Solid-state additive manufacturing and repairing by cold spraying: A review

High-performance metal additive manufacturing (AM) has been extensively investigated in recent years because of its unique advantages over traditional manufacturing processes. AM has been applied to form complex components of Ti, Fe or Ni alloys. However, for other nonferrous alloys such as Al alloys, Mg alloys and Cu alloys, AM may not be appropriate because of its melting nature during processing by laser, electron beam, and/or arc. Cold spraying (CS) has been widely accepted as a promising solid-state coating technique in last decade for its mass production of high-quality metals and alloys, and/or metal matrix composites coatings. It is now recognized as a useful and powerful tool for AM, but the related research work has just started. This review summarized the literature on the state-of-the-art and problems for CS as an AM and repairing technique.     

基于图像处理的骨架提取算法的应用研究

骨架在图像分析与形状描述中是一个非常重要的变换,是图像几何形态中普遍存在而又难以描述的重要拓扑结构。骨架提取技术在图像处理学领域一直是人们关注的焦点。在广泛调研文献的基础上,对骨架提取方法进行了较为全面的综述,重点总结了其在农业领域中的应用,并对骨架提取技术在其他方面的应用也进行了概述。最后指出了目前存在的问题以及骨架提取算法的主要发展趋势,并对其进行了总结和展望,以期为该领域的发展和相关研究提供借鉴与参考。     

A Simple Electrode‐Level Chemical Presodiation Route by Solution Spraying to Improve the Energy Density of Sodium‐Ion Batteries

The formation of a solid electrolyte interface (SEI) on the surface of a carbon anode consumes the active sodium ions from the cathode and reduces the energy density of sodium‐ion batteries (SIBs). Herein, a simple electrode‐level presodiation strategy by spraying a sodium naphthaline (Naph‐Na) solution onto a carbon electrode is reported, which compensates the initial sodium loss and improves the energy density of SIBs. After presodiation, an SEI layer is preformed on the surface of carbon anode before battery cycling. It is shown that a large irreversible capacity of 60 mAh g^?1 is replenished and 20% increase of the first‐cycle Coulombic efficiency is achieved for a hard carbon anode using this presodiation strategy, and the energy density of a Na_0.9[Cu_0.22Fe_0.30Mn_0.48]O₂||carbon full cell is increased from 141 to 240 Wh kg^?1 by using the presodiated carbon anode. This simple and scalable electrode‐level chemical presodiation route also shows generality and value for the presodiation of other anodes in SIBs.     

Production of Flexible Transparent Conducting Films of Self‐Fused Nanowires via One‐Step Supersonic Spraying

Scalable and economical manufacturing of flexible transparent conducting films (TCF) is a key barrier to widespread adoption of low‐cost flexible electronics. Here, a simple, robust, and scalable method of flexible TCF formation using supersonic kinetic spraying is demonstrated. Silver nanowire (AgNW) suspensions are sprayed at supersonic speed to produce self‐sintered films of AgNWs on flexible substrates. These films display remarkably low sheet resistance, <10 Ω sq^?1, combined with high transmittance, >90%. These electrically conducting, transparent, and flexible coatings can be deposited over a 100 cm² area in ≈30 s. Theoretical analysis reveals the underlying physical mechanism behind self‐sintering, showing that self‐sintering is enabled by the high velocity of impact in supersonic spraying.     

Thermal cycling behavior of nanostructured 8YSZ，SZ/8YSZ and 8CSZ/8YSZ thermal barrier coatings fabricated by atmospheric plasma spraying

The nanostructured single-ceramic-layer (SCL) 8YSZ thermal barrier coatings (TBCs), double-ceramic-layer (DCL) Sm₂Zr₂O₇ (SZ)/8YSZ and SZ doped with 8 wt% CeO₂ nanoscale particles (8CSZ)/8YSZ TBCs were fabricated by atmospheric plasma spraying (APS) on nickel-based superalloy substrates with NiCoCrAlY as the bond coating. The thermal cycling behavior of the three as-sprayed TBCs was investigated systematically at 1000 ℃ and 1200 ℃. The results reveal that the thermal cycling lifetime of the nanostructured DCL 8CSZ/8YSZ TBCs is the longest among them, which is largely due to the fact that the intermediate layer buffer effect of the DCL structure, more porosity and improvement of thermal expansion coefficient from doping CeO₂ nanoparticles can relieve thermal stress to a great extent at elevated temperature. The failure mechanism of the nanostructured TBCs has been discussed in detail.     

Structure and mechanical properties of hydroxyapatite coatings produced on titanium using plasma spraying with induction preheating

Coatings of hydroxyapatite (HAp) were prepared by plasma spraying with induction preheating of titanium substrate from 200 to 1000 °C. The combination of conventional plasma spraying and induction preheating ensured high mechanical properties of HAp coatings. The coatings produced in the temperature range 400–600 °C were characterized by homogeneous nanostructure of splats with an average grain size of 12–31 nm. According to the results of nanoindentation HAp coatings with high hardness 0.9–1.2 GPa and elastic modulus 7–16 GPa were formed on the titanium.     

机器人喷涂流水线上的工序能力设计

从机器人的喷房尺寸、动作方式、运枪速率、喷涂效率等参数设计方面讨论了机器人喷涂流水线上的工序能力设计。     

Microwave processing of sprayed alumina composite for enhanced performance

To meet the challenging in-service requirements, surfaces of many mechanical components need to be modified. This can be achieved by altering the surface properties through deposition technique followed by suitable post processing. Apart from the conventional methods, laser treatment is the most popular post processing technique. Of late, microwave heating is emerging as one of the potential post processing sources. Microwave processing of materials is fundamentally different from traditional techniques. In microwave processing, energy is directly transferred to the material through interaction of electromagnetic waves with molecules leading to volumetric heating. However, for processing of transparent (to microwaves) materials, a technique known as microwave hybrid heating (MHH) can be used. In this study, MHH is used for post processing of plasma deposited alumina–titania ceramic composite coatings on steel substrate; resulting properties of the post processed coatings are evaluated. Results show reduction in porosity, enhancement in microhardness, and wear resistance of the irradiated coatings owing to microstructural changes and densification. Results are discussed with suitable illustrations.     

Investigation of Plasma-Sprayed Dysprosia Coatings

Plasma-sprayed coatings of dysprosia were made and characterized. The coatings consisted mostly of the metastable, monoclinic phase and minor amounts of the cubic phase. Grinding did not transform the high-temperature monoclinic phase, but, on annealing in air at 800° for 5 h, 50% reversion to the cubic phase occurred. Commercial yttria-stabilized zirconia thermal barrier coatings out-performed unannealed plasma-sprayed dysprosia coatings in terms of wear resistance.     

均相沉淀法制备纳米Al2O3先驱体

以分析纯硫酸铝铵和碳酸氢铵为原料，采用均相沉淀法制备纳米Al23先驱体。结果表明，溶液的混合方式，超声振动，陈化时间对粉体的尺寸和形貌有很大的影响。采用先缓慢滴加，然后喷雾混合的方式可获得平均粒径为10mm的NH4Al(OH)2CO3粉体，并对粉体进行了扫描电镜（SEM），透射电镜（TEM），比表面积（BET），X射线衍射（XRD），红外光谱分析（IR），热重／差热（TG／DTA）等表征。