International Journal of Modern Physics B

We have modified the mineral oil used in transformers by dispersing 1-wt.% metal oxide nanostructures (commercially available ${\mathrm{\text{TiO}}}_2$, ZnO and ${\mathrm{\text{Fe}}}_3{\mathrm{\text{O}}}_4$ spherical structures and ZnO rod-shaped structures synthesized by arc discharge) into the oil through ball milling without surfactant. A good dispersion that lasted for at least 24 h was obtained for all nanofluids, however sedimentation was discovered by 72 h after ball milling. All nanofluids with different nanostructures exhibited enhanced thermal conductivity compared with the raw transformer oil. The nanofluid with ZnO nanoparticles showed better thermal conductivity than the nanofluids with ${\mathrm{\text{TiO}}}_2$ and ${\mathrm{\text{Fe}}}_3{\mathrm{\text{O}}}_4$ nanoparticles. The nanofluid with elongated ZnO nanoparticles (nanorods) synthesized by arc discharge showed the best thermal conduction among all the nanofluids studied in this work over the whole measurement period. The enhanced thermal conductivity of the nanofluid with elongated nanostructure is considered to be due to the rod-shaped nanostructure creating heat flow paths with lower thermal resistance. The arc discharge provides a cost-effective and scalable method to fabricate metal oxide nanostructures for potential nanofluid applications.

${\mathrm{\text{NiO/TiO}}}_2$ sub-microrods have been synthesized via a simple two-step route. First, the precursors were prepared by a facile ethylene glycol-mediated method; then, ${\mathrm{\text{NiO/TiO}}}_2$ sub-microrods were obtained by a limited-oxygen atmosphere deriving from the decomposition of urea at $450^{\circ }$C for 3 h in air. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The obtained ${\mathrm{\text{NiO/TiO}}}_2$ sub-microrods exhibit cubic NiO structure with high crystallinity and anatase ${\mathrm{\text{TiO}}}_2$. Both SEM and TEM show the typical sub-microrods with lengths of $\sim 380$ nm and diameters of $\sim 180$ nm. The uniform sub-microrods have great electrocatalytic performance for methanol oxidation reaction in alkaline solution. This material may have potential applications in direct methanol fuel cells.

${\mathrm{\text{SnO}}}_2$ porous nanotubes containing oxygen vacancies were prepared by electron spinning and H plasma treatment. The morphology and crystal structure of the samples were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The ethanol-sensing properties of the ${\mathrm{\text{SnO}}}_2$ sensor were tested. The results show that the samples treated with H plasma for 20 min have the best performance. Its working temperature is $230^{\circ }$C lower than $290^{\circ }$C of the original sample, with a sensitivity of 17 at 100 ppm, which is seven times higher than the original sample. It also shows good selectivity to some common interfering gases. This enhancement can be ascribed to the introduced oxygen vacancy. This work provides an efficient way to design high-performance gas sensor materials.

Ultrafine silicon oxycarbide (SiOC) fiber mats were prepared through a sol–gel method combined electrospinning technique. The influence of sol–gel solution viscosity on its spinnability has been studied. By partially removing solvents after the sol–gel preparation, the solution could be stably spun and resulted in fiber mats with an average fiber diameter of 560 nm. The formation, morphology and composition of the SiOC fiber mats have been studied by TGA, FT-IR, SEM, XPS and XRD. Due to flexibility and free-standing property, the SiOC fiber mats will have a wide range of applications.

Dried plum-like ZnO assemblies consisting ZnO nanoparticles were synthesized by an ultrasonic spray pyrolysis method (USP). ZnO assemblies were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS) and field-emission transmission electron microscopy (TEM). The results show the size of ZnO assemblies is in the range of 300–870 nm, and that of ZnO nanoparticles is from 33 nm to 39 nm. The microstructure and size of ZnO assemblies were successfully controlled by the concentration of the precursor solution.

To enhance the ionic conductivity of lithium garnets, a co-doping strategy was adopted with both strontium and zirconium for ${\mathrm{\text{Li}}}_{6+y}{\mathrm{\text{La}}}_{3-y}{\mathrm{\text{Sr}}}_y{\mathrm{\text{NbZrO}}}_{12}$ ($y=0$, 0.25, 0.5, 0.75 and 1.0) (LLSNZO). By increasing the content of Sr, lithium garnet ceramics maintain cubic structure when $y$ is in the range of 0–0.75. A secondary phase of ${\mathrm{\text{SrZrO}}}_3$ appeared in the ceramic when $y=1.0$. We also studied the cross-section of lithium garnets with silver electrode. Results showed that the density of LLSNZO ceramics increased continuously against the increase of Sr content, while their total ionic conductivity enhanced initially and then reduced, with the maximum reached when $y=0.5$. It is indicated that ionic conductivity of lithium garnets is not only decided by the density but also decided by the concentration and the mobility of ${\mathrm{\text{Li}}}^{+}$.

We present the design of a high-performance 2 V asymmetric supercapacitor made of graphene-based hybrid nanocomposites in 1 M KOH electrolyte. rGO-CNT-FeOOH (GC-F) was used as the cathode and rGO-CNC-MnO₂ (GC-M) as the anode. Both composites well balanced each other in the asymmetric device and gave a high electrochemical performance. The energy density of this ASC is 66.6 W h kg${}^{-1}$ at 3.8 kW kg${}^{-1}$ power density with an excellent capacitance retention of 88% after 3000 galvanostatic charge-discharge cycles.

The chemical plating methods were used to prepare nanoshell Si/Cu composites. The methods delivered a high initial discharge and charge capacity of 1312.1 and 1008.8 mAh/g, respectively. The electrochemical properties of the composites retained about 662.6 mAh/g after 100 cycles. The Cu coating improved the electrical conductivity but hindered the direct contact of the Si particles and the electrolyte, which suppressed the SEI growth.

In this work, Ag nanoparticles were deposited in the TiO${}_{2-X}$ nanotube films through magnetron sputtering to form Ag-TiO${}_{2-X}$ nanocomposite. Scanning electron microscopy (SEM) was used to study microstructure and surface morphology. Rhodamine B (RhB) was deposited on the surface of Ag-TiO${}_{2-X}$ substrate for Raman spectroscopy test. The size of Ag nanoparticles can be controlled by changing the magnetron sputtering time. The result indicated that sputtering for 30 s obtained the highest Raman enhancement.

The semiconducting thin film solar cell based on Cu₂ZnSnS₄ (CZTS) materials is considered as a promising candidate for very large-scale application due to high absorption coefficient and low cost. In this study, the performances of n-ZnO/n-CdS/p-CZTS solar cells were numerically simulated using the AFORS-HET software. The influences of double-graded bandgap and thickness of CZTS layer on the performances of the solar cell were investigated. The calculated results show that double-graded bandgap structure can greatly optimize the conversion efficiency of CZTS thin film solar cell. The optimal dual gradient structure is 1.4 eV-1.3 eV-1.5 eV, the optimal thickness ratio is 11:1, and the conversion efficiency could be 26.63%. The results of this study can serve as a guide in fabricating CZTS solar cell.

Silicon, an anode material for lithium ion batteries, has the highest theoretical specific capacity ($\sim 4200$ mAh/g). The actual lithium storage capacity of $\sim 3579$ mAh/g is about 10 times that of the graphite anode materials class. This study involves magnesium heat reduction of the SiO₂ preparation of silicon carbon composites. The Si/SiC composite shows a high initial specific capacity of 1406.7 mAh/g with a current density of 0.1 A/g. The morphology and pore size inherited from the SiO₂ aerogel counteracts the volume expansion during the lithiation/delithiation process. This paper provides an articulate methodology for designing silicon anode material for high-performance rechargeable lithium-ion batteries.

In this work, we reported a Chevrel phase ${\mathrm{\text{Mo}}}_6{\mathrm{\text{S}}}_8$, which was synthesized by a molten salt approach, and its electrochemical performance as a cathode material for rechargeable magnesium batteries. The phase composition and micromorphology of the product were measured and analyzed by X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The Chevrel phase sulfide delivered an excellent specific capacity of 91 mAh g${}^{-1}$ at a current density of 0.2 C after 70 cycles. Its excellent reversible capacity, rate performance and cycle stability demonstrate the feasibility of the Chevrel phase ${\mathrm{\text{Mo}}}_6{\mathrm{\text{S}}}_8$ materials for future rechargeable magnesium batteries.

Metal mining wastes have caused severe environmental pollution. Bisphenol A (BPA) is a typical pollutant that comes from flotation reagent. This work studied the efficiency of direct photodegradation of BPA under multi-wavelength medium-pressure ultraviolet light (MP-UV). The effects of photo-exposure time, initial pH, BPA concentration, and existence of anions, cations, ${\mathrm{\text{H}}}_2{\mathrm{\text{O}}}_2$ and ${\mathrm{\text{Na}}}_2{\mathrm{\text{S}}}_2{\mathrm{\text{O}}}_8$ on the BPA degradation behavior were studied. The results showed that MP-UV could effectively degrade BPA. The reaction follows the apparent first-order kinetic model, with a mineralization rate of 27.6% and accumulation of acidic intermediates. The degradation rate decreases with increasing initial concentration but the total amount of degraded BPA increased. With increasing pH, the degradation rate increases, which is related to the morphology of BPA. The promotion degree of BPA photodegradation follows the order of $\mathrm{\text{Fe}}\mathrm{\text{(III)}}>\mathrm{\text{Sb}}\mathrm{\text{(III)}}>{\mathrm{\text{NO}}}_3^{-}>{\mathrm{\text{SO}}}_4^{2-}>\mathrm{\text{Pb}}\mathrm{\text{(II)}}>{\mathrm{\text{Cl}}}^{-}$, while the inhibition degree follows the order of $\mathrm{\text{Cu}}\mathrm{\text{(II)}}>\mathrm{\text{Cd}}\mathrm{\text{(II)}}$. Furthermore, the half-life of ${\mathrm{\text{MP-UV/H}}}_2{\mathrm{\text{O}}}_2$ system was 11.55 min; and $\cdot \mathrm{\text{OH}}$ is the main oxidative active substance in the system. The half-life of ${\mathrm{\text{MP-UV/Na}}}_2{\mathrm{\text{S}}}_2{\mathrm{\text{O}}}_8$ system was 12.65 min; and ${\mathrm{\text{SO}}}_4^{-}\cdot$ is the main oxidative active substance in the system.

Novel red light-emitting ${\mathrm{\text{Li}}}_2{\mathrm{\text{MgSiO}}}_4\mathrm{\text{:}}x{\mathrm{\text{Eu}}}^{3+}$ ($x=0.005$–$0.05$) phosphors were prepared by solid state reaction. The crystal phase structure and powder morphology were measured by X-ray powder diffraction (XRD) and scanning electron microscope (SEM), respectively. The photoluminescence (PL) properties were investigated. The excitation spectrum shows a wide coverage in the UV-Vis region, and the ${}^5{\mathrm{\text{D}}}_0{\to }^7{\mathrm{\text{F}}}_2$ transition with the maximum peak of 613 nm governs the emission spectrum. The lifetime of ${\mathrm{\text{Li}}}_2{\mathrm{\text{MgSiO}}}_4\mathrm{\text{:}}x{\mathrm{\text{Eu}}}^{3+}$ ($x=0.005$–$0.05$) phosphor is temperature-independent as well as the ${\mathrm{\text{Eu}}}^{3+}$ doping content because of the existence of defect. In ${\mathrm{\text{Li}}}_2{\mathrm{\text{MgSiO}}}_4$ lattice, the Eu${}^{3+}$ ions substitute for the ${\mathrm{\text{Li}}}^{+}$ ions, and the charge compensation mechanism could be ascribed to the dipole complex (${{\mathrm{\text{Eu}}}_{\mathrm{\text{Li}}}}^{\cdot \cdot }-2{{\mathrm{\text{V}}}_{\mathrm{\text{Li}}}}^{\prime }$) combined by ${\mathrm{\text{Li}}}^{+}$ vacancy (${{\mathrm{\text{V}}}_{\mathrm{\text{Li}}}}^{\prime }$) and positive charge (${{\mathrm{\text{Eu}}}_{\mathrm{\text{Li}}}}^{\cdot \cdot }$).

The development of photocatalysts with low cost, high reactivity and easy recovery provides great potentials for environmental remediation. In this study, polyacrylonitrile (PAN) nanofibers containing titanium dioxide (${\mathrm{\text{TiO}}}_2$) nanoparticles were successfully fabricated using a facile electrospinning technique. The effects of ${\mathrm{\text{TiO}}}_2$ content, PAN concentration and thermal treatment on the adsorption and photocatalysis properties of ${\mathrm{\text{PAN/TiO}}}_2$ nanofibers have been investigated. The results indicate that the embedded ${\mathrm{\text{TiO}}}_2$ nanofibers possess the property to effectively decompose rhodamine B (RhB) under simulated sunlight irradiation. The enhanced photocatalytic activity can be attributed to the loading of ${\mathrm{\text{TiO}}}_2$ nanoparticles and the property of polymer matrix.

Structurally colored stainless steel (SS) surfaces were produced by using femtosecond laser at normal incidence at ambient conditions. The influence of laser polarization on the surface properties was investigated. The surface morphologies, roughness and color of the laser-treated surface were characterized by using environmental scanning electron microscope (ESEM), roughmeter and atomic force microscope (AFM). Results indicated that the circular polarization leads to more random structures than the horizontally linear polarization. Specimen with the highest surface roughness shows the brightest color. Different colors are cyclically exhibited by changing view angles due to different orders of diffraction. This investigation developed the technique of using femtosecond laser in situ preparation of periodic structures on 304 SS, and indicating that laser polarization is an important parameter to control surface structures to achieve different colors.

Cleanliness control is one of the most important processes for final optics assembly (FOA) in high-power laser systems. In this paper, an “Ultra Clean Manufacturing (UCM)” concept is put forward for the first time to satisfy the cleanliness requirements for FOA. First, the challenges and requirements for cleanliness in FOA are introduced and the concept of UCM is proposed. Significant surface cleaning technologies for mechanical parts and optics are then expounded. Finally, surface cleanliness control techniques, such as “gas knife” and “laser cleaning”, are developed as online cleaning methods for the surface cleanliness in FOA.

There has been a steadily increasing demand for magnetic materials in devices and charging systems over recent decades. The advent of in-road inductive power transfer (IPT) charging systems in the near future will massively increase the demand. Better, nonbrittle and affordable magnetic materials are required so that vehicles can run over charging pads built into the road without destroying them. This will require innovative solutions and new magnetic material sources to meet these needs in an economically viable way. Here, we have scoped New Zealand’s (NZ) natural magnetic materials and their ability to be included as a viable magnetic material for our roads. We have investigated the magnetic permeabilities of NZ natural magnetic mineral deposits for IPT application in roads.

The ${\mathrm{\text{Cu}}}_2{\mathrm{\text{ZnSnS}}}_4$ (CZTS) thin film is a photovoltaics material with excellent photoelectric properties and has good potential applications. The CZTS thin films with different spin-coated layers and sulfurized temperatures were successfully prepared by a sol–gel spin-coating technique. The relationships of microstructure, surface morphology and processing parameters were studied using XRD, SEM and EDS. The results indicate that the grain size of the sample sulfurized at $600^{\circ }$C was larger than that of the sample sulfurized at $550^{\circ }$C. With increasing layers of spin, coatings, the films showed better crystalline structure. The sulfureted CZTS thin films prepared by six spin-coating possess uniform elemental distribution.

${\mathrm{\text{ZnO/Zn}}}_{1-x}{\mathrm{\text{Mg}}}_x$O asymmetric quantum barriers on JGS1 quartz glass and ${\mathrm{\text{Al}}}_2{\mathrm{\text{O}}}_3$ substrates were prepared by a pulsed laser deposition (PLD) technique. Microstructure characterization confirmed the designed structure. Because of the design of ${\mathrm{\text{ZnO/Zn}}}_{1-x}{\mathrm{\text{Mg}}}_x\mathrm{\text{O}}$ asymmetric quantum barrier, representative exciton peaks were observed in the optical absorption spectrum at room-temperature. This confirmed that the designed ${\mathrm{\text{ZnO/Zn}}}_{1-x}{\mathrm{\text{Mg}}}_x\mathrm{\text{O}}$ asymmetric quantum barrier structure realized the quantum-binding effect at room-temperature. Moreover, when $x=0.15$, the asymmetric quantum barrier structure had optimum performance compared with other $x$ values.

MoS₂ self-lubricating films were prepared on long-range ordered porous anodic alumina (PAA) by an electrophoretic deposition (EPD) method. The PAA was prepared by two-step anodization of aluminum plates. Oxalic-acid-based electrolytes were used in the first step and phosphoric-acid-based electrolytes were used in the second step. This process offers a new approach to preparing PAA with wide adjustable boundary distances (43.5–21 nm) by increasing the voltage from 80 V to 100 V. The boundary distances were decreased from 78 nm to 42.2 nm by increasing the solution concentration, which increased the interpore distance. The coefficient of friction and hard-wearing of the MoS₂ lubrication film on the PAA were studied by a ball-on-disk friction and wear tester. The results showed that the nanotubes stored MoS₂ particles, which provided continuous lubrication.

Porous electrodes in microfluidic fuel cell (MFC) operate with nonuniform reaction rate. It is intriguing to improve the utilization degree of the porous electrodes. In this work, a three-dimensional computational model is developed for MFC with flow-through porous electrodes. Characteristics of the reaction rate distributions under different electrode geometries are examined. The results show that reaction rate varies noticeably along the electrode width direction, but minimally along the electrode length direction. High reaction rate region locates in the vicinity of the interface between the porous electrode and the middle channel. A relatively high aspect ratio, defined as the ratio of the electrode length to width, is beneficial to improve the utilization degree of the porous electrodes. Yet, concentration losses increase due to the decreased fluid velocity. Considering the cell performance, optimal electrode aspect ratios are derived for the anode and cathode, respectively.

The key to battery management systems (BMS) is an accurate and real-time prediction on State of Charge (SOC) of the power battery. The methods of estimating SOC of power battery were analyzed. The gray neural network model was introduced into the field of SOC estimation. The model is used to establish the relationship of SOC, discharge current and rebound voltage. The model can be used to estimate SOC of battery on line by detecting the values of rebound voltage and discharge current during the discharge process. The model of SOC estimation is proved feasible by comparing the experimental data with calculated data.

Titanium dioxide (${\mathrm{\text{TiO}}}_2$) is a kind of wide bandgap transparent metal oxide semiconductor and has shown great potential applications in photocatalysis, gas sensors and biomedical fields due to its superior properties, such as nontoxic, high photocatalytic efficiency and physicochemical stability. In this work, one-dimensional ${\mathrm{\text{TiO}}}_2$ nanostructure was successfully synthesized by hydrothermal method. The morphology and crystalline quality of ${\mathrm{\text{TiO}}}_2$ were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The results demonstrate that the structure of ${\mathrm{\text{TiO}}}_2$ evolved from “flower-like” structure to nanowire with the acid concentration increment. The sintering temperature has an important effect on the structure and crystalline quality of ${\mathrm{\text{TiO}}}_2$. The crystalline quality of ${\mathrm{\text{TiO}}}_2$ nanobelt was improved with the annealing temperature increment. When the sintering temperature increased to 1000${}^{\circ }$C, the phase of ${\mathrm{\text{TiO}}}_2$ would transfer from anatase to rutile.

Surface modification has been used as a method to create defects on ${\mathrm{\text{TiO}}}_2$ materials, which can improve their desirable properties. In this paper, defected ${\mathrm{\text{TiO}}}_2$ nano-powder was successfully synthesized by chemical reduction using ${\mathrm{\text{NaBH}}}_4$ as the reducing agent at 300–400${}^{\circ }\mathrm{\text{C}}$ under argon atmosphere. High defect concentration can be produced by increasing process temperature. The modified ${\mathrm{\text{TiO}}}_2$ shows good visible light absorption and photocatalytic activity on degradation of Rhodamine B (4–9 times higher than the pristine ${\mathrm{\text{TiO}}}_2$) with the visible light irradiation. Further XPS analysis and theoretical studies using full potential linearized augmented plane wave (FP-LAPW) method as implemented in wien2k code revealed the existence of oxygen vacancy and ${\mathrm{\text{Ti}}}^{3+}$ in the modified samples. These types of defects were responsible for the modifications of the electronic and optical properties of ${\mathrm{\text{TiO}}}_2$, resulting in the improved photocatalytic activity in visible light irradiation.

The blended elemental (BE) route is currently the main way for obtaining cost-affordable titanium alloys. Via post-consolidation processes like hot isostatic pressing (HIP) or thermomechanical processing, the material can improve its mechanical properties. In this work, a titanium alloy is processed via the BE approach, combined with thermomechanical processing of the sintered billets and subsequently heat treated. The tensile behavior of the sintered, extruded and heat-treated Ti-6Al-4V alloy was studied, finding an overall improvement of the properties after extrusion and a considerable increase in strength without compromising ductility after heat treatment. The high cycle fatigue behavior of the as-extruded alloy was studied by means of axial testing. There is a strong dependence between the location of the initiation of failure of the alloy and its fatigue life, but the defects that initiated failure were facets, not pores. The fatigue life of the as-extruded alloy is comparable to that of other fully-dense powder metallurgy (PM) and wrought Ti-6Al-4V alloys. These findings encourage the use of this route of processing as a balanced approach between low-cost and high-performance titanium alloys.

The hot deformation behavior of powder metallurgy Ti-5Al-5V-5Mo-3Cr (Ti-5553) alloy was investigated by isothermal compression test at the wide temperature range of $700$–$1150^{\circ }$C, under an intermediate strain rate of 0.1 s${}^{-1}$, and with the sample deformation degree of 30%, 50% and 70%. Results suggested that the flow stress was very sensitive to the deformation variables and it decreased with increasing the deformation temperature. Flow localization occurred when the temperature was lower than $800^{\circ }$C, accompanied by the dynamic morphology changing of $\alpha$ phase. Dynamic recovery (DRV) features appeared when the temperature was over $850^{\circ }$C, while dynamic recrystallization (DRX) took a more important role than DRV for the alloy compressed at $900$–$1000^{\circ }$C.

Titanium alloys have poor wear performance, with severe adhesive wear and three-body abrasion being dominant mechanisms. To extend the use of titanium to applications demanding better wear properties, modifications can be made to the alloys. This can include the addition of hard particulates or interstitial strengthening, by increasing the oxygen or nitrogen content. The metal additive manufacturing process of selective laser melting (SLM) has been shown to enable manufacture of these modified titanium alloys in situ. In this study, small amounts of boron and titanium dioxide powders were added to Ti-6Al-4V (Ti64) and processed using SLM. To compare wear performance of these modified materials, reciprocating pin on plate tests in brine solution were performed. Increased oxygen content increased the hardness of the material, which reduced wear. The presence of boron increased wear in the short term but reduced the long-term wear rate. Incorporating of oxygen and boron has been shown to improve the saline solution wear properties of Ti64 against silicon nitride.

The self-made high chromium content flux-cored wire was used to surfacing low carbon steel under self-protection. The effect of Ti contents on the microstructure, hardness and wear resistance of surfacing layer was investigated. The results showed that the surfacing layer was mainly composed of martensite, ${\mathrm{\text{M}}}_7{\mathrm{\text{C}}}_3$ carbide and residual austenite. As Ti content in surfacing layer increased, the shape of carbides in surfacing layer varied from lath to granular and the amount of carbides was gradually increased. The hardness of the surfacing layer was slightly increased while the wear resistance was significantly enhanced. The improved wear property could be ascribed to the increasing Ti content and the corresponding increasing amount of Ti (C, N). Ti (C, N) takes the role of heterogenous nucleation particles in the surfacing layer and promotes the formation of fine-grained hard phase (e.g., ${\mathrm{\text{M}}}_7{\mathrm{\text{C}}}_3$ carbide). With the increase of the density of fine-grained hard phase in the surfacing layer, the resistance of cutting motion during abrasive wear test also increased, resulting in a decreased wear loss and significantly enhanced wear performance.

Laser surface quenching technology was used to modify the surface microstructure of as-cast Ni-Al bronze (NAB). The modified microstructure was studied by scanning electron microscopy (SEM), and the effect of laser process parameters on microstructure evolution was investigated. It was found that a fine-grained zone with fully $\beta$ phase microstructure formed on the surface of NAB. The depth of the fine-grained zone increased with the increase of laser power, and surface melting occurred when the power reached a threshold value. Laser scanning at a low rate caused the coarsening of grain boundary, while too high rate led to incomplete quenching. Spot overlap ratio determined the microstructure of the superimposed area, and unsuitable ratio would cause bulky $\kappa$ precipitation at the grain boundary or incomplete transformation from $\alpha$ phase to $\beta$ phase.

This work focuses on developing near-alpha Ti alloys via the selective addition of small concentrations of low-cost eutectoid $\beta$-stabilizers like Cu and Mn. In particular, these newly designed near-alpha Ti alloys are manufactured via the cheapest powder metallurgy route of cold pressing plus sintering. Moreover, thermomechanical deformation of the sintered alloys via hot forging in the $\alpha +\beta$ and $\beta$ field was also investigated aiming to enhance the mechanical properties through reduction of the residual porosity and microstructural control. It is found that the initial addition of a small amount of eutectoid $\beta$-stabilizers leads to higher tensile properties with comprision to pure Ti produced by powder metallurgy, and this is due to the formation of a coarse lamellar structure due to the presence of $\beta$-stabilizers. Further enhancement of the strength is achieved by means of hot thermomechanical processing thanks to sealing of the residual pores, texturing, and refinement of the microstructural features.

A powder metallurgy approach was applied for the synthesis of an $\alpha +\beta$ Ti-2Al-3Fe alloy. Blends of the elemental Ti, Al and Fe powders were compacted and subsequently sintered. High-frequency induction heating (HFIH) instead of conventional high-vacuum furnace heating was used for the sintering, due to its high efficiency. The effect of temperature on the level of densification, residual porosity and mechanical properties was studied. Electron dispersive spectrum analysis was used to study the dissolution and homogenization of the alloying elements. The results showed that a short induction sintering (IS) cycle in the range of 10–15 min is sufficient to achieve significant powder consolidation, evident by the increase of the density and mechanical properties. The residual porosity diminishes with the increase of the sintering temperature. Full dissolution of the alloying powders is completed after sintering at temperatures above those of $\alpha$- to $\beta$-phase transformation.

SUS301L-MT (MT-middle tensile) stainless steel is widely used in metro structures due to its excellent mechanical properties and corrosion resistance. However, since steel is metastable, hydrogen-sensitive deformed martensite may easily form during cold rolling, which affects the hydrogen embrittlement behavior of the steel. In this paper, tensile tests were carried out after electrochemical hydrogen charging. Fracture morphology and microstructure analysis were conducted to investigate the hydrogen embrittlement behavior. The results showed that as charging current density increased, the strength and elongation loss got greater. The most deteriorated sample had strength loss of 7.11% and the elongation loss reached 25.94%. The fracture of charged sample showed three regions including tough zone, transition zone (TZ) and brittle fracture zone (BFZ). The side surface was covered with microcracks, as a result of the dissolved hydrogen atoms accumulated in the stress concentration regions on the surface of the sample, forming local high pressure and promoting plastic deformation. Martensite was sensitive to hydrogen, which weakened the atomic bonding force. Hydrogen embrittlement caused the surface of the SUS301L-MT stainless steel to become brittle and finally brittle fracture occurred.

Ti-6Al-4V alloy is widely used for the deep-sea manned submersible. In addition to the normal cyclic loading, the manned cabin will experience a period of dwell time in each cycle during their service life. In this research, the fatigue and dwell-fatigue crack growth behavior of Ti-6Al-4V alloy under different dwell time were studied experimentally. The mechanism of dwell-fatigue crack growth was investigated. The acceleration phenomenon of the dwell-fatigue crack growth can be directly observed in the experiment. The relationship between the crack length and the dwell time was captured under different $\mathrm{\Delta }K$ within one cycle. The results presented that there is a saturation time for the dwell-fatigue crack growth. A prediction model is proposed to predict the dwell-fatigue crack growth behavior considering the effects of dwell time.

Fe and Fe-based alloys are great candidates for biodegradable metal implants. In order to achieve high density pure Fe and Fe-35Mn structures, the correct implementation of process strategies and parameters needs to be studied to achieve high density parts. In this study, pure Fe and Fe-35Mn were successfully processed via SLM with a relative density over 99.5%. The lower melting temperature of Fe-35Mn introduced porosity, resulting in a lower processability compared to the pure Fe. In terms of process optimization, most of the typical quality indicators (roughness, density and apparent density) could be correlated to the energy density.

The influence of rolling on nanomechanical and mechanical behavior of Mg-7Li alloy was investigated by nanoindentation, tensile test and scanning electron microscopy (SEM), respectively. The $\alpha$-Mg phase elongated along the rolling direction and gradually cracked. As the rolling ratio increased from 3 to 10, the hardness of $\alpha$-Mg and $\beta$-Li phase increased by 7.35% and 20.75%, respectively. The fracture of alloys changed from ductile fracture to quasi-cleavage fracture. The yield strength and ultimate tensile strength increased by 23 MPa and 12 MPa, respectively, while elongation reduced by 12.5%.

This work deals with the consolidation of a TiAl alloy powder by spark plasma sintering (SPS). Pre-alloyed powder with a composition of Ti–48Al–2Cr–2Nb (at.%) was consolidated in a SPS furnace at temperatures between 1200${}^{\circ }$C and 1325${}^{\circ }$C and with a pressure of 50 MPa. The microstructures obtained after SPS depend on the sintering temperature. Tensile tests at room temperature were performed. The alloy SPSed at temperatures not less than 1250${}^{\circ }$C exhibits good properties at room temperature.

Drawing deformation behaviors of AISI 1070 steel in conventional lubrication and electrochemical environments were compared. The anodic polarization in the electrochemical drawing not only decreases much the deformation resistance but also eliminates the work hardening. This can only be attributed to the reaction on the surface of the wire before it passes through the die. This chemomechanical effect, which is governed by surface dissolution rate, facilitates dislocation slip and permits a much smooth high speed drawing. It was a promising technology for the forming of brittle hard metal materials.

A series of ${\mathrm{\text{TiO}}}_2$-modified Cu coatings were developed via a sol-enhanced electrodeposition process. The effect of ${\mathrm{\text{TiO}}}_2$ sol on the properties of fabricated ${\mathrm{\text{Cu–TiO}}}_2$ nanocomposites is studied. Phase composition and microstructures of ${\mathrm{\text{Cu–TiO}}}_2$ deposits were characterized using X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). Mechanical properties of the fabricated ${\mathrm{\text{Cu–TiO}}}_2$ coatings were also examined. The proper addition of ${\mathrm{\text{TiO}}}_2$ sol gives rise to refined coating surface with well-distributed ${\mathrm{\text{TiO}}}_2$ nanoparticles, leading to significantly enhanced properties. The microhardness and wear resistance of the ${\mathrm{\text{Cu–TiO}}}_2$ nanocomposite coating (12 mL/L ${\mathrm{\text{TiO}}}_2$ sol) upsurges owing to the strengthening effect of highly dispersed ${\mathrm{\text{TiO}}}_2$ nanoparticles. We also suggest that the excessive addition of ${\mathrm{\text{TiO}}}_2$ sol should be avoided as it will result in an inferior coating quality with a loose structure for the prepared ${\mathrm{\text{Cu–TiO}}}_2$ deposits.

This study applied the pulse electrodeposition and duplex electrodeposition techniques to improve the mechanical properties of Cu–Sn–Zn–TiO₂ nanocomposite coatings. The phase constituents and surface morphologies of prepared coatings were characterized. The cross-sectional information was recorded. The mechanical properties were determined by microhardness and wear tests. All the prepared coatings presented a nodular surface. Both the addition of TiO₂ particles and nickel inner layer refined the coating surface. The pulse electrodeposition led to increased microhardness, while the addition of nickel inner layer further increased the mechanical performance. The best mechanical performance was achieved for the duplex Cu–Sn–Zn–TiO₂/Ni nanocomposite coating prepared via pulse electrodeposition.

Microcontact printing ($\mu$CP) is a type of soft-lithography technique, which is widely used for patterning self-assembled monolayers (SAMs). It is a convenient method to form SAMs of bio/chemical ink onto different surfaces such as polymers, palladium, silver and gold. A wide range of applications of this technology includes micromachining, patterning proteins, cells or DNA in biosensors. However, the application primarily depends on the type of the ink used. Here, we present an experimental study that provides information about the parameters that affect the $\mu$CP process. Two different thiol inks (dithiothreitol (DTT) and glutathione (GSH)) have been used for obtaining SAMs on gold-coated substrates. Our findings suggest that transferring the alkanethiols over the gold surface is extremely dependent upon the molecular weight of thiol compound, concentration of the thiol solution and pH value of the buffer used. Furthermore, higher the molecular weight, concentration and pH value of the ink, lower is the time required for the process of $\mu$CP.

Nanostructured WC-17Co, 2C-12Co coatings and conventional WC-17Co coating were prepared by High Velocity Oxygen Flame (HVOF) spray technique. The elastic modulus, fracture toughness and crack spread path were studied. The residual stress, different phases, microstructure from surface to the depth of coatings were also analyzed. While the nanostructured WC-12Co coating showed the highest elastic modulus, the nanostructured WC-17Co coating has the highest fracture toughness. The compressive residual stress of the nanostructured coatings was higher than the conventional coating. Both WC and W₂C phases showed compressive residual stress, but Co₆W₆C phase showed tensile stress. The distribution of residual stress showed that the stress is the lowest at the surface and the highest close to the interface.

In order to obtain a laser-cladded coating with no cracking and good corrosion resistance, this paper investigated laser cladding of a mixture of 17-4PH stainless steel and Ni60 powders on ASTM 1045 steel substrate. The surface cracking, mechanical properties and corrosion resistance of the coatings were assessed by various characterization methods. The experimental results demonstrated that a crack-free coating can be obtained by adding 30% (or above) 17-4PH stainless steel into Ni60 alloy. The mechanical properties of the coatings were determined by adding 17-4PH, but stabilized at about 79% of pure Ni60 alloy, which is acceptable considering the benefit of elimination of surface cracking. Decrease in the mechanical properties were caused by the dilution of the strengthening elements and reduction of population of hard phases. Composite coating having 30% of 17-4PH also exhibited the smallest corrosion current, lowest corrosion potential and slowest corrosion rate, and therefore the best corrosion resistance.

Different structural $\mathrm{\text{(Ti,Al,Si)N}}$ coatings were designed and deposited on WC-Co cemented carbide by the technology of multiarc ion plating. Monolayered $\mathrm{\text{(Ti,Al,Si)N}}$ coating was deposited using cathode of ${\mathrm{\text{Ti}}}_{0.5}{\mathrm{\text{Al}}}_{0.4}{\mathrm{\text{Si}}}_{0.1}$. Multilayered (Ti,Al)N/$\mathrm{\text{(Ti,Al,Si)N}}$ coating and $\mathrm{\text{(Ti,Al,Si)N}}$ coating with gradual silicon content were deposited using two cathodes of ${\mathrm{\text{Ti}}}_{0.5}{\mathrm{\text{Al}}}_{0.5}$ and ${\mathrm{\text{Ti}}}_{0.5}{\mathrm{\text{Al}}}_{0.4}{\mathrm{\text{Si}}}_{0.1}$ simultaneously. The surface and cross-section morphology, compositions, and phase structure were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The dense $\mathrm{\text{(Ti,Al,Si)N}}$ coatings with droplets on the surface and without obvious columnar structure on the cross-sections were obtained. All coatings had the strong peaks of (200) orientation. The different angular shift occurred with different combination of cathodes and processes. The introduction of multilayered and gradient structure effectively reduced the lattice distortion of coatings. Meanwhile, the coating-substrate adhesion strength increased from 38.57 N to 60.17 N with a coating thickness of approximately 3.5 $\mu$m by scratch tests. The highest hardness of $\mathrm{\text{(Ti,Al,Si)N}}$ coating obtained in this paper were $39.40\pm 0.64$ GPa by nanoindentation. The multilayered coating showed better toughness.

Low phosphorus electroless Ni-P alloy coating has many advantages over medium and high phosphorus electroless Ni-P alloy coatings because of its special microstructure and composition, which can meet more special performance requirements. In addition, reducing the plating temperature can reduce energy consumption. The preparation process of electroless Ni-P plating at medium temperature and low-P was studied by single factor and orthogonal experiment. The results show that electroless Ni-P alloy coatings with 4–6% P can be obtained at 60–80${}^{\circ }$C and pH=5–6. The hardness, deposition rate and corrosion resistance of the coating were also evaluated.

Copper matrix composites reinforced with graphene nanoplatelets (GNPs) were prepared by vacuum hot pressing of ball milled mixtures of powders. Two grades of GNPs were used; one with average thickness of 2 nm and average lateral size of 6 $\mu$m and another with much larger lateral size of 80 $\mu$m. Microstructure and properties of as-prepared composites containing 10 vol.% GNPs were studied. The GNPs sheets are uniformly distributed and well aligned in the Cu matrix. The microstructure observation shows that the GNPs-2–6 exhibits a better dispersion in the Cu matrix than GNPs-2–80. The addition of fine GNPs-2–6 lead to $\sim$31% higher tensile strength and approximately same electrical conductivity of the Cu matrix, while the GNPs-2–80/Cu composite only shows a $\sim$15% increase of tensile strength and a lower electrical conductivity than the Cu matrix.

In this work, a composite composed of $\beta$-Sialon (Z=4) and ZrN has been fabricated by a two-step gas-pressure sintering method, and the effects of ZrN content and applied pressure on the phase behavior, densification and mechanical properties have been investigated. The phase behaviors were mainly dependent on the ZrN content and the applied pressure. The composites composed of $\beta$-Sialon (Z=4), ZrN, 15R-Sialon (0.4 MPa) and 12H-Sialon (0.7 MPa) as major phases, with different intermediate phases depending on the ZrN content. It is revealed that with the two-step sintering technique, a higher applied gas pressure has a positive effect on mass loss, and significantly improved the mechanical properties. The addition of ZrN particles greatly helped the densification behavior, reduced the mass loss, and increased fracture toughness of the composites, but decreased hardness due to formation of intermediate phases and grain coarsening. The addition of ZrN increased the fracture toughness due to the toughening mechanisms of crack branching, crack deflection and crack bridging.

This study investigates the influence of sintering conditions on electrical properties and positive temperature coefficient of resistance (PTCR) of ${\mathrm{\text{Ba}}}_{1.005}({\mathrm{\text{Ti}}}_{1-x}{\mathrm{\text{Nb}}}_x){\mathrm{\text{O}}}_3$ (BTNO) ceramics, fired at $1190^{\circ }$C for different times from 1 to 6 h in a reducing atmosphere and reoxidised within the temperature range of $600$–$900^{\circ }$C for 1 h. The results showed that the room-temperature (RT) resistance and the resistance jump of the multilayer BTNO ceramics decreased with an increase in the firing time. Furthermore, the RT resistance of the BTNO samples gradually increased at first and then rapidly increased with increasing reoxidation temperature. In addition, the influence of sintering times on the microstructure of ceramics was also investigated.

High modulus SiC fibers can be used in complex working environment with alternating heat and cold. In this paper, SiC fibers with various oxygen contents and crystal size were fabricated by polymer-derived ceramics routes. The effects of oxygen content and crystal size on the elastic modulus of SiC fibers were studied in detail. It was found that the elastic modulus of SiC fibers can be improved by reducing the oxygen content and increasing the crystal size of SiC fibers when the crystal size was less than 2 nm. When the oxygen content decreased from 21.5 wt.% to 11.7 wt.%, the elastic modulus of SiC fibers was increased from 131 GPa to 167 GPa. Particularly, the highest elastic modulus of CVC treated hypoxic SiC fibers is close to 200 GPa when the crystallite size is about 2 nm.

This paper evaluates the feasibility of using SiC and TiC as reinforcement particulates for titanium metal matrix composites (Ti-MMC). The SiC and TiC particles were coated with titanium using a chemical coating technology in order to achieve a homogeneous mixing when they were mixed with pristine Ti. The Ti-MMC with these specially prepared reinforcements were fabricated by a conventional press and sinter route. The effects of sintering temperature in Ti matrix were investigated with respect to phase constituents, microstructure and tribology properties. No in situ phases were observed during sintering and the reinforcement and matrix show sufficient bonding, which acts as a major parameter to enhance hardness and wear resistance compared to pure Ti. All the composite samples had a high sintered density. The hardness of the composites increased with an increase in the sintering temperature. It was also noticed that with the increase in the temperature ranging from $1200^{\circ }$C to $1300^{\circ }$C, improvement in the mechanical and tribological properties of the developed titanium matrix composites could be observed. The highest hardness value $385\pm 20{\mathrm{\text{HV}}}_1$ was recorded for Ti-2 wt.% Ti-coated SiC composite when sintered at $1300^{\circ }$C for 3 h.

Copper/diamond composites can be used as heat-sink materials for high-power electronic devices due to their potential high thermal conductivity. However, it is challenging to obtain well-bonded interface between the copper matrix and the diamond particles. In this paper, we fabricated copper/diamond composites with $x$ wt.% of chromium additive ($x=1$, 3 and 7.4, and the corresponding composite was referred to as 1Cr-Cu/Dia, 3Cr-Cu/Dia and 7Cr-Cu/Dia, respectively) by hot forging of powder preforms. Results showed that only Cr₃C₂ interfacial layer formed between the copper matrix and the diamond particles for the 1Cr-Cu/Dia and 3Cr-Cu/Dia composites with a thickness of about 100 and 500 nm, respectively. A Cr/Cr₃C₂ dual layer interface formed in the 7Cr-Cu/Dia composite and its thickness was $1\mu$m. The coverage of diamond surface by the interface layer increased with increasing the adding amount of chromium in the composites. The 3Cr-Cu/Dia composite achieved the highest relative density and bonding strength, comparing to 1Cr-Cu/Dia and 7Cr-Cu/Dia composites, attributed to the formation of an optimal interface structure.

The $\mathrm{\text{Ti(C, N)}}$–${\mathrm{\text{Al}}}_2{\mathrm{\text{O}}}_3$ cermet to 40Cr steel joint was conducted by liquid phase diffusion bonding under the auxiliary pulse current and using 73Cu–27Ti amorphous foil/Cu foil/72Ag–28Cu foil sandwich foils as the interlayer. The effect of holding time and duty ratio of the pulse current on interfacial structure at the $\mathrm{\text{Ti(C, N)}}$–${\mathrm{\text{Al}}}_2{\mathrm{\text{O}}}_3$ cermet side and joint strength were studied. The results showed that the longer bonding time can improve the melting of Cu–Ti foil and the dissolution of Cu interlayer to obtain a higher joint strength. The interfacial structure was composed of the TiCu compounds and Cu solid solution at the cermet side, and ${\mathrm{\text{TiCu}}}_4$ compounds and Cu solid solution at the Cu interlayer side. The auxiliary pulse current was beneficial to reach a higher joint strength in a shorter holding time. A higher duty ratio would accelerate the dissolution and reaction of cermet to the interlayer, but continuous increase on the duty ratio would result in the over dissolution of cermet into the interface to produce the Ti(C, N) and ${\mathrm{\text{Al}}}_2{\mathrm{\text{O}}}_3$ ceramic particles and the decrease on the joint strength.

The AA7075/AZ31/AA7075 laminated composites were fabricated by hot roll bonding. The effects of pretreatment of Mg plate by severe plastic deformation (SPD) and heat treatment on its interface, microstructure and mechanical properties were studied. The diffusion layer is formed at the interface between Al and Mg layers, which is composed of the hard and brittle intermetallic phases $\beta {\mathrm{\text{-Al}}}_3{\mathrm{\text{Mg}}}_2$ and $\gamma {\mathrm{\text{-Al}}}_{12}{\mathrm{\text{Mg}}}_{17}$, and become the weak zone of the laminated composites where the crack is first-generated and propagated to cause the delamination at the interface of the laminated composites. The hardness of laminated composites at the interface reaches 300–400 HV. Meanwhile, Mg plate pretreatment can increase the plastic matching and the deformation compatibility of the Al and Mg layers, and can effectively improve the mechanical properties of the laminated composites to a certain extent. The bending strength of the laminated composites with pretreated Mg plates are 1080 MPa.

Friction stir brazing (FSB) with ultrahigh rotation speed was applied to join 6061 aluminum to pure copper with the aid of zinc foil. The effects of different shoulder diameters on the microstructure and mechanical properties of Al/Cu FSB joints were investigated combined with temperature and axial force. In the joint brazed by a 7 mm diameter shoulder, the filler metal layer exhibited the original zinc. Meanwhile, a layer of thick ${\mathrm{\text{CuZn}}}_5$ was found on the Cu interface. As the diameter of the shoulder was increased to 10 mm, the homogeneous structure of Al–Zn eutectic formed at the Al–Cu interface. Further increasing the shoulder diameter to 12 mm, however, resulted in the interlayer obtaining a microstructure of Al–Zn eutectic with refined and dispersed ${\mathrm{\text{CuZn}}}_5$. When the shoulder diameter increased to 15 mm, brittle intermetallic compounds (IMCs) such as ${\mathrm{\text{Al}}}_2\mathrm{\text{Cu}}$ and ${\mathrm{\text{Al}}}_{4.2}{\mathrm{\text{Cu}}}_{3.2}{\mathrm{\text{Zn}}}_{0.7}$ were generated and holes appeared owing to the high-temperature and axial force. Shear tensile tests showed that the joint brazed by a 12 mm diameter shoulder achieved the highest shear tensile strength.

Self-shielded flux-cored wire is a new type of welding material that has the advantages of outdoor and high-efficiency application, and it has been used widely for rail repair. A self-shielded flux-cored wire with high alkalinity and rare earth elements was taken for research, and the microstructure, inclusions, hardness and the impact toughness were studied. Rare earth elements could eliminate the oxygen and sulfur when they were added into the molten pool. The addition amount has been optimized to the range of 4% in the self-shielded flux-cored wire when used for rail repairing.

The SMA490BW weathering steel is a key material used in train bogies. The quality of its welded structures is the main constrain of the rail speed and safety. To study the influence of humidity on crack propagation in welding joints, the welding operation was performed under environments of 50%, 60%, 70%, 80% and 90% humidity. The crack propagation test against the microstructure observation was carried out. Results show that the crack propagation rate is mainly affected by the microstructure of the material and the humidity had little influence.

A newly self-protecting flux-cored wire was used for simulated U75V rail repairing and five welding process parameters were applied. The influence of welding parameter on the hardness and microstructure of the wire and solder layers was investigated. The single-pass welding process with different preheating parameters and post-treatment parameters were also taken into research. The results showed that the welding process parameters have a significant influence on the weld quality, and mismatched parameters will increase the welding defects. The number of welding layers has a great influence on the hardness and structure. Increasing preheating temperature and a post-heat treatment at a high-temperature can enhance the hardening effect.

The stress corrosion cracking (SCC) property of laser-MAG hybrid welded 304 stainless steel and Q345 steel was evaluated through cycle-immersion testing in 3.5 wt.% NaCl solution. The average SCC crack propagation rate of different zones under different initial stress intensity factors was calculated, and the SCC fracture and crack propagation path were observed. The microstructure and mechanical properties of the weld joint have also been examined. The result indicates that the fusion zone (FZ) is extremely prone to SCC. The average SCC crack propagation rate in FZ is $5.4489\times 10^{-6}$ mm/h, while no obvious SCC was found in the base metal (BM) and heat-affected zone (HAZ). The steel BM and HAZ may also suffer SCC, but not as fast as in FZ. Grooves caused by SCC were found on the fracture surface with a large amount of corrosion products accumulated close to the interface between the pre-crack section and SCC section. Crystallized-sugar-shaped pattern was found on the SCC zone of FZ. Crack jumping, deflection and crack closure occurred in the crack propagation path. Martensite on the FZ was considered to be the major reason that the FZ has a higher SCC propagation rate.

12Cr10Co3W2MoNiVNbNB (Co3W2) is a new type of martensitic heat-resistant steel, which is mainly used in high-temperature dynamic, static blades, high-temperature bolts and other components of ultra-supercritical steam turbines. The Co3W2 steel was joined by vacuum electron beam welding, and the microstructures of the joints were analyzed. The hardness, tensile strength and impact toughness of the joints were investigated. The results show that the joints mainly consist of weld metal, fusion-line, heat-affected zone (HAZ) and base metal, the microstructure of the weld metal is a coarse martensite. The hardness of the weld metal is about 326 HV higher than that of the base metal, and the tensile strength of the joints is 939 MPa, which can reach 98.63% of base metal. The impact absorbed energy of weld metal is such that the weakest part of the welded joints during the impact process is about 18.5 J.

A three-dimensional numerical model of arc in gas metal arc welding (GMAW) with single cable-typed wire was established based on the theory of arc physics. The influences of different shielding gas flow rates on the features of temperature field, velocity field and pressure field were investigated. The results showed that the maximum velocity of arc plasma along radial direction and the arc pressure on the surface of workpieces were increased obviously with the increase of the shielding gas flow rate, while the arc temperature was changed little. This phenomenon was mainly attributed to the increasing collisions between arc plasmas and the self-rotation action of cable-typed wires. The arc temperature at the tip of the cable-typed wire reached the maximum. The maximum flow velocity of arc plasma was located at the tip of wire (2–8 mm). The arc pressures in the central axis reached the maximum pressure. The simulation results were in agreement with the experimental results.

The joining of magnesium alloy to galvanized steel was realized by cold metal transfer method with AZ31 magnesium alloy welding wire. Weld appearance, microstructure and tensile properties of Mg–steel joints under various welding parameters were investigated with different welding heat inputs. The results showed that magnesium alloy-steel brazed joints had good weld appearance. When the welding heat input was 141 J/mm, Zn elements were enriched in the Zn-rich zone (ZRZ), and the interface layer was composed of a large portion of Mg–Zn phases and minor Mg–Al phases. With the increase of welding heat input, Zn elements in the ZRZ gradually decreased, Fe/Al phase appeared in the interface layer, and the strength of welding joint increased. When the welding heat input was 159 J/mm, the tensile strength of welding joint reached the maximum value of 198 MPa. However, when the welding input was increased to 181 J/mm, Zn element in the ZRZ was burnt and volatilized seriously, resulting in poor wetting and spreading properties of liquid phase at the interface zone of the steel.

Duplex stainless steel, consisting of ferrite and austenite, has good corrosion resistance and is often used in harsh marine environments. In this paper, welding on SAF2507 duplex stainless steel with 5 mm thickness was finished by laser beam welding (LBW) and gas tungsten arc welding (GTAW). The post-weld solid solution treatment was also conducted at temperature of $1050^{\circ }$C followed with cooling by water after 1 h. The results showed that both LBW and GTAW could produce well-produced welds. The microstructures of the welds were composed of ferrite and austenite phases. After solid solution treatment at $1050^{\circ }$C, the two-phase structure of LBW joint became uniform, while $\sigma$ phase was produced in GTAW joint. The impact test of welded joints at room-temperature was carried out. After solid solution treatment at $1050^{\circ }$C, the impact toughness of LBW joints obviously increased, but the impact toughness of GTAW joint decreased with the fracture morphology of brittle mode. The electrochemical experiments on the welded joints showed that the pitting corrosion resistance of LBW joints improved after solid solution treatment, while the pitting corrosion resistance of GTAW joints decreased.

The stress corrosion resistance of 30 mm-thick narrow-gap rotating laser welding (NG-RLW) 5A06 aluminum (Al) joint was investigated by slow strain rate testing (SSRT). The results show that the average ultimate tensile strength (UTS) of the joints in 3.5% NaCl solution is about 11% lower than that in air, and its elongation is only half of that in air. The stress corrosion index $I_{\mathrm{\text{SSRT}}}$ of the joint is $\sim 0.498$, which is at the middle level of the range of $I_{\mathrm{\text{SSRT}}}$. Moreover, the failure positions of the SSRT specimens in air are weld metal (WM), while the failure positions in the corrosive medium are base metal (BM). This indicates that the stress corrosion resistance of BM is slightly lower than that of WM due to the different microstructures. Many dimples are formed on the fracture surface of the specimen in air, which is a typical ductile fracture. But the fracture surface shows the characteristics of ductile and brittle mixture with obvious corrosion products. This result indicates that the NG-RLW 5A06 Al joint has a tendency to brittle fracture in 3.5% NaCl solution.

Hybrid laser-arc welding (HLAW) was carried out on high strength thermo-mechanical controlled process (TMCP) steel of 14 mm thickness using single-pass welding (SPW) and multi-pass welding (MPW) processes. Well-formed weld joints with good performance were successfully obtained. The results showed that the microstructure of weld was pre-eutectoid ferrite, acicular ferrite and some granular bainite. There were mainly lath bainite, granular bainite and acicular ferrite in the heat-affected zone. The grain sizes of SPW were thicker than MPW, and the bainite content of MPW was higher than SPW. The average hardness value of the fusion zone was lower than that of the Heat affected zone, but higher than that of the base material. The weld was divided into upper arc domain zone (ADZ) and lower laser domain zone (LDZ). The ADZ was harder than the LDZ. The average absorbed energy of SPW and MPW in the fusion zone at −40${}^{\circ }$C was 125.5 and 92 J/cm², respectively. The influences of microstructure on impact toughness were summarized by analyzing the hardness distribution and microstructure of the welded joint. The brittle transition temperatures of the two processes obtained by the energy criterion and the morphology criterion were close to each other.

Most haze removal methods are based on the classical haze imaging model, which can effectively describe the image from the haze, where one of the key factors is the atmospheric light. Existing methods either depend on the user input or keep to the color constancy. In this paper, we present a new and effective method for computing the atmospheric light based on the salient region of the input haze image. The method computes the salient map and the darkness channel map of the input image and adaptively selects the region of the atmospheric light according to the assumption that the atmospheric light does not belong to the salient region of the input image. Then, the atmospheric light is estimated by combining the statistical characteristics between the darkness channel and the region of the atmospheric light. Finally, the transmission map is computed and refined by the weight-guided filter and the clear image without the haze is produced. Compared with some existing methods, a number of experimental results show that the proposed method can not only accurately recover the atmospheric light, but also effectively remove the haze from bad weather condition and improve the image quality such as the contrast, sharpness and color.

Daytime star sensor provides accuracy navigation information to air vehicles near the ground in the daytime by observing stars. It has been an important development of modern star sensors. In order to achieve a high signal-to-noise ratio, daytime star sensors work in the infrared band to avoid interferences from sky background. Daytime star sensors output accurate attitudes by identifying the observed stars in the field of view (FOV) according to the loaded guide star catalog. Guide stars are usually required to be distributed uniformly on the celestial sphere to improve the performance of star pattern identification. The parameters including limiting magnitude and FOV are determined by processing the 2MASS star catalog as the original star data and performing star distribution statistics. After constellation features are discussed, the idea of distributing stars in the local FOV to constellations is put forward by using the star pair angular separations. An optimization algorithm to build the guide star catalog for daytime stars is proposed to achieve evenly distributed guide stars. The guide star catalog is established and analyzed, proving that the proposed algorithm has simple calculation and easy realization. The Boltzmann entropy of obtained guide star catalog drops two orders of magnitude. Guide stars are distributed more uniformly.

This paper proposes a six-pole radial-axial hybrid magnetic bearing (RAHMB) used in a flywheel system. The radial and axial bias fluxes are generated by one permanent magnet and the radial control coils are driven by a three-phase converter. So, it has the advantages of compact structure, low power consumption and simple driver. First, the work principle is introduced. Then, the mathematical model is built. The force-current characteristics with different eccentricities, the coupling between radial two degrees of freedom (DOF) and the coupling between radial and axial DOF are analyzed based on the analytical model. Finally, the analyses are validated by 3D finite element analysis in the Maxwell software. The results have shown that the coupling between radial and axial DOF is very small. However, the force-current curves of radial two DOFs turn out to be nonlinear and coupled with the increase of rotor eccentricity.