The extreme condition of high-speed metal deformation under intense current flow is commonly encountered in the realms of national defense, military, and industry. However, there has always been a lack of effective research method for the micro deformation mechanism of metal under this extreme condition. We have developed a high current and high strain rate tensile (HCHST) testing platform based on RC circuits, which is used to research the micro-deformation mechanisms of CuCrZr alloy under this extreme condition. The dynamic tensile tests of CuCrZr alloy at different high strain rates (1401s- 1, 2957 s- 1, 5503 s- 1, 8012 s- 1) under the high current density (6550 A/mm2) condition were conducted using the HCHST experimental platform. The mechanical properties and microstructure of CuCrZr alloy under the HCHST were analyzed by combining TEM and EBSD. The research results indicate that the microhardness of the alloy in the HCHST #1 environment (6550 A/ mm2,1401s- 1) is almost the same as the original state. This is attributed to the strong current promoting the movement of dislocations and reducing the accumulation of dislocations. Under condition like HCHST#1, the dislocation annihilation rate and dislocation formation rate of CuCrZr alloy almost reach equilibrium. At higher strain rates, the dislocation multiplication rate is much higher than the dislocation annihilation rate caused by strong current. This imbalance leads to dislocation entanglement and the formation of dislocation cells, resulting in an increase in the microhardness of the material. Additionally, EBSD was used to analyze the changes in grain size, average volume fraction of LAGBs, average KAM value, and texture of the samples, further verifying the dislocation evolution and microhardness changes of copper alloys under HCHST conditions. Our research results provide strong theoretical for the application of CuCrZr in the field of electrical thermal mechanical coupling.

High-entropy alloys (HEAs) exhibit good tradeoff between strength and ductility at cryogenic temperature, and their deformation mechanisms have aroused great research interest. Here, a non-equiatomic CoCrFeNiW 0.2 HEA strengthened by mu phase precipitates was prepared using vacuum arc melting, and its mechanical properties, microstructural evolution and deformation mechanisms were investigated systematically at room and cryogenic temperature. As the tensile temperature decreased from 298 K to 100 K, the yield strength of the HEA increased from 371 MPa to 627 MPa, combined with an elongation decreased from 33.9% to 21.5%. Dislocations slip is dominant during plastic deformation at all temperatures. Only a small amount of deformation twins can be found at 100 K, and they are suppressed by mu phase precipitates. The formation of slip bands and stacking faults contributed to enhanced work-hardening behavior. The interfaces between slip bands and matrix serve as major obstacle to block the dislocations motion, which is able to diminish the mean free path of dislocation. The results are helpful to understand the precipitates-strengthened CoCrFeNiW 0.2 HEA and expand the potential applications at cryogenic temperature.

High performance CoCrFeNiW 0.2 and CoCrFeNiW 0.2 + 3 at% C HEAs were prepared by vacuum arc melting, which are promising candidates for extreme environment applications. To study the current-carrying wear behavior of the two HEAs under different current conditions, a pin -on -ring test rig was custom-designed. The microstructures, hardness, wear properties and mechanisms of the HEAs were investigated. The results reveal that the HEAs exhibit outstanding wear resistance in the absence of current, as evidenced by the very low wear rates and the relatively smooth worn surfaces. With the increasing of current intensity, it simultaneously exacerbates the abrasive wear, adhesive wear, oxidative wear and arc erosion. The HEAs show the worst wear resistance due to the melt ejection and arc discharge at 10 A. However, when the current reaches 20 A, the elevated temperature promotes material transfer and the formation of dense and complete oxide film, which has lubricating and protective effect to separate the worn surfaces, resulting in the reduction of COFs and wear rates. The rupture and regeneration of oxide film play an opposite effect on sliding contact friction, and their competitive relationship dominates the wear resistance of the HEAs under the large current. The CoCrFeNiW 0.2 + 3 at% C HEA exhibits superior wear resistance than CoCrFeNiW 0.2 HEA under various conditions because the WC carbide is harder than mu phase particle and can impede plastic deformation of FCC matrix during tribological process more efficiently.

High entropy alloys (HEAs) have been a new-type of structural materials, which show good performance in various extreme conditions. In the present study, we systematically investigated the high temperature deformation behavior of as-cast CoCrFeNiW0.2 HEA under different temperatures from 298 to 1173 K and various strain rate of 1 x 10(-4) s(-1) to 5 x 10(-3) s(-1). An obvious temperature dependence of yield strength can be found with a remarkable decrease from 362 MPa at 298 K to 119 MPa at 1173 K. The normal Portevin-Le Chatelier (PLC) effect was presented in the intermediate temperature range of 673 K to 1073 K, the serrated flow transformed in the sequence of A -* A + B -* A + C -* B + C -* C with the increasing temperature, which is caused by dynamic strain aging (DSA). W atoms played an important role in the interaction between solute atoms and dislocations. Fractography analysis suggests the failure mode transition from transgranular fracture to intergranular fracture. Electron backscatter diffraction (EBSD) demonstrates that the high temperature deformation mechanism of the HEA is dominated by dynamic recovery (DRV). Additionally, transmission electron microscopy (TEM) was performed to observe the dislocation configurations and the interaction between dislocations and mu phase precipitates at various temperatures, and these results further identify the high temperature deformation mechanism. To summarize, this study indicates the proposed HEA has excellent high temperature mechanical properties and a wide range of potential applications in many fields.

The failure issue of electromagnetic railgun rails is a widely researched problem, but effective research methods are lacking in studying the microstructure of rail materials. The high current and high strain rate tensile (HCHST) testing platform was designed to simulate the high current density and high strain rate deformation service conditions of pure copper rails used in electromagnetic guns. The microstructural and mechanical properties of commercially pure copper were analyzed using TEM and EBSD under high current density (2680 A/mm2) and various high strain rates (epsilon = 3404s-1, epsilon = 6808s- 1)using the HCHST test platform. The obtained results were then compared with those obtained from the as-received state and the quasi-static current-assisted tensile (QCAT) test. The findings indicate that the deformation mechanism of pure copper specimen under HCHST is similar to that of QCAT, where dislocation and slip are the main mechanisms. However, distinct differences in microstructure were observed. Specifically, a significant number of dislocation walls were present in the grains under QCAT, whereas numerous dislocation cells were formed in the grains under HCHST. In the high-current density environment of 2680 A/mm2, as the strain rate increased, the number of dislocation cells increased while their size decreased. The grains became extremely refined, and the KAM value also increased. Furthermore, the Vickers hardness of pure copper significantly improved after undergoing the HCHST. Based on the experimental findings, it was observed that during the service process of the pure copper rail in electromagnetic railguns (under the influence of high current density and high strain rate deformation), the surface of the rail material experienced significant dislocation entanglement. This resulted in a significant increase in the strength and hardness of the surface of the rail with high strain rate deformation. However, the uneven distribution of strength and hardness throughout the surface layer of the rail eventually made it more susceptible to deformation and failure.

High performance CoCrFeNiW0.2 and CoCrFeNiW0.2 + 3at.% C HEAs were prepared by vacuum arc melting, which are promising candidates for extreme environment applications. To study the current-carrying wear behavior of the two HEAs under different current conditions, a pin-on-ring test rig was custom-designed. The microstructures, hardness, wear properties and mechanisms of the HEAs were investigated. The results reveal that the HEAs exhibit outstanding wear resistance in the absence of current, as evidenced by the very low wear rates and the relatively smooth worn surfaces. With the increasing of current intensity, it simultaneously exacerbates the abrasive wear, adhesive wear, oxidative wear and arc erosion. The HEAs show the worst wear resistance due to the melt ejection and arc discharge at 10A. However, when the current reaches 20A, the elevated temperature promotes material transfer and the formation of dense and complete oxide film, which has lubricating and protective effect to separate the worn surfaces, resulting in the reduction of COFs and wear rates. The rupture and regeneration of oxide film play an opposite effect on sliding contact friction, and their competitive relationship dominates the wear resistance of the HEAs under the large current. The CoCrFeNiW0.2 + 3at.% C HEA exhibits superior wear resistance than CoCrFeNiW0.2 HEA under various conditions because the WC carbide is harder than μ phase particle and can impede plastic deformation of FCC matrix during tribological process more efficiently.

Electrically-assisted manufacturing (EAM) has many advantages than ambient temperature manufacturing and thermoforming for the building of hard-to-deform alloys. The EAM technique of High entropy alloys (HEAs), a newer alloy category, is an issue worth of research, especially the deformation mechanism in the process of EAM. In the paper, the electrically-assisted compressive mechanical behavior of CoCrFeNiW0.5 HEA composed of face centered cubic phase and mu phase precipitate was studied under current density and strain rate region of 0-40 A/ mm2 and 0.0005 s-1-0.1 s-1, respectively. At high current density and strain rate, the reduction of yield stress is remarkable. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) techniques were utilized to analyze the effect of current density on the flow stress behaviors and microstructure evolution under plastic deformation. The results show that the introduced electric current enhances the movement and annihilation of dislocations as well as dynamic recovery, resulting in the continuous decrease of flow stress. Additionally, we can clearly observed that the dislocation-free ring or some very low dislocation density regions around the mu phase precipitates, that's because mu phase precipitate can lead to severe lattice distortion and thus increase the electron scattering, and then the local high temperature appeared around the defect regions due to local Joule heating effect, which is recognized as the principal reason leading to the significant decrease of mechanical properties during electrically-assisted compression.

To investigate the influence of damage characteristics,dynamic response,and failure mechanism on reinforced concrete(RC)square columns under multi-point simultaneous initiation,a series of experiments were conducted on RC square columns subjected to synchronous contact explosive loading using single,double,and four-point charges.Furthermore,LS-DYNA was used to analyze the damage characteristics and stress evolution process based on the experimental results obtained from the explosive loading.The analysis results indicate that the damage effect of RC square columns relies on both the number of detonation points and the placement position,given the same total mass of explosives.Multi-point simultaneous initiation causes superior damage to RC square columns with both crushed and punched damage,as compared to single-point explosions.Additionally,the degree of damage and acceleration response of the RC square columns is the highest at the condition of four-point charges on adjacent sides.The effectiveness of enhancing the damaging effect on RC square columns is directly correlated with the increase in the number of detonation points.The RC square column initially enters a high-stress state throughout the entire section,and in the condition of four-point charges placed on all four sides,there are four corners where the concrete stress is concentrated,leading to enhanced damage effects.During single-point initiation,the stress inside the concrete at the measuring point decreases as the distance from the center of the explosion increases.However,during multi-point initiation,when multiple explosion stress waves are combined within the cross-section of the RC square column,the stress at the central concrete significantly increases.Taking into account the spatial coupling and superposition of stress waves,the concrete's peak stress at the center of the RC square column section increased significantly under the explosive conditions of four-point charges on adjacent sides.Specifically,the peak stress reached 37.3 MPa,with stress increases of 3.82 times,1.21 times,and 0.67 times compared to the other three explosion conditions.The increase in stress coupling is the primary factor contributing to the extensive damage observed in the RC square column.

Direct-current treatment (DC-treatment) was employed to tune the microstructural evolution of deformed Al0.1CoCrFeNi high-entropy alloy (HEA) in this paper. The time that partial recrystallization required during the DC-treatment is far less than that of conventional annealing at similar temperatures. The observation of dislocations configuration and stacking faults confirmed that the accelerated effect of DC-treatment on the promoted recrystallization of deformed Al0.1CoCrFeNi HEA, especially the distinct role of the athermal effect. Besides, results of EBSD and GND density also evidence the promoted recrystallization and the corresponding dislocations distribution under DC-treatment.

Ever-harsher service environments in the future will call for systematic studies on service behaviors of high-entropy alloys (HEAs) under multi-field coupling. Instead of focusing solely on service behaviors under conventional conditions, the promoted serration behavior of Al-0.1 CoCrFeNi HEA, commonly known as Portevin-Le Chatelier (PLC) effect, under coupled electron-heat field was quantitatively analyzed in terms of several characteristic parameters in this work. The obvious PLC phenomenon with severe serration can boost the decrease of tensile strength and elongation in the service environment of coupled electron-heat. Our results indicate that this macroscopic serrated behavior can be rationalized by defect-level microstructural interaction, namely the enhanced repetitive pinning and de-pinning effect of solute atoms on mobile dislocations, according to the mechanism of dynamic strain aging. This was proved by the increased kinking and bowing morphologies of dislocations, as well as abundant stacking faults under coupled electron-heat field. (C) 2021 Elsevier B.V. All rights reserved.

The poor interfacial interactions and bonding between short carbon fibers (CFs) and polyetheretherketone (PEEK) resin matrix is a great challenge to manufacture high-performance 3D printed CF/PEEK composites. Therefore, this paper presents a research focusing on the compatibility of CFs and PEEK. We propose an effective method to graft polyetherimide (PEI) onto activated CFs, then, composite filaments with modified fiber contents of 2.5%, 5%, 7.5% and 10% were prepared using fused filament fabrication (FFF). The chemical structures and surface morphologies of modified CFs were characterized, and the rougher surfaces with more polar groups can enhance the wettability of these CFs, which is improve the physical adhesion with PEEK. The thermal properties and mechanical properties of CF/PEEK composites within different carbon fiber contents were investigated. The results show that the tensile strength, flexural strength and interlaminar shear strength (ILSS) of 3D printed 5 wt% PEI@CF/PEEK parts were greatly improved by 40.85% (92.4 MPa), 35.70% (151.3 MPa) and 130.22% (26.59 MPa), respectively, which caused by the improvement of interfacial adhesion between CFs and PEEK resin. The results suggested that this modification is an effective approach to coating PEI on the surface of carbon fiber and enhance the mechanical properties of 3D printed PEEK composites. This method provides new insights for fabricating high-performance 3D printed thermoplastic composites.

This paper reports on the optimized parameters of the rolling reduction (RR) and aging treatment (AT) of Fe-Si-Mn aluminum sheets with the aim of reducing the anisotropy and improving the deep drawing performance of the material. Results show that with an increase in the RR, the ultimate tensile strength increases while the elongation decreases. As a result of this treatment, the proportion of Cube texture and Copper texture in specimens is found to decrease gradually and transform into the Brass texture. The transition sequence of texture is found to be Cube→Goss→Brass along the α -orientation line, and the transition path of the Copper texture is found to be Copper→S→Brass along the β -orientation line. The aluminum alloy exhibits the minimum anisotropy (IPA% = 8.74%) and the best deep drawing performance (an Erichsen number of 7.51) obtained in this work when the RR was 29.4%. Subsequently, the AT can effectively reduce the density of dislocations near the grain boundaries and further improve the Erichsen number (from 7.14 to 8.01, an increase of 12.2%). Our results demonstrate that the deep drawing performance of Fe-Si-Mn aluminum sheets can be enhanced effectively via RR and AT; this work provides a design strategy for improving the fracture consistency of the Fe-Si-Mn aluminum alloy.

In this study, electrical pulses were used as a treatment to investigate the role played by dislocations in the deformation mechanism of the Al0.1CrFeCoNi high-entropy alloy (HEA) at different stages of deformation. The results demonstrated that the HEA was completely deformed through dislocation slip during compression, and no twins were evident. Under the action of Electric pulse treatment (EPT), the specimen expanded thermally owing to Joule heating. Additionally, the pulse current accelerated the movement of the dislocations and led to dislocation annihilation, softening the material without changing the grain shape. However, further application of EPT with the same parameters failed to produce significant changes in the dislocation density, a phenomenon that has rarely been reported before. Our results provide strong theoretical and technical support for the rapid annealing of metallic materials during processing and the use of HEA in electrical structural components, such as wear-resistant coatings or parts resistant to galvanic corrosion.

In this study, ultrasonic shot peening (USP) was used to enhance the surface of a Ti-6Al-4V alloy. Samples strengthened with different amplitudes were characterized and their wear resistance was tested and analyzed. The results demonstrate that the surface morphology of the Ti-6Al-4V alloy changed significantly after USP treatment, and the surface roughness increases at first, then stabilizes as the amplitude increases. The surface grain of the material is refined due to severe plastic deformation, and the average grain size after USP treatment is 27.93% finer than the original sample. Due to the effect of fine grain strengthening and work hardening, the microhardness of the material’s near-surface layer is also enhanced in varying degrees, showing a gradient decrease throughout the depth of the cross-section. Furthermore, USP produces residual compressive stress as high as -791.01 MPa in the near-surface layer. When the USP amplitude is 80% and the treatment time is 240 s, the wear resistance of Ti-6Al-4V alloy is substantially enhanced under the combined action of hardness, residual compressive stress, and surface pits, reducing wear width and wear rate. The wear mechanism is primarily abrasive wear and oxidation wear.

High entropy alloys (HEAs) with excellent mechanical properties and corrosion resistance show promising potential for use in many fields including marine environment. In order to make a good tradeoff between the mechanical properties and corrosion resistance, the microstructure of HEA is adjusted by proper heat treatment. Herein, the non-equiatomic CoCrFeNiW0.5 HEA with dual FCC and mu phase was prepared by using an electromagnetic levitation melting method, and the microstructure, mechanical properties and corrosion resistance of these alloys with annealing temperature range from 600 to 1200 ? for 3 h have been investigated. After annealing at 1000 ?, a large number of needle-like mu phase precipitates was firstly observed in the matrix, the volume fraction of the mu phase is 26.64 %, which is about twice as higher as under the as-cast conditions (13.35 %). This alloy exhibited the highest compression yield strength of 1253.9 MPa with a considerable fracture strain of 40.8 % and the highest Vickers hardness value of 369.6 HV. The decomposition of mu phase precipitates was observed when annealing temperature up to 1200 ?, which lead to the mechanical properties of the alloy decreased slightly. All the alloys were found to show excellent corrosion resistance in 3.5 wt% NaCl solution, and corrosion occurs preferentially on the FCC matrix and phase boundaries, the increase of mu phase volume fraction result in more severe galvanic corrosion of alloys. Our results offer insights into analyzing the evolution of both mechanical properties and corrosion resistance of HEAs caused by heat treatment. (c) 2022 Elsevier B.V. All rights reserved.

As a rapidly developing additive manufacturing technology, fused deposition modeling (FDM) has become widespread in many industry fields. It can fabricate complicated geometries using filament of thermoplastic materials such as PP, polylactic acid, acrylonitrile butadiene styrene, etc. However, poor mechanical properties of raw materials limit their application. Poly-ether-ether-ketone is a type of special engineering plastic with high performance, which could be further reinforced by adding carbon fibers (CFs). During FDM process, the mechanical properties of printed parts are largely subject to careful selection of process parameters. To improve the mechanical properties of PEEK and CF/PEEK 3D-printed parts, the effects of various process parameters including building orientation, raster angle, nozzle temperature, platform temperature, ambient temperature, printing speed, layer thickness, infill density, and number of printed parts on mechanical properties were investigated. The tensile fracture interfaces of printed parts were observed by scanning electron microscope (SEM) to explain the influence mechanism of process parameters. In the single factor experiments, flat and on-edge specimens show the best tensile and flexural strength, respectively; the specimens with raster angle ±45° and 0° show the best tensile and flexural strength, respectively. When the nozzle temperature at 500°C, platform temperature at 200°C, ambient temperature at 150°C, printing speed is 20 mm/s, layer thickness is 0.2 mm, and infill density is 100%, the printed parts exhibit the best mechanical properties.

A miniaturized periodic element for constructing bandpass frequency selective surface (FSS) independent of incident angles and polarizations is presented. An interdigital resonator (IR) with one extending finger to connect the two separate parts of the interdigital capacitor is explored to achieve parallel resonance. The equivalent circuit model (ECM) and electric field distributions are introduced to explain frequency performance of FSS. The whole structure has only one layer and possesses a low profile (a thickness of 0.001 5 lambda, where lambda represents the resonant wavelength in free space) as well as a small size (0.03 lambda x0.03 lambda). This FSS performs as a spatial bandpass filter which exhibits a great angular stability with incident angles ranging from 0 degrees to 80 degrees for both transverse electric (TE) and transverse magnetic (TM) polarizations. As an example, a prototype of one proposed FSS is fabricated and tested. The measured results show a good angular stability.

In this letter, a shifted double-sided frequency selective surface (FSS) with miniaturized unit cells is proposed to achieve superior performance in angular insensitivity. Two identical FSS screens mounted on both sides of a thin substrate have lateral displacement relative to each other. We shed light into effect of shifting by investigating current and field distributions, and present the operating principles of the proposed FSS along with the equivalent circuit model. The whole structure has a lower profile (a thickness of 0.001λ, where λ represents the resonant wavelength in free space) as well as a small size (0.043λ × 0.043λ). This FSS as a bandpass spatial filter is stable with respect to different polarizations, polarized angles, and incident angles of the illuminating waves. A prototype of the proposed FSS is fabricated and tested. The measured frequency responses agree well with the simulated results.

Two novel low melting pointing metals (LMPMs), Bi-21In-18Pb-12Sn alloy and Ga-13.5Sn alloy as phase change materials (PCMs), were firstly proposed to work for thermal management in aerospace applications. Their phase change characteristics and thermal stability were investigated in comparison with that of conventional paraffin PCMs (i.e. C26H58 and C17H36). The results indicate that the latent heat per unit volume in the LMPMs is higher than that of the paraffin PCMs, leading to much better thermal capacity of the former, and this can effectively reduce the volume proportion of LMPMs in use. LMPMs exhibit excellent thermal conductivity compared with the paraffin PCMs, and this contributes to rapid absorption of the heat released by the temperature-controlled target, and consequently the temperature of the target could remain stable near the phase change temperature. Besides, the Al2O3 coating by the spraying method could act as effective corrosion inhibitor in protecting Al alloy container used for electronic packaging from the liquid Ga-Sn alloy. The temperature control characteristic and temperature gradient of LMPMs consequently could suit the applied requirement of spacecraft device operated in vacuum condition. Therefore, low melting point metals with better thermal conductivity and stability would be promising candidates for PCMs applied in the field of aerospace.

Models are presented for predicting the melting point and the latent heat of low-melting alloys to facilitate the design of phase change materials (PCMs). Based on the characteristics of entropy and enthalpy during the transition of material phase, the prediction models of melting point and latent heat for eutectic binary system were established at first, and then the models were extended into multicomponent system. Calculated melting points and latent heats of 15 selected low-melting alloys were compared with measurement results using DSC, and it is found that there exists a good agreement between the prediction and the experimental data. A criterion for preparation of metallic PCMs was also proposed. In order to obtain a higher latent heat alloys, an element with higher latent heat should be selected as component of the alloy, and the mole fraction of the element should be increased. The advantage of the models proposed is that the melting point and the latent heat of a certain PCM can be predicted mathematically, avoiding many experiments needed in conventional ways.