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Dissimilar metal of T2 copper and 1060 aluminum alloys were welded by plasma arc welding-brazing method with a lap joint, and SiO2 nanoparticles were added in the welding pool to control the interfacial intermetallic compounds (IMC). The interfacial microstructure and phase composition of the weld joint were identified by scanning electron microscope (SEM) and electron probe microanalysis (EPMA). IMC formation mechanism, weld joint tensile strength, and IMC nanohardness was also discussed. The results show that after adding SiO2 nanoparticles, due to the adsorption of the nanoparticles on the copper surface, the total interface energy between the aluminum liquid and the copper substrate would be reduced, and the wetting angle would be reduced. So that the aluminum melts can have better wetting ability, and the barrier effect of SiO2 nanoparticles formed prevents the further diffusion and reaction of copper atoms and aluminum atoms, and inhibits the growth of the IMC layer to a certain extent. The weld fracture occurred at the aluminum-based material added with nano-SiO2, showing typical dimple morphology. The phase with the highest hardness in the IMC layer is CuAl2. SiO2 nanoparticles exist in the CuAl2 intermetallic compound layer due to the adsorption of nanoparticles.

The difference of physical properties of Ti-6Al-4V alloy/aluminum dissimilar metals and the formation of intermetallic compound layer at the joint interface limit their reliable connection. The connection of Ti-6Al-4V alloy/aluminum was realized by plasma arc welding with lap joints of Ti-6Al-4V alloy plate on the top of aluminum. By changing the welding offset and current, a good welding joint can be obtained. The microstructure and mechanical properties of the joint were analyzed by optical microscope, scanning electron microscope (SEM), X-ray diffraction (XRD) and tensile test. Finally, the thermal process of the joint under different parameters was compared with the test, and the formation mechanism of the interface was discussed. The results show that the microstructure of the joint shows that the Ti-6Al-4V alloy is partially melted, and there is an unfused area, which is melted by heat conduction to the lower aluminum base metal, thus realizing metallurgical bonding. The interface transition layer is mainly the diffusion between titanium and aluminum atoms, and a lamellar TiAl3 intermetallic compound layer is formed on the aluminum side with a thickness of about 1 μm. The specimen is fractured on the side of aluminum base metal with the maximum load of 1.76 kN. The joint shows good mechanical properties. The results of finite element thermal analysis of the fusion zone of Ti-6Al-4V alloy and aluminum has good correspondence with the experimental results. When the current value increases, the weld center temperature and the size of the fusion area show an increasing trend. When the current value is 70A and the offset is 3 mm, it is conducive to the formation of good welded joint.

12Cr2Mo1R heat-resistant steel and 06Cr18Ni11Ti austenitic stainless steel are joined by Arc assisted activating TIG welding (AA-TIG) after using ERNiCr-3 and ER309 L filler metals pre-edge surfacing on the side of 12Cr2Mo1R. Scanning electron microscope (SEM) and optical microscope (OM) are used to study the microstructure of the joints. Microhardness, tensile strength and impact toughness are adopted to characterize the mechanical performances of the joints. Using CHI600D electrochemical workstation, and the potentiodynamic polarization and electrochemical impedance are employed to evaluate the corrosion resistance of the weld joints. The results show that the weld joints are formed well after pre-edge surfacing welding on the side of 12Cr2Mo1R base material. The microstructure of the weld by ERNiCr-3 and ER309 L welding wires pre-edge surfacing transition layer are single-phase austenite, austenite, and ferrite, respectively. The weld joint has excellent mechanical performances and corrosion resistance with the ER309 L welding wire pre-edge surfacing transition layer in the welding state.

There is great interest to deposit a layer of Inconel 625 nickel-base super-alloy on the surface of metallic substrate to increase the corrosion resistance for the services in harsh environment. In this work, we use the bypass-coupled micro-plasma arc welding to form a layer of Inconel 625 on the plate of QT-400 nodular cast iron and study the effect of the bypass current on the topology of the Inconel 625 layer. There exists spatial distribution of dendrites in the cladding layer along the direction normal to the bonding interface between the cladding layer and the plate of QT-400 nodular cast iron. The fusion zone near the interface between the cladding layer and the plate of QT-400 nodular cast iron has the largest Vickers hardness of 630 HV.

Background and purpose Subarachnoid hemorrhage (SAH) is a severe cerebrovascular condition. Some cases present with typical signs of SAH on head computed tomography (CT), whereas other cases have a condition known as pseudo-SAH, with no bleeding actually present. In our clinical experience, we noted that cases of hyperhemoglobinemia often also had pseudo-SAH. Here we investigated the relationship between hyperhemoglobinemia and pseudo-SAH and explored the underlying mechanism. Methods We retrospectively collected data for patients who were treated for hyperhemoglobinemia in our hospital and had available brain CT scans. An age-matched control group of patients with normal hemoglobin levels was used to compare the incidence of pseudo-SAH between individuals with elevated versus normal hemoglobin levels. Spearman correlation and logistic regression analyses were performed to identify correlations between pseudo-SAH and hemoglobin level as well as gender, history of chronic obstructive pulmonary disease, and smoking history. Results The incidence of pseudo-SAH was significantly higher in hyperhemoglobinemia group than in the control group (12.5% vs. 1.6%, respectively, P Conclusion Hyperhemoglobinemia may be a contributing factor to pseudo-SAH. Clinicians should be aware of this phenomenon and be careful to distinguish pseudo-SAH from SAH, particularly in patients with hyperhemoglobinemia.

The bypass-coupled wire arc additive manufacturing (WAAM) process was studied, and the arc characteristics and droplet transfer behavior during the deposition process were examined. The effects of the bypass current, wire feeding speed, wire feeding height, and wire feeding angle on the droplet transfer mode were investigated via a single variable experiment. The results show that with an increase in the bypass current, the arc first shrinks and then expands, and the corresponding droplet diameter and transfer period vary. There are two primary modes of droplet transfer during the deposition process: free droplet transfer and bridging transfer. When the transfer process is in the bridging transfer mode, a smooth deposition wall is obtained. As the wire feeding speed increases, the transfer mode of the droplet gradually changes from the free transfer mode to the bridging transfer mode. The larger the distance between the wire tip and the surface of the base metal, the higher the wire feed speed required to achieve bridging transfer. There is a linear relationship between the droplet diameter and the cubic root of the wire feeding speed. Finally, the droplet transfer behavior is discussed using droplet force analysis.

To solve the lack of sidewalls penetration in gas metal arc welding (GMAW), a swing TIG-MIG hybrid welding method was proposed and applied in the narrow gap welding. The arc shapes and voltage changes in MIG, TIG-MIG hybrid welding and swing TIG-MIG hybrid welding were compared. The result reveals that the swing TIG-MIG hybrid welding can be used in narrow gap welding to attain good sidewall penetration. The assisted TIG arc can widen the MIG weld width and obtain good sidewall penetration, and stabilize the MIG welding voltage thereby improving welding quality. The melted welding wire in the MIG welding molten pool will spread to the TIG welding molten pool, which makes the weld width increased and the welding spread improved.

A shielded metal arc welding (SMAW) process was used to join the 12Cr2Mo1R heat resistant steel plates in a butt configuration with R407C welding electrode. The microstructure of weld metal was examined by using the optical microscope, the morphology of the cracking and the propagation zones of the impact fracture surface were observed by the scanning electron microscopy. The small island-like M-A phases were found on the ferrite matrix, which composed by martensite and retained austenite with irregular shapes. With the increase of phosphorus impurity, the brittleness of weld metal increased and the impact toughness was sensitive to phosphorus impurity. The phosphorus impurity in the R407C welding electrode can change the fracture morphology of the weld joint.

In order to study the phenomenon of the weld pool free surface evolution from partial to full penetration in gas tungsten arc welding (GTAW), the measurement method based on the lattice laser reflection on the weld pool surface was designed. Lattice lasers information and the concavity-convexity in the weld pool free surface were analyzed. Based on the volume of fluid method and the basic principle of fluid mechanics, temperature field and the flow field model which considered the free surface in a fully penetrated weld pool in GTAW were established. Fluid flow including the factor of buoyancy force, electromagnetic force and surface tension gradient was numerically analyzed for a fully penetrated weld pool in stationary GTAW. The result shows that: thermal expansion of metals is the main reason for the convex surface of weld pool at partial penetration. When fully penetrated, the concave surface of the lower surface is greater than that of the upper surface.

The gas tungsten arc welding (GTAW) arc and weld pool are theoretically and experimentally determined to be rotated or deflected with an extra magnetic field (EMF). The configurations of variational GTAW with respectively extra axial magnetic field (EAMF) and extra transverse magnetic field (ETMF) are studied for their gradually increasing usage rate in magnetic control welding fields. Taking advantage of mathematical methode, we present the calculated results of temperature fields, flow fields, pressure fields in GTAW and with EMF for comparison. Especially for the explanation to the different flow patterns in the weld pool between GTAW and with EMF, the shear stresses and temperature distributions on the anode top surface of them are highlighted. The results of heat flux and current flux on the cathode and anode surfaces are calculated to analyze the heat transfer conditions between the arc and electrodes. Otherwise the metal vapour behaviours are also discussed on account of their different distributions in the arc with EMFs: in the EAMF, the metal vapour in the arc generates like a fountain; in the ETMF, the metal vapour gathers to one side in the deflected section and its mass fraction reaches 1.15%, hence the impact on the arc cannot be neglected any more. The increasing mixture conductivity of metal vapour and shielding gas in the low temperature region makes the current path on the anode top surface in GTAW to expand when even applying a weak ETMF (B = 0.001T).

Heat transfer and fluid flow of arc plasma and weld pool in tungsten inert gas (TIG) welding and activated flux tungsten inert gas (A-TIG) welding of SUS 304 stainless steel are investigated comparatively though a 3D unified model. The model differs from the previous ones in that it considers the arc length more realistic for welding production. Tungsten electrode, anode (work piece) and arc plasma are all included. The effects of buoyance, plasma drag force, Lorentz force and Marangoni force on the weld pool flow are taken into account. By solving the conservation equations of mass, momentum, energy as well as Maxwell equations, the distributions of temperature and velocity of arc plasma and weld pool are obtained for TIG and A-TIG welding. The heat flux, current density and shear stress at the weld pool are presented. Dimensionless numbers are employed to compare the relative importance of the driven forces and that of convection and conduction in heat transfer of the weld pool. It is demonstrated that there is no significant difference in the heat flux at the weld pool, and total heat input to the anode and thermal efficiency is almost equal for TIG and A-TIG welding. The current density and the heat flux at the weld pool are more concentrated in more realistic welding condition. As a result, both of the temperature of the weld pool for TIG welding and A-TIG welding increases, while the latter is more significant. Marangoni force ranges from zero to 100 Pa and dominant the weld pool flow. Compared with the conventional TIG welding, the reversion of the Marangoni force results in inward flow and thus causes inward heat convection in weld pool of A-TIG welding. Heat convection was the main mechanism of heat transfer for SUS 304 stainless steel, which results in directly both shallow weld pool shape in TIG welding and remarkably increased weld pool depth and slightly constricted weld pool width in A-TIG welding.

In this study, the welding-brazing process of pulsed double electrode gas metal arc welding (pulsed DE-GMAW) provides a potential method to join dissimilar metals (i.e., joining of aluminum alloys to galvanized mild steel). In order to evaluate the stability of welding process, a mathematical model of the alternation of droplet transfer for the pulsed DE-GMAW is established based on the spring-mass-damper model. The droplet alternative transfer is a free flight with short circuiting transfer mode, which is analyzed and detected during the welding process with double pulsed current. Meanwhile, the pulsed DE-GMAW technology is found to be feasible to join the aluminum alloys to the galvanized mild steel. The variable weldability process of aluminum-galvanized steel could be obtained with a wire by optimizing welding parameters. Microstructures of the intermetallic reaction layer and bonding mechanism of optimized weld-brazed specimens with aluminum ER4043 and ER5356 wires are analyzed and conducted by SEM and tensile test.

By the method of arc-assisted laser brazing with preset filler powder, the dissimilar metals butt welding experiment between 5A06 aluminum alloy and galvanized steel was conducted. The intermetallic compounds (IMCs) thickness was observed by scanning electron microscope (SEM), the spreading width was measured by micrometer and the tensile strength (TS) was tested by the tensile test machine. The effects of laser power, arc current, welding speed and the distance of heat sources on TS were investigated. The results show that the IMCs thickness increases with the increase of laser power, arc current, welding speed and the decrease of the distance of two heat sources. The assisted arc can improve spreading width with a low heat input. The TS is not only related to the IMCs thickness, but also related to the spreading width, the TS can be enhanced by improving the spreading width of aluminum liquid on steel side based on the IMCs thickness is less than 10 μm. The solder joint with good mechanical property can be obtained, and it’s IMCs thickness can be controlled in the range of 10 μm by using the optimum laser power, arc current, welding speed and the distance of heat sources that is 1.2 kW, 15 A, 10 mm/s, 15 mm, respectively. The maximum TS of joint is up to 163 MPa and the IMCs thickness of which is 8.7 μm.

The surface modification of Ti6Al4V in biomedicine aims at the regeneration and healing of bones. It prolongs the service life, which is the basic understanding of friction and corrosion occurring at the biomaterial/human fluid interface. To modify the Ti6Al4V surface, CO2 was added to the shielding gas during the arc cladding process so that the strengthening phase TiOx and TiC were obtained in the cladding layers. A continuous cladding layer is obtained on the surface of Ti6Al4V without any pores and slag inclusions. After adding CO2 in the shielding gas, a large amount of TiOx and TiC are obtained in the cladding layers. As the amount of TiOx phase and TiC phase increases in the cladding layer, the microhardness gradually increases from 350HV to about 600HV. The effect of electrochemical corrosion of different cladding layers was studied in 3.5% NaCl solution using tafel polarization curves and electrochemical impedance spectroscopy(EIS). With the increase of the CO2 flow rates in the shielding gas, the value of Icorr gradually decreases from (5.12 ± 1.1) × 10−8 A/cm2 to (2.45 ± 0.5) × 10−8 A/cm2, and the pits on the corroded surface are gradually reduced, which indicates that the corrosion resistance of the cladding layers is gradually improved.

Nanoindentation analysis of FCC single crystal copper with different crystal orientations under Berkovich indenter was carried out by molecular dynamics simulation. The influence of crystal orientation on load distribution under Berkovich indenter was studied and compared with the experiment. Simultaneously, by establishing the relationship between the load–displacement curve and the instantaneous defect structure, the defect formation and slip processes under different crystal orientations were analyzed. Finally, the dislocation density of different orientations was calculated. Meantime, the relationship between the dislocation density and the hardness was explored. The results show that the 〈1 0 0〉 orientation shows a slightly different anisotropy difference, and the load value is lower than the 〈1 1 0〉 and 〈1 1 1〉 orientations. The 〈1 1 1〉 load value is slightly greater than 〈1 1 0〉 and the hardness values also show the same trend as the load value. The launch time of the initial dislocation loop of 〈1 0 0〉 orientation is earlier than 〈1 1 0〉, 〈1 1 1〉. The crystallographic orientation has a great influence on the change of dislocation morphology during the indentation process. With different orientations, the main plastic deformation is incomplete dislocation nucleation. Under different orientations, different forms of dislocation proliferation, such as quadruple, double and triple symmetry, and different stacking slip directions activated during indentation are observed. The 〈1 1 0〉 orientation has a relatively small dislocation density value, the dislocation density ρ0.5 is proportional to the hardness, and the coefficient values are different with different orientations.

Based on the IN783 alloy of as-received state, post-serviced state and thermal-cycled state, this paper studied the Ni5Al3 phases appearing in the NiAl phase of IN783 alloy by optical microscope, transmission electron microscope. The type and formation process of Ni5Al3 phase were analyzed. The dynamic evolution of the crack initiation and propagation on as-received state and post-serviced state was in-situ observed by SEM, and the microcrack characteristic was studied. It is found that Ni5Al3 phase is present in the NiAl of IN783 alloy under post-serviced state and thermal-cycled state. There are two ways to form the Ni5Al3 phase in IN783 alloy. The Ni5Al3 phase formed during long-term service is due to element diffusion. The Ni5Al3 phase formed during the thermal cycle is mainly the crystal transformation of the M-NiAl phase to the Ni5Al3 phase. The crack of alloy in as-received state sprouts from the stress concentration of the matrix and expands in the matrix. There is no crack in the NiAl phase. In post-serviced state, the crack of the alloy starts from the NiAl phase, and then the cracks expand and connect, causing the material to break. After serving the alloy, the tensile strength increase, and the elongation decreases. After service, the hardness of NiAl phase decreases and the hardness of matrix increases, which makes the difference in mechanical properties between the two increase.

Using tungsten inert gas welding, a simple technique to additively construct single-channel multilayer Ti alloy (Ti-6Al-4V) was developed. In the manufacturing process, the flow rate of nitrogen is used to control the microstructure and composition of each individual layer. The use of nitrogen leads to the formation of TiN particles, whose amount increases with the flow rate of nitrogen. There is no significant difference in the elastic moduli among individual layers. Increasing the flow rate of nitrogen results in an increase in the compression strength of the individual layers and a decrease in the ductility of individual layers. The Vickers hardness increases gradually from 300 to 400 HV for the base metal to ∼1000 HV for the top layer of the Ti alloy, and the compressive strength of the Ti alloy reaches 1.92 GPa at a 1.5 L/min nitrogen flow rate. The technique developed in this work provides a feasible route to additively construct single-channel multilayer structures with spatial distributions of the composition and microstructures.

The complex residual stress and distortion experienced in wire arc additive manufacturing (WAAM) can have a serious impact on production. In this paper, a series of ten-layer depositing walls were deposited by WAAM using the same depositing direction and reverse depositing direction to study the effect of different heat conditions on the residual stress and distortion of the deposition wall. The temperature field, distortion, and residual stress under different paths were obtained by performing experiments. Meanwhile, to calculate the variations in the temperature, stress, and distortion under different depositing paths, a model of wire arc additive manufacturing was established by using a numerical model. The measured distortion in the same depositing directions is 25 % larger than that in the reverse directions. The stress distribution in the reverse directions is more uniform than that in the same directions. By comparison with the results from an experimental and numerical analysis, the same depositing directions have a large temperature gradient and produce greater plastic distortion during solidification.

As an admirable surface improvement method, arc surface cladding has been widely used in various fields. The surface properties of titanium alloy were improved by gas tungsten arc cladding. In the process of arc claddings, a certain amount of nitrogen was added in the shielding gas to form the hard phase of TiN in the cladding layer. Titanium alloy surface was cladded with the same process parameters and different nitrogen flow rate. The effects of nitrogen flow rate on the microstructure and mechanical performance of the cladding layer were studied through an optical microscope, scanning electron microscope (SEM), X-ray diffraction (XRD), Vickers hardness and friction wear testing machine. The results show that the increase of the nitrogen flow rate not only changes the shape of the arc but also forms a large number of TiN hard phases in the cladding layer. With the increase of the nitrogen flow rate, the number of TiN hard phases in the cladding layer increases gradually, which improves the mechanical property of the cladding layer. The Vickers hardness of the cladding layer is much larger than 600 HV and the friction coefficient is 0.419 when the nitrogen rate is 2 L/min.

Based on a unified three dimension mathematical model developed in previous studies, arc plasma and weld pool in double electrodes tungsten inert gas welding are numerically investigated with emphasizes on electrode separation. The effects of small amounts of oxygen (4%) added to shielding gas on the weld pool dynamics are studied by neglecting its effect on the arc plasma reasonably. The distributions of current density, heat flux and shear stress at the anode are analyzed for various electrode separations. It is found that the electrode separation has a significant influence on the flow and temperature fields of arc plasma while has insignificant effect on the maximum temperature of it. With increase in the electrode separation, the distributions of current density, heat flux and temperature at the anode range from one peak profiles to two-peak profiles, while total heat input to the anode changes little. As the electrode separation increases, the extension of the weld pool alters from the direction vertical to the line through the two electrodes to that parallel to the line. The constriction of the weld pool width and increase of the weld pool depth are induced by the reversed heat convection in the weld pool due to small amounts addition of the oxygen. With a certain electrode separation, there exist two peak temperatures at the anode and local inward flow in the weld pool with argon shielding, while local outward flow appears with oxygen addition.

The interfacial microstructures of aluminum and galvanized steel dissimilar joint formed by pulsed double electrode gas metal arc (Pulsed DE-GMA) welding–brazing were characterized. Electron probe microanalyzer (EPMA) analysis revealed that the intermetallic compound layer of the welding–brazing joint consisted of Fe2Al5 and FeAl3. Comprehensive analysis of the effect of the heat input parameters showed that, at a constant total welding current (Itotal), the thickness of intermetallic compound at the interface of aluminum and steel decreased with the increase of bypass current. Thermodynamic calculations were carried out to derive the Gibbs free energy diagram for Fe2Al5 and FeAl3. These calculations presented that Fe2Al5 firstly formed, subsequently FeAl3 precipitated during welding process. Further model of the Fe2Al5 and FeAl3 intermetallic compounds formation process was proposed.

A double-variable decoupling control scheme was proposed for GMAW-P process of aluminum helping to efficiently develop welding procedure. Weld pool width and arc length were both measured through vision sensing in welding process. Weld bead shape was improved by changing the current waveforms to adjust the heat input while the arc length was controlled to stabilize the welding process. An experimental system was developed to sense, observe and control the welding process real-timely. Experiments were conducted to verify the effectiveness of the scheme. The results show that good weld bead shape and stable welding process can be obtained through the double-variable decoupling control scheme without complex metal transfer control and considerable trial and error to identify suitable combinations of welding parameters in GMAW-P. This control scheme provides an alternative to obtain proper weld quality for GMAW-P.

The motion of twin boundaries in Ni–Mn–Ga ferromagnetic shape memory alloy (FSMA) particles embedded in a polymer matrix has been proposed as an effective mechanism for the dissipation of vibration energy. Indirect evidence of the motion of these boundaries through vibrating sample magnetometer measurements on FSMA/polyurethane matrix composite is shown.