Showing papers in "Journal of Materials Research in 2015"
TL;DR: In this paper, the contributions of ion irradiation to our understanding of irradiation effects, the options for emulating radiation effects in reactors, and experience with both proton irradiation and heavy ion irradiations.
Abstract: Development of new materials for current and advanced reactor concepts is hampered by long lead times and high cost of reactor irradiations coupled with the paucity of test reactors. Ion irradiation offers many advantages for emulating the microstructures and properties of materials irradiated in reactors but also poses many challenges. Nevertheless, there is a growing body of evidence, primarily for light ion (proton) irradiation showing that many, if not all of the features of the irradiated microstructure and properties, can be successfully emulated by careful selection of irradiation parameters based on differences in the damage processes between ion and neutron irradiation. While much less has been done to benchmark heavy- or self-ion irradiation, recent work shows that under certain conditions, the complete suite of features of the irradiated microstructure can be emulated. This study summarizes the contributions of ion irradiation to our understanding of irradiation effects, the options for emulating radiation effects in reactors, and experience with both proton irradiation and heavy ion irradiation.
167 citations
TL;DR: In this paper, four different fracture toughness test geometries in practice, all of them micromachined in the focused ion beam (FIB), were investigated to investigate the fracture toughness of Si(100) at the micrometer scale.
Abstract: Fracture toughness testing of materials at the micrometer scale has become essential due to the continuing miniaturization of devices accompanied by findings of size effects in fracture behavior. Many techniques have emerged in the recent past to carry out fracture toughness measurements at the relevant micro and nanolength scales, but they lack ASTM standards that are prescribed for bulk scale tests. Also, differences in reported values arise at the microscale due to the sample preparation technique, test method, geometry, and investigator. To correct for such discrepancies, we chose four different fracture toughness test geometries in practice, all of them micromachined in the focused ion beam (FIB), to investigate the fracture toughness of Si(100) at the micrometer scale. The average KIC that emerges from all four cases is a constant (0.8 MPa m1/2). The advantages and limitations of each of these geometries in terms of test parameters and the range of materials that can be tested are discussed.
139 citations
TL;DR: Pristine multiwalled carbon nanotubes (P-MWCNTs) were functionalized with carboxylic groups through oxidation reactions and then reduced to produce hydroxyl groups.
Abstract: Pristine multiwalled carbon nanotubes (P-MWCNTs) were functionalized with carboxylic groups (MWCNT-COOH) through oxidation reactions and then reduced to produce hydroxyl groups (MWCNT-OH). Pristine and functionalized MWCNTs were used to produce poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) nanocomposites with 0.5 wt% of MWCNTs. MWCNT functionalization was verified by visual stability in water, infrared and Raman spectroscopy, and zeta potential measurements. Pristine and functionalized MWCNTs acted as the nucleating agent in a PHBV matrix, as verified by differential scanning calorimetry (DSC). However, the dispersion of filler into the matrix, thermal stability, and direct current (DC) conductivity were affected by MWCNT functionalization. Scanning electron microscopy (SEM) showed that filler dispersion into the PHBV matrix was improved with MWCNT functionalization. The surface roughness was reduced with the addition and functionalization of MWCNT. The thermal stability of PHBV/MWCNT-COOH, PHBV/P-MWCNT, and PHBV/MWCNT-OH nanocomposites were 20, 30, and 30 °C higher than neat PHBV, respectively, as verified by thermogravimetry analysis (TGA). Addition of pristine and functionalized MWCNTs provided electrical conductivity in nanocomposite, which was higher for PHBV/P-MWCNTs (1.2 × 10−5 S cm−1).
117 citations
TL;DR: In this article, the authors summarize and highlight recent progress involving in situ TEM studies of energy storage materials, especially rechargeable batteries, and provide an overview of the in-person TEM imaging of batteries.
Abstract: Since the advent of the transmission electron microscope (TEM), continuing efforts have been made to image material under native and reaction environments that typically involve liquids, gases, and external stimuli. With the advances of aberration-corrected TEM for improving the imaging resolution, steady progress has been made on developing methodologies that allow imaging under dynamic operating conditions, or in situ TEM imaging. The success of in situ TEM imaging is closely associated with advances in microfabrication techniques that enable manipulation of nanoscale objects around the objective lens of the TEM. This study summarizes and highlights recent progress involving in situ TEM studies of energy storage materials, especially rechargeable batteries. The study is organized to cover both the in situ TEM techniques and the scientific discoveries made possible by in situ TEM imaging.
104 citations
TL;DR: A CoCrFeNiMn high-entropy alloy (HEA) was processed by high-pressure torsion (HPT) to produce a nanocrystalline (nc) HEA as discussed by the authors.
Abstract: A CoCrFeNiMn high-entropy alloy (HEA), in the form of a face-centered cubic (fcc) solid solution, was processed by high-pressure torsion (HPT) to produce a nanocrystalline (nc) HEA. Significant grain refinement was achieved from the very early stage of HPT through 1/4 turn and an nc structure with an average grain size of ∼40 nm was successfully attained after 2 turns. The feasibility of significant microstructural changes was attributed to the occurrence of accelerated atomic diffusivity under the torsional stress during HPT. Nanoindentation experiments showed that the hardness increased significantly in the nc HEA during HPT processing and this was associated with additional grain refinement. The estimated values of the strain-rate sensitivity were maintained reasonably constant from the as-cast condition to the nc alloy after HPT through 2 turns, thereby demonstrating a preservation of plasticity in the HEA. In addition, a calculation of the activation volume suggested that the grain boundaries play an important role in the plastic deformation of the nc HEA where the flow mechanism is consistent with other nc metals. Transmission electron microscopy showed that, unlike conventional fcc nc metals, the nc HEA exhibits excellent microstructural stability under severe stress conditions.
97 citations
TL;DR: In this paper, an overview of advanced scanning transmission electron microscopy (STEM) techniques used for characterization of irradiated BCC Fe-based alloys is provided, with an illustrated example of RIS in proton and self-ion irradiated T91.
Abstract: This paper provides an overview of advanced scanning transmission electron microscopy (STEM) techniques used for characterization of irradiated BCC Fe-based alloys. Advanced STEM methods provide the high-resolution imaging and chemical analysis necessary to understand the irradiation response of BCC Fe-based alloys. The use of STEM with energy dispersive x-ray spectroscopy (EDX) for measurement of radiation-induced segregation (RIS) is described, with an illustrated example of RIS in proton- and self-ion irradiated T91. Aberration-corrected STEM-EDX for nanocluster/nanoparticle imaging and chemical analysis is also discussed, and examples are provided from ion-irradiated oxide dispersion strengthened (ODS) alloys. Finally, STEM techniques for void, cavity, and dislocation loop imaging are described, with examples from various BCC Fe-based alloys.
93 citations
TL;DR: In this paper, the authors present a review of small-scale materials testing techniques and potential shortcomings based on examples from the literature, as well as introduce novel experimental approaches conducted using microcompression testing, microbend bar testing, and nanoindentation at ambient and nonambient conditions.
Abstract: Small specimen testing techniques have a long history in nuclear material research due to the limitations posed by nuclear facilities. The limited space in reactors and the fact that the samples are oftentimes radioactive in addition to the increasing need to obtain mechanical properties from ion beam irradiated samples require small specimen mechanical testing. With the application of modern focused ion beam sample preparation techniques and the enhancement of nanoindentation instruments, the size scale has been moved to even smaller scales and new geometries. Micrometer and even nanometer size samples are feasible, but raise the question of comparability to large scale properties for engineering applications. In this review, we summarize available small scale materials testing techniques and potential shortcomings based on examples from the literature, as well as introduce novel experimental approaches conducted using microcompression testing, microbend bar testing, and nanoindentation at ambient and nonambient conditions.
82 citations
TL;DR: In this paper, a new dislocation-density based constitutive model is developed to characterize the strain hardening effect and dynamic recovery behavior of a Ni-based superalloy, and an iterative algorithm is designed to predict the high-temperature deformation behaviors under time-variant hot working conditions.
Abstract: The strain hardening effect and dynamic recovery behavior of a Ni-based superalloy are studied by isothermal compressive tests. A new unified dislocation-density based constitutive model is developed to characterize the strain hardening effect and dynamic recovery behavior of the studied superalloy. In the developed constitutive model, some material parameters (yield stress, strain hardening coefficient, and dynamic recovery coefficient) are assumed as functions of initial grain size, deformation temperature, and strain rate. An iterative algorithm is designed to predict the high-temperature deformation behaviors under time-variant hot working conditions. The hot deformation parameters and material parameters can be updated in each strain increment. Comparisons between the experimental and calculated flow stresses indicate that the developed constitutive model can accurately describe the high-temperature deformation behavior of the studied superalloy. Furthermore, the developed constitutive model is also successfully used for analyzing time-variant hot working processes.
72 citations
TL;DR: In this article, the authors report flexible and stretchable touch sensors with two different patterns (interdigitated and diamond-shaped capacitors) made of screen-printed silver nanowire electrodes embedded in polydimethylsiloxane.
Abstract: In recent years wearable devices have attracted significant attention. Flexibility and stretchability are required for comfortable wear of such devices. In this paper, we report flexible and stretchable touch sensors with two different patterns (interdigitated and diamond-shaped capacitors). The touch sensors were made of screen-printed silver nanowire electrodes embedded in polydimethylsiloxane. For each pattern, the simulation-based design was conducted to choose optimal dimensions for the highest touch sensitivity. The sensor performances were characterized as-fabricated and under deformation (e.g., bending and stretching). While the interdigitated touch sensors were easier to fabricate, the diamond-shaped ones showed higher touch sensitivity under as-fabricated, stretching or even bending conditions. For both types of sensors, the touch sensitivity remained nearly constant under stretching up to 15%, but varied under bending. They also showed robust performances under cyclic loading and against oxidation.
56 citations
TL;DR: A straightforward and scalable approach to attach, align, and dynamically load cardiomyocytes on responsive liquid crystal elastomer (LCE) substrates for dynamic cell culture is demonstrated.
Abstract: Responsive, biocompatible substrates are of interest for directing the maturation and function of cells in vitro during cell culture. This can potentially provide cells and tissues with desirable properties for regenerative therapies. Here, we demonstrate a straightforward and scalable approach to attach, align, and dynamically load cardiomyocytes on responsive liquid crystal elastomer (LCE) substrates. Monodomain LCEs exhibit reversible shape changes in response to cyclic heating, and when immersed in an aqueous medium on top of resistive heaters, shape changes are fast, reversible, and produce minimal temperature changes in the surroundings. We systematically characterized the strain response of LCEs in water and demonstrated the attachment and alignment of neonatal rat ventricular myocytes on LCE substrates. Cardiomyocytes attached to both static and stimulated LCE substrates, and under cyclic stimulation, cardiomyocytes aligned along the primary direction of strain. This work demonstrates the potential of LCEs as stimuli-responsive substrates for dynamic cell culture.
51 citations
TL;DR: In this paper, the authors present the instrumentation used for conducting multi-ion beam irradiations and implantations as well as for characterizing bombarded samples at the JANNUS facility.
Abstract: JANNUS (Joint Accelerators for Nanosciences and Nuclear Simulation), the unique triple beam facility in Europe, offers the possibility to produce three ion beams simultaneously for nuclear recoil damage and implantation of a large array of ions for well-controlled modeling-oriented experiments. The first triple beam irradiation was performed in March 2010. Along with irradiation developments, continuous efforts have been made to implement ex situ and in situ characterization tools. In this study, we set out the present status of the JANNUS facility of the Saclay site. We focus on the instrumentation used for conducting multi-ion beam irradiations and implantations as well as for characterizing bombarded samples. On-line control of irradiation parameters, in situ modification monitoring using Raman spectroscopy or ion beam induced luminescence, and ex situ characterization by ion beam surface analysis [Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA), and elastic recoil detection analysis (ERDA)] of implanted samples are detailed. Some examples of single, dual, and triple beam irradiation configurations are presented. Access to the facility is provided by the French network EMIR for national and international users (
http://emir.in2p3.fr/
).
TL;DR: In this article, a backbone and porogen system is proposed to control porosity from 0 to 60% volume, achieving high chemical stability to various wet cleans, and delivering uniquely high mechanical strength at a given porosity.
Abstract: Reducing the delay of backend interconnects is critical in delivering improved performance in next generation computer chips. One option is to implement interlayer dielectric (ILD) materials with increasingly lower dielectric constant (k) values. Despite industry need, there has been a recent decrease in study and production of these materials in academia and business communities. We have generated a backbone and porogen system that allows us to control porosity from 0 to 60% volume, achieve k-values from 3.4 to 1.6, maintain high chemical stability to various wet cleans, and deliver uniquely high mechanical strength at a given porosity. Finite element modeling and experimental results demonstrate that further improvements can be achieved through control of the pore volume into an ordered network. With hopes to spur more materials development, this paper discusses some molecular design and nanoscale hierarchical principles relevant to making next generation low-k ILD materials.
TL;DR: In this article, the authors demonstrate the use of time-domain thermoreflectance (TDTR), a nondestructive thermal measurement technique, to study the effects of radiation damage on material properties.
Abstract: The progressive build up of fission products inside different nuclear reactor components can lead to significant damage of the constituent materials. We demonstrate the use of time-domain thermoreflectance (TDTR), a nondestructive thermal measurement technique, to study the effects of radiation damage on material properties. We use TDTR to report on the thermal conductivity of optimized ZIRLO, a material used as fuel cladding in nuclear reactors. We find that the thermal conductivity of optimized ZIRLO is 10.7 ± 1.8 W m−1 K−1 at room temperature. Furthermore, we find that the thermal conductivities of copper–niobium nanostructured multilayers do not change with helium ion irradiation doses of 1015 cm−2 and ion energy of 200 keV, demonstrating the potential of heterogeneous multilayer materials for radiation tolerant coatings. Finally, we compare the effect of ion doses and ion beam energies on the measured thermal conductivity of bulk silicon. Our results demonstrate that TDTR can be used to quantify depth dependent damage.
TL;DR: In this paper, a self-assembly-based method for producing honeycomb-structured porous polymer films was used to prepare pattern compressible, and microstructured dielectric layers for capacitive pressure sensors.
Abstract: Flexible touch sensors with high sensitivity show promise in biomedical diagnostics and for artificial “electronic skin” for robotics or prosthetic devices. For “electronic skin” applications, there exists a need for low-cost, scalable methods for producing pixels that sense both medium (10–100 kPa) and low pressures (<10 kPa). Here, the “breath figures” (BFs) method, a simple, self-assembly-based method for producing honeycomb-structured porous polymer films, was used to prepare pattern compressible, and microstructured dielectric layers for capacitive pressure sensors. Porous polystyrene BFs films served as molds for structuring polydimethylsiloxane dielectrics. Pressure sensing devices containing the BFs-molded dielectrics consistently gave pressure response with little hysteresis, high sensitivities at lower applied pressures, and improved sensitivity at higher pressures. Analysis of microstructure geometries and pressure sensor performance suggests that structures with higher aspect ratios (height-to-width) produce less hysteresis, and that less uniform, more polydisperse structures yield a more linear pressure response.
TL;DR: In this article, high-saturation magnetization values near 1.7 T were obtained for Fe-rich amorphous alloys of Fe-B-P-Si and Fe-C-Si-C systems.
Abstract: Some Fe-rich amorphous alloys of Fe–B–P–Si and Fe–B–P–Si–C systems were found to exhibit simultaneously good soft magnetic properties with high-saturation magnetization values near 1.7 T, which are higher than those for previously reported Fe-based amorphous and glassy alloys, in addition to rather good amorphous ribbon formability, good bending ductility, and rather high corrosion resistance. The corrosion resistance increased with increasing P content, accompanying by the increase in thermal stability of the amorphous phase. The decrease in the outer surface velocity of the wheel, which results in the increase of ribbon thickness, also causes an improvement of surface smoothness of the melt-spun amorphous alloy ribbons. The syntheses of new high-saturation Fe-based soft magnetic amorphous alloys without any other transition metals hold promise for future extension of Fe-based soft magnetic amorphous materials.
TL;DR: In this paper, the concept of entropically supported grain boundary (GB) segregation in alloys with a tendency to phase-separate and its role in stabilizing nanostructures therein was explored.
Abstract: Grain boundary (GB) segregation can markedly improve the stability of nanostructured alloys, where the fraction of GB sites is inherently large Here, we explore the concept of entropically supported GB segregation in alloys with a tendency to phase-separate and its role in stabilizing nanostructures therein These duplex nanocrystalline alloys are notably different, both in a structural and thermodynamic sense, from the previously studied “classical” nanocrystalline alloys, which are solid solutions with GB segregation of solute Experiments are conducted on the W–Cr system, in which nanoduplex structures are expected Upon heating ball-milled W–15 at% Cr up to 950 °C, a nanoscale Cr-rich phase was found along the GBs These precipitates mostly dissolved into the W-rich grains leaving behind Cr-enriched GBs upon further heating to 1400 °C The presence of Cr-rich nanoprecipitates and GB segregation of Cr is in line with prediction from our Monte Carlo simulation when GB states are incorporated into the alloy thermodynamics
TL;DR: In this article, the thermal conductivities of epoxy composites of mixtures of graphite and graphene in varying ratios were measured and the results showed unexpectedly high conductivities at a certain ratio filler ratio, which can be attributed to the lowering of overall thermal interface resistance due to small amounts of nanofillers improving the thermal contact between the primary microfillers (graphite).
Abstract: The thermal conductivities of epoxy composites of mixtures of graphite and graphene in varying ratios were measured. Thermal characterization results showed unexpectedly high conductivities at a certain ratio filler ratio. This phenomenon was exhibited by samples with three different overall filler concentrations (graphene + graphite) of 7, 14, and 35 wt%. The highest thermal conductivity of 42.4 ± 4.8 W/m K (nearly 250 times the thermal conductivity of pristine epoxy) was seen for a sample with 30 wt% graphite and 5 wt% graphene when characterized using the dual-mode heat flow meter technique. This significant improvement in thermal conductivity can be attributed to the lowering of overall thermal interface resistance due to small amounts of nanofillers (graphene) improving the thermal contact between the primary microfillers (graphite). The synergistic effect of this hybrid filler system is lost at higher loadings of the graphene relative to graphite. Graphite and graphene mixed in the ratio of 6:1 yielded the highest thermal conductivities at three different filler loadings.
TL;DR: In this article, the synthesis of high-quality and highly uniform few-layer graphene on silicon wafers, based on solid source growth from epitaxial 3C-SiC films, is presented.
Abstract: We introduce a novel approach to the synthesis of high-quality and highly uniform few-layer graphene on silicon wafers, based on solid source growth from epitaxial 3C-SiC films. Using a Ni/Cu catalytic alloy, we obtain a transfer-free bilayer graphene directly on Si(100) wafers, at temperatures potentially compatible with conventional semiconductor processing. The graphene covers uniformly a 2″ silicon wafer, with a Raman ID/ IG band ratio as low as 0.5, indicative of a low defectivity material. The sheet resistance of the graphene is as low as 25 Ω/square, and its adhesion energy to the underlying substrate is substantially higher than transferred graphene. This work opens the avenue for the true wafer-level fabrication of microdevices comprising graphene functional layers. Specifically, we suggest that exceptional conduction qualifies this graphene as a metal replacement for MEMS and advanced on-chip interconnects with ultimate scalability.
TL;DR: In this article, the Johnson-Kendall-Roberts (JKR) theory was recaptured and three complementary dimensionless parameters were summarized to help design adhesion measurement experiments compatible with the JKR theory.
Abstract: Adhesion between soft matter is a universal mechanical problem in bio-engineering and bio-integration. The Johnson–Kendall–Roberts (JKR) method is widely used to measure the work of adhesion and work of separation between soft materials. In this study, the JKR theory is recaptured and three complementary dimensionless parameters are summarized to help design adhesion measurement experiments compatible with the JKR theory. The work of adhesion/separation between two commonly used soft elastomers, polydimethylsiloxane (PDMS, Sylgard® 184) and Ecoflex® 0300, is measured by the JKR method using a dynamical mechanical analyzer. Effects of base polymer to curing agent mixing ratio and solvent extraction are examined. A unified adhesion mechanism is proposed to explain the different adhesion behaviors. It is concluded that chain–matrix interaction is the most effective adhesion mechanism compared with chain–chain or matrix–matrix interactions. Chain–chain interaction obstructs chain–matrix interaction as it either blocks or entangles with surface chains which could have interacted with the matrix.
TL;DR: In this paper, a machine learning algorithm was used to identify oxide phase growth during a high-throughput oxidation study of NiAl bond coats that used x-ray diffraction, Raman, and fluorescence spectroscopic techniques.
Abstract: Phase identification is an arduous task during high-throughput processing experiments, which can be exacerbated by the need to reconcile results from multiple measurement techniques to form a holistic understanding of phase dynamics. Here, we demonstrate AutoPhase, a machine learning algorithm, which can identify the presence of the different phases in spectral and diffraction data. The algorithm uses training data to determine the characteristic features of each phase present and then uses these features to evaluate new spectral and diffraction data. AutoPhase was used to identify oxide phase growth during a high-throughput oxidation study of NiAl bond coats that used x-ray diffraction, Raman, and fluorescence spectroscopic techniques. The algorithm had a minimum overall accuracy of 88.9% for unprocessed data and 98.4% for postprocessed data. Although the features selected by AutoPhase for phase attribution were distinct from those of topical experts, these results show that AutoPhase can substantially increase the throughput high-throughput data analysis.
TL;DR: In this paper, a combination of modern modeling techniques with controlled experimentation has specifically focused on improving the understanding of radiation-induced segregation, precipitate formation and growth under radiation, the stability of oxide nanoclusters, and the development of dislocation networks under radiation.
Abstract: Designing materials for performance in high-radiation fields can be accelerated through a carefully chosen combination of advanced multiscale modeling paired with appropriate experimental validation The studies reported in this work, the combined efforts of six universities working together as the Consortium on Cladding and Structural Materials, use that approach to focus on improving the scientific basis for the response of ferritic–martensitic steels to irradiation A combination of modern modeling techniques with controlled experimentation has specifically focused on improving the understanding of radiation-induced segregation, precipitate formation and growth under radiation, the stability of oxide nanoclusters, and the development of dislocation networks under radiation Experimental studies use both model and commercial alloys, irradiated with both ion beams and neutrons Transmission electron microscopy and atom probe are combined with both first-principles and rate theory approaches to advance the understanding of ferritic–martensitic steels
TL;DR: The results indicate that these Ag-doped borosilicate bioactive glass scaffolds may have potential in repairing bone coupled with providing a lower risk of bacterial infection.
Abstract: The development of synthetic scaffolds with a desirable combination of properties, such as bioactivity, the ability to locally deliver antibacterial agents and high osteogenic capacity, is a challenging but promising approach in bone tissue engineering. In this study, scaffolds of a borosilicate bioactive glass (composition: 6Na2O, 8K2O, 8MgO, 22CaO, 36B2O3, 18SiO2, 2P2O5; mol%) with controllable antibacterial activity were developed by doping the parent glass with varying amounts of Ag2O (0.05, 0.5, and 1.0 wt%). The addition of the Ag2O lowered the compressive strength and degradation of the bioactive glass scaffolds but it did not affect the formation of hydroxyapatite on the surface of the glass as determined by energy dispersive x-ray analysis, x-ray diffraction, and Fourier transform infrared analysis. The Ag2O-doped scaffolds showed a sustained release of Ag ions over more than 8 weeks in simulated body fluid and resistance against colonization by the bacterial strains Escherichia coli and Staphylococcus aureus. In vitro cell culture showed better adhesion, proliferation, and alkaline phosphatase activity of murine osteoblastic MC3T3-E1 cells on the Ag2O-doped bioactive glass scaffolds than on the undoped scaffolds. The results indicate that these Ag-doped borosilicate bioactive glass scaffolds may have potential in repairing bone coupled with providing a lower risk of bacterial infection.
TL;DR: In this paper, high energy x-rays from intense synchrotron light sources are used in transmission geometry to analyze ion-induced structural and chemical modifications throughout the ion tracks, particularly useful for characterizing the annealing kinetics of irradiation-induced material modifications.
Abstract: Recent efforts to characterize the nanoscale structural and chemical modifications induced by energetic ion irradiation in nuclear materials have greatly benefited from the application of synchrotron-based x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) techniques. Key to the study of actinide-bearing materials has been the use of small sample volumes, which are particularly advantageous, as the small quantities minimize the level of radiation exposure at the ion-beam and synchrotron user facility. This approach utilizes energetic heavy ions (energy range: 100 MeV–3 GeV) that pass completely through the sample thickness and deposit an almost constant energy per unit length along their trajectory. High energy x-rays (25–65 keV) from intense synchrotron light sources are then used in transmission geometry to analyze ion-induced structural and chemical modifications throughout the ion tracks. We describe in detail the experimental approach for utilizing synchrotron radiation (SR) to study the radiation response of a range of nuclear materials (e.g., ThO2 and Gd2TixZr2− xO7). Also addressed is the use of high-pressure techniques, such as the heatable diamond anvil cell, as a new means to expose irradiated materials to well-controlled high-temperature (up to 1000 °C) and/or high-pressure (up to 50 GPa) conditions. This is particularly useful for characterizing the annealing kinetics of irradiation-induced material modifications.
TL;DR: In this paper, a modified Pechini sol gel auto combustion method was used to synthesize barium hexaferrite powders and the powder samples were heat treated at 900 °C for 5 h and were subjected to structural, thermal, dielectric, magnetic, and optical studies.
Abstract: M-type barium hexaferrite powders were synthesized using modified Pechini sol gel auto combustion method. The powder samples were heat treated at 900 °C for 5 h and were subjected to the structural, thermal, dielectric, magnetic, and optical studies. X-ray powder diffraction patterns show the formation of pure phase of M-type hexaferrite. Thermal analysis reveals that the weight loss of precursor becomes constant after 680 °C. The presence of two prominent peaks near 430 and 580 cm−1 in Fourier transform infrared spectroscopy spectra indicates the formation of M-type hexaferrites. The M — H curve has been used to study the magnetic behavior. The maximum value of coercivity is found for x = 0.41, which is higher than that of the pure barium hexaferrite. The band gap dependency on composition was studied using UV–Vis NIR spectroscopy. It was found that the dielectric constant is high at low frequency and decreases with an increase in frequency. Hexagonal structure of hexaferrite is visualized in transmission electron images.
TL;DR: In this article, the influence of coherency on the radiation resistance of immiscible systems remains poorly understood, and the authors suggest that the coherent immiscibility interface is also effective to alleviate radiation induced damage.
Abstract: Recent studies have shown that chemical immiscibility is important to achieve enhanced radiation tolerance in metallic multilayers as immiscible layer interfaces are more stable against radiation induced mixing than miscible interfaces. However, as most of these immiscible systems have incoherent interfaces, the influence of coherency on radiation resistance of immiscible systems remains poorly understood. Here, we report on radiation response of immiscible Cu/Fe multilayers, with individual layer thickness h varying from 0.75 to 100 nm, subjected to He ion irradiation. When interface is incoherent, the peak bubble density decreases with decreasing h and reaches a minimum when h is 5 nm. At even smaller h when interface is increasingly coherent, the peak bubble density increases again. However, void swelling in coherent multilayers with smaller h remains less than those in incoherent multilayers. Our study suggests that the coherent immiscible interface is also effective to alleviate radiation induced damage.
TL;DR: In this article, an innovative approach through micro-nano-indentation testing with a cylindrical flat-tip indenter and coupled with computer modeling was proposed to characterize the material's elastic-plastic properties.
Abstract: Material property measurements at the micro-/nanoscale are required for within many materials systems, such as thin-films, coatings, nanostructured materials, and interface/interphase. An innovative approach through micro-/nano-indentation testing with a cylindrical flat-tip indenter and coupled with computer modeling was proposed to characterize the material’s elastic–plastic properties. A mechanical model proposed for directly extracting the yield strength of the tested materials, based on the hemi-spherical stress–strain distribution assumption, was analytically derived and numerically validated. Specimens being tested are aluminum alloy, low carbon steel, and alloy steel. A micro-/nano-indentation solid model was constructed and computer modeling was conducted. The load point in the indentation load–depth curve and the modifier for extracting the yield strength were identified through computer modeling and validated by indentation tests. The material properties measured by indentation were compared with tensile tests. The indentation testing errors induced by residual stresses in specimens were investigated by a residual stress measurement system.
TL;DR: The nonisothermal crystallization kinetics, fragility, and thermodynamics of high entropy bulk metallic glass (HE-BMG) have been investigated by differential scanning calorimetry.
Abstract: The nonisothermal crystallization kinetics, fragility, and thermodynamics of Ti20Zr20Cu20Ni20Be20 high entropy bulk metallic glass (HE-BMG) have been investigated by differential scanning calorimetry. The activation energies for the glass transition and crystallization events were determined by Kissinger and Ozawa methods. The value of local Avrami exponent is less than 1.5 in most cases for all the three crystallization events, indicating that the major crystallization mechanism is diffusion-controlled growth of pre-existing nuclei. The local activation energy is stable during the whole crystallization process and this further confirms that the crystallization occurs through a single mechanism. Ti20Zr20Cu20Ni20Be20 alloy can be classified into “strong glass formers” according to the estimated fragility index and also shows a relatively low value of Gibbs free energy difference. However, compared with Zr41.2Ti13.8Cu12.5Ni10Be22.5 BMG, the glass-forming ability of Ti20Zr20Cu20Ni20Be20 HE-BMG is much lower and the related reasons have been discussed.
TL;DR: In this paper, the kinetics and morphology of oxides formed during in situ proton irradiation-corrosion experiment were analyzed and the resulting oxide was compared with reference samples corroded in an autoclave, and literature data found on in-reactor formed oxide.
Abstract: The kinetics and morphology of oxides formed during in situ proton irradiation–corrosion experiment were analyzed. Experiments were conducted in 320 °C water with 3 wt ppm H2, while irradiated by a 3.2-MeV proton beam at a current density of 2 µA/cm2 producing a damage rate at 4.4 × 10−7 dpa/s. The resulting oxide was compared with reference samples corroded in an autoclave, and literature data found on in-reactor formed oxide. The corrosion rate of the sample irradiated in situ was 10 times faster than the in-pile corrosion rate. The cracked and porous irradiated oxide consisted of monoclinic equiaxed grains of zirconia with a preferential orientation of the oxide grains. Second phase particles (SPPs) consumed by the oxidation front were rapidly oxidized, but no SPPs were amorphized or dissolved in the metal matrix of the irradiated sample.
TL;DR: In this paper, the effect of heating and cooling rates on the crystallization and melting of poly(3-hydroxybutyrate) and carbon black (CB) compounds was investigated by differential scanning calorimetry (DSC), and its morphology analyzed by optical microscopy (OM).
Abstract: Compounds of poly(3-hydroxybutyrate) (PHB) and carbon black (CB) with CB content ranging between 0.5 and 10% were prepared in an internal mixer. The effect of heating and cooling rates on the crystallization and melting of PHB/CB compounds was investigated by differential scanning calorimetry (DSC), and its morphology analyzed by optical microscopy (OM). Results showed that PHB and its compounds partially crystallize from the melt during cooling and partially cold crystallize on reheating, with the amount of polymer crystallizing in each stage depending strongly on the cooling rate. Melting is usually shown in DSC scans as complex (double) peaks, which are influenced by the heating/reheating thermal cycles. The melting and cold crystallization temperatures, and the rates of phase change depend strongly on the cooling and heating rates and CB content. CB acts as a nucleating agent, promoting the melt and cold crystallization of PHB as well as increasing the number of spherulites, with a mild effect on the melting transition. Light microscopy images suggest that a secondary crystallization of PHB also occurs during storage at room temperature.
TL;DR: In this paper, the influence of dislocation pileups on strength and Bauschinger effects in micrometer-sized, focused ion beam milled bending cantilevers was investigated.
Abstract: Copper microcantilevers were produced by focused ion beam milling and tested in situ using a scanning electron microscope. To provide different interfaces for piling up dislocations, cantilevers were fabricated to be single crystalline, bicrystalline, or single crystalline with a slit in the region of the neutral axis. The aim of the experiment was to study the influence of dislocation pile-ups on (i) strength and (ii) Bauschinger effects in micrometer-sized, focused ion beam milled bending cantilevers. The samples were loaded monotonically for several times under displacement control. Even though the cantilevers exhibited the same nominal strain gradient the strength varied by 34% within the three cantilever geometries. The Bauschinger effect can be promoted and prohibited by the insertion of different interfaces.