关键词： FGM   titanium   hydroxyapatite   composite   SPS   powder metallurgy   mechanical properties   microstructure  

摘要： In this article, different functionally graded material specimens were made from titanium powder and hydroxyapatite (HA) submicron particles. The spark plasma sintering method was applied to fabricate the specimens. Two kinds of starting powder mixture were used: mixed powder and ball-milled powder. Percentage of HA was changed from 0 vol.-% to 40 vol.-% in the different number of layers (2, 3 and 5-layer). The effects of the number of the layers and ball-mill process were investigated on microstructure, microhardness, compressive strength and fracture surface. The results show that the grain size has been enhanced by increasing the amount of HA in the layers. In addition, the Vickers microhardness has been first increased by enhancing the percentage of HA, while it has been decreased in the layers with a higher amount of it. Furthermore, the highest compressive strength could be achieved in the five-layer samples. Moreover, specimens with ball-milled powder have higher microhardness and less compressive strength.

关键词： AFM   钢铁冶金材料   显微结构   分析   应用  

摘要： AFM(Atomic Force Microscope),原子力显微镜,这一显微镜技术是扫描力探针显微镜的重要组成部分,AFM在纳米材料的表征中具有很广泛的应用,此外,在钢铁冶金材料的纤维结构分析中也有较好的应用效果,良好的技术性能促进了AFM的良好发展。本文就AFM的性能和工作原理进行介绍,并探究其在钢铁冶金材料显微结构分析领域的具体应用情况,研究这一显微镜技术在钢铁冶金材料显微结构分析中的应用有效性。

关键词： 热电材料   氧化铟   聚(3,4-乙烯二氧噻吩)   正电子湮没  

摘要： 通过化学氧化合成的方法将纳米In_2O_3复合到聚(3,4-乙烯二氧噻吩)(PEDOT)中得到In_2O_3/PEDOT复合材料.利用X射线衍射、红外光谱、电子显微镜及正电子湮没等方法对复合材料的微观结构进行了系统研究,同时对材料的热学和电学性能进行了表征.结果表明,当In_2O_3的含量在22 wt%以下时,In_2O_3能很好地分散到PEDOT基体中.热电性能测试则显示In_2O_3/PEDOT复合材料的导电率随In_2O_3含量增加明显增大.纯PEDOT的电导率仅为7.5 S/m,而含12.3 wt%In_2O_3的复合材料的电导率达到25.75 S/m.该复合材料相应的功率因子(68.8×10^(-4)μW/m·K^2)相对于纯的PEDOT(14.5×10^(-4)μW/m·K^2)提高了近4倍.另外,复合材料的热导率相对于纯PEDOT也有所降低.最终复合材料的热电优值由0.015×10^(-4)提高到了0.073×10^(-4).结果表明,In_2O_3/PEDOT复合材料的热电性能相对于纯PEDOT的热电性能得到了比较明显的提高.

关键词： AZ31镁合金   材料微结构   Weibull分布   孪生形核与长大   孪晶变体  

摘要： 为了揭示金属镁合金晶粒大小、晶向及晶界倾角等微结构与孪生形核及长大之间的关联性,通过EBSD技术获取大量诸如晶粒尺寸、晶向及晶界倾角等微结构以及晶内孪生形核数、孪晶厚度等数据进行统计分析。对应变为4.9%的镁合金微结构的统计分析表明:晶粒大小、晶界倾角等微结构分布基本符合概率函数Weibull分布特征;大晶粒、高Schmid因子、小角度晶界有利于孪生形核,而孪晶长大对微结构的敏感度较弱;不是所有高Schmid因子的孪生变体都能够形核长大。由对孪生形核与长大随应变递增的演化分析结果可推测:相同晶粒内,不同位置对孪晶变体的形核强度有显著影响,很显然存在其他晶内微结构如缺陷、位错密度等对孪生形核产生重要影响;然而孪晶长大更多地受到晶内存在的孪生形核数和孪晶变体类型数量的强烈影响。本工作可为发展孪生形核长大与微结构的数学关系提供试验依据。

关键词： 醇热法   银   纳米线   卤离子   控制剂   微结构  

摘要： 纳米银的性能主要受其形貌和尺寸的影响,因此调控纳米银的微结构具有重要意义。本文采用醇热法,以AgNO_3为银源,乙二醇为溶剂和还原剂,聚乙烯吡咯烷酮K30(PVP)为结构导向剂和保护剂,含Cl^-或Br^-的钠盐为控制剂,对比研究了PVP浓度、卤离子(Cl^-或Br^-)种类与浓度对产物形貌的影响。采用SEM、TEM、SAED、XRD、EDS对产物的微观形貌、晶体结构和物相组成进行了表征。实验结果表明:Cl^-促进多重孪晶的形成,有助于一维纳米线的形成,但银线直径较大; Br^-能有效降低体系中自由Ag^+浓度,从而减小纳米银线的直径,但成线效果较差; Cl^-与Br^-协同作用能将纳米银线的直径缩小至约30 nm。

关键词： 真空热压烧结   铝基复合材料   硬度   XRD   金相组织  

摘要： 通过粉末冶金真空热压烧结法制备了不同Al_2O_3含量的氧化铝增强铝基复合材料,并利用X射线衍射、金相显微镜和扫描电子显微镜分析了微结构和微形貌对材料硬度的影响。结果表明,在Al_2O_3质量分数为1%~4%时,随着Al_2O_3含量增加,复合材料硬度呈现出先增加后降低的趋势。当Al_2O_3的质量分数为2%,烧结温度为400℃、压力为50 MPa时,复合材料的硬度最大,达到38. 7 HV。通过XRD图谱和金相组织图片可以发现,硬度提高的原因是Al_2O_3的加入可以细化Al基体的晶粒粒径和金相组织。

关键词： Ni-Ti-O纳米片   微观组织   水热合成   甲醇催化   电容  

摘要： 采用水热合成和热扩渗结合的方法在三维多孔泡沫镍支架上制备了Ni-Ti-O纳米片层。通过扫描电镜(SEM)、X射线衍射(XRD)、透射电镜(TEM)、高分辨透射电镜(HRTEM)对泡沫镍支架上NiO和Ni-Ti-O纳米片结构的微观形貌及物相进行了表征和分析。用循环伏安法和充放电性能测试探究了复合电极对甲醇的催化氧化性能及其电容性能。结果表明:泡沫镍上生长的Ni-Ti-O纳米片物相组成为NiO和TiO,并且为多晶形态;Ti的渗入会使得NiO纳米片中形成氧空位,并和Ni产生协同作用,使得Ni-Ti-O纳米片/泡沫镍电极对甲醇氧化的电催化性能优于Ni(OH)_2/泡沫镍和NiO/泡沫镍电极;在泡沫镍和钛粉质量比(R_(Ni/Ti))为1:24,电流密度为5 mA·cm^(-2)时,Ni-Ti-O电极的面积比电容值为2.15 F·cm^(-2),是纳米Ni(OH)_2/泡沫镍电极的3.2倍(0.67 F·cm^(-2))。

关键词： Microstructure reconstruction   Porous materials   Limited bimodal microstructural data   Stochastic data fusion  

摘要： Porous materials such as sandstones have important applications in petroleum engineering and geosciences. An accurate knowledge of the porous microstructure of such materials is crucial for the understanding of their physical properties and performance. Here, we present a procedure for accurate reconstruction of porous materials by stochastically fusing limited bimodal microstructural data including limited-angle X-ray tomographic radiographs and 2D optical micrographs. The key microstructural information contained in the micrographs is statistically extracted and represented using certain lower-order spatial correlation functions associated with the pore phase, and a probabilistic interpretation of the attenuated intensity in the tomographic radiographs is developed. A stochastic procedure based on simulated annealing that generalizes the widely used Yeong-Torquato framework is devised to efficiently incorporate and fuse the complementary bimodal imaging data for accurate microstructure reconstruction. The information content of the complementary microstructural data is systematically investigated using a 2D model system. Our procedure is subsequently applied to accurately reconstruct a variety of 3D sandstone microstructures with a wide range of porosities from limited X-ray tomographic radiographs and 2D optical micrographs. The accuracy of the reconstructions is quantitatively ascertained by directly comparing the original and reconstructed microstructures and their corresponding clustering statistics.

关键词： crystal plasticity   RTCP-FFT   forming limit diagram   3D microstructure   grain morphology   M-K model  

摘要： In this paper, the new rate tangent-fast Fourier transform-based elasto-viscoplastic crystal plasticity (CP) constitutive framework (RTCP-FFT) developed by Nagra et al (2017 Int. J. Plast. 98 65-82) is implemented in the so-called Marciniak-Kuczynski (M-K) (Marciniak and Kuczynski 1967 Int. J. Mech. Sci. 9 609-20) framework to predict the forming limit diagrams (FLDs) of face-centered cubic polycrystals. The RTCP-FFI approach that accounts for 3D grain morphologies and grain interactions is used to compute the FLDs for aluminum alloys (AAs). The model employs two statistically representative volume elements with identical initial microstructures, one inside the imperfection band region (required for M-K analysis) and other outside the imperfection band region of the sheet metal. The proposed RTCP-FFI -based M-K model is a full-field, mesh-free and efficient CP formulation that enables a comprehensive investigation of the effects of 3D microstructural features on the FLDs with extremely small computational times. The new model is validated by comparing the predicted FLDs for AA5754 and AA3003 AAs with experimental measurements. Furthermore, the predicted FLDs are compared with the well-known Taylor-type homogenization scheme-based M-K model (MK-Taylor) predictions. Furthermore, the effects of different grain shapes as well as local grain interactions on the FLD predictions are studied. The study reveals that among the various microstructural features, the grain morphology has the strongest effect on the predicted FLDs and the FLD predictions can be significantly improved if the actual grain structure of the material is properly accounted for in the numerical models.

摘要： The microstructural complexity of Li-rich cathode materials has so far hampered understanding the critical link between size, morphology and structural defects with both capacity and voltage fadings that this family of materials exhibits. Li2MnO3 is used here as a model material to extract reliable structure-property relationships that can be further exploited for the development of high-performing and long-lasting Li-rich oxides. A series of samples with microstructural variability have been prepared and thoroughly characterized using the FAULTS software, which allows quantification of planar defects and extraction of average crystallite sizes. Together with transmission electron microscopy (TEM) and density functional theory (DFT) results, the successful application of FAULTS analysis to Li2MnO3 has allowed rationalizing the synthesis conditions and identifying the individual impact of concurrent microstructural features on both voltage and capacity fadings, a necessary step for the development of high-capacity Li-ion cathode materials with enhanced cycle life.