关键词： MD距离   MD-RBM   聚类   材料微结构   成对约束  

摘要： 在传统的RBM神经网络的基础上提出一种新颖的MD RBM神经网络模型用于超高碳钢微结构高维图像数据的特征学习。该模型利用新的乘法距离(MD)取代欧式距离以计算高维图像数据之间的距离关系,有效缓解欧式距离在高维数据中的不稳定性问题。MD-RBM神经网络模型利用少量的成对约束监督信息引导其编码过程,使得一部分图像数据的隐藏层特征更加聚集在一起,而且同时使得一部分图像数据的隐藏层特征更加分散,由此得到高维图像数据的隐藏层特征表现出很好的聚类性能。实验选择两种经典聚类算法Affinity Propagation(AP)和Spectral Clustering(SC)作为对比,结果显示,基于MD-RBM模型的聚类识别算法比原始聚类算法、半监督算法以及基于RBM模型的聚类算法都表现出更优的聚类性能。

关键词： Austenitic stainless steel   Compression test   Continuous and discontinuous recrystallization   Stacking fault energy  

摘要： A low stacking fault energy material is subjected to warm working as well as hot working, i.e. in the temperature range 873K (600 degrees C)-1173K (900 degrees C). The evolution of microstructure is quantified using average grain size and grain size distributions. The microstructural transitions resulting from continuous dynamic recrystallization and discontinuous dynamic recrystallization are examined. The resultant softening is studied using macro- and micro-indentation experiments. The applicability of empirical relations between hardness and microstructural parameters is critically examined. The SFE at each of these temperatures is evaluated using a thermodynamic model and correlated with the softening mechanism.

关键词： Hot rolling   Work roll   High speed steel   Oxide scale   Microstructure   Residual stress  

摘要： Compact oxide scale at a high speed steel (HSS) work roll surface during hot rolling process can act as an effective solid lubricant and a protective layer for better product surface quality. In this study, considering practical hot rolling process time, microstructure and surface roughness of three oxide scales on a HSS work roll have been systematically characterized with a help of scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). It has been found that growth of the oxide scale follows a parabolic rate law and the dominant oxide phase is hematite. In addition, surface roughness increases dramatically when the oxidation time is less than 30min and then changes slightly, when the HSS specimens were isothermally oxidized at 600 degrees C in a dry air. Residual stress evolutions with oxidation time have also been examined in details using X-ray diffraction (XRD) method. Measurement of microhardness at the HSS specimen surface revealed that development of defects and decrease of compressive residual stress in the oxide layer lead to a slight decrease in the microhardness.

关键词： Nanocomposites   Biomedical   Mechanical alloying   SiC   Mechanical properties  

摘要： In this study, SiC/Ti-Cu nanocomposite was fabricated by mechanical alloying and sintering process. Effects of SiC nano-reinforcement on phase transformation, microstructure and tribological and antibacterial properties Ti-Cu intermetallic alloy were studied. The microstructure of the powders and sintered materials was investigated using X-ray diffraction, and scanning/transmission electron microscopy. The results exhibited the formation of major TiCu and TiCu4, and minor Ti2Cu and Ti2Cu3 nanocrystalline phases in the sintered Ti-Cu and SiC/Ti-Cu samples. With the addition of the nanoparticles, the amount of TiCu4 phase increased. Reinforcing Ti-Cu intermetallic alloy by SiC nanoparticles resulted in a considerable improvement in antibacterial activity, hardness, wear resistance, and reduction in friction coefficient. The excellent wear resistance of SiC/Ti-Cu nanocomposite is attributed to the formation of hard TiCu and TiCu4 phases with a homogeneous distribution of the phases in the nanocomposite as a result of SiC addition.

关键词： Heat treatment process   WC-binderless   WC-Co   Mechanical property   Microstructure  

摘要： In this study, the heat treatment process was performed to improve the mechanical properties of WC-binderless and WC-Co hard materials pre-fabricated by PCAS process. The microstructural and mechanical properties were varied significantly by the heat treatment process with the treatment time. To increase the fracture toughness value, the heat-treatment process of the WC-binderless, WC-5 wt.% Co and WC-10 wt% Co hard materials were performed at (1,300, 1,150, and 950) degrees C under (5 and 48) h, respectively. Enhancement of fracture toughness that focused on the major reasons was estimated for four mechanisms. Firstly, the microstructure formation of a mechanism was investigated to demonstrate the grain coarsening behavior for variation of heat treatment time. Secondly, the fraction of the coherent interface at WC/Co to the existing in the specific plane orientation was investigated. In particular, the texture distribution of WC (0001)(hcp) plane and Co (111)(fcc) plane were discussed in the EBSD micrograph. Thirdly, the increase of the mean free path by the Co content was exhibited in relation to the variation of mechanical properties. Finally, the mechanism of the decarburization effect of WC, which occurs during the heat treatment process under specific condition were demonstrated in the XRD peaks and FE-SEM analysis. In this chemical reaction, the separated W phases were locally precipitated, resulting in an increase in fracture toughness. (C) 2019 Elsevier B.V. All rights reserved.

关键词： 电化学法   聚苯胺   石墨烯   超级电容器  

摘要： 采用电化学方法制备出聚苯胺/石墨烯复合材料,并通过扫描电子显微镜(SEM)、傅里叶红外光谱仪(FT-IR)、紫外-可见分光光度计(UV-Vis)对氧化石墨烯、聚苯胺和聚苯胺/石墨烯复合材料的结构进行表征。结果表明,聚苯胺纳米颗粒均匀分布在石墨烯片层间。聚苯胺/石墨烯复合材料的比电容最大为238 F/g。循环1 000次以后,聚苯胺的电容衰减24. 5%,而复合材料的电容衰减15%。与聚苯胺相比,聚苯胺/石墨烯复合材料的电容量高、循环稳定性好,电导率从5 S/cm提高到10 S/cm。

关键词： 柔性应变传感器   碳纳米管   微结构   可穿戴   运动监测  

摘要： 设计了一种具有双层微结构的柔性压阻式应变传感器,并进行了制备方法研究。通过在半固化的环氧树脂基底(Ecoflex~? 00-30)表面制备形成碳纳米管(MCNTs)/环氧树脂(Ecoflex~? 00-30)复合薄膜,用毛刷制备微结构。通过测试分析可得,该柔性应变传感器具有高度可拉伸性能,可承受200%的应变,在0～80%,80%～170%,170%～195%的应变区间,GF值分别为10.5,40.5,190.5。将传感器进行可穿戴运动监测测试,可验证本传感器既可以实现手指和手腕运动等大动作应变的监测,输出电阻值相对变化达到7.5倍;也可以监测肌肉形变弯曲等小应变,输出电阻值相对变化达到1.4倍。

关键词： 微孔注塑   微观结构   聚丙烯   退火   冲击强度  

摘要： 通过二次开模微孔发泡注塑工艺制备不同聚四氟乙烯(PTFE)含量的聚丙烯(PP)微孔发泡材料,对比常规注塑成型的 PP 未发泡材料,研究不同退火温度对材料微结构及冲击强度的影响规律。结果表明,经二次开模微孔发泡注塑成型,再经退火处理能有效提高微孔发泡材料的冲击强度,达到退火前材料的 1.45 倍,而退火工艺对微孔发泡材料的微结构影响与对未发泡材料的影响基本相似。退火处理时PP材料结构中软无定型区的分子链进一步松弛,使材料更易于塑性变形,而其它软无定型区分子链易于规整重排,转变为硬无定型区,原硬无定型区的分子链同样进一步规整重排,甚至转变为结晶区,变得更硬,从而提高材料软硬兼具的抗冲击性能。

关键词： Intermetallic compound   Corrosion   EBSD   Dissimilar material joining   TEM   Friction stir welding  

摘要： The use of aluminum in conjunction of steel can reduce the weight of structures but dissimilar materials welded structure results in the formation of intermetallic compounds and inhomogeneous distribution of grains. Since aluminum is more active than the steel, the structures made from such dissimilar materials can be affected from corrosion medium which needs to be investigated. In the present work, friction stir welding has been used to join AA6061-T6 and AISI304 in lap configuration, each having a thickness of 1mm under varied process parameters. The detailed investigations have been made which includes understanding the effect of process variables on microstructures, intermetallic compounds and their phases, and thereby on corrosion of the aluminum-steel welded joint. SEM with integrated EBSD detector and XRD analyses have been carried out to characterize the weld interface that revealed the evolution of grain boundaries and existence of phases such as Fe2Al5 and AlCrFe2. The grain size of the weld zone has been found to be decreasing with increase in weld speed and plunge depth. The temperature profiles have shown a faster rate of heating and cooling with increase in welding speed and plunge depth which led to the refinement of microstructure. The evolution precipitates mainly comprised of Al, Mg and Si as the major elements. The corrosion rate was found to be increasing with decrease in grain size. Samples were corroded by pitting corrosion, inter-granular corrosion, and environmental corrosion. Severity of pits have been found to be non-uniform in the along weld cross-section.

关键词： Voronoi   多晶集合体   晶体塑性有限元   晶体取向   各向异性  

摘要： 材料的力学性能,尤其是在有限变形下所呈现的宏观各向异性,是材料结构设计和服役寿命考虑的关键因素。由于宏观模型不能较好地反映材料微观结构(晶粒的形貌和取向等)对宏观塑性各向异性的影响,因此,本文建立了能实际反映晶粒形貌的三维Voronoi模型,并基于晶体塑性理论对铝合金在有限变形下的响应进行计算。首先,建立反映材料微结构的代表性体积单元RVE模型进行计算,并与实验结果进行对比验证。然后,以单向拉伸为例,分析了有限变形过程中试件的晶粒形貌和取向分布等微观因素对宏观各向异性演化的影响,并从材料和结构两个层面讨论了微观结构对宏观力学性能的影响。结果表明,本文模型能够反映微观结构对宏观力学性能的影响,为实际生产制造领域构件的力学性能提供可靠的预测。