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Microstructural evolution and mechanical properties of an aging 6061 Al alloy subjected to laser shock processing treatment (post-aging LSP treatment) were investigated by transmission electron microscopy (TEM) and mechanical tests. Results showed that the precipitates formed during aging treatment still remained, and the grain was refined by the ultra-high plastic strain plastic deformation during subsequent LSP treatment. Moreover, the precipitates effectively interacted with the dislocations induced by LSP. These typical microstructures contributed to the improvement in mechanical properties of the Al alloy. Relatively higher microhardness and strength were observed for the post-aging LSP Al sample. Furthermore, the synergistic strengthening mechanism involving the interaction of precipitate with dislocation, dislocations, and refined grains were clearly revealed.

Semiconductor-based photocatalytic materials have emerged as promising candidates for solar-driven hydrogen production and oxygen evolution reactions. Direct Z-scheme photocatalysts offer competitive advantages that are superior to single-component or intensively studied heterojunction photocatalysts in photocatalytic water splitting. The development of high-performance direct Z-scheme photocatalysts is crucial to improving solar-driven water splitting efficiency. Herein, we report the fabrication of a novel g-C3N4/MoS2/Ag3PO4 ternary composite and its application in photocatalytic oxygen evolution under white light LED illumination. As-exfoliated, highly conductive two-dimensional molybdenum disulfide (2D MoS2) nanoflakes and modified graphitic carbon nitride (g-C3N4) nanosheets were employed simultaneously to couple with oxygen-evolving silver orthophosphate (Ag3PO4), forming a dual direct Z-scheme g-C3N4/MoS2/Ag3PO4 (CMA) composite photocatalytic system for highly improved oxygen evolution from water splitting. The optimal CAM-20 exhibits the fastest oxygen-producing rate of 232.1 μmol L-1 g-1 h-1, which is 5 times higher than that of bulk Ag3PO4. The enhancement in the photocatalytic oxygen evolution can be ascribed to synergistic effects of improved visible light absorption, more efficient separation of photoexcited electron-hole pairs and a specific charge transfer pathway of tandem dual direct Z-scheme configuration under light illumination. This work paves the way for the construction of direct Z-scheme composite photocatalytic systems in water splitting.

A facile approach to fabricate a surface nanocomposite structure by embedding SiC nano-particles (NPs) via laser micro-melting is reported. A high fidelity model is adopted to reveal transient temperature distributions and the embedding of the SiC NPs into an Al molten pool during laser micro-melting. Special attention is paid to the embedding dynamic behaviours within the molten pool affected by Marangoni convection. Fluid flow and migration characteristics of the SiC NPs into the molten pool, as well as the resultant bubble motion and pore defects formation, are considered. Simulation results show that the temperature distribution is basically symmetrical with respect to the laser beam, and the Marangoni convection in the molten pool tends to embed the SiC NPs into the Al surface layer together with gas bubbles. This phenomneon is well validated by the experimental study on the surface morphology and the SiC NPs distribution in the Al surface layer. Microstructural characterizations indicate that a relatively flat reinforced SiC/Al surface can be formed at an optimized laser energy of 0.6 J. These studies may provide a new strategy for constructing nanocomposite structure on metal alloy surface. Keywords: Laser micro-melting, SiC nano-particles (NPs), Simulation, Marangoni convection, Embedding dynamic behavior, Microstructure

Solar-driven water splitting over semiconductor-based photocatalysts provides direct conversion of solar energy to chemical energy, in which electron-hole separation and charge transport are critical for enhancing the photocatalytic activity of semiconducting materials. Moreover, the search for active photocatalysts that efficiently oxidize water remains a challenging task. Here, we demonstrate that a series of Ag 3 PO 4 /Ag/graphene/graphitic carbon nitride (g-C 3 N 4 ) heterostructured materials can drive photocatalytic water oxidation efficiently under LED illumination. The water oxidation behavior of as-prepared composite photocatalysts in relation to the added amount of g-C 3 N 4 and the roles of electron mediators was investigated in detail. Based on the illuminated Z-scheme photocatalytic mechanism, the photogenerated electrons and holes can be separated effectively and the electron-hole recombination of bulk material is suppressed. The reduced metallic Ag nanoparticles were found to function as the center for the accumulation of electrons from Ag 3 PO 4 and holes from g-C 3 N 4 . By exploiting the proper addition of g-C 3 N 4 into the composite, photocatalytic oxygen evolution performance over the heterostructured materials could be suitably tuned, which resulted in highly efficient water oxidation.

Semiconductor-based photocatalysis has been considered as one of the most effective techniques to achieve the conversion of clean and sustainable sunlight to solar fuel, in which the construction of novel solar-driven photocatalytic systems is the key point. Here, we report initially the synthesis of modified graphitic carbon nitride (g-C 3 N 4 ) nanorods via the calcination of intermediates obtained from the co-polymerization of precursors, and the in-situ hybridization of Ag 3 PO 4 with as-prepared modified g-C 3 N 4 to produce g-C 3 N 4 nanorod/Ag 3 PO 4 composite materials. The diameter of modified rod-like g-C 3 N 4 materials is determined to be around 1 μm. Subsequently the morphological features, crystal and chemical structures of the assembled g-C 3 N 4 nanorod/Ag 3 PO 4 composites were systematically investigated by SEM, XRD, XPS, UV–vis diffuse reflectance spectra (DRS). Furthermore, the use of as-prepared composite materials as the catalyst for photocatalytic oxygen evolution from water splitting was studied. The oxygen-generating results showed that the composite photocatalyst modified with 600 mg rod-like g-C 3 N 4 demonstrates 2.5 times higher efficiency than that of bulk Ag 3 PO 4 . The mechanism behind the enhancement in the oxygen-evolving activity is proposed on the basis of in-situ electron spin resonance (ESR) measurement as well as theoretical analysis. The study provides new insights into the design and development of new photocatalytic composite materials for energy and environmental applications.

Ni35 thin coatings were prepared on 40Cr steel by preset powder laser cladding technology. The effects of powder size and preset thickness on the dilution rate, microstructure, and properties of the coating were systematically studied. The results showed that the coating with smaller powder size and larger preset thickness had smaller grain size, denser microstructure, a flatter bottom of the molten pool, and lower dilution rate. The micro-hardness of the coating with large powder size and preset thickness was higher. The friction coefficient of the coating with small powder size and small preset thickness was smaller, but the latter had larger curve fluctuation and wear volume loss. The corrosion rate of the coating was high during the first 24 h, then relatively stable after 68 h, and the corrosion rate and loss of the coating with small powder size and large preset thickness were smaller.

The microstructure and wear behavior of AISI 304 stainless steel after Nd:YAG pulsed laser surface melting (LSM) were investigated. The microstructural features of the LSM layer were characterized by field emission scanning electron microscope and high-resolution transmission electron microscope. Experimental results showed that the microstructure was obviously refined to the nano- and sub-micrometer scales on the AISI 304 stainless steel surface after LSM treatment. Fine grains with grain size of less than 200 nm were obtained when the applied laser energy densities were in the range of 1.90 × 1 0 7 to 3.52 × 1 0 7 J / m 2 during LSM. The results indicated that the calculated surface temperature, cooling rate, and measured grain size are closely related to the adopted laser energy densities. The lower the laser energy density is, the lower the surface temperature, and the faster the cooling rate, the finer the grain size. In addition, the microhardness and wear resistance of the stainless steel was significantly improved. Finally, the wear mechanism after LSM process was revealed.

Oxygen evolution has been considered as the rate-determining step in photocatalytic water splitting due to its sluggish four-electron half-reaction rate, the development of oxygen-evolving photocatalysts with well-defined morphologies and superior interfacial contact is highly important for achieving high-performance solar water splitting. Herein, we report the fabrication of Ag3PO4/MoS2 nanocomposites and, for the first time, their use in photocatalytic water splitting into oxygen under LED light illumination. Ag3PO4 nanoparticles were found to be anchored evenly on the surface of MoS2 nanosheets, confirming an efficient hybridization of two semiconductor materials. A maximum oxygen-generating rate of 201.6 μmol · L-1 · g-1 · h-1 was determined when 200 mg MoS2 nanosheets were incorporated into Ag3PO4 nanoparticles, which is around 5 times higher than that of bulk Ag3PO4. Obvious enhancements in light-harvesting property, as well as electron-hole separation and charge transportation are revealed by the combination of different characterizations. ESR analysis verified that more active oxygen-containing radicals generate over illuminated Ag3PO4/MoS2 composite photocatalysts rather than irradiated Ag3PO4. The improvement in oxygen evolution performance of Ag3PO4/MoS2 composite photocatalysts is ascribed to wide spectra response in the visible-light region, more efficient charge separation, and enhanced oxidation capacity in the valence band (VB). This study provides new insights into the design and development of novel composite photocatalytic materials for solar-to-fuel conversion.

Novel morphologies of chromium sesquioxide (Cr2O3) were successfully formed on AISI 304 stainless steel surface by Nd: YAG pulsed laser oxidation in air. The obtained Cr2O3 presented mainly dendritic, gear-like, flower-like and regular hexagonal morphologies with sizes from hundred nanometers to several micrometers. These various morphologies chiefly originated from two groups of diverse growth directions within (0 0 0 1) basal plane, i.e., 〈 2 1 ¯ 1 ¯ 0 〉 and 〈 0 1 1 ¯ 0 〉 directions. The preferential growth along different directions determined the final Cr2O3 morphologies. And the crystallographic analyses basically accorded with the experimental results. Moreover, the growth mechanism of the hexagonal Cr2O3 was analyzed in detail from its morphology evolution, and a corresponding growth model was reasonably proposed.

We evaluated the electrochemical performances of LaNiFeO (LNFO) and LaNiCoO (LNCO) perovskites as cathodes in LaSrGaMgO (LSGM) electrolyte-supported solid oxide fuel cell. Both samples show excellent chemical compatibility with the LSGM electrolyte up to 900 °C, and exhibit small-polaron type electrical conduction with a high conductivity σ ≈ 510 (430) S·cm at 800 °C and a small activation energy E = 54.9 (44.4) meV for LNFO (LNCO). The oxygen-reduction reaction evaluated in a symmetric LNFO(LNCO)|LSGM|LNFO(LNCO) cell gives a polarization resistance R ≈ 0.51 (0.34) Ω·cm at 800 °C in air and an activation energy E = 1.61 (1.87) eV. For a single cell composed of LNFO (LNCO) cathode, 300-μm-thick LSGM electrolyte, and a composite Ni + Gd-doped ceria anode, the maximum power densities reach P = 490 (650) and 850 (1015) mW·cm at 800 and 850 °C, respectively. These results demonstrated that LNFO and LNCO are promising cathode materials for the IT-SOFCs., This work was supported by the National Science Foundation of China (Grant No. 51402019, 51573021) and Beijing Natural Science Foundation (Grant No. 2152011). HQL is supported by the project about the promotion of innovation in Beijing universities funded by Beijing Municipal commission of education of China (Grant No. TJSHG201510017024). JAA grateful acknowledges the Spanish MINECO for granting the project MAT2013-41099-R. JBG was supported by the Robert A. Welch Foundation, Houston, TX (Grant No. F-1066).

Sintered Nd–Fe–B magnets with and without Dy2O3 were prepared by powder blending method. The temperature-dependent magnetic properties, thermal stability, microstructure and corrosion resistance of sintered magnets were investigated. The temperature-dependent magnetic properties revealed that with intergranular addition of Dy2O3, the reversible temperature coefficients β and α in the range of 293–373 K were both lowered, indicating that the thermal stability was effectively improved. This was also verified by the decreased irreversible flux loss (hirr) and the increased maximum operating temperature (MOT). Moreover, the electrochemical and accelerated corrosion results clearly evidenced that the corrosion resistance of Nd–Fe–B magnet was also modified by addition of Dy2O3. Furthermore, the related mechanisms on improved thermal stability and corrosion resistance were systematically discussed.

A novel method, laser shock processing coating (LSPC), has been developed to fabricate a particle-reinforced coating based on laser shock processing (LSP). In this study, a nano-SiC coating is successfully prepared on pure Al surface via LSPC. The surface and cross section morphologies as well as the compositions of nano-SiC coating are investigated. Moreover, a finite element method (FEM) is employed to clarify the formation process of nano-SiC coating. On the basis of the above analyzed results, a possible formation mechanism of the nano-SiC coating is tentatively put forward and discussed. Furthermore, the nano-SiC coating shows superior microhardness over the Al substrate.

Surface oxidation phenomenon of AISI 304 stainless steel induced by Nd:YAG pulsed laser in air was investigated using scanning electron spectroscopy (SEM), high resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that there were different morphologies and phase compositions in one laser spot from the center to the edge on stainless steel surface after pulsed laser oxidation. The morphologies were mainly nano-spheres and hexagons. It was proved using XRD that they were basically γ-Fe, Cr 2 O 3 , Fe 2 O 3 and a small amount of MnO 2 . The elemental compositions in the edge region were rich in Cr and deficient in Fe, while it had an opposite distribution trend in the center of the laser spot. XPS measurement confirmed the formed oxides on the stainless steel surface, indicating that most of the elements were in oxidation states. Moreover, the oxidation behavior of the stainless steel in one laser spot was assessed using thermodynamics and kinetics of laser oxidation process. And the oxidation mechanism was also clearly revealed.

The butt welding of 304 stainless steel plates with thickness of 3 mm and 6 mm were achieved by YLR-6000 fiber laser under Ar protective gas. The weld appearance, microstructure, composition distribution and microhardness of welded joint were emphatically investigated. The results showed that the narrow and fully penetrated welded joint without marco-defects can be obtained with tightly focused 2 kW fiber laser power and 20 mm/s welding speed. The weld bead was smooth, and various microstructures typically formed at different zones of the welded joint. The fine columnar and equiaxed crystals existed in the edge and center of weld bead, respectively. Both were different with the microstructure of the stainless steel substrate. However, the composition distribution of the welded joint had no obvious changes. Furthermore, the superior microhardness of welded joint over the stainless steel substrate was mainly attributed to its finer microstructure.

Different surface morphologies on AISI 304 stainless steel have been obtained after millisecond Nd:YAG pulsed laser oxidation. The effects of laser processing parameters, especially pulse width and laser energy density on the surface morphologies of the stainless steel were emphatically investigated. The results showed that surface morphologies were significantly changed with increasing laser pulse widths and laser energy densities. When the pulse width was 0.2–1.0 ms and laser energy density was 4.30×10 6 –7.00×10 6 J/m 2 , the surface was obviously damaged and the morphologies varied gradually from craters to ripple structures. However, when the pulse width was longer than 1 ms and the laser energy density was increased from 1.90×10 7 to 3.16×10 7 J/m 2 , the sizes of craters got smaller until disappeared and the surface became flatter and smoother. Nevertheless, the smooth surface was not obtained under overhigh laser energy densities. In addition, the schematic relationship was used to describe the formation process and mechanism of different surface morphologies.

Different laser energy densities were utilized to treat AISI 304 stainless steel via Nd:YAG pulsed laser surface melting (LSM). The surface composition and microstructure of the stainless steel were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM). In particular, the corrosion behaviors of the stainless steel surface without and with LSM were evaluated by the electrochemical polarization measurement in 3.5 wt.% NaCl aqueous solution at room temperature. The results showed that the stainless steel surface without LSM suffered severe localized pitting under the testing conditions. A thin surface oxide protective layer was produced on the stainless steel surface with LSM, which considerably improved the corrosion resistance properties of the stainless steel. The height differences of the corrosion regions on the stainless steel surface with LSM were measured to establish more corrosion resistant region, using scanning confocal laser microscopy. The underlying corrosion mechanism of the stainless steel with LSM was revealed.

The laser surface melting (LSM) technique was adopted to modify the surface layer microstructure of the AISI 304 stainless steel in this paper. The results showed that the hexagonal morphologies have been successfully fabricated on the surface after LSM. These hexagons had side lengths of about 0.5–1 μm and were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), field emission scanning electron microscope (FESEM) and high resolution transmission electron microscope (HRTEM). It was proved by the XRD that the stainless steel surface mainly consisted of γ-Fe, Cr2O3, Fe2O3 and some manganese oxides. The FESEM micrographs showed that the hexagonal oxides were regular hexagons in geometry. The HRTEM micrographs also indicated the presence of the hexagons on the surface of the stainless steel. The spacing values were calculated from the HRTEM micrograph and the SAED pattern, and the hexagonal oxide phases determined by these spacing values were consistent with those verified by the XRD. After LSM, the microhardness of the stainless steel was significantly improved.

To improve the corrosion resistance and magnetic properties, Al85Cu15 (at.%) compound powders were added to (Pr, Nd)14.8Fe78.7B6.5 sintered magnets as grain boundary modifiers. The corrosion resistance was found to be remarkably improved by small additions of Al85Cu15 powders. When 1.2 wt% Al85Cu15 was added, the corrosion rate of magnets in humid environments was reduced by two orders of magnitude. This is partly due to the stability enhancement of the (Pr, Nd)-rich intergranular phase by Cu and Al. In addition, the occurrence of the Cu-rich phase ((Pr, Nd)22Fe56Cu10Al2O10), whose open-circuit potential is higher than the (Pr, Nd)-rich intergranular phase, may be another reason for the improvement of the corrosion resistance. Furthermore, the magnetic properties of (Pr, Nd)14.8Fe78.7B6.5 were also improved by adding 0.3–1.2 wt% Al85Cu15. Optimum addition amount was 0.6 wt%. The improvement of the magnetic properties may be related to the microstructural modification and the increase of magnet density.

To improve the magnetic properties and corrosion resistance of magnet, SiO 2 nanopowders were added into Nd 28.25 Dy 2.75 Fe bal Al 0.15 Ga 0.1 Nb 0.1 B 0.98 -sintered magnets as grain boundary modifiers. It was found that the intrinsic coercivity ( H cj ), remanence ( B r ) and corrosion resistance were all improved with addition of certain amount of SiO 2 nanopowders. The optimum addition amount of SiO 2 nanopowders was found to be 0.01 wt%. Thermodynamic calculation in combination of energy dispersive X-ray spectroscopy (EDX) analyses indicated that SiO 2 nanopowders reacted with Nd of Nd-rich phase. As a result, the intergranular phase was modified, and the grain growth of main phase was restrained. It led to the optimization of microstructure.

To decrease the temperature coefficients of sintered Nd-Fe-B magnets, the influencing factors on temperature coefficients, especially the reversible temperature coefficient ? of intrinsic coercivity Hcj, were analyzed. The results showed that the absolute value of ? decreased with increasing Hcj and also the ratio of microstructure parameter c to Neff, indicating that the increase of magnetocrystalline anisotropy field HA and c/Neff can effectively decrease the absolute value of ?. On the basis of this analysis, a sintered Nd-Fe-B magnet with a low temperature coefficient of Hcj was fabricated through composition design, and the value of ? was only -0.385%/?C in the temperature interval of 20-150?C.

Sintered permanent magnets have been prepared by blending Nd–Fe–B jet-milled powders with Cu nanopowders (0, 0.05, 0.1 and 0.2 wt%) before pressing in a perpendicular magnetic field. Permanent magnetic properties, Curie temperature ( T c ), microstructures and corrosion resistance of the sintered magnets were investigated. Microstructural characterization revealed that the grain size of Nd 2 Fe 14 B phase was refined and more homogeneous, and the grain boundaries became clear and smooth by the addition of Cu nanopowders, resulting in the improvement of coercivity H c j . Moreover, the corrosion resistance of Nd–Fe–B magnets was also improved. However, T c remained nearly unchanged with Cu addition, which was consistent with the elemental analysis results. Cu was not detected in the matrix phase Nd 2 Fe 14 B, but concentrated in the intergranular region.