Developing low‐cost and high‐activity pH‐universal hydrogen evolution reaction (HER) catalysts is very crucial to the industrialization of water electrolysis. However, the high price, low yield, and ...poor stability of current HER catalysts make them difficult to meet practical requirements. Herein, a plasma spraying technique is employed to prepare self‐supported Cu catalysts with tensile strain for the first time. The tensile strain upshifts the d‐band of Cu, improves the water dissociation and H* adsorption, eventually improves the intrinsic HER catalytic activity. As such, Cu electrode achieves overpotentials of 182 mV in 0.5 m H2SO4, 261 mV in 1 M PBS, and 121 mV in 1 M KOH at 10 mA cm–2. In addition, Cu electrode also performs well at high current densities, the overpotentials at 1 A cm–2 are much lower than those of Pt foil in acid, neutral, and alkaline solutions.
The Cu electrode prepared by plasma spraying exhibits an excellent pH‐universal HER catalytic activity, superb long‐term stability, and marvelous corrosion resistance. The superb HER activity is attributed to self‐supported porous structure, abundant active sites, tensile strain enhanced intrinsic catalytic activity, and small charge transfer resistance.
Thermal barrier coatings (TBCs) can effectively protect the alloy substrate of hot components in aeroengines or land-based gas turbines by the thermal insulation and corrosion/erosion resistance of ...the ceramic top coat. However, the continuous pursuit of a higher operating temperature leads to degradation, delamination, and premature failure of the top coat. Both new ceramic materials and new coating structures must be developed to meet the demand for future advanced TBC systems. In this paper, the latest progress of some new ceramic materials is first reviewed. Then, a comprehensive spalling mechanism of the ceramic top coat is summarized to understand the dependence of lifetime on various factors such as oxidation scale growth, ceramic sintering, erosion, and calcium-magnesium-aluminium-silicate (CMAS) molten salt corrosion. Finally, new structural design methods for high-performance TBCs are discussed from the perspectives of lamellar, columnar, and nanostructure inclusions. The latest developments of ceramic top coat will be presented in terms of material selection, structural design, and failure mechanism, and the comprehensive guidance will be provided for the development of next-generation advanced TBCs with higher temperature resistance, better thermal insulation, and longer lifetime.
To enhance the mechanical strength of an ultrasonic spot-welded Al/Al joint, an Al 2219 particle interlayer was placed between the two Al sheets during the ultrasonic spot welding process. The ...effects of the interlayer thickness on the microstructure and mechanical performances of the joints were systematically investigated. The results showed that, the optimum thickness of the Al 2219 particle interlayer was 10 μm, which was beneficial to enhance the weld interface temperature up to 402 °C. The bonding interface of Al/Al 2219 with a wave-like shape was sound, and no significant diffusion layer occurred. The peak lap shear tensile strength (~84.8 MPa) was obtained, which was 36% higher than that (~67.3 MPa) for the joint without the Al 2219 particle interlayer. The strengthening mechanism is caused by the increase of plastic deformation and contact areas in the weld interface.
A self-supported silver electrode was prepared by plasma spraying and used for catalysing the hydrogen evolution reaction. Thanks to the non-equilibrium synthetic conditions, the silver catalyst ...exposes high-energy (200) crystal planes, which enhance the adsorption of hydrogen and improve the intrinsic catalytic activity. As a result, the silver catalyst delivers an overpotential of 349 mV at 10 mA cm
−2
, which was much lower than those of Ag foil (742 mV) and commercial Ag powder (657 mV). This work provides a new idea of preparing active electrocatalysts by traditional processes.
A physical technique, plasma spraying, was adopted to grow a self-supported silver electrode with a high-energy (200) surface, which improves the intrinsic activity for the hydrogen evolution reaction.
Al2O3 dispersion copper alloy powder was prepared by intemal oxidation, and three consolidation methods--high-velocity compaction （HVC）, hot pressing （HP）, and hot extrusion （HE）--were used to ...prepare Al2O3 dispersion-strengthened copper （Cu-Al2O3） alloys. The microstructures and properties of these alloys were investigated and compared. The results show that the alloys prepared by the HP and HE methods exhibited the coarsest and finest grain sizes, respectively. The alloy prepared by the HVC method exhibited the lowest relative density （98.3% vs. 99.5% for HP and 100% for HE）, which resulted in the lowest electrical conductivity （81% IACS vs. 86% IACS for HP and 87% IACS for HE）. However, this alloy also exhibited the highest hardness （77 HRB vs. 69 HRB for HP and 70 HRB for HE）, the highest compressive strength （443 MPa vs. 386 MPa for I/P and 378 MPa for HE）, and the best hardness retention among the investigated alloys. The results illustrate that the alloy prepared by the HVC method exhibits high softening temperature and good mechanical properties at high temperatures, which imply long service life when used as spot-welding electrodes.
Ultrasonic spot welded Cu/Cu joints with and without Cu nanoparticles (Cu NPs) interlayer were successfully achieved. Cu NPs interlayer, possessing the characteristics of high hardness and low melt ...point, could promote to eliminate the un-contacted areas in the weld interface and generate
more effectively net welded areas, leading to the increase of bond density. The peak T-peel force (279.6 N) of the Cu/Cu joint with Cu NPs interlayer was 18.3% higher than that (236.3 N) of the Cu/Cu joint without Cu NPs interlayer. In addition, for the Cu/Cu joint with Cu NPs interlayer,
only welded regions with obvious facture dimples could be observed in the fracture morphology.
This work was attempted to modify the current technology for thermal barrier coatings (TBCs) by adding an additional step of surface modification, namely, supersonic fine particles bombarding (SFPB) ...process, on bond coat before applying the topcoat. After isothermal oxidation at 1000 °C for different time, the surface state of the bond coat and its phase transformation were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectrometry (EDS), transmission electron microscopy (TEM) and Cr3+ luminescence spectroscopy. The dislocation density significantly increases after SFPB process, which can generate a large number of diffusion channels in the area of the surface of the bond coat. At the initial stage of isothermal oxidation, the diffusion velocity of Al in the bond coat significantly increases, leading to the formation of a layer of stable α-Al2O3 phase. A great number of Cr3+ positive ions can diffuse via diffusion channels during the transient state of isothermal oxidation, which can lead to the presence of (Al0.9Cr0.1)2O3 phase and accelerate the γ→θ→α phase transformation. Cr3+ luminescence spectroscopy measurement shows that the residual stress increases at the initial stage of isothermal oxidation and then decreases. The residual stress after isothermal oxidation for 310 h reduces to 0.63 GPa compared with 0.93 GPa after isothermal oxidation for 26 h. In order to prolong the lifespan of TBCs, a layer of continuous, dense and pure α-Al2O3 with high oxidation resistance at the interface between topcoat and bond coat can be obtained due to additional SFPB process.
The influence of the certain specific vacuum pre-oxidation process on the phase transformation of thermally-grown oxides (TGO) was studied. The CoCrAlY high temperature corrosion resistance coatings ...were produced onto the nickel-based superalloy substrate by high velocity oxygen fuel (HVOF). It suggests that the TGO usually consists of a great number of chromium oxides, cobalt oxides and spinel oxides besides alumina during the initial period of the high temperature oxidation if the specimens are not subjected to the appropriate vacuum pre-oxidation process. Furthermore, the amount of alumina is strongly dependent on the partial pressure of oxygen; while the CoCr2O4 spinel oxides are usually formed under the conditions of higher partial pressure of oxygen during the initial period and the lower partial pressure of oxygen during the subsequent period of the isothermal oxidation. After the appropriate vacuum pre-oxidation process, the TGO is mainly composed of alumina that contains lower Y element, while alumina that contains higher Y element sporadically distributes, and the spinel oxides cannot be found. After a longer period of the isothermal oxidation, a small amount of porous CoCr2O4 and the chrome oxide sporadically distribute near the continuous alumina. Additionally, after the appropriate vacuum pre-oxidation process, the TGO growth rate is relatively slow.
The measurement of fracture toughness of plasma-sprayed ceramic coatings is usually performed using a standard double cantilever beam approach. The design of specimen geometry using a tapered double ...cantilever beam (TDCB) approach makes the compliance of specimens be linearly proportional to crack length. Fracture toughness in terms of critical strain energy release rate can be obtained by measuring fracture load only. Three varieties of the TDCB specimens are used to examine the effect of the geometry and size of specimens on the results. These are simple TDCB, modified and long TDCBs. Plasma-sprayed Al
2O
3 coatings are used in test. It was found that linearly proportional relations are experimentally obtained between the compliance of the specimen and crack length for all three varieties of the TDCB samples. Fracture toughness of plasma-sprayed Al
2O
3 coating is independent on the geometry of the test piece used in the study. The TDCB approach is a simple and reliable approach to measure fracture toughness of thermal spray coatings without the measurement of crack length.
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