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Results for “Microstructural evolution”
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Microstructure evolution during laser direct energy deposition of a novel Fe-Cr-Ni-W-B hardfacing coating
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Spatially resolved texture and microstructure evolution of additively manufactured and gas gun deformed 304L stainless steel investigated by neutron diffraction and electron backscatter diffraction
In this study, we report the characterization of a 304L stainless steel cylindrical projectile produced by additive manufacturing. The projectile was compressively deformed using a Taylor Anvil Gas Gun, leading to a huge strain gradient along the axis of the deformed cylinder. Spatially resolved neutron diffraction measurements on the HIgh Pressure Preferred Orientation time-of-flight diffractometer (HIPPO) and Spectrometer for Materials Research at Temperature and Stress diffractometer (SMARTS) beamlines at the Los Alamos Neutron Science CEnter (LANSCE) with Rietveld and single-peak analysis were used to quantitatively evaluate the volume fractions of the α, γ, and ε phases as well as residual strain and texture. The texture of the γ phase is consistent with uniaxial compression, while the α texture can be explained by the Kurdjumov–Sachs relationship from the γ texture after deformation. This indicates that the material first deformed in the γ phase and subsequently transformed at larger strains. The ε phase was only found in volumes close to the undeformed material with a texture connected to the γ texture by the Shoji–Nishiyama orientation relationship. This allows us to conclude that the ε phase occurs as an intermediate phase at lower strain, and is superseded by the α phase when strain increases further. Furthe, we found a proportionality between the root-mean-squared microstrain of the γ phase, dominated by the dislocation density, with the α volume fraction, consistent with strain-induced martensite α formation. In conclusion, knowledge of the sample volume with the ε phase from the neutron diffraction analysis allowed us to identify the ε phase by electron back scatter diffraction analysis, complementing the neutron diffraction analysis with characterization on the grain level.
Microstructure Evolution of Low Carbon Steel via Flash Processing
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Electrochemical Characterization and Microstructure Evolution of Ni-Rich Layered Cathode Materials by Niobium Coating/Substitution
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Probing Impedance and Microstructure Evolution in Lithium–Sulfur Battery Electrodes
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4D-STEM Coupled with Unsupervised Machine Learning to Reveal at Large-Scale the Microstructural Evolution in Li- and Mn-Rich Cathodes
Li- and Mn-rich (LMR) layered oxides are known to exhibit a thin surface reconstruction layer, which grows during electrochemical cycling in a manner that depends on exposed crystallographic facets, cycling conditions, and electrolyte chemistry. Direct characterization of this layer has traditionally relied on high-resolution electron microscopy, which is inherently limited to small fields of view. Here, we employ four-dimensional scanning transmission electron microscopy (4D-STEM) combined with unsupervised machine-learning clustering to quantitatively map phase distributions over large areas and track their evolution in LMR cathodes during electrochemical aging. Our results show that the surface reconstruction layer consists predominantly of a rocksalt phase, whose thickness varies across different facets following activation cycling and becomes substantially thicker and more uniform during calendar aging. In contrast, a spinel-like phase is observed within the particle bulk. Large-area phase mapping and correlative high-resolution imaging reveal that this spinel-like phase preferentially nucleates at bulk crystallographic defects, including boundaries between 60°-rotated layered domains and associated mixed-phase regions, rather than exclusively at the particle surface. Our findings establish a mechanistic distinction between surface-driven rocksalt formation and bulk-defect-mediated spinel nucleation while demonstrating the unique capability of 4D-STEM to provide statistically robust, mesoscale insight into complex phase-evolution processes in LMR cathodes.
Relating Structural and Microstructural Evolution to the Reactivity of Cellulose and Lignin during Alkaline Thermal Treatment with Ca(OH) 2 for Sustainable Energy Production Integrated with CO 2 Capture
The transition toward a low carbon economy necessitates the implementation of a wide range of negative emissions technologies, including bioenergy integrated with CO 2 capture and storage. Advancing large-scale or modular technologies for bioenergy with carbon capture and storage requires a fundamental understanding of chemo-morphological coupling in these material systems. In this context, integrated chemical pathways such as alkaline thermal treatment (ATT) of biomass which involves the production of bio-H 2 while converting and storing CO 2 as solid carbonates provides promising potential for integrating bioenergy with carbon capture and storage. We elucidate the structural and morphological changes when biomass feedstocks such as cellulose and lignin are reacted with calcium hydroxide to capture, convert, and store CO 2 as calcium carbonate while producing energy carrier such as H 2 . These structural and morphological changes were monitored using synchrotron based in operando multiscale X-ray scattering measurements. Enhanced CO 2 capture at temperatures above 375 °C was evident from the significant growth of the calcium carbonate phase at these conditions. Increase in the surface area and porosity of cellulose was noted compared to lignin due to the relatively fast decomposition of cellulose. Pore–solid interfaces in Ca(OH) 2 + cellulose system became smoother in the temperature range of 500–700 °C compared to Ca(OH) 2 + lignin system, where the interfaces became rougher. Enhanced roughness of the pore–solid interfaces in the presence of lignin is attributed to the simultaneous slow decomposition of lignin and formation of calcium carbonate.
Investigating microstructure evolution in block copolymer membranes
Block copolymer self-assembly in conjunction with nonsolvent-induced phase separation (SNIPS) has been increasingly leveraged to fabricate integral-asymmetric membranes. The large number of formulation and processing parameters associated with SNIPS, however, has prevented the reliable construction of high performance membranes. In this study, we apply dynamical self-consistent field theory to model the SNIPS process and investigate the effect of various parameters on the membrane morphology: solvent selectivity, nonsolvent selectivity, initial film composition, and glass transition composition. We examine how solvent selectivity and concentration of polymers in the film impact the structure of micelles that connect to form the membrane matrix. In particular, we find that preserving the order in the surface layer and forming a connection between the supporting and surface layer are nontrivial and sensitive to each parameter studied. Furthermore, the effect of each parameter is discussed, and suggestions are made for successfully fabricating viable block copolymer membranes.
On the microstructure evolution of AA6061 with pulsed laser powder bed fusion
Not Available
Monitoring microstructural evolution in-situ during cyclic loading with high-resolution reciprocal space mapping
Abstract not provided
How relative defect migration energies drive contrasting temperature-dependent microstructural evolution in irradiated ceramics
Ceramic materials have become widely used in various fields of material science, and ceramic oxides such as cubic zirconia (c- ZrO 2 ) and magnesia (MgO) are candidate materials for nuclear energy applications. For the corresponding in-service conditions of these materials, there is a crucial need in studies at moderate or high temperatures of the physical phenomena underlying the damage buildup under irradiation. Here in the present work, we show, using x-ray diffraction, that these two materials exhibit a similar damage accumulation process under ion irradiation at fixed temperature. However, they display an unexpected opposite damaging rate to changes in the irradiation temperature. In fact, as the temperature is increased, the final damage state is reached earlier in c- ZrO 2 while it is delayed in MgO. Rate equation cluster dynamics simulations show that defect clustering is favored over defect recombination in c- ZrO 2 , but the situation is reversed for MgO, explaining the observed opposite response to temperature of the two materials. This contrasting behavior can be rationalized in terms of nonequivalent interstitial versus vacancy defect migration energies in MgO. We finally demonstrate that these results allow for a qualitative prediction of the evolution of the experimental irradiation-induced disorder with temperature, henceforth potentially reducing the cost in selecting and developing ad hoc materials.
Modeling the Distribution of Oxygen Partial Pressure in the Electrolyte of Solid Oxide Cells and its Implication on Microstructure Evolution in the Hydrogen Electrode
18th International Symposium on Solid Oxide Fuel Cells (SOFC-XVIII), Boston, MA, May 28-June 2, 2023
Microstructural Evolution of Irradiated LPBF 316 Stainless Steel using Neutrons and Ions
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Microstructure Evolution in Ion-Irradiated Oxidized Zircaloy-4 Studied with Synchrotron Radiation Microdiffraction and Transmission Electron Microscopy
The corrosion process (oxidation and hydriding) of zirconium alloy fuel cladding is one of the limiting factors on fuel rod lifetime, particularly for Zircaloy-4. The corrosion rate of this alloy shows indeed a great acceleration at high burnup in light water reactors (LWRs). Understanding the corrosion behavior under irradiation for this alloy is an important technological issue for the safety and efficiency of LWRs. In particular, understanding the effect of irradiation on the metal and oxide layers is a key parameter in the study of corrosion behavior of zirconium alloys. In this study, Zircaloy-4 samples underwent helium and proton ion irradiation up to 0.3 dpa, forming a uniform defect distribution up to 1 pm deep. Both as-received and precorroded samples were irradiated to compare the effect of metal irradiation to that of oxide layer irradiation. After irradiation, samples were corroded to study the impact of irradiation defects in the metal and in preexisting oxide layers on the formation of new oxide layers. Synchrotron X-ray microdiffraction and microfluorescence were used to follow the evolution of oxide crystallographic phases, texture, and stoichiometry both in the metal and in the oxide. In particular, the tetragonal oxide phase fraction, which has been known to play an important role in corrosion behavior, was mapped in both unirradiated and irradiated metals at the submicron scale and appeared to be significantly affected by irradiation. These observations, complemented with electron microscopy analyses on samples in carefully chosen areas of interest, were combined to fully characterize changes caused by irradiation in metal and oxide phases of both alloys.
Experimental Validation of UO 2 Microstructural Evolutions for NEAMS Tool MARMOT (Final Report)
The project was aimed at experimentally validating the NEAMS tool MARMOT for predicting the GB migration and pore and GB interaction in UO 2 oxide fuel under the driving forces of high temperatures and large temperature gradient anticipated in a LWR fuels. By performing the well-aligned experiments and simulations simultaneously using precisely defined initial conditions, the high-quality experiment data will provide a direct benchmarking of the MARMOT code by evaluating the fidelity of physics, materials science principles and models, and the coupling of multi-physics solutions. A bottom up approach will be used by studying each specific behavior while the code will be statistically validated again the overall structural evolution. The GB energy, specific GB mobility, grain growth kinetic, GB interaction with pores, and effects of large temperature gradients will be specifically studied using experiments. The isothermal grain growth, grain growth under large temperature gradient, and pore and GB interactions will be modeled using 2-D or 3-D simulations. Four questions will be answered at the conclusion of this project: Is the anisotropic grain boundary energy model able to better represent a real view the grain property and would it have a significant impact on the grain growth behavior? Is the classical Zener pinning model in MARMOT sufficient for representing the retarding effect on grain gain boundary migration from pores? Does the temperature gradient have a minimum impact on the average grain growth behavior at varied average temperatures and temperature gradients? Does the pore migrate towards the high temperature domain at the velocities predicted by MARMOT code?