查看更多>>摘要：? 2022 Elsevier B.V.Zr co-doped TiO2:Ag nanoparticles were synthesized by the co-precipitation method and the influence of Zr co-dopant with varying content on the structural, optical and photocatalytic properties of TiO2:Ag photocatalysts was investigated. X-ray diffraction and Raman spectroscopy confirmed the anatase-rutile mixed phase of TiO2 and Zr content eased the anatase-rutile phase transformation. X-ray diffraction peak shift with Zr content indicated the substitutional doping of Zr4+ ions into TiO2 lattice. The optical properties of the nanoparticles were investigated with diffuse reflectance spectroscopy, photoluminescence and Fourier transform infrared spectroscopy. Zr dopants induced the Burstein-Moss effect, resulting in the broader bandgap and photoluminescence shift. X-ray photoelectron spectroscopy was utilized to reveal the surface chemical environment of the Zr co-doped TiO2:Ag nanoparticles and found the presence of Zr4+ ions on the photocatalyst surface, which act as electron traps. The dependence of operational parameters such as photocatalytic load, dye concentration and pH on Zr co-doped TiO2:Ag nanocatalyst was also monitored. The photocatalysts demonstrate improved photocatalytic activity toward methylene blue degradation with maximum efficiency achieved by the photocatalyst having the highest Zr content. 20 mg and 10.35 μM were found to be the optimum values for photocatalytic load and initial methylene blue concentration, respectively. Further, at alkaline pH, complete decolorization of the reaction mixture was observed in only 60 min with 92.6% efficiency by highest co-doped photocatalyst. The effect of Zr content on degradation rate with different parameters was also explored with a possible mechanism to understand the effect of dopants on photocatalytic activity of the photocatalysts.
查看更多>>摘要：? 2022 Elsevier B.V.The focus of this study is to fabricate thermal management materials integrating thermal and electrical structural and functional materials by preparing graphene film reinforced Cu laminated composites. Strengthening the interface is a core scientific issue. Graphene is considered a good reinforcement phase because of its excellent electrical and thermal conductivity. The production route includes electroless Cu coating on graphene film and ball milling Cu powder into Cu flake. Due to the particularity of the film and the Cu flake through vacuum hot pressing sintering, laminated composite materials can be obtained. The transfer of electrons and internal energy within a material determines the electrical and thermal conductivity of the material. With the increase of content of graphene films, electrical properties of laminated composites and thermal conductivity on the plane direction increase, while the thermal conductivity on thickness direction decreases. The best thermal conductivity and electric conductivity can reach 457 W m?1 K?1 and 175 MS/m, respectively. However, when the graphene films contents exceed 30 vol%, the thermal conductivity in the plane direction decreases due to the severe interfacial cracks. In summary, copper coating on the graphene films surfaces can generally improve the interfacial bonding and thermal properties of laminated composites. It provides an effective method to perform the development of novel thermal management structures and functional materials.
查看更多>>摘要：? 2022 Elsevier B.V.In this study, an Al/Cu/Sn/Ni multi-layer composite (MLC) was produced by a two-step process (i.e., accumulative roll bonding and subsequent heat treatment) for up to six cycles. The effect of the two-step process on the macro/microstructure of the Al/Cu/Sn/Ni MLC was investigated using optical microscopy, scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy, and x-ray diffraction pattern. The results show that the Ni and Sn layers in the sandwich cycle and the Cu layer in the 1st cycle fractured in the Al matrix. Finally, during the 6th cycle of the two-step process, a uniform distribution of Ni, Cu, and Sn reinforcement layers was achieved in the Al matrix. Moreover, during the 3rd cycle, an Al3Ni2 intermetallic compound was formed at the interface of the Al/Ni layer. Also, during the 6th cycle, in addition to the formation of the Al3Ni2, an AlCu intermetallic compound was formed at the interface of the Al/Cu layer. The recrystallization phenomenon in the Al matrix occurred during the sandwich, 3rd, and 6th cycles, too. In addition, during the various cycles, grain growth also occurred in the Al matrix so that the size of some grains in the Al matrix during the 3rd and 6th cycles reached about 2 and 1 μm, respectively.
查看更多>>摘要：? 2022 Elsevier B.V.Solid solution softening is an unusual adjustment behavior that is attractive for material strength. In this paper, the effect of boron alloying on the strength of Ti2AlC is investigated by first-principles calculations. Our results show that the elastic modulus and ideal strength of Ti2AlC decrease overall due to alloying with boron, which indicates that solid solution softening occurs. Conversely, ductility and plasticity of Ti2AlC are greatly enhanced by alloying with boron. This phenomenon in Ti2AlC is mainly related to the reduction of Peierls stress and generalized stacking fault energies caused by alloying with boron. Our work provides an ideal candidate platform to study the solid solution softening effect in ceramics and provides theoretical guidance for engineering applications of MAX phase materials.
查看更多>>摘要：? 2022 Elsevier B.V.To further understand the effect of Ta additive on the creep damage for polycrystalline Ni-base superalloys, creep rupture tests on powder metallurgy (PM) superalloys with various Ta were carried out under different conditions in this study. The results indicated that the multiple crack propagation and damage mechanisms could occur at the identical creep condition. These different fracture mode areas had distinct boundaries on the fracture surface, its size could be altered by Ta addition. However, the effects of Ta were radically changed by the creep conditions. The creep rupture mechanism transformed significantly with temperatures and applied stresses, and even subversive laws appeared in the creep life for high-Ta alloys. The substructure observation after creep rupture demonstrated that the annealing coherent twin boundaries gradually lose coherence with the matrix, which could become sites for cavities nucleation or crack propagation that followed. Furthermore, the creep-induced microtwins were critical for the creep damage and rupture. The electron back-scattered diffraction (EBSD), high-resolution transmission electron microscope (TEM) imaging, and quantitative elemental analysis assisted in comprehending these alterable creep rupture mechanisms.
查看更多>>摘要：? 2022 Elsevier B.V.The microstructure evolution and tensile behavior of Ti2AlNb alloy (Ti-22Al-23Nb-1Mo-1Zr) processed by two-pass hot extrusion and two-step heat treatment were investigated. After extruding deformation in the B2 phase field, the B2 grains were refined from about 1500–50 μm through dynamic recrystallization. The microstructures subjected to solution treatment in the B2 + α2 phase field and aging treatment in the B2 + O phase field include B2 matrix, lamellar O, rim O and lamellarα2/O phases. The microstructure and tensile properties are sensitive to aging temperature. As the increase of the aging temperature, the content of the B2 phase and the size of the lamellar O phase increase, resulting in low strength and high ductility. The alloy aged at 800 °C has a good match of strength and ductility. It has an elongation of 6.3% with a tensile strength as high as 1225 MPa due to the precipitation strengthening of numerous lamellar O phase and fine grain strengthening. The tensile fracture mode predominantly shows quasi-cleavage characteristics with typical cleavage facets and massive dimples, which is consistent with the good balance of tensile strength and ductility. An in-depth understanding of the relationship between microstructure and tensile properties in this study can be helpful for the engineering application of the Ti2AlNb alloy.
查看更多>>摘要：? 2022 Elsevier B.V.The effect of concentration on the charge storage of supercapacitors is one of the crucial parameters. In the current work, we have successfully deposited the 1D–3D aggregate structure of the nickel oxide (NiO) with its various content concentration of the nickel nitrate precursor on stainless steel (SS) via the simplest hydrothermal technique. The influence of the molarities of the NiO on the nanostructures as well as electrochemically charge storage applications has been studied. The X-Ray diffraction (XRD), scanning electron microscopy (SEM), and FTIR were used for structural, and morphological analysis of the nickel oxide. Here, we observed the cubic structure with the Fm-3 m space group of NiO nanomaterials. SEM images depict the 1D-columnar flakes along with aggregate 1D–3D morphology. The flakes like NiO nanomaterials exhibit a highly electrochemically charge storage pseudocapacitive nature. The optimized 0.40 M of NiO nanomaterial electrode shows the highest specific capacitance value is 639.3 Fg?1 at 5 mVsec?1 in aqueous 1 M KOH in an aqueous electrolyte. The observed maximum specific energy (SE) and specific power (SP) are 74.13 Whkg?1 and 2.07 KWkg?1. The optimized NiO//reduced Graphene Oxide (rGO) based asymmetric hybrid supercapacitor device (AsHSD) shows an excellent specific capacitance value is 34.8 Fg?1 with the highest charging-discharging capability of 83 % up to 100 cycles.
查看更多>>摘要：? 2022 Elsevier B.V.In this study, a sonochemical reactor was used to synthesize Mn1?xCuxLa0.1Fe1.9O4 nanoferrites with different compositions of x (0.09, 0.18, 0.27, and 0.36). Mn1?xCuxLa0.1Fe1.9O4 nanoferrites were subjected to X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), vibrating sample magnetometer, and electrochemical impedance spectroscopy to investigate their magnetic, electrical, and structural properties. Formation of a cubic crystalline structure was observed by the XRD patterns. The decreases in crystalline size could have been caused by an increase in Cu2+ ions in Mn1?xCuxLa0.1Fe1.9O4 nanoferrites. The impedance analysis revealed the presence of pseudocapacitance and resistive behavior in Mn1?xCuxLa0.1Fe1.9O4 nanoferrites. The hysteresis loops promoted the soft ferromagnetic behavior present in Mn1?xCuxLa0.1Fe1.9O4 nanoferrites. A decrease in saturation magnetization and an increase in coercivity were observed with an increase in the Cu2+ content of Mn1?xCuxLa0.1Fe1.9O4 nanoferrites.
查看更多>>摘要：? 2022 Elsevier B.V.Ultra-fine grained (UFG) hexagonal-close-packed (HCP) hafnium (Hf) and Hf-5 wt%Y2O3 (HYO) were prepared by a combination of high-energy ball milling and spark plasma sintering (SPS), and both possess high relative density (95–99%), high hardness, and low electrical conductivity. The HYO sample shows superior hardness of 12.11 GPa, which is about 6–7 times of that of coarse-grained Hf, and electrical conductivity of 2 × 105 S/m, which keeps constant and is almost independent of temperature. It is very possible for HYO with these good properties to become an excellent plasma torch cathode. The analysis of the microstructure under transmission electron microscope (TEM) and scanning electron microscope (SEM) shows that the superior hardness of the samples originates from the grain boundary (GB) strengthening and the pinning effects of the Y2O3 particles, while their almost temperature-independent electrical conductivity originates from the combining effects of the dispersion of large electrical resistivity particles Y2O3 and the dense high-angle grain boundaries (GBs).
查看更多>>摘要：? 2022 Elsevier B.V.With growing interest in Laser Additive Manufacturing (LAM) of High-entropy alloys (HEAs) during most recent years, compositional elements design and process strategies innovation are primary methods to overcome undesirable microstructures and defects. Here we propose a new approach, a novel real-time laser shock modulation of melt pool (LSMMP) to obtain melt pool modifications for yielding HEAs with desired characteristics. LSMMP utilizes a pulsed laser shocking a liquid melt pool caused by a continuous wave laser, enabling non-destructive and real-time modulations for high-performance HEAs. The numerical simulation reveals the convection mechanism of the melt pool in the LSMMP process, and the intervention of the pulsed laser promotes melt pool flow type to convert the Marangoni effect into a multi-convective ring, which accelerates melt pool flow and inhibits columnar crystal growth. Experimental results show the evolution law of the microstructure in the LSMMP process. The microstructure of CrFeCoNi HEAs undergoes a Columnar-Equiaxed Transition (CET), and higher hardness is obtained. Laser shock is demonstrated to be an effective in-situ modulative tool for controlled additive manufacturing.
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