关键词： Quantitative microstructure representation (QMR)   N-point polytope functions   Heterogeneous materials   Microstructure evolution   Multi-modal imaging data  

摘要： Effective and accurate characterization and quantification of complex microstructure of a heterogeneous material and its evolution under external stimuli are very challenging, yet crucial to achieving reliable material performance prediction, processing optimization and advanced material design. Here, we address this challenge by developing a set of hierarchical statistical microstructural descriptors, which we call the "n-point polytope functions" P-n, for quantitative characterization, representation and modeling of complex material microstructure and its evolution. These polytope functions successively include higher-order n-point statistics of the features of interest in the microstructure in a concise, expressive, explainable, and universal manner;and can be directly computed from multi-modal imaging data. We develop highly efficient computational tools to directly extract the P-n functions up to n = 8 from multi-modal imaging data. Using simple model microstructures, we show that these statistical descriptors effectively "decompose" the structural features of interest into a set of "polytope basis", allowing one to easily detect any underlying symmetry or emerging features during the structural evolution. We apply the P-n functions to quantify and model a variety of heterogeneous material systems, including particle-reinforced composites, metal-ceramic composites, concretes, porous materials;as well as the microstructural evolution in an aged lead-tin alloy. Our results indicate that the P-n functions can offer a practical set of basis for quantitative microstructure representation (QMR), for both static 3D complex microstructure and 4D microstructural evolution of a wide spectrum of heterogeneous material systems. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

关键词： 超材料   石墨烯   吸波性能   微结构材质   仿真设计  

摘要： 本文利用石墨烯开发了一种新型超材料微结构材质,并将其应用于W型钡铁氧体吸波涂层的改进设计,分析了改进设计对吸波性能的影响,并对吸波机理进行了研究。通过仿真发现,经过超材料改进设计的吸波涂层的吸波性能得到了大幅提高,1.0 mm吸波涂层的有效吸收带宽可从0大幅增加到11.3 GHz,2.0 mm吸波涂层?20 dB的吸收带宽可达11.4 GHz。本文通过仿真还对经超材料改进设计的吸波涂层在不同频点处的电场、磁场和能量损耗分布情况进行了分析和讨论。

关键词： AlCrSiWN   Powder metallurgic target   Crystal structure   Mechanical properties   Tribological properties  

摘要： When synthesizing magnetron sputtered films with a complex stoichiometry, integrating the desired coating constituents into one target material is favorable in order to avoid nanolaminar film depositions and to enable a homogenous film growth. In contrast to alloyed targets, segmented plug targets allow to merge elements with different physical properties in one target material. Two targets, amalgamating 20 and 48 hot-pressed 85.6Cr9.9Si4.5W (at %) plugs, respectively, into a monolithic aluminum target were fabricated and employed in a direct current magnetron sputtering process to deposit AlCrSiWN films on high-speed steel (AISI M3:2, 1.3344). The cathode powers for the Al(CrSiW)20 and Al(CrSiW)48 targets were varied between 7.5 and 17.5 W/cm(2) to analyze how differently composed targets and various cathode powers affect the microstructure and tribological properties of the sputtered films. The results revealed that the chemical composition as well as the thickness of the films strongly depend on the target setup. All AlCrSiWN films exhibited a Cr/Si/W ratio of approximately 84/11/6. The Cr and Al contents were dominant (19-29 at %), while the Si and W contents varied between 2 and 3 at %. Especially the Al/Cr ratio of the films is affected by the varying Al/CrSiW surface area ratio of the manufactured plug targets. Furthermore, the mechanical properties are significantly influenced by the Al/Cr ratio, which is responsible for a dense coating growth and the crystalline structure of the films. All AlCrSiWN films were (111) textured indicating a B1 (Al, Cr, W)N structure, which exhibited a finer crystalline growth with an increasing cathode power on the Al(CrSiW)20 target. Tribological analyses of the films against Al2O3 balls further revealed that thinner films resulted in a decreased wear coefficient.

关键词： Erosion   Gadolinium zirconate (GZ)   Suspension plasma spray   Yttria fully stabilized zirconia (48YSZ)   Yttria partially stabilized zirconia (8YSZ)   Atmospheric plasma spray  

摘要： In this work, three different TBC compositions comprising of yttria partially stabilized zirconia (8YSZ), yttria fully stabilized zirconia (48YSZ) and gadolinium zirconate (GZ) respectively, were processed by suspension plasma spray (SPS) to obtain columnar microstructured TBCs. Additionally, for comparison, lamellar microstructured, 7YSZ TBC was deposited by air plasma spray (APS) process. SEM analysis was carried out to investigate the microstructure and white light interferometry was used to evaluate the surface morphology of the as-sprayed TBCs. Porosity measurements were made using water intrusion and image analysis methods and it was observed that the SPS-YSZ and APS-YSZ TBCs showed higher porosity content than SPS-GZ and SPS-48YSZ. The as-sprayed TBC variations (APS-YSZ, SPS-YSZ, SPS-GZ, and SPS-48YSZ) were subjected to erosion test. Results indicate that the erosion resistance of APS-YSZ TBC was inferior to the SPS-YSZ, SPS-GZ and SPS-48YSZ TBCs respectively. Among the SPS processed TBCs, SPS-YSZ showed the highest erosion resistance whereas the SPS-48YSZ showed the lowest erosion resistance. SEM analysis of the eroded TBCs (cross section and surface morphology) was performed to gain further insights on their erosion behavior. Based on the erosion results and post erosion SEM analysis, erosion mechanisms for splat like microstructured APS TBC and columnar microstructured SPS TBCs were proposed. The findings from this work provide new insights on the erosion mechanisms of columnar microstructured TBCs and lamellar microstructured TBCs deposited by plasma spray.

关键词： Anode microstructure   Knudsen diffusion   Tortuosity factor   Micro-channels   Triple phase boundary   Mass transport  

摘要： In this study, we aim to parametrically reveal the dependence of electrochemical performance on a variety of microstructural characteristics at multi-length scale in a micro-tubular solid oxide fuel cell to shed light on the advanced electrode design. Numerical Direct Simulation Monte Carlo method is used on the tomographically-reconstructed 3D microstructure of the anode to characterise the tortuosity factors as a function of the porosity and pore diameter accounting for the Knudsen flow. These are subsequently incorporated in the mass transport in 2D electrochemical simulations. Results show that the Knudsen tortuosity factor is two times larger than that estimated by the continuum physics. High substrate porosity and pore size show unnoticeable effect in facilitating the mass transport provided that the micro-channels span over 60% of the radial thickness. The width and radial distribution of the micro-channels have little influence on the mass transport, but the compactness greatly affects the global performance. Optimal designs are identified as i) 80% micro-channel length and 27% substrate porosity to reach maximum power density (1.18 W cm(-2)) with lowered mechanical strength, or ii) 60% micro-channels length and 27% porosity to obtain a more balanced performance (0.96 W cm(-2)) with better long-term structural integrity.

关键词： Composite phase change materials   Thermal energy storage   Microstructure   Effects of particle size and density   Thermophysical properties   Mechanical strength  

摘要： MgO has been used as a popular ceramic skeleton material (CSM) for shape-stablising inorganic salt based composite phase change materials (CPCMs) for medium to high temperature thermal energy storage applications. This work aims to understand the effects of particle size and density of MgO on the microstructures, and thermophysical and mechanical properties of the CPCMs. A eutectic carbonate salt of NaLiCO3 was used as the phase change material (PCM) with a melting temperature of around 500 degrees C and graphite flakes as the thermal conductivity enhancement material (TCEM). Two types of MgO were used in the work with one being light MgO and the other heavy MgO. The results demonstrated clear evidence of salt migration within the CPCMs made from both types of MgO during thermal cycling, leading to a more homogenous distribution of the salt as well as the CSM and TCEM. For a given particle size and TCEM loading, the light MgO (with a higher surface energy) gave a more considerable extent of particles migration and rearrangement than the heavy MgO (with a lower surface energy). Due to the higher surface energy, a much denser structure and better PCM containment of the CPCMs were observed with the light MgO formulations. For a given MgO type, smaller MgO particles yielded smaller internal pores and a more rigid structure, leading to a better containment of the PCM and more stable composite structure during thermal cycling. The microstructural characteristics observed were also found to be closely related to the thermophysical and mechanical properties of the CPCMs;a CPCM composite made with ingredients of a similar size gave a more compact structure and hence a better combination of thermal conductivity and mechanical strength.

关键词： 4D printing   Carbon nanotube   Angle-ply laminated preform   Rectangular braided preform   Shape memory property  

摘要： Four-dimensional (4D) printing technology, combining 3D printing with stimuli-responsive materials, has attracted extensive attention for smart additive manufacturing. This work focuses on microstructural design, shape recovery behavior and recovery force characterization of 4D printed angle-ply laminated and rectangular braided preforms and their silicone elastomer matrix composites. The angle-ply laminated and rectangular braided preforms were printed using polylactic acid (PLA) and carbon nanotube reinforced PLA (CNT/PLA) based shape memory polymer (SMP) filaments. The X-ray micro-computed tomography, a high resolution and nondestructive imaging technique, was employed to characterize the microstructures of 4D printed specimens and their post-bending damage morphology. The effects of microstructure, CNT filler and silicone elastomer matrix on shape recovery behavior, recovery force and flexural property were studied. The infilling of CNT enabled earlier initiation of specimen shape recovery process, improved the recovery force up to 144% and enhanced the flexural load and modulus. The infusion of silicone matrix increased the final shape recovery ratio to 97.3%, improved the recovery force and enhanced flexural property. The knowledge gained in this research will benefit future design optimization for smarter, faster and stronger actuators.

关键词： 针阀体   密封微结构   仿真分析   优化设计  

摘要： 针对某型号针阀偶件在工况下,高压油易从针阀体和针阀套间的接触端面泄露的问题,利用Solidworks三维软件建立针阀体密封端面不同微结构的三维模型,并使用ANSYS仿真分析软件对针阀体上的微结构进行静力学仿真分析,根据仿真分析结果对比选出最优微结构。仿真结果表明:针阀体密封微结构可以起到增大密封端面接触面积的作用;且密封微结构的最优设计为抛物线凹状环槽,可使针阀体与针阀套之间的密封问题得到改善。

关键词： 壳聚糖   淀粉   复合材料   流变性能   粘弹性能  

摘要： 本文选择4种具有不同微结构的壳聚糖,与淀粉形成复合材料,并对复合溶液的流变、粘弹性能以及复合薄膜的机械性能进行探讨,利用复合材料对含药片剂进行薄膜包衣,考察其控释性能。实验结果发现,壳聚糖/淀粉复合溶液具有假塑性流体特征,壳聚糖粘均分子量越大,剪切稀化现象越明显。同时,在复合薄膜制备过程中,壳聚糖可促进淀粉分子链的排布,提升复合薄膜的抗拉强度、断裂伸长率,调控壳聚糖微观结构可改善复合薄膜的机械性能。当包衣片剂运转至模拟肠液,借助壳聚糖上的-NH3+与淀粉的-OH间的氢键作用,片剂外可形成凝胶层,阻碍药物的释放,壳聚糖分子量越大,药物从复合薄膜包衣片剂中释放的累积量越小。以粘均分子量2.543×10^5 g/mol的壳聚糖CTS60与玉米淀粉制备的复合薄膜包衣片剂,约有70.59%药物可递送至肠道,其中有21.83%释放于模拟小肠,48.77%释放于模拟结肠,表现出一定的控释性能。

关键词： 超长寿命疲劳   微结构敏感性   疲劳裂纹萌生   小裂纹扩展  

摘要： 高速列车、航空航天、核电等国家重大工程与装备的高速发展,促使关键部件需具备在超高周次条件(107~109周次)下的高可靠性与安全性.近30年的材料超长寿命疲劳研究发现,疲劳裂纹萌生与小裂纹扩展在疲劳失效过程中有着至关重要的作用,并且其发展演化过程与材料微结构有极大的相关性.从疲劳强度、疲劳裂纹萌生与小裂纹扩展的微结构敏感性3个方面对近年来最新实验与研究成果进行阐述,分析金属材料微结构性质、形态、分布等特征下的超长寿命疲劳行为与失效机理,为新型抗疲劳材料的设计与研发提供基础性依据.