Influence of laser surface texturing on the flexural strength of Al2O3 and Si3N4

Laser surface texturing (LST) is well known to be capable of improving the tribological performance and reducing the friction of ceramic surfaces. However, the influence of LST on the flexural strength of ceramics has rarely been researched.In this study, we examine the influence of LST on high purity (> 99.5 wt%) dense-sintered fine Al₂O₃ and hot-pressed fine Si₃N₄ with polished and laser-textured surfaces based on the biaxial ball-on-3-balls (B3B) test. A heat transfer simulation of the LST process is performed to understand the occurrence of residual stress. In addition, the B3B strength of Al₂O₃ and Si₃N₄ texture groups is calculated by adapting the previous formula based on the finite element (FE) simulation. Subsequently, the stress distribution in the FE simulation is used to calculate the effective volume and effective surface to study the size effect on both ceramics. It is found that LST improves the strength of Al₂O₃ and Si₃N₄ due to two reasons: it induces compressive residual stress on the tensile-loaded surface of ceramic specimens; more importantly, it reduces the effective volume and effective surface remarkably, thus improving the component strength significantly.     

Negative potential dissolution (NPD)-advanced and rapid texturing method of as-cut silicon

Texturing of as-cut p-type boron doped (1 1 1) oriented silicon has been carried out by negative potential dissolution (NPD) in KOH solutions in the dark. The use of KOH in concentrations of 16-32 wt.% results in massive silicon texturing with a formation of coined triangles pits morphology. This morphology can be formed within a short etching time of less than a minute. At higher KOH concentrations (50 wt.% KOH) and under similar conditions as-cut silicon surface is being polished. NPD current-time profile has a distinguished “U” shape. Detailed mechanism accounting for NPD texturing is provided explaining this characteristic. NPD process allows a rapid etching of as-cut (1 1 1) p-type silicon by a factor of 100, compared with etching rate at OCP. NPD allows the texturing of silicon within a very short period of time once the potentials are more negative than −10 V. As the potential is further negatively shifted, silicon etch-rate increases, as well. NPD also provides a marked distinguish between two processes: texturing and polishing; a transformation between texturing and polishing is feasible once.     

提高涤纶拉伸变形丝的退绕速度

ATF-12型加弹机生产的涤纶拉伸变形丝(DTY)退绕速度达不到后道高速织造退绕要求。通过优化工艺参数尤其是分析设备影响因素并安装"Z"形导丝器,有效地提高了DTY丝筒的退绕速度,达到了2000 m/min以上。     

FTF12E3加弹机EB成型系统存在问题分析及改进

针对FTF12E3加弹机生产出的丝饼出现的凸肩和绊丝现象,根据加弹机EB系统的工作原理,分析查找产生问题的原因,并相应采取改造措施。     

Laser surface texturing and numerical simulation of heat flux on Cr2AlC MAX phase heat exchangers

The energetic worldwide emergency demands a significant drop in fossil energy to renewable energies as part of the sustainable solutions for global energy consumption. MAX phase materials, such as Cr₂AlC, are potential candidates for heat exchanger applications due to their excellent oxidation and corrosion resistance, good thermal shock response and relatively high thermal conductivity. This study uses laser surface texturing (LST) technology to design plate heat exchanger patterns on the Cr₂AlC MAX phase. Furthermore, performing numerical simulations on textured plate models under molten salt conduction and convection conditions, accessing temperature gradient and heat transfer behaviour were conducted on Cr₂AlC, as well as on 316 L stainless steel and alumina for comparison. As a result, combined microtextures with a corrugated surface and spaced V-shape channels were obtained using LST in a single step. The parametric study indicated that the optimal channels (groves) were found for 25 W in air and 20 s laser conditions, with approximately 145 µm width and 340 µm depth. Furthermore, the numerical simulation showed that ceramics materials present better heat transfer conditions than 316 L stainless steel, where Cr₂AlC and alumina only differ in 1.9% heat flux. In addition, the corrugated surface plate with 2.6% width of the total thickness increases heat transfer by 9.8%.     

Effect of EDT surface texturing on tribological behavior of aluminum sheet

Surface texturing, which fabricates micro dimples or micro channels on the surface of parts, is a growing technique for improving tribological characteristics of materials. Currently, electrical discharge texturing (EDT) technique, one surface texturing method suitable for mass production, is being used to texture aluminum sheets for the applications in automotive industry. It has been widely accepted in industry that EDT improves the forming behavior of aluminum sheets due to better friction behavior. However, how the textures on the surface of sheet metal change the friction behavior has not been investigated. In this paper, the influence of EDT on the friction behavior of aluminum automotive sheet at different contact pressures and sliding speeds is investigated based on both experimental studies and numerical simulations. To fully investigate the tribological behaviors, a flat-on-flat friction test device was built and a numerical code based on mixed lubrication theory was developed. It was found that EDT texturing can reduce the friction coefficient of contacting pair at high contact pressure, however, increase friction coefficient at low contact pressure. Numerical simulations confirmed this finding. Furthermore, the model provides valuable information for the prediction of friction behavior of EDT sheets and helps to optimize processing parameters for various forming processes using EDT aluminum sheets.     

正弦织构化表面等离子喷涂熔滴铺展成形分析

目的 分析等离子喷涂熔滴在表面织构内的铺展、凝固规律,为了解表面织构化对等离子喷涂涂层结合机制的影响以提升涂层的结合强度提供理论辅助.方法 基于Flow 3D建立熔滴填充微织构的数值模型,研究等离子喷涂熔滴填充正弦形织构的温度场及铺展成形规律,并对比分析织构边缘凸起及织构形状的影响.同时,基于激光织构化表面等离子喷涂试验,分析不同织构对涂层形貌的影响.结果 无边缘凸起织构的散热速度比有边缘凸起织构的快约0.7μs,凹坑织构的散热速度最慢,计算结束时,其最高温依然高于熔滴液相线(1728.4 K)约44.7 K.基体最高温度约1680.5 K,其主要分布于织构边缘凸起顶端、基体平面与织构内壁的拐点以及织构内壁上的凸点位置.有边缘凸起正弦织构的凝固熔滴由中间向两侧逐渐变薄,熔滴在无边缘凸起织构外部呈规则的圆盘状,凹坑织构底部存在"空腔"特征.涂层截面形貌分析发现,有边缘凸起的织构表面的涂层形貌较优,凹坑织构涂层含有较多缺陷,形貌最差.结论 镍基涂层与织构化表面为机械结合.相比凹坑织构,正弦和直线织构更有利于提高涂层的质量.织构边缘凸起的存在对提高喷涂质量也是有利的.     

Influence of texture feature size on spherical silicon solar cells

The effects of surface texturing on spherical silicon solar cells were investigated. Surface texturing for spherical Si solar cells was prepared by immersing p-type spherical Si crystals in KOH solution with stirring. Two kinds of texture feature sizes (1 and 5μm pyramids) were prepared by changing stirring speed. After fabrication through our baseline processes, these cells were evaluated by solar cell performance and external quantum efficiency. The cell with 1 and 5μm pyramids shows the short circuit current density ( Jsc ) value of 31.9 and 33.2 mA·cm-2 , which is 9% and 13% relative increase compared to the cell without texturing. Furthermore, the cell with 5 μm pyramids has a higher open-circuit voltage (0.589 V) than the cell with 1 μm pyramids (0.577 V). As a result, the conversion efficiency was improved from 11.4% for the cell without texturing to 12.1% for the cell with 5 μm pyramids.     

径向不对中微织构气体箔片轴承静态特性分析

为进一步探究表面形貌对气体箔片轴承的影响,采用数值分析方法分析不对中情况下表面粗糙度和表面微织构对径向气体箔片轴承静特性的影响。利用超松弛迭代(SOR)和有限差分法对气体箔片轴承的Reynolds控制方程进行求解,通过模拟仿真分析不同微织构形状、深度、数量、占比以及表面粗糙度下轴承的静特性。研究结果表明：不同形状微织构对气体箔片轴承性能影响不同,椭圆形微织构提高轴承静特性的效果较好;微织构深度、数量和占比存在一组相对最优值,可在提升轴承承载力的同时降低摩擦力矩;与无微织构轴承相比,具有特定参数微织构的径向气体箔片轴承承载力提高了36.32%,摩擦力矩降低了1.66%。     

溶剂热法制备织构化Bi0.5Na0.5TiO3陶瓷的影响因素

以Bi(NO₃)₃·5H₂O和Ti片为原料,无水乙醇为溶剂,采用溶剂热法合成了具有取向性的织构化Bi_0.5Na_0.5TiO₃(BNT)无铅压电陶瓷.采用X射线衍射(XRD)、场发射扫描电子显微镜(FE-SEM)和能谱仪(EDS)对BNT无铅压电陶瓷物相、显微形貌和成分进行了表征.系统研究了NaOH浓度、[Bi³⁺]浓度、表面活性剂和溶剂等因素对BNT晶粒物相、微观形貌和成分的影响.结果表明:NaOH浓度为1 mol·L^-1,[Bi³⁺]浓度为0.1 mol·L^-1,聚乙二醇(PEG)加入量为1~6 mL,且溶剂为无水乙醇时可以制备出织构化BNT陶瓷,产物颗粒尺寸平均为10~20μm.