The contraction phase of solar evolution.
Gravitational contraction of stars of one solar mass examined, using Henyey method for calculating stellar evolutionary tracks
GRAVITATIONAL COLLAPSE↗
SEARCH · Engineering Papers
Results for “Phase evolution”
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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The pre-Hayashi phase of stellar evolution
Structure and evolution of protostellar disks and outer rings in stellar evolution prior to Hayashi track
Cameron, A. G. W.↗
Accelerating phase-field-based microstructure evolution predictions via surrogate models trained by machine learning methods
Abstract The phase-field method is a powerful and versatile computational approach for modeling the evolution of microstructures and associated properties for a wide variety of physical, chemical, and biological systems. However, existing high-fidelity phase-field models are inherently computationally expensive, requiring high-performance computing resources and sophisticated numerical integration schemes to achieve a useful degree of accuracy. In this paper, we present a computationally inexpensive, accurate, data-driven surrogate model that directly learns the microstructural evolution of targeted systems by combining phase-field and history-dependent machine-learning techniques. We integrate a statistically representative, low-dimensional description of the microstructure, obtained directly from phase-field simulations, with either a time-series multivariate adaptive regression splines autoregressive algorithm or a long short-term memory neural network. The neural-network-trained surrogate model shows the best performance and accurately predicts the nonlinear microstructure evolution of a two-phase mixture during spinodal decomposition in seconds, without the need for “on-the-fly” solutions of the phase-field equations of motion. We also show that the predictions from our machine-learned surrogate model can be fed directly as an input into a classical high-fidelity phase-field model in order to accelerate the high-fidelity phase-field simulations by leaping in time. Such machine-learned phase-field framework opens a promising path forward to use accelerated phase-field simulations for discovering, understanding, and predicting processing–microstructure–performance relationships.
36 MATERIALS SCIENCE↗
PyJMAK: An Open-Source Python Toolkit for Modeling Solid-State Metallurgical Phase Transformations
Accurate prediction of metallurgical phase transformations is an essential basis for autonomous optimization and rapid part qualification. Several methods can be used to estimate the evolution of phase fractions such as JMAK kinetics-based models, phase-field models, thermodynamic models, and data-driven machine learning models. Thermodynamic and phase-field-based methodologies solve multiphysics equations requiring numerous calibration parameters and significant computational resources. As a result, the computation domain is limited to a point or on order of micron-meters. The data-driven models rely on large datasets from experiments and simulations. While the JMAK model only provides information about phase fraction evolution, it can predict this evolution in near real-time using thermal history and thermodynamic data without restriction on the domain. JMAK models have been popularly used by researchers to model phase transformations occuring during additive manufacturing or over arbitrary temperature profiles. Commercial proprietary software such as Abaqus and Ansys or closed-source in-house implementations offer the ability to model JMAK based kinetics to predict phase transformation. However, these software packages are not open-source or freely available for use and development in conjunction with manufacturing machines, sensors, and machine learning algorithms. In addition, the use of the model is restricted by a license token. In contrast, given temperature profiles at multiple points in the domain, this Python-based PyJMAK model can compute phase evolution in parallel due to its stand-alone modular, voxel-based structure, and it can be executed on high-performance computing resources without any license restrictions.
Prabhune, Bhagya [Oak Ridge National Laboratory (O↗
In situ study of microstructure evolution and α → ω phase transition in annealed and pre-deformed Zr under hydrostatic loading
The detailed study of the effect of the initial microstructure on its evolution under hydrostatic compression before, during, and after the irreversible α → ω phase transformation and during pressure release in Zr using in situ x-ray diffraction is presented. Two samples were studied: one is plastically pre-deformed Zr with saturated hardness and the other is annealed. Phase transformation α → ω initiates at lower pressure for a pre-deformed sample but for a volume fraction of ω Zr, c > 0.7, a larger volume fraction is observed for the annealed sample. This implies that the proportionality between the athermal resistance to the transformation and the yield strength in the continuum phase transformation theory is invalid; an advanced version of the theory is outlined. Phenomenological plasticity theory under hydrostatic loading is outlined in terms of microstructural parameters, and plastic strain is estimated. During transformation, the first rule is suggested, i.e., the average domain size, microstrain, and dislocation density in ω Zr for c < 0.8 are functions of the volume fraction, c of ω Zr only, which are independent of the plastic strain tensor prior to transformation and pressure. The microstructure is not inherited during phase transformation. Surprisingly, for the annealed sample, the final dislocation density and the average microstrain after pressure release in the ω phase are larger than for the severely pre-deformed sample. The results suggest that an extended experimental basis is required for the predictive models for the combined pressure-induced phase transformations and microstructure evolutions.
36 MATERIALS SCIENCE↗
Gas-Phase Composition as a Predictive Metric for Calendar Life Behavior of Next-Generation Silicon Anodes
The expansion of renewable technologies and electrification of the transportation sector is driving increased demand for next-generation battery materials that provide higher power and energy density with superior cycling and calendar life stability. Silicon (Si) has a theoretical capacity nearly 10x that of graphite, and is therefore a promising anode material candidate to meet these rigorous performance demands. While leading Si anode battery demonstrations are approaching target metrics for cycle life, a series of complex and interrelated modes of reactivity lead to reduced calendar life and therefore challenge practical adoption of these materials. Deconvoluting the degradation processes that impact Si calendar life is critical to informing the rational and accelerated design of improved Si materials. In the present work, we employ novel sampling techniques and GC-MS-FID characterization to measure gas-phase composition during initial Si cycling, which we tie to selective mechanisms of Si passivation. We utilize a tiered analysis approach to identify and quantify the gas-phase reaction products associated with three advanced Si material candidates under practical operating conditions. Ex situ analysis of Si powders (pure chemical reactivity) is coupled with nondestructive in situ sampling of Si electrodes in a practical pouch-cell format (coupled chemical and electrochemical reactivity). We link the observed gas-phase species evolution to electrochemical behavior and measured calendar life of the three Si materials. Further, we evaluate the voltage-resolved evolution of gas-phase species for one such Si nanomaterial, where nonmonotonic gas generation implies competition between passivating reaction pathways. The measured gas-phase compositional data serves as a critical input for our advanced electrochemical SEI models to identify favorable vs unfavorable reaction pathways to stabilize Si. In addition to bolstering a fundamental understanding of Si reactivity, the present approach informs specific and quantifiable gas-phase metrics tied to calendar life improvements in Si, which can streamline and accelerate the process of next-generation material development.
DIRECT ENERGY CONVERSION,ENERGY STORAGE↗
Global effects of thermal conduction on two-phase media
The evolution of two-phase systems of astrophysical gases which change mass between the phases is studied to see whether a steady state is ever reached. The criterion for thermal instability in a cloudy medium is derived. The evolution of the pressure and density of the intercloud medium under the combined effects of heating and radiative cooling of the intercloud gas on the one hand and evaporation and condensation of the clouds on the other is determined. The equilibrium density to which the system evolves is determined for the case when the pressure is fixed. The theory is illustrated by the case in which the intercloud gas is heated by Compton scattering in a hard radiation field and cooled by bremsstrahlung and inverse Compton scattering.
Begelman, Mitchell C.↗
Long-term observations reveal non-negligible temperature contributions to moist static energy during the MJO transition from suppressed to active phases
The evolution of moist static energy (MSE) is widely used to understand the organization and propagation of the Madden-Julian oscillation (MJO). Past studies, largely based on reanalysis or short-term observations, have highlighted humidity as the dominant driver of MJO evolution. Using 14 years of bias-corrected radiosonde observations from the Department of Energy – Atmospheric Radiation Measurement (DOE-ARM) Facility site at Manus in the western Pacific, we show that temperature has a significant influence on the vertically-integrated MSE during MJO’s transition from suppressed to active phase. Specifically, during the transition phase in boreal winter (spring), ~48% (~31%) of the vertically-integrated MSE anomalies are attributed to temperature anomalies. This temperature contribution is confined to the mid- and upper troposphere, where temperature and MSE anomalies exhibit a strong correlation. These findings have important implications for MJO theory and provide new constraints for evaluating MJO transition processes in models.
Alex, Nirmal↗
In situ study on medium-range order evolution during the polyamorphous phase transition in a Pd-Ni-P nanostructured glass
Engineering multiscale structural hierarchies in glassy alloys enable a broad spectrum of potential applications. Metallic glasses were born in hierarchical structures from atomic-to-nanometer scales. However, the frozen-in structures in traditional metallic glasses prepared by rapid quenching techniques are challenging to tailor. Here, we show that a Pd 40 Ni 40 P 20 bulk nanostructured glass of polyamorphous interfacial structures was prepared by inert-gas condensation with a laser evaporation source, and its multiscale structures could be engineered. In-situ scattering experiment results reveal polyamorphous phase transitions occurred in the interfacial regions, which are accompanied by the evolution of medium-range order and the nanoscale heterogeneous structures during the condensation process of glassy nanoparticles under high pressure and the following heating process. Moreover, changes in the cluster connectivity resulting from repacking of the local ordering induced by pressure and temperature could be observed. The thermophysical and mechanical properties, including boson peaks, hardness, and elasticity modulus, could be changed as a function of heat-treatment parameters. In conclusion, our findings would shed light on the synthesis of bulk nanostructured glassy alloys with tailorable thermodynamic and dynamical behavior as well as mechanical properties based on the understanding of metastability for polyamorphous interfacial phases.
36 MATERIALS SCIENCE↗
Uncovering the Size-dependent Thermal Solid Transformation of Akaganéite
Investigating the structural evolution and phase transformation of iron oxides is crucial for gaining a deeper understanding of geological changes on diverse planets and preparing oxide materials suitable for industrial applications. In this study, we employed in-situ heating techniques in conjunction with transmission electron microscopy (TEM) observations and ex-situ characterization to thoroughly analyze the thermal solid-phase transformation of akaganéite one-dimensional (1D) nanostructures with varying diameters. Our findings offer compelling evidence for a size-dependent morphology evolution in akaganéite 1D nanostructures, which can be attributed to the transformation from akaganéite to maghemite (?-Fe2O3) and subsequent crystal growth. Specifically, we observed that akaganéite nanorods with a diameter of around 50 nm transformed into hollow polycrystalline maghemite nanorods, which demonstrated remarkable stability without arresting crystal growth under continuous heating. In contrast, smaller akaganéite nanoneedles or nanowires with a diameter ranging from 20 to 8 nm displayed a propensity for forming single-crystal nanoneedles or nanowires through phase transformation and densification. By manipulating the size of the precursors, we have developed a straightforward method for the synthesis of single-crystal and polycrystalline maghemite nanowires through solid-phase transformation. These significant findings provide new insights into the size-dependent structural evolution and phase transformation of iron oxides at the nanoscale.
Wang, Xiang↗
Phase transformations, microstructural refinement and defect evolution mechanisms in Al-Si alloys under non-hydrostatic diamond anvil cell compression
Non-hydrostatic compression of materials using a diamond anvil cell (DAC) can transform equilibrium microstructure of an alloy to novel, potentially metastable states. In this study, in situ synchrotron X-ray diffraction (XRD) during compression up to 24 GPa and subsequent ex situ, high resolution analytical electron microscopy (AEM) after decompression of an Al-Si alloy provided insight into the crystallographic changes during the compression as well as microstructural refinement, and defect structures caused by such a high pressure compression-decompression process. Pressure resolved in-situ synchrotron XRD was used to detail the phase transformation pathway of the eutectic Si phase in Al-Si alloy, from Si-I → Si-XI → Si-V during compression, and a final transformation predominantly to Si-III after decompression. Using scanning and transmission electron microscopy (S/TEM), site specific analysis of the alloy immediately underneath the anvil contact surface demonstrated a highly complex microstructure. A narrow region of thick amorphous Al oxide interspersed with nanocrystalline grains was found at the top surface. Underneath this Al oxide, while the majority the eutectic Si was transformed into highly-deformed, polycrystalline (PC) Si-III, a complex intermediate layer was discovered at the interface between Al and Si, comprised of a small fraction of Al nanocrystals and a majority of nanocrystalline Si-I. This combination of pressure resolved in-situ synchrotron XRD coupled with subsequent high resolution, electron microscopy resolved the phase transformation as well as non-equilibrium microstructures in a metallic alloy induced by a non-hydrostatic high pressure compression followed by decompression.
36 MATERIALS SCIENCE↗
Phase-Field Methods for Structure Evolution in Sheared Multiphase Systems
A homogeneous disordered phase separates into ordered structures when quenched into a broken-symmetry phase. The competition of broken-symmetry phases to select an equilibrium state may be studied in terms of coarse-grained order parameters described by a suitable Landau free-energy function. A network of equilibrium-phase domains develops on quenching and coarsens with time with a topology that may be controlled by shear. We use three-dimensional simulations, in which time-dependent models for conserved-order parameters coupled to Navier-Stokes fluid models are solved, to investigate the evolution of such domains, e.g. spinodal decompositions of polymeric materials under shear. The numerical problems are formidable because of the strong nonlinearities inherent in the coupled model, and these are amongst the first 3D calculations undertaken. In linear shear fields we find stable nanostrings, also recently seen in experiments. The affinity of the ordered phases to boundaries plays a role in the form of the structures that develop, with stacked plate-like phase distributions emerging under certain conditions. Such methods appear quite promising for design and analysis of multiphase and complex fluid formulations. The behavior of foams in such conditions is of particular interest in microgravity environments. Additional information can be found in the original extended abstract.
Badalassi, Vittorio↗
Morphological evolution of X-ray flare structures from the rise through the decay phase
The morphological evolution of 12 solar X-ray subflares from onset through the decay phase has been studied using photographic X-ray images obtained from Skylab. The spatial configurations are found to vary widely from flare to flare, but they appear to be composed of two basic kinds of structures. The first, termed 'X-ray kernels', are brightest during the rise phase; the second, looplike structures, appear during the maximum and decay phases of the event. The X-ray kernels are small pointlike structures which may be related to the nonthermal phases of flares.
Kahler, S. W.↗
Stellar Neutrino Emission across the Mass–Metallicity Plane
We explore neutrino emission from nonrotating, single-star models across six initial metallicities and 70 initial masses from the zero-age main sequence to the final fate. Overall, across the mass spectrum, we find metal-poor stellar models tend to have denser, hotter, and more massive cores with lower envelope opacities, larger surface luminosities, and larger effective temperatures than their metal-rich counterparts. Across the mass–metallicity plane we identify the sequence (initial CNO → 14 N → 22 Ne → 25 Mg → 26 Al → 26 Mg → 30 P → 30 Si) as making primary contributions to the neutrino luminosity at different phases of evolution. For the low-mass models we find neutrino emission from the nitrogen flash and thermal pulse phases of evolution depend strongly on the initial metallicity. For the high-mass models, neutrino emission at He-core ignition and He-shell burning depends strongly on the initial metallicity. Antineutrino emission during C, Ne, and O burning shows a strong metallicity dependence with 22 Ne(α, n) 25 Mg providing much of the neutron excess available for inverse-β decays. We integrate the stellar tracks over an initial mass function and time to investigate the neutrino emission from a simple stellar population. We find average neutrino emission from simple stellar populations to be 0.5–1.2 MeV electron neutrinos. Lower metallicity stellar populations produce slightly larger neutrino luminosities and average β decay energies. This study can provide targets for neutrino detectors from individual stars and stellar populations. We provide convenient fitting formulae and open access to the photon and neutrino tracks for more sophisticated population synthesis models.
79 ASTRONOMY AND ASTROPHYSICS↗
Irradiation-induced shift in the thermodynamic stability of phases and the self-healing effect in transformative high entropy alloys
Here, this work investigated Fe 40 Mn 20 Cr 15 Co 20 Si 5 high entropy alloy (CS-HEA), which exhibits transformation induced plasticity (TRIP) from γ-fcc → ε-hcp, as a probable candidate for nuclear applications. CS-HEA is an extensively-explored, low stacking fault energy alloy with superior strength, ductility, fatigue resistance, and corrosion resistance. This study delved into the effect of irradiation on the shift in thermodynamic stability of the phases and thus radiation tolerance. The evolution of phases, lattice parameters, and transformation volume, V γ→ε , were evaluated from X-ray diffraction experiments along with the mechanical response from nanoindentation. The alloy exhibited a recently-proposed novel self-healing mechanism possible due to the TRIP effect to minimize irradiation damage by restraining the γ-fcc → ε-hcp transformation via thermal aid; this self-healing mechanism was confirmed by transmission electron microscopy. The results were corroborated by a negative change in V γ→ε and a low |V γ→ε |, which is an important criterion for recovery of parent γ-fcc phase. Thus, this alloy was deemed a good radiation-tolerant candidate for nuclear application.
36 MATERIALS SCIENCE↗
Parameterization of vacancy production rate in phase-field models of fission gas bubble evolution in nuclear fuel
Phase-field modeling has increasingly been used to study microstructural evolution in fission gas bubbles in nuclear fuel to improve understanding of fission gas release. To improve computational efficiency, often only vacancies and gas atoms are included as defect species. In this case, the net effects of vacancy and interstitial production, recombination, and biased sink absorption are included as a net vacancy source, or net vacancy source combined with an effective sink. However, there has been a lack of clarity on what parameter values should be used for these approaches to best match the more complete physical picture that includes interstitials and vacancies. Here, we compare a phase-field model of void growth to analytical models for the source-only and source plus sink approach to gain insight into how the phase-field models can be parameterized effectively. The source-only approach provides greater flexibility to match growth rates determined from the full vacancy-interstitial picture. A strategy was developed for determining the value of the net vacancy source term by comparing to an analytical model that includes vacancy and interstitial production, recombination, and biased sink absorption. Finally, this strategy can be used to parameterize phase-field models of fission gas bubble growth.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
Phase equilibria and microstructure evolution in the Ni-rich region of binary Ni-Ce and ternary Ni-Ce-X (X=Al, Nb, Cr, Ti) systems at 900 °C
The equilibrium compositions of all phases in the Ni-rich region of binary Ni-Ce and ternary Ni-Ce-X (X=Al, Nb, Cr, Ti) systems at 900 °C were determined experimentally through isothermal annealing for up to 500 h and compared with currently available computational thermodynamic descriptions. Additionally, the study examined how adding a third element to the binary system affects the microstructure by analyzing changes in the volume fraction of the intermetallic phase in the eutectic region. It was observed that Nb and Ti addition lowered the intermetallic fraction in the eutectic region while Al and Cr addition did the opposite. The fraction of intermetallic phase in the eutectic region is very important because it contributes to extreme brittleness of these alloys. Also, Al, Nb and Ti addition promoted different precipitates upon annealing when added in sufficient amounts. The collected data on composition and phase equilibria provides crucial information for improving the thermodynamic assessments of the binary and ternary alloy systems.
energy dispersive spectrometry↗