3D printing of Fe-based bulk metallic glass composites with combined high strength and fracture toughness

3D printing of crack-free high strength Zr-based bulk metallic glass composite by selective laser melting

Bulk metallic glasses (BMGs) being metallic materials without long-range order have attracted a considerable amount of interest from academia and industry in the past three decades due to their unique and outstanding properties. However, the manufacturing of glassy components with large dimension and complex geometries has remained a considerable challenge. The main obstructions in this regard arise from the oftentimes limited glass-forming ability (GFA) of most metallic systems, which requires extremely fast quenching of the corresponding melts and, consequently, limits the obtainable dimensions. In addition, BMGs generally have a poor machinability due to their intrinsic high hardness and extreme brittleness. The emerging 3D printing technology (also called additive manufacturing), as an advanced bottom-up manufacturing process, seems to be a viable route to circumvent these deficiencies inherent to conventional processing routes. Additive manufacturing theoretically allows the fabrication of large-sized BMGs and components with complex geometries, greatly extending the range of applications of BMGs as both structural and functional materials. The 3D printing technology has given fresh impetus to the field of BMGs and represents an approach, which is intensely explored in the BMG’s scientific community at the moment. In this review, we present a comprehensive overview of the state-of-the-art research on various aspects related to 3D printing of BMGs. It covers various 3D printing techniques for manufacturing BMGs, the microstructures (e.g. structural heterogeneities and fused-related defects) found in 3D-printed BMGs, the crystallization behavior in additively manufactured glasses and the associated alloy selection criterion, the observed mechanical properties and deformation mechanisms, and finally the functional properties and potential applications of 3D-printed BMGs and BMG matrix composites, in terms of catalysis, wear, corrosion, and biocompatibility. This article also identifies a number of key questions to be answered in the future in this important research direction in order to successfully bridge the gap from fundamental research to large-scale application of additively manufactured bulk metallic glasses.

3D printing of bulk metallic glasses

Nitrogen is an essential element to plants, animals, human beings and all the other living things on earth. Nitrogen fixation, which converts inert atmospheric nitrogen into ammonia or other valuable substances, is a very important part of the nitrogen cycle. The Haber-Bosch process plays the dominant role in the chemical nitrogen fixation as it produces a large amount of ammonia to meet the demand from the agriculture and chemical industries. However, due to the high energy consumption and related environmental concerns, increasing attention is being given to alternative (greener) nitrogen fixation processes. Among different approaches, plasma-assisted nitrogen fixation is one of the most promising methods since it has many advantages over others. These include operating at mild operation conditions, a green environmental profile and suitability for decentralized production. This review covers the research progress in the field of plasma-assisted nitrogen fixation achieved in the past five years. Both the production of NOx and the synthesis of ammonia are included, and discussion on plasma reactors, operation parameters and plasma-catalysts are given. In addition, outlooks and suggestions for future research are also given.

Recent Progress of Plasma-Assisted Nitrogen Fixation Research: A Review

Bulk metallic glasses are a fascinating class of metallic alloys with an isotropic amorphous structure that is rapidly quenched from liquid melts. The absence of a crystalline micro-structure endows them with a portfolio of properties such as high strength, high elasticity, and excellent corrosion resistance. Whereas the limited plasticity and hence poor workability at ambient temperature impede the structural application of bulk metallic glasses, the unique superplasticity within the supercooled liquid region opens an alternative window of so-called thermoplastic forming, which allows precise and versatile net-shaping of complex geometries on length scales ranging from nanometers to centimeters that were previously unachievable with conventional crystalline metal processing. Thermoplastic forming not only breaks through the bottleneck of the manufacture of bulk metallic glasses at ambient temperature but also offers an alluring prospect in micro-engineering applications. This paper comprehensively reviews some pivotal aspects of bulk metallic glasses during thermoplastic micro-forming, including an in-depth understanding of the crystallization kinetics of bulk metallic glasses and the thermoplastic processing time window, the thermoplastic forming map that clarifies the relationship between the flow characteristics and the formability, the interfacial friction in micro-forming and novel forming methods to improve the formability, and the potential applications of the hot-embossed micro-patterns/components.

Thermoplastic Micro-Forming of Bulk Metallic Glasses: A Review

A thermoplastic forming map of a Zr-based bulk metallic glass

Development and prospect of direct-current circuit breaker in China

In this paper, a new kind of coupling mechanical high-voltage direct current (HVDC) circuit breaker topology based on pulse transformer is proposed and its working principle is analysed in detail. On the basis of the requirement of 160 kV rated voltage, and 9 kA breaking current, the varying trend and design principle of parameters are given by the theoretical calculation. The prototype design of 160 kV HVDC circuit breaker is completed and type test passes. Results prove that the prototype of 160 kV HVDC circuit breaker has natural bi-directional breaking capacity. It can interrupt the current below 9 kA and withstand transient interruption voltage 272 kV. The breaking time is <5 ms.

Design and test of a new kind of coupling mechanical HVDC circuit breaker

Electrical tree structure is one of the most important influencing factors for electrical treeing characteristics in polymers. In this paper, we focused on the structure characteristics of electrical treeing in cross-linked polyethylene (XLPE) insulation under high-frequency voltages. The tree structure characteristics include structure distribution characteristics and structure conversion characteristics. The influences of voltage, frequency, and pin-plane spacing on tree structure characteristics were analyzed based on the experimental results. It can be concluded that tree structures regularly change with the local electric field and frequency. The electric field in a very small zone near the needle tip is an important influencing factor for the formation of bush-like trees, and the lowest frequencies for the observed pure-vine-like trees increased with voltage. For double-structure trees, the local electric field at the transition location of the two structures remained almost unchanged with voltage and pin-plane spacing, but obviously increased with frequency. In order to investigate the relations of the growth rate and fractal dimension with tree structure characteristics, a new parameter, the energy threshold W t , has been introduced and calculated for different tree structures.

Structure characteristics of electrical treeing in XLPE insulation under high frequencies

In order to meet the fast operation demands of DC circuit breakers, a high-speed vacuum mechanical switch (VMS) driven by a repulsive force actuator is focused. To improve the drive speed and energy conversion efficiency (ECE) of the actuators, the dynamic characteristics of the double sided coil repulsive force actuators are investigated, and two generalized optimization design methods focusing on the aspect ratio of the driving coils (defined as ARF) and the electrical parameters (defined as EF) are developed. FEM simulation models’ simulation and tests of VMS prototypes are conducted to verify the optimization methods. Results prove that the ARF method could improve the ECE of a VMS from 1.05% to 7.55%, and EF method could improve ECE of the same VMS from 1.05% to 6.61%, the combination of ARF and EF could improve the value of VMS’s ECE to 10.50%, thus proving the validity and accuracy of the optimization methods.

/pdf/research-on-ultra-fast-vacuum-mechanical-switch-driven-by-44xjg112b4.pdf

Research on ultra-fast vacuum mechanical switch driven by repulsive force actuator

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