International Journal of Modern Physics B

The nonlinear ultrasonic (NLU) technique has been proposed to monitor structure health. It is well known that damage of materials is generally accompanied by increase of the materials’ nonlinearity. However, after processing such as welding, the microstructure of the material will change, which might affect the behavior of materials’ nonlinearity after degradation, further, inducing inaccuracy in evaluation of the structure life. An NLU system is developed to characterize the damage due to plastic deformation in S355J2W weathering resistant steel specimens which underwent different heat treatment processes. The experimental results show that the NLU system is effective and accurate for the measurement of higher harmonic components, and acoustic nonlinear parameters (ANP) increase with the increase of tensile stress. The results also show that ANP response relates to the grain size.

An investigation has been conducted to figure out the effect of plate thickness on the fatigue crack growth rate (FCGR) of a low carbon bainitic steel. Based on the standard ASTM E647, standard compact tension specimens with three different plate thicknesses were used in fatigue crack growth test and the crack closure was taken into consideration when calculating crack lengths. When analyzing the data obtained in fatigue tests, two different mathematic models were used to fit the relationship curve between crack length a and cycle number N. Results show that the low carbon bainitic steel with a bigger plate thickness has a lower crack growth rate in a short crack growing period. More information for crack growth behavior was obtained via the scanning electron microscope technique.

Certain high-speed trains often suffer from the erosion of wind-drift sand during the serving period. The present paper simulated this sand-blasting process with consideration of sand-blasting pressure, angle, distance and sand particle size representing different natural conditions. Results show that the grit size has the greatest influence on roughness and residual stress of the 7N01 aluminum alloy based on the orthogonal test. The samples after low intensity sand-blasting (LISB) were characterized by micro-hardness, surface morphology and fatigue test. Results show that the surface of the blasted sample was severely impinged in form of extruded ridges crater-like morphology, representing different roughness values. The LISB causes a similar spoon shape residual stress distribution along the depth direction and it also increases the hardness of the surface zone. Finally, the residual compressive stress plays an important role in the improvement of the fatigue life, and the increase of roughness can seriously shorten the fatigue life.

In this research, Cu–Zr diffusion couples were heated by pulse current and a conventional heating method, respectively. Comparative analyses on the diffusion behavior of Zr and Cu atoms, interfacial structure and growth behavior of diffusion reaction area were carried out. The results show that applying pulse current can accelerate the migration rate of atoms, promote the diffusion of Zr atoms to the copper substrate in a short holding time, achieve a metallurgical bonding and form a continuous, dense reaction layered structure with a two-layer interface. The pulse current heating can induce the formation of lamellar ZrCu phase in the copper substrate interface. After holding for a relatively short period of time, a large number of Zr atoms crossed through the ZrCu phase, formed ZrCu₃ phase in the copper rich phase side and grew gradually along the depth direction of copper substrate. Meanwhile, the growth rate of ZrCu phase was relatively slow due to the weak diffusion ability of Cu atom to in zirconium matrix.

To analyze the influence of penetration resistance for different steel plate configurations, different steel plates impacted by various projectiles were studied using the LS-DYNA code. The calculation results obtained using the LS-DYNA code and prior experimental results reported in the literature agree well with the damaged image of projectiles penetrating steel plates and the initial residual velocity curve of the projectile. The Q235 steel constitutive model is modified based on the Johnson–Cook model. It can be concluded that the LS-DYNA code analysis is reliable when compared with the experimental results. We then used the LS-DYNA code to conduct an extensive study into the penetration resistance of monolithic, contact-type double-layered and gap-type double-layered targets with the same surface density, impacted by different projectiles. The failure mode of the steel plate, initial residual velocity, ballistic limit velocity, energy absorption and plastic deformation of the monolithic and double-layered plates were studied. The results in this paper can provide guidance for the design and application of structural protection using steel plates.

Fe-based amorphous alloys are important materials with a high potential for commercialization by evaluating their corrosion performances. In this work, amorphous Fe${}_{73.5}$Cu₁Nb₃Si${}_{13.5}$B₉ alloy was chosen as a target material to investigate the effects of the addition of C on the corrosion properties by an electrochemical method. Alloy ingots Fe${}_{73.5}$Cu₁Nb₃Si${}_{13.5}$C${}_x$B${}_{9-x}$ (x = 0, 1, 2, 3 at.%) were prepared using an arc melting system, under argon atmosphere. Planar flow melt spinning of the alloys was carried out to obtain amorphous ribbons of the width $\sim$5 mm and the thickness about 30 $\mu$m. Effects of the addition of C into Fe${}_{73.5}$Cu₁Nb₃Si${}_{13.5}$B₉ amorphous soft magnetic alloys were investigated in acidic solutions. Studies of potentiodynamic polarization and electrochemical impedance revealed the passivation ability and corrosion resistance of the amorphous ribbons with C in the 0.1M H₂SO₄ media at room-temperature. The amorphous ribbons showed excellent corrosion resistance with formation of a stable passive film. It can be obviously observed that the addition of C significantly improves the corrosion resistance.

Attention has been focused on the fatigue problem for compacted graphite iron, when detonation pressure and temperature becomes higher and higher in combustion chamber for a long time. The compacted graphite iron plays an important role in the cylinder head of diesel industry for its good combination of thermal and mechanical properties. The damage mechanisms of compacted graphite iron under fatigue loading are observed in this study by scanning electron microscope (SEM) and in situ technique at elevated temperatures. The results show that tensile strength of compacted graphite iron decreases slightly at first, then decreases dramatically with the increasing temperature, which is a common phenomenon, even of various metallic materials. For the compacted graphite iron, these two stages are mainly controlled by different transformation mechanisms: the former mechanism, slip band stage, is affected by the inhibition of dislocation movement including strain strengthening, dynamic strain aging and precipitation hardening; and the latter, boundary sliding stage, is controlled by the vacancy diffusion. The newly proposed mechanisms can provide a new clue for the optimization of cast iron design. These damage mechanisms lay the foundation for the application of the crack technology.

We studied the flow-induced vibration (FIV) and fretting wear of fuel rod with grid relaxation. According to the flow distribution around a type of pressurized water reactor (PWR) fuel rod, the power spectral density (PSD) is obtained to characterize the turbulence excitation. By combining the correlation of PSD test parameters, the mean square value of the vibration displacement of each rod mode is found, and then the wear depth of dimple position is calculated based on the ARCHARD wear formula. The grids may relax due to inaccurate manufacturing, fuel transportation and in-core irradiation. The absence of grid clamping force would significantly influence the rod mode and thereby changes its FIV responses. Simulation results show that the failure of the leaf spring has negligible effect on the rod natural frequency whereas the dimple failure near the location with larger FIV amplitude has a much significant effect. The lateral flow velocities at the inlet and outlet of the core are larger. For the fully clamped fuel rod, the responses amplitude of turbulent excitation at the bottom and top of the fuel rod are larger. This is even more obvious with a failed dimple at these locations. Comparatively, the effect of dimple support failure in the middle is less influential. The influence of dimple support failure on the rod wear depth depicts basically the same trend as on the maximum FIV amplitude.

The loosening experiments of bolted joints under shear load have been carried out. The effects of the initial tightening torque, the shear load amplitude, and the material of bolts on loosening behavior are studied. The results indicate that there exists a critical value for the shear load amplitude, below which complete loosening would not occur. It is also found that the bolted joints made of quenched and tempered steel and stainless steel have a significant anti-loosening performance. Damage mechanisms of the contact thread surfaces are adhesive wear, delamination and oxidative wear.

Fatigue short crack replica tests of a carbon structural steel, i.e., LZ50 steel, were carried out under tension–torsion loading using MTS electro hydraulic servo machine. Totally eight specimens with smooth axial hourglass shape were tested. The results show that short fatigue cracks generally initiate from the ferrite grain boundary or in the ferrite grain. In the microstructural short crack (MSC) stage, the crack grows slowly, but the growth rate will decrease when the crack encounters microstructural barriers, such as the ferrite grain boundary and the rich pearlite banded structure. In the physical short crack (PSC) stage, the crack breaks through the rich pearlite banded structure and meanwhile the dominant effective short fatigue crack (DESFC) has established its dominant position. As a result, the size and the growth rate of the crack increase rapidly. Based on the fatigue failure mechanism and the safety in tail region predictions, the statistical evolution of the DESFC size and the life fraction was analyzed respectively by comparing six commonly used statistical distributions. The statistical results show that the extreme minimum value (EMV1) distribution is a good assumed distribution for both the DESFC size and the life fraction.

Multi-direction isothermal forging of 7050 aluminum alloy at 10³s¹ strain rate and temperature of 300⁰C are observed. EBSD is used to characterize the grain structure, and the Vickers hardness and intergranular corrosion (IGC) properties are tested. The results of EBSD indicate that the sub-grains increase and the grain size decreases gradually as the pass of isothermal forging increases. The volume fraction of sub-grain has great effect on the corrosion resistance. The more sub-grains are included in the grain structure, the better the corrosion resistance and the mechanical properties. The grain size also influences the corrosion resistance, and the decreasing of the grain size is adverse to the corrosion resistance but is good for mechanical properties.

In order to understand the evolution law of material comprehensive performance of S38C steel for high speed railway axle, the new axle and other one were characterized after serving 4.3 million kilometers. In this paper, the surface morphology and microstructure were observed and the hardness, tensile properties, residual stress were examined. Results show that fretting fatigue wear happened on the 4.3 million-kilometer axle and the damage of the wheel seat surface was relatively serious. After the high-frequency quenching, a dense martensitic structure was formed on the surface of the axle, which improved the strength and hardness of the axle surface. The surface hardness and cross-section hardness distribution of the two axles were basically consistent. There was little difference in tensile mechanical performance of the two axles. But, the tensile mechanical property of the material in the surface quenching zone was much higher than that of the central matrix material. After the axle was serviced for 4.3 million kilometers, the residual stress both on the surface and in the cross-section at the wheel seat increased.

The Ni–Zn–P alloy coating has excellent physical and chemical properties that have been exploited for various industrial applications. Using sodium citrate as a complexing agent and lactic acid as a stabilizer, the effects of temperature and pH on the deposition rate and corrosion resistance of electroless plated Ni–Zn–P coating were studied. The results indicated that, when the temperature was 85${}^{\circ }$C, a good deposition rate was obtained with stable plating solution. pH value of 9.0 is preferred for the coating process by considering the stability of plating bath and deposition rate. The Ni–Zn–P alloy coating deposited with plating temperature of 85${}^{\circ }$C and bath pH of 9.0 has good quality, and a uniform and smooth surface texture without porosity.

A Ni–Fe–B–Si–Nb amorphous alloy was deposited on a steel substrate surface via a laser cladding process, and a laser cladding plus laser remelting process. The wear behavior of the laser processed samples and the bulk metallic glass (BMG) sample with the same nominal composition were tested using a pin-on-disc type testing machine. The nano-mechanical properties of the samples were measured with a nano-characterization system. The friction wear tests showed that deep grooves and wear debris were formed on the worn surface of the laser cladded coating, while only shallow grooves for the laser remelted coatings. The friction coefficients of laser remelted coatings and BMG were lower than the laser cladded coating. The wear mass losses of the laser remelted coating were less than the BMG when the laser remelting scanning speed was higher than 6 mm/min. The nano-hardness and elastic modulus of the remelted coating is higher than that of the laser cladded coating. Also, they increase with the increasing laser scanning speed with 1227.9 HV and 277.4 GPa when the remelting scanning speed is 8 m/min. Based on the nano-indentation and friction wear tests results, it was found that the friction wear properties of the laser cladded coating, laser remelted coatings and BMG related well to the ratio of H³/E². A higher value of H³/E² can lead to a better wear resistance property.

This study explores the preparation and application of polyethylene glycol (PEG)-modified PbO₂ electrodes. The PEG-modified PbO₂ coatings were electrodeposited on a Ti/SnO₂-Sb substrate from a methanesulfonate electrolytic bath containing different amounts of PEG. Structural and morphologic characterization was carried out for the deposited electrodes. The presence of PEG in the deposition bath represses the nucleation process and grain growth process in PbO₂ deposition. Increasing PEG addition results in an increased $\alpha$-PbO₂ content and decreased crystallite size. At a limited PEG addition $\le$4 g/L, a rough and pyramidal surface morphology is presented in the PbO₂ coatings. A higher PEG addition at 6 g/L leads to a dense and smooth coating surface yet with less uniformity. Electrochemical characterization reveals a great electrocatalytic activity for the modified PbO₂ electrodes when the PEG addition is $\le$4 g/L.

For film deposition, the substrate sheath properties, such as the plasma density, ion-to-atom ratios around the substrate, are more important for the film structure. In this paper, titanium thin films were deposited on grounded substrates by high-power pulsed magnetron sputtering (HPPMS) with the peak current in the range of 113–185 A. A simple and new equivalent circuit model of the sheath was established to study the plasma density around the substrate sheath. The Ti ion-to-atom ratios near substrate were studied by optical emission spectroscopy (OES), and the film structure was detected by transmission electron microscopy (TEM). The results showed that the calculated plasma density was from 0.8 × 10${}^{17}$ to 1.4 × 10${}^{17}$ m${}^{-3}$ at different peak current. These were consistent with the results measured by a modified one-grid ion collector using saturation current probe method, which proved our proposed equivalent circuit model was correct. The Ti ion-to-atom ratios around the substrate were estimated at about 24%–62%. The plasma density and ion to atom ratio around the substrate increased with the peak current, and this could lead to a higher film crystallization and preference growth on Ti (101) and (100).

Titanium (Ti) thin films with (002) or (100) texture are favored for many applications. In this paper, Ti thin films were prepared by high-power pulsed magnetron sputtering, and the texture of Ti thin films was successfully tailored by adjusting the pulse width, substrate bias and magnetic field strength. It is found that the peak power and average power of the Ti target are increased by increasing sputtering pulse width and decreasing magnetic field strength, which raise the Ti plasma flux and ion/atom ratio of Ti ions in front of the substrate simultaneously. Ti thin films with a highly (002) out-of-plane texture can be obtained with higher pulse width and lower magnetic field strength. The Ti thin films with highly (100) out-of-plane texture can be achieved with shorter pulse width, lower magnetic field strength and substrate bias.

The attractive key-enabling nanotechnology manufacturing technique of atomic layer deposition (ALD) is well-known to deposit ultra-thin, uniform, conformal and pinhole-free nano-films on complex topography. Over the years it has been used to deposit ultra-thin films in a multitude of industry applications such as microelectronics, solar cells, superconductors, fuel cells, and water purification membranes, among other applications. This study investigates the ALD process effects in the fabrication of Al₂O₃ thin film over the substrate. The mass fraction coverage over the substrate and deposition rate contours in a Gemstar 6 ALD reactor are examined. The analysis technique illustrates the parameter behavior over a Cartesian coordinate sector in a three-dimensional illustration. The governing laws of the conservation of mass, momentum, energy, species, and kinetic chemical reactions are analyzed numerically by ANSYS Fluent and ChemkinPro. The deposition rate profiles correlated with previous experimental findings in the literature, producing an average growth rate of 1.3 Å/cycles.

Duplex Ni-P-TiO₂/Ni coatings were deposited on the brass substrate by using two baths. Ni-P-TiO₂ nanocomposite coatings were electroplated as the outer layer on the Ni-plated brass substrate by adding transparent TiO₂ sol (0–50 mL/L) into the Ni-P plating solution. The microstructure, mechanical property and corrosion resistance of the duplex Ni-P-TiO₂/Ni nanocomposite coatings were systemically investigated. The results show that the interface of duplex coating was uniform and the adhesion between two layers was extremely good. The microhardness of duplex Ni-P-12.5 mL/L TiO₂ /Ni coating was $\sim$616 HV${}_{50}$ compared to $\sim$539 HV${}_{50}$ of Ni-P /Ni coating and $\sim$307 HV${}_{50}$ of single Ni coating. Meanwhile, the wear resistance and the corrosion resistance of the duplex nanocomposite coating have also been improved remarkably compared with single Ni coating. However, adding excessive TiO₂ sol (more than 12.5 mL/L) caused the agglomeration of TiO₂ nanoparticles and led to a porous structure in the outer layer, resulting in the deterioration of coating properties.

Computer Simulation Technology EM and Computer Simulation Technology Microwave Studio electromagnetic simulation software were used to simulate the carbon fiber composite materials with a new type of wide frequency electromagnetic shielding coating. DC magnetic field, low-frequency electromagnetic fields, and mid-high frequency electromagnetic shielding effectiveness analysis model were established in order to study the influence of permeability, conductivity, coating thickness and other parameters in the typical frequency range research on the shielding effectiveness. The results show that the composite coating material with reasonable design can effectively enhance the electromagnetic shielding performance of carbon fiber composite materials in the DC $\sim$18 GHz frequency range.

In order to improve the high-temperature oxidation resistance of the hydrogen-resistant steel, Al coatings were firstly deposited on the hydrogen-resistant steel by arc-ion plating and then the thermal diffusion treatment was used to produce the Al-based composite coatings on the hydrogen-resistant steel. The effect of thermal diffusion parameters on the structure of Al-based composite coatings was studied. The crystal structure, composition and morphology of Al-based composite coatings were analyzed by using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). The results showed that the double inner diffusion layer was formed on Al coatings treated at 700${}^{\circ }$C. And the single inner diffusion layer with uniform composition distribution could be formed on Al coatings treated at 950${}^{\circ }$C. The Al-based composite coating prepared by thermal diffusion treatment at 950${}^{\circ }$C had a dense and thick $\alpha$-Al₂O₃ surface layer, and it exhibited good high-temperature oxidation resistance.

TiO₂ hierarchical structure composed of H₂Ti₃O₇ nanoribbons and TiO₂ anatase nanoparticles was synthesized via a two-step hydrothermal process, including the recrystallization of TiO₂ precursor into nanoribbons and the subsequent deposition of TiO₂ nanoparticles on nanoribbon surface. The coated nanoribbons exhibited a good photocatalytic activity to degrade Rhodamine B (RhB) with a kinetics constant of 0.0269/min, 10 times higher than that of the as-produced nanoribbon (0.0026/min). They also possess good sedimentation properties compared to the pristine TiO₂ anatase particles. The excellent photocatalytic performance together with sedimentation property makes these hybrid nanostructures effective and recyclable photocatalysts for wastewater treatment in industrial applications.

Novel Ag/TiO₂ nanotubes electrode has been synthesized by successive ionic layer adsorption reaction (SILAR) using TiO₂ nanotubes as the catalyst support. Scanning electron microscopy and energy dispersive spectroscopy analysis show that Ag nanoparticles have been successfully deposited on the top of TiO₂ nanotubes. The Ag/TiO₂ nanotubes electrode has a superior electro-catalytic property for hydrazine oxidation with a low onset potential and high current density. The result indicates that Ag/TiO₂ nanotube electrode has a potential application for hydrazine sensor and hydrazine fuel cell.

The microstructure, microhardness and wear property of electroplated Ni–ZrO₂ nanocomposite coatings with different ZrO₂ concentration were analyzed using SEM, microhardness and wear tests. It was found that in the composite coatings, incorporation of ZrO₂ particles improves the mechanical property of Ni coatings and the effect of ZrO₂ nanoparticles concentration on the surface morphology, microstructure and mechanical property of electroplated coatings was discussed. The mechanical properties of Ni–ZrO₂ coatings reach the optimum value when the ZrO₂ concentration is 10 g/L.

N-doped TiO₂ nanotube arrays were prepared by an electrochemical anodization method and subsequent ammonia annealing. Microstructures, morphology, optical properties and photocatalytic properties of the N-doped TiO₂ nanotube arrays were measured and analyzed. In the degradation of Acid Orange II(AO-II), the photocatalytic degradation efficiency of the N-doped TiO₂ nanotube arrays assisted by H₂O₂ are 12 times, 2 times and 5 times higher than TiO₂ nanotube arrays, TiO₂ nanotube arrays assisted by H₂O₂ and H₂O₂, respectively. Experimental results show that the N-doped TiO₂ nanotube arrays is a promising photocatalytic material for organic pollutant degradation under visible light, especially under the assistance of H₂O₂.

The coating deformation behavior and stress evolution of the plasma sprayed Cr₃C₂–NiCr coating during nanoindentation process were analyzed by finite element modeling based on its real elastic-plastic properties. The effects of indentation depth and the coating thickness on the mechanical response of the coating were studied. The results show that once the indentation depth exceeded 13% of the coating thickness, the coating material near the indenter was extruded and piled up on the top surface. Meanwhile, high equivalent stress was developed along the coating-substrate interface rather than inside the coating. Even when the indentation depth was smaller than 13% of the coating thickness, the substrate still influences the mechanical behavior of the coating, inducing different reaction force to the indenter.

The article investigated the properties of 6N01 aluminum alloy joints with Sn-80Zn semi-solid solders by ultrasonic soldering. It was found that semi-solid solders consisted of Zn-rich phase with short rod-like dentrite, which had the lower solidus temperatures, while Zn-rich phase with long dentritic grains used the conventional solders. The joints soldered with Sn-80Zn conventional filler metal reached maximum shear strength of 73 MPa at the soldering temperature of 390${}^{\circ }$C. The joint using Sn-80Zn semi-solid solder obtained higher shear strength of 90 MPa at the lower temperature of 370${}^{\circ }$C. The effects of the ultrasonic time and the soldering temperature on the mechanical properties of the joints were also investigated with the Sn-80Zn semi-solid solders.

We propose an ultrasound-assisted laser–metal inert gas hybrid welding process, where acoustic effects are introduced by applying ultrasonic vibration in the axial direction of the arc. We studied the acoustic characteristics in the space between the acoustic radiating and reflecting surfaces. Based on a simplified two-dimensional model, we used the finite-element method to study the influence of the height and inclination of the radiating surface on the acoustic characteristics. The simulated sound pressure distribution was highly sensitive to the height and inclination of the radiating surface. The sound pressure decreased as the height of the radiating surface increased from a maximum value at the resonance height, and decreased as the inclination of radiating surface increased. Experimental results of the detachment of a water droplet from a needle were consistent with the simulation results. We simulated the distribution of the standing-wave field under different radiating concave-sphere surfaces to evaluate the acoustic focusing effects. Both experimental and simulation results for ultrasonic standing-wave levitation of plastic beads revealed the concave-sphere shape to be optimal.

In this study, rotating laser was employed to reduce the porosity defect in laser-MIG hybrid welding A6N01 aluminum alloy. The influence of laser rotating frequency and rotating radius on the weld were researched respectively. The images of the molten pool were acquired by the high-speed camera, and X-ray images of the weld were calculated by binarization. The result shows that rotating laser-MIG hybrid welding has a dramatic effect on suppressing the generation of porosity, which indicates the possibility to obtain the A6N01 aluminum alloy weld with few pores. With proper parameters about rotation frequency (50 Hz) and rotation radius (2 mm), the porosity decreased obviously from 8.41% to 5.68%, and there was hardly distinct change in the weld penetration. The keyhole stability of rotating laser-MIG hybrid welding was improved, compared with the conventional laser-MIG hybrid welding. On account of laser beam stirring the metal molten pool, it was beneficial for the pores to escape from the molten pool. The rotating laser-MIG hybrid welding shows a good prospect.

We butt-welded AA6061 aluminum alloy to Ti6Al4V titanium alloy, dissimilar light metals, by using laser-MIG hybrid welding–brazing without grooves. The parameters of the laser and arc were optimized to produce sound joints with good formation and mechanical properties. The microstructure of the layer of intermetallic compounds (IMCs) was investigated by scanning electron microscopy and energy dispersive spectroscopy. We also tested the tensile strength of the joints with and without reinforcement. The morphology and thickness of the IMCs varied throughout the joints. A continuous thin layer of TiAl₃ appeared on the top surface of the Ti6Al4V, on which some rod-like IMCs grew toward the fusion zone. In the upper region of the butt plane, because more heat accumulated there from the high-power laser coupled with the MIG arc, double-layer IMCs with a thickness of $\sim$10.0 $\mu$m formed, composed of TiAl (near the Ti alloy) and TiAl₃ (near the fusion zone). In the lower region of the butt plane, the double-layer IMCs became continuous and uniform, the serrated morphology disappeared, and the thickness of the IMC layer decreased to 4.0 $\mu$m. On the backside of the joint, the thickness of the compound layer (TiAl₃) was about 1.0 $\mu$m. The average tensile strengths of the reinforced and unreinforced joints were 226 MPa and 210 MPa, respectively, which are up to 88% and 81% of the AA6061 tensile strength, respectively.

The inspection of rail defects is of importance in high-speed railway operation and maintenance. As a highly efficient method for both nondestructive testing and structural health monitoring of the rail, ultrasonic guided waves (UGWs) inspection provide increased sensitivity to smaller defects. These advantages can be fully exploited only if the complexities of UGWs propagation between the medium of air and rail are unveiled and managed for the given inspection method. The development and validation of modeling procedure for the rail based on coupled structural–acoustic model is presented in this paper. Acoustic–structure interaction between air and rail is simulated based on COMSOL Multiphysics software. The transient response and natural characteristics of UGWs in the rail was computed and predicted. Moreover, the displacement distribution of UGWs in the defective rail and nondefective rail are analyzed both in time and frequency domain. A feasible method for detecting small defects in the rail is proposed in the paper. The results indicated that a defect of 8 mm in rail head can be inspected effectively using UGWs with frequencies of 40 kHz and above. And for small defects in rail web, the X-crystallographic direction ultrasonic transducer should be chosen for inspection.

The welding residual stress has different effects on the mechanical properties of aluminum alloy welded joints, such as size stability, fatigue strength and stress corrosion cracking. Therefore, it is very important to evaluate the welding residual stress accurately. In this paper, the residual stress of A7N01 aluminum alloy welded joints was measured by X-ray diffraction. In contrast to the traditional method, the cos$\alpha$ method was used in this paper, the results were compared with those obtained by the conventional ${sin}^2\psi$ method. In addition, the influence of oscillation unit on the test results of the cos$\alpha$ method was studied.

Due to the good conductivity of ions and free electrons in the arc column, arc plasma possesses a remarkable magnetic controllability. Thus, a new technique of electromagnetic stirring has been developed which is of great interest during welding process by applying superimposed external magnetic field. However, few researches have focused on arc behavior with a coupled electrode under a magnetic field. In this paper, a three-dimensional plasma arc model coupled cathode was developed, and the distributions of current density, electric potential, magnetic field, pressure, velocity and temperature of plasma arc were obtained by solving the conservation equations of momentum, mass and energy coupled Maxwell’s equations. By applying finite volume method, when the intensity of applied electromagnetic field exceeded a threshold value, it reveals that arc contraction near cathode and arc divergence near anode are induced resulting in mutation phenomenon. The distributions of arc temperature and pressure deviate from the axis of tungsten and exhibit a bimodal shape. This is distinctly different from that of the free arc under natural combustion condition. In addition, the maximum velocity of the plasma flow appears on both sides of the arc symmetry axis. Moreover, arc plasma presents a behavior of heavy reflow and eddy, and a low-temperature area and a negative pressure zone appear in the central axis of arc plasma.

The two-dimensional morphology of the cladding layer has an important influence on the quality of the cladding layer and the crack tendency. Using the powerful nonlinear processing ability of the single hidden layer feedforward neural network, a prediction model between the cladding technological parameters and the two-dimensional morphology of the cladding layer is established. Taking the cladding parameters as the input and the two-dimensional morphology of the cladding as the output, the experimental data is used to train the network to achieve a high-level mapping of the input and output. On this basis, the algorithm of extreme learning machine is used to optimize the single hidden layer feedforward neural network to overcome the problems of slow convergence speed, more network training parameters and easy local convergence in back-propagation algorithm. The results show that the relationship between the cladding process parameters and the two-dimensional morphology of the cladding layer can be roughly reflected by the back-propagation algorithm. However, the prediction results are not stable and the error rate is between 10% and 40%. The neural network optimized by the extreme learning machine is utilized to get a better prediction result. The error rate is 10–20%.

The high manganese steel surfacing layer was deposited on Q235 steel by flux-cored wire gas shielded welding. The as-welded surfacing layer was heated at 1050${}^{\circ }$C and quenched in the water, then was tempered at 300${}^{\circ }$C. The microstructure, hardness and wear resistance of as-welded surfacing layer and that after heat treatment were comparatively analyzed. The results showed that compared with the as-welded surfacing layer, a large number of fine carbides dispersed in the austenite matrix for the surfacing layer after heat treatment. Meanwhile, the hardness and wear resistance of surfacing layer were slightly improved. The furrow in the abrasive wear for surfacing layer was shallower. Under the action of work hardening, the hardness of high manganese steel surfacing layer gradually increased while the loss weight decreased with the wear time less than 30 min. The hardness of surfacing layer reached the maximum and the loss weight of wear remained unchanged when the wear time was 30–60 min.

A three-dimensional numerical model of double-arc in tandem gas metal arc welding (GMAW) was established based on the theory of arc physics, momentum equation, energy equation, continuous equation and Maxwell equations. The effects of different welding current on temperature field, velocity field and pressure field on the surface of workpieces were investigated. The results showed that the maximum values of arc temperature, arc plasma velocity and arc pressure on workpieces surface were increased with the increasing welding current. These maximum values occurred at the tip of double-wire. The current density and axial deflection angle of coupling arc were increased following the increasing welding current.

Joining of super duplex stainless steel (SDSS) is still a challenge, in particular, the need to control the phase balance in the weld metal. In this paper, laser-MIG hybrid welding process was used to join SAF 2507 SDSS plates. The effects of welding parameters on weld appearance, microstructure and phase distribution and mechanical properties were studied systematically. Results showed that the arc/laser hybrid effect was more significant when the arc led the laser with 2 mm distance. It was indicated that arc current mainly affected the weld width while laser power mainly affected weld penetration depth. The composition and microstructure varied a lot at different positions in the weld due to the differences in peak temperature and cooling rate. From top to root, the content of ferrite phase increased and austenite phase decreased. With optimized welding parameters, due to the increase of heat input and the introduction of welding wire, the ferrite/austenite phase balance in the weld metal was obtained. Mechanical property tests showed that the joints exhibited higher tensile strength but lower toughness compared to base metal.

The residual stress beneath the surface is crucial to the safety of the structures. Neutron Diffraction and Hole-drilling are the two methods being used to measure the inner residual stress. Longitudinal Critically Refracted (LCR) wave transmission that is propagated parallel to surface also can be used for measuring residual stress, but measurements are within an effective depth and need to be further studied. In this paper, the parameters of K are separately tested in WZ, HAZ and BM zone. The welding process of 6082-T6 aluminum alloy welded joints is simulated in SYSWELD, the finite element model has been verified by the X-ray diffraction method. The residual stress value calculated by SYSWELD and the values obtained from the ultrasonic measurement show a good agreement. It is demonstrated that the residual stress of 6082-T6 aluminum alloy welded plate can be evaluated by using the ultrasonic method.

In this paper, the corrosion-fatigue behavior of 301L stainless steel (SS) welded joints using narrow gap laser wire welding under the different stress ratio and concentrations of Cl${}^{-}$ has been investigated. Corrosion fatigue life curve (S-N) under different conditions was tested and fitted to obtain the fatigue limit. The microstructures and fracture surfaces of specimens were examined by optical microscopy (OM) and scanning electron microscopy (SEM). EBSD results have shown that chromium depletion in the weld heat-affected zone (HAZ) contributes to the decrease of corrosion fatigue properties in the HAZ.

The cold metal transfer (CMT) with addition of pulses (CMT$+$P) process is a new CMT welding method. This paper uses a high-speed camera and electrical signal synchronization acquisition system to perform a CMT$+$P welding test on a 10 mm thick Q235 steel plate, and performs arc characteristic and droplet transfer behavior in the welding process. It has been founded that under relatively small currents and voltages, the CMT$+$P transfer mode is a combination of a projected transfer mode with one droplet in the pulse period and a short circuit transfer mode during the CMT period. The process is stable with little spatter; at relatively large currents and voltages, the transition mode is the combination of pulse transfer, spray transfer and short circuit transfer. It results in one or more droplets that enter the pool both in pulse transfer in the spray transfer mode during the pulse period and in the short circuit transfer mode during the CMT period in a weld cycle.

Wear behaviors of two U71Mn K and U71Mn G rail steels have been systematically investigated with the simulated experiments during the tolling contact fatigue using samples taken from their base materials, the heat-affected zones near the weld, and the weld zones, respectively. The results demonstrate that there are significant differences between the nonweld and the weld zones for both steels. With higher hardness of U71Mn G over U71Mn K, the U71Mn G steel has mild abrasion damage, reduced weight loss from wear and reduced corrugations of the weld zone during the experiment with increased simulative speed; while its other features such as the plastic deformation and cracks are almost the same compared with the U71Mn K steel. The U71Mn G steel demonstrates superior performance over U71Mn K at the high-speed rolling experiment.

The hydrogen-induced stress corrosion cracking (HISCC) behavior of SUS301L-MT stainless steel laser-arc hybrid welding (LAHW) joints was investigated using slow strain rate tensile (SSRT) method in 3.5 wt.% NaCl solution under different cathodic potentials. With the negative shift of applied potentials from open circle potential (OCP) to −1400 mV${}_{\mathrm{\text{SCE}}}$, the HISCC susceptibility index ($I_{\mathrm{\text{SSRT}}}$) decreased from 0.15 (OCP) to 0.06 (−400 mV${}_{\mathrm{\text{SCE}}}$), then increased to 0.28 (−1400 mV${}_{\mathrm{\text{SCE}}}$). The specimens tested in air and under OCP to −800 mV ruptured in weld metal zone with ductile features of dimples. While with the potential turned more negative, the specimens ruptured in base metal zone with brittle features of transgranular cleave in martensite, intergranular failure and secondary cracks [Chen et al., Int. J. Adv. Manuf. Technol. 73, 1695 (2014)].

A7N01 aluminum alloy is widely used in rail transit industry due to its excellent comprehensive mechanical properties. However, due to its sensitivity to stress corrosion cracking (SCC), especially in hydrogen-containing moisture environment, the mechanical properties of hydrogen-charged A7N01 aluminum alloy friction stir welding (FSW) joints were tested through the tensile testing machine. The scanning electron microscopy (SEM) was used to study the tensile fracture morphology. The results indicate that the ductility and tensile strength loss of A7N01 Al alloy FSW joints are large in conditions of charging hydrogen. This is due to the embrittlement of the material caused by hydrogen infiltrating into the grain boundary of the aluminum alloy material.

This study has analyzed the welding joint of carbon fiber reinforced plastics (CFRP) and aluminum alloys. The surface of CFRP and 5083 Al alloy was modified by electroplating with nickel at first. Then the effect of electroplating parameters on coating was explored. SEM images revealed that the coating gradually became well but then began to fall off with the current density and the plating time increased. CFRP and aluminum alloys were brazed at 285${}^{\circ }$C and held for 20 s. Shear test was used to evaluate the strength of the joint and the strength was probably 7.56 MPa. SEM and EDS tests showed that there existed diffusion of the elements in the welding process and the joint reached the bonding of atomic or molecular sizes. Thus, this experiment achieved the tight brazing joining between thermoset CFRP and aluminum alloys providing the joining method of the application for CFRP.

In this paper, we study the droplet transition behavior of narrow gap laser wire filling welding under the condition of changing welding speed and wire feeding speed, and it was observed by high-speed photography. It was found that with the increase of welding speed, the frequency of droplet transfer was reduced and the transition period was prolonged. With the increase of wire feeding speed, the wire was not fully melted and finally inserted into the molten pool.

The coupling model of temperature-phase transformation-mechanics is constructed in this paper. The effect of solid state phase transformation and different hardening models on the residual stress distribution of S355J2W welded joints have been studied with finite element method (FEM) simulation. The microstructure, micro hardness and residual stress of welded joints are also studied. It has been shown that the microstructure of weld seam is composed of bainite structure with little martensite, while the base metal is ferrites and pearlites. The simulation results by FEM were in good accordance with the X-ray results. The maximum tensile residual stress is 463 MPa in the weld. The tensile residual stress was decreased with the larger distance to the weld.

The residual stress with different degree is inevitable to be introduced during the welding process for high strength 7N01 Al alloys, which will deteriorate the mechanical properties in service. Therefore, a proper characterization method is of vital importance to obtain the detailed residual stress distribution. The conventional X-ray diffraction method can only measure the residual stress of near surface but cannot determine the internal bulk stress with nondestructive way. In the present work, a new Short-Wave X-Ray Diffraction (SWXRD) test methodology was utilized, which can evaluate not only the surface but also the internal residual stress of a crystalline material by applying the monochromatic short-wave X-ray of high-energy. The results show that there is a “M” shaped distribution of residual stress of longitudinal direction (LD) in different affected zone. Furthermore, the characterization of residual stress along weld depth direction demonstrates that the middle part of weld joint is subjected to tensile stress while the rest is subjected to compressive stress.

In this work, the in situ SiC/Al composites were successfully fabricated by the method of combustion synthesis and hot press consolidation in an Al-C-Si system. The effect of alloying elements (Mn, Zn, Ti) on the phase constitution and microstructure of in situ SiC/Al composites were investigated. Results indicated that the Al${}_{11}$Mn${}_{14}$ and Ti${}_x$Si${}_y$ phases were formed in the SiC/Al composites with the addition of Mn and Ti, respectively. By the addition of Mn, the size of the synthesized SiC particles was obviously reduced, and consequently the amount of SiC particles was increased. Meanwhile, the percentage of the submicro SiC particles increased about from 22% to 83%. However, the addition of Zn and Ti had little effect on the size of SiC particles.

A kind of radar absorber is designed and produced based on circular microstructure, which is composed of a circular microstructure, carbonyl iron rubber radar absorbing patch and metal backboard composition. Numerical simulation of effect of the circular microstructure on absorbing properties of carbonyl iron rubber radar absorbing patch is performed by means of the time domain finite integral method. Simulated results indicate that by using the holding absorber with the unchanged thickness of 2.5 mm, when the absorber unit size was P = 30 mm and the circular radius was R = 5 mm, the value of the minimum absorption peak can reach −43 dB, −10 dB absorption band shifted from 5.8–9.3 to 4.6–8.2 GHz, changing the parameters of circular microstructure greatly, expanding the absorbing bandwidth of microwave absorbing patch, reducing the reflectivity of resonance frequency. According to the simulation results, the samples are prepared and tested. The test results are in agreement with the simulation results.

Different time air plasma treatment was conducted on acrylonitrile–butadiene rubber (NBR) surface, the wettability and friction behavior of the samples surface were measured after two months of storage. The changes in surface composition and microstructure during storage process were observed by X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM), respectively. The results show that the wettability of modified surface has obvious “hydrophobic recovery” phenomenon in the storage process, and the range of contact angle increase is closely related to the plasma treatment time, mainly because the change in surface composition at various time treatment are different during storage; the frictional behavior of plasma-modified NBR surface has not exhibited a “recovery” phenomenon after two months of storage, and the friction coefficient of the surface treated for 4 min and 8 min were even smaller than those before storage, which is due to the smoother and lower roughness of the surface morphology after storage. This study demonstrates that air plasma treatment is a promising technique for improving the wettability and tribological properties of NBR rubber, but the proper treatment time is needed to make the surface have the best wetting and frictional behavior.

The low ductility and insufficient strength of the TiAl alloy are still two major obstacles for its applications. It was demonstrated that Ti₅Si₃ could improve the ductility of TiAl alloy, while it can’t obviously improve the strength. In order to further improve the strength of Ti₅Si₃/TiAl composite to obtain TiAl materials with excellent strength and ductility, the effects of alloying elements (Cu, Zn, W and Mo) on the compression strength of the in-situ nano-Ti₅Si₃/TiAl composite were investigated in this work. With the addition of 2 at.% Me (Me $=$ Cu, Zn and W, respectively), the compression true yield strength (${\sigma }_{\mathrm{\text{true}}}^y$) of the composite increases from 613 MPa to 840, 660 and 706 MPa, respectively. Moreover, the addition of Zn results in the increase of the ${\sigma }_{\mathrm{\text{true}}}^y$ with no obvious sacrifice of ductility. Finally, the 4 vol.% nano-Ti₅Si₃/TiAl-2Zn composite obtained the best comprehensive properties. Compared with the TiAl alloy, the ${\sigma }_{\mathrm{\text{true}}}^y$, ${\sigma }_{\mathrm{\text{true}}}^{\mathrm{\text{UCS}}}$ and ${𝜀}_{\mathrm{\text{true}}}^f$ of the Ti₅Si₃/TiAl-2Zn composite increases by 195, 140 MPa and 2.6%, respectively.

The mechanical-annealing referred in this work is also named pre-strain, which is widely investigated in TRIP steel, stainless steel, magnesium alloy and aluminum alloy. In this case, we used preloading to input energy into a bulk metallic glass (BMG) to observe the changes in the structure and mechanical properties. We selected Zr${}_{56}$Co${}_{26}$Al${}_{18}$ BMG as a model material owning to its outstanding glass forming ability and excellent mechanical properties. The samples were kept at a constant pressure of 1900, 1700 and 1500 MPa (below the yield strength) for 40, 55 and 70 h. The study found out that the density of those samples increased after being pre-loaded. Then, the samples underwent aging treatment at room-temperature for more than 30 days after unloading. After re-compressing the samples, the results show that the yield strength and fracture strength of the samples decreased, and the amplitude of the serrated plastic flow increased during the plastic stage. Our finding might have some implications for understanding the plastic deformation of BMGs.

Bulk metallic glasses are often used well below their glass transition temperatures, T_g, because of their change in the physical properties of the material through its glass transition, which is not considered a phase transition; rather it is a phenomenon extending over a range of temperature and is defined by a viscosity threshold of 10^{1 2} Pa ⋅ s. In this work, a Zr-based metallic glass upon annealing below glass transition temperature (T_g–30 K) was quasi-in-situ investigated. The structural and elastic properties were observed carefully by utilizing an in-house designed density testing device and an ultrasonic testing device. We found out that the density, the shear velocity, the longitudinal wave velocity, and the elastic modulus increased through annealing at 719 K for 300, 900 and 1500 s. A possible explanation was presented based on the free volume theory and it was found that the relaxation kinetics in this study obeyed the Kohlraush–Williams–Watts (KWW) relaxation function with $\beta$ = 0.420 $<$ 1 implying that the relaxation mechanisms were multiple ones.

The thickness of corroded concrete layer and the compressive strength of prisms under the action of sulfate and chloride salt were investigated by ultrasonic test and compression test, respectively. The results show that under the single action of sulfate, the strength of concrete experienced two stages: a slow growth stage and a rapid descent stage. Correspondingly, under the combined action of sulfate and chloride, the concrete strength experienced another two stages: a slow growth stage and a slow degradation stage. The existence of chloride inhibited the corrosion damage of concrete in a certain extent. It was found that higher concentration of chlorine salt would lead to a stronger inhibition effect. A good consistency was observed among corrosion layer thickness, compressive strength and X-ray diffraction results. The inhabitation of chloride to the sulfate corrosion of concrete was proved.

Graphene/Fe₃O₄/Ni nano-composite materials were prepared by one-step hydrothermal method from RGO, FeCl₃ ⋅ 6H₂O and purity Ni. The structure and electromagnetic microwave absorbing properties were investigated systematically by field emission scanning electron microscope (FESEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS) and vector network analyzer (VNA). The reflectance was simulated based on the electromagnetic parameters to evaluate the absorption properties of the sample. The results show that Fe₃O₄ and Ni are on the surface of graphene evenly, the composites exhibit excellent microwave absorption properties, reflection loss and broad effective absorption bandwidth are −16.38 dB and 3.60 GHz, as the paraffin wax is 40% and the matching thickness is 2.00–3.50 mm.

2-methacryloyloxyethyl phosphorylcholine (MPC) polymers have good biocompatibility and hydrophilicity because the function of the phospholipid polar groups of MPC side-chain is similar to the natural articular cartilage. MPC has a potential application on surface modification of artificial joints. In this research, MPC was grafted on ultra-high molecular weight polyethylene (UHMWPE) by the photo-induced graft polymerization to form poly 2-methacryloyloxyethyl phosphorylcholine (PMPC) layer. The microstructure of PMPC layer was studied by Fourier-transform infrared (FT-IR) spectroscopy with attenuated total reflection (ATR) equipment, X-ray photoelectron spectroscopy (XPS). The surface wettability of PMPC layer was evaluated by the contact angle test. The wear resistance of MPC modified UHMWPE was evaluated by the wear test. The results show that the PMPC layer has a good lubricating effect and it can reduce the friction coefficient effectively. The benzophenone pretreatment time is an important factor in the graft stability of MPC.

Fluorinated diamond-like carbon (DLC) films have good biocompatibility and bloodcompatibility. When they are used in cardiac valve prosthesis, the wear resistance has to be investigated in more detail. In this paper, the tribological behavior of fluorinated DLC films under different loads and sliding speeds in bull serum albumin (BSA) solutions were investigated by ball-on-disc friction tests. The results show that the proteins in BSA solutions promoted the DLC film adhesion failure because of the increased friction coefficients and accelerated corrosion rate. The fluorine doping can lower the corrosion rate of DLC film, thereby improving the adhesion stability and wear resistance of DLC in BSA solutions.

A new hindered phenol with branched structure (chemical formula: 2-(((3,5-ditert-butyl-4-hydroxybenzoyl)oxy)methyl)-2-ethylpropane-1,3-diyl bis(3,5-ditert-butyl-4-hydroxybenzoate)) was synthesized and characterized, and its thermo-oxidative stability as antioxidant into nitrile rubber (NBR) was assessed by the measurements of accelerated aging, with two antioxidants (AO-80 and AO-2246) as a comparison. By measuring and analyzing the oxidative induction temperature, oxidative induction time and dynamic mechanical properties of NBR with addition of 0.5 wt.% antioxidants, it is confirmed that new hindered phenol with branched structure could effectively inhibit the oxidation degradation of NBR.

Nanostructured copper hydroxyl salts have raised researchers’ attention due to its potential application in photocatalysis. In this paper, copper hydroxyl sulfates were synthesized by titrating NaOH solution to CuSO₄ solution with the suggested pH from modeling software Visual MINTEQ. Brochantite nanostructures was produced at the end point pH 5 and 6, meanwhile the mixture of brochantite and posnjakite was obtained at pH 10. These results show the usability of Visual MINTEQ in determining the operating parameter (pH) range for the particular crystal synthetizations. In addition, these crystals show a good visible light absorption, which extends its function to wider applications.

Developing efficient and low-cost bi-functional electrolytes for energy applications such as fuel cells and rechargeable metal-air batteries is highly desirable. Here, we have synthesized spinel Ni${}_{0.5}$Cu${}_{0.5}$Co₂O₄ (NCC) nanoparticles as nonprecious bi-functional electrocatalysts by a simple hydrothermal reaction method. The phase structure and the morphology of NCC nanoparticles have been investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) while the electrocatalytic activity of the samples has been studied in alkaline solution by using rotating disk electrode technique. The electrocatalysts have showed a comparable ORR and OER catalytic activities compared with of those of the other transition metal oxides, suggesting the feasibility of the NCC as the bi-functional electrolytes materials for ORR and OER.