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Ion beam implantations are widely performed to understand the effects of irradiation-induced displacement damage on nuclear structural materials. However, the volume of material that can be investigated is often limited by the maximum energies of accelerator facilitates, leading to a limitation in the thickness of samples whose mechanical properties can be evaluated. The Lawrence Berkeley National Laboratory's 88-Inch Cyclotron offers a wide range of ions and energies, allowing for material ion implantations at larger scales than typical. Four HT-9 SS-J-geometry tensile specimens were polished and then irradiated with deuterons at the 88-Inch Cyclotron to doses of approximately 0.2 dpa prior to small scale tensile testing. The results from this study show irradiation hardening characterized by the tensile test results and black dot irradiation defects. Additionally, a comprehensive look at low temperature irradiations of high-Cr F/M steels is presented and our results show agreement with the available data.

This research investigated palm biodiesel production via solid base-catalyzed transesterification in an intensified kitchen fruit blender. Studied parameters included methanol to palm oil molar ratio, CaO catalyst loading, reaction temperature and reaction volume. Characteristics of CaO catalyst were investigated by X-ray diffraction (XRD) and Fourier-transform infrared (FT-IR) spectroscopy techniques. An optimal condition was achieved with 15:1 of methanol to palm oil molar ratio, 5 wt.% of CaO dosage, 60oC of reaction temperature and 1,000 mL of reaction volume, obtaining the highest FAME production of 97.58% and yield efficiency of 1.56×10-3 g/J. Crystal structure of catalyst showed structural change after calcination while FT-IR illustrated alteration of various functional groups through reusability experiment demonstrating exceptional activity stability. Properties of biodiesel produced conformed to international standards. Use of CaO catalyst in biodiesel production provides positive effect on reuse, reduces wastewater from washing process, lowers production cost and is environmentally responsible.

Mechanical testing of materials at smaller length scales enables targeted studies into microstructural features while considering the limitations and handling of irradiated samples. However, sample preparation is a timely and costly task via conventional methods; as a result, data at small length scales suffer from limited statistics. Femtosecond laser machining has been shown to enable the rapid and consistent fabrication of micro-mesoscale samples. In this study, femtosecond laser machining was employed to produce micromechanical test specimens of a range of sample geometries and dimensions. Specifically, the machining and testing of three overall geometries was explored: laser SSJ2, laser lathe, and laser sheet. Associated with the development of machining procedures for these samples was the development of testing setups. The testing data from initial specimens show that both an increased throughput of small-scale mechanical testing and the generation of reliable data are possible with these methods.

Pyrolytic carbon (PyC) plays a critical role in many applications for its unique properties. In ceramic composite systems, the elastic properties of PyC at the fiber/matrix interface drive toughening mechanisms, enabling structural performance at increased operating temperatures. PyC expresses a wide range of crystallographic texture depending on fabrication parameters. As a result, modelling and optimization requires direct understanding of the texture-property relationships at the relevant length scales. This research leverages high-resolution transmission electron microscopy (HRTEM) to link the PyC microstructure to the elastic response observed via digital image correlation (DIC) during micropillar compression. The HRTEM and DIC results quantitatively resolve a gradient for microstructural texture and Young's modulus respectively, showing that disordered texture increases compressive stiffness normal to the average orientation of the PyC basal planes. The values for modulus ranged from 55 to 150 GPa, which are large compared to most experimental methods, but may be more realistic considering the uniaxial stress state and length scale. The behavior supports findings from numerical homogenization models, suggesting that this advanced technique may provide a path forward for optimization and validation of these nanoscale elasticity models.

The next generation of nuclear reactors will expose materials to conditions that, in some cases, are even more extreme than those in current fission reactors, inevitably leading to new materials science challenges. Radiation-induced damage and corrosion are two key phenomena that must be understood both independently and synergistically, but their interactions are often convoluted. In the light water reactor community, a tremendous amount of work has been done to illuminate irradiation-corrosion effects, and similar efforts are under way for heavy liquid metal and molten salt environments. While certain effects, such as radiolysis and irradiation-assisted stress corrosion cracking, are reasonably well established, the basic science of how irradiation-induced defects in the base material and the corrosion layer influence the corrosion process still presents many unanswered questions. In this review, we summarize the work that has been done to understand these coupled extremes, highlight the complex nature of this problem, and identify key knowledge gaps.

In situ and post-print defects, including excessive residual stresses and poor microstructural properties, are important concerns in the part design and setup stages of powder bed fusion (PBF) manufactured parts. Laser scan strategies are well known to be correlated with the development of these defects; however, due to the lack of complex scan strategy descriptors and the consequential imposition of simple scan strategies, these correlations are not well understood and are difficult to investigate. This work proposes a methodology for an intuitive quantitative descriptor of scan strategies that has the potential to provide quick prognoses to predict defects. To demonstrate this, a neural network is trained to accurately predict post-print residual stress distributions using the descriptor of a specified path. It is envisioned that this descriptor could allow for the circumvention of current costly prevention mechanisms and increase confidence and reliability in metal additive manufacturing technologies.

Fatty acid methyl esters (FAMEs) are sustainable biofuel that can alleviate high oil cost and environmental impacts of petroleum-based fuel. A modified 1,200 W high efficiency fruit blender was employed for continuous transesterification of various refined vegetable oils and waste cooking oil (WCO) using sodium hydroxide as a homogeneous catalyst. The following factors have been investigated on their effects on FAME yield: baffles, reaction volume, total reactant flow rate, methanol-oil molar ratio, catalyst concentration and reaction temperature. Results indicated that the optimal conditions were: 2,000 mL reaction volume, 50 mL/min total flow rate, 1% and 1.25% catalyst concentration for refined palm oil and WCO, respectively, 6:1 methanol-to-oil molar ratio and 62 - 63oC, obtaining yield efficiency over 96.5% FAME yield of 21.14 ´ 10-4 g.J-1 (for palm oil) and 19.39 ´ 10-4 g.J-1 (for WCO). All the properties of produced FAMEs meet the EN 14214 and ASTM D6751 standards. The modified household fruit blender could be a practical and low-cost alternative biodiesel production apparatus for continuous biodiesel production for small communities in remote areas.

The deformation behavior of materials that exhibit a ductile-to-brittle transition have traditionally been characterized ex-situ and limited to bulk samples. Here, we use a unique experimental setup to perform in-situ cryogenic mechanical testing of Sn 96 solder alloy in a clamped beam configuration at − 142 °C, well below the alloy’s DBTT. Electron backscattered diffraction analysis before and after the in-situ experiments showed how deformation ahead of the crack tip is accommodated by the Sn matrix or intermetallic phase particles. Similar to behavior observed in pure Sn, within the Sn matrix of the Sn 96 alloy deformation twinning is the primary deformation mechanism below the DBTT. Similar to the twins previously observed in pure Sn, twinning behavior in the Sn matrix is consistent with the formation of the {301} and {101} twins in Sn. Within the intermetallic phase in Sn96, slip steps were observed that were not observed prior to bending.

Helium implantation in surfaces is of interest for plasma-facing materials and other nuclear applications. Vanadium as both a representative bcc material and a material relevant for fusion applications is implanted using a Helium ion beam microscope, and the resulting swelling and nanomechanical properties are quantified. These values are put in correlation to data obtained from micro-residual stress measurements using a focused ion beam-based ring-core technique. We found that the swelling measured is similar to literature values. Further, we are able to measure the surface stress caused by the implantation and find that it approaches the yield strength of the material at blistering doses. The simple calculations performed in the present work, along with several geometrical considerations deduced from experimental results confirm the driving force for blister formation comes from bulging resulting mainly from gas pressure buildup, rather than solely stress-induced buckling. Graphic abstract: [Figure not available: see fulltext.]

While application of clustering algorithms to atom probe tomography data have enabled quantification of solute clusters in terms of number density, size, and subcomposition there exist other properties (e.g., volume, surface area, and composition) that are better determined by defining an interface between the cluster and the surrounding matrix. The limitation in composition results from an ion selection step where the expected matrix ion types are omitted from the cluster search algorithm to enhance the contrast between the matrix and cluster and to reduce the complexity of the search. Previously, composition determination within solute clusters has utilized a secondary envelopment and erosion step on top of conventional methods such as maximum separation. In this work, we present a novel stochastic method that combines the particle identification fidelity of a conventional clustering algorithm with the analytical flexibility of mesh-based approaches through the generation of alpha shapes for each identified cluster. The corresponding mesh accounts for concave components of the clusters and determines the volume and surface area of the clusters; additionally, the mesh boundary is utilized to update the total composition according to the internal ions.

Advancement of optoelectronic and high-power devices is tied to the development of wide band gap materials with excellent transport properties. However, bipolar doping (n-type and p-type doping) and realizing high carrier density while maintaining good mobility have been big challenges in wide band gap materials. Here P-type and n-type conductivity was introduced in beta-Ga2O3, an ultra-wide band gap oxide, by controlling hydrogen incorporation in the lattice without further doping. Hydrogen induced a 9-order of magnitude increase of n-type conductivity with donor ionization energy of 20 meV and resistivity of 10-4 Ohm.cm. The conductivity was switched to p-type with acceptor ionization energy of 42 meV by altering hydrogen incorporation in the lattice. Density functional theory calculations were used to examine hydrogen location in the Ga2O3 lattice and identified a new donor type as the source of this remarkable n-type conductivity. Positron annihilation spectroscopy confirmed this finding and the interpretation of the results. This work illustrates a new approach that allows a tunable and reversible way of modifying the conductivity of semiconductors and it is expected to have profound implications on semiconductor field. At the same time it demonstrates for the first time p-type and remarkable n-type conductivity in Ga2O3 which should usher in the development of Ga2O3 devices and advance optoelectronics and high-power devices, Comment: 15 pages, 7 figures

A study was conducted to better understand the roles of irradiation defects and cavities on the mechanical properties of 304 stainless steel. Micropillars were fabricated using focused ion beam techniques, and pillars were heat treated at 300°C to serve as a control, irradiated in situ to 5 dpa with 1 MeV krypton ions at 300°C, or pre-implanted with a specific amount of helium and then irradiated. Micropillars were compression tested in situ in a transmission electron microscope (TEM) using a picoindenter. The load–displacement curves were converted into stress–strain curves and mechanical properties were extracted. Irradiation hardening was observed with the yield stress being the highest in the pillar implanted with the least helium. TEM and energy-dispersive spectroscopy analysis showed the presence of irradiation-induced defects in krypton-irradiated samples and the presence of cavities.

Uranium dioxide is the standard fuel of the current nuclear reactor fleet and a potential fuel for future generation IV reactors. Enhancing the performance of uranium dioxide fuels necessitates a broader understanding of the fuel pellet/cladding mechanical interaction; this can be achieved through further study of the mechanical behavior of UO2. Small-scale mechanical testing can be used to evaluate the mechanical properties of materials while reducing the total volume of material required for testing. This is beneficial when studying nuclear materials because small test samples reduce the dose to the researcher and can reduce costs by permitting mechanical testing to be performed outside of hot cells. In this work in situ transmission electron microscopy microcantilever and nanoindentation testing was used to evaluate the deformation of UO2 at room temperature. The in situ testing was also used along with an innovative helium implantation technique to evaluate the effect of helium bubbles on the low temperature deformation of UO2. It was found that, under similar testing conditions, the unimplanted material formed a single critical crack while material containing helium bubbles at a dose of 1018 ions/cm2 responded with a large number of nanocracks, enhancing the toughness of the material.

Positron annihilation spectroscopy is a powerful tool to quantify the amount of vacancies and vacancy clusters in materials. The technique has been utilized to study the induced defects in materials after ion beam and neutron irradiations. This paper makes the case for how the technique can and should be utilized to quantify the defects created by irradiation in situ during irradiation to foster a more thorough understanding of the surviving defects after initial collision cascades. This paper outlines a future experimental approach and its meaning for the nuclear materials community, being able to benchmark commonly used rate theory models of damage evolution.

Electrochemical impedance spectroscopy (EIS) is a powerful technique for the non-destructive, dynamic measurement of electrochemical corrosion behavior in condensed environments, and is a demonstrated, in situ method for monitoring oxide films formed on metal surfaces in liquid metals. To characterize this capability, the impedance properties of three kinds of oxide films (anodic titanium oxide films, deposited Fe2O3 films, and thermally oxidized Fe samples) in liquid metals were examined using the EIS technique. The results show that the impedance response is related to the oxide film thickness and quality. The impedance of thin oxide films ( 200 nm) shows that the oxide film without cracks is stable in LBE and protects the substrate from corrosion. EIS is a promising method for accessing the electrochemical behavior of oxide films on metals and alloys in liquid metals.

Migration of water and ions dissolved in water through concrete is of interest in civil engineering. In particular, the behavior of radionuclides dissolved in water is of great interest to the nuclear industry because significant numbers of nuclear structures contain large amounts of concrete, acting as a barrier to radionuclides against entering the environment. Study of the migration of water molecules and ions in concrete hitherto required destructive chemical analysis. In this work, we present a non-destructive probe to investigate the uptake of uranium, iodine and water into mortar in situ using a time-of-flight neutron imaging method that allows selecting different neutron energies, providing elemental sensitivity in the analysis of the absorption process. First results indicate that water molecules are the fastest migrating species while iodine is significantly slower, and uranium was not observed to migrate through the structure within the time frame of the experiment and furthermore blocks the migration of water.

The deformation of materials at cryogenic temperature is of interest for space, arctic, and fundamental science applications. In this work, a custom-built cooling system attached to a commercial picoindenter was used for in situ cryogenic microcompression testing of equal-channel angular-pressed copper with real-time electron backscatter diffraction. Stress-driven grain growth at cryogenic temperatures was observed during a series of elastic and plastic deformations. These results provide direct evidence for the previously predicted phenomenon, whereas previous ex situ examinations demonstrated coarsening after cryogenic loading when samples were not maintained at cryogenic temperatures between deformation and characterization.

Focused ion beam machining revolutionized the way samples are studied in materials science. The introduction of this tool enabled researchers to break into new frontiers of research. While this method focused on the nanometer length scale, the mesoscale manufacturing of samples has not seen such advances. It remains a challenge to manufacture sample geometries too large for focused ion beam milling yet too small for conventional machining. Femtosecond laser ablation opens this length scale of sample space and allows the fabrication of numerous useful geometries. This paper outlines a state-of-the-art femtosecond laser machining system that can be used for rapid, micro- and mesoscale sample preparation. To illustrate the utility of this system, stress–strain data are presented for single-crystal Cu micropillars and three microscale tensile test specimens prepared from physical-vapor-deposited Cu and Ni foils.

The effect of thermal oxide layer on He implanted 316L stainless steel was studied to evaluate experimentally how thermal oxidation affects the diffusion and distribution of He in the material. In the case of thermal oxidation of a He implanted sample, with an increase in oxidation time, the max swelling height increases logarithmically as a function of time and finally saturates for all samples except for the lowest dose of implanted He. Concerning TEM results, two void regions are identified. Similar to the calculation, the total irradiated depth was around 250 nm and the large void region was formed around 100–150 nm depth. On the other hand, the small void region was observed immediately under oxide layer from the thermal oxidation. In contrast, there were no voids in the altered zone near the metal/oxide interface in the non-thermal oxidized/He implanted sample. This description of the phenomena was justified using the Kirkendall effect and the Point Defect Model.

Nickel-based alloys are extensively used in a wide range of extreme environments because of their exceptional mechanical properties. The excellent strength of these alloys is derived from the addition of long-range ordered precipitates, introduced by thermal aging. The interactions between the dislocations and LRO precipitates dictate the deformation modes and plastic response in these alloys. While the majority of studies have focused on L12-structured precipitate-strengthened Ni-based alloys, less work has considered the Ni-based alloys containing Pt2Mo-structured, Ni2(Cr,Mo)-typed precipitates. In these alloys, Pt2Mo-structured precipitates enable room-temperature deformation twinning in addition to slip, which increases strain hardenability measured from bulk mechanical testing. Although previous geometric-based model suggested that deformation twinning is favored over slip, the factors that influence the activation between twinning versus slip have not been thoroughly explored in this class of Ni-based alloys. In this work, molecular dynamics examined the possible types of dislocation and Pt2Mo-structured precipitate interactions at low temperature. Combined with in situ micromechanical testing, the role of resolved shear stresses on dislocation partials were shown to directly influence the activation of slip versus twinning. Additionally, using an energy-based approach, molecular dynamics results demonstrated a novel twin formation process, caused by the dislocation interaction with the Pt2Mo-structured precipitates.