双屏蔽(B4C-W)/6061Al层状复合板设计与性能

基于B₄C和W良好的屏蔽中子和γ射线性能,采用6061铝合金作为基体,设计了一种新型双屏蔽(B₄C-W)/6061Al层状复合材料,通过放电等离子烧结后加热轧制成板材,对制备的复合材料微观组织和力学性能进行了研究。结果表明,屏蔽组元B₄C和W颗粒均匀地分布在6061Al基体中,层界面、B₄C/Al、W/Al异质界面之间结合良好,无空隙和裂纹。在颗粒与基体界面处形成扩散层,扩散层的厚度约为6 μm (W/Al)和4 μm (W/Al)。轧制态的(B₄C-W)/6061Al层状复合板的屈服强度(109 MPa)和极限抗拉强度(245 MPa)明显优于烧结态的复合材料,但断裂韧性降低。强度提高的原因主要是轧制后颗粒的二次分布、均匀性及界面结合强度提高,基体合金的晶粒尺寸减小,位错密度增加。层状复合板的断裂方式为基体合金的韧性断裂和颗粒的脆性断裂。      

Microstructure, chemistry and coating properties of ion-plated TiN on type 304 stainless steel

Characterization of TiN coatings on type 304 stainless steel was carried out using a Zeiss EM 902A energy filtering transmission electron microscope equipped with an electron energy loss spectroscopy (EELS) detector. TiN thin films were produced by a hollow cathode discharge ion plating coater. It was found by plan-view transmission electron microscopy that the microstructure of the TiN coatings is thickness dependent. The grain size of TiN ranges from 88 nm at the coating surface down to 9 nm near the TiN/steel interface. In addition, the TiN surface layer shows some degree of texture, but the subsurface and internal TiN layers are mainly equiaxial and randomly oriented. Chemical analysis by EELS shows that the relative oxygen content increases linearly from the TiN surface to the TiN/steel interface, whereas the relative nitrogen content first decreases slowly and then drops rapidly near the interface. The presence of a Ti₂N phase and the deficiency of nitrogen near the TiN/steel interface suggest that the early-deposited TiN is nonstoichiometric. By the periodic cracking method, the ultimate shear stress at the TiN/steel interface and the residual stress in the TiN thin film were estimated to be 2.2 GPa and 12.8 GPa, respectively.     

连续石墨纤维增强铝基复合材料准静态拉伸损伤演化与断裂力学行为

针对连续石墨纤维增强铝基(CF/Al)复合材料,采用三种纤维排布方式的代表体积单元(RVE)建立了其细观力学有限元模型,采用准静态拉伸试验与数值模拟结合的方法,研究了其在轴向拉伸载荷下的渐进损伤与断裂力学行为。结果表明,采用基体合金和纤维原位力学性能建立的细观力学有限元模型,对轴向拉伸弹性模量和极限强度的计算结果与实验结果吻合良好,而断裂应变计算值较实验结果偏低。轴向拉伸变形中首先出现界面和基体合金损伤现象,随应变增加界面发生失效并诱发基体合金的局部失效,最后复合材料因纤维发生失效而破坏,从而出现界面脱粘后纤维拔出与基体合金撕裂共存的微观形貌。细观力学有限元分析结果表明,在复合材料制备后纤维性能衰减而强度较低条件下,改变界面强度和刚度对复合材料轴向拉伸弹塑性力学行为的影响较小,复合材料中纤维强度水平是决定该复合材料轴向拉伸力学性能的主要因素。     

Ab initio study on the lattice instability of silicon and aluminum under [0 0 1] tension

Two different single crystals, Si with the diamond structure and Al with face-centered-cubic, are subjected to [0 0 1] tension in ab initio molecular dynamics (static) simulations based on Bachelet–Hammann–Schlüter (BHS) pseudopotential. Not only the ideal tensile strength under isotropic Poisson contraction, but also the crystal stability and bifurcation to anisotropic contraction are discussed in terms of the elastic stiffness matrix and the change in the charge density. The ideal tensile strengths are overestimated to as high as =0.18, σ=18.7 GPa for Si and =0.25, σ=23.5 GPa for Al, respectively. These values are inconsistent with the experimentally observed characteristics such as the hardness of Al being lower than that of Si. The elastic stiffness matrix reveals that the crystals become unstable at far lower strain and stress, =0.094, σ=10.7 GPa for Si and =0.055, σ=5.65 GPa for Al, and bifurcate to the lower energy pass of the anisotropic contraction. The change in the electronic structure suggests that nucleation/passage of a partial dislocation would take place in the bifurcated anisotropic contraction. Thus the instability point indicates the onset of the nonelastic deformation and is much more important than the ideal tensile strength.     

Fracture toughness of selectively reinforced Al2124 alloy: precrack tip in the aluminium alloy side

Abstract

The fracture toughness of Al2124/Al2124+SiC bimaterials is affected by thermal residual stresses, elastic/plastic mismatch, precrack tip position, and failure mechanism. When the precrack tip is in the Al2124 side, final catastrophic failure occurs when ductile fracture of the Al2124 layer between the precrack tip and the composite side takes place, followed by fracture of the composite layer. For a precrack tip 2·0 mm from the interface, K _Q(5%) values are lower than the 'Al2124 only' value due to the near crack tip tensile residual stresses and higher stress triaxiality within the Al alloy ligament. At 0·5 mm from the interface, K _Q(5%) values increase and are usually as high as the 'Al2124 only' value due to the stronger shielding of the elastic/plastic mismatch. If the precrack tip is 2·0 mm from the interface, K _crit values of the bimaterial are higher than the 'Al2124 only' value and this is deduced to be due to the elastic/plastic mismatch shielding. At 0·5 mm from the interface, K _crit values are reduced because both the near tip tensile residual stress is higher and stress triaxiality levels of the ductile ligament are higher, although the elastic/plastic mismatch shielding is also higher at this position.     

Mechanisms of Peeling Failures of Bonds During Ultrasonic Wedge Bonding

The metallization of wire bonding pads on Si-based integrated circuits (ICs) contains Ti, TiN, and Al layers with vertical W-plugs located through the Ti and TiN layers. One percent Si-Al wire (32 µm in diameter) was bonded on the pads by an ultrasonic transducer using a wire bonding machine. Peeling failures occurred during the ultrasonic bonding process. The peeling fractures were examined using a scanning electron microscope (SEM) with an energy-dispersive spectroscopy (EDS) system. The results showed that bonds peeled off from the interface between the Al layer and the top surface of the W-plugs or from the interface between the Si-base and the bottom surface of the W-plugs. The distribution of W-plugs also affected the bond peeling from the top or bottom surfaces of the W-plugs. Mechanisms giving rise to the peeling failure of bonds were analyzed based on the acoustic impedance of materials, which determined the amount of ultrasonic energy transmitted from one material to another. Two different paths of ultrasonic energy transmission occurred during the bonding process due to the different acoustic impedances of the materials. One is from the Al layer, through the TiN and Ti layers, to the IC. The other is from the Al layer, through the W-plugs, to the IC. The different distributions of ultrasonic energy at the positions with W-plugs and without W-plugs caused stress concentrations around the top or bottom surfaces of the W-plugs, which resulted in peeling failures of the bonds.     

Reinvestigation of the tensile strength and fracture property of Ni(1 1 1)/α-Al2O3(0 0 0 1) interfaces by first-principle calculations

First-principle calculations are performed to reinvestigate the mechanical tensile property and failure characteristic of Ni/Al₂O₃ interfaces, in order to clear the inconsistence existed in the literatures. Four types of interface models without initial lateral stresses are used, i.e., Al-terminated O-site, O-terminated Al-site, Al-terminated Al-site and Al-terminated H-site models. Two kinds of tensile methods, viz., uniaxial extension and uniaxial tension, are adopted to check the mechanical responses of these interface models. It is found that the results under uniaxial extension are generally consistent with those under uniaxial tension, including the overall shapes of stress–strain curves and the values of tensile strengths. Moreover, the initial lateral stresses have an apparent influence on the mechanical properties of the interfaces during the loading process, such as tensile strength, fracture strain and the work of separation. Our simulation results also clarified that, under tensile loading, the most stable O-terminated Al-site interface model tends to fracture in a brittle way along the sublayer between in-plane Ni–Ni atomic bonds, while all of the Al-terminated interface models will fail in a ductile fracture manner with relatively lower stress levels, breaking along the interlayer between the Ni(1) and Al(1) layers.     

界面结构对SiCf／Al复合材料性能和声发射行为的影响

运用高分辨场发射扫描电镜（ＦＥ－ＳＥＭ）和声发射（ＡＥ）测试研究了ＳｉＣ纤维铝基复合材料的不同界面组成和界面产物及其对复合材料性能和ＡＥ行为的影响发现富碳自理的ＳｉＣｆ／Ａｌ生成Ａｌ４Ｃ３脆性界面,在伸过程中界面脆断产生许多中幅ＡＥ信号,而富ＳｉＯ２处理的ＳｉＣｆ／Ａｌ生成韧工较高的富氧产物,界面强度较高,在形变过程中不易发生界面断裂,不产生中幅ＡＥ信号。     

热轧高含量B4C颗粒增强Al基复合材料的成形性能

高含量B₄C (B₄C≥30wt%)颗粒增强Al基(B₄C_P/Al)复合材料具有优异的结构和功能特性,尤其是具有优异的中子吸收性能,在核防护领域被用做屏蔽材料使用。但由于高含量B₄C颗粒的加入,使B₄C_P/Al复合材料变形困难。采用ABAQUS数值模拟方法对不同变形量下B₄C_P/Al复合材料的热轧过程进行数值模拟分析,在480℃温度下对热压烧结的B₄C_P/Al复合材料坯料进行轧制,并对其微观组织和力学性能进行分析。数值模拟结果表明,热轧变形量达到60%以上时,B₄C_P/Al复合材料板材表面中间区域应力较小,侧面应力较大,在板材边缘容易产生残余应力。研究结果表明,随轧制下压量的增加,B₄C_P/Al复合材料中B₄C颗粒分布明显均匀,位错密度增加。当轧制变形量达到70%时,B₄C_P/Al复合材料的屈服强度提高至249.46 MPa,极限抗拉强度提高至299.56 MPa。在拉伸过程中,B₄C颗粒优先断裂,但并未与基体界面脱黏,B₄C颗粒承受了主要载荷,Al基体发生塑性流动,从而提高了B₄C_P/Al复合材料的强度。      

密度对C/C复合材料热力学性能的影响

采用针刺预制体经化学气相沉积与沥青浸渍-高压碳化致密工艺制备C/C复合材料,通过控制沥青浸渍-高压碳化致密次数,获得了密度分别为1.70g/cm~3、1.82g/cm~3、1.89g/cm~3的三种C/C材料,测试材料的力学、热学性能。结果表明材料拉伸强度随密度升高而降低。当密度较低时,纤维/基体界面结合强度相对较低,可以延缓纤维断裂的发生;拉伸断口显示出假塑性断裂特征,有利于材料拉伸强度的提高。材料的压缩强度与剪切性能密切相关,且均随密度升高表现出先升后降的趋势。材料的热膨胀系数随密度升高而增大,材料中微晶之间的空隙在受热过程中可以吸收一部分膨胀量,因此对于C/C材料,降低密度有利于降低热膨胀系数。材料导热系数随密度升高而明显增大,且随密度升高,微晶尺寸增大,有利于晶格振动的传递,从而使得导热系数增大。热应力因子随密度升高而先升后降,作为热结构件使用时,采用密度为1.82g/cm~3的C/C材料可以获得相对较高的抗热震能力。在C/C材料研究开发中,可以综合对材料力学、热学性能的要求来对C/C材料密度指标进行设计。     

High-strength and highly-uniform composite produced by anodizing and accumulative roll bonding processes

The anodizing and accumulative roll bonding (ARB) processes are used in this paper as a new, effective alternative for manufacturing high-strength and highly-uniform aluminum/alumina composites. Four different thicknesses of alumina layers are grown on the substrate using an anodizing process and the microstructural evolution and mechanical properties of the resulting aluminum/alumina composite are investigated. Microscopic investigations of the composite show a uniform distribution of alumina particles in the matrix. It is found that alumina layers produced by the anodizing process neck, fracture, and depart as the number of accumulative roll bonding passes increases. During ARB, it is observed that as strain increases with the number of passes, the strength and elongation of the produced composites correspondingly increase. Also, by increasing alumina quantity, tensile strength improves so that the tensile strength of the Al/3.55 vol.% Al₂O₃ composite becomes ∼3.5 times greater than that of the annealed aluminum used as raw material.     

Alteration of internal stresses in SiO2/Cu/TiN thin films by X-ray and synchrotron radiation due to heat treatment

A break of wiring by stress-migration becomes a problem with an integrated circuit such as LSI. The present study investigates residual stress in SiO₂/Cu/TiN film deposited on glass substrates. A TiN layer, as an undercoat, was first deposited on the substrate by arc ion plating and then Cu and SiO₂ layers were deposited by plasma coating. The crystal structure and the residual stress in the deposited multi-layer film were investigated using in-lab. X-ray equipment and a synchrotron radiation device that emits ultra-high-intensity X-rays. It was found that the SiO₂ film was amorphous and both the Cu and TiN films had a strong {1 1 1} orientation. The Cu and TiN layers in the multi thick (Cu and TiN:1.0 μm)-layer film and multi thin (0.1 μm)-layer film exhibited tensile residual stresses. Both tensile residual stresses in the multi thin-layer film are larger than the multi thick-layer film. After annealing at 400 °C, these tensile residual stresses in both the films increased with increasing the annealing temperature. Surface swelling formations, such as bubbles were observed in the multi thick-layer film. However, in the case of the multi thin-layer films, there was no change in the surface morphology following heat-treatment.     

X-ray reflectivity study on TiN/Ti/Si structures before and after annealing

X-ray reflectivity was employed as a powerful tool for studying the surface and interface roughness and thickness, as well as density, of TiN/Ti/Si layers. X-ray reflectivity of the as-deposited samples, with nominal thickness of 17.5 nm of Ti and 3.0 nm of TiN, shows uniform oscillations. When the samples are annealed at 710°C, residual strongly attenuated oscillations are still observed, while the 850°C-annealed sample does not show oscillations, indicating high surface and interface roughness of the formed nitride and silicide layers. It is demonstrated that increased interface roughness, even for a layer with a larger average electron density difference, reduces the oscillations in the reflectivity curve very rapidly. For comparison, cross sectional transmission electron microscopy was employed to find the thickness of the surface and interface layers in silicide structures, which are in good agreement with the X-ray reflectivity results. The work was also supported by tapping mode atomic force microscopy observations, where we have observed nearly flat structures for the as-deposited sample surface and needle-like protrusions for the annealed samples. The surface roughness of the top TiN layer was used to obtain simulated X-ray reflectivity spectra in good agreement with the experimental results. Preliminarily, the crystallography of the layers in the samples was determined by the grazing angle X-ray diffraction technique, to acquire knowledge on the Ti and Si compounds formed in the samples after the annealing.     

水下搅拌摩擦焊对铝/铜接头组织与性能的影响

目的 采用搅拌摩擦焊,对比分析大气环境和水下环境下铝/铜接头的组织与性能,以期获得力学性能更优异的铝/铜焊接接头。方法 利用搅拌摩擦焊,在焊接速度为40 mm/min、旋转速度为1 000 r/min的条件下,分别在大气环境和水下环境下对厚度为9 mm的6061铝合金板和T2纯铜板进行焊接。然后,对铝/铜界面、焊核区进行扫描电镜及能谱分析,并对铝/铜界面及焊核区进行物相分析,确定产物相组成。最后,对铝/铜试样进行拉伸及硬度检测。结果 铝/铜接头均无裂纹、气孔等缺陷。铜颗粒弥散分布在焊核区,铝/铜界面形成金属间化合物层。水下搅拌摩擦焊下界面元素扩散距离明显变短,且金属间化合物厚度更薄。铝/铜接头的金属间化合物为AlCu和Al4Cu9。大气环境焊接下接头的抗拉强度为130.6 MPa,断裂方式为脆性断裂;水下焊接下接头的抗拉强度为199.5 MPa,断裂方式为韧性断裂。水下环境下的接头硬度值更高,其中热影响区的硬度最低值约为65HV。结论 水下搅拌摩擦焊铝/铜接头无裂纹、气孔等缺陷。组织上,水下搅拌摩擦焊的铝/铜接头界面元素扩散距离更短,硬脆的金属间化合物更少;性能上,水下搅拌摩擦焊的铝/铜接头强度更高,抗拉强度达到199.5 MPa,达到母材的74.4%。     

Diffusion and adhesion properties of Cu films on polyimide substrates

Copper thin films were prepared on polyimide (PI) substrates by physical vapor deposition (PVD) and chemical vapor deposition (CVD). Titanium nitride (TiN) diffusion barrier layers were deposited between the copper films and the PI substrates by PVD. Auger electron spectroscopy compositional depth profile showed that TiN barrier layer was very effective in preventing copper diffusion into PI substrate even after the Cu/TiN/PI samples were annealed at 300 °C for 5 h. For the as-deposited CVD-Cu/PI, CVD-Cu/TiN/PI, and as-deposited PVD-Cu/PI samples, the residual stress in Cu films was very small. Relatively larger residual stress existed in Cu films for PVD-Cu/TiN/PI samples. For PVD-Cu/TiN/PI samples, annealing can increase the peeling strength to the level observed without a diffusion barrier. The adhesion improvement of Cu films by annealing treatment can be attributed to lowering of the residual tensile stress in Cu films.     

The Fabrication and Properties of the Squeeze-Cast TiN/Al Composites

Co-continuous TiN/Al composites with different volume fractions of Al phase have been fabricated by the squeeze-casting method. TiN porous ceramics with different porosities were fabricated through carbothermal reduction by changing the content of TiN and were used as preforms. The outstanding mechanical properties were attributed to the absence of excessive interface reaction between TiN and Al for the co-continuous TiN/Al composites. With the increase of Al content in the composites, the flexural strength and the microhardness decreased, and the fracture toughness increased. The strengthening and toughening mechanism of composites included dislocation strengthening, ductile rupture, crack deflection, and secondary cracks.     

Effect of thermal cycling on the adhesion strength of Ti/Ni/Ag films on AlN substrate

The adhesion strength of Ti/Ni/Ag multi-layers on AlN substrates before and after thermal cycling treatment was studied. The Ti/Ni/Ag layers with thicknesses of 0.6, 1.0, and 0.2 μm, respectively, were deposited sequentially on bulk AlN substrates using direct current (DC) sputtering. Thermal cycling test (TCT) was conducted for 0, 15, 100, and 300 cycles to measure the adhesion strength of Ti/Ni/Ag on AlN. The adhesion strength of the deposited specimen increased slightly over 15 thermal cycles and increased abruptly after 100 thermal cycles. After 100 thermal cycles, Ti reacted with AlN substrate to form TiN and TiO. The formation of TiN and TiO at the Ti/AlN interface may be responsible for the increase of the adhesion strength after a large number of thermal cycles.     

SiCp／Al复合材料的微观结构与界面

对用压力铸造法制造的碳化硅颗粒增强铝合金（ＳｉＣｐ／Ａｌ）复合材料的微观结构和界面进行了研究。结果表明：碳化硅颗粒在复合材料中均匀分布，复合材料的基体中有较高的位错密度，碳化硅颗粒中有少量的层错。研究还发现ＳｉＣｐ／Ａｌ复合材料中界面结合良好，没有反应物生成，并且在界面处没有发现孔隙存在。在复合材料拉伸断口上没有发现裸露的碳化硅颗粒，说明在复合材料拉伸破坏时ＳｉＣｐ－Ａｌ界面没有开裂，反映了压铸ＳｉＣｐ／Ａｌ复合材料中良好的界面结合。     

Influences of Fe-impurity on the production process of SiC fiber reinforced Al for electric cables

As electrical power demands increase every year, the need becomes stronger for light weight electric cables which have high transmission capacity, high thermal resistance and low sag. We have developed a SiC fiber reinforced aluminum electrical cable to meet this need. Mechanical properties of the SiC/Al composite conductor are very susceptible to iron impurity which becomes mixed in the Al matrix during manufacture of the composite conductor. In this work, we studied the effects of Fe impurity in Al on fracture behavior of the composite conductor. A preformed wire was prepared by dipping a bundle of 1500 pieces of SiC fiber (Si: 63.7, C: 35.8, O: 12.3 mass %) into molten Al in which 0.36 mass % Fe and 0.5 mass % Ti were mixed. The Ti was added to improve the wetting property. Test samples were prepared by bundling seven preformed wires together. A tensile test was carried out for the composite conductor, and pull-out behavior of SiC fiber at the fracture surface was observed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and electron probe micro analysis (EPMA). Pull-out of SiC fiber was observed at the fracture surface of the composite conductor using Fe-free Al. However, pull-out of SiC fiber was not observed at the fracture surface of the composite conductor using Fe-containing Al since Al was combined inseparably with the SiC and Fe. The fracture origin of the Fe-containing sample was a precipitated Fe-compound at the SiC/Al interface. Tensile strength of the Fe-containing sample was a half of that of the Fe-free sample. We propose the following the precipitation mechanism for the Fe compound. In manufacturing of the preformed wire, molten Al solidifies from the surface to the SiC/Al interface because of the low thermal conductivity of the SiC fiber. In the cooling process, Fe-free Ti-compound precipitates in the molten Al by a peritectic reaction. This leads to a higher concentration of Fe in the molten Al near the interface, and finally, FeAl₃ compound precipitates at the SiC/Al interface.     

Adsorption of the oxygen to the Al (1 1 1) surface

The interaction of the oxygen with the Al (1 1 1) surface is investigated by using the density-functional theory and the pseudopotential technique. We find that the oxygen molecule becomes unstable near the surface, which is induced by the charge transfer from the surface to the molecule. This result suggests that the experimentally observed “hot adatoms” of oxygen is due to the dissociation of the molecule in the area where the direct interaction with the Al atoms is weak.