Residual microstructure associated with impact craters in TiB2/2024Al composite

Residual microstructures associated with hypervelocity impact craters in 55 vol.% TiB(2)/2024Al composite were investigated by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). TiB(2)-Al interface, TiB(2) particles and Al matrix before and after hypervelocity impact were compared to discuss the effect of hypervelocity impact. A new Al(x)O(1-x) phase with the fcc structure and the crystal parameter of 0.69 nm was formed at TiB(2)-Al interface. Stacking fault with width of 10-20 nm was formed along the (001) plane of TiB(2) particle. Formation of nanograins (≈ 100 nm) was observed within Al matrix, moreover, lamellar S' phase was transformed into lenticular or spherical S phase after hypervelocity impact.     

SEM and TEM characterization of the microstructure of post-compressed TiB2/2024Al composite

In the present work, 55 vol.% TiB(2)/2024Al composites were obtained by pressure infiltration method. Compressive properties of 55 vol.% TiB(2)/2024Al composite under the strain rates of 10(-3) and 1S(-1) at different temperature were measured and microstructure of post-compressed TiB(2)/2024Al composite was characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). No trace of Al(3)Ti compound flake was found. TiB(2)-Al interface was smooth without significant reaction products, and orientation relationships ( [Formula: see text] and [Formula: see text] ) were revealed by HRTEM. Compressive strength of TiB(2)/2024Al composites decreased with temperature regardless of strain rates. The strain-rate-sensitivity of TiB(2)/2024Al composites increased with the increasing temperature. Fracture surface of specimens compressed at 25 and 250°C under 10(-3)S(-1) were characterized by furrow. Under 10(-3)S(-1), high density dislocations were formed in Al matrix when compressed at 25°C and dynamic recrystallization occurred at 250°C. Segregation of Mg and Cu on the subgrain boundary was also revealed at 550°C. Dislocations, whose density increased with temperature, were formed in TiB(2) particles under 1S(-1). Deformation of composites is affected by matrix, reinforcement and strain rate.     

Optical properties of Co/Al2O3 nano-array composite structure

Co/Al₂O₃ nano-array composite structure assemblies with Co grown in the pores of an anodic alumina membrane (AAM) were obtained by alternating current electrodeposition. X-ray diffraction pattern results show that a mixture of face-centred cubic and hexagonal-close-packed structures, with a preferred (100) direction, co-exists in the Co nanowires. The transmission electron microscopy image reveals that the nanowires are both very regular and uniform, with an average diameter of about 20 nm. The transmission ratio of Co/Al₂O₃ composite in the near-IR and mid-IR wavebands decreases with the increasing of the electrodeposition time, while it rises with the increasing of the pore-widening time. The Co/Al₂O₃ composite has good polarization in the near-IR waveband, and its extinction ratio increases significantly when extending the electrodeposition time. With the expanding of pores in the AAM, the extinction ratio first decreases and then rises. PACS 78.67.-n; 81.05.-t; 81.05.Rm; 81.40.Tv; 82.80.Fk     

Interfacial structure of sub-micron Al2O3 particles in aluminum matrix

The surfaces of ellipsoidal Al₂O₃ particles with average size of 0.15 μm and the interfaces between the Al₂O₃ particles and 1070Al were investigated by transmission electron microscopy (TEM) and high resolution electron microscopy (HREM).The results show that the surfaces of Al₂O₃ particles appear to be polyhedrons consisting of crystal planes with small angle, while every plane of the polyhedrons could be considered as a stepped structure composed of close-packed planes along the close-packed direction. The interfaces of the 0.15 μm Al₂O₃p/1070Al composite bond well, without any interfacial reaction products. It is proposed that there are several kinds of crystallographic orientation relationships between the aluminum matrix and Al₂O₃particles due to the polyhedral structure. In our study, such orientation relationships are found to be {110} _Al ||{1100} _Al2O3 and ?110? _Al ||?1126? _Al2O3 .     

Interfacial characteristics of Al/Al2O3/ZnO/n-GaAs MOS capacitor

The interfacial characteristics of Al/Al2O3/ZnO/n-GaAs metal-oxide-semiconductor (MOS) capacitor are investigated. The results measured by X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) show that the presence of ZnO can effectively suppress the formations of oxides at the interface between the GaAs and gate dielectric and gain smooth interface. The ZnO-passivated GaAs MOS capacitor exhibits a very small hysteresis and frequency dispersion. Using the Terman method, the interface trap density is extracted from C-V curves. It is found that the ZnO layer can effectively improve the interface quality.     

Interfacial microstructures and impact properties for Nb/MOSi2 laminate composites

The purpose of present work is to investigate effects of fabricating temperature and ZrO₂, SiC and NbSi₂ addition on interfacial reaction layer and impact properties for Nb/MoSi₂ laminate composites. Four types of laminate composites alternating four layers of Nb foil with each MoSi₂, mixture layer containing ZrO₂. SiC and NbSi₂ particles were fabricated by hot pressing. The volume fraction of Nb foil involved in these system was nominally 10 vol%. It has been found that the impact value of Nb/MoSi₂ laminate composites decreased at a fabricating temperature higher than 1523 K, since the thickness of reaction layer between Nb and MoSi₂ increased along with fabricating temperature. However, the addition ofZrO₂ particles to Nb/MoSi₂ laminate composites fabricated at 1623 K resulted in a change of the interfacial microstructure as well as a reduction of the reaction layer. Nb/MoSi₂-ZrO₂ laminate composites maintained the same density as that of Nb/MoSi₂ laminate composites fabricated at 1773 K and showed a higher impact value than that of Nb/MoSi₂ laminate composites at 1523 K.     

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。     

The deformation of B4C particle in the B4C/2024Al composites after high velocity impact

In the present work, B₄C/2024Al composites with volume fraction of 45% were prepared by a pressure infiltration method. The microstructure of the crater bottom of B₄C/2024Al composite after impact was characterized by transmission electron microscope (TEM), which indicated that recovery and dynamic recrystallization generated in Al matrix, and the grain size distribution was about from dozens of nanometer to 200 nm. Furthermore, the plastic deformation was observed in B₄C ceramic, which led to the transformation from monocrystal to polycrystal ceramic grains. The boundary observed in this work was high-angle grain boundary and the two grains at the boundary had an orientation difference of 30°.     

Electrochemical behavior of Al2O3/Al composite coated Al electrodes through surface mechanical alloying in alkaline media

The behavior of $A{l}_2{O}_3/Al$ composite coated Al electrodes fabricated by surface mechanical alloying ‘SMA’ was studied. The work was accomplished using Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques in alkaline media $2MKOH$ were done at room temperature. Results show hydroxyl ions accumulate on the surface due to Al deformation micro cavities filling with $A{l}_2{O}_3$ until full charge blockage reached. A barrier cover layer development causing an increase of both resistance and capacitance as it becomes more stable and thinner with exposure time increase. Migrating hydroxyl ion inside micro cavity changed its composition from Al₂O₃ to stable tetrahedral $Al{\left(OH\right)}_4^{?}$ aluminate ions. Therefore future benefits could be reached by developing such surfaces having charge accumulation that enables environmental interaction.     

The epoxy-siloxane/Al composite coatings with low infrared emissivity for high temperature applications

Low infrared emissivity coatings with good thermal resistance were prepared by using epoxy-siloxane and aluminum as adhesive and pigment, respectively. The influence of chemical composition, surface texture, roughness and thickness on the infrared emissivity was systematically investigated. The detailed results of experimental investigation indicate that the cured composite coatings could possess low emissivity value. Due to reducing infrared absorption and forming uniform and compact char construction, the infrared emissivity decreases obviously. Both the surface roughness and thickness have a critical value, respectively. Too large roughness or thickness would not contribute to the decrease of the emissivity. Moreover, the composite coatings were tested for thermal stability in air to explore the effect of high-temperature environment on the emissivity. The results indicate that the composite coatings, still possessing low emissivity after the test, exhibit favorable thermal ageing and thermal shock resistance.     

Dielectric breakdown phenomena in Al2O3 filled DGEBA/MDA/SN composite system

Dielectric breakdown phenomena by electrical treeing deterioration was investigated in the new epoxy resin system DGEBA/MDA/SN filled with Al₂O₃. As the filler content increased, the maximum electric field at breakdown increased and then decreased with increase of defects such as voids, impurities and delamination or peeling between filler and matrix. As the electrode separation increased, the breakdown voltage increased, but the breakdown strength decreased and then saturated to 17 kV/mm. Also, the maximum electric field at the tip when the system was failed increased. The electrical tree initiated from the side of the needle electrode was not from the tip where the reinforced field is the highest. The electrical tree was blocked by the filler. The interface condition of filler and polymer matrix played an important role in the electrical treeing resistance. The final breakdown phenomena showed fan-type crack as observed in the non-filled system.     

Fracture characteristics of bulk metallic glass under high speed impact

High speed impact experiments of rectangular plate-shaped Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 bulk metallic glass (BMG) were performed using a two-stage light gas gun. Under spherical shock waves with impact velocities ranging from 0.503 km/s to 4.917 km/s, obvious traces of laminated spallation at the back (free) surface and melting (liquid droplets) at the impact point were observed. The angles about 0?, 17?, 36?, and 90? to the shocking direction were shown in the internal samples because of the interaction between the compressive shock waves and the rarefaction waves. The compressive normal stress was found to induce the consequent temperature rise in the core of the shear band.     

Al/AlO_x/Al超导隧道结的制备工艺研究

研究了在高阻硅衬底上Al/AlO x/Al隧道结的制备技术,采用电子束蒸发制备Al/AlO x/Al三层材料,湿法刻蚀制备底电极和上电极以及电路连线,PECVD法生长绝缘层(SiO2)保护超导隧道结,RIE刻蚀上电极窗口。在400mK温度下测量了Al/AlO x/Al隧道结样品,得到了较好的隧道结I-V曲线,能隙电压Vg为0.325mV,超导临界电流I c为55nA,漏电流为5nA。     

A study of TiB2/TiB gradient coating by laser cladding on titanium alloy

TiB₂/TiB gradient coating has been fabricated by a laser cladding technique on the surface of a Ti–6Al–4V substrate using TiB₂ powder as the cladding material. The microstructure and mechanical properties of the gradient coating were analyzed by SEM, EPMA, XRD, TEM and an instrument to measure hardness. With the increasing distance from the coating surface, the content of TiB₂ particles gradually decreased, but the content of TiB short fibers gradually increased. Meanwhile, the micro-hardness and the elastic modulus of the TiB₂/TiB coating showed a gradient decreasing trend, but the fracture toughness showed a gradient increasing trend. The fracture toughness of the TiB₂/TiB coating between the center and the bottom was improved, primarily due to the debonding of TiB₂ particles and the high fracture of TiB short fibers, and the fracture position of TiB short fiber can be moved to an adjacent position. However, the debonding of TiB₂ particles was difficult to achieve at the surface of the TiB₂/TiB coating.     

Cavity enhancement of the magneto-optic Kerr effect in glass/Al/SnO2/PtMnSb/SnO2 structure

The cavity enhancement effect of the transparent semiconductor SnO₂ on the magneto-optical Kerr response of the glass/Al/SnO₂/PtMnSb/SnO₂ multilayer structure has been investigated using a matrix method. It has been demonstrated that device optimization leads to large Kerr rotation and figure of merit (FOM) with a vanishing ellipticity in the visible portion of the electromagnetic spectrum, especially at short wavelengths. This optimization is of interest in view of optical data storage technology. Using numerical simulations, we have also shown that in the optimum condition, the device readout parameters behave smoothly against the design variables.     

Properties of strontium titanate in the SrTiO3/CeO2/Al2O3 multilayered structure

Studies of the crystal structure, elemental composition, and dielectric properties of strontium titanate films in SrTiO₃/CeO₂/Al₂O₃ multilayered structures are reported. Data on the crystal lattice and impurity contents have been obtained, and temperature and electric field dependences of the dielectric properties of SrTiO₃ films in the microwave range have been measured. An analysis of the results is made to establish the reason for the nonmonotonic dependence of the small-signal dielectric permittivity of SrTiO₃ films on temperature. Fiz. Tverd. Tela (St. Petersburg) 39, 1024–1029 (June 1997)     

TiN/TiB2纳米复合材料的合成与性能

 结合高能球磨和高温高压实验技术,制备了块体TiN/TiB₂纳米复合材料。通过X射线衍射和拉曼光谱对材料的微观结构进行了研究。结果表明,采用金属Ti和六方BN为原料,在球磨过程和高温高压实验过程中,TiN先于TiB₂形成,球磨70 h后有少量的纳米晶TiN开始形成。在高温高压实验中,在样品腔的合成温度低于1 300 ℃时,没有TiB₂出现;当温度达到1 300 ℃后,合成出了TiN和TiB₂的复合材料。对所合成的块状材料的热膨胀性和导电性能进行了测试。