Micro-scale fracture toughness of textured alumina ceramics

Enhanced fracture resistance of textured alumina is ascribed to crack deflection along grain boundaries. In this work, we quantify and compare the micro-scale fracture toughness of textured alumina grains and grain boundaries by micro-bending tests. Notched micro-cantilevers were milled from single alumina textured grains (perpendicular to the [0001] direction) and across several textured grains (along the [0001] direction), using a focused ion beam technique. Bending tests were performed with a nanoindenter. A shape function for notched pentagonal-shaped cantilevers was developed using finite element analysis. The critical stress intensity factor at the notch tip was determined based on the measured fracture loads. The micro-scale fracture toughness of the textured alumina grain boundaries (2.3 ± 0.2 MPa m^1/2) was about 30% lower than that of the grains (3.3 ± 0.2 MPa m^1/2). These findings at the micro-scale are paramount for understanding the macroscopic fracture behaviour of textured alumina ceramics.     

Screening and manipulation by segregation of dopants in grain boundary of Silicon carbide: First-principles calculations

The effect of segregation behavior of non-metallic dopants (H/He/O) and metallic dopants (Be/Al/Mg/Y) on the performance of grain boundary (GB) in SiC has been systematically investigated by first-principles calculations. Firstly, the GB energy and excess volume of different GBs have been studied to evaluate the stability of GB and the capacity to accommodate dopant atoms. The solution energies of dopant atoms greatly reduce in the GB region compared with those in the bulk, which makes the dopant atoms inside the grain tend to segregate and aggregate near the GB. The driving force of GB on dopant segregation generally decreases with the increase of distance from GB plane, and the preferential site of dopant is closely correlated with the atomic size of dopant. In addition, H and Y atom possesses the lowest segregation energy at the interstitial and substitutional site near the GB, respectively. Next, the segregation of single dopant induced the changes in the strength and stability of GB have been explored. It is found that non-metallic dopants have the significant embrittlement effects on GB strength. However, the segregation of most metallic dopants could strengthen the GB and Mg atom has the most significant strengthening effect on the GB. The stability of GB can be greatly improved by segregation of Al and Y dopants. Besides, the aggregation of H atoms has the obvious embrittlement effect on the GB. Furthermore, the co-segregation behavior of different dopants has also been explored. Be and Mg dopants have the most significant inhibition effect on the segregation of detrimental impurities H/He/O due to the repulsive interaction between dopant atoms. The present results provide a new insight into the effect of dopant segregation on GB properties and are expected to be a useful guidance for screening the chemical composition and manipulating the performance of SiC-based ceramics.     

Synthesis,sintering, and grain growth kinetics of Hf6Ta2O17

A systematic study of the solid-state synthesis, pressureless sintering, and grain growth kinetics of Hf₆Ta₂O₁₇ is presented. The ideal conditions for solids-state synthesis of Hf₆Ta₂O₁₇ powder with minimal particle necking was 1250 °C for 2 h in air. The resultant powder has an average particle size of 210 ± 70 nm. The combined synthesis and ball-milling procedure produces highly sinterable Hf₆Ta₂O₁₇ powder, achieving > 97 % of theoretical density after pressureless sintering at 1600 °C for 2 h in air. The grain growth mechanism was sensitive to processing conditions, appearing to be primarily driven by surface diffusion below 1600 °C and grain boundary diffusion above 1650 °C. The respective activation energies for grain growth were found to be Q_S = 659 ± 79 kJ mol⁻¹ and Q_GB = 478 ± 63 kJ mol⁻¹.     

Quasiplastic deformation in shocked nanocrystalline boron carbide: Grain boundary sliding and local amorphization

Materials respond to shock in many ways such as plastic flow in metals and amorphization in ceramics. It is very challenging to characterize the deformation mechanisms of ceramics under shock compression due to extreme loading conditions. Here we report the shock response of nanocrystalline boron carbide (n-B₄C) using large-scale molecular dynamics simulations with a machine-learning force field. We identify three quasiplastic deformation mechanisms in shocked n-B₄C: grain boundary (GB) sliding, intergranular amorphization, and intragranular amorphization. As the deformation mechanism changes from GB sliding to intergranular amorphization at ～40 GPa, a bilinear Hugoniot behavior occurs, consistent with experimental observations. At higher pressure (>～100 GPa), intragranular amorphization becomes dominant, causing a complete loss of shear strength. These quasiplastic mechanisms may play an important role in the shock behaviors of ceramics.     

基于多个微控制器粗纱机控制系统的研制

为解决当前电脑粗纱机同步控制、抗干扰效果不理想等问题,研制了基于多个微控制器的粗纱机控制系统.在硬件上以多个微控制器组合成的嵌入式系统代替分离的电机控制器,软件上使用基于自适应预测的智能控制算法.在粗纱机上的应用效果表明:新型控制系统具有较强抗干扰能力,并提高了粗纱机的恒张力控制精度.     

制丝设备辅机改造中需注意的几个问题

结合实例,讨论了制丝设备改造中辅机设备的合理选型、设备维护、零部件的通用化等问题。设备选型应考虑经济性、劳动保护和可靠性的要求;设备的维护保养要简单易行,排除故障方便、快捷;设备供需双方应密切合作,尽量提高零部件的通用化水平,增大互换性,从而简化生产管理和提高经济效益。     

大麦压片机的研制

对大麦压片机的主要参数进行了分析和结构设计，既可生产大麦片，也可生产薏仁米片，小麦片等。     

Sintering and Electrical Characterization of La and Nb Co‐doped SrTiO3 Electrode Materials for Solid Oxide Cell Applications

Single‐phase lanthanum and niobium co‐doped strontium titanate (Sr_1–3x/2La_xTi_0.9Nb_0.1O₃; x = 0–0.02) ceramics were prepared. Dilatometry in reducing atmosphere showed an increase in the sintering rate and sintered density with an increase in La amount. Microscopy of fractured surfaces of sintered samples showed that the average grain size increased drastically in reducing conditions with increasing La content (and associated A‐site vacancies). By incorporating 2 mol.% La, the electronic conductivity significantly improved from 80 to 135 S cm⁻¹ at 1,000 °C, and even larger improvements were observed at lower temperatures. These observations demonstrate the flexibility in tailoring the microstructure and electronic transport properties by doping small amounts of La into the Nb‐doped SrTiO₃ and show that Sr_1–3x/2La_xTi_0.9Nb_0.1O₃ is a potential electrode material for solid oxide cells.     

D3-1000型整经机部分机构的改造实践

针对金丸D3-1000型整经机生产过程中存在的问题,进行了以下改造:用光电式断经自停装置取代触点式断经自停装置;改进了导纱钩形状,减少了经纱绞头疵点;对经轴夹盘磨损部位采取更换局部部件的方法,节约了维修费用;设计并加装了机前安全防护装置,实现了对生产人员的安全防护.     

基于支持向量机预测偏振模式

基于多光谱多角度偏振辐射探测研究了大气偏振模式预测方法。首先,介绍了航空多角度偏振辐射计的探测原理与支持向量机回归算法;然后,从矢量传输模型出发,说明大气状况不变时,偏振模式主要取决于地表特征与观测几何,并介绍了观测几何与姿态之间的关系以及地表特征的表达形式;最后,在考虑平台姿态与地表特征的情况下,利用支持向量机回归算法预测了航空多角度偏振辐射计的探测偏振度,并对预测与实际试验探测的偏振度进行了比较。结果显示:偏振度预测误差小于1%,影响模型精度的主要因素不是姿态变化本身,而是姿态改变造成的观测地表特性变化。