No abstract

Magnesium (Mg) alloys have been extensively used in various fields, such as aerospace, automobile, electronics, and biomedical industries, due to their high specific strength and stiffness, excellent vibration absorption, electromagnetic shielding effect, good machinability, and recyclability. Friction stir processing (FSP) is a severe plastic deformation technique, based on the principle of friction stir welding. In addition to introducing the basic principle and advantages of FSP, this paper reviews the studies of FSP in the modification of the cast structure, superplastic deformation behavior, preparation of finegrained Mg alloys and Mg-based surface composites, and additive manufacturing. FSP not only refines, homogenizes, and densifies the microstructure, but also eliminates the cast microstructure defects, breaks up the brittle and network-like phases, and prepares fine-grained, ultrafine-, and nano-grained Mg alloys. Indeed, FSP significantly improves the comprehensive mechanical properties of the alloys and achieves low-temperature and/or high strain rate superplasticity. Furthermore, FSP can produce particle-and fiber-reinforced Mg-based surface composites. As a promising additive manufacturing technique of light metals, FSP enables the additive manufacturing of Mg alloys. Finally, we prospect the future research direction and application with friction stir processed Mg alloys.

new energy sources, such as hydrogen, has attracted much attention in recent years. [1][2][3] Electrochemical water splitting technology is a highly efficient and promising technology for green hydrogen production. The entire water-splitting process consists of a cathodic hydrogen evolution reaction (HER) and an anodic oxygen evolution reaction (OER). [4,5] The electrocatalyst is a key part in the process of driving the reaction and reducing power consumption. Conventional electrocatalysts are mainly based on rare precious metal nanomaterials, such as Pt, Ru, Rh, Ir, Pd and RuO 2 , IrO 2 , etc. They are considered to be the most efficient HER and OER electrocatalysts. [6][7][8] However, their high price and low abundance have led to limited large-scale applications in industry. Therefore, it is necessary to develop economical, stable, and highly active nonprecious metal catalysts as an alternative. 2D transition metal dichalcogenides (2D TMDs) materials based on earth-abundant elements have triggered a surge of research due to their unique optical and electrical properties. [9] Among them, MoS 2 , a typical representative of TMDs, has a hexagonal crystal system with a 2D structure, a narrow and flexible band gap, a peelable layered structure, a tunable active site, and a transformable phase structure (2H-MoS 2 to 1T/1T′-MoS 2 ), which are effective ways to improve its catalytic performance. [10][11][12][13][14][15] In theory, MoS 2 has a hydrogen adsorption-free energy close to that of the precious metal Pt. Being a non-precious metal material with both costeffectiveness and high efficiency, it is affirmed by researchers as a promising application in the field of hydrogen energy. [16,17] In the same way that the catalytic activity of most inorganic solid catalysts depends on the number and stable mass of active reaction sites, the catalytic activity of MoS 2 is limited by the sparse number of surface sites exposed by the layered structure, while the bulk material is relatively inert. [18] All possible catalytically active reaction centers of MoS 2 have been investigated as promising low-cost catalysts for applications. They are mainly the grain boundary sites located at the basal plane, the generation of sulfur vacancy defect sites, and the structurally undercoordinated molybdenum atomic sites at the edge plane. [19][20][21] It is well known that the (002) crystal plane is the main exposed basal plane of 2D MoS 2 . It has a centrosymmetric Mo-2S structure. Next is the (100) edge plane, which has high surface energy as well as a non-centrosymmetric Mo-2S structure with 2D molybdenum disulfide (MoS 2 ) is developed as a potential alternative non-precious metal electrocatalyst for energy conversion. It is well known that 2D MoS 2 has three main phases 2H, 1T, and 1T′. However, the most stable 2H-phase shows poor electrocatalysis in its basal plane, compared with its edge sites. In this work, a facile one-step hydrothermal-driven in situ porousizing of MoS 2 into self-supporting nano islands to maximally expose the e...

Numerous antibacterial biomaterials have been developed, but a majority of them suffer from poor biocompatibility. With the purpose of reducing biomaterial-related infection and cytotoxicity, friction stir processing (FSP) was employed to embed silver nanoparticles (Ag NPs) in a Ti–6Al–4V (TC4) substrate. Characterization using scanning electron microscopy, transmission electron microscopy, and three-dimensional atom probe tomography illustrates that NPs are distributed more homogeneously on the surface of TC4 as the groove depth increases, and silver-rich NPs with a size from 10 to 20 nm exist as metallic silver diffused into the substrate, where the silver content is 4.3–5.6%. Electrochemical impedance spectroscopy shows that both FSP and the addition of silver have positive effects on corrosion resistance. The modified samples effectively inhibit both Staphylococcus aureus and Escherichia coli strains and slightly reduce their adhesion while not displaying any cytotoxicity to bone mesenchymal stem cells in vitro. The antibacterial effect is independent of Ag-ion release and is likely due to the number of embedded silver NPs on the surface, which directly contact and subsequently destroy the cell membrane. Our study shows that the TC4/Ag metal matrix nanocomposite is a potential infection-related biomaterial and that embedding Ag NPs tightly on a biomaterial surface is an effective strategy for striking a balance between the antibacterial effect and biocompatibility, providing an innovative approach for accurately controlling the cytotoxicity of infection-related biomaterials.