Nanoporous Al sandwich foils using size effect of Al layer thickness during Cu/Al/Cu laminate rolling

The roll bonding technique is one of the most widely used methods to produce metal laminate sheets. Such sheets offer interesting research opportunities for both scientists and engineers. In this paper, we report on an experimental investigation of the ‘thickness effect’ during laminate rolling for the first time. Using a four-high multifunction rolling mill, Cu/Al/Cu laminate sheets were fabricated with a range of thicknesses (16, 40, 70 and 130 μm) of the Al layer. The thickness of the Cu sheets was a constant 300 μm. After rolling, TEM images show good bonding quality between the Cu and Al layers. However, there are many nanoscale pores in the Al layer. The fraction of nanoscale pores in the Al layer increases with a reduction in the Al layer thickness. The finite element method was used to simulate the Cu/Al/Cu rolling process. The simulation results reveal the effect of the Al layer thickness on the deformation characteristics of the Cu/Al/Cu laminate. Finally, we propose that the size effect of the Al layer thickness during Cu/Al/Cu laminate rolling may offer a method to fabricate ‘nanoporous’ Al sandwich laminate foils. Such foils can be used in electromagnetic shielding of electrical devices and noisy shielding of building.     

Experimental and numerical approach on interfacial properties of W/Al bilayer films for electronic devices manufacturing

The aim of this article is to provide a systematic method for performing experimental tests and theoretical evaluations on interfacial adhesion properties of the W/Al bilayer thin films interface. Samples W/Al bilayer thin films assembly is deposited on the quartz glass by using radio frequency magnetron sputtering. Based on the analysis of the experimental indentation data, the elastic modulus and hardness of the sample are investigated. The test results show that both of the values are easily influenced by the indentation depth. At the meantime, a finite element model is built to simulate the interface mechanical properties. The analysis shows that stress is mainly centralized close to the indenter and the maximum stress occurs in the lower layer Al film, not in the upper W film. The comparison between the experiment and the simulation shows the validity of the test and the modeling of each other to a certain extent. The investigation builds a basis for future work such as the fabrication of W/Al bilayer thin films for micro/nano manufacturing.     

空间遥感器高体份SiC/Al复合材料反射镜组件设计

为消除反射镜与支撑结构材料线胀系数差异产生的热变形对反射镜面形精度、系统成像质量的影响, 采用高体份SiC/Al复合材料作为新型反射镜组件的材料。首先, 通过合理的结构设计及有限元分析比较, 确定了Ф600 mm口径反射镜结构参数, 然后, 对反射镜组件进行了静力学和动力学分析, 在1 g重力载荷作用下, 反射镜X、Y、Z方向去除刚体位移后的镜面变形RMS值分别为12.6, 12.7, 12.6 nm, 达到了λ/50(λ=632.8 nm)。最后, 为了验证高体份SiC/Al复合材料反射镜组件的结构性能及检验结构在振动条件下的抗干扰能力, 对反射镜组件进行了力学试验, 反射镜组件的一阶谐振频率为556.6 Hz。力学试验前后, 反射镜镜面面形误差RMS分别为0.021λ、0.025λ, 没有明显变化。实验结果表明:高体份SiC/Al复合材料反射镜达到了与SiC材料反射镜相同的设计指标要求, 能够满足空间应用。     

Investigation of Fe/Al interface as a function of annealing temperature using XPS

This article describes the systemic investigation of the interface chemical and electronic properties of ultrathin Fe/Al multilayer structure (MLS) as a function of annealing temperature. For this purpose electron beam evaporated [Fe/Al]_×15 ML samples have been prepared under ultrahigh vacuum conditions. The chemical and electronic information of the interfaces at different depth has been obtained from XPS technique.The core level study show a gradual change in the nature of the electronic bonding at the interface as a result of annealing. In particular, the MLS annealed at 200 °C and 400 °C clearly show shifts in the binding energy position of Fe-2p_3/2 core line towards higher energy and Al-2p_3/2 core line towards lower energy side as compared to as-deposited sample, suggesting the formation of FeAl alloy phase at the interface. Another important finding with annealing is that the intensity of peak corresponding to pure Al-2p increases and that of Fe-2p decreases as compared to as-deposited case. The increase in intensity of Al-2p core line suggests the migration of Al atoms towards the surface owing to annealing induced inter-diffusion. The corresponding valence band spectra show appreciable changes in the Fe-3d as well as Al-3s density of states due to strong hybridization of sp-d states at the Fermi level as a result of charge transfer and also provide strong evidence for FeAl alloy formation.     

Critical temperature and interface transparency of N/S/N triple layers: theory and experiment

The influence of the finite transparency, , of superconductor/normal metal (S/N) interface on the critical temperature of proximity coupled layered structures is investigated in the dirty limit on the basis of the microscopic equations solved exactly by a matrix method. The calculated theoretical curves satisfactory reproduce the experimental dependencies of the critical temperature on the thickness of the superconducting layers in N/S/N trilayers. The relation between the transparency coefficient and the normal metal coherence length is also discussed.     

SiC过渡层制备温度对碳化硅/氟化类金刚石复合薄膜血液相容性的影响

以316L不锈钢为基底,SiC晶体为靶材,Ar为源气体,采用磁控溅射法在不同温度下制备出系列SiC过渡层.然后以高纯石墨作靶,Ar和CHF_3为源气体,在同一工艺条件下再续镀一层氟化类金刚石(F-DLC)薄膜,形成SiC/F-DLC复合薄膜.研究表明,相比于F-DLC薄膜,复合薄膜的附着力显著增加,血液相容性明显改善.通过样品的拉曼和红外光谱分析了不同温度下制备的SiC过渡层以及复合薄膜结构的演变.结果表明,控制SiC过渡层制备温度可以有效调制过渡层中C=C键的比例以及—C—C—不饱和键的密度,复合薄膜中保留较高比例的芳香环式结构以及合适的F/C比是薄膜的血液相容性得以进一步改善的原因,SiC过渡层制备温度控制在500℃左右效果尤为明显.SiC薄膜和F-DLC两种薄膜的界面处形成一定比例的Si—C键和C=C键是导致复合薄膜附着力显著上升的直接原因.适当条件下在316L不锈钢和F-DLC薄膜之间增加SiC过渡层对于增强薄膜的附着力、改善其血液相容性是可行、有效的.     

Self electrization during a phase transition of thin crystalline layers of naphthalene as a function of thickness

The self electrization during solidification of thin monocrystalline layers of naphthalene is studied as a function of the thickness x. Samples of naphthalene of different electrical conductivities are investigated. It is found that k, the electrical charge per mass of crystal, is an exponential function of x, each sample exhibiting two exponentials. The values of k are higher for the more conducting samples.     

Effect of thickness and porous structure of SiC layers on the spectral response of the Pd/SiC-pSi Schottky photodiodes

In this work, we study the effect of the thickness and porous structure of silicon carbide (PSC) layers on the electrical properties of Schottky photodiodes by using a palladium (Pd) layer deposited on non-porous silicon carbide (SiC) and porous-SiC (PSC) layers. The non-porous and porous-SiC layers were realized on a p-type silicon (Si(1 0 0)) substrate by pulsed laser deposition using a KrF laser (248 nm) and thermal deposition of a thin Pd layer. The porous structure of the SiC layer deposited was developed by an electrochemical (anodization) method. The electrical measurements were made at room temperature (295 K) in an air ambience. The effect of the porous surface structure and the thickness of the SiC layer were investigated by evaluating electrical parameters such as the ideality factor (n) and barrier height (?_Bp). The thickness of the porous layer significantly affects the electrical properties of the Schottky photodiodes. Analysis of current-voltage (I-V) characteristics showed that the forward current might be described by a classical thermal emission theory. The ideality factor determined by the I-V characteristics was found to be dependent on the SiC thickness a value For a thin SiC layer (0.16 μm) n was around 1.325 with a barrier height 0.798 eV, while for a thick layer (1.6 μm), n and ?_Bp were 1.026 and 0.890 eV, respectively for Pd/SiC-pSi. These results indicate Schottky photodiodes with high performance are obtained for thicker SiC layer and for thin layer of PSC. This effect showed the uniformity of the SiC layer. In the same case the ideality factor (n) decreases for Pd/PSC-pSi(1 0 0) for low SiC thickness by report of Pd/PSC-pSi(1 0 0) Schottky photodiodes, but for Pd/PSC-pSi(1 0 0) n increase for large SiC thickness layer. We notice that the barrier height (?_Bp) was reversely depend by report of ideality factor. A spectral response value of (SR) of 34 mA/W at λ = 400 nm was measured for Pd/0.16 μm SiC-pSi Schottky photodiode with low SiC thickness. On the other hand, a value of SR = 0.14 mA/W at λ = 900 nm was obtained when we used PSC layer (Pd/PSC-pSi(1 0 0)). A reverse behaviour occurs for thicker SiC layer. Finally, it was found that the thickness and surface porous structure have strong effect on sensitivity.     

Magnetization and compensation temperature of transition-metal–rare-earth multilayers in a model with long-range interactions

A model is proposed to describe the behavior of magnetization and compensation temperature in transition-metal–rare-earth multilayers. Long-range exponentially decreasing ferromagnetic (antiferromagnetic) interactions are considered between the same (different) kind of atoms. The magnetization and compensation temperature are shown to decrease with increasing single layer thickness. Good agreement is obtained with experimental data on Tb/Co system.     

Rapid initiation of reactions in Al/Ni multilayers with nanoscale layering

Research into nanoenergetic materials is enabling new capabilities for controlling exothermic reaction rates and energy output, as well as new methods for integrating these materials with conventional electronics fabrication techniques. Many reactions produce primarily heat, and in some cases it is desirable to increase the rate of heat release beyond what is typically observed. Here we investigate the Al-Ni intermetallic reaction, which normally propagates across films or foils at rates lower than 10 m/s. However, models and experiments indicate that local heating rates can be very high (10⁷ K/s), and uniform heating of such a multilayer film can lead to a rapid, thermally explosive type of reaction. With the hopes of using a device to transduce electrical energy to kinetic energy of a flyer plate in the timescale of 100's of nanoseconds, we have incorporated a Ni/Al nanolayer film that locally heats upon application of a large electrical current. We observed flyer plate velocities in the 2-6 km/s range, corresponding to 4-36 kJ/g in terms of specific kinetic energy. Several samples containing Ni/Al films with different bilayer thicknesses were tested, and many produced additional kinetic energy in the 1.1-2.3 kJ/g range, as would be expected from the Ni-Al intermetallic reaction. These results provide evidence that nanoscale Ni/Al layers reacted in the timescale necessary to contribute to device output.     

长条型SiC反射镜轻量化及支撑结构的设计

从满足空间光学遥感器反射镜在复杂工况下综合面形误差要求的角度出发,介绍了长条型反射镜柔性支撑结构材料的选择,讨论了反射镜轻量化及柔性支撑结构的设计方法,采用有限元法进行了工程分析及多次迭代优化,设计出了一种在不同重力方向下引入面形误差变化量RMS值小于λ/40(λ=632.8nm)的反射镜柔性支撑结构。检测实验证明,各项指标均满足设计要求。     

X-ray micro-computed tomography of beech wood and biomorphic C,SiC and Al/SiC composites

The microstructures of beech wood and of beech wood-derived carbon, silicon carbide (SiC), and an aluminum/SiC composite were studied using both scanning electron microscopy (SEM) and synchrotron X-ray micro-computed tomography (µCT). As opposed to traditional two-dimensional imaging techniques, the µCT data allowed nondestructive evaluation of relatively large sample volumes. Nondestructive three-dimensional data analysis led to the observation of microstructural features, such as varying pore-wall topographies not previously seen in SEM, calculations of the volume fraction of porosity and characterization of the interconnectivity of porosity in the SiC material.     

FEM simulations and experimental studies of the temperature field in a large diamond crystal growth cell

We investigate the temperature field variation in the growth region of a diamond crystal in a sealed cell during the whole process of crystal growth by using the temperature gradient method (TGM) at high pressure and high temperature (HPHT). We employ both the finite element method (FEM) and in situ experiments. Simulation results show that the temperature in the center area of the growth cell continues to decrease during the process of large diamond crystal growth. These results are in good agreement with our experimental data, which demonstrates that the finite element model can successfully predict the temperature field variations in the growth cell. The FEM simulation will be useful to grow larger high-quality diamond crystal by using the TGM. Furthermore, this method will be helpful in designing better cells and improving the growth process of gem-quality diamond crystal.     

超轻量化SiC反射镜有限元分析及应用

对超轻量化SiC反射镜进行了有限元分析。设计了超轻量化SiC反射镜的镜体结构。采用MSC.Nastran分析软件对其进行了有限元工程分析。分析结果表明,可满足SiC反射镜面形精度的要求和轻量化的要求。介绍了一种SiC反射镜无镜框支撑结构。     

计算超薄镜最接近球面的非球面梯度法及有限元分析

利用超薄镜的弹性变形,通过主动光学技术将超薄球面镜变形为所需精度的非球面镜,可以避开大口径超薄非球面镜的制造难题。在分析了传统的非球面超薄镜最接近球面选择原则的基础上,提出了以非球面梯度作为选择原则的依据。针对一个实例,用非球面梯度法和最小二乘法分别求出两个最接近球面并对它们进行有限元法的变形分析,对它们变形后的面形精度和最大应力进行了比较。结果表明,在相同的边界条件、加载个数和加载位置的条件下,以非球面梯度法求出的最接近球面在变形后不仅应力小,且更有利于提高面形精度。     

Deformation field in deep flat punch indentation and the persistence of dead-metal zones

The indentation of metal by a flat punch is a model system for forming processes and intimately linked with hardness testing. Here, we perform first-in-class, high-fidelity finite element (FE) simulations in an arbitrary Lagrangian–Eulerian (ALE) framework to study the deformation field in deep punch indentation of annealed copper. The use of ALE allows indentation depth to punch width ratios as high as 1.6, while the use of Lagrangian tracer particles reveals pathlines of material transport. Field quantities such as the plastic strain, strain rate and velocity are obtained at high resolution. A low-strain, dead-metal zone (DMZ) that is stationary with respect to the indenter forms immediately below the punch. Crucially, it is found that DMZs are unavoidable in deep punch indentation, forming at the outset and irrespective of the coefficient of friction. However, the area of this zone shrinks as the indentation progresses at a rate that is inversely related to the friction. The simulations thus explain why Prandtl’s view of punch indentation, which incorporates DMZs, is physically more accurate than Hill’s view. The computations successfully reproduce the strain field inhomogeneity seen in recent in situ imaging experiments. While DMZ formation is impervious to the hardening model used, Zerilli–Armstrong hardening provides more accurate indentation force estimates than Johnson–Cook hardening. Lastly, the residual impression and factors affecting its shape are studied. The sides of impressed metal are never vertical, but at an inclination to it. Methods to modify such features, of potential interest in metal forming, are discussed briefly.     

基于第一性原理的Si/SiC、Al/SiC界面成键特性和结合强度对比研究

采用半固态搅拌铸造法制备Al Si7-Si C复合材料,并利用真空压铸工艺实现了其近净成形,结合第一性原理计算方法研究了共晶Si对Si C颗粒和基体界面结合强度的影响.结果显示,在Al Si7-Si C复合材料中,发现较为严重的共晶Si偏析现象,当Si C颗粒同时处于共晶Si和α-Al边界时,形成了少量的共晶Si夹杂、被大量共晶Si包裹、完全被共晶Si包裹三种典型的界面.第一性原理计算结果显示,在C端和Si端的Si/Si C界面中,弛豫后top Si¹配位方式具有最大的粘附功,与Al/Si C界面相比,Si/Si C界面具有更高的结合强度.Si偏析相提高了界面处的电荷密度,因而具有更好的界面结构稳定性.