物理气相沉积中等离子体参数表征的研究进展

物理气相沉积作为制备表面防护薄膜的重要方法,一直是表面薄膜领域研究重点,而物理气相沉积中等离子体作为直接影响薄膜性能的关键因素,其参数的表征对优化沉积工艺和提高薄膜性能具有重要指导意义.概述了常用物理气相沉积方法及其发展,包括电弧离子镀、磁控溅射和电弧磁控复合技术的原理及发展历程.归纳了目前生产中常用的等离子体参数表征方法——Langmuir探针法、汤姆逊散射法、微波干涉法和发射光谱法,阐明了这些表征方法诊断等离子体参数的原理,分析了不同表征方法的优缺点和存在的主要问题,并对常用物理气相沉积中等离子体参数表征相关研究的发展和现状作了综合论述和总结,分别整理了电弧离子镀和磁控溅射中等离子体参数诊断的发展历程和近期研究.两种物理气相沉积方法最常用的等离子体参数表征方法都是Langmuir探针法和发射光谱法,早期的研究侧重于探索等离子体瞬态参数和薄膜结构性能的关系.随着现代技术的进步,早期诊断方法不断与新技术融合,研究方向也逐渐偏向于研究等离子体参数的时间变化和优化薄膜工艺、性能评价方法.最后分析了当前物理气相沉积中等离子体参数表征存在的问题和不足,展望了等离子体参数未来的研究趋势.     

Research on the effects of surface modification of ceramic powder on cure performance during digital light processing (DLP)

Digital light processing (DLP) is one of the most important additive manufacture technologies to fabricate ceramic parts with complex geometries. Compared with pure photosensitive resin, the cure performance of ceramic suspensions is obviously different due to the optical property change after the addition of ceramic powders. In this paper, a unique oxidation process was used to modify the optical properties of nitride powders including AlN and Si₃N₄. The properties of oxidized ceramics were investigated and the cure performance of ceramic suspensions was then characterized. The effect of oxidation time on cure performance was evaluated. The results showed that for AlN, oxidation process leads to the smaller cure depth and smaller excess cure width as compared with non-oxidized AlN and for Si₃N₄, oxidation process leads to the larger cure depth and larger excess cure width as compared with non-oxidized Si₃N₄, indicating that both refractive index and light absorbance of ceramic powders have obvious effects on cure behaviors. Additionally, the cure behavior of oxidized ceramic suspension in this study shows that the relationship of cure depth vs. incident energy agrees well with Beer- Lambert model, but the excess cure width vs. incident energy is not consistent with quasi Beer-Lambert model due to the nature of digital micromirror device (DMD).     

Local microstructure of Ge layers buried in a silicon crystal studied by extended X-ray absorption fine structure

The local structure of Si-capped Ge quantum dots formed in Stranski–Krastanov growth mode on a (001) Si substrate was probed by X-ray absorption at the Ge K-edge. Analysis by extended X-ray absorption fine structure (EXAFS) was performed under the assumption of a solid solution model of the Si distribution inside the quantum dots (QDs) and taking into account polarization effects. It was found that QDs formed for 8 ML are strained and the Ge–Ge and Ge–Si bond lengths vary with direction. The Si content inside the QDs was found to be at a level of ∼25 at.% for strained (8 ML sample) QDs and ∼12 at.% for unstrained (10 ML sample) QDs. This work demonstrates the usefulness of EXAFS analysis for the determination of the local atomic structure in covered low-dimensional structures.     

Fabrication of piezoelectric nano-ceramics via stereolithography of low viscous and non-aqueous suspensions

A high-performance piezoelectric nano-ceramic was fabricated through stereolithography of low viscosity and high solid loading ceramic/polymer composite suspensions. Through the proper fitting calculation of experimental data, the maximum theoretical solid loading, rheological and curing behaviors of the suspension system were evaluated and lucubrated. The suspensions with a 40 vol% solid loading of the BaTiO₃ nanoparticles displayed shear thinning behavior and a relatively low viscosity of 232 mPa·s at 46.5 s⁻¹ shear rate. After post-process, the 3D printed ceramic specimens showed a nanometer-level grain size with a density of 5.69 g/cm³, which corresponds to about 95% of the theoretical density. The printed ceramics exhibit a piezoelectric constant of 163 pC/N and relative permittivity of 2762 respectively. The results achieved in this research indicate that the stereolithography process is a promising 3D printing technology to fabricate piezoelectric materials with complex geometries and exquisite features for the applications of ceramic components.     

高温防护涂层的熔盐热腐蚀研究进展

高温热腐蚀是热元件主要失效形式之一,Na₂SO₄和NaCl熔盐会加速高温下的热腐蚀,甚至导致灾难性事故发生。本文就Na₂SO₄和/或NaCl熔盐引起的热腐蚀进行了讨论,其中Na₂SO₄是主要的腐蚀反应物,详细介绍了2种典型的热腐蚀行为和性能特点。重点介绍了几种热腐蚀模型和机理,以及Na₂SO₄、NaCl、Na₂SO₄+NaCl熔盐的反应公式和腐蚀机理。根据目前的研究状况来看,制备防护涂层是缓解热腐蚀的最佳途径,总结了近年来MCrAlY涂层、NiAl涂层、热障涂层和新型涂层的发展情况,并探讨了进一步提高涂层耐腐蚀性能的方法。最后,展望了防护涂层的未来发展方向。     

In Brief

• United States Patent and Trademark Office
• Datakey
• Sun Microsystems
• Departments of Defense
• Interior
• NASA
• Department of Defense
• Frost & Sullivan
• Transport for London
• Cubic Transportation Systems Ltd
• London Buses
• Transport for London
• EDS
• TranSys
• Microsoft
• Network Associates
• Visa
• Verisign
• Amazon
• eBay
• Coalition on Online Identity Theft
• Federal Trade Commission
• Emosyn
• ATMI
• Bioscrypt
• Little Rock National Airport
• HID’s
• General Services Administration
• BearingPoint
• Marks and Spencer
• Intercede’s
• Infineon Technologies
• Cubic Corporation
• LaserCard Systems Corporation
• Drexler Technology Corporation
• Schlumberger Smart Cards & Terminals
• Visa
• ISO
• ANSI
• Open Security Exchange
• IEEE Industry Standards and Technology Organization
• Computer Associates
• Gemplus
• HID
• Tyco Fire & Security’s Software House
• Hypercom Corporation
• MasterCard’s
• Fazoli’s
• National Bank of Serbia
• Giesecke & Devrient
• GlobalPlatform
• ICC Solutions

     

Preparation of highly dispersive solid microspherical α-Al2O3 powder with a hydrophobic surface for stereolithography-based 3D printing technology

The present research demonstrates the feasibility of the preparation of a highly dispersive, solid microspherical α-Al₂O₃ powder with a hydrophobic surface using a simple, rapid, and low-cost method for stereolithography-based 3D printing technology, including the synthesis of a precursor based on the in situ hydrothermal reaction of aluminum sulfate and urea, heat treatment, and surface modification using sodium oleate. The dependence of the morphologies of the precursors and α-Al₂O₃ powders on the type of aluminum salt, reaction time, and temperature was studied. The formation conditions of the solid spherical structure were explored. The results indicate that the formation of a solid spherical structure strongly depends on the type of aluminum salt, reaction time, and temperature. A spherical structure is only obtained by mixing aluminum sulfate with urea. Very high reaction times and temperatures facilitate the transformation of the microstructure from a solid sphere to a hollow sphere. The optimum hydrothermal reaction conditions are as follows: aluminum sulfate concentration of 0.05 mol/L, urea concentration of 0.2 mol/L, reaction temperature of 120 °C, and reaction time of 2 h. The optimum surface modification is obtained by using 3 wt% of sodium oleate, which can be used for the preparation of a 50 vol% α-Al₂O₃ ceramic UV-curable suspension with a viscosity of 1.66 Pa s at 30 s^-1. An alumina part with a sintering density of 95.5% was fabricated using stereolithography-based 3D printing technology. The analysis of the formation mechanism of the solid spherical structure indicates that the high decomposition temperature of urea, homogeneous dissolution of urea in aluminium sulfate solution, slow OH^- release by urea in the hydrothermal system, and strong coordination ability of SO₄²⁻ effectively restrain the hydrolysis of Al³⁺ and facilitate the formation of the solid spherical precursor Al₄(OH)₁₀SO₄. The solid microspherical α-Al₂O₃ powder is prepared by heat treatment of the precursor.     

Cu含量对激光选区熔化CoCrMoCu合金微观组织及表面摩擦磨损性能的影响

目的 阐明不同Cu含量对激光选区熔化(Selective Laser Melting,SLM)制备的CoCrMoCu合金微观组织的影响及其在表面摩擦磨损和腐蚀性能使役行为方面的作用。方法 采用Co CrMo合金粉和纯Cu粉通过行星球磨机进行机械混合,制备了Cu质量分数为2%、4%、6%的CoCrMo/Cu混合粉末,并通过SLM技术制备相应的试样。对不同Cu含量的SLMCoCrMoCu的相组成、微观结构、硬度、摩擦磨损和腐蚀性能进行检测和分析。结果 Cu含量对SLMCoCrMoCu的相组成和微观组织没有明显影响,在不同Cu含量的试样中,试样的微观组织均主要为胞状等轴晶。在力学性能方面,随着Cu含量的升高,试样的硬度先提升后降低,在含2%Cu的情况下达到最大值(429.2HV0.2),在含6%Cu的情况下达到最小值(367.7HV0.2)。CoCrMoCu的摩擦因数和磨损率随着Cu含量的升高而降低,在4%时摩擦因数和磨损率达到最低(2.7×10^-5 mm³/(N·m)),摩擦磨损性能最好。随着Cu质量分数进一步增加到6%,由于硬度降低,磨损性能下...     

Fabrication of Al2O3/AlN composite ceramics with enhanced performance via a heterogeneous precipitation coating process

To improve the thermal and mechanical properties of Al₂O₃/AlN composite ceramics, a novel heterogeneous precipitation coating (HPC) approach was introduced into the fabrication of Al₂O₃/AlN ceramics. For this approach, Al₂O₃ and AlN powders were coated with a layer of amorphous Y₂O₃, with the coated Al₂O₃ and AlN powders found to favor the formation of an interconnected YAG second phase along the grain boundaries. The interconnected YAG phase was designed to act as a diffusion barrier layer to minimize the detrimental interdiffusion between Al₂O₃ and AlN particles. Compared with samples prepared by a conventional ball-milling method, the HPC Al₂O₃/AlN composites exhibited less AlON formation, a higher relative density, a smaller grain size and a more homogeneous microstructure. The thermal conductivity, bending strength, fracture toughness and Weibull modulus of the HPC Al₂O₃/AlN composite ceramics were found to reach 34.21 ± 0.34 W m⁻¹ K⁻¹, 475.61 ± 21.56 MPa, 5.53 ± 0.29 MPa m^1/2 and 25.61, respectively, which are much higher than those for the Al₂O₃ and Al₂O₃/AlN samples prepared by the conventional ball-milling method. These results suggest that HPC is a more effective technique for preparing Al₂O₃/AlN composites with enhanced thermal and mechanical properties, and is probably applicable to other composite material systems as well.