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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Multi-scale modeling of fuel fragmentation and microstructural evolution

An overview of NEAMS program activities to model fuel fragmentation and microstructual evolution to a group of industry attendees at a meeting hosted by EPRI. Topics include atomistic methods to determine grain boundary strength, phase-field fracture modeling to determine critical pressure at grain boundaries, and coupled phase-field-cluster dynamics to model microstructural evolution.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Effect of Zinc Interlayer in Microstructure Evolution and Mechanical Properties in Dissimilar Friction Stir Welding of Aluminum to Titanium

The welding of aluminum (Al) and titanium (Ti) is difficult and challenging due to the differences in their chemical and physical properties, and the formation of brittle intermetallic phases. In the present experiment, a zinc (Zn) interlayer was used during friction stir welding of Al to Ti. The weld was characterized in detail to understand the mechanisms associated with microstructural evolution and improvement in mechanical properties of the weld. X-ray computed tomography results reveal three-dimensional distribution of particles and flakes of titanium in the weld nugget. It was also observed that Ti particles are inhomogeneously distributed in the weld and the distribution depends on their morphology. Such a distribution of Ti was informative in understanding material flow. In addition, the consolidation of Zn in the Al matrix reveals the nature of material flow in the weld nugget as well. The importance of the Zn interlayer and mechanism of phase formation was explored in this study. It was characterized that the mechanical mixing of Zn with Al and Ti alters phase evolution and restricts the formation of conventional Al{sub 3}Ti intermetallic phase. The presence of zinc homogenizes elemental distribution and inhibits the formation of brittle intermetallic phases, which leads to a substantial improvement in mechanical properties of the weld.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Effect of microalloying additions on microstructural evolution and thermal stability in cast Al-Ni alloys

Enhancement of thermal stability in Al-Ni alloys through microalloying with slow-diffusing elements, specifically Zr, has been previously reported which is attributed to Zr segregation at the Al/Al 3 Ni interface. In this study, we explore the influence of microalloying Al-Ni alloys with Zr, Ti, V, and Fe on microstructural evolution, hardness, and electrical and thermal conductivity across a range of heat-treatment temperatures from 300 to 450 °C. The distribution of microalloying elements and precipitates after heat treatment is characterized using atom probe tomography (APT). Our investigation confirms Zr segregation to the Al/Al 3 Ni interface, while similar interfacial segregation is absent with the addition of Ti, V, and Fe. Additionally, our analysis of the Al 3 Ni microfiber morphology reveals that their coarsening and spheroidization rates are similar with and without interfacial segregation; thus, retaining the fiber reinforcement through interfacial segregation of slow diffusing elements may not be an effective strategy. Precipitation of L1 2 nanoparticles was found to be the dominant mechanism affecting enhanced hardness and electrical conductivity in Al-Ni-Zr alloys, attributed to precipitation strengthening and solute depletion, respectively. Similar precipitation was not observed for additions of Ti, V, and Fe following heat treatment. We provide a thermodynamic explanation for this limitation. Furthermore, the findings of this study suggest that an effective approach for designing Al-Ni alloys should involve prioritizing microalloying elements to maximize L1 2 precipitation and minimize solute content in the FCC-Al matrix post heat treatment, rather than focusing on Al/Al3Ni interfacial segregation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

On the mobility of defect clusters and their effect on microstructure evolution in fcc Ni under irradiation

Here, µs-scale molecular dynamics studies of vacancy and interstitial clusters in fcc Ni revealed three- and one- dimensional (3-D and 1-D) modes of the cluster motion. The 1-D mobility of interstitial defects is known to enhance swelling rate. The theoretical analysis performed here suggests two novel mechanism by which the 3-D mobile clusters affect microstructure evolution under irradiation. First, the mobility of vacancy clusters hinders nucleation of stable voids due to recombination with interstitial-type loops and edge dislocations. Second, the capture efficiency of dislocations is higher for 3-D mobile vacancy and interstitial clusters than single defects, with the combined effect depending on relative fractions of clustered vacancies and interstitials produced in cascades. The observed differences in radiation damage of most fcc and bcc metals is attributed to the difference in cascade-produced vacancy defects: immobile SFTs and loops in fcc metals and mobile clusters in bcc metals. In this context, fcc Ni is similar to bcc metals due to its high stacking fault energy.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Investigating microstructural evolution in SolidStir™ extruded oxide dispersion strengthened 14YWT alloy fuel cladding tube

Structural components for extreme environments require advanced materials and manufacturing processes. One such advanced material is oxide dispersion strengthened (ODS) Fe–14 wt.%Cr–3W–0.4Ti–0.3Y 2 O 3 (14YWT), which is developed for components to be used in Gen IV and fusion nuclear reactors. However, the conventional manufacturing processes to produce components, such as fuel cladding tubes, either do not retain the desired microstructural attributes or are costly and less efficient. As a result, a more attractive option is a novel manufacturing process developed on the principle of friction stir welding or processing (FSW/P) and commercially referred to as SolidStir™ Extrusion (SSE). Here this study used the SSE technique to study the manufacturing and microstructural evolution of a fuel cladding tube made of ODS 14YWT alloy. The cladding extrusion by the SSE technique involved the use of ball-milled 14YWT powders with Y, Ti, and O in the solid solution and the use of a specially designed W-25Re-Hf tool for consolidation and extrusion of the powders. A scanning electron microscope (SEM), electron backscattered diffraction (EBSD), and transmission electron microscope (TEM) were utilized for microstructural characterization. A Keyence microscope captured macrostructural photographs of the extruded tube. EBSD examination of the extruded tube on both transverse and longitudinal cross-sections showed the presence of dynamically recrystallized grains and revealed that the average grain size of the transverse cross-section was smaller than that of the longitudinal cross-section. The texture was weak and consisted of some amount of shear texture. The presence of nano-oxide clusters or precipitates of Y, Ti, and O (pyrochlores) in the extruded tube was determined by TEM. Aging heat treatment caused the average precipitate size to decrease and the density to increase compared to the as-processed condition. The results indicated that SSE is a viable tool for manufacturing fuel cladding tubes with the desired microstructural attributes.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Microstructure Evolution and Implications for Cu Nanointerconnects and Beyond

The continued scaling of Cu low k technology is facing serious challenges imposed by basic limits from materials, processing and reliability. This has generated great interests recently to further develop Cu nanointerconnects and alternates, particularly Co and Ru nanointerconnects beyond the 10nm node. The performance and reliability are important considerations for the development of nanointerconnects in addition to challenges from processing complexity and manufacturing cost. In this paper, we investigate the microstructure evolution in Cu, Co and Ru nanointerconnects and the effects on resistivity and electromigration (EM), two key factors contributing to the RC delay and reliability of the nanointerconnects.

36 MATERIALS SCIENCE↗
DOE OSTI2021

In-situ TEM observation of shear induced microstructure evolution in Cu-Nb alloy

Phase boundaries in multiphase alloys govern defect interaction and chemical intermixing across different phases during plastic deformation. Dynamic interaction of defects with phase boundaries in multiphase alloys, especially for immiscible alloys, has been topic of significant research interest in recent years. In this work, we describe a novel approach for carrying out in-situ TEM shear deformation to directly observe interfacial microstructural evolution of a Cu-Nb alloy. A unique double shear specimen geometry is microfabricated by a focused ion beam technique to apply shear deformation upon push loading inside the TEM. From the real-time observation, we discover that the phase boundary with a zigzag morphology effectively blocks stacking faults nucleated in a Cu grain from slipping into a Nb grain. Meanwhile, the Cu phase bears the most plastic deformation through slip or twinning mechanisms. This work sheds light on understanding the shear deformation and the behavior of phase boundaries in multiphase alloys during shear deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

EBSD analysis of surface and bulk microstructure evolution during interrupted tensile testing of a Fe-19Cr-12Ni alloy

Highlights: • Similar deformation structures are obtained for surface and bulk grains. • A lower strain is needed for twinning in surface grains than in bulk grains. • A reduced ability to cross-slip due to low SFE leads to an increasing LAB density. • Twinning reduces the dislocation slip length. • High strain-hardening rate is maintained up to high strains. - Abstract: The microstructure evolution in both surface and bulk grains in a pure Fe-19Cr-12Ni alloy has been analyzed using electron backscatter diffraction after tensile testing interrupted at different strains. Surface grains were studied during in situ tensile testing performed in a scanning electron microscope, whereas bulk grains were studied after conventional tensile testing. The evolution of the deformation structure in surface and bulk grains displays a strong resemblance but the strain needed to obtain a similar deformation structure is lower in the case of surface grains. Both slip and twinning are observed to be important deformation mechanisms, whereas deformation-induced martensite formation is of minor importance. Since the stacking fault energy (SFE) is low, ~17 mJ/m{sup 2}, dynamic recovery by cross slip of un-dissociated dislocations is unfavorable. This reduces the annihilation of dislocations which in turn leads to a significant increase of low angle boundaries with increasing strain. The low SFE also favors formation of deformation twins which reduces the slip distance, leading to a hardening similar to the Hall-Petch relation. The combination of a low ability for cross-slip and a reduced slip distance caused by twinning is concluded to be the main reason for maintaining a high strain-hardening rate up to strains close to necking.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Understanding Weld Formation and Microstructure Evolution in Laser Welded Stainless Steels and Ti-6Al-4V

High energy density welding processes are used for many industrial applications, such as aerospace and defense, and certain joint configurations and welding situations render post-weld inspection techniques difficult. Due to the inability to confirm penetration, there is a continual industrial need to improve prediction capabilities to aid in parameter selection. It is also necessary to understand the microstructural evolution to modify phase fractions and mitigate weldability related concerns such as solidification cracking or reduced corrosion performance.

42 ENGINEERING↗
DOE OSTI2017

Microstructure evolution and dynamic recrystallization behavior of a powder metallurgy Ti-22Al-25Nb alloy during hot compression

The flow behavior of a powder metallurgy (P/M) Ti-22Al-25Nb alloy during hot compression tests has been investigated at a strain rate of 0.01 s{sup −1} and a temperature range of 980–1100 °C up to various true strains from 0.1 to 0.9. The effects of deformation temperature and strain on microstructure characterization and nucleation mechanisms of dynamic recrystallization (DRX) were assessed by means of Optical microscope (OM), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) techniques, respectively. The results indicated that the process of DRX was promoted by increasing deformation temperature and strain. By regression analysis, a power exponent relationship between peak stresses and sizes of stable DRX grains was developed. In addition, it is suggested that the discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) controlled nucleation mechanisms for DRX grains operated simultaneously during the whole hot process, and which played the leading role varied with hot process parameters of temperature and strain. It was further demonstrated that the CDRX featured by progressive subgrain rotation was weakened by elevating deformation temperatures. - Highlights: •Flow behavior of a P/M Ti-22Al-25Nb is studied by hot compression tests. •Microstructure evolution of alloy is affected by deformation temperature and strain. •The relationship between peak stress and stable DRX grain size was developed. •The process of DRX was promoted by increasing deformation temperature and strain. •Nucleation mechanisms of DRX were identified by EBSD analysis and TEM observation.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Heavy ion irradiation-induced microstructural evolution in pyrochlore Lu{sub 2}Ti{sub 2}O{sub 7} at room temperature and 723 K

Polycrystalline pyrochlore Lu{sub 2}Ti{sub 2}O{sub 7} pellets were irradiated with 600 keV Kr{sup 3+} at room temperature and 723 K to a fluence of 4×10{sup 15} ions/cm{sup 2}, corresponding to an average ballistic damage dose of 10 displacements per atom in the peak damage region. Irradiation-induced microstructural evolution was examined by grazing incidence X-ray diffraction, and cross-sectional transmission electron microscopy. Incomplete amorphization was observed in the sample irradiated at room temperature due to the formation of nano-crystal which has the identical structure of pyrochlore, and the formation of nano-crystal is attributed to the mechanism of epitaxial recrystallization. However, an ordered pyrochlore phase to a swelling disordered fluorite phase transformation is occurred for the Lu{sub 2}Ti{sub 2}O{sub 7} sample irradiated at 723 K, which is due to the disordering of metal cations and anion vacancies. - Graphical Abstract: Polycrystalline pyrochlore Lu{sub 2}Ti{sub 2}O{sub 7} pellets were irradiated with 600 keV Kr{sup 3+} to a fluence of 4×10{sup 15} ions/cm{sup 2} at room temperature and 723 K, Incomplete amorphization was observed in the sample irradiated at room temperature due to the formation of nano-crystal. However, an ordered pyrochlore phase to a swelling disordered fluorite phase transformation is occurred for the Lu{sub 2}Ti{sub 2}O{sub 7} sample irradiated at 723 K, which is due to the disordering of metal cations and anion vacancies. - Highlights: Pyrochlore Lu{sub 2}Ti{sub 2}O{sub 7} pellets were irradiated by heavy ions at RT and 723 K. At RT irradiation, ~75% of amorphization was achieved. The nano-crystals were formed in the damage layer at RT irradiation. The formed nano-crystals enhanced the radiation tolerance of Lu{sub 2}Ti{sub 2}O{sub 7}. A pyrochlore to fluorite phase transformation was observed at 723 K irradiation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Microstructure Evolution and Mechanical Response of Nanolaminate Composites Irradiated with Helium at Elevated Temperatures

In this paper, we summarize recent work on helium (He) interaction with various heterophase boundaries under high temperature irradiation. We categorize the ion-affected material beneath the He-implanted surface into three regions of depth, based on the He/vacancy ratio. The differing defect structures in these three regions lead to the distinct temperature sensitivity of He-induced microstructure evolution. The effect of He bubbles or voids on material mechanical performance is explored. Finally, overall design guidelines for developing materials where He-induced damage can be mitigated in materials are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Hot Deformation Behavior and Microstructural Evolution of Antibacterial Austenitic Stainless Steel Containing 3.60% Cu

Hot deformation behavior of as-cast antibacterial austenitic stainless steel containing 3.60% copper was investigated in a temperature range of 900-1150 °C and strain rate range of 0.01-20 s{sup −1}. At strain rates higher than 1 s {sup −1}, the flow stress curves were corrected considering adiabatic heating. Kinetic analysis indicated that the hot deformation activation energy of steel was 376.02 kJ mol{sup −1}. The microstructural evolution under different temperatures was observed by optical microscopy. The nucleation sites for recrystallization and different orientations and twin ratios under different strain rates were analyzed by electron backscatter diffraction. The results showed that hot deformation was dominated by continuous dynamic recrystallization in the high-temperature and high-strain-rate region (1050-1150 °C, 1-20 s{sup −1}). On increasing the temperature and strain rate, the degree of recrystallization and twinning increased simultaneously. These phenomena promoted one another. Thus, the volume fraction of the recrystallized and twinned grains increased with the addition of Cu.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Mechanical response and microstructure evolution from multiaxial stress relaxation in textured zircaloy nuclear cladding

Modern energy markets provide motivation for nuclear reactors to increase operational flexibility and load following capacity of existing reactor designs. The operational power changes result in fuel pellet expansion and contraction resulting in pellet-cladding mechanical interaction (PCMI) and high cladding stresses that are strongly related to stressed corrosion cracking (SCC) which can lead to fuel rod failure. This work aims to quantify the stress fields in cladding with a focus on multiaxial stress relaxation response from an imposed strain and the resulting microstructure changes in textured zircaloy claddings. Stress relaxation tests resulting in multiaxial stress fields are performed to measure the material response of Zircaloy-4 nuclear cladding. Multiple experiments using samples from the same piece of cladding are performed so samples with the same processing history may be removed at strategic points throughout mechanical testing for microstructure characterization. The microstructure evolution is analyzed with mechanical response to evaluate the static recovery impact on crystallographic texture and grain morphology. Experiments are performed at Idaho National Laboratory using an experimental device capable of applying internal pressure and independent axial load to commercial nuclear cladding at elevated temperatures with stress- or strain-controlled experimental capability. X-ray diffraction and electron backscatter diffraction are used for microstructure analysis. Rheological models are used to visualize the multiaxial stress-strain relationships and isolate elastic, plastic, and viscoplastic material properties for analysis.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Microstructure evolution and mechanical performance of nickel based superalloy C1023 at elevated temperatures

Highlights: • Growth and strengthening mechanisms of carbide in superalloy C1023 were investigated. • Carbide dendrite primary arm grows selectively based on the vertex of blocky carbonitride. • Monolayer or multilayer carbide dendrite arm has certain crystal relationship with γ′ and γ. • Plastic deformation of γ hinders interior crack propagating from MC to matrix at 650 °C. • Oxidation of GBs significantly weakens the tensile strength of the superalloy at 850 °C. - Abstract: Microstructure evolution of polycrystalline nickel based superalloy C1023 casting was investigated by comparing as cast superalloy and heat treated superalloy in the paper. Influences of strengtheners and carbides on the tensile behaviors of heat treated superalloy at different temperatures (20 °C, 650 °C, and 850 °C) were studied. Resulting data from deep corrosion suggested that growth mode of scripted carbide included nucleation on the vertex of blocky carbonitride, expansion of dendrite arm in C-rich area, and enlargement of dendrite cap. Decomposition of MC carbide generated numerous octahedral M{sub 23}C{sub 6} carbide as well as nanoscale Cr-Mo-rich nuclei. Diffusion of Mo from γ to precipitates such as γ', MC, and M{sub 23}C{sub 6}, occurred during the heat treatment while irregular γ' (4 nm–500 nm) transformed into cuboidal particles. At 650 °C, no significant deterioration of tensile strength was found while plastic deformation ability of γ base was improved. Oxidation of grain boundaries (GBs) dominated the crack behavior of the superalloy at 850 °C.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Analysis of contact conditions and microstructure evolution in shear assisted processing and extrusion using smoothed particle hydrodynamics method

Shear assisted processing and extrusion (ShAPE) is a solid-phase processing technique that adds an additional shear force as compared with a conventional extrusion approach. Recently, ShAPE has demonstrated the capability of extruding high-performance aluminum alloy 7075 (AA7075) tubes at speeds up to 12.2 m/min without surface tearing. However, the relationship among the ShAPE processing parameters, thermomechanical conditions, contact conditions, heat generation, and microstructure evolution remains primarily empirical because an insightful understanding of the associated physics is still lacking. To help elucidate these relationships, this work proposes a thermomechanical meshfree model for the first time for ShAPE processing of AA7075 using the smoothed particle hydrodynamics (SPH) method. The meshfree model is first validated thoroughly by experimental data in terms of material flow, die face temperature, and extrusion force with various processing parameters. The validated model is then used to analyze the steady-state contact conditions and heat generation rates during ShAPE processing. Distributions of the average grain size of AA7075 being extruded are calculated using the SPH model output. The meshfree model results reveal that extrusions conducted at lower temperatures and higher strain rates yield more refined grains and possibly higher material strength, which is also consistent with the experimental observations.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructural evolution of ω assisted α precipitates in β-CEZ alloy during ageing process

Highlights: • Ultrafine Athermal ω precipitates were formed in β-CEZ alloy by quenching from above the β transus temperature. • In the ageing process, these ω precipitates coarsen, accompanied by the form of needle-like α phase. • ω precipitates were formed by {111}β planes shift 0.5d222 along the direction. • The superfine α particles are formed in close proximity of the ω/β interface. - Abstract: The microstructural evolution in β-CEZ (Ti-5Al-2Sn-4Zr-4Mo-2Cr-1Fe wt%) alloy, after quenching and ageing, has been investigated by combining results from orientation imaging microscopy, transmission electron microscopy, high-resolution TEM (HRTEM). Ultrafine Athermal ω precipitates (about 1 nm) are formed in this alloy by quenching from above the β transus temperature. In the ageing process, these ω precipitates coarsen, accompanied by the form of needle-like α phase. The scale of ω assisted α increased from 5 to 10 nm in width and about 50 nm in length to 10 nm in width and 100–300 nm in length while extending ageing time from 2 h to 5 h at 350 °C. However, when going on extending the ageing time from 5 h to 20 h at 350 °C, the scale of α didn't grow dramatically but the density of α increased clearly. When increasing the ageing temperature from 350 °C to 450 °C, the scale of ω assisted α grow dramatically. Furthermore, the structural relationship of ω and α is observed by HRTEM images. It can be found that ω precipitates were formed by {111}β planes shift 0.5d222 along the <111> direction, and the superfine α particles are formed in close proximity of the ω/β interface.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Effect of Impact and Penetration on Microstructural Evolution of High-performance Concretes

Due to the increased concern of public safety in recent years, blast resistance of infrastructures has become an emerging research focus in the cement and concrete industry. Ultra High Performance Concrete (UHPC) with fiber reinforcement usually possesses compressive strengths greater than 200 MPa, which makes them promising candidates for blast-resistant building materials. In the current project, two UHPC materials, Ductal and ERDC-M, were subject to projectile penetration testing. The microstructural evolution due to projectile impact was examined via scanning electron microscopy and X-ray diffraction. Possible phase changes were observed in the impact volume, which was likely a result of the high temperature and high pressure induced by the impact.

Ren, Fei↗