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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Kink bands promote exceptional fracture resistance in a NbTaTiHf refractory medium-entropy alloy

Single-phase body-centered cubic (bcc) refractory medium- or high-entropy alloys can retain compressive strength at elevated temperatures but suffer from extremely low tensile ductility and fracture toughness. We examined the strength and fracture toughness of a bcc refractory alloy, NbTaTiHf, from 77 to 1473 kelvin. This alloy’s behavior differed from that of comparable systems by having fracture toughness over 253 MPa·m 1/2 , which we attribute to a dynamic competition between screw and edge dislocations in controlling the plasticity at a crack tip. Whereas the glide and intersection of screw and mixed dislocations promotes strain hardening controlling uniform deformation, the coordinated slip of <111> edge dislocations with {110} and {112} glide planes prolongs nonuniform strain through formation of kink bands. These bands suppress strain hardening by reorienting microscale bands of the crystal along directions of higher resolved shear stress and continually nucleate to accommodate localized strain and distribute damage away from a crack tip.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Spall damage mechanisms in laser powder bed fabricated stainless steel 316L

This paper reports on spall damage mechanisms in laser powder bed fusion (LPBF) fabricated stainless steel 316L (SS316L) subjected to uniaxial, strain plate-impact loading and explores failure evolution with increasing impact velocity and peak pressure. Analysis of velocimetry profiles reveals a heterogeneous failure response with several different failure mechanisms activated during impact and resulting spall. The analysis is supported by optical microscopy and electron backscattered diffraction (EBSD) observation of soft recovered impacted samples, which show evidence of localized nano-twinning, twin growth, severe grain rotation, and grain refinement along the spall plane, in addition to pore nucleation, coalescence, and growth. Furthermore, the observed failure mechanisms, including crack formation and propagation along high angle grain boundaries (HAGBs), are not consistently indicative of ductile fracture typical of wrought stainless steel.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Visualizing Lithium Dendrite Formation within Solid-State Electrolytes

Solid-state electrolyte (SSE) is promising for application in allsolid-state lithium metal batteries because of its reliable safety and longevity. The failure of SSE to suppress dendrite formation of Li metal anodes has been conventionally explained by uneven Li deposition at Li/SSE interfaces and its subsequent dendritic growth. While Li deposition within SSE has been recently proposed as another key cause for SSE failure, little is known regarding the Li growth details inside the SSE itself. In this work, we performed in situ microscopic observation of Li deposition inside the SSE and obtained visualized evidence regarding the dynamic process of Li dendrite formation and growth. Here, Li is seen to directly nucleate and propagate within the SSE, leading to its structural cracking. Such behavior should be caused by the presence of P- and S-based crystalline defects in Li 3 PS 4 SSE, which is consistent with the cryo-transmission electron microscopy observations and theoretical calculations. This observation provides important insights into the growth mechanisms of Li dendrites within a working lithium battery.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Low-temperature failure mechanism of [001] niobium micropillars under uniaxial tension

The plasticity of body-centered cubic (bcc) metals is dependent of temperature as well as sample dimension at the micrometer scale, but the effects of cryogenic temperature on the plasticity and the related failure process in micron-sized bcc metals have not been studied under uniaxial tension. In this work, we utilized in situ cryogenic micro-tensile tests, transmission electron microscopy, and dislocation dynamic simulations to examine the plasticity and failure processes of [001]-oriented bcc niobium micropillars. Our study reveals that a strong suppression of cross-slip at low temperatures prevents dislocation multiplication and leads to a dislocation starvation state, at which no mobile dislocation exists due to the rapid annihilation of dislocations at free surfaces. New dislocations are then nucleated until stress concentration at a slip step creates a micro-crack, the propagation of which leads to catastrophic failure. As a result, this unique failure process results from the combined effects of sample dimension and temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Effect of a novel starch-based temperature rise inhibitor on cement hydration and microstructure development: The second peak study

Temperature rise inhibitor (TRI) modifies the exothermic process of cement hydration at early age and mitigates the buildup of cumulative heat, which sheds new light on solving the thermal cracking issue. After the main hydration peak, a broader “second peak” appears and brings the cumulative heat back to normal level within 7 days (for additions less than 0.15%). This study shows that the “second peak” can be attributed, almost exclusively, to C{sub 3}S hydration while triggered by C{sub 3}A hydration. In a pure C{sub 3}S system, the heat flow is depressed by TRI during the main hydration peak but never recovers after. In a monophase system composed of C{sub 3}S, C{sub 3}A and gypsum or a real cement paste, the ongoing precipitation of ettringite helps to pump out TRI polymer from the pore solution and eliminate the restriction on C-S-H nucleation. Afterwards, the precipitation of C-S-H accelerates again to form the “second peak”.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Real-Time Observation of Nanoscale Kink Band Mediated Plasticity in Ion-Irradiated Graphite: An In Situ TEM Study

Graphite IG-110 is a synthetic polycrystalline material used as a neutron moderator in reactors. Graphite is inherently brittle and is known to exhibit a further increase in brittleness due to radiation damage at room temperature. To understand the irradiation effects on pre-existing defects and their overall influence on external load, micropillar compression tests were performed using in situ nanoindentation in the Transmission Electron Microscopy (TEM) for both pristine and ion-irradiated samples. While pristine specimens showed brittle and subsequent catastrophic failure, the 2.8 MeV Au2+ ion (fluence of 4.378 × 1014 cm−2) irradiated specimens sustained extensive plasticity at room temperature without failure. In situ TEM characterization showed nucleation of nanoscale kink band structures at numerous sites, where the localized plasticity appeared to close the defects and cracks while allowing large average strain. We propose that compressive mechanical stress due to dimensional change during ion irradiation transforms buckled basal layers in graphite into kink bands. The externally applied load during the micropillar tests proliferates the nucleation and motion of kink bands to accommodate the large plastic strain. The inherent non-uniformity of graphite microstructure promotes such strain localization, making kink bands the predominant mechanism behind unprecedented toughness in an otherwise brittle material.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A Multiphysics Multiscale Simulation Platform for Damage, Environmental Degradation, and Life Prediction of CMCs in Extreme Environments

This project successfully developed a multiphysics, multiscale computational framework to enhance the design and development of CMCs, with a focus on modeling highly nonlinear, time-dependent damage mechanisms and material degradation under extreme conditions, such as those experienced in turbine service environments. The project made significant advances in improving our understanding of progressive damage, oxidative degradation, and time-dependent inelastic deformation in CMCs, with particular attention to the role of uncertainties in predictions. Key outcomes include the integration of advanced material characterization, uncertainty quantification, and multiphysics constitutive models to predict the behavior of CMCs over their service life. A novel multiscale methodology was employed, which integrated microscale constituent behaviors with structural-scale responses, enabling the manufacturing defects in the microstructure that are prone to damage nucleation. Through the development of DL algorithms, the project advanced the prediction of damage initiation and crack propagation, taking into account the defect morphology and statistical variations across multiple scales. The framework was rigorously validated using thermomechanical experiments, which tested CMCs under various mechanical loadings at elevated temperatures, further enhancing the model's predictive capability. Overall, the research outcomes have provided a more accurate, reliable method for predicting CMC component life, significantly advancing material design, and improving component reliability in extreme environments. This work has strong implications for the optimization of turbine components and other high-performance applications where CMCs are used.

03 NATURAL GAS↗
DOE OSTI2025

Laser damage of crazed electron-beam high-reflectors following infrared and ultraviolet irradiation in the nanosecond pulse regime

Laser damage of optical components can be a limiting factor in scaling the energetics of high-peak and average power laser systems. Specifically for optical coatings, damage under nanosecond pulsed irradiation is initiated by pre-existing defects in the coating layers, including those that cause discontinuities in the structure, like craze lines. Crazing or cracking in a multilayer dielectric optical coating is induced when the overall coating stress is sufficiently tensile, and is an occasionally observed issue when employing more porous deposition techniques like electron-beam evaporation. Here, in this study, electron-beam high-reflectors were fabricated utilizing process parameters that are known to induce crazing based on prior processing history to systematically evaluate the impact of crazing on reflector damage performance for 1064 and 355 nm lasers. The crazing that was observed was apparently nucleated at nodular defects. When the cross-section of these nodules was investigated, it was observed that there were cracks into the fused silica substrate of approximately 5 µm in depth. The craze lines were irradiated with 1064 and 355 nm light at fluences slightly above the onset of damage initiation fluence of the coating. The 1064 nm irradiated sub-apertures exhibit laser damage but with no spatial correlation with the craze line, whereas the 355 nm irradiated area exhibited many damage sites along the craze line. Finite-difference time-domain electric-field simulations were conducted, and ∼2× field amplification in hafnia was observed for the 355 nm wavelength case. The laser damage can be attributed to a slight electric-field intensification coincidental with an area where UV damage-prone precursors are known to occur. The 355 nm laser damage in uncoated fused silica substrates has been previously correlated to initiate through localized UV absorption at the broken silica bonds in the tips of fractures.

Harthcock, Colin [Lawrence Livermore National Labo↗
DOE OSTI2023

A phase-field model for hydraulic fracture nucleation and propagation in porous media

Many geo-engineering applications, for example, enhanced geothermal systems, rely on hydraulic fracturing to enhance the permeability of natural formations and allow for sufficient fluid circulation. Over the past few decades, the phase-field method has grown in popularity as a valid approach to modeling hydraulic fracturing because of the ease of handling complex fracture propagation geometries. However, existing phase-field methods cannot appropriately capture nucleation of hydraulic fractures because their formulations are solely energy-based and do not explicitly take into account the strength of the material. Thus, in this work, we propose a novel phase-field formulation for hydraulic fracturing with the main goal of modeling fracture nucleation in porous media, for example, rocks. Built on the variational formulation of previous phase-field methods, the proposed model incorporates the material strength envelope for hydraulic fracture nucleation through two important steps: (i) an external driving force term, included in the damage evolution equation, that accounts for the material strength; (ii) a properly designed damage function that defines the fluid pressure contribution on the crack driving force. In conclusion, the comparison of numerical results for two-dimensional test cases with existing analytical solutions demonstrates that the proposed phase-field model can accurately model both nucleation and propagation of hydraulic fractures. Additionally, we present the simulation of hydraulic fracturing in a three-dimensional domain with various stress conditions to demonstrate the applicability of the method to realistic scenarios.

15 GEOTHERMAL ENERGY↗
DOE OSTI2022

Influence of weave architecture on mechanical response of SiC f -SiC m tubular composites

Due to their high resistance to radiation damage and elevated temperature, silicon carbide fiber-reinforced, silicon carbide matrix composites (SiC f -SiC m ) are identified as potential cladding structures for use in nuclear reactors. In this study, four composite architectures with varying ply numbers along the thickness direction and different biaxial or triaxial plain weave orientations at either 45° or 60°, were systematically evaluated under various stress states to assess the influence of weave architecture on mechanical performance. Experiments were conducted on SiC f -SiC m composite tubes under tensile hoop, axial compression, and rotating flexural loading to evaluate the mechanical response and investigate the failure modes using high-speed imaging and digital image correlation (DIC) techniques. It was found that for tensile hoop burst and flexural loading, the braiding angle had the most significant influence on the strength of the composite, whereas the effect of fiber angle was more limited for compression testing. Under axial compression a unique failure mode where a microcrack nucleates and grows only to a length equal to the thickness of a single yarn was identified. This crack growth behavior is reflected as periodic oscillations in the load-displacement response. For both axial and hoop loading, regardless of weave angle and number of plies, failure always initiated parallel to the tube axis in a single yarn and the cumulative interaction of these microcracks lead to either axial burst or fracture at an angle to the tube axis along a yarn. Furthermore, these results point to the importance of customizing the design of tube architecture for enhanced performance in specified nuclear applications.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Mesoscale-architecture-based crack evolution dictating cycling stability of advanced lithium ion batteries

The cracking phenomenon of Ni-rich NMC (LiNixMnyCo1-x-yO2, x = 0.6) secondary particles is frequently discovered and believed to be one of critical reasons deteriorating the long-term cycling stability of NMC cathode in lithium ion batteries (LIBs). However, the initiation and evolution of those cracks is still controversial due to the limited quantification especially by in situ monitoring, leading to the challenge of identifying an efficient approach to inhibit the formation of the fractures during repeated cycling. Herein, the irreversible, anisotropic cycling lattice and mesoscale expansion/shrinkage of nano-grain during the first cycle, as revealed by in situ X-ray diffraction (XRD) and in situ atomic force microscopy (AFM), have been quantified and confirmed to be the dominant driving forces of microcracks initiation at the grain boundaries. These microcracks preferentially nucleates at the core region with random oriented nano-grains in early stage. The further growth and aggregation of microcracks into macrocrack eventually results in microfracture propagation radially outward to the periphery region with more uniform nano-grain orientation. This mesoscale nano-grain architecture controlled cracking process highlight the importance of predictive synthesis of cathode materials with controllable multiscale crystalline architecture for high-performance LIBs.

25 ENERGY STORAGE↗
DOE OSTI2023

The effect of microstructure on the dynamic shock response of 1045 steel

Herein, the effect of microstructure on the shock response of 1045 steel is investigated via plate impact experiments and postmortem characterization. Three unique microstructures are explored: ferrite-pearlite, martensite, and ferrite with spheroidal cementite (i.e. spheroidized). Two spall recovery experiments, at approximate peak pressures of 3.2 and 3.5 GPa, are conducted to assess the Hugoniot elastic limit (HEL), spall strength, and damage morphology of the various microstructures. The ferrite-pearlite and martensite microstructures exhibit continuous yielding at both quasi-static and dynamic rates, while the spheroidized condition displays discontinuous yielding. Discontinuous yielding of the spheroidized microstructure is attributed to a combined low initial dislocation density coupled with a low dislocation nucleation rate. The spall strength of ferrite-pearlite is consistently lower than the spheroidized microstructure, attributed to elongated cementite that is more susceptible to cracking than more spherical cementite precipitates. Despite a high density of boundaries, martensite exhibits the highest spall strength. A large percentage of the boundaries within the martensite microstructure are found to be low energy (i.e. Σ3 or low angle), and are thus less susceptible to spall damage. Overall, the high spall strength of martensite is likely linked to traditional strengthening mechanisms that limit dislocation motion.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Low-loss superconducting titanium nitride grown using plasma-assisted molecular beam epitaxy

Titanium nitride (TiN) is a known superconducting material that is attractive for use as passive components in superconducting circuits for both conventional and quantum information devices. In contrast to conventional synthesis techniques, here, plasma-assisted molecular beam epitaxy is reported to produce high-quality TiN on bare silicon wafers. Using a rf-plasma source to crack the nitrogen molecules and a conventional high-temperature effusion cell for titanium, TiN growth is completed under nitrogen-rich conditions. The growth and nucleation is monitored in situ, while the structure and composition are characterized using x-ray diffraction, atomic force microscopy, x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and scanning transmission electron microscopy. The stoichiometric TiN (111) films sit on an amorphous nitride layer with low impurity concentrations. The films superconduct with Tc=5.4 K, and coplanar waveguide resonators are fabricated with a small center width of 6 μm that demonstrate single-photon quality factors approaching 1M and high-power quality factors over 5M without observing saturation.

Richardson, C. J. K. (ORCID:0000000188175347)↗
DOE OSTI2020

Multiscale Thermomechanical Damage Model with Internal State Variables for Ceramic Matrix Composites

A length scale-dependent matrix damage model has been developed to simulate the response of ceramic matrix composites (CMCs). This model captures damage initiation and propagation in the brittle matrix material by employing internal state variable (ISV) theory within a multiscale modeling framework to obtain damaged matrix stress-strain constitutive relationships at each length scale. Material degradation due to matrix cracking is captured by a damage variable determined using fracture mechanics and the self-consistent scheme. An additional state variable is introduced to capture the nucleation and growth of matrix porosity, a key mechanism contributing to matrix nonlinearity. Porosity occurs as a result of material diffusion around grain boundaries and the growth of the porosity state variable is related to the material entropy dissipation and the volumetric strain. The nonlinear predictive capabilities of the material model are demonstrated for monolithic silicon carbide, unidirectional (UD) carbon fiber/silicon carbide matrix (C/SiC) CMC, and five-harness satin (5HS) woven C/SiC CMC.

Skinner, Travis D.↗
DOE OSTI2024

Fracture behavior of irradiation induced nanocrystalline UO 2 studied by in-situ mechanical testing in transmission electron microscopy

Uranium Dioxide (UO 2 ) is widely used as a fuel in current light water reactors (LWRs). Upon accumulation of radiation damage, LWR UO 2 fuel pellets start to develop a different microstructure at the pellet periphery when fuel burnup exceeds 45–50 GWd/tHM. The resulting porous, nanocrystalline microstructure is one of the most prominent microstructural changes occurring in such fuel. Its fracture mechanisms, which causes fuel fine fragmentation, could impact safety limits when the cladding breaches. Direct measurements of these properties are challenging, therefore a surrogate obtained via ion irradiation can be used. In this study, multiple microcantilevers were fabricated by focused ion beam from both fresh UO 2 and UO 2 irradiated with 84 MeV Xe 26+ ions to a peak dose of 1357 displacements per atom (dpa). Further, the irradiation produced a pseudo high burnup structure approximately 2 µm below the surface. In-situ nano-mechanical bending tests were conducted to investigate the fracture behavior and the effect of the surrogate UO 2 high burnup structure on local fracture properties. Fresh UO 2 fuel was observed to fracture in transgranular mode without nucleation or movement of dislocations. However, the Xe-irradiated nanocrystalline microcantilevers fractured along the grain boundaries, with no influence from the pre-existing micro-cracks in the microcantilever. Fracture toughness for this type of surrogate high burnup UO 2 structure is reported for the first time in literature. Both the fracture stress and toughness show degradation for UO 2 as a result of Xe-irradiation.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Understanding the Role of Borohydride Doping in Electrochemical Stability of Argyrodite Li 6 PS 5 Cl Solid‐State Electrolyte

This work elucidates the mechanism by which lithium borohydride (LiBH 4 ) doping into argyrodite-type Li 6 PS 5 Cl (LBH-LPSCl) solid-state electrolyte (SSE) enhances electrochemical stability. State-of-the-art electrochemical performance is achieved with 5 wt% borohydride. Symmetric cells achieve critical current density (CCD) of 7.3 mA cm −2 , versus 2.6 mA cm −2 for baseline-LPSCl. All solid-state batteries (ASSBs) employing lithium metal and NMC811 cathode are stable over 400 cycles at 0.5C, with capacity retention of 83%. An anode-free ASSB (AF-ASSB) is stable over 600 cycles, with capacity loss of 0.04% per cycle. 5LBH-LPSCl allows for enhanced low temperature operation, down to −14 °C. Yet the difference in electrolytes’ bulk microstructures and hardnesses are minimal, while ionic conductivity is incrementally improved (≈50%). Theoretical modeling indicates limited effect of substitution on thermodynamic stability of PS 4 3- units, which decompose when contacting Li. Instead, enhanced electrochemical stability is site-specific kinetic effect: In situ electrodeposition experiments using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) reveal tri-layer SEI based predominately on Li 3 P/LiBH 4 /Li 2 S that blocks electrons while facilitating ion transport. This SEI manifests reduced interface resistance and accelerated nucleation and growth of metallic Li. With baseline-LPSCl the SEI based on Li 3 P/Li 2 S is substantially thicker, generating localized stresses that promote interfacial cracking while cycling.

argyrodite↗
DOE OSTI2022

Exceptional fracture toughness of CrCoNi-based medium- and high-entropy alloys at 20 kelvin

Medium- and high-entropy alloys based on the CrCoNi-system have been shown to display outstanding strength, tensile ductility and fracture toughness (damage-tolerance properties), especially at cryogenic temperatures. Here we examine the J Ic and (back-calculated) K JIc fracture toughness values of the face-centered cubic, equiatomic CrCoNi and CrMnFeCoNi alloys at 20 K. At flow stress values of ~1.5 GPa, crack-initiation K JIc toughnesses were found to be exceptionally high, respectively 235 and 415 MPa√m for CrMnFeCoNi and CrCoNi, with the latter displaying a crack-growth toughness K ss exceeding 540 MPa√m after 2.25 mm of stable cracking, which to our knowledge is the highest such value ever reported. Characterization of the crack-tip regions in CrCoNi by scanning electron and transmission electron microscopy reveal deformation structures at 20 K that are quite distinct from those at higher temperatures and involve heterogeneous nucleation, but restricted growth, of stacking faults and fine nanotwins, together with transformation to the hexagonal closed-packed phase. The coherent interfaces of these features can promote both the arrest and transmission of dislocations to generate respectively strength and ductility which strongly contributes to sustained strain hardening. Indeed, we believe that these nominally single-phase, concentrated solid-solution alloys develop their fracture resistance through a progressive synergy of deformation mechanisms, including dislocation glide, stacking-fault formation, nano-twinning and eventually in situ phase transformation, all of which serve to extend continuous strain hardening which simultaneously elevates strength and ductility (by delaying plastic instability), leading to truly exceptional resistance to fracture.

36 MATERIALS SCIENCE↗