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AbstractThe Second Target Station (STS) at the Spallation Neutron Source of the U.S. Department of Energy’s Oak Ridge National Laboratory is being designed to become the world’s highest peak brightness source of cold neutrons. As the STS project evolves, neutronics and other engineering analyses will inform many design iterations. To facilitate this process, a fully automated optimization workflow was developed to convert a parameterized computer-aided-design model of the target into an unstructured mesh geometry model and then to run a neutronics calculation and (optionally) a mechanical analysis for each design iteration. This workflow enables efficient, high-fidelity modeling; simulation; and optimization of new designs, as has been demonstrated for the optimization of the STS neutron moderators. In this paper, we present the results of our first major effort to automate the design optimization process for a spallation target. In the first analysis, the goal is to find optimal dimensions of a monolithic tungsten target coupled with an optimal super-Gaussian proton beam profile to deliver maximum brightness of the resulting neutron beams while maintaining good mechanical properties of the target. In the second analysis, geometric and beam parameters are optimized for an alternative design with tungsten plates, which can reach superior mechanical performance without compromising the neutronics performance. [ABSTRACT FROM AUTHOR]

This study investigates the role of geometrically necessary dislocations (GNDs) and microstructure on void nucleation and growth in wrought and additively manufactured (AM) tantalum subjected to high-strain rate loading. Multi-modal 3D data was collected using TriBeam tomography to calculate GND densities and their spatial relationship to voids. A microstructural comparison between the wrought and AM samples identified distinct void shapes and locations, with intragranular voids and more spherical voids frequently observed in the AM dataset. Results indicate that voids preferentially form at both high-angle grain boundaries and low-angle subgrain boundaries, the latter of which are frequently observed in the AM material. Through a radial distribution analysis of all voids in the datasets, significant GND localization to near-void-surface regions was observed in both samples. 3D crystal plasticity simulations were employed to extend the experimental observations, revealing higher void growth rates in [111] oriented grains when compared to [001] grains. The simulations also suggest that GNDs can be generated as part of the void growth process, with more GND accumulation for growth in a [111] grain than a [001] grain. These findings provide valuable insights into the links between nanoscale void nucleation, mesoscale void growth, and microstructural effects in dynamically loaded tantalum.

Shock wave loading of heterogeneous materials was numerically investigated using three models: a homogeneous alloy model with experimental parameters, an additive approximation model with parameters calculated from the constants and concentrations of the components, and a discrete numerical model constructed based on a random concentration distribution of components over the sample volume. The verification of the computational schemes was done by calculating the shock wave loading of homogeneous materials. Hugoniot curves were plotted and compared with experimental data to show a less than 5% deviation of the numerical results. A series of numerical simulations of spall fracture in homogeneous plates revealed that the free surface velocity profile resulting from spall fracture corresponds to the experimental profile. A relationship was derived to determine the ultimate spall strength for a heterogeneous medium based on the fracture parameters of its homogeneous components. The found homogeneous material parameters were used to simulate the shock wave loading of plates made of nickel titanium and tungsten carbide/cobalt cermet constructed with heterogeneous models. It was shown that the heterogeneous models can be effectively applied to problems of shock wave loading with spall fracture, and the deviation between the calculated free surface velocity of a heterogeneous plate and the experimental data does not exceed 10%. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of High Pressure Physics is the property of Chinese Journal of High Pressure Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A new design of spallation target has been installed and operated at the first target station of the ISIS Neutron and Muon Source (ISIS TS-1), as part of the recently completed “TS-1 Project”. Detailed Finite Element Analysis (FEA) simulations were used to guide the design process and predict target performance. Since the TS-1 Project target began operation in November 2022, operating data has been collected and used to validate the target simulation approach. Measured temperatures of 9 out of 10 target plates showed good agreement with FEA simulations of both steady-state and transient behaviour. However, the front target plate temperature was elevated compared to predictions. Because the installed target was now too radioactive to permit hands-on inspection, FEA simulations became an indispensable tool to understand the possible causes and safety implications of this anomalous behaviour. The anomalous elevated temperature appears to be highly localised; a combination of simulations and experiments indicates the mostly likely cause is poor thermal contact between the thermocouple and the bulk of the target plate. In all other respects the target is operating as predicted, and is running reliably at up to 120 kW. [ABSTRACT FROM AUTHOR]

In this study, effect of Fe concentration on the high temperature oxidation and microstructural stability of Fex(CrAlNi)100−x alloys (x = 25, 35, 45, 55, 65) at 1100 °C up to 168 h was investigated in air. Increasing Fe concentration decreased the molar fraction of B2 phase in as-cast alloys. However, microhardness values experienced only a 10% reduction (Fe25: 517.7 ± 19 HV, Fe65: 470.6 ± 22 HV) due to well-distributed B2 precipitates. After the exposures, coarsening of B2 precipitates was observed in all alloys, leading to a microhardness reduction of 20–25% after 168 h. Single-phase α-Al2O3 scales were formed on Fe25–Fe55 alloys. However, increasing Fe concentration resulted in deeper depletion zones due to reduced molar fraction and Al concentration of B2 phase. Moreover, Fe65 alloy failed to develop a protective α-Al2O3 scale due to decreased molar phase fraction and Al concentration of B2 precipitates, along with the low Cr concentration of the A2 phase. Additionally, α-Al2O3 scales were highly wrinkled due to the absence of reactive elements. Absence of reactive elements also resulted in oxide spallation and seemed to intensify with the increasing Fe concentration. Possible reasons for the increased oxide spallation with the increasing Fe concentration are discussed. Nevertheless, Fe25–Fe55 alloys displayed oxidation properties comparable to those of lean FeCrAl alloys while also possessing enhanced mechanical properties due to B2 reinforcement. [ABSTRACT FROM AUTHOR]

Mechanical properties of additively manufactured alloys are momentously affected by the fabrication defects, thus limiting their applications in extreme conditions. Here we report on a near fully dense 316L stainless steel via optimized laser processing parameters. The results reveal that the dynamic mechanical response exhibits much greater sensitivity to defects than the quasi-static one. The densest specimen (porosity

To organize the safe handling of activated material, knowing the residual dose rates is crucial. In this work, we present the pre-experiment activation analysis for an experiment in which tungsten blocks are irradiated by 800-MeV protons. In this analysis, we use the Monte Carlo N-Particle (MCNP) code for radiation transport, Attila4MC for unstructured mesh generation, and Activation in Accelerator Radiation Environments (AARE), including CINDER2008, for activation analysis. If the tungsten blocks must be removed within a day after the experiment, then exposure to personnel entering the room must be reduced. One exposure-reduction strategy is to add carbon steel shielding around the tungsten blocks, efficiently reducing the dose from the activated tungsten. However, the shielding becomes activated itself during irradiation: 56Mn is the dominant contributor for short decay times. The actual schedule at the time of the experiment allowed sufficient cool-off time for the tungsten in the room so that additional shielding was not necessary. A less rigorous comparison of the calculated values with the post-experiment measurements showed reasonable agreement. [ABSTRACT FROM AUTHOR]

The target segments of the Oak Ridge National Laboratory Second Target Station (STS) neutron production facility become highly activated due to spallation reactions or nuclei transmutation by primary protons and emitted neutrons. Once the target segments are removed from their location within the core vessel, decay dose rates must be accurately quantified to determine the shielding configurations of remote-handling tools and transport casks and to aid in planning maintenance activities. For this analysis, we utilized a hybrid unstructured mesh (UM)/constructive solid geometry approach for calculating spallation products and neutron fluxes, activation calculations using the AARE package that includes the CINDER2008 activation code to calculate the decay photon source at different cooling times, and the ADVANTG code to accelerate the final decay photon transport calculation. Both Type 316 stainless steel (SS-316) and lead were investigated as candidates for shielding materials. The decay photon transport calculation through the thick SS-316 or lead shields exhibited between 25 and 30 orders-of-magnitude attenuations in the radial direction, depending on the shield. Such a difficult shielding calculation required advanced variance reduction. ADVANTG has some missing features, which limits its usability in spallation neutron source applications. It does not support volumetric sources created for MCNP6.2 UM capability. An approximate source was created for this problem. Not only was this approximate source needed for running the ADVANTG calculation to generate the weight windows, but also it was essential to develop source biasing (SB) parameters that were crucial for dramatically accelerating the decay photon transport in this problem. With this approximate source, the analysis was completed in a very reasonable computational time, and the design of the STS remote-handling equipment was finalized. This paper compares the efficiency of Monte Carlo simulations with different weight window and SB parameters calculated using different approximate ADVANTG calculations. [ABSTRACT FROM AUTHOR]

The European Spallation Source (ESS) is a pulsed spallation neutron source currently being built in Lund, Sweden. At full power and beam energy, ESS will accelerate protons to 2 GeV at 5 MW (average pulse current of 62.5 mA, pulse length of 2.86 ms, and repetition rate of 14 Hz) onto a rotating, helium-cooled, tungsten target. This target is in a heavily shielded structure referred to as the target monolith, which is located inside the ESS target building. Directly on top of the target monolith shielding is a room referred to as the connection cell, which contains many important utility connections and control systems. Many connections from components in the target monolith, e.g., cooling water and electrical connections, exit the monolith into the connection cell and pass through the walls of the connection cell to reach other areas of ESS. When the accelerator is operating at ESS, the connection cell will be off limits to humans. This paper evaluates the prompt dose rates to several important materials in the connection cell and suggests an algorithm for evaluating the suitability of materials that might be used in the connection cell. [ABSTRACT FROM AUTHOR]

At the U.S. Department of Energy's Oak Ridge National Laboratory, the Second Target Station (STS) beamline sources for preliminary design have been used to perform a shielding analysis of the bunker. Prompt total effective dose rates (i.e., neutron plus photon effective dose rates when the proton beam is on) were calculated on top of the bunker roof and outside the bunker wall. These areas outside the bunker will be generally accessible, so the prompt total dose rate in these areas should not exceed 2.5 μSv‧h−1 (0.25 mrem‧h−1). This paper presents the required shielding thicknesses to meet this dose rate limit. In one instance, this dose rate limit is not met: For a combination of populated and unpopulated beamlines, the prompt total dose rate outside the bunker across from the unpopulated beamline, which has less shielding because of the lack of beamline shielding, slightly exceeds 2.5 μSv‧h−1. Once more details are known regarding the STS high-density concrete density and composition, a future analysis will investigate the shielding modifications required to reduce the calculated prompt total dose rates for this configuration to less than 2.5 μSv‧h−1. [ABSTRACT FROM AUTHOR]

Thermal spallation is the erosion of brittle materials subjected to high heat fluxes, such as a hot fire in a concrete structure. While experimental investigations provide valuable data on the spallation process, they lack generality to be extrapolated to other materials or loading conditions. This paper presents a numerical method for predicting bulk quantities of the spallation process, such as the average recession rate, for crystalline materials. The method is based on direct numerical simulations of the microstructure. The crystal grains and their boundaries are modeled with finite elements and cohesive zones. These elements have anisotropic and temperature-dependent physical properties, a novel level of fidelity and one that accurately captures known crystal phenomena including the α – β quartz transition. These models of the crystalline material and the thermal spallation process are validated against experiment results for Barre granite, and then applied to predict the thermal spallation of Martian basalt. Highlights: This paper presents a high-fidelity model of a process called thermal spallation. Each individual grain within a rock is simulated directly, with material properties that are both temperature- and direction-dependent. This computational model reproduces experimental results for Barre granite. The model is then used to predict thermal spallation of Martian basalt, which is relevant to landing large robot and human missions on Mars. [ABSTRACT FROM AUTHOR]

There is still a lack of understanding of a possible mechanical ablation mechanism and the causes of thermal degradation of thin indium tin oxide (ITO) films. A dual hyperbolic two temperature model is applied to the ultrashort pulsed laser ablation process of 100 nm indium tin oxide films. The model describes transient optical properties by taking into account the changes in the complex dielectric function due to laser excitation. The laser excitation is modelled by free electron dynamics and a nonlinear absorption coefficient for a laser pulse duration of 700 fs and a central wavelength of 1056 nm. For peak fluences F ≤ 0:35 J/cm², we find that the modeled strain exceeds the yield strain in the regions where the experimental craters show signs of mechanical ablation behavior. For larger peak fluences F > 0:35 J/cm² the model predicts lattice temperatures Tl exceeding the melting temperature Tmelt; ITO of indium tin oxide. The computed depth where Tl ≤ Tmelt;ITO agrees with the measured ablation crater depths. [ABSTRACT FROM AUTHOR]

High-energy heavy ions produced by accelerators are used in industrial and medical applications. Recently carbon ions have been used in the treatment of cancerous tumors. Heavy ions by the spallation process will activate the soft tissue components before tumors. In this research by GEANT4 toolkit and MCNPX code simulation were tried to calculate the secondary particles and radioactive elements produced in the soft tissue around tumors by the carbon ions spallation process. In the MCNPX code, the F8 tally card with the FT8 command was used to extract the activation and spallation information of secondary particles in the Z1=1 to Z2=25 atomic numbers range. It was shown that a wide range of radioactive elements was produced in healthy tissues in carbon therapy. In addition to produced secondary particles, the Be-10 and C-14 radioactive elements were produced in high-energy carbon ions in soft tissue. Also, the GEANT4 toolkit result of produced secondary particles dosimetry was shown that the secondary particles dose per carbon ion is between 1.66 to 33.54 nGy for carbon ion energy between 1140 to 5160 MeV. The tail for 3480, 4080, and 5160 MeV of carbon ion energy are 0.12, 1.01, and 11 cm respectively. The carbon ion beam divergence increases with beam energy and achieve to 33 mm for 5160 MeV carbon ion. [ABSTRACT FROM AUTHOR]

Three different chemical vapor deposition (CVD) aluminizing processes were adopted for preparing of (Ni, Pt)Al metallic coatings, whose microstructure, element content, phase constituent and gas hot corrosion performance were evaluated and comparatively analyzed. YSZ ceramic coatings were subsequently fabricated via electron beam physical vapor deposition (EB-PVD) technique on top of the optimized (Ni, Pt)Al bond coat surface, and thermal barrier coating (TBC) specimens were subjected to 1373 K long-term thermal shock. The surface of aluminized sample with a single external reaction generator is relatively compact, and no defects such as micropores and microcracks are observed. Only a large number of protruding sediments are detected at grain boundary as well as the degree of rumpling and cross-links of these sediments is more obvious. A large amount of Pt is enriched at that grain boundary, while elemental content of Al is lower at the same location. Meanwhile, such sample basically displays β-(Ni, Pt)Al phase, and only three very weak diffraction peaks belonging to ζ-PtAl2 coexist. After long-term thermal shock, the exposed region of bond coat shows two kinds of micro-morphology. The biggest distinction between them is that the composition of Pt and Al elements is evidently different. The interfacial separation of TBCs is mainly concentrated at interface between thermally grown oxide (TGO) and bonding layers, and a very small amount of TGO layer is merely adhered to bond coat surface. It demonstrates that TGO layer is densified and thickened with the extension of thermal exposure period, and then the mismatching of thermal expansion between Al2O3 and (Ni, Pt)Al bond coat occupies the dominant factor. In addition, the grain boundary ridges and undulations on bonding layer surface can also induce accumulation of the tensile stress and further accelerate degradation of the critical interlayer interface during cooling stage of thermal shock.

The mechanism of homo-heterogeneous melting of aluminum with subsequent fragmentation of the melt under the influence of an ultrashort laser pulse is implemented within the framework of a nonequilibrium continuum model with dynamically adapting computational grids. The interaction of slow heterogeneous and fast homogeneous melting is investigated. Melt parameters and features of mechanical fragmentation of the liquid phase of the metal due to negative pressure developing in the hydrodynamic unloading wave are determined. [ABSTRACT FROM AUTHOR]

Both the nanoscale helium (He) bubble and grain boundaries (GBs) play important roles in the dynamic mechanical behavior of irradiated nanocrystalline materials. Using molecular dynamics simulations, we study the shock-induced deformation and spallation failure of bicrystal copper with a nanoscale He bubble. Two extreme loading directions (perpendicular or parallel to the GB plane) and various impact velocities (0.5–2.5 km/s) are considered. Our results reveal that the He bubble shows hindrance to the propagation of shock waves at lower impact velocities but will accelerate shock wave propagation at higher impact velocities due to the local compression wave generated by the collapse of the He bubble. The parallel loading direction is found to have a greater effect on He bubble deformation during shock compression. The He bubble will slightly reduce the spall strength of the material at lower impact velocities but has a limited effect on the spallation process, which is dominated by the evolution of the GB. At lower impact velocities, the mechanism of spall damage is dominated by the cleavage fracture along the GB plane for the perpendicular loading condition but dominated by the He bubble expansion and void growth for the parallel loading condition. At higher impact velocities, micro-spallation occurs for both loading conditions, and the effects of GBs and He bubbles can be ignored. [ABSTRACT FROM AUTHOR]

The energy needed to deform an elastic solid may be recovered, while in Newtonian fluids, like water and glycerol, deformation energy dissipates on timescales of the intermolecular relaxation time τM. For times considerably longer than τM the existence of shear elasticity requires long-range correlations, which challenge our understanding of the liquid state. We investigated laser- driven free surface bubbles in liquid glycerol by analyzing their expansion and bursting dynamics, in which we found a flow- dominating, rubber- like elasticity unrelated to surface tension forces. In extension to findings of a measurable liquid elasticity at even very low deformation frequencies [L. Noirez, P. Baroni, J. Mol. Struct. 972, 16--21 (2010), A. Zaccone, K. Trachenko, Proc. Natl. Acad. Sci. U.S.A. 117, 19653--19655 (2020)], that is difficult to access under increased strain, we find a robust, strain rate driven elasticity. The recovery of deformation energy allows the bursting bubble to reach Taylor--Culick velocities 20- fold higher than expected. The elasticity is persistent for microseconds, hence four orders of magnitude longer than τM. The dynamic shows that this persistence cannot originate from the far tail of a distribution of relaxation times around τM but must appear by frustrating the short molecular dissipation. The longer time should be interpreted as a relaxation of collective modes of metastable groups of molecules. With strain rates of 106 s-1, we observe a metastable glycerol shell exhibiting a rubber- like solid behavior with similar elasticity values and characteristic tolerance toward large strains, although the molecular interaction is fundamentally different. [ABSTRACT FROM AUTHOR]

Adhesion strength between a substrate and its oxide scale grown on hot-rolled low carbon steel was evaluated by a hybrid numerical-experimental analysis of artificial spallation results. Interfacial fracture of the scale was reproduced by a scratch tester, in which the onset of interfacial fracture was identified by examining the mechanical responses along with microscopic observation. Critical traction at interface was solved quantitatively by numerical inverse analysis with finite element method. Influence of residual stress on adhesion strength was also investigated. Finally, validity of the identified adhesion strength was confirmed by analytical comparison with energy release rate reported in previous research. [ABSTRACT FROM AUTHOR]

The present study aimed to provide new insights into the behavior of high-strength low-alloy steel under dynamic compression and to promote its use in high-stress applications. The dynamic compression response of a Cr-Ni-Mo-V steel under shock stresses ranging from 3.54 GPa to 19.76 GPa was investigated using loading technology. The free surface velocity of the specimen was measured using a displacement interferometer system with the range of 166–945 m/s. The Hugoniot elastic limit (HEL), spalling fracture, and microstructure evolution of specimens under different shock stresses were determined. The results showed that an α→ε phase transition occurred in the material at an impact stress of 15.63 GPa, leading to a change in particle velocity. The relationship between the shock wave velocity and particle velocity was found to be linear. The HEL of the steel was found to be consistent at 2.28 GPa, while the spall strength showed a more complex relationship with the increasing shock stress. Initially, the spall strength increased and then decreased with increasing shock stress before increasing again after the phase transformation. The fracture mode of the steel shifted from brittle fracture to ductile fracture with the increasing impact stresses, which is related to the previous plastic deformation under different impact loads. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of High Pressure Physics is the property of Chinese Journal of High Pressure Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Thin-walled castings made from Cr–Ni austenitic steels offer a combination of light weight of a near-net component with significant high temperature corrosion protection by forming a surface oxide layer. However, above critical service conditions (temperature, atmosphere, thermal cycling), oxidized surface can result in intensive surface degradation due to scale spallation. Scale spallation can decrease the wall thickness which could be detrimental to the in-service life of thin-walled castings. Experiments and stochastic simulations of spallation assisted oxidation were performed with three cast austenitic heat-resistant steels having different Cr–Ni concentrations at temperatures between 900 and 1000 ℃ on air and water vapor containing combustion atmosphere. The recorded specimen and spalled scale weight together with SEM and TEM analysis were used to predict the oxidation constant to form adherent layer and spallation intensity. Three oxidation modes, including oxidation controlled by diffusion with forming a strongly adherent to steel surface multi-layered scale, spallation assisted oxidation, and oxidation with additional partial vaporization of scale components in the water vapor environment were distinguished. It was revealed that the Cr and Ni concentrations moved temperature boundaries between these surface degradation mechanisms depending on the exposed oxidation environment. Our approach is aimed to alleviate an appropriate alloy selection for service conditions. [ABSTRACT FROM AUTHOR]

Mo(Si,Al)2 with different yttrium (Y) additions (up to 2 at.%) was synthesised by dry powder mixing followed by compaction and sintering. In as-sintered materials, Y was present as yttrium aluminium garnet. The materials were exposed in air at 1500 °C for up to 250 h to study the effect of Y on oxidation behaviour. The oxides formed were investigated using scanning electron microscopy (SEM)-based techniques and X-ray diffraction. While the Y-free Mo(Si,Al)2 formed a scale consisting of Al2O3 and a small amount of mullite, the Y-containing samples formed oxides containing both yttrium silicate and larger fractions of mullite, in addition to Al2O3. Oxidation rate, scale spallation, as well as the evaporation of Mo, all increased with Y addition. [ABSTRACT FROM AUTHOR]

We performed tomographic investigation of the most heavily perturbed (thus highly radioactive) rod and its pristine/unirradiated replicate from the target No. 12 of the Swiss neutron spallation source (SINQ). The tomographic dataset reveals the 3D re-distribution of the lead filling inside the irradiated Zircaloy tube. The change in the linear attenuation coefficient of both the lead filling and the Zircaloy tube of the irradiated rod (due to the presence of the entrapped spallation products) in comparison with the pristine/unirradiated material is quantified. The dataset provides valuable input for the enhancement of safety and efficiency of future spallation targets at SINQ. [ABSTRACT FROM AUTHOR]

Cr–Ni austenitic steels offer significant high temperature corrosion protection by forming a surface oxide layer. However, above critical service conditions (temperature, atmosphere, thermal cycling), oxidized surface can experience intensive degradation because of scale spallation, which could be detrimental to the in-service life. To predict the effect of scale spallation on oxidation kinetics, a simulation was implemented using a stochastic model. The model considers topological parameters and intensity of spallation which can occur, while delivering a true oxidation constant. The experimental procedure identified the amount of formed spalled scale and topology of spallation based on the use of element mapping of the surface. This information was used to determine a true kinetic constant for a corresponding spallation intensity in oxidized Cr–Ni austenitic steel. To illustrate the capability of the stochastic model, a parametric analysis was performed. The model verified how the spallation parameters could change the oxidation processes from parabolic growth of an adhered oxide layer without spallation to a mixed linear-parabolic, or with a constant thickness of residual scale at high spallation intensity. The spallation model will be used in a separate article to characterize high temperature surface degradation of several Cr–Ni austenitic steels during harsh oxidation environments. [ABSTRACT FROM AUTHOR]

Laser shock loading is a more promising technology for investigating spallation damage in materials under shock-wave loading. In this paper, shock-induced spallation in a 90W–Ni–Fe alloy at an ultrahigh tensile strain rate of 106 s−1 is investigated using a superintense ultrafast laser facility. The spallation of the 90W–Ni–Fe alloy was dominated by a transgranular fracture of tungsten(W) particles with a high spall strength of 6.46 GPa. Here, we found an interesting phenomenon that the formation of nanograins inside W particles leads to a new mode of transcrystalline fracture of W particles during the laser shock loading. Futhermore, most voids were nucleated inside the W particles rather than at the W/γ-(Ni, Fe) matrix-phase interface. This result contradicts the fracture theory under quasi-static loading, which posits that the W/γ-(Ni, Fe) matrix-phase interface is not the preferred site for the initial failure under shock loading.

In this work, the high-temperature corrosion behaviour of pure Ni3Al (P–Ni3Al) and alloyed (2.99 wt.%Ti) Ni3Al (Ti–Ni3Al) was investigated in Ar-0.2%SO2 gas at 900–1100 °C for up to 100 h. The corrosion kinetics of P–Ni3Al and Ti–Ni3Al reveal that Ti addition increased the total weight gain at all temperatures by approximately 10 times than without Ti (P–Ni3Al). The alloy initially gained more weight with the increase in temperature; but later on, the corrosion kinetics changed. Because of the extensive scale spallation during cooling, which causes the creation of large and deep geometric voids, the corrosion kinetics of P–Ni3Al deviated from the parabolic rate law. At all temperatures, Ti strengthened the scale adherence as it occupied the Al substitutional sites with a broad atomic radius, and facilitated the creation of ordered phases known as the gamma prime phase (γ′). Owing to the ordered structure, it was assumed that the diffusion of occupying atoms would be slower, thereby increasing the scale adherence. Darker inclusions were found in Ti–Ni3Al at the scale–matrix interface, which were rich in TiS owing to inward sulphur diffusion.

[Display omitted] • SLM-316L exhibit much larger sensitivity to defects on the dynamic mechanical response than the quasi-static case. • Intrinsic pore defects should be responsible for the anisotropic spallation behavior of the SLM-316L. • Dislocation slip dominates the spallation mechanism, accompanying by a small amount of twinning and martensite transition. Mechanical properties of additively manufactured alloys are momentously affected by the fabrication defects, thus limiting their applications in extreme conditions. Here we report on a near fully dense 316L stainless steel via optimized laser processing parameters. The results reveal that the dynamic mechanical response exhibits much greater sensitivity to defects than the quasi-static one. The densest specimen (porosity < 0.01 %, 260W-316L) exhibits superior spall strength of 3.87 GPa and negligible damage fraction of 0.03 % at peak stress of 4.8 GPa, which are 12 % higher and 92 % smaller than those of 0.18 % porosity specimen (300W-316L). For both horizontal and vertical impacts, hardly any anisotropy of spall strength is observed in 260W-316L, demonstrating the crucial role of the pore defects on the dynamical behavior. Moreover, dislocation slip dominated spallation mechanisms have been observed in the additively manufactured 316L specimens, accompanied by a small amount of deformation twinning and martensitic transitions. This comprehensive understanding of the defect-dependent spallation behavior and deformation mechanisms provides valuable insights for optimizing the dynamic mechanical properties of additively manufactured metals and alloys. [ABSTRACT FROM AUTHOR]

The experiment AMS on the International Space-Station has produced accurate cosmic ray spectra for many chemical elements, both primaries like He, C, O, Fe, other cosmic ray (CR) primaries like Ne, Mg, and Si, secondaries like Li, Be, B, and of mixed provenance, like N, Na, and Al. The AMS spectra demonstrate that interaction is seriously diminishing fluxes up to a rigidity of about 100 GV, and so the existing models for CR interaction have to be re-examined. Based on earlier well-established ideas a model is proposed here that focusses on the cosmic ray interaction first in the wind shock shell of super giant stars, when the supernova driven shock races through, and second in the OB-Superbubble surrounding the SN: These stars include both red super-giant stars and blue super-giant stars; both produce black holes in their explosion, and drive winds and jets with electric currents. Variability of these winds or jets gives rise to temporary electric fields, as has recently been demonstrated, and discharge (so lightning) acceleration gives steep spectra, with synchrotron losses to p − 5 in momentum p ; these spectra are typically observed in both Galactic and some extragalactic radio filaments. Analogous hadron spectra p − 4 excite a flat spectrum of magnetic irregularities in the bubble zone, which in turn yields a steep dependence of residence time versus energy, with power − 5 / 3. This spectrum is indicated by the AMS data and appears to be required to explain the CR spectra below 100 GV. The emphasis in this paper is to work out the interaction of the freshly accelerated cosmic ray particles. In the model presented here the interaction is derived as a function of time, and then integrated, or developed to long times. The model gives a rigidity dependence of the secondary/primary ratio of slope − 1 / 3 as well as the strong reduction of the primary fluxes below a rigidity of about 100 GV, relative to a power-law injection spectrum, with slope + 2. The two key aspects based on blue super-giant stars and a magnetic irregularity spectrum in the bubble zone given by lightning are (i) a much larger column of interaction, allowed because of heavy element enrichment of the interaction zone, and (ii) even He, C, and O may have a small secondary contribution, as the difference to the Fe spectrum suggests; this small secondary component is visible in the 3 He/ 4 He ratio. The model may also explain the spectrum of CR anti-protons, the gamma-ray spectra of the Galaxy and the high energy neutrino spectrum of our Galaxy, including also red super-giant stars as sources. ISM-SNe, i.e. SN Ia and neutron-star SNe, contribute to CR protons and CR He nuclei. [ABSTRACT FROM AUTHOR]

[Display omitted] • Failure of the mass-on-spring system is discussed. • Fracture delay and strength increase for high rates are studied. • The oscillator model is calibrated to address three sets of experimental data. • Analogies between the oscillator model and the incubation time model are shown. The work considers failure of a linear oscillator (a mass-on-spring system) and the corresponding simple engineering approach to dynamic fracture of solids. The system is studied when subjected to two distinct types of load: a short pulse load and a linearly increasing load. These two cases are used to reveal two key dynamic fracture effects observed in dynamically loaded media: the fracture delay and increase of the system strength for high-rate loading. The inertia of the mass helps to capture these effects and thus to clearly show inapplicability of standard strength models when dynamic loads are considered. The linear oscillator is shown to be a basis for an easy to operate yet capable fracture model which admits "ad-hoc" application to various dynamic fracture cases. In this work the model is calibrated in order to fit known experimental results on dynamic crack initiation in plates and on spallation observed in rods. The model shows good performance despite its simplicity and strength of the made assumptions. [ABSTRACT FROM AUTHOR]

Both the nanoscale helium (He) bubble and grain boundaries (GBs) play important roles in the dynamic mechanical behavior of irradiated nanocrystalline materials. Using molecular dynamics simulations, we study the shock-induced deformation and spallation failure of bicrystal copper with a nanoscale He bubble. Two extreme loading directions (perpendicular or parallel to the GB plane) and various impact velocities (0.5–2.5 km/s) are considered. Our results reveal that the He bubble shows hindrance to the propagation of shock waves at lower impact velocities but will accelerate shock wave propagation at higher impact velocities due to the local compression wave generated by the collapse of the He bubble. The parallel loading direction is found to have a greater effect on He bubble deformation during shock compression. The He bubble will slightly reduce the spall strength of the material at lower impact velocities but has a limited effect on the spallation process, which is dominated by the evolution of the GB. At lower impact velocities, the mechanism of spall damage is dominated by the cleavage fracture along the GB plane for the perpendicular loading condition but dominated by the He bubble expansion and void growth for the parallel loading condition. At higher impact velocities, micro-spallation occurs for both loading conditions, and the effects of GBs and He bubbles can be ignored.

Targeted Alpha Therapy (TAT) has shown very high potential for the treatment of cancers that were not responsive to other therapy options (e.g., β− therapy and chemotherapy). The main constraint to the widespread use of TAT in clinics is the limited availability of alpha-emitting radionuclides. One of the most promising candidates for TAT is 225Ac (t 1/2 = 9.92 days), which can be used directly in combination with selective biomolecules (e.g., antibodies, peptides, etc.) or be a generator source of 213Bi (t 1/2 = 45.6 min), another shorter-lived TAT radionuclide. Several strategies are currently under investigation to increase the supply of 225Ac. One of the most attractive options is the irradiation of natural thorium-232 targets with high-energy protons (≥100 MeV). However, there are several challenges associated with this production method including the development of an efficient radiochemical purification method. During irradiation of natural thorium with proton energy above 100 MeV, several Ra isotopes (223,224,225Ra) are produced. 223Ra (t 1/2 = 11.43 days) is used for the treatment of bone metastases and can also be used as a generator source for 211Pb. Additionally, 225Ra (t 1/2 = 14.9 days) can be a valuable source of isotopically pure 225Ac. In the present work, we address the radiochemical separation aspects of isolating Ac and Ra isotopes from irradiated thorium targets. [Display omitted] • Actinium-225 (t 1/2 = 9.92 d) is one of the most promising candidates for Targeted Alpha Therapy (TAT) • The irradiation of natural thorium with high energy protons can provide clinically relevant amounts of 225Ac/213Bi and 223Ra • Ac and Ra can be isolated from the bulk mass of Th(IV) and co-produced fission products via cation exchange chromatography in trichloacetic acid • DN Resin allows the purification of Ac from lanthanides [ABSTRACT FROM AUTHOR]

The isothermal oxidation behavior of Ni–25Cr–10Fe–xSi (x = 1, 2, 3, 4 wt%) alloys at 1000°C in ambient air was investigated. The thermodynamics and kinetics of the oxidation behavior were analyzed using scanning electron microscopy with energy‐dispersive X‐ray spectroscopy, Raman spectroscopy, and the Thermo‐Calc software with the TTNI8 database. The weight gain per unit area of the four alloys showed a parabolic relationship with the oxidation time. The weight gain of the oxides decreased with the addition of larger amounts of Si from 1 to 3 wt%; however, this trend was lost when excessive addition of Si (4 wt% Si) was added. A sufficient amount of discontinuously distributed SiO2 precipitates resulted in better oxidation resistance and adhesion properties than continuous SiO2 layers. The spallation resistance of the oxide scales is believed to be mainly dependent on the distribution of the SiO2 layer rather than the content of SiO2; 3 wt% is a reasonable reference value for Si addition for improving the oxidation resistance of Ni–25Cr–10Fe alloys. [ABSTRACT FROM AUTHOR]

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Bond coats in environmental barrier coatings (EBCs) prevent oxidants from penetrating the substrate, mediate the mismatch of the coefficient of thermal expansion (CTE), and improve the adhesion strength between adjacent layers. However, the development of bond coats is rarely studied systematically. In this paper, the research status of the bond coats in EBCs is introduced in detail, including the materials and deposition methods. Thus far, Si, modified‐Si, mullite, etc., have been employed as bond coats. Nevertheless, visible drawbacks of each bond coat limit their application at high‐temperatures in extreme environments. Si bond coat is easily oxidized and forms thermally grown oxides that form cracks, resulting in delamination, spallation, and failure of EBCs. In the Si–HfO2 bond coat, the optimal ratios of Si/HfO2, deposition methods, distribution of Si and HfO2, and oxidation of Si remain completely unsolved. For mullite bond coat, SiO2 suffers selective evaporation in the water vapor environment, and the ratios of the Al2O3 and SiO2 in mullite coatings restrict its service lifetime. HfSiO4 is a potential candidate acting as a next‐generation bond coat in EBCs is proposed. Furthermore, choosing reasonable deposition methods is beneficial to improve the performances of the bond coats in EBCs. [ABSTRACT FROM AUTHOR]

In the paper, we study the formation of laser-induced periodic surface structures (LIPSS) on diamond-like nanocomposite (DLN) a-C:H:Si:O films during nanoscale ablation processing at low fluences—below the single-pulse graphitization and spallation thresholds—using an IR fs-laser (wavelength 1030 nm, pulse duration 320 fs, pulse repetition rate 100 kHz, scanning beam velocity 0.04–0.08 m/s). The studies are focused on microscopic analysis of the nanostructured DLN film surface at different stages of LIPSS formation and numerical modeling of surface plasmon polaritons in a thin graphitized surface layer. Important findings are concerned with (i) sub-threshold fabrication of high spatial frequency LIPSS (HSFL) and low spatial frequency LIPSS (LSFL) under negligible surface graphitization of hard DLN films, (ii) transition from the HSFL (periods of 140 ± 30 and 230 ± 40 nm) to LSFL (period of 830–900 nm) within a narrow fluence range of 0.21–0.32 J/cm2, (iii) visualization of equi-field lines by ablated nanoparticles at an initial stage of the LIPSS formation, providing proof of larger electric fields in the valleys and weaker fields at the ridges of a growing surface grating, (iv) influence of the thickness of a laser-excited glassy carbon (GC) layer on the period of surface plasmon polaritons excited in a three-layer system "air/GC layer/DLN film". [ABSTRACT FROM AUTHOR]

The effectiveness of small-bubble gas injection to mitigate cavitation-induced erosion damage and decrease strain in Spallation Neutron Source (SNS) target vessels was characterized using photography, laser-line scanning, and in-situ vessel strain measurements. Observations from early targets showed that erosion damage caused appreciable mass loss along the target vessel inner wall. Later target designs incorporated a cavitation mitigation technique called small-bubble gas injection, in which small helium gas bubbles were introduced into the flowing mercury during operation. Samples removed from target vessels after operation revealed that gas injection greatly reduced or eliminated erosion damage. Photographs of the target interiors showed areas where significant erosion damage occurred in targets that were operated without gas injection. The same areas had no observable erosion damage in targets that were operated with gas injection. Laser-line scan measurements were performed on samples from several target vessels operated with and without gas injection to measure the extent of erosion damage and quantify the effect of gas injection on erosion. In-situ strain measurements during operation showed that gas injection reduced the target vessel strain by 25%–75%. These results provide conclusive confirmation that gas injection effectively mitigated erosion damage and reduced strain in SNS target vessels during operation.