关键词： Co-Cr alloy   fabrication techniques   CAD/CAM   microstructure   mechanical properties  

摘要： The microstructures and mechanical properties of cobalt-chromium (Co-Cr) alloys produced by three CAD/CAM-based processing techniques were investigated in comparison with those produced by the traditional casting technique. Four groups of disc- (microstructures) or dumbbell- (mechanical properties) specimens made of Co-Cr alloys were prepared using casting (CS), milling (ML), selective laser melting (SLM), and milling/post-sintering (ML/PS). For each technique, the corresponding commercial alloy material was used. The microstructures of the specimens were evaluated via X-ray diffractometry, optical and scanning electron microscopy with energy-dispersive X-ray spectroscopy, and electron backscattered diffraction pattern analysis. The mechanical properties were evaluated using a tensile test according to ISO 22674 (n = 6). The microstructure of the alloys was strongly influenced by the manufacturing processes. Overall, the SLM group showed superior mechanical properties, the ML/PS group being nearly comparable. The mechanical properties of the ML group were inferior to those of the CS group. The microstructures and mechanical properties of Co-Cr alloys were greatly dependent on the manufacturing technique as well as the chemical composition. The SLM and ML/PS techniques may be considered promising alternatives to the Co-Cr alloy casting process.

关键词： Microstructure   Phase field   Green function   Fourier   Two-scale   FE-FFT  

摘要： The purpose of this work is the development of a two-scale phase-field-based computational model for coupled microstructure evolution and macroscopic mechanical material behavior. To this end, the mechanical behavior of the macroscopic continuum is based on a model for each of its material elements or points as a unit cell (UC) whose average properties determine those of the corresponding material point. The UC model itself is based on materially inhomogeneous elasticity, with material inhomogeneity resulting from microstructure evolution in the UC, driven in particular by stress relaxation. Since the focus of the current work is on computational aspects, microstructure evolution is restricted here for simplicity to bulk structural rearrangement (e.g., austenite-martensite transformation). Consequently, the corresponding phase fields are non-conservative. As well for simplicity, the current formulation is restricted to geometric linearity. The algorithmic formulation and numerical solution of the microscopic initial-boundary-value problem (IBVP) for mechanical equilibrium and relaxational dynamics in the UC is based on Green function and (fast) Fourier transform (FFT) methods. On the other hand, the algorithmic formulation and numerical solution of the macroscopic BVP for quasi-static macroscopic mechanical equilibrium is based on finite element (FE) methods. To demonstrate its capabilities, the current two-scale computational approach is applied in the last part of the work to the modeling and simulation of single-and polycrystalline UCs undergoing structural rearrangement from austenite into multiple martensite variants during loading of the macroscopic continuum. (C) 2016 Elsevier B.V. All rights reserved.

关键词： Mars   Atmospheres   Dynamics   Geophysics   Regoliths  

摘要： As Viking Lander 1 touched down on Mars one of its footpads fully penetrated a patch of loose fine-grained drift material. The surrounding landing site, as observed by VL-1, was found to exhibit a complex terrain consisting of a crusted surface with an assortment of rocks, large dune-like drifts and smaller patches of drift material. We use a temperature sensor attached to the buried footpad and covered in fine-grained material to determine the thermal properties of drift material at the VL-1 site. The thermal properties are used to investigate the microstructure of the drift material and understand its relevance to surface-atmosphere interactions. We obtained a thermal inertia value of 103 +/- 22 tiu. This value is in the upper range of previous thermal inertia estimates of martian dust as measured from orbit and is significantly lower than the regional thermal inertia of the VL-1 site, of around 283 tiu, obtained from orbit. We estimate a thermal inertia of around 263 +/- 29 tiu for the duricrust at the VL-1 site. It was noted the patch of fine-grained regolith around the footpad was about 20-30 K warmer compared to similar material beyond the thermal influence of the lander. An effective diameter of 8 +/- 5 mu m was calculated for the particles in the drift material. This is larger than atmospheric dust and large compared to previous estimates of the drift material particle diameter. We interpret our results as the presence of a range of particle sizes, <8 mu m, in the drift material with the thermal properties being controlled by a small amount of large particles (similar to 8 mu m) and its cohesion being controlled by a large amount of smaller particles. The bulk of the particles in the drift material are therefore likely comparable in size to that of atmospheric dust. The possibility of larger particles being locked into a fine-grained material has implications for understanding the mobilisation of wind blown materials on Mars. (C) 2016 Elsevier Inc. All right

关键词： 铝   铜   异种金属   力学性能   摩擦焊  

摘要： 以6082-T6铝和商业纯铜为对象,研究了Al-Cu的连续驱动摩擦焊,利用光学显微镜、扫描电子显微镜和X射线衍射分析技术分析了焊接界面的微结构。结果表明,接头的拉伸强度比铝母材的强度高3.8%。焊接接头的拉伸断裂位置发生在铝侧,断裂形貌表明失效形式为韧窝状结构的韧性断裂。

关键词： NbSiN纳米复合膜   显微结构   超硬效应   强化机制  

摘要： 采用NbSi复合靶,通过调节Nb与Si的比例,利用磁控溅射射频工艺,在单晶硅片上沉积不同Si含量的NbSiN纳米复合膜。利用X射线衍射仪、纳米压痕仪和高分辨透射电镜等,研究了Si含量对NbSiN纳米复合膜的微观结构和力学性能的影响。结果表明:随着薄膜中Si含量的增加,其结晶程度先升高,然后降低,硬度和弹性模量先增加后降低,当n(Si):n(Nb)=5:20时,NbSiN薄膜硬度和弹性模量均达到最大值33.6和297.2 GPa。微观组织观察表明,此时NbSiN薄膜内部形成Si_3N_4界面相包裹NbN纳米晶粒的纳米复合结构,Si_3N_4界面相呈结晶态协调相临NbN纳米晶粒间的位向差,并与NbN纳米晶粒之间形成共格外延生长,其微结构可用nc-NbN/c-Si_3N_4模型来表示,表明其超硬效应源于NbN基体相和Si_3N_4界面相之间形成的共格外延生长界面。

关键词： 小籽粒种子   排种   物理机械特性   测量  

摘要： 小籽粒种子的排种物理机械特性参数是排种方法和原理选择、排种器结构和性能设计的重要依据。本文对谷子、苜蓿、油菜等小籽粒种子的千粒重、密度、外形尺寸、硬度、摩擦系数进行了测量。结果表明：所测种子千粒重、密度范围分别为1.98-3.30g、0.55-0.68g·cm-3;三轴尺寸长、宽、高范围分别为1.80-3.50mm、1.69-2.23mm、1.14-2.00mm;硬度范围为11.04-41.76N;对钢材的静、动摩擦系数最小,范围为0.488-0.627、0.377-0.565。小籽粒种子排种物理机械特性参数的测量为排种原理方法的选择、排种器结构性能的设计提供了理论依据。

关键词： 水化硬化机理   水泥基材料   构形   中国硅酸盐学会   南召   学术交流   物理力学性能   研讨内容  

摘要： 为了促进学科发展，充分发挥中国硅酸盐学会的学术交流优势和《硅酸盐学报》作为开展学术交流、学术争鸣重要阵地的作用，定于2016年8月14日～16日在山东省济南市举办水泥基材料水化硬化机理与微结构形成研讨会，研讨内容为：水泥基材料的组成、水化硬化机理、微结构形成及其与物理力学性能的关系。

关键词： X射线成像   复合阳极   三维结构   连通性  

摘要： 固体氧化物燃料电池(Solid Oxide Fuel Cell,SOFC)阳极不仅提供了电化学反应的三相界面(Three-phase boundary,TPB)区域,而且在物质传输、扩散和燃料电池反应中不同物质之间的隔离起到积极作用。在运行期间,电极微结构发生变化。对SOFC阳极微结构演变的研究能够帮助我们理解长期运行的SOFC性能损失的原因。近年来不断发展的X射线纳米CT(Computed Tomography)技术使得可以无损地获得测试前后的阳极三维微结构。本文利用硬X射线纳米CT技术对Ni-YSZ复合阳极进行了三维重建,并采用自主开发的一些定量分析方法来获得阳极微结构的关键参数,如颗粒尺寸、每种相的体积分数和连通率等。发现在电池测试后,Ni颗粒尺寸增大,与之相对是由于Ni颗粒的聚集导致Ni相的连通性和三相界面长度明显下降。结果表明,在电池测试过程,Ni颗粒发生了团聚,电极微结构发生了改变,进而导致SOFC性能损失。阳极结构的数据表明,X射线纳米CT技术能够作为一个强力工具研究能源材料的微结构,为阳极结构优化提供重要参考数据。

关键词： Bamboo   Biomechanics   Viscoelasticity   Microstructure   Multi-scale mechanical characterization   Molecular dynamics simulation  

摘要： In this study, the intrinsic viscoelastic mechanical behavior of a hierarchical bio-composite, structural bamboo material, was experimentally investigated and correlated with its microstructural constituents and molecular building blocks. The macroscopic viscoelastic responses of bulk bamboo at ambient temperature and dehydrated condition were evaluated through dynamic compression experiments with various loading frequencies, whereas the localized viscoelasticity of bamboo's microstructural phases, viz, fibers and parenchyma cells, were evaluated separately through series of nano-indentation studies. The viscoelastic responses of the bamboo's building blocks were further evaluated at the molecular level, using the computational creep tests via constant force Steered Molecular Dynamics (SMD) simulations. A phenomenological viscoelastic model was then developed to explain the observed microstructure viscoelastic property relationship. Based on the model and conducted microstructural characterizations, it was believed that the small evolved viscous phases within the parenchyma cells were mainly responsible for the smaller viscoelasticity in bulk bamboo at lower loading frequencies, whereas the exhibited larger viscoelasticity at higher loading frequencies was stemmed out from the concurrent contribution of fibers and parenchyma cells. The findings could be important for understanding the intrinsic viscoelasticity in other biological materials with hierarchical structures, as well as for optimizing the design of bio-inspired composites with favorable structural properties. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Irradiation   bcc   Dislocation channel   Localization   Crystal plasticity  

摘要： A continuum crystal plasticity framework is used to study the effect of microstructure and mesoscopic factors on dislocation channeling and flow localization in an irradiated model bcc alloy. Simulated dislocation channeling characteristics are correlated to the dislocation and defect densities in the substructure, local Schmid factor, and stress triaxiality, in terms of their temporal and spatial evolution. A metric is introduced to assess the propensity for localization and is correlated to the grain-level Schmid factor. It is found that localization generally takes place in grains with a local Schmid factor in the range 0.42 or higher. Surface slip step heights are computed at free surfaces and compared to relevant experiments. Published by Elsevier Ltd on behalf of Acta Materialia Inc.