Fabrication and testing of sputtered-sliced kinoform style Fresnel zone plate

The Fresnel zone plate (FZP) is a type of lens for focusing X-rays. We have fabricated a kinoform style FZP with a 30-step structure composed of concentric multilayer of alternating Cu layer, Al layer, and 28 composite material (Cu, Al) layers. The multilayer was deposited using a magnetron sputtering apparatus with two DC-sputtering guns. The focusing characteristics were evaluated at the synchrotron radiation beamline of SPring-8, and the focused beam size measured by knife-edge scanning was 0.8 μm at 40 keV. The peak diffraction efficiencies measured using ion chambers for 1st- and 2nd-order diffraction were 42% and 12% at 40 keV and 20 keV, respectively. High-order X-ray diffraction was also examined using the data obtained from a CCD camera.     

Quasi-blazed type multilayer zone plate for X-rays

In order to attain high diffraction efficiency in high-energy X-ray region, we have developed multilevel-type (6-step) multilayer FZPs with the diameter of 70 μm, which composed of concentric multilayers of alternating high-Z (Cu), low-Z (Al), and four types of composite materials (Cu, Al) layers. Such a multilevel-type FZP with high diffraction efficiency contributes the reduction of the radiation damage to biological specimens, the simplification of the X-ray optical system. Some FZPs are fabricated and their diffraction efficiencies were evaluated at the beamline of SPring-8. For one FZP, the peak efficiency for the 1st-order diffraction of 51% has been obtained at 70 keV. The efficiencies higher than 40% have been achieved in the wide energy range of 70-90 keV. That for the 2nd-order diffraction of 46% has been obtained at 37.5 keV. For another FZP, the peak efficiency for the 1st-order diffraction of 52% has been obtained at 41.3 keV. The efficiencies higher than 45% have been achieved in the wide energy range of 33-49.5 keV.     

Effects of intermediate metal layer on the properties of Ga–Al doped ZnO/metal/Ga–Al doped ZnO multilayers deposited on polymer substrate

Ga–Al doped ZnO/metal/Ga–Al doped ZnO multilayer films were deposited on polyethersulfone (PES) substrate at room temperature. The multilayer films consisted of intermediate Ag metal layers, top and bottom Ga–Al doped ZnO layer. The multilayer with PES substrate had advantages such as low sheet resistance, high optical transmittance in visible range and stable mechanical properties. From the results, sheet resistances of multilayer showed 9 Ω/sq with 12 nm of Ag metal layer thickness. Average optical transmittance of multilayer film showed 84% in visible range (380–770 nm) with 12 nm of Ag metal layer thickness. Moreover the multilayers showed stable mechanical properties than single-layered Ga–Al doped ZnO sample during the bending test due to the existence of ductile Ag metal layer.     

Ultrasound-assisted brazing of Cu/Al dissimilar metals using a Zn–3Al filler metal

Ultrasound-assisted brazing of Cu/Al dissimilar metals was performed using a Zn–3Al filler metal. The effects of brazing temperature on the microstructure and mechanical properties of Cu/Al joints were investigated. Results showed that excellent metallurgic bonding could be obtained in the fluxless brazed Cu/Al joints with the assistance of ultrasonic vibration. In the joint brazed at 400 °C, the filler metal layer showed a non-uniform microstructure and a thick CuZn₅ IMC layer was found on the Cu interface. Increasing the brazing temperature to 440 °C, however, leaded to a refined and dispersed microstructure of the filler metal layer and to a thin Al_4.2Cu_3.2Zn_0.7 serrate structure in the Cu interfacial IMC layer. Further increasing the brazing temperature to 480 °C resulted in the coarsening of the filler metal and the significantly growth of the Al_4.2Cu_3.2Zn_0.7 IMC layer into a dendrite structure. Nanoindentation tests showed that the hardness of the Al_4.2Cu_3.2Zn_0.7 and CuZn₅ phase was 11.4 and 4.65 GPa, respectively. Tensile strength tests showed that all the Cu/Al joints were failed in the Cu interfacial regions. The joint brazed at 440 °C exhibited the highest tensile strength of 78.93 MPa.     

Multilevel-type multilayer X-ray lens (Fresnel zone plate) by sputter deposition

We have developed a multilevel-type multilayer X-ray lens (Fresnel zone plate, FZP) using sputter deposition. Such a multilevel-type FZP can attain high diffraction efficiency which results in the reduction of radiation damage to biological specimens and the simplification of the X-ray optical system because unwanted diffraction orders are considerably suppressed. Previously, we have reported the effectiveness (i.e., realizing high diffraction efficiency) of a multilevel multilayer FZP with 4-step structure. This paper presents two experimental results on the FZP: (1) the focusing test of a multilayer FZP with 6-step structure in order to realize higher efficiency and (2) the change over time of the focusing characteristic of the FZP with 4-step structure. For (1), the diffraction efficiency of the 1st order focus and the focused beam size measured by knife-edge scanning were found to be more than 50% and 0.8 μm, respectively, at 41.3 keV, and superior to the previous results. For (2), no significant differences have been observed: it can be said that the multilevel FZP is stable at least for 9 months.     

Investigation of annealing treatment on the interfacial properties of explosive-welded Al/Cu/Al multilayer

In this study, an Al/Cu/Al multilayer sheet was fabricated by explosive welding process and the effects of annealing temperature on the interfacial properties of explosively bonded Al/Cu bimetal have been investigated. For this purpose, hardness changes along the thickness of the samples have been measured, and the thickness and type of intermetallic compounds formed at the joining interface have been explored by means of optical microscopy (OM), scanning electron microscopy (SEM) and also energy dispersive spectroscopy (EDS). The obtained results indicate that, with the increase of the annealing temperature, the thickness of intermetallic compounds has increased and the amount of hardness along the thickness of the joining interface has diminished. In the annealed sample at 400 °C for 30 min, it was observed that intermetallic layers have formed at the interface of Al/Cu bimetals. These layers consist of the intermetallic compounds AlCu₃, Al₂Cu and AlCu, and their thickness gets to about 5 μm at some points. The examinations performed by the SEM, following the Vickers micro-hardness test, indicated the existence of a number of microcracks at the top and bottom interface of the sample annealed at 400 °C. This shows the formation of brittle intermetallic compounds at the joining interface, and also indicates the low ductility of these compounds.     

Structure and properties of ductile CuAlMn shape memory alloy synthesized by mechanical alloying and powder metallurgy

A ductile Cu–Al–Mn–Ti–B shape memory alloy with high fatigue strength has been prepared via mechanical alloying and powder metallurgy. With increasing milling time, the size of the crystallite grains decreases. Cu diffraction pattern appeared only after milling at a speed of 300 rpm for 25 h. The single phase CuAlMnTiB solid solution powder after 35 h milling was hot-pressed and extruded to form the final alloy. The quenched alloy had a single β phase at room temperature and its yield strength, maximum strength and strain were measured to be 390 MPa, 1015 MPa and 14.4%, respectively. The aged alloy showed a martensite structure at room temperature and had a shape memory recovery of 92% after 120 cycles.     

Effect of copper content on the thermal conductivity and thermal expansion of Al–Cu/diamond composites

Al–Cu matrix composites reinforced with diamond particles (Al–Cu/diamond composites) have been produced by a squeeze casting method. Cu content added to Al matrix was varied from 0 to 3.0 wt.% to detect the effect on thermal conductivity and thermal expansion behavior of the resultant Al–Cu/diamond composites. The measured thermal conductivity for the Al–Cu/diamond composites increased from 210 to 330 W/m/K with increasing Cu content from 0 to 3.0 wt.%. Accordingly, the coefficient of thermal expansion (CTE) was tailored from 13 × 10⁻⁶ to 6 × 10⁻⁶/K, which is compatible with the CTE of semiconductors in electronic packaging applications. The enhanced thermal conductivity and reduced coefficient of thermal expansion were ascribed to strong interface bonding in the Al–Cu/diamond composites. Cu addition has lowered the melting point and resulted in the formation of Al₂Cu phase in Al matrix. This is the underlying mechanism responsible for the strengthening of Al–Cu/diamond interface. The results show that Cu alloying is an effective approach to promoting interface bonding between Al and diamond.     

Characterisation of micro-sized and nano-sized tungsten oxide-epoxy composites for radiation shielding of diagnostic X-rays

Characteristics of X-ray transmissions were investigated for epoxy composites filled with 2–10 vol% WO₃ loadings using synchrotron X-ray absorption spectroscopy (XAS) at 10–40 keV. The results obtained were used to determine the equivalent X-ray energies for the operating X-ray tube voltages of mammography and radiology machines. The results confirmed the superior attenuation ability of nano-sized WO₃-epoxy composites in the energy range of 10–25 keV when compared to their micro-sized counterparts. However, at higher synchrotron radiation energies (i.e., 30–40 keV), the X-ray transmission characteristics were similar with no apparent size effect for both nano-sized and micro-sized WO₃-epoxy composites. The equivalent X-ray energies for the operating X-ray tube voltages of the mammography unit (25–49 kV) were in the range of 15–25 keV. Similarly, for a radiology unit operating at 40–60 kV, the equivalent energy range was 25–40 keV, and for operating voltages greater than 60 kV (i.e., 70–100 kV), the equivalent energy was in excess of 40 keV. The mechanical properties of epoxy composites increased initially with an increase in the filler loading but a further increase in the WO₃ loading resulted in deterioration of flexural strength, modulus and hardness.     

Gap-filling of Cu–Al alloy into nanotrenches by cyclic metalorganic chemical vapor deposition

In this work, Cu–Al alloy thin films with lower values of electrical resistivity than that of an Al-free Cu thin film were produced by cyclic metalorganic chemical vapor deposition (MOCVD), followed by thermal annealing of the Cu/Al multilayer formed, with controlled Cu and Al precursor delivery times. The Ru-coated SiO₂ trench with the opening width of 50 nm and aspect ratio of 1:6.7 could be completely filled by the Cu–Al alloy. The Ru/SiO₂ trench, filled conformally and voidlessly by the Cu–Al (0.7 at.%) alloy, showed no presence of intermetallic compounds.     

Investigation of Cu coatings deposited by kinetic metallization

Interfacial characterisation of Kinetic Metallization (KM) sprayed Cu coatings applied on metal substrates was performed using optical and electron microscopy, as well as microindentation hardness testing and microchemical analysis. The interfacial characterisation of KM coatings remains scarce to date. Cross sectional observations of KM coatings on light metal substrates revealed an undulating, patelliform profile with thin-lipped cusps at the interface. Pure Al and Mg substrates exhibited a mechanically impinged zone <~5 μm on the substrate material, approximately the size of deformed Cu powder particles. Examination of the Cu side of the interface indicated there was no long range interaction in the coating. On the substrate side of the interface, the KM process induced phase transformations (i.e. recrystallisation and an alloyed zone) in thin layers contiguous to the interface on pure Al and Mg substrates. Zones of elemental interdiffusion were identified at the interface upon Al and Mg substrates using scanning TEM. The width of intermixing zones was in the vicinity of < 1 μm. This metallurgical interaction at the interface occurred on the length scales involving the initial single layer of Cu particles bonded on the substrate.     

A new filler metal with low contents of Cu for high strength aluminum alloy brazed joints

The effect of Cu with low contents of 10, 12, 15 wt.% on the microstructure and melting point of Al–Si–Cu–Ni alloy has been investigated. Results showed that low-melting-point properties of Al–Si–Cu–Ni alloys with low contents of Cu were attributed to disappearance of Al–Si binary eutectic reaction and introduction of Al–Si–Cu–Ni quaternary reaction. With raising Cu content from 10 to 15 wt.%, the amount of complex eutectic phases formed during low temperature reactions (Al–Cu, Al–Si–Cu and Al–Si–Cu–Ni alloy reactions) increased and the melting temperature of Al–Si–Cu–Ni filler metals declined. Brazing of 6061 aluminum alloy with Al–10Si–15Cu–4Ni (all in wt.%) filler metal of a melting temperature range from 519.3 to 540.2 °C has been carried out successfully at 570 °C. Sound joints can be obtained with Al–10Si–15Cu–4Ni filler metal when brazed at 570 °C for holding time of 60 min or more, and achieved high shear strength up to 144.4 MPa.     

Improved version of the triode electron gun

Results of the triode electron gun which delivers 500 mA current pulses of 2 μs duration at an energy of 40 keV are presented. This new gun uses LaB₆ cathode as emitter indirectly heated by a tungsten filament, a focusing electrode, non-intercepting modulating anode and anode. Various improvements and additions carried out to the earlier gun which delivered only 120 mA current pulses is described.     

Corrosion resistance of directionally solidified Al–6Cu–1Si and Al–8Cu–3Si alloys castings

The aim of this article is to compare the electrochemical corrosion resistance of two as-cast Al–6 wt.% Cu–1 wt.% Si and Al–8 wt.% Cu–3 wt.% Si alloys considering both the solutes macrosegregation profiles and the scale of the microstructure dendritic arrays. A water-cooled unidirectional solidification system was used to obtain the as-cast samples. Electrochemical impedance spectroscopy (EIS) and potentiodynamic anodic polarization techniques were used to analyze the corrosion resistance in a 0.5 M NaCl solution at 25 °C. It was found that the Al–8Cu–3Si alloy has better electrochemical corrosion resistance than the Al–6Cu–1Si alloy for any position along the casting length. At the castings regions where the Cu inverse profile prevailed (up to about 10 mm from the castings surface) the corrosion current density decreased up to 2.5 times with the decrease in the secondary dendrite arm spacing.     

Transient liquid phase (TLP) bonding of Al7075 to Ti–6Al–4V alloy

TLP diffusion bonding of two dissimilar aerospace alloys, Ti–6Al–4V and Al7075, was carried out at 500 °C using 22 μm thick Cu interlayers for various bonding times. Joint formation was attributed to the solid-state diffusion of Cu into the Ti alloy and Al7075 alloy followed by eutectic formation and isothermal solidification along the Cu/Al7075 interface. Examination of the joint region using SEM, EDS and XPS showed the formation of eutectic phases such as, ?(Al₂Cu), T(Al₂Mg₃Zn₃) and Al₁₃Fe along grain boundaries within the Al7075 matrix. At the Cu/Ti alloy bond interface a solid-state bond formed resulting in a Cu₃Ti₂ phase formation along this interface. The joint region homogenized with increasing bonding time and gave the highest bond strength of 19.5 MPa after a bonding time of 30 min.     

Effect of in situ synthesized TiB whisker on microstructure and mechanical properties of carbon–carbon composite and TiBw/Ti–6Al–4V composite joint

Carbon–carbon composite (C–C composite) and TiB whiskers reinforced Ti–6Al–4V composite (TiB_w/Ti–6Al–4V composite) were brazed by Cu–Ni + TiB₂ composite filler. TiB₂ powders have reacted with Ti which diffused from TiB_w/Ti–6Al–4V composite, leading to formation of TiB whiskers in the brazing layer. The effects of TiB₂ addition, brazing temperature, and holding time on microstructure and shear strength of the brazed joints were investigated. The results indicate that in situ synthesized TiB whiskers uniformly distributed in the joints, which not only provided reinforcing effects, but also lowered residual thermal stress of the joints. As for each brazing temperature or holding time, the joint shear strength brazed with Cu–Ni alloy was lower than that of the joints brazed with Cu–Ni + TiB₂ alloy powder. The maximum shear strengths of the joints brazed with Cu–Ni + TiB₂ alloy powder was 18.5 MPa with the brazing temperature of 1223 K for 10 min, which was 56% higher than that of the joints brazed with Cu–Ni alloy powder.     

Diffusion bonding of 410 stainless steel to copper using a nickel interlayer

In the present work, plates of stainless steel (grade 410) were joined to copper ones through a diffusion bonding process using a nickel interlayer at a temperature range of 800–950 °C. The bonding was performed through pressing the specimens under a 12-MPa compression load and a vacuum of 10^? 4 torr for 60 min. The results indicated the formation of distinct diffusion zones at both Cu/Ni and Ni/SS interfaces during the diffusion bonding process. The thickness of the reaction layer in both interfaces was increased by raising the processing temperature. The phase constitutions and their related microstructure at the Cu/Ni and Ni/SS diffusion bonding interfaces were studied using optical microscopy, scanning electron microscopy, X-ray diffraction and elemental analyses through energy dispersive spectrometry. The resulted penetration profiles were examined using a calibrated electron probe micro-analyzer. The diffusion transition regions near the Cu/Ni and Ni/SS interfaces consist of a complete solid solution zone and of various phases based on (Fe, Ni), (Fe, Cr, Ni) and (Fe, Cr) chemical systems, respectively. The diffusion-bonded joint processed at 900 °C showed the maximum shear strength of about 145 MPa. The maximum hardness was obtained at the SS–Ni interface with a value of about 432 HV.     

Influence of copper substitution on magnetic and electrical properties of MgCuZn ferrite prepared by microwave sintering method

Polycrystalline MgCuZn ferrites with chemical formula Mg_0.50-xCu_xZn_0.50Fe₂O₄ (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) were prepared by microwave sintering method. These powders were calcined, compacted and sintered at 950 °C for 30 min. Structural, microstructural and elemental analyses were carried out using X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectrometry (EDS), respectively. The lattice parameter is found to increase with increasing copper content. A remarkable densification is observed with the addition of Cu ions in the ferrites. The sintered ferrite was characterized for initial permeability, dielectric constant and dielectric loss tangent and ac conductivity measurements. The temperature variation of the initial permeability of these samples was carried out from 30 °C to 200 °C. The dielectric constant, dielectric loss tangent and ac conductivity have been measured in the frequency range of 100 Hz to 1 MHz. Initial permeability and dielectric constant were found to increase and dielectric loss decreased with Cu substitution for Mg, up to x = 0.20. The ferrite powder prepared is suitable for the application in multilayer chip inductor due to its low-temperature sinterability, good magnetic properties and low loss at high frequency.     

Interface microstructure and mechanical properties of zinc–aluminum thermal diffusion coating on AZ31 magnesium alloy

The zinc–aluminum (Zn–Al) alloy coating with excellent wear and corrosion resistance was fabricated on the surface of magnesium substrate (AZ31) using thermal diffusion technique. The microstructure, phase constitution and chemical composition were investigated. The experimental observation exhibited that the interfacial microstructures were composed of network eutectic structures and lamellar eutectoid structures at heating temperature of 350 °C for holding time of 30 min under 0.1 MPa in a vacuum of 10⁻³ Pa. X-ray diffraction (XRD) pattern analysis identified that α-Mg, Mg₇Zn₃ and MgZn phases were formed in the diffusion layer. The interdiffusion of Mg and Al atoms were restricted by Mg–Zn intermetallic compounds (IMCs). The value of microhardness at the diffusion layer increased due to the formation of Mg–Zn eutectic phases. This technique is beneficial to improving poor wear and corrosion resistance of magnesium alloy.     

Interfacial structure and fracture behavior of 6061 Al and MAO-6061 Al direct active soldered with Sn–Ag–Ti active solder

Micro-arc oxidation (MAO), a novel coating method capable of depositing compact, ultra-hard ceramic composite coatings on Al and its alloys, is applied to heat sink surfaces. A micro-porous Al₂O₃ layer was synthesized on 6061 Al-Alloy (MAO–Al) using the MAO technique. The microstructure, shear strength and fracture of Al/Al, MAO–Al/MAO–Al, and Al/MAO–Al joints were determined after direct active soldering in air with the Sn3.5Ag4Ti(Ce) active solder at 250 °C for 30 s. During active soldering, Al dissolves into SAT solder to form a coarse Al–Ag–Sn solid solution around the solder. Also, the active element Ti concentrates to and reacts with the MAO–Al layer to form both Ti-oxidized (e.g., TiO and TiO₂) or rich-Ti(Al,Sn)₃, and subsequently Ag₃Sn nanoparticles are adsorbed at the solder/MAO–Al interfaces. The shear-tested bonding strengths were 15.3 ± 1.38 MPa for Al/Al, 10.45 ± 1.53 MPa for MAO–Al/Al, and 8.25 ± 1.53 MPa for MAO–Al/MAO–Al joints. In the Al/Al specimen, the fracture occurred in Al–Ag–Sn compounds of the active matrix after shear testing. In the MAO–Al/MAO–Al and MAO–Al/Al specimens, the fracture occurred in the MAO–Al/active solder interface.