SEARCH · Search NASA

Results for “Microstructure characterization”

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.

SourceResearch connectionFrom yearThrough year

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

At least 55 records · Page 3

All sources NASA NTRS DOE OSTI

DOE OSTI2024

High-Throughput Microstructural Characterization and Process Correlation Using Automated Electron Backscatter Diffraction

The need to optimize the processing conditions of additively manufactured (AM) metals and alloys has driven advances in throughput capabilities for material property measurements such as tensile strength or hardness. High-throughput (HT) characterization of AM metal microstructure has fallen significantly behind the pace of property measurements due to intrinsic bottlenecks associated with the artisan and labor-intensive preparation methods required to produce highly polished surfaces. This inequality in data throughput has led to a reliance on heuristics to connect process to structure or structure to properties for AM structural materials. In this study, we show a transformative approach to achieve laser powder bed fusion (LPBF) printing, HT preparation using dry electropolishing and HT electron backscatter diffraction (EBSD). This approach was used to construct a library of > 600 experimental EBSD sample sets spanning a diverse range of LPBF process conditions for AM Kovar. This vast library is far more expansive in parameter space than most state-of-the-art studies, yet it required only approximately 10 labor hours to acquire. Build geometries, surface preparation methods, and microscopy details, as well as the entire library of >600 EBSD data sets over the two sample design versions, have been shared with intent for the materials community to leverage the data and further advance the approach. Using this library, we investigated process–structure relationships and uncovered an unexpected, strong dependence of microstructure on location within the build, when varied, using otherwise identical laser parameters.

Characterization and Analytical Technique↗

DOE OSTI2016

Microstructural Characterization of Irradiated Fuels and Materials for the United States High Performance Research Reactor Fuel Development Program and the Fuel Cycle Research and Development Program

In an effort to contribute to the development of advanced nuclear fuel for research reactors, monolithic and dispersion plate fuels will be examined to determine how irradiation parameters such as fission density, fission rate, and irradiation temperature, as well as mechanical parameters such as composition and fabrication, affect the final microstructure of the fuel, post irradiation. Electron Backscatter Detection (EBSD) analysis capabilities of irradiated materials will be developed as well as improvements on irradiated sample preparation in order to provide higher quality samples for SEM, FIB, and TEM. In addition, image analysis techniques developed at Idaho National Laboratory (INL) will be employed to examine microstructural features such as fission product precipitates and fission gas bubbles. The main goals are to further develop EBSD capabilities on irradiated material; characterize microstructure of irradiated fuel to support qualification; develop a consistent, effective process for image analysis using INL developed software; and provide repeatable, statistically-confident, critically assessed data to further modeling efforts. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2017

Microstructure characterization and nano & micro hardness of tri-modal microstructure of titanium alloy under different hot working conditions

Highlights: • The contents and sizes of α{sub p} and α{sub l} are determined by the processing parameters of first and second step. • The morphology of α{sub s} embedded in β phase is determined by the accumulated distortional strain energy and dislocations. • α{sub p} becomes harder as the strain rate of the first step increases due to the constantly enhanced work hardening effect. • β{sub t} is always harder than α{sub p} and α{sub l} due to the interfacial-strengthening effect. • The hardness of α{sub l} makes the greatest contribution in the integrated hardness of tri-modal microstructure. - Abstract: In this work, the dependences of tri-modal microstructure parameters and corresponding nano & micro hardness on through-process processing parameters were quantitatively studied during the three-step thermo-mechanical processing of TA15 titanium alloy. It is found that the processing parameters of first step, especially for the deformation temperature and strain rate, mainly affect primary equiaxed α (α{sub p}) through the α → β phase transformation and the competition between dynamic recovery and dynamic recrystallization. The second processing step primarily affects the content and thickness of lamellar α (α{sub l}). In the third processing step, compared with low-temperature aging, normal annealing provides sufficient driving force for α{sub l} and secondary lamellar α (α{sub s}) growing, which leads to thicker α{sub l} and α{sub s}. As for the nano & micro hardness, in one sample undergoing different process, transformed β matrix (β{sub t}) is always harder than α{sub l} and α{sub s} due to the interfacial-strengthening effect. In addition, with increasing strain rate of the first step, α{sub p} becomes harder due to the constantly enhanced work hardening effect while the hardness of β{sub t} varies little because of the competition between interfacial strengthening and distribution disorder degree. However, the nano hardness of α{sub l} decreases firstly and then increases with strain rate, which presents the same trend with the micro hardness of integrated hardness at different processing conditions.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Microstructure Characterization and Modeling for Improved Electrode Design

This presentation summarizes fiscal year 2018-2019 work under U.S. Department of Energy's Computer-Aided Engineering of Batteries (CAEBAT) program to develop computational tools for improved electrode design and to provide deeper fundamental understanding of the physics that limit the performance and cause degradation in lithium-ion batteries. Successes include (1) development of an electrode microstructure characterization tool box to be published open source later in 2019, (2) development of a large deformation electrochemical model capturing the volume expansion and performance limits of electrodes utilizing silicon and (3) development of a solid mechanics damage model describing the fracture of polycrystalline nickel-manganese-cobalt cathode materials with cycling.

30 DIRECT ENERGY CONVERSION↗

DOE OSTI2017

Graphite Microstructural Characterization Using Time-Domain and Correlation-Based Ultrasonics

Among techniques that have been used to determine elastic modulus in nuclear graphites, ultrasonic methods have enjoyed wide use and standards using contacting piezoelectric tranducers have been developed to ensure repeatability of these types of measurements. However, the use of couplants and the pressures used to effectively couple transducers to samples can bias measurements and produce results that are not wholly related to the properties of the graphite itself. In this work, we have investigated the use of laser ultrasonic methods for making elastic modulus measurements in nuclear graphites. These methods use laser-based transmitters and receivers to gather data and do not require use of ultrasonic couplants or mechanical contact with the sample. As a result, information directly related to the elastic responses of graphite can be gathered even if the graphite is porous, brittle and compliant. In particular, we have demonstrated the use of laser ultrasonics for the determination of both Young’s modulus and shear modulus in a range of nuclear graphites including those that are being considered for use in future nuclear reactors. These results have been analyzed to assess the contributions of porosity and microcracking to the elastic responses of these graphites. Laser-based methods have also been used to assess the moduli of NBG-18 and IG-110 where samples of each grade were oxidized to produce specific changes in porosity. These data were used to develop new models for the elastic responses of nuclear graphites and these models have been used to infer specific changes in graphite microstructure that occur during oxidation that affect elastic modulus. Specifically, we show how ultrasonic measurements in oxidized graphites are consistent with nano/microscale oxidation processes where basal plane edges react more readily than basal plane surfaces. We have also shown the use of laser-based methods to perform shear-wave birefringence measurements and have shown how these measurements can be used to assess elastic anisotropy in nuclear graphites. Using models developed in this program, ultrasonic data were interpreted to extract orientation distribution coefficients that could be used to represent anisotropy in these materials. This demonstration showed the use of ultrasonic methods to quantify anisotropy and how these methods provide more detailed information than do measurements of thermal expansion – a technique commonly used for assessing anisotropy in nuclear graphites. Finally, we have employed laser-based, ultrasonic-correlation techniques in attempts to quantify aspects of graphite microstructure such as pore size and distribution. Results of these measurements indicate that additional work must be performed to make this ultrasonic approach viable for quantitative microstructural characterization.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

DOE OSTI2024

FFTF HT9 Cladding Microstructure Characterization

The sodium-cooled fast reactor (SFR) is a promising candidate for next generation nuclear reactors, operating at extreme conditions which include high temperatures (>500?C core outlet temperature) and significant neutron damage. High-Cr martensitic HT9 steel is an excellent candidate for SFR cladding and duct material due to its compatibility with liquid sodium, good thermal conductivity, resistance to void swelling, and strong creep rupture strength [1-4].However, the harsh in-core environment of SFRs can cause complex microstructural changes and mechanical property degradation in HT-9. Ensuring the safe use of HT9 cladding for metallic fuel requires both a thorough understanding of its mechanical response to microstructure evolution as well as reliable microstructure-sensitive modeling predictions. Microstructure-sensitive modeling of high temperature creep behavior in HT9 cladding for SFR applications currently lack experimental data to model the phenomena accurately. To fill this need, methods to perform microstructural characterization have been developed and performed on HT9.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Microstructural characterization of annealed U-20Pu-10Zr-3.86Pd and U-20Pu-10Zr-3.86Pd-4.3Ln

Palladium is being investigated as a potential additive to metallic fuel to bind fission product lanthanides, with the goal of reducing or preventing fuel-cladding chemical interactions (FCCI). A primary cause of FCCI is the lanthanide fission products moving to the fuel periphery and interacting with the cladding. This interaction will lead to wastage of the cladding and eventually to a cladding breach. The current study is the microstructural characterization of annealed U-20Pu-10Zr-3.86Pd and U-20Pu-10Zr-3.86Pd-4.3Ln in wt. %, where Ln = 53Nd-25Ce-16Pr-6La, using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). In both alloys, the matrix is comprised of ζ-U 0.4 Pu 0.6 and δ-(U,Pu)Zr 2 . Based on the matrix compositions, modifications to the room temperature extrapolated U-Pu-Zr ternary phase diagram are suggested. In U-20Pu-10Zr-3.86Pd, there is very little δ phase, due to formation of PdZr 2 . In U-20Pu-10Zr-3.86Pd-4.3Ln, a lanthanide-rich phase is present, although it does not have the crystal structure for 53Nd-25Ce-16Pr-6La. Furthermore this phase cannot be identified based on known compounds. (Ln,Pu)Pd is the primary lanthanide phase, with Pu substituting into the crystal structure in place of Nd.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2017

Microstructural characterization of an irradiated RERTR-6 U-7Mo/AA4043 alloy dispersion fuel plate specimen blister-tested to a final temperature of 500°C

The Material Management and Minimization (M3) Reactor Conversion Program, in the past called the Reduced Enrichment for Research and Test Reactor (RERTR) Program, is developing low-enriched uranium (LEU) fuels for application in research reactors. U–Mo alloy dispersion fuel is one type being developed. Blister testing has been performed on different fuel plate samples to determine the margin to failure for fuel plates irradiated to different fission densities. Microstructural characterization was performed using scanning electron microscopy and transmission electron microscopy on a sample taken from a U-7Mo/AA4043 matrix dispersion fuel plate irradiated in the RERTR-6 experiment that was blister-tested up to a final temperature of 500°C. The results indicated that two types of grain/cell boundaries were observed in the U- 7Mo fuel particles, one with a relatively low Mo content and fission gas bubbles and a second type enriched in Si, due to interdiffusion from the Si-containing matrix, with little evidence of fission gas bubbles. With respect to the behavior of the major fission gas Xe, a significant amount of the Xe was still observed within the U-7Mo fuel particle, along with microns into the AA4043 matrix. For the fuel/matrix interaction layers that form during fabrication and then grow during irradiation, they change from the as-irradiated amorphous structure to one that is crystalline after blister testing. In the AA4043 matrix, the original Si-rich precipitates, which are typically observed in as-irradiated U-Mo dispersion fuel, get consumed due to interdiffusion with the U-7Mo fuel particles during the blister test. Lastly, the fission gas bubbles that were originally around 2 nm in diameter and resided on a fission gas superlattice in the intragranular regions of as-irradiated U-7Mo fuel grew in size (up to ~20 nm diameter) during blister testing.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2018

Microstructural characterization of SiO2/Ni nanocomposites electrodeposited from a sulphate bath modified by PEI

Highlights: • SiO{sub 2}/Ni + PEI nanocomposites are deposited from the sulphate bath containing PEI. • PEI allows incorporation of higher SiO{sub 2} vol% in SiO{sub 2}/Ni + PEI nanocomposites. • PEI in the form of a thin layer surrounds spherical Ni nanograins and SiO{sub 2} clusters. • PEI action ensures high hardness, tribological properties and corrosion resistance. - Abstract: SiO{sub 2}/Ni nanocomposite coatings containing well-dispersed SiO{sub 2} nanoparticles were electrodeposited from a sulphate bath with and without the addition of polyethylenimine (PEI) as a cationic surfactant. The surface morphology and microstructure in the cross-sections of the deposited nanocomposites were examined by scanning electron microscopy. More detailed microstructure characterization was performed using transmission, scanning-transmission and high resolution transmission electron microscopy. It was determined that the addition of 0.05 g/L and 0.1 g/L of PEI allows the incorporation of SiO{sub 2} nanoparticles in the nickel matrix to be increased in comparison with the nanocomposite deposited without a surfactant. Based on high spatial resolution microanalysis, performed using high count rate energy dispersive spectroscopy of characteristic X-rays in the scanning-transmission mode, the distribution of SiO{sub 2} nanoparticles in the nanocomposite was visualized on elemental maps. Image analysis of the electron microscopy images enabled the mean equivalent circle diameters of grains in the nickel matrix to be determined, together with the volume fraction of SiO{sub 2} nanoparticles in the nanocomposites. The volume fraction of SiO{sub 2} clusters in the SiO{sub 2}/Ni + PEI nanocomposites with the addition of 0.05 g/L and 0.1 g/L of PEI is equal to 18.4% and 13.3%, respectively. Furthermore, the PEI addition allows the nickel grain size in the matrix to be reduced. The combination of different imaging techniques confirmed that PEI is not only present as a surfactant in the electrolytic bath, but also incorporates into the microstructure of the nanocomposite. Nanocomposites electrodeposited in the presence of 0.05 g/L of PEI exhibit higher hardness, good tribological properties and improved corrosion resistance. Although increasing the PEI concentration in the bath up to 0.1 g/L strongly promotes grain size reduction and increase of the SiO{sub 2} volume fraction, it also causes an increase in the PEI fraction embedded in the microstructure, which results in deterioration of the properties of the SiO{sub 2}/Ni + PEI nanocomposites.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2016

Microstructure characterization of LAE442 magnesium alloy processed by extrusion and ECAP

The magnesium alloy LAE442 was processed by extrusion and equal channel angular pressing (ECAP) to achieve ultrafine grained microstructure. Detailed characterization of the microstructure was performed by scanning electron microscope, electron back scattered diffraction (EBSD) and transmission electron microscope. The initial, as-cast, microstructure consisted of large grains of ~ 1 mm. The grain refinement due to the processing by severe plastic deformation led to a decrease of the average grain size to ~ 1.7 μm after the final step of ECAP. A detailed characterization of secondary phases showed the precipitation of Al{sub 11}RE{sub 3}, Al{sub 2}Ca and Al{sub 10}RE{sub 2}Mn{sub 7} intermetallic phases. X-ray diffraction measurements proved that Li is dissolved within the magnesium matrix in the as-cast condition. Newly formed Al{sub 3}Li phase was observed after ECAP. The texture formation due to the extrusion and ECAP was different from that in the other magnesium alloys due to the activation of non-basal slip systems as a result of the decrease of the c/a ratio. - Highlights: • Combined extrusion and equal channel angular pressing results in significant grain refinement by factor 1000 approximately. • Al{sub 11}RE{sub 3}, Al{sub 2}Ca and Al{sub 10}RE{sub 2}Mn{sub 7} secondary phases are present in the as-cast material while Li was dissolved in the Mg matrix. • Extrusion and ECAP have no effect on the composition of the secondary phases but they influence strongly their distribution. • Texture evolution is affected by decrease of c/a ratio due to the presence of Li and resulting activation of non-basal slip.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Generalizable Image Segmentation for Microstructure Characterization Through Integrated SEM and EBSD Analysis

We demonstrate generalizable semantic segmentation using minimal ground truth data. Correlated scanning electron microscopy (SEM) images and electron backscatter diffraction (EBSD) measurements of frictionstir processed 316L stainless steel plates were used to train deep learning models for grain boundary segmentation. Secondary electron (SE) imaging taken at an accelerating voltage of 10 keV correlated to EBSD-derived grain boundaries produced the best performing model. Notably, an ensemble of three models trained on a single SE image produced accurate segmentation over a series of BSE images of samples manufactured under different processing parameters, with a resultant mean absolute error in grain size of 0.34 µm. The striking generalizability of the models likely results from the similar escape depths of the SE training input and the EBSD training output and the reduced probability of dislocation artifacts appearing in the image. This finding highlights the importance of considering the physical principles behind imaging in the development of robust segmentation models for microstructure characterization.

Taufique, Mohammad Fuad Nur↗

DOE OSTI2017

Shock and Microstructural Characterization of the α-ω Phase Transition in Titanium Crystals

In this paper, a multicrystal comprised of a small number of large crystals of high-purity titanium and a [ 0001 ] oriented high-purity single crystal titanium sample were shock loaded using gas gun plate impact experiments. Tests were performed at stresses above the α − ω phase transition stress (for high-purity polycrystalline specimens) to observe the behavior of oriented crystals under similar conditions. Post-mortem characterization of the shocked microstructure was conducted on the single crystal sample to measure textures, and quantify phases and twinning. The apparent activation of plastic and transformation mechanisms was dependent upon crystal orientation. Specifically, the [ 0001 ] crystal showed a higher Hugoniot elastic limit than the [ 10 1 ¯ 0 ] or [ 3 1 ¯ 4 ¯ 4 ] orientations. The slope of velocity as a function of time was lower in the [ 0001 ] orientation than the other orientations during plastic deformation, indicating sluggish transformation kinetics for the α to ω phase transition for the [ 0001 ] oriented crystal. Finally, microtexture measurements of a recovered [ 0001 ] oriented single crystal revealed the presence of retained ω phase after unloading, with orientations of the constituent phase fractions indicative of the forward α→ω transition, rather than the reverse ω→α transition, suggesting that the material never achieved a state of 100% ω phase.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Thickness and microstructure characterization of TGO in thermal barrier coatings by 3D reconstruction

Yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) are prepared by plasma spraying. Thermally grown oxide (TGO) would be formed between YSZ topcoat and bond coat after 50 h thermal service for YSZ TBCs. The electron back scattered diffraction (EBSD) results reveal that the TGO layer is composed of α-Al{sub 2}O{sub 3} and cubic Al{sub 2}NiO{sub 4} layers. Measured values of TGO thickness from the 2D-SEM image are greater than or equal to its real thickness due to the fact that the TGO layer is much rolling so that up and down surfaces of the TGO can't be completely perpendicular to the cross-section direction confirmed by 3D-SEM. Furthermore, 3D-SEM results reveal that the real thickness of TGO layer is 3.10 μm instead of 7.1 μm. In addition, 3D-EBSD confirmed that α-Al{sub 2}O{sub 3} layer in TGO is composed of single layer of grains and Al{sub 2}NiO{sub 4} layer consist of multilayer of grains while α-Al{sub 2}O{sub 3} layer is mixed with single layer and multilayer of α-Al{sub 2}O{sub 3} grains from observation of the 2D-EBSD image. It provides a new method to characterize real thickness and microstructure of TGO, which is also applied to other film materials. - Highlights: •This work provides a new method to measure the real thickness of TGO. •YSZ TBCs were prepared by plasma spraying. •TGO is formed in TBCs by simulating thermal service at 1100 °C for 50 h. •Real thickness and microstructure of TGO were investigated by 3D reconstruction.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Microstructural Characterization of High Dose Irradiated HT9

The present report provides a short summary of the recent efforts to irradiate various HT9 heats and compositions to a high damage level (>500 peak dpa) and characterize the changes to the microstructure. The majority of the data reported here will focus on characterizing the “INL” HT9 heat. This particular heat was chosen due to its high volume fraction of tempered martensite (>90%) in the microstructure. The results show that very little swelling is present in INL HT9 up to doses up to 600 peak dpa. Voids are only observed in the near surface region. Some carbides are also observed to accompany the irradiation. Comparison of void swelling with published neutron irradiation shows good agreement. Additional investigations into the response of delta ferrite grains show a very different distribution of voids and significantly higher void swelling compared to the tempered martensite grains.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2014

Microstructure characterization and mechanical behaviors of a hot forged high Nb containing PM-TiAl alloy

In this work, the effects of deformation on the microstructure and mechanical behaviors of TiAl alloy were investigated. Deformed microstructure observation was characterized by scanning electron microscopy, electron back scattered diffraction technique, transmission electron microscopy and DEFORM-3D software. Results indicated that the core area of the TiAl pancake was characterized by completely dynamically recrystallized microstructures, however some residual lamellar colonies can be observed near the edge area, which are primarily caused by a temperature drop and inhomogenous plastic flow. The main softening mechanism is dynamic recrystallization of γ grains. The as-forged alloy exhibited excellent mechanical properties at both room temperature and high temperature. Tensile test results showed that the ultimate tensile strength of the alloy increased from 832 MPa at room temperature to 853 MPa at 700 °C, while the elongation increased from 2.7% to 17.8%. Even at the temperature of 850 °C, the ultimate tensile strength maintained 404 MPa, and the elongation increased to 75%. The as-forged alloy also exhibited remarkable low-temperature superplasticity at 850 °C, with an elongation of 120%. - Highlights: • The core area of the TiAl pancake was characterized by DRX microstructure. • The elongation at RT is higher than that of other high Nb-containing TiAl alloys. • The forged alloy exhibited low-temperature superplasticity at 850 °C.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Microstructure and water absorption of ancient concrete from Pompeii: An integrated synchrotron microtomography and neutron radiography characterization

There is renewed interest in using advanced techniques to characterize ancient Roman concrete due to its exceptional durability and low-carbon footprint. In the present work, samples were drilled from the “Hospitium” in Pompeii and were analyzed by synchrotron microtomography (μCT) and neutron radiography to study how the microstructure, including the presence of induced cracks, affects their water adsorption. The water distribution and absorptivity were quantified by neutron radiography. The 3D crack propagation, pore size distribution and orientation, tortuosity, and connectivity were analyzed from μCT results using advanced imaging methods. Porosity was also measured by mercury intrusion porosimetry (MIP) as a reference. Ductile fracture patterns were observed once cracks were introduced. Compared to Portland cement mortar/concrete, the Pompeii samples had relatively high porosity, low connectivity, and a similar coefficient of capillary penetration. In addition, permeability was predicted from models based on percolation theory and pore structure data to evaluate the fluid transport properties. Understanding the microstructure of ancient Pompeii concrete is important because it could inspire the development of modern concrete with high durability.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Microstructural Characterization of Alloy 617 Crept into the Tertiary Regime

The microstructure of Alloy 617 was characterized following creep tests interrupted at total creep strains ranging from 2-20%. A range of creep temperatures (750-1000oC) and initial creep stresses (10-145 MPa) produced creep test durations ranging from 1 to 5800 hours. Image analysis of optical photomicrographs on longitudinal sections of the gage length was used to document the fraction of creep porosity as a function of creep parameters. Creep porosity was negligible below tertiary creep strains of 10% and increased with tertiary creep strain, thereafter. For a given temperature and total creep strain, creep porosity increased with decreasing creep stress. Creep porosity increased linearly with duration of the creep experiment. TEM performed on the gage sections did not reveal significant creep cavity formation on grain boundaries at the sub-micron level. It was concluded that the onset of tertiary creep did not result from creep cavitation and more likely arose due to the formation of low energy dislocation substructures with increasing tertiary strain.

Alloy 617↗

DOE OSTI2022

Microstructural Characterization of the Second High Fluence Baffle-Former Bolt Retrieved from a Westinghouse Two-loop Downflow Type PWR

As one of the pressurized water reactor (PWR) internal components, baffle-former bolts (BFBs) are subjected to significant mechanical stress and neutron irradiation from the reactor core during the plant operation. Over the long operation period, these conditions lead to potential degradation and reduced load-carrying capacity of the bolts. In support of evaluating long-term operational performance of materials used in core internal components, the Oak Ridge National Laboratory (ORNL), through the Department of Energy (DOE), Light Water Reactor Sustainability (LWRS) Program, Materials Research Pathway (MRP) has harvested two high fluence BFBs from a commercial Westinghouse two-loop downflow type PWR. The two bolts of interest, i.e. bolts # 4412 and 4416, were withdrawn from service in 2011 as part of a preventative replacement plan. No identification of cracking or potential damage was found for these bolts during their removal in 2011. However, the bolts required a lower torque for removal from the baffle structure than the original torque specified during installation. Irradiation displacement damage levels in the bolts range from 15 to 41 displacements per atom. The goal of this project is to perform detailed microstructural and mechanical property characterization of BFBs following in-service exposures. The information from these bolts will be integral to the LWRS program initiatives in evaluating end of life microstructure and properties. Furthermore, valuable data will be obtained that can be incorporated into model predictions of long-term irradiation behavior and compared to results obtained in high flux experimental reactor conditions. In this report, we present our latest study in FY22 on microstructural characterizations of the second high fluence baffle-former bolt, i.e., bolt # 4412. Analytical electron microscopy and atom probe tomography characterization were performed. The radiation-induced defects in the material add to the large wealth of knowledge for neutron-induced defects in 304/316 grades of stainless steels, specifically for radiation-induced precipitation after high fluence commercial PWR irradiation. The main findings are summarized as follows: 1) The cavity size was considerably larger in the bolt thread section than in the bolt head, with the bolt thread section having a bimodal distribution of cavities greater than ~6 nm in diameter and less than ~3 nm in diameter. The bolt head only had the small-sized cavities. In addition, there was a denuded zone of large cavities near grain boundaries in the thread section of the bolt. 2) Radiation-induced precipitation in the BFB #4412 was highly complex, with the volume fraction, size, and number density of Ni/Si and Cu-rich precipitates depending strongly on the radiation temperature/dose. In many cases, co-precipitates of adjoined clusters were found with Ni/Si-rich precipitates sandwiched between Cu-rich clusters and Mo/Cr/P-rich clusters. 3) Solute segregation out of solution was highest for most solutes in the thread section of the bolt #4412 with the exception of Cu, which experienced more separation out of solution into Curich clusters in the bolt head section. This highlights the difference in the mechanisms for precipitation of Ni/Si clusters, which have the Ni 3 Si phase composition, and precipitation of Cu-rich clusters. 4) There appear to be multiple simultaneous influences that affect the microstructural variation along the length of the bolt that overcomes the ~2X difference in irradiation dose between the bolt head and the bolt thread. The irradiation temperature, thermal/fast neutron ratio variation, potential strain gradient, and exposure to PWR coolant water that each section of the bolt sees may have more influence on the microstructural evolution than the total irradiation dose. The bolt thread and shank, with higher temperature, higher relative fast neutron flux, higher strain, and exposure to coolant but lower dose, underwent more enhanced cavity formation, precipitation, and solute segregation than the bolt head section.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗