热障涂层TGO界面应力分布及裂纹扩展行为的研究进展

热障涂层以其优异的抗氧化? 隔热? 耐腐蚀性而广泛应用于热端部件表面.在超过1000℃高温的服役环境下,外界的氧元素通过陶瓷层扩散到粘接层界面,与其中的金属元素发生氧化反应生成一层热生长高温氧化物(TGO)? 随着服役时间的增加,TGO不断生长,TGO界面产生较大的热应力,导致裂纹的萌生与扩展,使得涂层大面积剥落,因此TGO氧化失效的研究既是难点也是热点问题.总结了研究TGO界面建立的主要几种模型,例如同心圆界面模型? 曲线弦界面模型和真实界面模型,其中曲线几何结构通常只需要振幅和波长即可很好地描述界面,因此大多数模型建立采用了曲线模型.在此基础上,重点综述了界面形貌、界面粗糙度和TGO厚度对应力分布的影响,以及从应变能释放率和裂纹路径两个角度探讨了界面损伤行为.上述研究很好地阐明了TGO生长过程,但是仅考虑了形态特征对应力分布的影响,接下来的研究应考虑真实TGO界面并完善模拟的准确性,同时发展有限元技术实现在实际条件下裂纹扩展路径和使用寿命的预测.     

Structural characteristics and microwave dielectric properties of Zn1−xBixVxW1−xO4-based ceramics for LTCC applications

Herein, the improvement of the microwave dielectric properties and sintering characteristics of Zn_1?xBi_xV_xW_1?xO₄(x = 0–0.15)-based ceramics is reported. The results showed that an appropriate amount of doping could not only reduce the optimum sintering temperature from 1100° to 900°C, but also enhance the densification of the microstructures and increase the Q×f value from 5351 to 42525 GHz. Additionally, various structural parameters including the phase composition, crystal structure, vibrational and chemical bond characteristics that are correlated with the dielectric properties were systematically investigated. By considering the chemical bond characteristics, the first-principles calculations and the acquired Raman spectra, the interaction between W-O is stronger than Zn-O in the ZnWO₄ structure, while the interaction between V-O is stronger than Bi-O in BiVO₄. Interestingly, when the Zn_0.97Bi_0.03V_0.03W_0.97O₄-based ceramics were sintered at 900 °C, improved microwave dielectric properties were acquired (ε_r =18.32, Q×f=42525 GHz, τ_f=?67.51 ppm/°C), which provides a promising candidate in low-temperature co-fired ceramics technology.     

Cold sintering assisted CaF2 microwave dielectric ceramics for C-band antenna applications

A cold sintering process is adopted to pre-densify CaF₂ ceramics from 85.7% at 300 MPa to 91.7% at 750 MPa. Subsequent post-annealings at 1000–1150 °C lead to further improvements in densification, where great enhancements of grain size and crystallinity are also observed from the scanning and transmission electron micrographs. Significant advances in Qf values are achieved in the post-annealed CaF₂ ceramics. The optimum Qf value (80,522 GHz) is achieved after cold sintering at 750 MPa and post-annealing at 1000 °C, which is three times higher than the conventional sintered one at 1000 °C (26,448 GHz). Moreover, the obtained low-ε_r (5.9–6.5) of CaF₂ ceramics suggests broad application prospects in the high-band microwave communications. A microstrip patch antenna is fabricated using the CaF₂ ceramics as the substrate, which operates at 7.89 GHz in the C-band, with an S₁₁ of ?13.4 dB, simulated high gain and efficiency of 6.41 dBi and ?0.56 dB, respectively.     

基于知识库的输电线路巡检机器人的越障控制

介绍了一种高压输电线路巡检机器人越障控制方法。高压输电线路巡检机器人在翻越同一障碍物时重复同一套操作动作,可通过在实验室进行越障过程示教,离线学习形成操作知识库,实际越障时自动调用操作知识库并与在线信号相结合完成自主越障动作。讨论了知识库的一般组成和功能,并分析了激光传感器定位的方法以实现巡检机器人滚动轮与导线“对中”。经过实验验证,该控制方法具有稳定可靠,硬件结构简便,能可靠地完成控制任务,实现自主越障。     

Synthesis and crystal structure of scandium(III) and cadmium(II) thiocyanato complexes with dimethylsulfoxide

Two novel complex compounds, molecular fac-[Sc(NCS)₃(DMSO)₃] and polymeric chain [Cd(NCS)_4/2(DMSO)₂]_∞ (DMSO = dimethylsulfoxide), were synthesized and structurally characterized. In both complexes, the metal atoms have octahedral coordination with the NCS⁻ ion serving two different functions: as a terminal ion with the coordination via N in Sc complex and as a bridge ligand with the coordination via N and S in the case of Cd compound, respectively. The DMSO ligands are coordinated by oxygen atoms.     

Mechanical properties and oxidation resistance of chemically vapor deposited TiSiN nanocomposite coating with thermodynamically designed compositions

TiSiN coating with nanocrystallite surrounded by amorphous phase has attracted a broad interest because of its high hardness and excellent oxidation resistance desired for cutting tools. In the present work, TiSiN coatings were designed and prepared from a gaseous mixture of TiCl₄, SiCl₄, NH₃ and H₂ by low pressure chemical vapor deposition (CVD) process under the guidance of calculated CVD phase diagrams. The calculated compositions and phases in the deposited coatings agree well with the experimental ones. The deposited TiSiN coatings consist of nano-crystalline TiN and amorphous Si₃N₄ (a-Si₃N₄). A maximum hardness of about 2800 HV_0.02 was obtained, corresponding to a minimum crystallite size of 17.7 nm and a-Si₃N₄ volume fraction of 13.3% for TiSiN coating deposited at 1123 K under 3.0 kPa. After oxidation at 973 K for 1 h, TiSiN coating kept intact while TiN was completely oxidized. TiSiN nanocomposite coating formed by Si incorporation to TiN displayed superior hardness and oxidation resistance in comparison with those of TiN. The correlation of TiSiN coating hardness with volume fraction of a-Si₃N₄ and TiN grain size was discussed. The present work demonstrates a novel strategy of thermodynamic calculations and key experiments to deposit CVD TiSiN coatings highly efficiently, which is equally valid for the design of other CVD hard coatings.     

An interactive fuzzy multi-objective optimization method for engineering design

The coupling of performance functions due to common design variables and uncertainties in an engineering design process will result in difficulties in optimization design problems, such as poor collaboration among design objectives and poor resolution of design conflicts. To handle these problems, a fuzzy interactive multi-objective optimization model is developed based on Pareto solutions, where the metric function and some additional constraints are added to ensure the collaboration among design objectives. The trade-off matrix at the Pareto solutions was developed, and the method for selecting weighting coefficients of optimization objectives is also provided. The proposed method can generate a Pareto optimal set with the maximum satisfaction degree and the minimum distance from ideal solution. The favorable optimal solution can be then selected from the Pareto optimal set by analyzing the trade-off matrix and collaborative sensitivity. Two examples are presented to illustrate the proposed method.     

非理想反电动势无刷直流电机的转矩脉动抑制仿真研究

在伺服系统中要求电机转速平稳,抑制转矩脉动是实现转矩平稳的关键,而非理想反电势会引起较大转矩脉动。为了有效平滑无刷直流电机转矩,分析了两种不同的方法：根据定子电流和反电势与转矩表达式的关系,对于一台给定的电机,只要其反电势一定,通过优化定子电流就可以消除主要的转矩谐波分量,从而达到减小转矩波动的目的;通过坐标变换在厶=0时求解产生恒定电磁转矩所需的q轴电流,并在dq坐标系下通过矢量控制对q轴参考电流进行跟踪实现转矩脉动抑制。利用MATLAB／SIMULINK仿真平台建立系统的仿真模型,对系统模型进行仿真和分析并比较了这两种方法的特点,为实际电机的控制提供了研究方向。     

Effect of Mn:Mg ratio on sintering behavior and microwave dielectric properties of (Mn,Mg)V2O6 ceramics at ultra-low sintering temperature

Ultra-low-firing-temperature ceramics (Mn_1−xMg_x)V₂O₆ (x = 0–1) were prepared using the conventional solid-state reaction method. The effects of the Mn:Mg ratio on the crystal structure and microwave dielectric properties of the prepared ceramics were systematically investigated. The results indicated that an appropriate Mn:Mg ratio effectively improves the dielectric properties of the compounds. Specimens with x = 0.01 and x = 0.93 sintered at 630 °C exhibited the following microwave dielectric properties: ε_r = 12.4 and 9.8, high Q×f = 57,000 and 21,000 GHz, and τ_f = –15 and −24 ppm/°C, respectively. This suggests that the (Mn_0.99Mg_0.01)V₂O₆ ceramic is a potential material for ULTCC applications.