Phase and Texture Evolution of Ag/Ni Composite-Sheathed Bi-2223 Tapes with Different Thickness

The influence of green tape thickness on the Bi-2223 phase formation and texture evolution in Ag/Ni composite-sheathed tapes fabricated by the “powder-in-tube” technique has been studied. Microstructural observations by SEM as well as critical current density (J _c) measurements at 77 K, 0 T have been performed to analyze the performance of the tapes. The results show an important influence of the green tape thickness on the critical current depending on the content and texture of Bi-2223 phase. The J _c increases with decreasing thickness. Moreover, texture measured by omega scans shows that the texture of the Bi-2223 phase is significantly influenced by the thickness of the green tape after the first and final sintering processes. Alignment of Bi-2223 grains in the thin tapes is much better. Higher performance of Ag/Ni composite-sheathed Bi-2223 tapes can be obtained by controlling the thickness of the green tapes.     

Relationship Between Growth Speed, Microstructure, Mechanical and Electrical Properties in Bi-2212/Ag Textured Composites

Transport properties on Bi-2212 superconductors can be improved by grain orientation methods while mechanical ones can be tuned up by the addition of metallic silver. Both processes can be performed simultaneously using the Laser Floating Zone (LFZ) method. In this work, Bi₂Sr₂CaCu₂O _x /3 wt.%Ag textured composite materials were prepared by a LFZ melting technique at different growth speeds (5, 15, 30, and 60?mm/h). In all cases, the observed microstructure after annealing shows the Bi-2212 phase as the major one. Although growth speed has no effect on the measured T _c values, a drastic change on the J _c values has been found. The best results, both mechanical and transport properties, have been obtained for samples grown at 15?mm/h.     

Mechanical Properties and Fracture Behavior of Mg-Al/AlN Composites with Different Particle Contents

In this study, magnesium matrix composites reinforced with different loading of AlN particles were fabricated by the powder metallurgy technique. The microstructure, bending strength and fracture behavior of the resulting Mg-Al/Al N composites were investigated. It showed that the 5 wt% AlN reinforcements led to the highest densification and bending strength. The total strengthening effect of AlN particles was predicted by considering the contributions of CTE mismatch between the matrix and the particles,load bearing and Hall–Petch mechanism. The results revealed that the increase of dislocation density,the change of Mg17Al12 phase morphology, and the effective load transfer were the major strengthening contributors to the composites. The fracture of the composites altered from plastic to brittle mode with increasing reinforcement content. The regions of clustered particles in the composites were easy to be damaged under external load, and the fracture occurred mainly along grain boundaries.     

不同淬火温度下NM500/Q345复合板耐磨层的摩擦磨损性能研究

耐磨钢/碳钢复合板不仅具有高强耐磨的双重性能优势,还可以降低能耗及生产成本.针对不同淬火工艺研究该复合板耐磨层NM500的耐磨性,对NM500/Q345复合板进行不同淬火温度下的干滑动摩擦磨损试验.借助显微硬度计测量试样表面的硬度,利用扫描电子显微镜(SEM)、白光干涉三维表面轮廓仪等分析该复合板耐磨层NM500的金相组织、磨痕的宏/微观形貌以及磨损机理.研究结果表明,当淬火温度为860～920℃时,淬火前后的硬度差别很大,淬火后的试样相比淬火前的试样硬度有很大的提高,随温度的上升先增加再降低,在温度为880℃时达到最高;摩擦因数曲线完全符合标准的干滑动摩擦磨损曲线,先快速上升然后有一定程度下降,最后趋于平稳;淬火后的磨损体积相比于淬火前会有很大程度减小,在淬火温度为860℃时,磨损量最少,耐磨性最好.     

低镍球墨铸铁低温冲击性能及断裂机理研究

使用激光共聚焦显微镜、扫描电镜和示波冲击等实验手段研究了镍元素(0.0%～0.9%,质量分数,下同)对球墨铸铁的微观组织和低温冲击性能的影响,对低温断裂机理进行了探讨。结果表明:含镍0.7%退火态球墨铸铁的韧脆转变温度低于-60℃,其-70℃下冲击功高于12J;适量镍元素添加能有效地细化晶粒和强化基体,改善球墨铸铁的低温冲击性能。     

Numerical Studies of Thermally Induced Residual Strain/Stress in Bi2Sr2Ca2Cu3O x /Ag/Ag Alloy Composite Tapes and the Dependence of Material Properties on the Temperature

Thermally induced residual strain/stress in Bi₂Sr₂Ca₂Cu₃O _x (Bi2223)/Ag/Ag alloy composite tapes and the dependence of material properties on the temperature have been studied numerically. Based on both the straight and bending 3D tape models, and with the temperature dependence on material properties (especially the coefficient of thermal expansion) among the constituents (Bi2223, Ag and Ag alloy sheath) of Bi2223 multifilament composite tapes, the residual strain accumulation and the distribution of the residual stress have been obtained. We found that by taking account of the temperature dependence on material properties of Bi2223 composite tapes the residual strain in the current transportation direction is up to 15 % larger than that without taking temperature dependence into account. Furthermore, by considering the distribution of the stress induced from the changing temperature, we analyzed the mechanical strength of Bi2223 composite tapes and concluded that the initial mechanical failure due to large temperature circle (intrinsically induced from the mismatch of the coefficient of thermal expansion of each constituent in composite tapes) comes from the following aspects: (i) the tensile fracture in the Bi2223 filaments occurring at the center of the tape and (ii) the delamination most likely arising at the interface between the Bi2223 filaments and Ag matrix near both edges of the cross-section of the tape, which originates at the Bi2223 side of the interface.     

Structure and Growth Mechanism of V/Ag Multilayers with Different Periodic Thickness Fabricated by Magnetron Sputtering Deposition

V/Ag multilayers with different periodic thicknesses were fabricated by magnetron sputtering deposition. The columnar structure and the orientation relationship of the multilayers were investigated by transmission electron microscopy, high resolution transmission electron microscopy, selected-area electron diffraction and X-ray diffraction. It was found that the multilayered structure became flatter as increasing individual layer thickness from 2 to 6 nm, and then became waved as the individual layer thickness increases to 8 nm. At the beginning of the growth, the morphology of the multilayers with small periodic thickness was influenced mainly by thermodynamic instabilities, and the morphology of the multilayers with larger periodic thickness was mainly influenced mainly by the columnar growth of V. When the waved interfaces were formed, the continuum growth of the multilayers was also influenced by the shadowing effect and the finite atomic size effect. All of these factors resulted in the columnar structure of the multilayers. Multilayers with small periodic thickness presented strong orientation relationship. Nano-hardness tests indicated that multilayers with flat sublayer morphology and clear interfaces exhibited larger hardness.     

不同应力比下Cu/WCp复合材料疲劳裂纹扩展行为及影响机制分析

通过粉末冶金工艺制备了一种高压电触头用Cu/WCp颗粒增强复合材料。研究了不同应力比下Cu/WCp颗粒增强复合材料的疲劳裂纹扩展行为,并结合裂纹闭合模型和两参数驱动力模型分析了应力比对Cu/WCp颗粒增强复合材料疲劳裂纹扩展速率的影响机制。研究结果表明:随着应力比R的增大裂纹扩展速率增大,尤其在近门槛值附近裂纹扩展速率差别最明显。裂纹闭合模型和两参数驱动力模型均可以较好地将不同应力比R下(da/d N-ΔK)关系曲线关联起来,且两参数驱动力模型的相关性更好。这说明导致不同应力比R下Cu/WCp颗粒增强复合材料疲劳裂纹扩展速率差异的原因主要是Kmax引起裂纹尖端单调损伤,其次是裂纹闭合效应。根据SEM断口分析发现高应力比的断面较低应力比的粗糙,低应力比时断口以基体撕裂为主而高应力比时以颗粒基体脱粘为主。     

碳毡及编织结构碳/碳复合材料常温力学性能研究

为研究两种不同预制体增强的碳/碳(C/C)复合材料的损伤破坏机制差别,将为该材料应用于结构件提供依据,对碳毡及2.5D编织结构增强的C/C复合材料的常温弯曲、剪切、压缩性能进行了测试,并用扫描电镜观察其断面形貌,对C/C复合材料在静态载荷下的力学性能及损伤破坏行为进行研究,探讨有关因素对材料性能和损伤破坏的影响.研究结果表明:两种不同增强体的C/C复合材料的断裂机理存在很大差异,且密度对C/C复合材料的常温力学性能有较大的影响.     

EMG作增容剂的PPS/PA1010合金的力学性能及增容机理

将用4,4′-二苯基甲烷二异氰酸酯(M D I)化学处理过的PPS(简称CPPS)与PA 1010及高分子量的乙烯、马来酸酐、甲基丙烯酸缩水甘油酯三元共聚物(简称EM G)共混,制备了一系列不同配比的CPPS/PA 1010/EM G共混物,并对这些共混物的力学性能进行了测试。结果表明,当M D I含量在2.0份~2.5份之间时,材料的综合力学性能较好。而随着EM G含量的增加,材料的冲击强度显著提高,且其它的力学性能基本保持不变。并推测了增容机理。     

Ni-P/CaF_2复合镀层的高温抗氧化及耐磨性能

基于化学镀 Ni- P镀层的耐腐蚀和 Ca F2 粒子的高温自润滑性能 ,设计并获得了化学镀 Ni- P/Ca F2 复合镀层 ,通过自行设计制造了用于高温耐磨性能测试的试验机。研究表明 ,该镀层在高温条件下具有优异的抗氧化性能和自润滑减磨性能。而且在 70 0℃以下 ,随测试温度的增加 ,镀层的磨损量降低     

Ni-P/CaF2复合镀层的高温抗氧化及耐磨性能

基于化学镀Ni-P镀层的耐腐蚀和CaF2粒子的高温自润滑性能,设计并获得了化学镀Ni-P/CaF2复合镀层,通过自行设计制造了用于主温耐磨性能测试的试验机,研究表明,该镀层在高温条件下具有优异的抗氧化性能和自润滑减磨性能,而且在700℃以下,随测试温度的增加,镀层的磨损量降低。     

Behavior of a PCM at Varying Heating Rates: Experimental and Theoretical Study with an Aim at Temperature Moderation in Radionuclide Concrete Encasements

Phase-change materials (PCMs) can store/release thermal energy within a small temperature range. This is of interest in various industrial applications, for example, in civil engineering (heating/cooling of buildings) or cold storage applications. Another application may be the moderation of temperature increases in concrete encasements of radionuclides during their decay. The phase-change behavior of a material is determined by its heat capacity and the peak it exhibits near a phase change. We analyze the behavior of such peaks for a selected PCM at heating rates varying between \(0.1\,^{\circ }\hbox {C}\cdot \hbox {min}^{-1}\) and \(1\,^{\circ }\hbox {C}\cdot \hbox {min}^{-1}\), corresponding in real situations to different decay rates of radionuclides. We show that experimentally measured peaks can be plausibly described by an equilibrium theory that enables us to calculate the latent heat and phase-change temperature from experimental data.     

The Critical Temperature and Reproducibility of Al/Au Bilayer Thermometers Fabricated with Different Al/Au Thickness Ratios by Vacuum Evaporation Techniques

We present further results from a study of Al/Au bilayer thermometers constructed for third sound detection. Here we report the transition temperature of such thermometers as a function of the Al/Au thickness ratio. We also report on the reproducibility of fabrication.     

The Effects of Different Cranial Modules on Mechanical Properties of Cranial Suture in Lewis Rats and Same-aged C57BL/6 Mice

Abstract:  In this study we aimed at investigating size effects on mechanical properties of cranial suture in different animal research models. Lewis rats and C57BL/6 mice were selected as the larger research model and smaller research model, respectively. The objective of this study was to determine the mechanical properties of different cranial modules of cranial sutures in Lewis rats and same-aged C57BL/6 mice. Ten sagittal sutures were harvested from 4-month-old Lewis rats and C57BL/6 mice. The specimens, kept moist, were mounted fresh and distracted until rupture. A load–displacement curve was constructed. The stiffness, Young's modulus, fracture stress and fracture energy were calculated. Moreover, scanning electron microscope (SEM) images and fracture mechanisms are discussed. Cranial modules in Lewis rats and same-aged C57BL/6 mice are also provided. The results show differences between the two groups, with higher values from Lewis rat. Higher mechanical properties occurred mainly on the large type of cranial module in this mammalian system.     

Correlation Between the Degradation of Perpendicular Anisotropy and the Double Hysteresis Behavior in [Pd/Co]$_{rm n}$/FeMn Exchange Biased Thin Films

We clearly detected double hysteresis by increasing Co layer thickness and decreasing the number of bilayers in perpendicular exchange biased [Pd(0.6)/Co$(t)$] $_{rm n}$/FeMn(11.6 nm) thin films. In-plane tensile stress calculations confirmed that the appearance of double hysteresis is closely related to the degradation of stress-induced perpendicular anisotropy in the [Pd/Co] multilayers. Furthermore, annealing at the magnetic field applied perpendicular to the film plane directly verified that the enhancement of thermally induced perpendicular anisotropy, $K_{rm eff-induced}$, in the [Pd/Co] multilayers is the main physical reason for removal of the double hysteresis. All our experimental and theoretical results demonstrated that perpendicular anisotropy is the dominant factor in controlling the double hysteresis behavior of perpendicularly magnetized [Pd/Co]$_{rm n}$/FeMn exchange biased thin films.      

The First-principles Study on the Occupation Behavior and the Ductility Mechanism of Zr in Ni-Ni3Al System with Lattice Misfit

The influence of lattice misfit on the occupation behavior and the ductility effect of Zr in Ni-Ni3Al alloys were explored. It is found in energy analysis that the preferable site of Zr between Ni sublattice and Al sublattice will change under different lattice misfit, however, the Zr prefers to segregate Ni phase rather than Ni3Al phase in all lattice misfit range, which makes it impossible for Zr to go into Ni3Al phase to occupy Al sublattice in Ni-Ni3Al system. Bond order （BO） analysis shows that the localized ductility effect of Zr differs in different region, and the comparison between Zr-free and Zr-doped BO analysis successfully explain the mechanism of the embrittlement of Ni-Ni3Al alloys and the ductility effect of Zr.