Microstructure and Properties of Magnesium Alloy Joints Bonded by Using Gallium with the Assistance of Ultrasound at Room Temperature.

Although magnesium alloys show potential as structural and functional materials, they are difficult to join using traditional welding methods because of their low melting points and active chemical properties. Their poor weldability impedes their universal application. Ultrasound-assisted transient liquid-phase bonding (U-TLP) is a novel method used for magnesium alloy bonding, but in almost all related studies, a heating device has been required, and the types of solders are limited. In this study, gallium was used as solder to bond AZ31 magnesium alloy with ultrasonic assistance at room temperature (without a heating device) due to the low melting temperature of gallium and its compatibility with other metals when forming intermetallic compounds (IMCs). The variations in the products, microstructure, fracture characteristics, and shear strength of the joints were investigated. A reliable joint composed of IMCs (Mg2Ga5, H-MgGa2, and Mg2Ga) and a eutectic structure was obtained after an ultrasonic duration of 3 s. Significantly, the plasticity of the joint was improved due to ultrasonic effects, which included the accelerated element diffusion process, the refinement of grains to nanometer particles, and the homogenization of organization. Thus, the highest shear strength of 14.65 MPa at 4 s was obtained, with obvious cleavage fracture characteristics in the region of the IMCs.

The Effect of Buffer Types on the In0.82Ga0.18As Epitaxial Layer Grown on an InP (100) Substrate.

In0.82Ga0.18As epitaxial layers were grown on InP (100) substrates at 530 °C by a low-pressure metalorganic chemical vapor deposition (LP-MOCVD) technique. The effects of different buffer structures, such as a single buffer layer, compositionally graded buffer layers, and superlattice buffer layers, on the crystalline quality and property were investigated. Double-crystal X-ray diffraction (DC-XRD) measurement, Raman scattering spectrum, and Hall measurements were used to evaluate the crystalline quality and electrical property. Scanning electron microscope (SEM), atomic force microscope (AFM), and transmission electron microscope (TEM) were used to characterize the surface morphology and microstructure, respectively. Compared with the In0.82Ga0.18As epitaxial layer directly grown on an InP substrate, the quality of the sample is not obviously improved by using a single In0.82Ga0.18As buffer layer. By introducing the graded InxGa1−xAs buffer layers, it was found that the dislocation density in the epitaxial layer significantly decreased and the surface quality improved remarkably. In addition, the number of dislocations in the epitaxial layer greatly decreased under the combined action of multi-potential wells and potential barriers by the introduction of a In0.82Ga0.18As/In0.82Al0.18As superlattice buffer. However, the surface subsequently roughened, which may be explained by surface undulation.

The relationship between the dislocations and microstructure in In0.82Ga0.18As/InP heterostructures.

In this work, we propose a formation mechanism to explain the relationship between the surface morphology (and microstructure) and dislocations in the In0.82Ga0.18As/InP heterostructure. The In0.82Ga0.18As epitaxial layers were grown on the InP (100) substrate at various temperatures (430 °C, 410 °C and 390 °C) using low pressure metalorganic chemical vapor deposition (LP-MOCVD). Obvious protrusions and depressions were obseved on the surface of the In0.82Ga0.18As/InP heterostructure because of the movement of dislocations from the core to the surface. The surface morphologies of the In0.82Ga0.18As/InP (100) system became uneven with increasing temperature, which was associated with the formation of dislocations. Such research investigating the dislocation of large lattice mismatch heterostructures may play an important role in the future-design of semiconductor films.

Seeded preparation of ultrathin FeS2 nanosheets from Fe3O4 nanoparticles.

FeS2 nanomaterials with two-dimensional features hold great promise for electrochemical and photovoltaic applications. However, the preparation of ultrathin FeS2 nanosheets is still challenging because of the lack of a tailor-made approach. In this work, FeS2 nanosheets with a thickness of 2.1 nm are prepared through a Fe3O4-seeded approach. Uniform Fe3O4 nanoparticles are foremost synthesized via the standard method in organic media. The injection of a S solution leads to the replacement of O in Fe3O4 through anion-exchange, which generates (110) facet-enriched FeS2 nuclei. The subsequent (110) facet-mediated oriented attachment and fusion of FeS2 nuclei produce ultrathin FeS2 nanosheets. As catalysts in the hydrogen evolution reaction, FeS2 nanosheets exhibit good electrochemical activity.

Colloidal synthesis of greigite nanoplates with controlled lateral size for electrochemical applications.

The excellent electrochemical performance of greigite (Fe3S4) coupled with its vast abundance and low toxicity make it a good prospect as an anode material for lithium ion batteries (LIBs). In this research, a simple and feasible approach for producing pure phase, small sized, shape-controllable, and stable Fe3S4 nanoplates (NPs) through hot injection of sulfur solution into Fe(iii) solution was demonstrated. The growth of Fe3S4 NPs involves the primary formation of a pyrite (FeS2) nucleus and subsequent Fe(iii) doping. The lateral size of the Fe3S4 NPs was controlled further by tuning the experimental variable-dependent reactivity of Fe sources in the nucleation and growth stage. The Fe3S4 NPs embedded in LIBs present a low electrochemical resistance and are highly active in lithiation/delithiation processes.