Investigation and Improvement Strategies for Mold Fracture: A Study on the Application of a Pulse Electrodeposition Method for Enhancing Mold Lifespan.

An investigation on the fracture of a mold, comparing it with a normal part using specific techniques, such as EDX, SEM, and AES, is presented in this study. The EDX analysis revealed that the composition of the normal part was consistent with that of low-carbon steel, mainly comprising Fe and C. In contrast, the fractured part exhibited cracks due to nonconforming nonmetallic inclusions and reticular carbides, with fractures resulting from microporosity agglomeration and cleavage fracture. The SEM and AES analyses further presented the causes of mold fracture, highlighting the mechanism by which the dimples on the specimen edge contributed to the fracture. The EDX analysis confirmed that the mold experienced thermal brittleness during use. To enhance mold durability and extend its lifespan, a pulse electrodeposition method was employed to create a NiCo alloy coating as a replacement for the Cr layer on the metal surface. The coating exhibited a smooth and scratch-free surface. The prepared NiCo special coating significantly increased the mold yield strength by approximately 313.8%, facilitated a 13% increase in plastic deformation, and reduced the fracture strain by 25%, effectively preventing mold fracture and improving its service life.

Preparation of shape-controlling VO2(M/R) nanoparticles via one-step hydrothermal synthesis.

In this study, we developed a facile one-step hydrothermal process that allows to synthesize high-purity VO2(M/R) nanoparticles with various morphologies such as nanorods, nanogranules, nanoblocks, and nanospheres. W dopants are successfully implanted in VO2(M/R) unit cells with high doping efficiency, which allows to regulate the size, morphology, and phase of obtained nanoparticles. The underlying regulation mechanism is presented in detail to reveal how hydrothermal products vary with W doping contents, which provides a synthetic strategy for the preparation of shape-controlling VO2(M/R) nanoparticles with high purity to satisfy different specific demands for corresponding applications in the field of thermochromic smart windows.

Supercapillary Architecture-Activated Two-Phase Boundary Layer Structures for Highly Stable and Efficient Flow Boiling Heat Transfer.

Development of smaller, faster, and more powerful electronic devices requires effective cooling strategies to efficiently remove ever-greater heat. Phase-change heat transfer such as boiling and evaporation has been widely exploited in various water-energy industries owing to its efficient heat transfer mode. Despite extensive progress, it remains challenging to achieve the physical limit of flow boiling due to highly transitional and chaotic nature of multiphase flows as well as unfavorable boundary layer structures. Herein, a new strategy that promises to approach the physical limit of flow boiling heat transfer is reported. The flow boiling device with multiple channels is characterized with the design of micropinfin fences, which fundamentally transforms the boundary layer structures and imparts significantly higher heat transfer coefficient even at high heat flux conditions, in which boiling heat transfer is usually deteriorated due to the development of dryout starting from outlet regions and severe two-phase flow instabilities. Moreover, the approaching of physical limit is achieved without elevating pressure drop.

Robust surface state transport in thin bismuth nanoribbons.

While a two-dimensional (2D) metallic surface state in bismuth has been proposed, experimental 2D evidence of quantum transport, e.g., angular dependent Shubnikov-de Haas (SdH) oscillations is still lacking. Here, we report the angular-dependent magnetoresistance measurements in single-crystal Bi nanoribbons, and found that both the low-field weak antilocalization behavior and the high-field angle-dependent SdH oscillations follow exactly the 2D character, indicative of the 2D metallic surface states which dominate the transport properties of thin Bi nanoribbons. Moreover, by controllable exposing the ribbons to ambient environment (1 atm and room temperature), the metallic surface states were found to be robust to the oxidation although the carrier density in the surface states are modified after the exposures. These results suggest that the metallic surface states in Bi nanoribbons should be topologically protected which can provide key information in understanding the surface properties of Bi in nanometer scale.

Evidence of topological two-dimensional metallic surface states in thin bismuth nanoribbons.

Understanding the exotic quantum phenomena in bulk bismuth beyond its ultraquantum limit remains controversial and gives rise to renewed interest. The focus of the issues is whether these quantum properties have a conventional bulk nature or just the surface effect due to the significant spin-orbital interaction and in relation to the Bi-based topological insulators. Here, we present angular-dependent magnetoresistance (AMR) measurements on single-crystal bismuth nanoribbons of different thicknesses with magnetic fields up to 31 T. In thin nanoribbons with thickness of ∼40 nm, a two-fold rational symmetry of the low field AMR spectra and two sets of 1/2-shifted (i.e., γ = 1/2) Shubnikov-de Haas (SdH) quantum oscillations with exact two- dimensional (2D) character were obtained. However, when the thickness of the ribbon increases, a 3D bulk-like SdH oscillations with γ = 0 and a four-fold rotational symmetry of the AMR spectra appear. These results provided unambiguous transport evidence of the topological 2D metallic surface states in thinner nanoribbons with an insulating bulk. Our observations provide a promising pathway to understand the quantum phenomena in Bi arising from the surface states.

One-dimensional weak antilocalization in single-crystal Bi2Te3 nanowires.

Angle-dependent magnetoconductance was measured on an individual surface-curved Bi2Te3 single-crystal nanowire fabricated by electrochemical deposition, where the evolution of surface conduction with wire diameters was investigated. It was found that the magnetoconductance of these nanowires in low field regime can be well described by one-dimensional (1D) weak antilocalization (WAL) model, where the dephasing length of the electrons follows T(-1/3) dependence but insensitive to the wire diameter. Meanwhile, such a 1D surface WAL was found to be enhanced significantly with the decrease of the wire diameter.

Synthesis, field-emission and electric properties of metastable phase VO2 (A) ultra-long nanobelts.

High quality single crystalline metastable phase VO(2) (A) ultra-long nanobelts were synthesized by hydrothermal method using inorganic V(2)O(5) sol as precursor and polyethylene glycol (PEG) as both surfactant and reducing agent. It was found that the oriented attach growth mechanism is responsible for the formation of VO(2) (A) nanobelts. In addition to an endothermic peak, an unusual exothermic peak was detected in DSC curve of the nanobelts. The temperature dependence of the lattice parameters have been studied, and it was found that the a-axis expands while the c-axis contracts in the high-temperature XRD test. The VO(2) (A) nanobelt has a low turn-on field of 3.8 V µm(-1) and a high field enhancement factor of 1739 in the field emission measurement. Electrical transport measurement of a single VO(2) (A) nanobelt gives a relative low hoping activation energy of 0.28 eV.