关键词： Friction stir welding   Aluminum alloy   Tool eccentricity   Microstructural properties   Material flow   Kinematics  

摘要： The effect of tool eccentricity on friction stir welding of AA6061-T651 aluminum alloy plates is evaluated. Microstructural characterization reveals that surface roughness of the weld bead is increased, while material flow and mixing in the stir zone is enhanced with increasing tool eccentricity. Moreover, grain size of examined regions are refined with increased tool eccentricity. Softening at the lower region of the stir zone was observed using both an aligned and 0.2 mm eccentric setup, where a high density of platelet-shaped precipitates are present. (C) 2020 Elsevier B.V. All rights reserved.

关键词： Grouting material   Nano-clay   Chloride ion penetration   Permeability   Theoretical model   Microcosmic structure  

摘要： The main objective of this study was to investigate the influence of nano-clay (NC) on the mechanical and microcosmic properties of sulfoaluminate cement grouting material in 5% sodium chloride (NaCl) solution. All specimens were prepared with a water/cement ratio (W/C) of 1.0. The setting time, bleeding ratio, flow time, mass change rate, and uniaxial compressive strength were obtained by various tests. Further, the resistance toward chloride ion penetration and the permeability of pastes were also evaluated. Hydration products and micro-morphology were investigated through X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope, and energy dispersive spectroscopy. The test results revealed that with the addition of NC, both the setting time and flow time were significantly shortened and bleeding capacity and mass loss rate decreased;nonetheless, the uniaxial compressive strength increased significantly. Moreover, addition of NC reduced the chloride ion penetration and permeability. Furthermore, the theoretical model based on permeability and immersion time was established, and its correctness was successfully verified by experimental data. As a result, the grouting material with added 2% NC exhibited the best experimental performance, whereas 3% and more content of NC resulted in inferior performance;however, it was still better than that of the control group (NC = 0%). Moreover, microcosmic test results showed that ettringite is the main product of the dominant hydration reaction. It was thus proved that NC could promote the hydration process, and thus it weakens the chloride ion erosion due to the porosity reduction effect. (C) 2020 Elsevier Ltd. All rights reserved.

摘要： We present the first results of laser-driven flyer plate experiments on a nanocrystalline copper-tantalum (NC-Cu-Ta) alloy. A pulsed Nd:YAG laser (1.2J/pulse, 10ns) is used to accelerate an Al foil disk (25 mu m x similar to 800 mu m) off a glass substrate at velocities of 0.8 and 2.4km/s through a small air gap and impact the NC-Cu-Ta target. The flyer velocities were determined from a high-speed video and extensive post-impact analyses were conducted using advanced electron microscopy revealing the formation of a band structure leading to a non-trivial upper bound for the breakdown of an extremely stable NC-microstructure and physical-properties.

关键词： 激光光学   飞秒激光   湿法腐蚀   晶体材料   微纳结构  

摘要： 晶体材料微加工技术是制备微电子器件、微机电系统器件的关键技术。飞秒激光辐照结合湿法腐蚀加工技术不仅可以去除飞秒激光诱导微结构表面缺陷,提高微结构表面光滑度,还在制备高纵横比结构、内部通道等方面具有独特的优势,为晶体加工开辟了新的道路。本文概述了飞秒激光辐照结合湿法腐蚀加工技术特点、原理和优势,总结了其在硅、碳化硅、蓝宝石晶体材料微结构制备中的研究进展,讨论了该技术的不足及其未来发展。

关键词： 位置精度   疲劳断口   金属材料   大科学装置   微结构损伤   破坏行为   疲劳损伤   点光源  

摘要： 长期以来,科学家通过测量表面裂纹长度和辨识疲劳断口揭示小试件的破坏行为,并依此来表征大块金属材料的疲劳损伤机制,从而建立了工程结构抗疲劳断裂设计的科学基础和评价体系。虽然断口保存了材料破坏过程的全部信息,但很难标定缺陷的空间形貌及与其他缺陷的耦合情况,无法提取到三维空间中真实临界缺陷尺寸。低通量点光源工业CT探测的缺陷形貌、尺寸及位置精度不足,尤其不能实现高时空分辨下的动态原位加载。

关键词： Python语言   GUI插件   材料微结构   晶体学取向   二次开发  

摘要： 基于Voronoi图基本原理,通过编写Python语言在ABAQUS中构造出三维多晶体微结构几何模型。利用ABAQUS/CAE内嵌的GUI插件开发辅助工具RSG对话框构造器,定制合理的参数对话框,编写内核Python程序开发出材料微结构前处理建模插件Polycrystal Toolkit,利用该插件可以快速构造微结构几何模型并赋予晶体学取向。采用该方法建立的有限元模型结合大型仿真软件ABAQUS分别对2种任意取向下的圆柱多晶体进行扭转变形模拟。结果表明:通过编写Python语言生成的Voronoi多晶模型可以很好地描述实际多晶体变形过程中内部变形的不均匀性,验证了模型及插件的有效性,为以后织构演化行为的研究提供了有利的建模基础。

关键词： 组织支架   生物相容性材料   破骨细胞   表面微结构  

摘要： 骨组织工程的发展对支架材料提出了更高要求。基于再生医学的完全再生理论,要求骨移植替代物具备骨诱导性的同时,还能被破骨细胞降解并替换为新生骨组织。可吸收支架材料能被破骨细胞降解,且材料的理化性质也影响着破骨细胞的行为。其中材料表面微结构是启动骨诱导性的关键,对破骨细胞行为具有重要影响。此外,材料表面粗糙度在一定范围内可增强破骨细胞的功能活性。就材料表面微结构对破骨细胞调控作用的研究进展作一综述,以进一步探讨其作用机制,为制备性能更佳的组织工程支架材料提供参考。

关键词： 纳米VO2(B)   微观形貌   结构缺陷   电化学性能  

摘要： 以V2O5为原料、草酸为还原剂,采用水热法制备不同草酸浓度下的系列纳米VO2(B)样品(c(H2C2O4)/c(V2O5)=x,1.00≤x≤2.50),对所制备样品的物相结构、微观形貌和电化学性能进行表征和分析.结果表明:所制备的样品均为单斜结构的纯相VO2(B);随着还原剂浓度的增大,VO2(B)样品的形貌逐渐由较小的纳米片变成较长的纳米棒;VO2(B)样品的结构缺陷主要为微孔;所得VO2(B)样品均具有较好的可逆性和循环稳定性,其中,当x=1.75时,VO2(B)样品具有较小的氧化还原峰电位差(0.111 V)和较小的电阻(0.770Ω),且当电流密度为30 mA/g时,具有最大的比电容值(105.00 F/g),表现出更好的电化学性能.

关键词： recycling   hot extrusion   metal–metal composite   phosphor bronze chips   aluminum powder  

摘要： Despite the existence of conventional methods for recycling chips,solid-state techniques have become popular,whereby waste metals are directly recycled into consolidated products with the desired shapes and *** investigated the feasibility of recycling phosphor bronze chips through a hot extrusion process using aluminum powder as a metal binder for the fabrication of a metal-fiber-reinforced aluminum matrix *** do so,mixtures containing 20 vol%–50 vol%of chips were prepared,cold-compacted,and *** quality of the consolidated samples was evaluated by determining the density of the fabricated composites and studying their *** addition,we performed tensile and hardness tests to evaluate the mechanical properties of the fabricated *** also analyzed the fracture surfaces of the samples to study the fracture mechanism as a function of the volume fraction of phosphor bronze chips in the fabricated *** results indicated that the most effective consolidation occurred in the sample containing 20 vol%of chips extruded at 465℃in which the chips serve as ideal fibers for improving the mechanical properties,especially the ultimate tensile strength,in comparison with those of Al matrixes that contain no chips but are produced under the same conditions.