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It is extremely important to predict the growth, aggregation, and coalescence failure of voids during the dynamic tensile fracture of ductile metals. In the present work, we used the finite element—smoothed particle hydrodynamics (FE-SPH) adaptive method to simulate the plate impact of tantalum simultaneously from macro- and meso-scales. For macro simulation results, the spallation phenomena and free-surface velocity were in good agreement with the experimental results, verifying the correctness of the simulation method and material model. Moreover, the free surface velocity profiles simulated by the FE-SPH adaptive method is closer to the experiment than those by the finite element method. According to the magnified details of the damage, we envisaged that the deleted elements are converted to SPH particles to represent the formation of voids. By comparing the porosity, we demonstrated the rationality of this envisagement and determined the fine mesh size to simulate growth, aggregation, and coalescence of actual meso-voids. On this basis, we proposed a void-position tracking method to accurately track the temporal and spatial information of voids. Such information would provide a detailed range of damage and describe the features and macro factors affecting void evolution. In general, the fine mesh FE-SPH method can well predict the damage distribution of spallation simultaneously in macro- and meso-scales, and this simple method has important applications. [ABSTRACT FROM AUTHOR]

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]

Aluminum nanoparticles (Al NPs) are an attractive material for plasmonic and energetic applications. Herein, we investigate the response of spherical and nonspherical (cubes, pyramids, and pentagonal rods) Al NPs to rapid laser heating. Rapid surface diffusion reconfigures the shaped Al NPs toward a spherical geometry. Based on simulations, the surface diffusion occurs below the bulk Al melting temperature. When exposed to sufficient laser flux, Al NPs of all geometries spall. The critical laser flux to induce spallation depends on pulse duration and initial particle geometry. Thermal simulations indicate that complete Al melting occurs in less than 5 ns, with steady state occurring before 20 ns. Experimentally, spallation was observed between 18 and 79 ns. The laser conditions to induce spallation in an oxygen-deprived environment (<200 ppm oxygen) are identical to those in open air, suggesting a thermomechanical spallation mechanism rather than a diffusion-reaction mechanism. [ABSTRACT FROM AUTHOR]

When the severity of high-temperature environments increases, the oxidation mode changes from a normal oxidation mode, when a formed oxide layer protects the surface of austenitic heat-resistant cast steels, to an extreme mode, when scale spallation and partial vaporization intensify surface degradation. These processes can also influence each other. On the example of two oxidized austenitic heat-resistant steels with different alloying levels, we show how the described simulation/experimental methodology may be applied to analyze and quantify the synergetic kinetics of the extreme surface degradation processes. The surface degradation processes were formulated using diffusion-controlled parabolic oxidation, time-dependent vaporization, and spallation with an intensity cross-linked to the instantaneous thickness of the oxide layer. The 400 h tests were performed in air and water vapor-containing combustion gases at upper working temperatures. Three experimentally obtained surface degradation quantities included changing the weight of the specimen with adherent oxide, the weight of the spalled scale, and the thickness of the formed adherent oxide. These experimental quantities were used to compute the values of oxidation, vaporization, and spallation kinetic constants for each uninterrupted oxidation test. An additional interrupt every 100-h test was also performed to verify the model-predicted trends. It was shown that the alloying level in austenitic heat-resistant cast steel determines its ability to withstand surface degradation at extreme oxidation mode by the synergetic effects of oxidation, vaporization, and spallation. The described approach can be used for the metallic component lifetime prediction in severe gaseous environments. [ABSTRACT FROM AUTHOR]

In this study, dynamic mechanical response and the corresponding atomic mechanisms of single-crystal tungsten under extreme strain rates (109 s−1) are investigated using molecular dynamics simulations. The results show that crystal orientation plays an important role in the stress–strain relationship. The critical stresses for the beginning of plastic deformation are 59.4, 48.0, and 25.2 GPa for quasi-isentropic tensile loading along [111], [110], and [100] crystal orientations, respectively. The atomic behavior during plastic deformation suggests that [100] and [110] experience stress relaxation through phase transitions, while not in the [111] tensile direction. During spallation, sub-grain boundaries formed at twin junction in the [100] and [110] directions serve as nucleation sites for voids. The void grows in a planar way (along the twin) after generation, while stops growing at another misoriented twin junction. In the [111] tensile test, spallation occurs in the stress-concentration area, and finishes in a very short time interval with huge void coalescence. Our findings not only provide atomic insights into the anisotropic mechanical behaviors during spallation of tungsten under high strain rates, but also shed lights on the colorful plastic deformation behaviors from laser-shock experimental observation. [ABSTRACT FROM AUTHOR]

Purpose: High-energy heavy ions generated by accelerators utilized in industrial and medical uses. Ar, C, and He heavy ions have been used in the treatment of cancer. In this research, it was tried to calculate the radioactive elements production in healthy tissues around tumors by heavy ions spallation process in the direct usage of highenergy ions for the treatment of cancerous tumors. Materials and Methods: The radioactive elements production in body tissues irradiated with heavy ions was calculated by Monte Carlo N Particle X-version (MCNPX) code based on the Monte Carlo method. The F8 tally card with FT8 command was utilized to derive the activation and spallation data in the range of Z1 to Z2 atomic numbers. Results: A wide range of radioactive elements was created in healthful tissues in Ne, C, Ar, and He heavy ions therapy. Results show that 10Be,14C, 26Al, 36Cl, 39Ar, 40K, 39Ar, 32Si, 22Na, and 36Cl radioactive materials were produced for high-energy heavy ions spallation in healthy soft tissue. Conclusion: The results of this research show that due to using directly high-energy ions to treat internal tumors, healthy soft tissue is activated. Also, by irradiated Ne, C, Ar, and He ions, the radioactive elements are produced with high gains and long half-lives. Therefore, in the therapy of cancerous tumors with high-energy ions, due to the production of radioactive agents, healthy tissues are at high risk. [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.

AbstractAn innovative design is introduced for neutron transmutation employing a proton accelerator in conjunction with a compact subcritical system. The transmutation converter comprises a spherical target enveloped by a subcritical assembly. The subcritical assembly consists of a moderator and low-enriched uranium in shell plates. The subcritical assembly has an inner radius of 10 cm and a thickness of 40 or 55 cm. The material used for the target is lead, and beryllium or beryllium oxide is used as a moderator. Low-enriched uranium in the subcritical assembly contains 5% 235U. The transmutation half-life is inversely proportional to the integral of epithermal 99Tc capture rates. The MCNP6 simulation demonstrates that the transmutation half-life is less than 1 year when exposed to 1-GeV protons at 5 mA. Additionally, it is notable that this half-life can be further reduced with increased proton energies and currents. Previous studies have reported that the 99Tc transmutation half-life using fast reactors and an accelerator-driven system ranges from tens to hundred years; this design concept represents a substantial advancement to previous research efforts. [ABSTRACT FROM AUTHOR]

Interferometry allows to measure microscopic displacements in the nanometer scale. This work introduces an imaging pump-probe interferometer that enables to detect the spatially resolved phase shift of the probe radiation being reflected on a sample surface after ultrashort pulsed laser excitation with a temporal resolution of 40 fs and a maximum temporal delay of 3 ns. The capability of the pump-probe interferometer is demonstrated on the spallation of a thin gold film upon femtosecond laser irradiation. The pump-probe interferometer enables to measure a minimum phase change of Δ φ < π / 10 which corresponds to a displacement of Δ h < 12.5 nm for the applied probe wavelength of 500 nm. Upon irradiation, two distinct phase changes are observable: First, an abrupt minor phase shift has been measured in the femtosecond range, which is attributed to the changed optical properties of the sample surface after excitation. Second, a more pronounced continuing phase shift increase is detectable after a few tens of picoseconds resulting from the onset of spallation. Based on the measured spatially resolved phase shift, the transient surface topography during the spallation is reconstructed. The determined velocity of the ablated material reaches a maximum of a few 1000 m/s at ten picosecond after irradiation and decreases to 250 m/s afterwards. Consequently, the introduced imaging pump-probe interferometer provides important insights into the physical processes during laser excitation as well as the subsequent laser-induced ablation, and will enable to validate theoretical models quantitatively in following studies. [ABSTRACT FROM AUTHOR]

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]

Recent research work revealed that Ni43.9Co22.4Fe8.8Al10.7Ti11.7B2.5 HEA is one of the ultra-high strength and ductile superlattice alloys. In this work, high-temperature oxidation behavior of the as-cast Ni43.9Co22.4Fe8.8Al10.7Ti11.7B2.5 alloy was investigated at 1000 ℃ up to 100 h. The oxidized samples were characterized using X-ray Diffractometer, Energy Dispersive Spectroscopy, and X-ray Photoelectron Spectroscopy. The results revealed that the initial microstructure of the alloy consists of face centered cubic (FCC) and L12 structures. High-temperature exposure resulted in the formation of Al2O3 and TiO2 scales during the initial hours of oxidation, which eventually spall-off after 25 h of exposure allowing further oxidation. The results showed that protective oxide layers such as Al2O3 and TiO2 were not present after 100 h of exposure. The external layer of the 100 h oxidized sample was composed of Fe, Co, and Ni-rich oxides which are known to have mere effective resistance against oxygen ingression. The alloy which has superior strength and ductility may be used for high temperature applications after attaining the thermally stable fine-grain microstructure by suitable thermomechanical processing / providing oxidation resistance coating / by doping with elements having superior oxidation resistance.

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.)

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

Purpose: High-energy heavy ions generated by accelerators utilized in industrial and medical uses. Ar, C, and He heavy ions have been used in the treatment of cancer. In this research, it was tried to calculate the radioactive elements production in healthy tissues around tumors by heavy ions spallation process in the direct usage of high-energy ions for the treatment of cancerous tumors. Materials and Methods: The radioactive elements production in body tissues irradiated with heavy ions was calculated by Monte Carlo N Particle X-version (MCNPX) code based on the Monte Carlo method. The F8 tally card with FT8 command was utilized to derive the activation and spallation data in the range of Z1 to Z2 atomic numbers. Results: A wide range of radioactive elements was created in healthful tissues in Ne, C, Ar, and He heavy ions therapy. Results show that 10Be,14C, 26Al, 36Cl, 39Ar, 40K, 39Ar, 32Si, 22Na, and 36Cl radioactive materials were produced for high-energy heavy ions spallation in healthy soft tissue. Conclusion: The results of this research show that due to using directly high-energy ions to treat internal tumors, healthy soft tissue is activated. Also, by irradiated Ne, C, Ar, and He ions, the radioactive elements are produced with high gains and long half-lives. Therefore, in the therapy of cancerous tumors with high-energy ions, due to the production of radioactive agents, healthy tissues are at high risk.

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]

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.)

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]

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]

• The spall strength of Al 0.1 CoCrFeNi HEA is improved via pre-strain. • Pre-strain smears elastic–plastic transition upon shock loading. • Pre-strain affects the spatial features of damage evolution in Al 0.1 CoCrFeNi HEA. The effects of pre-strain on spallation damage of an Al 0.1 CoCrFeNi high-entropy alloy are investigated with plate impact loading. During the pre-strain process, Kink bands and dislocations are generated in the microstructures. Pre-strain smears elastic–plastic transition upon shock loading and improves spall strength via dislocation strengthening. Although the level of pre-strain does not affect the ductile damage mode, it has a pronounced effect on damage evolution. [ABSTRACT FROM AUTHOR]

Failure and healing behavior of oxide scales for powder metallurgy superalloy with varying Nb contents (0, 0.5, 1, 2 wt%) during cyclic oxidation were studied. The cyclic oxidation test of four alloys was conducted using the discontinuous thermogravimetric method which consists of 100 cycles of 1 h exposure in air from 20 °C to 900 °C. The oxide scales after cyclic oxidation were systematically characterized by scanning electron microscope (SEM), laser scanning microscopy (LSM) etc. It has been found that the spallation of oxide scale in all alloys took place via expanding of the initiated cracks at grain boundaries into grain matrix. After spallation, the exposed alloy matrix would be re-oxidized into a Cr 2 O 3 layer to recover the failed oxide scales. The spallation tendency of oxide scale was significantly inhibited by Nb addition. This can be ascribed to the faster regeneration of Cr 2 O 3 layer in alloy with higher Nb content. • Nb addition significantly decreased the spallation of oxide scales. • The spallation in oxide scales starts in terms of cracks near grain boundaries. • The repetitive regeneration of Cr 2 O 3 of high-Nb alloy resulted in a smaller spallation area of the oxide scales. [ABSTRACT FROM AUTHOR]

• Shock response of CoCrNi-based MPEAs tuned with Fe/Mn elements was investigated. • Fe/Mn elements reduce the defect nucleation barrier and improve the plastic deformability. • Mn element significantly reduces the Hugoniot elastic limit (HEL) and spall strength. • Two modes of void nucleation induced by waveform profiles were revealed. Recent researches on concentrated solid solutions have emphasized the role of various solute interactions in determining anomalous dislocation core and plastic deformation. However, the influence path of element tuning under extreme conditions is still unclear. Here, we investigated shock-induced deformation and fracture in CoCrNi-based multi-principal element alloys (MPEAs) tuned by Fe/Mn elements using large-scale molecular dynamics simulations. It was found that Fe/Mn elements could reduce the defect nucleation barrier and improve the plastic deformability. When single-element tuning is applied, the Mn element significantly reduces the production of dislocations, favoring more phase transitions from FCC to BCC or amorphous phase. The results show that Mn significantly reduces the Hugoniot elastic limit (HEL) and spall strength, while the addition of Fe element to CoCrNiMn can alleviate this effect by reducing the degree of lattice distortion. Specially, we analyzed the relationship between void nucleation and shock wave propagation, and explained the single-negative-pressure-zone nucleation as well as complex double-negative-pressure-zone nucleation phenomena. Empirical equations for the spall strength of CoCrNi-based MPEAs adjusted by Fe/Mn elements were established. This work demonstrates a potential strategy for elemental tuning to tailor the mechanical properties of polymorphism in MPEAs. [Display omitted] [ABSTRACT FROM AUTHOR]

Plate impact experiments are conducted on high-entropy alloy Al 0.3 CoCrFeNi with different microstructures to investigate the effects of grain size, precipitates and heterogeneous structure on dynamic response. Free surface velocity histories are obtained. All initial and postmortem samples are characterized with transmission electron microscopy and electron backscatter diffraction. Nanoscale L1 2 precipitates result in a considerable increase in dynamic yield stress. Spall strength is higher for the heterogeneous structure, the large grain size (200 μm) and small grain size (63 μm) with L1 2 precipitates by ∼4%, 19% and 10% than for the small grain size (77 μm) without precipitates. After shock compression, dislocation slip, stacking faults, the Lomer-Cottrell locks and nanotwins are found in the samples without the L1 2 precipitates. L1 2 precipitates increase the energy barrier and inhibit deformation twinning. Spall damage is ductile in Al 0.3 CoCrFeNi. For the homogeneous structures, intragranular voids are predominant. Voids are preferentially distributed in the fine-grain domains or at the fine-grain–coarse-grain domain boundaries of the heterogeneous structure. • Various microstructures are obtained via different heat treatments. • The L1 2 precipitates improve both dynamic yield stress and spall strength. • At 12 GPa, the deformation twinning is inhibited due to L1 2 precipitate. • The heterogeneous structure can enhance the spall strength. • The spall strength shows inverse Hall–Petch behavior. [ABSTRACT FROM AUTHOR]

The formation of void damage and spalling failure in ductile metallic materials under strong impact is a well-established phenomenon. In aerospace and defense technology engineering design, understanding the spalling failure process and related mechanisms is of utmost importance. This paper develops an explicit Gurson-type phase-field model that can simulate the void evolution and spalling damage of three-dimensional ductile metallic materials under high-velocity impacts based on the study of Aldakheel et al.. The model incorporates the Gurson-type void evolution equation and the phase-field approach while taking into account the pressure-dependent bulk modulus and inertia effects. This model is used to study the main processes and mechanisms of impacted layer cracking of metals in different dimensions. Meanwhile based on the study of complex spallation cracking processes in metals in two and three dimensions, observing and proposing the formation mechanism of complex spallation cracking modes in materials due to lateral and edge (base angle) rarefied effects. • An explicit Gurson-type phase-field model is developed to simulate the void evolution and spalling process in ductile metallic materials. • The model considers the pressure-dependent bulk modulus, inertia effects, heat generation and diffusion during large plastic deformation. • The processes of different impact spallation cracking problems in 1, 2, and 3 dimensions are verified and studied. • The 2D flat plate non-parallel spallation cracking mechanism and the spallation cracking cut-off mechanism are investigated; the mechanisms of different damage regions of the 3D conical spallation cracking process are given. [ABSTRACT FROM AUTHOR]

This work studies the hot corrosion behavior of GH4169 Ni-based superalloy, deposited with a mixture of salts comprising 95 wt% Na 2 SO 4 and 5 wt% NaCl, across three distinct temperatures (i.e., 650 °C, 800 °C and 950 °C). Corrosion and non-corrosive exposure experiments were compared, yielding data on mass loss and gain, respectively. Material characterization results revealed that the corrosion layer was mainly comprised of Cr 2 O 3 , Fe 2 O 3 , NiO, Al 2 O 3 , TiO 2 , NbS 2 and MoS 2. Notably, as the temperature ascended from 650 °C to over 800 °C, the corrosion mechanisms underwent a transition from pitting to uniform corrosion, corresponding to low-temperature hot corrosion and high-temperature hot corrosion, respectively. At 650 °C, a large number of semi-ellipsoidal corrosion pits manifested on the surface. Conversely, at 800 °C and 950 °C, the corrosion layer on the surface exhibited nearly uniform spallation. The pit growth model and spallation dynamics model were, respectively, developed based on the observed microstructure features. The models serve as tools for quantitative examination of the hot corrosion process of the superalloy at different temperatures. • The hot corrosion behaviors and mechanism of GH4169 superalloy at 650 °C, 800 °C, and 950 °C were comparatively and quantitatively studied by material characterization method. • As temperature ascended from 650 °C to over 800 °C, the corrosion mechanisms underwent a transition from pit corrosion to spallation corrosion. • A pit growth model and a spallation dynamics model were developed to the quantitative examination of the hot corrosion process of the superalloy. [ABSTRACT FROM AUTHOR]

• Study of ultrashort laser irradiation of metals with Two Temperature Models (TTMs) • Boundary conditions and mesh independent benchmark Two Temperature Models (TTMs) • Inclusion of spallation and explosive boiling ablation regimes. • Inclusion of Kerr lens effect for accurate estimation of ablated widths. Ultrashort lasers are an evolving field in both the researching and industrial world, mainly due to their ability to give very small Heat Affected Zones (HAZ) during the irradiation of a material, making them efficient for micro- and nanostructuring. Two Temperature Models (TTMs) are widely used in literature to simulate the irradiation of a material by an ultrashort laser, however, still now, they have some significant limitations, such as boundary conditions and mesh size dependency and low accuracy in predicting ablation depth and crater diameter. The novelty of the current paper is that it proposes an advanced methodology for the development of heat transfer-only TTMs, with boundary conditions and mesh size independency, that are able to predict ablation depth and crater diameter with very high accuracy, as they take into consideration phenomena such as spallation, explosive boiling and Kerr effect. As an example, this methodology has been applied on the ultrashort laser irradiation of Au. [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.

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]