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The residual stresses in a dense yttria‐stabilized zirconia (YSZ) layer bonded to a porous NiO‐YSZ substrate were measured by X‐ray diffraction in air between 25°C and 900°C. It was found that the residual stresses on the outer surface of the YSZ layer were compressive, that their magnitude increased with decreasing temperature, and that the temperature dependence was nonlinear particularly at temperatures below 600°C. An elastic model that incorporates micromechanics and laminate theory was formulated to successfully predicts the nonlinearity of the temperature dependence of the residual stresses by accounting for the effect of the order‐disorder transition experienced by YSZ around 600°C and the magnetic transition of NiO at the Néel temperature around 265°C, on the properties of these materials. The implications of the results for the reliability of solid oxide fuel cells are discussed. [ABSTRACT FROM AUTHOR]

Internal short circuit of large-format Li-ion pouch cells induced by mechanical abuse was simulated using a modified mechanical pinch test. A torsion force was added manually at ∼40% maximum compressive loading force during the pinch test. The cell was twisted about 5° to the side by horizontally pulling a wire attached to the anode tab. The combined torsion-compression force created small failure at the separator yet allowed testing of fully charged large format Li-ion cells without triggering thermal runaway. Two types of commercial cells were tested using 4–6 cells at each state-of-charge (SOC). Commercially available 18 Ahr LiFePO 4 (LFP) and 25 Ahr Li(NiMnCo) 1/3 O 2 (NMC) cells were tested, and a thermal runaway risk (TRR) score system was used to evaluate the safety of the cells under the same testing conditions. The aim was to provide the cell manufacturers and end users with a tool to compare different designs and safety features. [ABSTRACT FROM AUTHOR]

The physical and mechanical properties of two barium alkali silicate glasses were determined as a function of temperature. Their Young's modulus and Poisson's ratio were determined by resonant ultrasound spectroscopy; their viscosity, thermal expansion, and glass transition temperature were determined using a thermomechanical analyzer. The wetting behavior of the two glasses on alumina and 8 mol% yttria stabilized zirconia (8 YSZ) substrates was determined by measuring contact angles in air as a function of temperature and time. Values of Young's modulus for both glasses were in good agreement with those predicted by the Makishima and MacKenzie model. The physical and mechanical properties of these glasses are discussed in the context of their potential use for sealing applications in solid-oxide fuel cells. [ABSTRACT FROM AUTHOR]

The properties that determine the thermal shock resistance in materials are reported for porous cordierite, a leading candidate material for the fabrication of diesel particulate filters. Fracture toughness and slow crack growth tests were performed on test specimens obtained from the walls of diesel particulate filter monolithic substrates using the double-torsion test method at temperatures between 20°C and 900°C. The thermal expansion and elastic properties were characterized between 20°C and 1000°C. The role of the microstructure of porous cordierite in determining its unusual thermal expansion and elevated temperature Young's modulus and fracture toughness are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Lightweight, robust woven graphite-fiber structures were developed for heat exchangers which provide high conductivity paths along the direction of the graphite fibers. These structures were produced and characterized for air permeability/pressure drop and thermal (heat transfer) performance. Results indicate that the materials are suitable for use in ultra-light weight heat exchanger applications such as vehicle radiators or other areas where light weight, compact, conformable heat transfer devices are needed. [Copyright &y& Elsevier]

Abstract: The fatigue crack growth process involves damage accumulation and crack extension. The two sub-processes that lead to fatigue crack extension were quantified separately in a recent model for small fatigue crack growth applicable to engineering alloys. Here, we report the results of an experimental investigation to assess the assumptions of that model. The fatigue striation formation in an aluminum alloy is modeled, and it is verified that the number of cycles required for striation formation is related to the cyclic crack-tip opening displacement. The striation spacing is related to the value of the monotonic crack-tip displacement. It is concluded that extensive crack-tip geometry changes due to plasticity in the aluminum alloy causes a reduction in the slope of the fatigue crack propagation curves. The implications of these results on the fatigue crack propagation lifetime calculations are identified. [Copyright &y& Elsevier]

Test procedures for the mechanical evaluation of diesel particulate filter (DPF) substrate materials have been developed and applied for the characterization of porous cordierite under ambient conditions. Specifically the double-torsion test method was employed to characterize fracture toughness and slow crack behavior while resonant ultrasound spectroscopy (RUS) was used to determine the elastic properties of the substrate walls. A dry grinding procedure was developed to fabricate test specimens for these tests. The fracture behavior of porous cordierite was related to the pore structure inside the filter wall. Implications of the test results on the mechanical reliability of DPFs are discussed. [ABSTRACT FROM AUTHOR]

Due to the increase in power demand and limited investment in new infrastructure, existing overhead power transmission lines often need to operate at temperatures higher than those used for the original design criteria. This has led to the accelerated aging and degradation of splice connectors, which have been manifested by the formation of hotspots that have been revealed by infrared imaging during inspection. The implications of connector aging is twofold: 1) significant increase in resistivity of the splice connector (i.e., less efficient transmission of electricity) and 2) significant reduction in the connector clamping strength, which could ultimately result in separation of the power transmission line at the joint. Therefore, the splice connector appears to be the weakest link in the electric power transmission lines. This paper presents a protocol for integrating analytical and experimental approaches to evaluate the integrity of a full tension single-stage splice connector assembly. [ABSTRACT FROM AUTHOR]

The changes in porosity and elastic moduli of YSZ-containing nickel-based anode materials for solid oxide fuel cells were studied as a function of the fraction of reduced NiO. Anode samples were reduced in a gas mixture of 4% hydrogen and 96% argon for different periods of time at 800°C and their Young's and shear moduli were determined afterward at room temperature using resonant ultrasound spectroscopy and line pulse excitation. It was found that the magnitude of Young's and shear moduli decreased significantly with increasing fraction of reduced NiO and that the magnitude of the elastic moduli of a fully reduced Ni--YSZ anode was ∼45% lower than that of unreduced NiO--YSZ. Because the elastic moduli of NiO are close to those of Ni, the observed decrease in the magnitude of the elastic moduli was found to be caused mainly by the significant increase in the porosity of the sample as a result of NiO reduction. Expressions are presented for the amount of porosity and the magnitude of the elastic moduli as a (unction of the fraction of reduced NiO. [ABSTRACT FROM AUTHOR]

The mechanical behavior and cracking patterns of thermally‐shocked additively manufactured alumina were investigated. The flexural strength of test specimens that had been heated to temperatures ranging from 200°C to 1000°C and then rapidly quenched in water was determined at ambient temperature by four‐point bending. Results indicated that the surface cracking patterns had a multifractal structure and that an increase in the thermal shock temperature led to an increase in the density and uniformity of the crack network. The flexural strength results were analyzed with Weibull statistics, where the Weibull moduli for most of the thermal shock conditions tested were found to be statistically indistinguishable. It was also found that a significant decrease (∼50%) in flexural strength occurred for heating temperatures ≥300°C. The effect of the manufacturing method on cracking patterns is discussed, as well as the implication of the material behavior for practical applications of these materials. [ABSTRACT FROM AUTHOR]

Examines the effect of oxidation on the stress-rupture behavior of fiber bundles with focus on engineering. Relationship between tensile strength distributions for bundles and the constituent fibers; Why the performance of nonoxide Continuous Fiber-reinforced Ceramic Composites is limited; Results and discussion.

This paper describes results from the mechanical evaluation of unirradiated SiC fiber–reinforced SiC matrix composite tubes under a controlled high-temperature steam environment. The experiments were aimed at identifying key material degradation behavior under environments relevant to loss-of-coolant accidents of light water reactors. Mechanical tests of the SiC composite tubes at 1000 °C under steam and inert environments were conducted using a unique test capability. The material tested was a duplex tube with a thick monolithic SiC layer on the outer surface. The tubes were subjected to preloading at ∼100 MPa in tension before exposure to high-temperature steam with up to 75 % of the preload at a constant displacement. In the presence of matrix cracks, the steam exposure caused embrittlement of the SiC composite tubes and failure at a stress level below the pretest stress. The material degradation was explained by a fiber oxidation model, which can be applied to various SiC cladding concepts. The embrittlement could be a limiting factor for using SiC cladding subjected to loss-of-coolant accident conditions. [ABSTRACT FROM AUTHOR]

We report the physical and mechanical properties of ceramic composite materials fabricated by binder jet 3D printing (BJ3DP) with silicon carbide (SiC) powders, followed by phenolic resin infiltration and pyrolysis (IP) to generate carbon, and a final reactive silicon melt infiltration step. After two phenolic resin infiltration and pyrolysis cycles; porosity was less than 2%, Young's modulus was close to 300 GPa, and the flexural strength was 517.6 ± 24.8 MPa. However, diminishing returns were obtained after more than two phenolic resin infiltration and pyrolysis cycles as surface pores in carbon were closed upon the formation of SiC, resulting in reaction choking and residual‐free carbon and porosity. The instantaneous coefficient of thermal expansion of the composite was found to be independent of the number of phenolic IP cycles and had values of between 4.2 and 5.0 ppm/°C between 300 and 1000℃, whereas the thermal conductivity was found to have a weak dependence on the number of phenolic IP cycles. While the manufacturing procedures described here yielded highly dense, gas impermeable, siliconized SiC composites with properties comparable to those of bulk siliconized silicon carbide processed according to conventional techniques, BJ3DP enables the manufacture of objects with complex shape, unlike conventional techniques. [ABSTRACT FROM AUTHOR]

Carbide/refractory metal cermets possess attractive combinations of thermal and mechanical properties for ultra-high temperature structural applications. Using a high-throughput computational thermodynamic approach, 16 carbide/refractory metal cermet systems were identified, out of 1808 possible combinations, that could be fabricated by the displacive compensation of porosity (DCP) method using molten copper alloys as infiltrators at 1300 °C. Experimental results for ZrC/W and ZrC/Mo, and other proposed systems in the literature provide a level of validation to this approach. We found that copper alloys are more suitable for DCP than aluminum alloys owing to the low melting temperature of copper alloys (e.g., Zr 2 Cu and Ti 2 Cu), and the minimal chemical reaction as well as very limited mutual solid solubility of copper with refractory metals. Our results show that high-throughput thermodynamics calculation is a robust approach for systematically and thoroughly identifying refractory metal cermets that are suitable for DCP. Image 1 [ABSTRACT FROM AUTHOR]

The thermal expansion of a thermally sprayed coating material is an important design-relevant property from both processing and application service points of view. High thermal stresses and residual strains can arise during deposition, and thermal exposure in service. The linkage to process conditions which can impact both physical and chemical attributes of the microstructure and consequently its expansion behavior is of great importance. The observed dilation response of various coatings is discussed based on the processing effects that induce differences in microstructural features and the impact of residual strain and annealing of defects on the dilation behavior during first thermal exposure. The coefficient of thermal expansion (CTE) of coatings was found to approach the bulk when the material is not sensitive to oxidation in-flight. For those materials sensitive to oxidation, mathematical models used to describe effective properties of composite materials were adopted to describe the CTE property. A large irreversible dilation change was found in the first heating cycle due to defect annealing (referred to as thermal shakedown). Several reasons are hypothesized for the magnitude of such dilation change. Together, the paper presents a comprehensive analysis of thermal expansion behavior of a diversity of thermal spray processed materials. [ABSTRACT FROM AUTHOR]

A key consideration for the successful operation of hybrid energy systems will be the environmental stability of materials used for their construction, particularly when experiencing service environments containing water vapor at high temperatures. Here, we report results from the characterization of siliconized silicon carbide (Si‐SiC) prepared via binder jet additive manufacturing and reactive silicon melt infiltration after being exposed to environments representative of those in solid oxide fuel cell (SOFC) anodes, and to exhaust gases inside a microturbine operating on natural gas. In both cases, it was found that oxide scales formed on the surface and that these scales were dense, continuous, and well‐bonded to the substrates, although there was evidence of transverse and longitudinal cracking most likely as a result of mismatches in the thermal expansion of the scale and the substrate. Measured values of the thickness of the oxide scale were compared to those predicted by parabolic oxidation kinetics of silicon, but the potential effects of silica volatilization induced by water vapor, and silica reduction when exposed to hydrogen are discussed. The overall results showed that the oxide scale is expected to be protective under the conditions of hybrid power generation systems. [ABSTRACT FROM AUTHOR]

In this paper, we study the elastic properties of the entropy-stabilized oxide (Mg, Co, Ni, Cu, Zn)O using experimental and first principles techniques. Our measurements of the indentation modulus on grains with a wide range of crystallographic orientations of the entropy-stabilized oxide revealed a high degree of elastic isotropy at ambient conditions. First principles calculations predict mild elastic anisotropy for the paramagnetic structure, which decreases when the system is considered to be non-magnetic. When the antiferromagnetic state of CoO, CuO, and NiO is accounted for in the calculations, a slight increase in elastic anisotropy is observed, suggesting a coupling between magnetic ordering and the orientation dependent elastic properties. Furthermore, an examination of the local structure reveals that the isotropy is favored through local ionic distortions of Cu and Zn—due to their tendencies to form tenorite and wurtzite phases. The relationships between the elastic properties of the multicomponent oxide and those of its constituent binary oxides are reviewed. These insights open up new avenues for controlling isotropy for technological applications through tuning composition and structure in the entropy-stabilized oxide or the high-entropy compounds in general. [ABSTRACT FROM AUTHOR]

Polymeric heat exchangers (PHXs) have been used in applications involving weight restrictions, chemical compatibility, and fouling issues. Additive manufacturing (AM) or 3D printing provide new solutions to previously inaccessible combinations of properties and geometries. There are some advancements in the PHXs by AM; however, the process and the properties of materials still need further investigation to improve the overall performance. In this study, additively manufactured polyethylene terephthalate glycol (PETG) composites reinforced with graphite and pitch-based carbon fibers were evaluated for their potential application as PHXs. The thermal conductivity, volumetric heat capacity, coefficient of thermal expansion, creep behavior, and long-term performance were studied in detail. Our results reveal that the composites have an anisotropic thermal conductivity. The thermal conductivity along the printing direction is higher than the layer building direction due to the shear-induced alignment of the fillers. The printed composites achieve good thermal stability with 80% lower CTE at room temperature than neat PETG. Creep tests suggest the creep and creep recovery were highly temperature-dependent, and the deformation can be recovered when the temperature is below glass transition. These results suggest additive manufactured composites be potentially used for heat exchanger applications at low temperatures. [ABSTRACT FROM AUTHOR]

SiC‐fiber–reinforced SiC matrix composite cladding for light water reactor fuel elements must withstand high‐temperature steam oxidation in a loss‐of‐coolant accident scenario (LOCA). Current composite designs include an outer monolithic SiC layer, in part, to increase steam oxidation resistance. However, it is not clear how such a structure would behave under high‐temperature steam in the case when the monolithic layer cracks and carbon interphases and SiC fibers are exposed to the environment. To fill this knowledge gap, stress‐rupture tests of prototypic SiC composite cladding at 1000°C under steam and inert environments were conducted. The applied stress was ∼120 MPa, which was beyond the initial cracking stress. The failure lifetime under steam was 400–1300 s, while 75% of the composite specimens did not fail after 3 h of total exposure under inert gases. Microstructural observations suggest that steam oxidation activated slow crack growth in the fibers, which led to failure of the composite. The results from this study suggest that stress rupture in steam environments could be a limiting factor of the cladding under reactor LOCA conditions. [ABSTRACT FROM AUTHOR]

The internal friction and creep deformation behavior of La0.8Ca0.2CoO3 and pure LaCoO3 mixed ionic electronic conducting perovskite ceramics have been studied by Dynamic Mechanical Analysis and uniaxial compression under constant applied load, respectively. It was found that both the internal friction and creep strain were almost an order of magnitude higher for Ca2+ doped LaCoO3 as compared to pure undoped LaCoO3. The difference in Ca2+ doped LaCoO3 behavior was attributed to the much higher concentration of point defects (e.g., oxygen vacancies) in the structure and their interaction with other mobile defects, such as ferroelastic domain/twin walls, stacking faults, dislocations, etc. Such interactions of numerous point defects with domain walls produce energetic barriers and slow down the movement of ferroelastic domain walls under applied stress. At the same time, the defects' interactions increase the internal friction resulting in a much higher creep strain of La0.8Ca0.2CoO3 as compared to pure LaCoO3, as the creep strain is determined by the distance between the domain wall and its equilibrium position at the onset of the creep process. Therefore, the high friction will result in the larger distance the wall has to move to reach the equilibrium which in turn results in higher creep strain. The expansion of LaCoO3 under constant applied compressive stress, named here as negative creep, was also discovered to occur during room temperature creep experiments. [ABSTRACT FROM AUTHOR]

One of the main factors responsible for the mechanical and physical properties of nanocomposites is the effectiveness of the interfacial region to transfer loads and mechanical vibrations between the nano-reinforcements and the matrix. Surface functionalization has been the preferred approach to engineer the interfaces in polymer nanocomposites in order to maximize their potential in structural and functional applications. In this study, amine-functionalized cellulose nanofibrils (mCNF-G1) were synthesized via silylation of the hydroxyl groups on the CNF surface using 3-aminopropyltrimethoxysilane (APTMS). To further increase the amine density (mCNF-G2), dendritic polyamidoamine (PAMAM) was grafted onto mCNF-G1 by the Michael addition of methacrylate onto mCNF-G1, followed by the transamidation of the ester groups of methacrylate using ethylenediamine. Compared to native CNF-reinforced, poly( l -lactide) (PLLA) nanocomposites, amine-functionalized CNF exhibited significantly improved dispersion and interfacial properties within the PLLA matrix due to the grafting of PLLA chains via aminolysis. It is also a more effective nucleating agent, with 15% mCNF-G1 leading to a crystallinity of 32.5%, compared to 0.1 and 8.7% for neat PLLA and native CNF-reinforced composites. We have demonstrated that APTMS-functionalized CNF (mCNF-G1) significantly improved the tensile strength compared to native CNF, with 10% mCNF-G1 being the most effective (i.e., >100% increase in tensile strength). However, we also found that excessive amines on the CNF surface (i.e., mCNF-G2) resulted in decreased tensile strength and modulus due to PLLA degradation via aminolysis. These results demonstrate the potential of optimized amine-functionalized CNF for future renewable material applications. [ABSTRACT FROM AUTHOR]

The article discusses that sustainable closed-loop manufacturing would become reality if commodity plastics can be upcycled by using facile processability. It introduces a circular model epitomized by upcycling a prominent thermoplastic, acrylonitrile butadiene styrene (ABS) into a recyclable, robust adaptive dynamic covalent network (ABS-vitrimer) which is reprintable via FFF. This study offers an imminently adoptable approach for advanced manufacturing toward the circular plastics economy.

The chemical and structural stability of two commercial multicomponent silicate glasses (SCN and G6) in contact with yttria-stabilized zirconia (YSZ) was investigated after exposure times of up to 40,000 h in air at 800 °C. With exposure time, interfacial layers develop at the SCN-YSZ and G6-YSZ interfaces, which were characterized in detail using both quantitative chemical analysis and atomic-resolution imaging. At the SCN-YSZ interface, a Ca-Ba-Si-O reaction phase was found to grow by diffusion control. In G6-YSZ, Raman spectroscopy and electron microscopy revealed a disorganized interfacial reaction later between G6 and YSZ, and the occurrence of cubic to tetragonal to monoclinic phase transformations in YSZ. This microstructural evolution is discussed in terms of devitrification resistance of glass and diffusion processes at interfaces. [ABSTRACT FROM AUTHOR]

Abstract: Amorphous and crystalline β-eucryptite (LiAlSiO4) specimens were prepared with controlled grain sizes and varying levels of microcracking, and their elastic moduli were determined using resonant ultrasound spectroscopy. It was found that the relationship between Young’s modulus, Poisson’s ratio and degree of microcracking in these materials can be described well with fracture-mechanics-based models. It was also found that if glassy β-eucryptite is considered to be a microcracked medium in which broken Si–O bonds, with respect to the crystalline material, constitute microcracks, then its elastic properties can be described equally well by these models. Such considerations are explained by noting the differences in atomic bond density among the different states of the material and by accounting for differences in strain energy release rate measurements on glass and ceramic specimens. [Copyright &y& Elsevier]

Abstract: Creep tests were performed at 875°C and 1050°C on commercially available FeCrAl foils (∼50μm, 2mil thickness) over a wide range of stress and duration. The oxide scales formed on the creep specimens were analyzed and compared to those that formed on unstressed specimens to assess the effect of stress and strain on oxide growth behavior. Below a specific stress threshold, the creep rate becomes moderately dependent on the applied load, the lifetime independent of that load, and rupture occurs due to the onset of breakaway oxidation. A creep rate model based on the strengthening of the FeCrAl foils due to load-bearing by the thermally grown alumina scale was observed to be in good agreement with the experimental results. [Copyright &y& Elsevier]

The Mode I fracture toughness of fibrous SiC and mullite materials with 60%–70% porosity was determined under ambient conditions using the double-torsion test method. The fracture toughness values obtained were 0.27 and 0.34 MPa·m1/2 for fibrous SiC and mullite, respectively. These fibrous ceramics exhibit greater fracture resistance than porous monolithic ceramics with similar levels of porosity. A higher degree of cross-linking between the fibers led to further improvement in the fracture characteristics of the fibrous material. The differences in fracture behavior can be explained by the microstructural differences between these two classes of materials. The combination of high porosity and high fracture toughness for fibrous materials makes them ideal candidates for applications in diesel particulate filtration. [ABSTRACT FROM AUTHOR]

Abstract: This paper addresses the relationship between surface integrity and fatigue life of hard turned AISI 52100 steel (60–62 HRC), with grinding as a benchmark. The impact of superfinishing on the fatigue performance of hard turned and ground surfaces is also discussed. Specifically, the surface integrity and fatigue life of the following five distinct surface conditions are examined: hard turned with continuous white layer, hard turned with no white layer, ground, and superfinished hard turned and ground specimens. Surface integrity of the specimens is characterized via surface topography measurement, metallography, residual stress measurements, transmission electron microscopy (TEM), and nano-indentation tests. High cycle tension–tension fatigue tests show that the presence of white layer does not adversely affect fatigue life and that, on average, the hard turned surface performs as well or better than the ground surface. The effect of superfinishing is to exaggerate these differences in performance. The results obtained from this study suggest that the effect of residual stress on fatigue life is more significant than the effect of white layer. For the hard turned surfaces, the fatigue life is found to be directly proportional to both the surface compressive residual stress and the maximum compressive residual stress. Possible explanations for the observed effects are discussed. [Copyright &y& Elsevier]

Presents a study on the effect of thermal shock and oxidation-induced damage on the thermal diffusivity of unidirectional Nicalon-LAS glass-ceramic composites. Experimental procedure; Results; Conclusions.

Studies ceramic composites with multilayer interface coatings. Fabrication of silicon carbide matrix composites from ceramic-grade Nicalon or Hi-Nicalon fibers; Use of chemical vapor infiltration to produce minicomposites; Tensile testing of minicomposites; Use of forced flow thermal-gradient chemical vapor infiltration in preparing multilayer interface materials.

Large-scale atomistic models for complex polycyclic aromatic hydrocarbon systems help understand the chemical properties and behaviors of complex feedstocks such as coal or petroleum. However, the development and utilization of large-scale models remain limited due to the difficulty in achieving the varied structural characteristics necessary to capture stochastic nature of these feedstocks. We demonstrate a systematic workflow to construct stochastic molecular systems from a broad analytical suite: high-resolution transmission electron microscopy (HRTEM), carbon-13 nuclear magnetic resonance spectroscopy (13C NMR), laser desorption ionization mass spectroscopy (LDI-MS), and elemental analysis. We present a model construction and analysis utility of a new Python-based module. We selected one subbituminous and three high-volatile bituminous coals to construct large-scale models (∼40,000 atoms). The constructed models were utilized to examine the affinity for solvent extraction (naphthalene or tetralin) and the effect of structural properties (e.g., aromatic cluster size, functional groups, and cross-linking) in reactive molecular dynamics simulations. Complex chemical reactions were monitored with bond order transitions, intermediates formation, and mass distributions. Reactive molecular dynamics simulations suggest a plausible chemical extraction process and products for the complex fossil feedstocks. The results indicated that radical formations with bond breaking of bridging oxygens and carbons were required at high temperatures to facilitate hydrogeneration and extraction of gas molecules from radical-free molecules. We observed that aliphatic chains of tetralin were easily decomposed and combined with radicals to form small size of molecules with aryl bonding, mainly increasing molecules in the 500–1000 Da, while naphthalene had little impact on chemical extraction process. [Display omitted] • Groundbreaking advance for the unbiased, autonomous construction of atomistic models for coals and pitches of arbitrary size. • Generated models well align with a diverse set of experimental data allowing chemical studies of coal and pitch materials. • Utilization of constructed models with MD simulations to understand conversion process of coals with solvent extraction step. [ABSTRACT FROM AUTHOR]

Partially ordered Fe16N2 thin films have been fabricated on Fe (001)-buffered GaAs (001) single-crystal substrates by a facing target sputtering process. The saturation magnetization has been systematically investigated as a function of N site ordering in partially ordered Fe16N2 thin films, which is found to be increased monotonically with the increase in the N site ordering parameter, reaching up to 2.68 T at high ordering case. A model discussion is provided based on the partial localization of 3d electron states in this material system, which successfully rationalizes the formation of the giant saturation magnetization in chemically ordered Fe16N2. We further demonstrate that the average magnetic moment of partially ordered Fe16N2 sensitively depends on the special arrangement of Fe6N clusters, which is the key to realize high magnetic moment in this material system. [ABSTRACT FROM AUTHOR]

Extrusion based big area additive manufacturing process is utilized for fabrication of dense anisotropic bonded magnets. High loading fraction (≥70 vol%) of magnequench anisotropic Nd–Fe–B powder in nylon is used for preparing anisotropic bonded magnets. A higher energy product of ~143.2 kJ/m3 is obtained for the post printed magnetic field aligned at 1 Tesla. These findings make an important step towards the fabrication of gap magnets with energy product between ferrite and Nd–Fe–B sintered magnets. Moreover, printed bonded magnets exhibited better thermal stability, mechanical properties and superior magnetic properties compared to commercial injection molded magnets. Development in energy product, BH max of additively manufactured anisotropic bonded NdFeB magnets using BAAM system. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Data‐driven science and technology have helped achieve meaningful technological advancements in areas such as materials/drug discovery and health care, but efforts to apply high‐end data science algorithms to the areas of glass and ceramics are still limited. Many glass and ceramic researchers are interested in enhancing their work by using more data and data analytics to develop better functional materials more efficiently. Simultaneously, the data science community is looking for a way to access materials data resources to test and validate their advanced computational learning algorithms. To address this issue, The American Ceramic Society (ACerS) convened a Glass and Ceramic Data Science Workshop in February 2018, sponsored by the National Institute for Standards and Technology (NIST) Advanced Manufacturing Technologies (AMTech) program. The workshop brought together a select group of leaders in the data science, informatics, and glass and ceramics communities, ACerS, and Nexight Group to identify the greatest opportunities and mechanisms for facilitating increased collaboration and coordination between these communities. This article summarizes workshop discussions about the current challenges that limit interactions and collaboration between the glass and ceramic and data science communities, opportunities for a coordinated approach that leverages existing knowledge in both communities, and a clear path toward the enhanced use of data science technologies for functional glass and ceramic research and development. [ABSTRACT FROM AUTHOR]

We report on the influence of boron segregation on the thermoelectric properties of CoSi. Contrary to previous suggestions, and in stark contrast to aluminum substitution, boron does not enter the lattice on the Si site, but rather segregates to the grain boundaries in these alloys. Through a combination of x-ray diffraction, scanning electron microscope, and scanning Auger techniques, we present clear evidence of the formation of a CoB phase at the grain boundaries. Consistent with the failure of B to substitute for Si, we observe no changes in the electron concentration or the Seebeck coefficient under boron substitution. The electrical resistivity, on the other hand, displays a non-monotonic behavior with increasing boron concentration, first decreasing for small amounts of boron, before increasing at higher levels of substitution. We attribute this behavior to a combination of an initial healing effect of boron on microcracks, followed by the eventual increase in electron scattering by the secondary CoB phase at higher concentrations. [ABSTRACT FROM AUTHOR]

The compositional dependence of the crystal structure and lattice thermal conductivity in the Cu3SbSe4-Cu3SbS4 system has been studied. The lattice parameters of the Cu3SbSe4-xSx compounds decrease linearly with x, and the tetragonal structure (space group 142m no. 121) of the end compounds is maintained at all compositions. The lattice thermal conductivity is much lower than that predicted by a simple rule of mixtures, which is typical for a solid solution. The Debye model produces a very reasonable fit to the experimental lattice thermal conductivity data when phonon scattering due to atomic mass and size differences between Se and S is taken into account. Compounds in this series are likely to improve upon the thermoelectric performance of Cu3SbSe4, which has shown ZT = 0.72 when optimized. [ABSTRACT FROM AUTHOR]

Abstract: An interlaboratory round robin study was conducted on the tensile strength of SiC‐SiC ceramic matrix composite (CMC) tubular test specimens at room temperature with the objective of expanding the database of mechanical properties of nuclear grade SiC‐SiC and establishing the precision and bias statement for standard test method ASTM C1773. The mechanical properties statistics from the round robin study and the precision statistics and precision statement are presented herein. The data show reasonable consistency across the laboratories, indicating that the current C1773‐13 ASTM standard is adequate for testing ceramic fiber reinforced ceramic matrix composite tubular test specimen. It was found that the distribution of ultimate tensile strength data was best described with a two‐parameter Weibull distribution, while a lognormal distribution provided a good description of the distribution of proportional limit stress data. [ABSTRACT FROM AUTHOR]

• Use of coals as raw materials for carbon fiber precursors is investigated. • Bituminous coals more efficiently converted to quinoline-soluble liquids. • Coals with similar botanical origins revealed similar maceral structures. • Distribution and classification of inorganic phases are shown in detail. • Datasets are combined to form a first approximation for precursor suitability. This work investigates the use of coals as raw materials for carbon fiber precursor production as a new alternative to coal utilization. Coal being a highly complex and heterogeneous material with different macerals and minerals complicates this task. Extensive microstructural characterization as well as preliminary digestion studies are performed on three bituminous coals (Herrin and Springfield from the Illinois Basin and the Blue Gem from the Central Appalachians) and one subbituminous coal from the Powder River Basin (Monarch), as raw material candidates. The subbituminous coal was richer in oxygen, lower in sulfur, and had a higher volatile matter yield. Microstructural investigations were performed using X-ray diffraction, X-ray/neutron computed tomography, scanning electron microscopy with energy dispersive spectroscopy, and petrology. Mild solvent extraction studies were conducted using creosote and decant oil as solvents in microreactors. The extraction yield was sensitive to temperature and time (350 to 450 °C between 30 and 120 mins.) for both creosote and decant oil digestions. While the Blue Gem coal had more desirable microstructural properties with less mineral content and cleaner macerals, it had the lowest coal conversion to quinoline soluble 'liquid' (of the bituminous coals). The lower coal conversion yield was hypothesized to be connected to the lack of FeS 2 which could act as a catalyst when Fe is liberated from the structure under solvent extraction conditions. The Herrin and Springfield coals revealed similar microstructures and coal conversion efficiencies (higher than Blue Gem). These coals were the most promising candidates for further examination from this first approximations study. The subbituminous Monarch coal, however, was deemed less suitable due to poor coal conversion and less desirable microstructures. Additionally, the presented results with combined microstructural data from multiple length scales established a framework necessary for a first approximations study in this new coal utilization approach. [ABSTRACT FROM AUTHOR]

The present work demonstrates the feasibility of increasing the values of Seebeck coefficient S and power factor of calcium cobaltite Ca 3 Co 4 O 9 ceramics through competing dopant grain boundary segregation. The nominal chemistry of the polycrystalline material system investigated is Ca 3−x Bi x Ba y Co 4 O 9 with simultaneous stoichiometric substitution of Bi for Ca and non-stoichiometric addition of minute amounts of Ba. There is continuous increase of S due to Bi substitution and Ba addition. The electrical resistivity also changes upon doping. Overall, the power factor of best performing Bi and Ba co-doped sample is about 0.93 mW m −1 K −2 , which is one of the highest power factor values ever reported for Ca 3 Co 4 O 9 , and corresponds to a factor of 3 increase compared to that of the baseline composition Ca 3 Co 4 O 9. Systematic nanostructure and chemistry characterization was performed on the samples with different nominal compositions. When Bi is the only dopant in Ca 3 Co 4 O 9 , it can be found at both the grain interior and the grain boundaries GBs as a result of segregation. When Bi and Ba are added simultaneously as dopants, competing processes lead to the segregation of Ba and depletion of Bi at the GBs, with Bi present only in the grain interior. Bi substitution in the lattice increases the S at both the low and high temperature regimes, while the segregation of Ba at the GBs dramatically increase the S at low temperature regime. [ABSTRACT FROM AUTHOR]

Under the sponsorship of the U.S. National Science Foundation, a workshop on emerging research opportunities in ceramic and glass science was held in September 2016. Reported here are proceedings of the workshop. The report details eight challenges identified through workshop discussions: Ceramic processing: Programmable design and assembly; The defect genome: Understanding, characterizing, and predicting defects across time and length scales; Functionalizing defects for unprecedented properties; Ceramic flatlands: Defining structure-property relations in free-standing, supported, and confined two-dimensional ceramics; Ceramics in the extreme: Discovery and design strategies; Ceramics in the extreme: Behavior of multimaterial systems; Understanding and exploiting glasses and melts under extreme conditions; and Rational design of functional glasses guided by predictive modeling. It is anticipated that these challenges, once met, will promote basic understanding and ultimately enable advancements within multiple sectors, including energy, environment, manufacturing, security, and health care. [ABSTRACT FROM AUTHOR]

The through thickness (interlaminar) shear strength and trans-thickness tensile strength of three different nuclear-grade SiC/SiC composites were evaluated at room temperature by the double-notched shear and diametral compression tests, respectively. With increasing densification of the interlaminar matrix region, a transition in failure locations from interlayer to intrafiber bundle was observed, along with significant increases in the value of the interlaminar shear strength. Under trans-thickness tensile loading, cracks were found to propagate easily in the unidirectional composite. The 2D woven composite had a higher trans-thickness tensile strength (38 MPa) because the failure mode involved debonding, fiber pull-out and fiber failure. [ABSTRACT FROM AUTHOR]

Higher manganese silicides (HMS) made of earth-abundant and non-toxic elements are regarded as promising p-type thermoelectric materials because their complex crystal structure results in low lattice thermal conductivity. It is shown here that the already low thermal conductivity of HMS can be reduced further to approach the minimum thermal conductivity via partial substitution of Mn with heavier rhenium (Re) to increase point defect scattering. The solubility limit of Re in the obtained Re xMn1- xSi1.8 is determined to be about x = 0.18. Elemental inhomogeneity and the formation of ReSi1.75 inclusions with 50−200 nm size are found within the HMS matrix. It is found that the power factor does not change markedly at low Re content of x ≤ 0.04 before it drops considerably at higher Re contents. Compared to pure HMS, the reduced lattice thermal conductivity in Re xMn1- xSi1.8 results in a 25% increase of the peak figure of merit ZT to reach 0.57 ± 0.08 at 800 K for x = 0.04. The suppressed thermal conductivity in the pure Re xMn1- xSi1.8 can enable further investigations of the ZT limit of this system by exploring different impurity doping strategies to optimize the carrier concentration and power factor. [ABSTRACT FROM AUTHOR]

Fracture toughness of thermal barrier coatings ( TBCs) has gained significant interest in recent years as one of the dominant design parameters dictating selection of materials and assessing durability. Much progress has been made in characterizing and understanding fracture toughness of relevant TBC compositions in their bulk form, but it is also apparent that the toughness is significantly affected by process-induced microstructural defects. In this investigation, a systematic study of the influence of coating microstructure on the fracture toughness of atmospheric plasma-sprayed TBCs has been carried out. Yttria partially stabilized zirconia ( YSZ) coatings were fabricated under different process conditions inducing different levels of porosity and defect densities. Fracture toughness was measured on free-standing coatings in as-processed and thermally aged conditions using the double torsion technique. Results indicate significant variance in fracture toughness among coatings with different microstructures including changes induced by thermal aging. Comparative studies were also conducted on an alternative composition, Gd2 Zr2 O7 which, as anticipated, shows significantly lower fracture toughness compared to YSZ. The results not only point toward a need for process and microstructure optimization for enhancing TBC performance, but also a framework for establishing performance metrics for promising new TBC compositions. [ABSTRACT FROM AUTHOR]

The uniaxial tensile stress-strain behavior of three porous ceramic materials was determined at ambient conditions. Test specimens in the form of thin beams were obtained from the walls of diesel particulate filter honeycombs and tested using a microtesting system. A digital image correlation technique was used to obtain full-field 2D in-plane surface displacement maps during tensile loading, and in turn, the 2D strains obtained from displacement fields were used to determine the Secant modulus, Young's modulus, and initial Poisson's ratio of the three porous ceramic materials. Successive unloading-reloading experiments were performed at different levels of stress to decouple the linear elastic, anelastic, and inelastic response in these materials. It was found that the stress-strain response of these materials was nonlinear and that the degree of nonlinearity is related to the initial microcrack density and evolution of damage in the material. [ABSTRACT FROM AUTHOR]

Twenty-six (Pb0.95Sn0.05Te)0.92(PbS)0.08–0.055% PbI2–SiC nanoparticle (SiCnp) composite thermoelectric specimens were either hot pressed or pulsed electric current sintered (PECS). Bloating (a thermally induced increase in porosity,P, for as-densified specimens) was observed during annealing at temperatures >603 K for hot-pressed specimens and PECS-processed specimens from wet milled powders, but in contrast seven out of seven specimens densified by PECS from dry milled powders showed no observable bloating following annealing at temperatures up to 936 K. In this study, bloating in the specimens was accessed via thermal annealing induced changes in (i) porosity measured by scanning electron microscopy on fractured specimen surfaces, (ii) specimen volume and (iii) elastic moduli. The moduli were measured by resonant ultrasound spectroscopy. SiCnpadditions (1–3.5 vol.%) changed the fracture mode from intergranular to transgranular, inhibited grain growth, and limited bloating in the wet milled PECS specimens. Inhibition of bloating likely occurs due to cleaning of contamination from powder particle surfaces via PECS processing which has been reported previously in the literature. [ABSTRACT FROM AUTHOR]

In waste heat recovery applications, thermoelectric (TE) generators are subjected to thermal gradients and thermal transients, creating mechanical stresses in the TE legs. Such stresses are functions of the elastic moduli of the TE material. For SnTe1±x matrices (where x = 0.0 or 0.016) composite specimens with 0-4 vol% SiC nanoparticle (SiCNP) additions, the elastic moduli (Young's modulus, shear modulus, and Poisson's ratio) were measured by resonant ultrasound spectroscopy from room temperature (RT) to 663 K. The effects of matrix composition and the SiCNP additions on the RT intercepts and the slopes of the elastic modulus as a function of temperature are also discussed. [ABSTRACT FROM AUTHOR]

Abstract: The feasibility of adding glass or inorganic binder to conventional SOFC cathode contact materials (CCM) in order to improve bonding to adjacent materials in the cell stack is assessed. Two glasses (SEM-COM SCZ-8 and Schott GM31107) and one inorganic binder (Aremco 644A) are mixed with LSM particles to produce composite CCM pastes. These are used to bond Mn1.5Co1.5O4-coated stainless steel mesh current collectors to anode-supported button cells. The cells are operated at 800 °C for about 1000 h. The cell with SCZ-8 addition to the CCM displays quite stable operation (3.9%/1000 h degradation), whereas the other additives lead to somewhat higher degradation rate. Bonding of the CCM to coated stainless steel coupons is also assessed. Interfacial fracture toughness is determined using a four-point bend test. The fracture toughness for LSM–Schott glass (12.3 N mm−1), LSM–SCZ-8 glass (6.8 N mm−1) and LSM–644A binder (5.4 N mm−1) are significantly improved relative to pure LSM (1.7 N mm−1). Indeed, addition of binder or glass is found to improve bonding of the CCM layer without sacrificing cell performance. [Copyright &y& Elsevier]

The coefficient of thermal expansion (CTE) is a key design parameter for thermoelectric (TE) materials, especially in energy harvesting applications since stresses generated by CTE mismatch, thermal gradients, and thermal transients scale with the CTE of the TE material. For the PbTe-PbS-based TE material (PbSnTe)(PbS)-0.055 % PbI over the temperature ranges of 293-543 and 293-773 K, a CTE, α, of 21.4 ± 0.3 × 10 K was measured using (1) dilatometry and (2) high-temperature X-ray diffraction (HT-XRD) for powder and bulk specimens. The CTE values measured via dilatometry and HT-XRD are similar to the literature values for other Pb-based chalcogenides. However, the processing technique was found to impact the thermal expansion such that bloating (which leads to a hysteresis in thermal expansion) occurred for hot pressed billets heated to temperatures >603 K while specimens fabricated by pulsed electric current sintering and as-cast specimens did not show a bloating-modified thermal expansion even for temperatures up to 663 K. The relationship of bloating to the processing techniques is discussed, along with a possible mechanism for inhibiting bloating in powder processed specimens. [ABSTRACT FROM AUTHOR]

The microstructural evolution in two potential solid oxide fuel cell (SOFC) sealing glass materials exposed to air and a gas mixture of steam + H + N at 800 °C up to 10000 h was determined. The glass exposures were performed on common SOFC substrates like alumina and zirconia. Characterization of the crystalline phases and pore size distribution was performed for the specimens with various exposure conditions. Comparison of the microstructural and chemical stability of the two glasses was performed based on known trends related to glass chemistry. It was observed that multicomponent glasses followed few rules for chemical and microstructural stability reported in the literature for glasses with fewer components. The two glasses examined in this study displayed adequate resistance to devitrification but marginal resistance to porosity changes in the SOFC environment exposure. The implications of the results for the design and long-term performance of SOFC seals are discussed. [ABSTRACT FROM AUTHOR]

A novel method to determine the fiber-matrix interfacial properties of ceramic matrix composites is proposed and evaluated; where micro-pillar samples containing inclined fiber/matrix interfaces were prepared from a SiC fiber-reinforced SiC matrix composites and then compression-tested using the nano-indentation technique. This new test method employs a simple geometry and mitigates the uncertainties associated with complex stress state in the conventional single-filament push-out method or tensile unloading-reloading hysteresis loop analysis method for the determination of interfacial properties. Based on the test results using samples with different interface orientations, the interfacial debond shear strength and the internal friction coefficient are explicitly determined and compared with values obtained by other test methods. SEM observation showed that micro compression caused an adhesive type of debonding between the fiber and the pyrolytic carbon interface. The results suggest that the debonding/failure behavior of the micro-pillars followed the Coulomb fracture criterion. The determined interfacial debond shear strength is ~100 MPa, which appears to be smaller than that determined from fiber push-out test for similar composite systems. The difference can be explained by the effect of normal stress (clamping stress) on the apparent interfacial debond shear strength. [ABSTRACT FROM AUTHOR]