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Developing a high electrically conductive and corrosion-resistant coating on metal bipolar plate is of prime importance for its application in polymer electrolyte membrane fuel cells. To achieve it and further improve its through-plane conductivity, we herein prepared a composite coating by introducing Au microdots onto TiN coated stainless steel (Au/TiN/SS). Au dots provide additional conduction paths and thus Au/TiN/SS exhibits a remarkably lower interfacial contact resistance than that of TiN/SS after 200 h of test, suggesting that incorporation of Au dots into TiN provides an effective approach to achieving dual merits of high conductivity and corrosion resistance.

Most of nanoparticles catalyst for hydrogen evolution reactions (HER) exhibit low electrocatalytic activity due to the use of binders. Considering the synergistic effect of high activity of NiCoP and good conductivity of the nanoporous copper (NPC), and we report self-supporting NiCoP/NPC composites by electrochemical depositing NiCoP micro-spheres on NPC. The NPC substrate leads to the uniform nucleation of NiCoP micro-spheres and the high resistance against aggregation. As a result, the cost-effective NiCoP/NPC composites possess promising HER performance, with a low overpotential of 80 mV at 10 mA cm−2 and Tafel slop of 48.9 mV dec−1 in 1 M KOH.

${\mathrm{TaAs}}_{2}$ and ${\mathrm{NbAs}}_{2}$ are members of the ${MPn}_{2}$ family with weak topological invariants of ${Z}_{2}$ = [0;111]. Here, we report the tip-induced superconductivity achieved on both materials using the point-contact technique. Although the weak ${Z}_{2}$ number leads to strongly crystal-orientation-dependent surface states, we observed a universal relationship between the zero-temperature upper critical field ${H}_{c2}(0)$ and the critical temperature ${T}_{c}$ for different crystal orientations. Combined with first-principles calculations, the findings here could identify a bulk band, instead of the much speculated surface bands, playing the dominant role in the induced superconductivity. These results predict a great possibility to realize superconductivity in other members of the ${MPn}_{2}$ family possessing similar band structures and provide clues to understand the mechanism of tip-induced superconductivity.

Tip-induced superconductivity at point contacts on the nonsuperconducting Weyl semimetal TaAs has been reported recently. Meanwhile, both the main tetragonal phase and the intergrown hexagonal phase of TaAs were identified to be topologically nontrivial according to theoretical calculations. Here, we report the observation of two independent local superconducting states induced at the point contacts formed on TaAs, which exhibit distinct temperature dependencies of the critical magnetic field ${H}_{c2}(T)$. A universal relationship between ${H}_{c2}(0)$, ${T}_{c}$, and the Fermi velocities of bulk bands near Weyl points of the two TaAs phases was uncovered, demonstrating the dominant role of the bulk bands in the emergence of superconductivity, rather than the surface states. These results provide a direction to study the mechanism of the tip-induced superconductivity in topological semimetals.

For precipitation-strengthened heat-resistant steels, property degradation resulted from phase coarsening is always one of the most critical challenges, and therefore, knowledge regarding the long-term influence of temperature on mechanical properties and microstructure is prerequisite for their applications. In this work, long-term thermal aging up to 10,000 h of typical alumina-forming austenitic (AFA) stainless steels was conducted, and evolution of microstructure and mechanical properties of these promising heat-resistant alloys were studied systematically. It was found that mechanical performance of the steel strengthened by secondary nanosized NbC showed not only much enhanced creep resistance, superior to that of most traditional heat-resistant steels, but also stable high-temperature strength even after long-term aging. The spheroidal secondary NbC particles showed extreme coarsening resistance with a low coarsening kinetic constant (almost six orders of magnitude smaller than that of the Laves Fe2Nb phase). The low interfacial energy of nanosize NbC, which was resulted from the cube-on-cube orientation relationship and semi-coherent interfacial structure with the matrix, gave rise to its sluggish coarsening kinetics. Our current findings not only confirm that the AFA alloys strengthened by dense precipitated, nanosized semi-coherent NbC is a promising structural material for long-term high-temperature applications, but also sheds new insights into understanding precipitation hardening mechanism for high-temperature materials in general.

The wear resistance of Ti45Zr16Cu10Ni9Be20 bulk metallic glass with a deep cryogenic-cycling treatment (DCT) was studied here. The specimens showed increased plasticity and decreased hardness after DCT. The higher wear resistance could be achieved by sacrificing partial hardness in macroscopic wear tests. Morphological observation revealed that the wear mechanism changed from severe fatigue wear to mild ductile ploughing, and the oxidation wear played a mild role. Nano-scratch tests were applied to explore the adhesion and ploughing contributions under the ramping-constant load mode. The competition between the lower hardness and the higher elastic recovery results in the lower friction coefficient. Therefore, DCT has great potential in the application of designing wear-resistant BMGs.

Due to excellent energy absorption efficiency under bending collapse, multi-cell beams are extensively used as the components of protection structures. However, the theoretical prediction of their responses is still an unsolved problem. In this paper, two methods: dimensionless analysis method and energy analysis method are employed to derive the bending moment response of multi-cell tubes. Numerical simulations of double-cell tubes with different section dimensions are conducted first. The dimensionless analysis method is then employed to correlate the bending moment of double-cell tubes with the ratio of width to thickness b/t, the flow stress and the bending rotation angle. Based on Kecman's model, a theoretical model of double-cell tubes is presented and the bending moment response is derived according to the energy equilibrium of the system. Finally, the expression of a rolling radius of plastic hinge lines in the energy analysis method is determined to bridge the two methods. A comparison shows that the predictions provided by the present two methods agree well with the numerical results. Quadruple-cell tubes are also employed to validate the present methods and results show that the present methods are applicable for multi-cell tubes with other cross-sections.

A hash service environment containing H2S and CO2 in oil industry usually causes corrosion of carbon steel. In this study, the chromized coatings with different deposited time were prepared on the surface of carbon steel by the method of pack cementation to enhance its corrosion resistance. Then the microstructure, hardness, corrosion resistance as well as the semiconductor behavior of coatings in the simulated solution with saturated H2S and CO2 were investigated. The results show that the content of Cr in coating was increased by prolonging deposited time, and both chromium carbides and chromium nitrides were formed. Furthermore, coatings display higher polarization resistance, Rp, than that of the substrate, indicating a higher resistance to charge transfer on coating surface. The corrosion rates of coatings with different deposited time were significantly lower than that of substrate. Chemical analysis showed the formation of heavy sulfides on the surface of substrates after corrosion, while the least corrosion products were detected on the surface of coating with deposited time of 12 h. Mott-Schottky results indicated that coating of 12 h displayed less defects than the other two coatings with deposited time of 4 h and 8 h, which will be beneficial to improve corrosion resistance. The investigation showed that chromized coatings exhibited high corrosion resistance and owned a potential application in oil industry for corrosion prevention.

In this study, a duplex Ni P with yttria-fully stabilised zirconia (YSZ) nanoparticle composite coating was prepared by electroless deposition on a carbon steel substrate. The characteristics of the coatings were evaluated using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The electrochemical and corrosion behaviour of the coating in a 3.5 wt.% NaCl solution was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). In addition, the effects of the YSZ nanoparticle concentration on the properties of the coatings were also discussed. The results show that the structures of the as-deposited duplex Ni-P-YSZ/Ni-P coating are amorphous, and it changes to a crystalline state after heat treatment. The surface roughness and morphology of the coating are affected by the addition of YSZ nanoparticles. The duplex coating exhibits both good microhardness and wear resistance as well as excellent corrosion resistance because of its special duplex structure.

We simulate the two-dimensional XY model in the flow representation by a worm-type algorithm, up to linear system size $L=4096$, and study the geometric properties of the flow configurations. As the coupling strength $K$ increases, we observe that the system undergoes a percolation transition $K_{\rm perc}$ from a disordered phase consisting of small clusters into an ordered phase containing a giant percolating cluster. Namely, in the low-temperature phase, there exhibits a long-ranged order regarding the flow connectivity, in contrast to the qusi-long-range order associated with spin properties. Near $K_{\rm perc}$, the scaling behavior of geometric observables is well described by the standard finite-size scaling ansatz for a second-order phase transition. The estimated percolation threshold $K_{\rm perc}=1.105 \, 3(4)$ is close to but obviously smaller than the Berezinskii-Kosterlitz-Thouless (BKT) transition point $K_{\rm BKT} = 1.119 \, 3(10)$, which is determined from the magnetic susceptibility and the superfluid density. Various interesting questions arise from these unconventional observations, and their solutions would shed lights on a variety of classical and quantum systems of BKT phase transitions.

The effect of Fe addition on the structure, mechanical and wear properties of Zr–Cu–Ni–Al bulk metallic glasses (BMGs) was systematically investigated by thermal analysis, transmission electron microscopy (TEM), the compression test, the pin-on-disk macroscopic wear test and the microscopic nanoscratch test. TEM observation revealed the formation of a second glassy phase with a few nanometers in diameter in the Zr63.6-xCu18Ni10.4Al8Fex (x = 1, 3, 5) BMGs. The results of the mechanical tests showed that although compression strength and hardness do not change much, a remarkable enhancement in plasticity occurs in the Zr58.6Cu18Ni10.4Al8Fe5 BMG, which is presumably due to the restriction of the nano-scale second phase on shear banding. Phase separation was also found to promote multiple shear bands, enhanced toughness and oxidative wear, which work synergistically during the tribological test to improve the wear resistance of Zr–Cu–Ni–Al BMGs. These findings provide some insights into the wear mechanisms of dual-phase BMGs, which may offer new strategies for design and optimization of BMGs with desired wear performance.

Improving the corrosion resistance while maintaining good electrical conductivity is of vital importance for the application of stainless steel in bipolar plates of polymer electrolyte membrane fuel cells (PEMFCs). Transition nitride coatings on steel surfaces, such as TiN, is considered as a possible solution. However, most coatings still fail to exhibit good corrosion resistance and high electrical conductivity simultaneously, especially after corrosion testing. This study prepares TiN on 316L stainless steel (SS) and conducts heat treatment on the TiN deposited samples at different temperatures. The corrosion behaviours of the prepared samples are investigated under the simulated working environments of fuel cell. Our results demonstrate that heat treatment at appropriate temperatures is an effective approach to improve the corrosion resistance of TiN coatings while maintaining a considerable electrical conductivity. The interfacial contact resistance (ICR) test results indicate that high temperature (450 °C) heat treatment has detrimental effect on the electrical conductivity of samples due to the formation of a thick oxide dominated layer, while samples heat treated at 300 °C only form graded layers with suitable oxide amount which endows the coated specimens with a very low ICR value both before and after corrosion tests. This suggests that the heat treatment of TiN coatings under suitable conditions is a feasible strategy to simultaneously achieve an enhanced corrosion resistance and a good electrical conductivity of the TiN coated samples for bipolar plates in PEMFCs.

Ni–Cr–Mo coating was prepared by a high power diode laser (HPDL) on X70 steel substrate (X70). In order to widen the application of this coating in oil industry, its surface morphology and corrosion behavior in simulated solutions separately with CO2, H2S as well as a mixed gas of them were studied and compared with those of X70 and 316 stainless steel (316 SS). The results show that X70 and 316 SS display inclusions on the surface before corrosion, while Ni–Cr–Mo coating exhibits a uniform and compact microstructure. Moreover, Ni–Cr–Mo coating has no change in morphology after corrosion, while X70 and 316 SS display severe corrosion and pitting corrosion, respectively. For each simulated solution, Ni–Cr–Mo coating exhibits higher corrosion resistance than X70 and 316 SS. Also, it shows higher polarization resistance than 316 SS and X70 as immersion time lasts, revealing an enhanced and stable anticorrosion performance. Furthermore, the variation trends of electrochemical response was opposite for X70 and 316 SS/Ni–Cr–Mo coating in simulated solutions with CO2, H2S as well as the mixed gas accordingly, which is caused by different corrosion mechanisms.

The susceptibility to stress corrosion cracking (SCC) of X70 pipeline steel under cathodic protection in near-neutral pH and acidic solutions was investigated by slow-strain-rate tensile test, circumferential-notch tensile (CNT) test, and three-point-bending (TPB) test. Results confirmed the existence of a hydrogen-induced plasticity (HIP) effect within a particular range of cathodic potentials. HIP effect lowered the SCC risk of X70 steel by releasing stress concentration at crack-initiation spots and then decreasing the stress intensity. Crack-growth behavior examined by CNT and TPB tests proved the existence of an HIP effect.

An LY12 aluminum alloy was coated with a self-assembled dodecyl phosphate film by employing a novel surface-modification protocol based on the chemisorption of sodium monododecyl phosphate from aqueous solution. The effect of solution pH on the self-assembled film properties was documented, and the corrosion resistances of the self-assembled film in a Cl−-containing solution and in a marine atmosphere were evaluated by electrochemical impedance spectroscopy and corrosion morphology analysis. Unlike self-assembled film formed in acidic and alkaline conditions, dodecyl phosphate films formed in neutral solution exhibited a multilayer structure with greater thickness and superior corrosion resistance due to the strong chemisorption and electrostatic attraction that are fostered in neutral solutions.

In this paper, dielectric columns with different dielectric constants are employed as dielectric materials in the packed bed reactor to investigate the dynamic behaviors of plasma interaction processes. The effects of the dielectric constants (zirconia: e=25 and PTFE: e=2.5) on the production of reactive species are studied for plasma catalysis applications. Comparison studies of discharge images, electrical characteristics, discharge dynamic evolution and spatial- temporal resolved optical emission spectroscopy are carried on when zirconia and PTFE columns are employed. The results show that there are four discharge processes existing in the packed bed reactor: surface streamer on the dielectric column, local discharge at the contact point, surface discharge on the grounded dielectric plate, and the volume discharge. The production of reactive species such as N2 (C3Пu), N2 + (B2Σu +) and O (3p 5P) depend on the discharge processes to a great extent. The production of the N2 + (B2Σu +) always accompanies the formation of the streamer by electrons direct impact process to excite the ground state nitrogen molecules to N2 + (B2Σu +). And the O(3p 5P) is generated in two different ways, which plays major role during the voltage pulse raising and falling time, respectively. The first way is the direct and fast one-step ionization and excitation by high energy electrons with O2. The second way is the energy transfer from the nitrogen metastable N2(A3Σu +) and the energetic electrons, in which way the O is first ionized from O2 and then be excited to O(3p 5P).Furthermore, compared with zirconia column, PTFE column is more conductive to the generation of reactive species.

The CoNi equiatomic alloy was undercooled and spontaneously solidified using the glass fluxing method. The dendrite growth behaviors were recorded by a high-speed high-resolution camera. Three dendrite growth stages (i.e., the power law growth stage when undercooling ΔT 135 K) were found and well predicted by a dendrite growth model. For the as-solidified microstructures, the average grain size increases with undercooling, indicating that unique grain “coarsening” instead of common spontaneous grain refinement occurs. Such a grain “coarsening” phenomenon was ascribed to stress accumulation upon rapid solidification. Furthermore, a plenty of sub-grains were observed within the abnormal coarse grains. From the electron back-scattering diffraction results, the angle difference between neighbouring sub-grains was less than 6°. The current work might be helpful for not only theoretically understanding dendrite growth but also practically controlling the non-equilibrium microstructures.

We report the realization of a robust and highly controllable two-dimensional (2D) spin-orbit (SO) coupling with topological non-trivial band structure. By applying a retro-reflected 2D optical lattice, phase tunable Raman couplings are formed into the anti-symmetric Raman lattice structure, and generate the 2D SO coupling with precise inversion and $C_4$ symmetries, leading to considerably enlarged topological regions. The life time of the 2D SO coupled Bose-Einstein condensate reaches several seconds, which enables the exploring of fine tuning interaction effects. These essential advantages of the present new realization open the door to explore exotic quantum many-body effects and non-equilibrium dynamics with novel topology., Comment: 6 pages, 4 figures

In this paper the physical and chemical grain refining of the Mg-10Sm alloy was investigated. Physical grain refinement was achieved by strongly shearing the melt above the liquidus temperature using a twin-screw string device and then cast at the near liquidus temperature. Chemical grain refiner was added into Zr master alloy in the melt. Casting the Mg-10Sm alloy at 730°C produced an extremely coarse microstructure consisting of huge dendritic grains. The physical grain refinement greatly refined the dendritic grains to smaller rosette grains, being reduced from several millimeters to about 200μm. Chemical grain refinement produced fine and equiaxed grain structure with size of approximated 111μm. Combination of the physical and chemical grain refinement creates more significant refining effect than either of the two methods.

Bulk metallic glasses (BMGs) are potential candidate materials for numerous structural applications. However, this class of materials has a major limitation for engineering applications due to their inferior resistance to fatigue wear. In present work, a novel micro-scale repetitive impact test was utilized for fatigue testing of ZrCu-based BMGs (Zr63.6-xCu18Ni10.4Al8Fex, x = 0, 3, 5 at.%), and specific attention was paid to the micro-alloying effect on wear resistance. Transmission electron microscopy of as-cast Zr58.6Cu18Ni10.4Al8Fe5 revealed amorphous structure with the formation of a second glassy phase of few nanometers in diameter. Although these structural changes have minor effects on hardness and modulus, they have a substantial influence on fatigue wear resistance. Phase separation was found to promote numerous shear bands, which induced strain hardening, and improved the crack resistance. Consequently, all these features are considered to contribute the improved wear resistance. On the contrary, a monolithic glass without Fe addition lacks any microstructural features that can provide means for the local arrest of shear bands and incipient fatigue cracks. These findings improve the understanding of the impact fatigue mechanisms and provide suggestions for the future design of BMGs with excellent wear performance.

The capacity of charge storage for supercapacitor depends on the size of the electrode surface area and the active material on the electrodes. In this article, we fabricate the three-dimensional microelectrodes with SU-8 photoresist based on the microelectromechanical system technology to increase the electrode surface area and to carry more active materials on the electrodes. The three-dimensional microelectrode was directly prepared by the method of anodic electrodeposition. Its surface and composition were characterized by scanning electron microscopy and energy dispersive spectroscopy. Moreover, cyclic voltammetry and galvanostatic charge–discharge current are also used to test the electrochemical characteristics of the manganese oxide electrodes. When the discharge density is 0.5 mA cm−2, the areal capacitance for the fabricated three-dimensional microelectrodes with microstructure and the two-dimensional planar microelectrodes without microstructure is 3.68 mF cm−2 and 1.0 mF cm−2, respectively. The experimental results show that the three-dimensional microelectrode structure prepared with microelectromechanical system technology can effectively increase the electrode surface area and carry more electroactive materials, thereby enhancing the charge storage capacity of the electrodes.

This paper studies the effect of the temperature-depended interface kinetics on the morphological stability of a spherical particle under the non-equilibrium solidification condition. The result shows that as the interfacial kinetics parameter increases, the growth velocity of the spherical particle decreases. Compared with the case of neglecting interfacial kinetics, the temperature-depended interfacial kinetics has the significant stable effect on the morphological stability of the spherical crystal and the critical stability radius increases as the interfacial kinetics parameter increases.

The Zr(V1−xFex)2 (x = 0.02, 0.05, 0.10, 0.15, 0.25) alloys were prepared by the arc-melt method and annealed at 1273 K for 168 h in an argon atmosphere. Phase structure investigations of the as-cast and annealed Zr(V1−xFex)2 alloys indicate the annealing treatment can eliminate the minority phases originating from the non-equilibrium solidification of as-cast alloys. The ZrV2-type phase becomes the dominant one in each annealed alloy. The substitution of Fe in V sites leads to the contraction of their lattice. For annealed Zr(V1−xFex)2 alloys, the P–t and PCT curves obtained between 673 K and 823 K give the evidence that the absorption process is controlled by a rate-controlling hydrogen diffusion. With the increase of iron, the equilibrium pressure and the plateau slope increase while the hydrogenation capacity and the absolute value of enthalpy and entropy decrease accordingly. The stability of metal hydride reduces gradually as the Fe content varies from x = 0.02 to 0.25 which promotes the hydrogen release and favors the practical applications of the Zr(V1−xFex)2 alloys.

Piston of cam engines for torpedo works in terrible condition and always be caused fatigue breakdown by thermal load. In this paper, the thermal boundary condition of different piston parts are ascertained, such as the crown surface of piston and high-temp gas, the side of piston and cooling water, and the skirt of piston and cooling oil. Then the piston’s temperature field is obtained by using the finite element analysis software. This result provides the practical reference for further improving the structure and optimizing the design of the piston. Keywords: cam engine; piston; heat-transfer coefficient; temperature field.

Non-equilibrium Green’s function method is applied to study the spin thermoelectric effects in a four-quantum-dot ring with two of the quantum dots magnetized. The influence of magnetic configuration on the spin thermoelectric transport through the system is investigated. In some magnetic configurations, a significant spin Seebeck coefficient [Formula: see text] can be generated with the variation of the quantum dot (QD) energy level. Appropriately tuning the QD energy level can let the present device work as a pure spin-up (spin-down) or a pure-spin-current thermal generator. The combined effect of the magnetization and magnetic flux (or Rashba spin-orbit coupling) is also investigated. Finally, the charge figure of merit [Formula: see text] and spin figure of merit [Formula: see text] are evaluated, it is found that the magnitude of the spin figure of merit can be comparable to that of the charge counterpart.

Cold atoms with laser-induced spin-orbit (SO) interactions provide intriguing new platforms to explore novel quantum physics beyond natural conditions of solids. Recent experiments demonstrated the one-dimensional (1D) SO coupling for boson and fermion gases. However, realization of 2D SO interaction, a much more important task, remains very challenging. Here we propose and experimentally realize, for the first time, 2D SO coupling and topological band with $^{87}$Rb degenerate gas through a minimal optical Raman lattice scheme, without relying on phase locking or fine tuning of optical potentials. A controllable crossover between 2D and 1D SO couplings is studied, and the SO effects and nontrivial band topology are observed by measuring the atomic cloud distribution and spin texture in the momentum space. Our realization of 2D SO coupling with advantages of small heating and topological stability opens a broad avenue in cold atoms to study exotic quantum phases, including the highly-sought-after topological superfluid phases., Comment: 27 pages, 5 figures

A prominent effect of the interface potential (IP) [E. L. Ivchenko and A. Yu. Kaminski, Phys. Rev. B 54, 5852 (1996); O. Krebs and P. Voisin, Phys. Rev. Lett. 77, 1829 (1996)], the optical anisotropy of the forbidden transitions in quantum wells has been observed by reflectance-difference spectroscopy. Predictions by the heavy-light-hole coupling IP models are qualitatively consistent with all the observed features of the forbidden and the allowed transitions. The fact that the predicted value of the relative, transition strength, which depends on neither the IP strength nor the electric field, disagrees with the observed one indicates that coupling involving X and/or L bands may also be important. [S0163-1829(99)04227-7].

The in-plane optical anisotropy which comes from the heavy-hole and the light-hole transitions in InAs submonolayers inserted in a (311)-oriented GaAs matrix is studied by reflectance-difference spectroscopy (RDS). The steplike density of states obtained from RDS demonstrates that the ultrathin InAs layers should be regarded as two-dimensional quantum wells rather than isolated clusters, even for the sample with only $$$\frac{1}{3}$-ML InAs. The degree of anisotropy is found to be independent of the layer coverage, and is within the intrinsic anisotropy of (311)-oriented ultrathin quantum wells, indicating that there is little structural or strain anisotropy in the InAs submonolayer grown on a (311) GaAs surface.