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The effects of the ordered and disordered arrangements of elements on radiation-induced defects production and evolution in NiFe alloys were investigated through atomistic simulations. Results present a sluggish evolution of the overall microstructure in ordered L10 NiFe. Although the disordered phase has fewer Frankel pair accumulation in cascade simulation attributed to the low thermal conductivity reduced by the intrinsic chemical disorder, the difference is negligible when PKA energy increases because of the direct formation of clusters. Interstitial diffusion is restricted in the ordered phase, where Ni and Fe layers are alternately arranged. This condition delays interstitials accumulation and leads to the formation of more Shockley partial loops rather than Frank loops which favor in the disordered phase. The higher stacking fault energy in the ordered phase renders it difficult to form stacking fault tetrahedra

Interstitial strengthening is one of the main approaches to improving the mechanical properties of high-entropy alloys (HEAs), but its effects on the irradiation resistance of HEAs need further study. Here, we investigated the irradiation-induced defects and swelling of Fe38Mn40Ni11Al4Cr7 HEAs with different carbon contents under 5 MeV Xe23+ irradiation at 300 °C and 500 °C. Results show that the irradiation-induced swelling was significantly suppressed as the carbon content increased. Under the observation of TEM, the size of irradiation-induced dislocation loops also decreases with increasing carbon content. By comparing the effects of carbon content at different temperatures on the evolution of defects, the pinning effect of interstitial carbon on irradiation-induced defects of HEAs was proposed and analyzed. Carbon atoms, which are stabilized in the octahedron clearance of HEAs with FCC structure, not only promote the recombination of point defects by enhancing the sluggish diffusion effect of HEAs, but also pin the common 1/3 faulted loops caused by irradiation. This pinning effect is the main mechanism of interstitial carbon for improving the irradiation resistance of HEAs below 300 °C. In summary, this study provides an essential experimental basis for the irradiation effects of carbon-doped HEAs and strives to reveal the effect of interstitial carbon on irradiation-induced defects at different temperatures.

A current-source inverter (CSI) has a natural output voltage boost feature that can be advantageous for traction applications. Switching frequency is one of the easily-controlled variables that can be adjusted to improve the CSI efficiency at different operating points when the boost function is used. This paper investigates a CSI-based double-pulse test (DPT) measurement that mimics normal operation of the CSI. A loss model of the CSI is developed based on the CSI-type DPT experimental results. The impacts of the switching frequency and voltage boost ratio on the CSI efficiency and output voltage ripple are investigated. Based on the loss model, a genetic algorithm has been introduced that makes it possible to optimize the CSI's switching frequency and modulation index to maximize its efficiency under any desired operating condition.

Nickel–graphene nanolayers with high-density interfaces are expected to have excellent resistance to helium (He) embrittlement and proposed as candidate materials for molten salt reactor systems. However, He irradiation effects on nickel–graphene nanolayers remains poorly understood at present. In this work, the influence of a nickel–graphene interface (NGI) on the nucleation and growth of He-related clusters was studied by using atomistic simulations. The NGI reduces formation energies and diffusion energy barriers for He-related clusters. The reduction makes He-related clusters easily be trapped by the interface, thus leading to significant segregation. Consequently, He concentration in the bulk is considerably reduced, and the nucleation and growth rates of He-related clusters in the bulk are delayed. Owing to the high mobility of He-related clusters at the NGI, these clusters easily coalesce to form larger clusters than those in the bulk. A reasonable design of nanolayers may promote He releasing from materials. Results of the current study can provide fundamental support for the service life assessment of nickel–graphene nanolayers in extreme environments.

In this paper, the effects of a 150 keV proton radiation on a GaAs sub-cell of GaInP/GaAs/Ge trip junction solar cells and its radiation damage were studied. The degradation behavior of the solar cells was analyzed by theoretical device modeling combined with electro-optical characterization techniques such as external quantum efficiency, IV measurements, and photoluminescence (PL). The degradation of cell output parameters by protons was plotted as a function of the displacement damage dose. The results show that the short-circuit currents degrades less than open-circuit voltages because the base region of GaAs is severely damaged. The PL results indicated that proton irradiation exerted destructive effect on the photoelectric properties of the material. Such destructiveness was due to the numerous defects introduced by proton irradiation, which destroys the integrity of the lattice space, resulting in a decrease in the diffusion length of the minority and an increase in the surface recombination velocity. By COMSOL simulation analysis, it is found that the reason of radiation degradation of GaAs is the decrease of minority carrier time after irradiation and simulation results show that the PL results are in good agreement with the simulation results which can provide a method for the calculation of internal defects and minority carriers in multi-junction solar cells.

Careful measurements of the power device characteristics are necessary to accurately estimate a power converter's losses and efficiency. The conventional double-pulse test (DPT) circuit is a well-known method to implement this laboratory characterization of power devices and power modules. However, the switching characteristics of a power device depend on the power electronics circuit in which it is connected as well as the power circuit's physical layout, in addition to the device's internal structure. Hence, the conventional DPT circuit configuration, which is tailored for a standard voltage-source inverter (VSI), is not well-suited for a current-source inverter (CSI). This paper demonstrates a previously-proposed CSI-based DPT measurement technique that is appropriate for normal CSI operation. The characteristics of SiC MOSFETs and series-connected SiC Schottky diodes used in a CSI are measured using this improved technique while taking temperature effects into account to yield more accurate loss predictions. The CSI losses, including the switching and conduction losses of SiC MOSFETs and SiC Schottky diodes, have been modeled using this approach. The total CSI losses and efficiency have been estimated based on the CSI DPT results and loss models.

Surface permanent magnet (SPM) machines are appealing candidates for traction applications because of high power density and high efficiency. Rare-earth magnets deliver high performance but raise concerns about material supply dependability, particularly if they use heavy rare-earth materials. This paper presents the design of a high-performance SPM machine without any heavy rare-earth material that is optimized specifically for a current-source inverter (CSI) traction drive. This machine is designed for a constant-power speed ratio (CPSR) of 3. A genetic algorithm has been performed to achieve a target of 50 kW/L active power density at speeds up to 20,000 rpm. Operation at a peak line-to-line voltage of 800 V can be achieved using 1200 V power devices with a safety margin. The predicted electromagnetic and rotor structural performance characteristics are presented using both analytical and finite element analysis (FEA) results.

A current-source inverter (CSI) has the natural capability of boosting the output voltage which is a notable advantage over voltage source inverter (VSI) in traction drive applications. This paper investigates the voltage boosting feature of the CSI to improve the overall efficiency of the CSI-based surface permanent magnet (SPM) machine drive system in the constant power region. The effects of the boost function on the total system losses, including the machine copper loss, core loss, and magnet loss, as well as the device conduction and switching loss in the CSI and dc/dc converter, are described using analytical models. The operating characteristics of the machine and CSI are validated by 2-D finite-element analysis (FEA) and simulations. Based on the loss model, the effects of the modulation index on the overall drive system losses and power factor have been analyzed. A genetic algorithm has been used to optimize the CSI’s boost ratio, demonstrating that the drive system efficiency can be increased by 1% to 2.5% along the constant-power regime envelope by using the boost function.

Surface permanent magnet (SPM) machines are considered to be strong candidates for traction applications due to their high power density and high efficiency. By adopting fractional-slot concentrated windings, SPM machines can achieve a wide constant power speed range. A carbon fiber sleeve is applied to ensure the retainment of the magnets at high speed operating conditions. The purpose of this paper is to present the design of a high speed SPM machine for traction applications with 25 kW/Liter active power density and a wide constant-power speed range that is consistent with guidelines and targets presented in the Electrical and Electronics Technical Team Roadmap published by the US Department of Energy. The predicted electromagnetic performance and structural characteristics are presented based on both analytical and FEA results.

Selective laser melting (SLM) provides a novel path to fabricate austenitic stainless steels used in the nuclear reactors. Meanwhile, obvious differences in the microstructures of materials present between SLM and conventional process, which causes a discrepancy in the helium (He) tolerance. In present work, an austenitic stainless steel (type 316L) manufactured through SLM was irradiated by He ions at 450 °C with the concentration approximately 0.8% and then characterized via multiple methods. Results showed the special microstructure containing cellular sub-grains and nano-oxide inclusions, which formed owing to the SLM process, still distributed in post-irradiated samples. A decrease in the bubbles density, swelling rate, and hardness change has also been observed compared with conventional stainless steel. The interfaces provided by the sub-grain boundaries and nano-oxide inclusions act as effective trap sites for helium bubbles, which contributed to the enhancement of helium tolerance.

Metal–graphene nanocomposites are expected to have excellent radiation tolerance, and may become a candidate structural material for advanced fission reactors. Nevertheless, whether the structural disorder of graphene introduced by preparation or irradiation can strongly affect the radiation tolerance of the composites is still unclear. Here we investigate the radiation tolerance of nickel–graphene nanocomposite by using 300 keV helium-ion irradiation at 823 K. Results showed that the intrinsic crystalline structure of graphene would be continuously disrupted by the elevated temperature and irradiation. However, lesser crystal defects, such as lattice swelling and stacking faults, and smaller helium bubbles are observed in the composite than those in its pure counterpart. The reason may be attributed to graphene's own capability in maintaining two-dimensional structure and inhibiting the formation of large-size defects. Thus, nickel–graphene interfaces can be maintained and their role in healing radiation-induced defects is still able to play. Results of the study highlight the potential of metal–graphene nanocomposites for use as radiation tolerance materials.

The self-healing mechanism of radiation-induced defects in nickel–graphene nanocomposite is investigated by atomistic simulations. Compared with pure nickel, nickel–graphene nanocomposite has less defects remained in the bulk region after collision cascades, illustrating self-healing performance. Nickel–graphene interfaces (NGIs) serve as sinks for radiation-induced defects and preferentially trap interstitials over vacancies. Energetic and kinetic calculations reveal that the defect formation energy and diffusion barrier are reduced in the vicinity of NGIs, and the reduction are pronounced for interstitials. When NGIs are loaded with interstitials, their segregation ability on radiation-induced defects improves significantly, and the radiation-induced defects near the NGIs diffuse more easily. Especially, the vacancies (or interstitials) near the NGIs tend to annihilate (or aggregate) with the interstitials trapped at the NGIs, which only happens at the interstitial-loaded side of NGIs. Therefore, nickel–graphene nanocomposite exhibits excellent radiation tolerance and shows promise as a structural material for advanced nuclear reactors due to its NGIs with the energetic and kinetic driving forces acting on radiation-induced defects.

Nickel–graphene (N–G) composites are potential candidate structural materials for molten salt reactors. A rapid preparation method for these composites by jet electrodeposition was developed, and the microstructure, microhardness, and corrosion properties of these composites were studied to explore the key parameters of the jet electrodeposition. Results indicated that the distribution of graphene in composites mainly depended on the concentration of graphene oxide (GO) in the plating solution. Composites deposited with GO concentration of 0, 0.5, 1 g/L showed surface root-mean-square roughness value (Rq) of 6, 12, and 28 nm, respectively. Meanwhile with the increase of GO concentration, the Hardness value became larger. The corrosion potential Ecorr and current Icorr of composites obtained at 0.5 g/L with the best surface quality were 193 mV and 5.7 × 10−6 A/cm2, respectively, which indicated the best electrochemical corrosion resistance. Hydrogen annealing can help self–repair of graphene microstructure.

This work designed and measured a remote sprayed fast-curing γ-radiation-shielding material that is used to encapsulate and collect radioactive wastes from places far away from high radiation areas in case of radioactive waste leakage accidents. The influence of the chemical composition design on curing time, shielding performance, thermal stability and mechanical performance of the γ-radiation-shielding material is discussed. Results showed that with the addition of catalysts, the cream time of the γ-radiation-shielding material increased remarkably to allow it to be ejected, while the tack-free time of the solidified composite material decreased to guarantee good encapsulation of the radioactive wastes. Due to the denser microstructure, the γ-radiation-shielding material with bis(2-dimethylaminoethyl) ether and phosphorus flame retardant V-490 show better γ-radiation-shielding performance and mechanical properties than other products. When the shielding functional filler content reached 60%, the composite presented excellent comprehensive properties and a good application prospect.

With a highly functional methyl vinyl silicone rubber (VMQ) matrix and filler materials of B4C, PbO, and benzophenone (BP) and through powder surface modification, silicone rubber mixing, and vulcanized molding, a flexible radiation shielding and resistant composite was prepared in the study. The dispersion property of the powder in the matrix filler was improved by powder surface modification. BP was added into the matrix to enhance the radiation resistance performance of the composites. After irradiation, the tensile strength, elongation, and tear strength of the composites decreased, while the Shore hardness of the composites and the crosslinking density of the VMQ matrix increased. Moreover, the composites with BP showed better mechanical properties and smaller crosslinking density than those without BP after irradiation. The initial degradation temperatures of the composites containing BP before and after irradiation were 323.6°C and 335.3°C, respectively. The transmission of neutrons for a 2-mm thick sample was only 0.12 for an Am–Be neutron source. The transmission of γ-rays with energies of 0.662, 1.173, and 1.332 MeV for 2-cm thick samples were 0.7, 0.782, and 0.795, respectively. Keywords: Flexible Composite, Neutron Shielding, Radiation Resistance, γ-ray Shielding

The manufacturing of the new generation of radiation-resistant structural materials is an extremely interesting and challenging topic in the field of additive manufacturing research. Understanding the special microstructure characteristics and the influence on the radiation resistance of these additive manufactured materials is still superficial. In this study, high-quality bulk 316L stainless steels (SSs) strengthened by dispersed nano TiC were successfully prepared by selective laser melting (SLM). The results of transmission electron micrograph and small angle neutron scattering showed that TiC existed in the matrix of 316L SSs in the form of nanoparticles with average size less than 50 nm. TiC particles were distributed inside the subgrains and on the subgrain boundaries. Smaller helium bubbles were observed after the same flux of He2+ ion irradiation in the case of 316L SSs with 4% TiC compared with pure SLM 316L SSs. In comparison with the case on the grain boundaries and intragranular, the helium bubbles at TiC/316L interfaces have the smallest size and the largest density. The results Nanoindentation results showed that 4% TiC doping had a remarkable inhibiting effect on irradiation-induced hardening at a low dose. This condition is because numerous interfaces of TiC/316L acted as sink/trap sites for the irradiation-induced defects.

This work shows that mechanical properties, thermal conductivity, and secondary gamma-ray shielding ability can be significantly improved when open-cell nickel foams are embedded into the shielding composites. The boracic polyethylene/polyethylene wax blends and open-cell nickel foam composites (PPNM) are designed and prepared by permeating homogeneous mixed melt fillers into open-cell nickel foams. The ratio of polyethylene and polyethylene wax is investigated to achieve higher filling rate. The quasi-static compressive response of PPNMs and polyethylene/polyethylene wax blends is measured, and the crystallization properties are studied by differential scanning calorimetry. The neutron and secondary gamma-ray shielding abilities of PPNMs are also simulated based on Monte Carlo particle transport method. Results show that the compression strength of PPNMs with boron carbide is slightly improved when compared with polyethylene/polyethylene wax blends. The nickel foams in PPNM composites improve the energy-...

Shielding against spatial high-energy electron radiation is essential to the success of space exploration. Honeycomb and foam systems, combined with a magnetic field, were proposed to shield against spatial high-energy electrons given the immense mass and large amount of secondary X-rays of a passive shield and the demand for a high-intensity magnetic field of an active method. The shielding capabilities of several structures were investigated using the Monte Carlo method. The influences of magnetic flux density and hollow cube size on shielding property were studied by simulating energy deposition in a Chinese male reference phantom. Results showed that the honeycomb and foam systems enhanced the shielding capability against high-energy electrons and reduced the penetration of secondary X-rays. The effective dose in the male phantom decreased with increasing magnetic flux density. The proposed structures exhibited excellent shielding capabilities with a small hollow cube. In addition, the foam structure performed better than the honeycomb structure. Thus, the presented systems may be used for space radiation protection in a high-energy electron environment.

The inverter-motor drive system is the main traction force in electric vehicles (EVs). The overall efficiency of inverter-motor will directly determine the energy consumption of EVs. In this paper, aiming at improving the overall efficiency of inverter-motor, a novel methodology is proposed. Firstly, the iron loss, copper loss and stray loss of motor, as well as the devices’ conduction loss and switching loss in inverter are modeled. Afterwards, based on previous loss model strategy and gold section search strategy, a novel hybrid efficiency-optimization control strategy is proposed. The proposed method combines each benefit in loss-model and gold section search, and can realize high efficiency operation of the inverter-motor system in large power range. Additionally, the proposed method manifests faster search speed and better accuracy compared to conventional methods. Experiment results validated the effectiveness of the proposed hybrid control strategy. Meanwhile, the impact of the efficiency improvement on the driving cycle is further investigated through Advanced Vehicle Simulator (ADVISOR) simulations.

The 2-D rotating magnetic field is demonstrated in electrical steel sheets, which are widely used in iron cores of motors, etc. In addition, the magnetic properties of a motor iron core are strongly affected by the compressive stress in the laminated direction induced by welding, bolt bundles, etc. In order to investigate the rotating magnetic properties of the material under laminated direction stress, a novel magnetic properties measurement system is developed in this paper. The compressive stress is loaded on cubic specimen in the laminated direction. A novel sensing structure with combined magnetic flux density $B$ and magnetic field strength ${H}$ sensing coils is developed with an assistance of a four-layer printed circuit board. Such structure yields more accurate ${B}$ and ${H}$ measurement. The accuracy of magnetic properties measurement of the apparatus is validated by finite-element analysis. Except for investigating the correlation between the compressive stress and its magnetic properties of the electrical steel sheets, the coupling relationship between the magnetic property in ${x}$ -axis direction and the counterpart in ${y}$ -axis direction is found in 2-D rotational magnetization. Furthermore, the impact of the compressive stress on the coupling relationship is explored. The experimental results are reported, and the mechanism analysis is employed to discuss the results.

With the expanding power demands and increasing use of renewable energy resources, microgrids have been widely supported. Wide bandgap semiconductor devices with higher blocking voltage capabilities and higher switching speeds, such as silicon carbide (SiC) devices, will become a critical component in building microgrids. This paper describes a comprehensive investigation of the effects of SiC Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) on the efficiency and power quality of the inverters used in low voltage microgrids compared with conventional inverters based on silicon (Si) Insulated-gate Bipolar Transistors (IGBTs). First, the characteristics of both SiC and Si are measured by a double pulse test (DPT), considering thermal effects. Then, conduction and switching losses under different temperatures are calculated based on DPT results. Second, phase voltage distortions are modeled and calculated according to the tested switching and conduction characteristics of SiC, resulting in harmonic components in the phase current. Finally, an experiment is implemented. The experimental results show that the SiC-inverter greatly increases the energy efficiency and improves the power quality in the microgrid; these results are consistent with the analytical results.

Metal–graphene nanocomposites are expected to have excellent radiation resistance. The intrinsic role of the graphene layers (GrLs) in their performance has not been fully understood. Five copper–graphene nanocomposite (CGNC) systems were used to investigate the detailed mechanisms underpinning this behaviour by atomistic simulation. Results showed that GrLs can reduce the formation, growth, and intensity of the thermal spike of CGNC; this effect became more evident with the increasing number of layers of graphene. The role of the GrLs can be explained by three mechanisms: first, the ultra-strength C–C bonds of graphene hindered the penetration of high-energy atoms, second, the number of recoiled atoms decreased with the increasing number of layers of graphene, and third, the energy dissipation along the graphene planes also indirectly weakened the damage caused to the entire system. These mechanisms may provide a pathway to prevent material degradation in extreme radiation environments.

In consideration of the ubiquity of swift particles in space environment, understanding the effects of ion irradiation on the adhesion force and mechanical properties of multi-walled carbon nanotube arrays is significant to apply the arrays as adhesive materials in space in the future. In this study, multi-walled carbon nanotube arrays prepared through chemical vapor deposition were irradiated by He2+ under different fluences and then characterized via multiple methods. The arrays were severely damaged when the fluence reached or exceeded 1 × 1016 cm−2. As the fluence increased, more amorphous carbons were generated from their original position in the carbon nanotubes. The adhesion force quickly decreased when the irradiation fluence rapidly increased, which limited the service life of the arrays as adhesive materials. Finally, the instantaneous modulus of the multi-walled carbon nanotube arrays initially increased and then decreased when the fluence increased because of the different contact modes between the indenter and the samples.

Traditional neutron-shielding materials usually have poor mechanical properties and secondary gamma-shielding capability. The new requirements of modern neutron-shielding materials are difficult to satisfy. A paraffin/nickel foam neutron-shielding composite was prepared and characterized in this study. Open-cell nickel foams were fabricated through electrodeposition. Subsequently, the paraffin/nickel foam composite were prepared by filling the open-cell nickel foams with melted paraffin. The intrinsic parameters of nickel foam and the content of neutron absorber (boron carbide) were controlled to optimize the composite. The mechanical properties of the composite were studied through a static compression test. The compressive strength improved to 0.4 times that of the nickel foams. The Am–Be source transmittance experiment showed that the 8 cm thick PFM presented a neutron transmittance of 56.1%, and the 6 cm thick boron carbide/paraffin/nickel foam (PFM-B) presented a neutron transmittance of 37.6%. The paraffin/nickel foam and PFM-B had approximately the same shielding efficiency as paraffin and boron carbide/paraffin, respectively. However, the second gamma ray shielding efficiency of the paraffin/nickel foam and PFM-B was significantly higher than that of paraffin and boron carbide/paraffin. The mechanical properties and secondary gamma ray-shielding capability of the composite can be improved by increasing the relative density of nickel foams.

Radiation shielding of high-energy electrons is critical for successful space missions. However, conventional passive shielding systems exhibit several limitations, such as heavy configuration, poor shielding ability, and strong secondary bremsstrahlung radiation. In this work, an aluminum/vacuum multilayer structure was proposed based on the electron return effects induced by magnetic field. The shielding property of several configurations was evaluated by using the Monte Carlo method. Results showed that multilayer systems presented improved shielding ability to electrons, and less secondary x-ray transmissions than those of conventional systems. Moreover, the influences of magnetic flux density and number of layers on the shielding property of multilayer systems were investigated using a female Chinese hybrid reference phantom based on cumulative dose. In the case of two aluminum layers, the cumulative dose in a phantom gradually decreased with increasing magnetic flux density. The maximum decline rate was found within 0.4-1 Tesla. With increasing layers of configuration, the cumulative dose decreased and the shielding ability improved. This research provides effective shielding measures for future space radiation protection in high-energy electron environments.

High temperature radiation damage in binary bcc Fe alloys containing 1 atomic % Au or Cu due to Fe ion irradiation at 550 °C to a peak dose of 2.8 and 8.3 dpa is studied. The precipitation behavior of gold and copper and its correlation to the irradiation-induced defects is studied by transmission electron microscopy and variable energy positron annihilation spectroscopy (VEPAS). The increase of S parameters from VEPAS indicates the formation of open volume defects upon irradiation. Disc-shaped Au precipitates, grown from the irradiation induced dislocations, are observed in the Fe-Au alloy. In the Fe-Cu alloy, spherical Cu particles are formed but no direct connection between Cu precipitates and radiation damage is detected. For the Fe-Au alloy, the surface hardness dramatically increases for a dose of 2.8 dpa, with a slight decrease as the irradiation dose is enhanced to 8.3 dpa. In the Fe-Cu alloy, radiation hardening increases continuously.