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At least 1,783 records · Page 99

Structural and Magnetic Properties of La{sub 1−x}(Ca,Sr){sub x}MnO{sub 3} Powders Produced by the Hydrothermal Method

La{sub 1−x}(Ca,Sr){sub x}MnO{sub 3} manganites have been produced using the hydrothermal method. The influence of the concentration of La, Ca, and Sr on the structural, morphological, and magnetic properties was studied and analyzed. The X-ray diffraction analysis showed that samples crystallized in rhombohedral or trigonal symmetries depending on the stoichiometry. The morphological analyses obtained by using scanning electron microscopy showed cauliflower-type microstructures in all samples. Energy-dispersive spectroscopy studies were also performed, evidencing not only the presence of the constituent elements but an oxygen deficiency and manganese-relative excess in all the samples. This fact is suggested as the cause of the unusual magnetic behavior where a low-temperature re-entrant phase was observed within the ferromagnetic matrix in some of the samples attributed to spin frustration. Furthermore, for some samples, a critical Curie temperature higher than the reported values is attributed to the relative excess of manganese ions, which can occupy other sites in the lattices as interstices or La, Ca, and Sr sites.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Electrodeposition and Characterization of Cr-MoS{sub 2} Composite Coatings

In this study, Cr-MoS{sub 2} composite coatings were electrodeposited from conventional Cr{sup +6} baths containing different amounts of MoS{sub 2} particles and various types of surfactant (cationic and anionic). The effect of bath chemical composition on the coatings properties like their microstructure, morphology, chemical composition, corrosion behavior, surface roughness and microhardness was investigated using x-ray diffraction, scanning electron microscopy (SEM), energy-dispersive x-ray analysis, potentiodynamic polarization, electrochemical impedance spectroscopy, surface profilometry and Vickers microhardness measurement techniques, respectively. The results showed that incorporation of MoS{sub 2} particles into the composite coatings is very limited and Cr matrix with very low crystallinity will be electrodeposited at various experimental conditions. The presence of MoS{sub 2} particles in the bath (up to an optimum value) leads to the formation of the composite coatings with lower surface roughness values than that of conventional chromium coating. Although more MoS{sub 2} particles will be incorporated into the electrodeposits when the solid content of the bath increases, chromium cannot be electrodeposited from baths containing high amounts of MoS{sub 2} particles. Application of cationic surfactant promotes incorporation of particles into the Cr metallic matrix. Moreover, the presence of surfactant in the bath results in the formation of coatings with less microcracks. All the composite coatings have more hardness values than that of conventional chromium coating; maximum hardness is attributed to the coatings that were electrodeposited from baths containing no surfactant. The corrosion test results revealed that the smooth coatings containing more MoS{sub 2} particles and less microcracks exhibit more corrosion resistance than the other ones.

36 MATERIALS SCIENCE↗

Development of Pore-Free Ti-Si-C MAX/Al-Si Composite Materials Manufactured by Squeeze Casting Infiltration

Open-porous MAX phase skeletons from Ti{sub 3}SiC{sub 2} were manufactured by Microwave-Assisted Self-propagating High-temperature Synthesis (MASHS) and subsequently subjected to squeeze casting infiltration with an Al-Si lightweight casting alloy (EN AC-44200). This alloy was chosen due to its high flowability, corrosion resistance and good machinability. The manufactured composites, together with a reference sample of the original alloy, underwent testing of thermal properties, including thermal conductivity and diffusivity, specific heat and thermal expansion in the temperature range 50-500 °C, which corresponds to the expected working temperatures of the material. The fabricated AlSi/Ti{sub 3}SiC{sub 2} composites have significantly increased thermal stability, with coefficients of thermal expansion (approximately 10-11 × 10{sup −6} °C{sup −1}) half that of the original alloy. As regards mechanical properties, the instrumental Young’s modulus and Vickers hardness of the composite materials are 170.8 and 8.5 GPa, respectively. Moreover, the microstructure and phase composition, structural defects and potential impacts between constituents of the manufactured composites were characterized using SEM, TEM and STEM microscopy and EDS and XRD analysis.

36 MATERIALS SCIENCE↗

Probing basal planes and edge sites in polygranular nuclear graphite by gas adsorption: Estimation of active surface area

Polygranular nuclear graphite, manufactured at 2800–3000 °C from a carbonized filler and binder mix, has high graphitization degree, crystalline structure close to perfect graphite, and about 20% porosity. The pore surfaces expose large regions of rough, defective prismatic edges of graphite crystallites which are the locus of graphite materials surface sites active for oxidation, chemisorption, and electron transfer. However, we show that high-resolution N 2 and Kr first monolayer adsorption on polygranular graphite (P/P 0 < 0.015) occurs in many ways like adsorption on graphitized carbon blacks. This proves the presence of energetically homogeneous basal planes domains in graphite porosity, which was not fully acknowledged before. Using classical analysis methods (Langmuir, Hill-de Boer, adsorption potential distribution) we quantity the basal plane area (BPA) of several polygranular graphite types and correlate it with their microstructure. Finally, we propose that gas adsorption is uniquely positioned to reliably estimate the active surface area of graphite by subtracting BPA from the BET total surface area. Direct estimation based on adsorption is preferable to indirect calculations based on microstructural information.

36 MATERIALS SCIENCE↗

Major trends and roadblocks in CFD-aided process intensification of biomass pyrolysis

Process intensification is critical to increase product yields and reduce external power consumption in biomass pyrolysis. Computational fluid dynamics offers great possibilities for fast and economical process intensification of biomass pyrolysis. This succinct but in-depth current-perspective feature article discusses the major trends and roadblocks with respect to CFD-aided process intensification of biomass pyrolysis. Major trends such as multiscale coupling, fast parametric analysis and design, and coupling between CFD and process modeling, are reviewed. Major roadblocks such as lack of accurate chemical kinetics, and difficulty in accurate description of microstructural change, are pointed out. In conclusion, it is believed that the clarification of these directions and problems will lead to a more objective but efficient application of CFD to process intensification of biomass pyrolysis.

09 BIOMASS FUELS↗

A molecular dynamics survey study of impact-induced amorphization in yttria nanoparticles

The impact of a single yttria (Y 2 O 3 ) nanoparticle onto a yttria substrate was studied as a function of particle velocity (300–1200 m/s) and diameter (5–12 nm) for three particle orientations and two substrate orientations using molecular dynamics simulations. Impacts resulted in minimal dislocation motion but extensive disordering of the crystal lattice without approaching the melting temperature. The resulting amorphous microstructure was both precisely coincident with plastic strain and retained until the end of the simulation, suggesting a deformation mechanism of amorphization-facilitated viscous flow. Further analysis revealed that the degree of amorphization depended primarily on the impact velocity and secondarily on the orientations of the particle and substrate, with significant second-order effects from variable interactions.

74 ATOMIC AND MOLECULAR PHYSICS↗

Impact of titanium content on the thermo-mechanical and oxidation response of TiAlTa

This study aimed to analyze how the addition of titanium (Ti) to TiAlTa alloys affects their mechanical properties (Young’s modulus and hardness) and oxidation behavior. Alloys with three different Ti additions and equi-atomic Al and Ta were fabricated with nominal compositions of 33Ti-33Al-33Ta at%, 50Ti-25Al-25Ta at%, and 70Ti-15Al-15Ta at%. Phase identification of as-processed and compositionally homogenized alloys was conducted by coupling various electron microscopy, diffraction, and chemical analysis techniques. Composition and structures were modeled using CALPHAD-based phase predictions and compared with experimental results. Each of the alloys exhibited a unique set of microstructures with distinctly different ordered precipitates, dependent on cooling rate and chemical composition. Subsequently, nanoindentation tests were performed at temperatures of 25°C, 250°C, 500°C, and 750°C. Oxidation studies were conducted under static air at 750°C for up to 200 h. 33Ti-33Al-33Ta at% and 70Ti-15Al-15Ta at% alloys showed higher hardness and modulus than 50Ti-25Al-25Ta at% at room temperature. The 50Ti-25Al-25Ta at% alloy exhibited higher hardness and modulus values but lower oxidation resistance at 750°C when compared with the other specimens. The X-ray photoelectron spectroscopy experiments were conducted to further analyze the oxides present in the samples. Despite each sample displaying combinations of mixed oxide layers, TiO 2 was the preferred oxide forming in the 50Ti-25Al-25Ta composition, while the other samples preferred to form Al 2 O 3 . In conclusion, the findings from this systematic exploration of phase evolution in the TiAlTa alloy space provide insights for optimized material chemistries, processing, and properties.

36 MATERIALS SCIENCE↗

Enhanced stimulated emission in ZnO thin films using microdisk top-down structuring

Microdisks were fabricated in zinc oxide (ZnO) thin films using a top-down approach combining electron beam lithography and reactive ion etching. These microdisk structured thin films exhibit a stimulated surface emission between 3 and 7 times higher than that from a reference film depending on the excitation power density. Emission peak narrowing, reduction in lasing threshold and blue-shifting of the emission wavelength were observed along with enhancement in the emitted intensity. Results indicate that this enhancement is due to an increase in the internal quantum efficiency combined with an amplification of the stimulated emission. An analysis in terms of waveguiding is presented in order to explain these effects. These results demonstrate that very significant gains in emission can be obtained through conventional microstructuration without the need for more onerous top-down nanostructuration techniques.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Aluminium composites prepared by laser cladding assisted by friction stir processing

Abstract A laser cladding and friction stir processing hybrid method was employed to produce an Al matrix composite layer. The microstructure, phase composition, microhardness and conductivity of the composites were investigated. A laser cladding layer with a thickness of approximately 200 μ m was prepared on a 1060 aluminium plate and it was broken up and distributed on the Al matrix after friction stir processing. The particle/Al interfaces exhibited extremely good interfacial integrity. Microstructural observations revealed that an obvious in situ reaction occurred at the particle/Al interfaces, which effectively improved the bonding between the reinforcement phase and the matrix. TEM analysis and selected area diffraction enabled the identification of the intermetallic compounds and confirmed them to be Al 5 Fe 2 and Al 3 Fe. The average microhardness values of the friction stir processed composites reached approximately 85 HV. The electrical resistivity of the friction stir processed composites is slightly higher than that of the aluminium matrix.

Wei, Yanni (ORCID:0000000244443642)↗

Materials Challenges and Opportunities for Energy Generation, Conversion, Delivery, and Storage (Applied Energy Tri-Laboratory Consortium Workshop Report)

This report documents the outcomes of the Tri-Laboratory Materials Workshop that was held July 31 and August 1, 2019 to begin addressing the needs, opportunities, and challenges associated with the development, fabrication, and testing of the needed materials and components for integrated hybrid energy systems (i.e., incorporating nuclear, fossil, and renewables for electric and thermal applications). This was accomplished by assembling the research program leads and principal investigators at Idaho National Laboratory (INL), National Energy Technology Laboratory (NETL), and National Renewable Energy Laboratory (NREL), who support the research and development of new technology and system integration. The team then identified and prioritized key materials development needs. This effort was intended to enhance communications and synergy among the Tri-Lab partners. Advanced functional and structural materials are central to transformative energy technologies for energy generation, conversion, delivery, and storage. With that in mind, the workshop focused on identifying and assessing the foundational materials research needs at both the basic and applied levels. Materials challenges include the ability to withstand harsh environments, such as high temperatures and pressures, corrosion, oxidation, or irradiation while maintaining flexible mission profiles and long service lifespans. Advanced energy system material challenges and needs range from materials for the capture, upgrading/concentration, storage, and delivery of low-grade heat to materials for high temperature environments that involve liquid metals, molten salt, and very high temperature gas heat delivery and storage systems. Material improvements are needed for hybrid energy systems due to accelerated corrosion and stress-fatigue failure of materials and equipment, which results from increased frequency and amplitude of thermal, mechanical, and electrical cycling of systems components. Multifunctional materials are needed for high temperature solid-oxide fuel cells, advanced electrochemical reactors, and in-process separation. Relative to materials manufacturing, application of advanced additive and subtractive methods need to be understood to develop both thin-layer homogenous materials and materials of graded composition. Materials modeling and machine learning will be critical to accelerate the design and production of power electronics, and nuclear reactor materials and fuel, as well as to gain an understanding of beneficial materials phenomena or deleterious microstructure evolution. There is also a need for standardized models, computational structures, data reporting protocols and modeling tools across the three laboratories. This would allow consistent results, analysis, and data sharing. Combining computational capabilities between the three laboratories (e.g., hardware, software) would greatly increase computational capabilities and throughput. The workshop identified the need for laboratories to anticipate and address problems that will occur during scale-up. Laboratory work must connect with industry to ensure that research focuses on processes that are scalable and marketable. Industry input and perspective are essential to guide laboratory research to meet these requirements and deploy new technology in industrial demonstrations. Another aspect of scale-up is the integration of multiple systems since new challenges often arise at the subsystem interfaces. Establishing a scale-up manufacturing demonstration/pilot plant, potentially as an industrial user facility, would be beneficial to the laboratories and industry. That modular scale-up manufacturing demonstration/pilot plant would allow researchers to find and resolve interface problems that cannot be identified by focusing only on individual parts. Communication exchanges among the organizers, attendees, and workshop survey responses indicate that the workshop was successful in achieving its goal to identify key technology gaps and research needs. Strong positive feedback was received on the sharing of ideas, capabilities, talent, and passion to move forward on the materials-related action items.

36 MATERIALS SCIENCE↗

Atom Probe characterization of neutron irradiated commercial ZIRLO® and AXIOM X2® alloys

As part of the Mechanistic Understanding of ZIrconium Corrosion (MUZIC) program, this team has been instrumental to obtain EPRI and Westinghouse sponsorships to prepare the neutron irradiated ZIRLO® and X2® from Vogtle nuclear power plant and ship them from Studsvik’s (Sweden) hot cells to Idaho National Laboratory (INL) to be part of the NSUF library. The uniqueness of these sets of neutron irradiated alloys is that they are at the same two extremes of the fuel cycles, allowing us to study the microchemistry evolution as a function of irradiation doses, exposure time and solute content. Advanced commercial Zirconium-Niobium (Zr-Nb) alloys, such as ZIRLO® and AXIOM®, have been developed by Westinghouse to enhance the corrosion resistance of fuel cladding material for longer service time. This study specifically aims at investigating the neutron irradiation induced Nb redistribution in AXIOM® X2® to understand the effect of neutron irradiation induced microchemistry changes and the irradiation enhanced corrosion resistance observed in ZrNb alloys. The detailed sample information on chemical composition and irradiation is given in shown in Table 1a and 1b respectively. To study the neutron IIP/nanoclusters and Nb concentration in the solid solution, atom probe tomography (APT) is the primary tool to obtain reliable chemical information. APT specimens were prepared in shielded focused ion beam (FIB) at the Irradiated Materials Characterization Laboratory (IMCL) at INL followed by APT analysis at CAES facility using LEAP 4000XR

36 MATERIALS SCIENCE↗

Harvesting Reactor Pressure Vessel Beltline Material from the Decommissioned Zion Nuclear Power Plant Unit 1

The decommissioning of the Zion Nuclear Power Plant (NPP) provided a unique opportunity to harvest and study service-aged reactor pressure vessel (RPV) beltline materials. This work, conducted through the U.S. Department of Energy’s Light Water Reactor Sustainability (LWRS) Program, aims to improve the understanding of radiation-induced embrittlement to support extended nuclear plant operations. Material segments containing the Linde 80 flux, wire heat 72105 (WF-70) beltline weld and the A533B Heat B7835-1 base metal, obtained from the intermediate shell region with a peak fluence of 0.7 × 10 19 n/cm 2 (E > 1.0 MeV), were extracted, cut into blocks, and machined into test specimens for mechanical and microstructural characterization. The segmentation process involved oxy-propane torch-cutting, followed by precision machining using wire saws and electrical discharge machining (EDM). A chemical composition analysis confirmed the expected variations in alloying elements, with copper levels being notably higher in the weld metal. The harvested specimens enable a detailed evaluation of through-wall embrittlement gradients, a comparison with the existing surveillance data, and the validation of predictive embrittlement models. This study provides critical data for assessing long-term reactor vessel integrity, informing aging-management strategies, and supporting regulatory decisions to extend the life of nuclear plants. This article is a revised and expanded version of a paper entitled, “Current Status of the Characterization of RPV Materials Harvested from the Decommissioned Zion Unit 1 Nuclear Power Plant”, PVP2017-65090, which was accepted and presented at the ASME 2017 Pressure Vessels and Piping Conference, Waikoloa, HI, USA, 16–20 July 2017.

harvesting beltline material↗

Tensile behavior and microstructural evolution of a Fe-25Ni-20Cr austenitic stainless steel (alloy 709) from room to elevated temperatures through in-situ synchrotron X-ray diffraction characterization and transmission electron microscopy

Uniaxial tensile tests were done on Fe-25Ni-20Cr Austenitic Stainless Steel (Alloy 709) along with in-situ synchrotron measurement at different temperatures (25 degrees C, 500 degrees C, 700 degrees C and 900 degrees C). The X-Ray diffraction data was collected in-situ in order to follow the phases present as well as to derive the dislocation density as a function of strain through peak broadening analysis based on the modified Williamson-Hall method and see how trends are affected as a function of temperature. The XRD data were complemented by TEM and STEM-EDX characterization done on the post-experiment samples to observe the deformed microstructures. Finally, the paper presents a depiction of the tensile behavior of this advanced steel by interpreting the stress-strain curves and the effect of temperature through the information gained by in-situ XRD and TEM observations as well as fractography done ex-situ on the samples tested to rupture.

36 MATERIALS SCIENCE↗

Ultrasonic deagglomeration of aluminum nanopowders with multi-walled carbon nanotube mixtures

Comprehensive investigations of aluminum nanopowders, multi-walled carbon nanotubes, and aluminum mixtures with multi-walled carbon nanotubes subjected to ultrasonic deagglomeration in a liquid medium were performed, using microstructural, X-ray diffraction, thermogravimetric, and calorimetric analyses, and specific surface area measurements. The regime of ultrasonic deagglomeration of aluminum nanopowders with multi-walled carbon nanotubes in a liquid medium is described, during which the division of large agglomerates and creation of homogeneous distribution of mixtures components in the volume takes place. It was determined that ultrasonic treatment influences the morphology and crystalline structure of investigated mixtures, contributes to the appearance of X-ray amorphous phase, decreases the specific surface area of the aluminum nanopowder from 13 to 12 m{sup 2}/g, and increases the pore volume and average size from 0.04 to 0.06 cm{sup 3}/g and from 12 to 19 nm, respectively. The size of coherently-diffracting domain was determined by the X-ray diffraction analysis is close to that estimated from the specific surface area and corresponds to average crystallites size in the materials under study.

36 MATERIALS SCIENCE↗

3D Bragg Coherent Diffraction Imaging of Extended Nanowires: Defect Formation in Highly Strained InGaAs Quantum Wells

InGaAs quantum wells embedded in GaAs nanowires can serve as compact near-infrared emitters for direct integration onto Si complementary metal oxide semiconductor technology. While the core–shell geometry in principle allows for a greater tuning of composition and emission, especially farther into the infrared, the practical limits of elastic strain accommodation in quantum wells on multifaceted nanowires have not been established. One barrier to progress is the difficulty of directly comparing the emission characteristics and the precise microstructure of a single nanowire. Here, in this study, we report an approach to correlating quantum well morphology, strain, defects, and emission to understand the limits of elastic strain accommodation in nanowire quantum wells specific to their geometry. We realize full 3D Bragg coherent diffraction imaging (BCDI) of intact quantum wells on vertically oriented epitaxial nanowires, which enables direct correlation with single-nanowire photoluminescence. By growing In 0.2 Ga 0.8 As quantum wells of distinct thicknesses on different facets of the same nanowire, we identified the critical thickness at which defects are nucleated. A correlation with a traditional transmission electron microscopy analysis confirms that BCDI can image the extended structure of defects. Finite element simulations of electron and hole states explain the emission characteristics arising from strained and partially relaxed regions. This approach, imaging the 3D strain and microstructure of intact nanowire core–shell structures with application-relevant dimensions, can aid the development of predictive models that enable the design of new compact infrared emitters.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Multiscale Modeling of Microstructural Evolution in Fused-Coating Additive Manufacturing

A quantitative phase field model with adaptive-computational-domain-expansion (ACDE) method was developed to simulate the microstructural evolution in fused-coating additive manufacturing process. A heat transfer and fluid flow model was established to investigate the solidification behavior of the molten pool in a single deposited layer. The solidification parameters such as temperature gradient and solidification rate were calculated from the macroscopic model and then fed into the phase field model to get the microstructure at different positions within a single deposited layer. Columnar dendrites were formed at the bottom of the deposited layer, and equiaxed dendrites appeared in the upper part of the layer. The ACDE method is used to improve the simulation efficiency. The metallographic experiments and energy-dispersive spectrometer analysis for composition were conducted on the fused-coating specimen, and the results were in good accordance with the simulations.

36 MATERIALS SCIENCE↗

Critical statistical assessment of data in metal additive manufacturing

Obtaining high quality data reflecting the relationships between the additive manufacturing (AM) process parameters, material microstructure and mechanical properties is crucial for the use of machine learning in AM. A database of over 4,000 data entries of metal AM was created thanks to a large number of literature studies on key process parameters and indicators of build quality. Meta-analysis reveals critical biases in the literature. Firstly, majority of studies report only high quality builds, these imbalances in reporting result in weak correlation between process parameters, properties and consolidation, limiting the ability of machine learning models to generalize beyond optimized conditions. Nevertheless, the trained models accurately predict yield strength ($R^2 = 0.85$), suggesting that certain process–property relationships are effectively captured within these models. Secondly, quantitative microstructural data are largely absent, limiting the learning of the microstructure-mechanical properties relationships. Finally, current process window identification is based largely on the consolidation, despite significant uncertainty in its measurement. It is important to identify the process map on the basis of not only the consolidation, but also mechanical behaviour under loading. Such a identification shows that 316 L and Inconel have much larger process map (i.e. highly printable) in comparison to the AlSi10Mg and Ti6Al4V.

Additive manufacturing↗

Impedance characteristics and PTCR effect in lead free BaTi1-xSnxO3 piezoceramics

Highlights: • The maximum d{sub 33} = 296 pC/N and P{sub r} = 6.92 μC/cm{sup 2} is observed for x = 0.08. • Nyquist plots reveal non-Debye type relaxation behavior of the samples. • Impedance studies indicate a possible correlation between d{sub 33} and microstructure. • Positive temperature coefficient of resistance (PTCR) is seen just above T{sub C}. - Abstract: BaTi{sub 1-x}Sn{sub x}O{sub 3} of compositions x = 0.07, 0.08, 0.09, 0.10 and 0.11 are synthesized to study their piezoelectric and impedance characteristics. The studies revealed that the composition x = 0.08 exhibits the maximum piezoelectric coefficient (d{sub 33} = 296 pC/N) and remnant polarization (P{sub r} = 6.92 μC/cm{sup 2}) values. The impedance analysis showed that the depressed semi-circular arc observed in the Nyquist’s plots gave evidence for the existence of non-Debye type relaxation behavior in the compounds. The impedance studies suggested a possible correlation between the d{sub 33} and microstructural properties. The activation energies extracted from ac conductivity plots strongly indicate the existence of defect dipole assisted conductivity mechanism in the samples. Notably, the samples displayed positive temperature coefficient of resistance (PTCR) just above their ferroelectric transition. The frequency dependent ac conductivity follows the Jonscher’s universal power law. The dominant conduction mechanism in the samples is determined to be the small polaron hopping mechanism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗