving deformation in bridgmanite. The strain rates of this phase under lower mantle pressures, temperatures and stresses are thus calculated by constraining diffusion and implementing a creep theoretical model. The viscosity of MgSiO3 bridgmanite resulting from pure climb creep is consequently evaluated and compared with the viscosity profiles available from the literature. We show that the inferred variability of viscosity in these profiles can be fully accounted for with the chosen variables of our calculation, e.g., diffusion coefficients, vacancy concentrations and applied stresses. A refinement of these variables is advocated in order to further constrain viscosity and match the observables.

58 GEOSCIENCES↗
DOE OSTI2025

Creep-enhanced vortex pinning revealed through nonmonotonic relaxation of the Campbell length

Here, we study the effects of flux creep on the linear AC response of the vortex lattice in single crystals Ca 3 ⁢Ir 4 ⁢Sn 13 by measuring the Campbell penetration depth, 𝜆 C ⁡(𝑇,𝐻,𝑡) . Thermal fluctuations release vortices from shallow pinning sites, only for them to become re-trapped by deeper potential wells, causing an initial increase of the effective Labusch parameter, which is proportional to the pinning well curvature. This effect cannot be detected in conventional magnetic relaxation measurements but is revealed by our observation of a nonmonotonic time evolution of 𝜆 C ⁡(𝑇,𝐻,𝑡) , which directly probes the average curvature of the occupied pinning centers. The time evolution of 𝜆 C ⁡(𝑇,𝐻,𝑡) was measured at different temperatures in samples with different densities of pinning centers produced by electron irradiation. The curves can be collapsed together when plotted on a logarithmic time scale 𝑡 → 𝑇 ⁢ln ⁡(𝑡/𝑡 0 ) confirming that the time evolution is driven by flux creep. The 𝜆 C ⁡(𝑇,𝐻,𝑡) is hysteretic with a noticeable nonmonotonic relaxation in the presence of a vortex density gradient (after zero-field cooling), but is monotonic after field cooling, where the vortex density is uniform. This result quantitatively corroborates the novel picture of vortex creep based on the strong pinning theory.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Micromechanical Surrogate Machine Learning Model for Creep Deformation Modeling

Process variability during the manufacture of gas turbine engine hot section components can significantly affect the material’s resulting microstructure. In casting, for instance, geometric variation within a component (thin sections versus thick sections, radial location) influences cooling rates and the resulting grain size. The high temperature creep response is known to be sensitive to grain size owing to a diffusional creep mechanism which occurs more readily along grain boundaries. Microstructural variation correspondingly drives mechanical behavior which propagates into component scale performance uncertainty. These factors are essential when planning inspection, maintenance, and repair strategies within a reliability framework. These benefits provide opportunities to increase overall energy efficiency through refined margins. Critically, there is an opportunity to bolster existing data-driven reliability models using physics-driven process-structure-property relations. Here we present recent work establishing a framework for evaluating the probabilistic creep performance of high-temperature materials. A novel microstructure-sensitive crystal plasticity finite element model is established that captures both grain boundary and crystallographic deformation effects. The computationally expensive physics model is calibrated using a statistical approach and this high-fidelity model is subsequently used to train a computationally efficient machine learning surrogate model. The surrogate model is essential for sampling a large ensemble of simulated structure-property pair results. The ensemble data are then mined to extract salient trends to be incorporated into a microstructure-sensitive reliability model. The proposed approach represents a novel way to capture microstructure-sensitive trends from physics-based models within a modern reliability framework.

Fernandez-Zelaia, Patxi [ORNL]↗
DOE OSTI2015

High fidelity measurement of room temperature creep in NW alloys

The objective of this work was to assemble instrumentation to do the best resolution strain measurements with available equipment overa long (goal of 3 month) period of time on 304L samples. Two creep tests were performed on 304L samples for 10 6 seconds and instrumented with both strain gages and extensometers. The results of the test show the difficulty in accurately instrumenting creep tests for long periods of time. While the data from the strain gages at 10 6 seconds proved to be still discernable from the background noise caused by temperature and air fluctuations and instrument noise, lower creep rates will require enhanced measurement techniques. An additional one to two orders of magnitude of elapsed time appears feasible.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Uniaxial Creep as a Control on Mercury Intrusion Capillary Pressure in Consolidating Rock Salt

The nature of geologic disposal of nuclear waste in salt formations requires validated and verified two-phase flow models of transport of brine and gas through intact, damaged, and consolidating crushed salt. Such models exist in other realms of subsurface engineering for other lithologic classes (oil and gas, carbon sequestration etc. for clastics and carbonates) but have never been experimentally validated and parameterized for salt repository scenarios or performance assessment. Models for waste release scenarios in salt back-fill require phenomenological expressions for capillary pressure and relative permeability that are expected to change with degree of consolidation, and require experimental measurement to parameterize and validate. This report describes a preliminary assessment of the influence of consolidation (i.e. volume strain or porosity) on capillary entry pressure in two phase systems using mercury injection capillary pressure (MICP). This is to both determine the potential usefulness of the mercury intrusion porosimetry method, but also to enable a better experimental design for these tests. Salt consolidation experiments are performed using novel titanium oedometers, or uniaxial compression cells often used in soil mechanics, using sieved run-of-mine salt from the Waste Isolation Pilot Plant (WIPP) as starting material. Twelve tests are performed with various starting amounts of brine pore saturation, with axial stresses up to 6.2 MPa (~900 psi) and temperatures to 90°C. This corresponds to UFD Work Package 15SN08180211 milestone “FY:15 Transport Properties of Run-of-Mine Salt Backfill – Unconsolidated to Consolidated”. Samples exposed to uniaxial compression undergo time-dependent consolidation, or creep, to various degrees. Creep volume strain-time relations obey simple log-time behavior through the range of porosities (~50 to 2% as measured); creep strain rate increases with temperature and applied stress as expected. Mercury porosimetry is used to determine characteristic capillary pressure curves from a series of consolidation tests and show characteristic saturation-capillary pressure curves that follow the common van Genuchten (1978, 1980) formulation at low stresses. Higher capillary pressure data are suspect due to the large potential for sample damage, including fluid inclusion decrepitation and pore collapse. Data are supportive of use of the Leverett “J” function (Leverett, 1941) to use for scaling characteristic curves at different degrees of consolidation, but better permeability determinations are needed to support this hypothesis. Recommendations for further and refined testing are made with the goal of developing a self- consistent set of constitutive laws for granular salt consolidation and multiphase (brine-air) flow.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Report on FY15 Alloy 617 SMT Creep-Fatigue Test Results

For the temperature range of 900°C − 950°C, Alloy 617 is a candidate IHX structural material for high temperature gas reactors (HTGRs) because of its high temperature creep properties. Also, its superior strength over a broad temperature range also offers advantages for certain component applications. In order for the designers to be able to use Alloy 617 for these high temperature components, Alloy 617 has to be approved for use in Section III (the nuclear section) of the ASME (American Society of Mechanical Engineers) Boiler and Pressure Vessel Code. A plan has been developed to propose a Code Case for use of Alloy 617 at elevated temperature in Section III of the ASME Code by September 2015. There has not been a new high temperature material approved for use in Section III for almost 20 years. The Alloy 617 Code Case effort would lead the way to establish a path for Code qualification of new high temperature materials of interest to other advanced SMRs. Creep-fatigue at elevated temperatures is the most damaging structural failure mode. In the past 40 years significant efforts have been devoted to the elevated temperature Code rule development in Section III, Subsection NH* of the ASME Boiler and Pressure Vessel Code, to ascertain conservative structural designs to prevent creep-fatigue failure.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2017

Shakedown Tests for Refurbished and Upgraded Frames and Initiation of Alloy 709 Creep Rupture Tests

This report describes the shakedown tests conducted on the upgraded frames, and initiation of creep rupture tests on refurbished frames. SS316H, a reference material for Alloy 709, was used in shakedown tests, and the tests were conducted at 816 degree C under three stress levels to accumulate 1% creep strain. 1/4” gage diameter specimen design was used. The creep rupture tests on Alloy 709 were initiated at 600 degree C under 330 MPa to target 1,500 h rupture time. 12 specimens with 3/8” gage diameter were prepared from the materials with 6 heat treatment conditions, 2 from each. The required mechanical load under 330MPa was calculated to be 5,286 lb for the 3/8” gage diameter specimen. Among the ART frames, 7 frames are equipped with 10,000 lb load cell including #5 to 8 and #88 to 90, and can be used. 7 tests were thus started in this stage of project, and remaining 5 will be continued whenever any of the 7 tests is completed.

36 MATERIALS SCIENCE↗