Copper Interlayer Research Articles

A direct method to measure the fracture toughness of indium tin oxide thin films on flexible polymer substrates

This work presents a straightforward method to measure the fracture toughness of thin films deposited on flexible substrates. A 200nm thick indium tin oxide (ITO) thin film is deposited on a 188μm thick terephthalate (PET) substrate by a radio frequency magnetron sputtering machine. Using nanoindentation to induce brittle fracture on the ITO thin films, the energy release is calculated from integrating the resulting load–depth curve. An approach that directly measures the fracture toughness of thin films deposited on flexible substrates is proposed. A comparison shows that the results of the proposed method agree well with those of other reports. Furthermore, in order to improve the toughness of the ITO thin films, a copper interlayer is added between the ITO thin film and PET substrate. It shows that the fracture toughness of the ITO thin film deposited on the copper interlayer is higher than that of the one without the interlayer, which agrees well with the critical load tested by micro scratch. Further observations on optical and electric performances are also discussed in this work.

Diffusion brazing of titanium aluminide alloy based on TiAl (γ)

The basic physical and chemical properties of titanium aluminide alloys based on intermetallic phases TiAl (γ) as well as their brazeability have been discussed. The principles of the diffusion brazing process and application conditions have been presented. The shear strength and structures of the joints of TiAl48Cr2Nb2 alloy based on the TiAl (γ) phase diffusion brazed with the use of sandwich type silver filler metal (grade B-Ag72Cu-780 and Ag96Cu alloy as a filler metal), copper (grade B-Cu100-1085) interlayers as well as brazing conditions have been given. The structural tests were conducted using light microscopy, scanning electron microscopy (SEM) and energy-dispersion spectrometer (EDS). The results of the shear strength tests were also presented.

Manufacturing and testing of W/Cu mono-block small scale mock-up for EAST by HIP and HRP technologies

ITER-like W/Cu mono-block plasma-facing components (PFCs) will be used in vertical target regions of the experimental advanced superconducting tokamak (EAST) divertor. The first W/Cu mono-block small scale mock-up with five W mono-blocks has been manufactured successfully by technological combination of hot isostatic pressing (HIP) and hot radial pressing (HRP). The joining of a W mono-block and a pure copper interlayer was achieved by means of HIP technology and the bonding strength was over 150MPa. The good bonding between the pure copper interlayer and a CuCrZr cooling tube was obtained by means of HRP technology. In order to understand deeply the process of HRP, the stress distribution of the mock-up during HRP process was simulated using ANSYS code. Ultrasonic Nondestructive Testing (NDT) of the W/Cu and Cu/CuCrZr interfaces was performed, showing that excellent bonding of the W/Cu and Cu/CuCrZr interfaces. The thermal cycle fatigue testing of the mock-up has been carried out by means of an e-beam device in Southwest Institute of Physics, Chengdu (SWIP) and the mock-up withstood 1000 cycles of heat loads up to 8.4MW/m2 with the cooling water of 2m/s, 20°C, 0.2MPa.

Formation of the structure of titanium and stainless steel in laser welding

The results of investigations of laser welded joints between titanium and titanium and titanium and 12Cr18Ni10Ti stainless steel are presented. It is shown that in welding of the specimens of VT1-0 titanium alloy in cooling from the high-temperature β-region, the structure of the metal of the welded joint is characterized by two typical morphological features: large polyhedral grains of the ‘transformed’ β-phase and the plate-shaped intragranular structure of the α-phase. The material failed through the parent metal and the failure was ductile. Welding of the titanium alloy with the austenitic stainless steel through a copper interlayer is accompanied by the formation of an intermediate layer based on intermetallic phases with the thickness of 100–150 μm on the side of the titanium alloy.

Microstructural characteristics of joint region during diffusion-brazing of magnesium alloy and stainless steel using pure copper interlayer

A novel joining method, double-stage diffusion-brazing of an AZ31 magnesium alloy and a 304L austenitic stainless steel, was carried out using a pure copper interlayer. The solid-state diffusion bonding of 304L to copper was conducted at 850 °C for 20 min followed by brazing to AZ31 at 520 °C and 495 °C for various time. Microstructural characteristics of the diffusion-brazed joints were investigated in detail. A defect free interface of Fe-Cu diffusion area appeared between the Cu alloy and the 304L steel. Cu-Mg reaction products were formed between AZ31 and Cu alloys. A layered structure including AZ31/Cu-Mg compounds/Cu/Fe-Cu diffusion layer/304L was present in the joint. With time prolonging, the reduction in the width of Cu layer was balanced by the increase in the width of Cu-Mg compounds zone. Microhardness peaks in the zone between AZ31 and Cu layer were attributed to the formation of Mg-Cu compounds in this zone.

Comparing deuterium retention in tungsten films measured by temperature programmed desorption and nuclear reaction analysis

Tungsten (W) films with thicknesses ranging between 1 and 12μm deposited by magnetron sputtering on silicon substrates were used as a model system for comparing the deuterium (D) retention measured by both temperature programmed desorption (TPD) and nuclear reaction analysis (NRA). Samples were loaded with deuterium ex-situ with an ECR plasma at 370 and 600K with an energy of 38eV per deuteron. To avoid diffusion of D into the silicon substrate and to increase adhesion a copper interlayer was applied. The results show that all implanted D atoms were retained exclusively in the W films. The distribution of D is homogenous throughout the W layer with an atomic fraction of 3±0.4×10−3. With increasing W thickness the D profile extends to correspondingly larger depths with practically identical D concentration. For W films with a thickness lower than the NRA information depth of about 8μm the total retained D amount measured by TPD and NRA is in excellent agreement. As expected, for films thicker than the NRA information depth, TPD deviates from NRA.

Effects of Copper Interlayer and Annealing on Structure and Mechanical Properties of Diamond-Like Carbon Films by Cathode Arc Evaporation

Diamond-like carbon (DLC) bilayer films with Cu interlayer were prepared on silicon substrate by direct-current and pulsed cathode arc plasma technique, and annealed at various temperatures in vacuum. Structure, morphology and mechanical properties of the bilayer films were investigated by Raman spectroscopy, Auger electron spectroscopy, scanning electron microscopy and atomic force microscopy, surface profilometer and Vickers sclerometer. The results show that Cu interlayer changes the bilayer microstructure, including the thickness and element distribution of diffusion layer, the relative fraction of sp3/sp2bonding and growth model of bilayer. A simple three-layer model was used to describe the interdiffusion between Cu and C layer. Cu interlayer could be more effective against graphitization upon annealing. Morphological characteristics of the films were studied by analyzing the surface features of substrate. Cu/DLC bilayer exhibits highly dispersed nano-agglomerates with smaller size on the surface due to low surface energy of Cu interlayer. The stress and hardness of the films were affected accordingly. Cu/DLC bilayer shows a relatively high hardness at low annealing temperature but the stress almost no change. By changing Cu interlayer and annealing temperature, excellent DLC films could be designed for the protective, hard, lubricating and wear resistant coatings on mechanical, electronic and optical applications.

Bonding behavior studies of cold sprayed copper coating on the PVC polymer substrate

Metallization of the polymer surface by cold spray technique is an attractive way of improving their electrical conductivity and erosive resistance properties. However, it is still challenging to achieve a dense and thick high-strength metal coating, such as copper, on the polymer surface by cold spray system, due to excessive surface erosion during the processing. In order to overcome these difficulties, in the present work, two different types of interlayers are proposed. The polyvinyl chloride (PVC) polymer substrate was initially coated with a spherical copper powder and a tin powder separately and then a thick copper coating was fabricated using a dendritic copper powder. The properties of the coatings, such as shear adhesion strength, Vickers hardness and electrical resistivity, were measured and the influence of the interlayer on the above properties and bonding behavior was studied using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and focused ion beam dissection (FIB) techniques. The results show that the deposition efficiency is highly sensitive to the glass transition temperature of the substrate, irrespective of the process gas pressure. The coating with spherical copper interlayer shows poor shear adhesion strength due to the dislodged polymer debris at the spherical/dendritic copper coating interface. The electrical conductivity of the coating is fairly low as compared to the bulk copper due to the pores and inter-particle defects.

Synthesis of Diamond-Like Carbon Film on Copper and Titanium Interlayer by Vacuum Cathode Arc Evaporation

Using direct-current (DC) and pulsed double-excitation cathode arc plasma technique, diamond-like carbon (DLC) bilayers with nano-scaled interlayer of Cu and Ti were synthesized on silicon substrate. The effect of interlayer on the structure, morphology and mechanical properties of bilayer films were investigated. The change in bilayers structure occurred during interlayer introduction and greatly affected the hardness and internal stress of bilayers. Interlayer nature changed the microstructure of bilayers that in the thickness and element content of diffusion layer. Ti/DLC bilayer exhibited a similarly morphological character to DLC monolayer, whereas Cu interlayer in DLC films leaded to a formation of nanostructured surface and lower root mean square roughness due to the absence of Cu-C bond.

Contact Reactive Joining of TA15 and 304 Stainless Steel Via a Copper Interlayer Heated by Electron Beam with a Beam Deflection

TA15 titanium alloy and 304 stainless steel were joined via a copper interlayer heated by electron beam with a beam deflection towards the stainless steel. Microstructures of the joints were analyzed by optical microscopy, scanning electron microscopy, and X-ray diffraction. The tensile strengths of the joints and the ultramicrohardness of the intermetallic compounds were also measured. The results showed that the joint was formed by three kinds of metallurgical processes. Copper interlayer and TA15 were joined by contact reaction with the reaction products of CuTi, Cu4Ti3, and Cu2Ti. While copper interlayer and 304 stainless steel were joined by fusion and solid state diffusion process. Tensile strength of the joint can reach to 300 MPa, equivalent to 55% of that of 304 stainless steel. Furthermore, the tensile strength was mostly dependent on the volume of the unmelted copper sheet, although the intermetallics layer was the weakest location in the joint.

Temperature and stress fields in electron beam welded Ti-15-3 alloy to 304 stainless steel joint with copper interlayer sheet

Electron beam welding of Ti-15-3 alloy to 304 stainless steel (STS) using a copper filler metal was carried out. The temperature fields and stress distributions in the Ti/Fe and Ti/Cu/Fe joint during the welding process were numerically simulated and experimentally measured. The results show that the rotated parabola body heat source is fit for the simulation of the electron beam welding. The temperature distribution is asymmetric along the weld center and the temperature in the titanium alloy plate is higher than that in the 304 STS plate. The thermal stress also appears to be in asymmetric distribution. The residual tensile stress mainly exists in the weld at the 304 STS side. The copper filler metal decreases the peak temperature and temperature grade in the joint as well as the residual stress. The longitudinal and lateral residual tensile strengths reduce by 66 MPa and 31 MPa, respectively. From the temperature and residual stress, it is concluded that copper is a good filler metal candidate for the electron beam welding of Ti-15-3 titanium alloy to 304 stainless steel.

Influence of various thickness metallic interlayers on opto-electric and mechanical properties of AZO thin films on PET substrates

Various thickness metallic interlayers to improve the opto-electric and mechanical properties of aluminum-doped zinc oxide (AZO) thin films deposited on flexible polyethylene terephtalate (PET) substrates are studied. The effects of the interlayers on the resistance and transmittance of the AZO thin films are discussed. The result shows that the metallic interlayers effectively improve the electric resistance but reduce the optical transmittance of the AZO thin films. These phenomena become more obvious as the interlayer thickness increases. However, the AZO with an aluminum interlayer still behaves an acceptable transmittance. Moreover, mechanical tests indicate that the aluminum interlayer increases the hardness and modulus, and reduce the residual stress of the AZO thin films. In contrast, the silver and copper interlayers decrease the AZO's mechanical properties. Comparing to those without any interlayer, the results show that the best interlayer is the 6nm thick aluminum film.

The formation of intermetallics in dissimilar Ti6Al4V/copper/AISI 316 L electron beam and Nd:YAG laser joints

The welds of titanium alloys with steels suffer from the brittleness of resulting intermetallic compounds. In present study, we report the feasibility of Ti6Al4V to stainless steel AISI 316L welding through pure copper interlayer carried out by electron beam and pulsed Nd:YAG laser. The nature and the localization of intermetallic phases in these welds have been studied by SEM, EDS, XRD and microhardness measurements. The simplified scenario of weld formation has been proposed in order to understand the mechanism of weld formation and to explain the way local phase content determines the mechanical properties.It can be concluded that the insertion of 500 μm pure copper interlayer allows reducing but not suppressing the formation of brittle Ti–Fe and Ti–Cr-based phases. The local accumulation of Cu–Ti and Cu–Fe–Ti-based phases is less detrimental to the strength of the welds, which makes joining possible. The thickness of brittle regions is reduced due to short lifetime of the melt and compensated by the ductilizing effect of copper. The tensile strength of the welds is limited by brittleness of CuTi2 + FeTi + α-Ti layer situated next to the solid Ti6Al4V.

Multiphysical modeling of dissimilar welding via interlayer

A multiphysical finite element modeling of dissimilar welding via interlayer material was proposed. A 2D model including heat transfer, fluid flow and level set problems allowed to simulate the morphology and the composition of melted zone in horizontal plane. The calculated thickness of melted interlayer was used as a main criterion for the choice of optimal welding conditions, when the chemical interaction between the joined materials must be avoided. A 1D diffusion model at the limit of melted zone allowed estimating the length and the composition of diffusion layer between one of the materials and the interlayer basing on previously calculated local temperature gradient. The simulations were carried out in finite element software COMSOL Multiphysics. The application of the models to dissimilar TA6V to stainless steel AISI 316L electron beam joining via copper interlayer allowed to study the effect of different welding conditions (beam offset and welding speed) on the mixing between three involved materials and thus to determine the favorable operational conditions basing on the properties of dissimilar system and to give the first approach of heterogeneous interface description. The comparison of modeling results with an experiment confirmed the presence of very narrow region of optimal conditions, which is in good correspondence with simulation.

Manufacturing, testing and post-test examination of ITER divertor vertical target W small scale mock-ups

ENEA is involved in the International Thermonuclear Experimental Reactor (ITER) R&D activities. During the last years ENEA has set up and widely tested a manufacturing process, named Hot Radial Pressing (HRP), suitable for the construction of high heat flux plasma-facing components, such as the divertor targets. In the frame of the EFDA contract six mock-ups were manufactured by HRP in the ENEA labs using W monoblocks supplied by the Efremov Institute in St. Petersburg, Russian Federation and IG CuCrZr tubes. According to the technical specifications the mock-ups were examined by ultrasonic technique and after their acceptance they were delivered to the Efremov Institute TSEFEY-M e-beam facility for the thermal fatigue testing. The test consisted in 3000 cycles of 15 s heating and 15 s cooling at 10 MW/m 2 and finally 1000 cycles at 20 MW/m 2. After the testing the ultrasonic non-destructive examination was repeated and the results compared with the investigation performed before the testing. A microstructure modification of the W monoblock material due to the overheating of the surfaces and the copper interlayer structure modification were observed in the high heat flux area. The leakage points of the mock-ups that did not conclude the testing were localized in the middle of the monoblock while they were expected between two monoblocks. This paper reports the manufacturing route, the thermal fatigue testing, the pre and post non destructive examination and finally the results of the destructive examination performed on the monoblock small scale mock-ups.

Influence of interfacial scattering on giant magnetoresistance in Co/Cu ultrathin multilayers

Hood et al. have developed an approach of the two spin channel currents based on the Boltzmann equation to examine the magnetotransport properties of iron based trilayers. We applied this approach to study the magnetoresistance (MR) of Co/Cu multilayers. The in plane MR is calculated numerically at room temperature for correlated quasiperiodic roughness interfaces. Numerical results show the strong dependence of MR with the interface roughness, as well as the influence of the proportion of the electrons removed from the reflected and transmitted beams at the Co/Cu interface on the behavior of the MR. We present also the evolution of the MR as function of copper interlayer thickness. Using this approach, we analyze the experimental results giving the antiferromagnetic maximum of the variation in MR with copper thickness.

Direct Laser Cladding of Cobalt on Ti-6Al-4V with a Compositionally Graded Interface

Direct laser cladding of cobalt on Ti-6Al-4V with and without a graded interface has been attempted using a continuous wave CO2laser. Graded interface is developed by depositing a thin copper layer on Ti-6Al-4V substrate prior to multiple laser cladding of cobalt on it. Presence of copper interlayer was found to suppress the formation of brittle intermetallics of Ti and Co. The effect of process parameters on the microstructures, compositions, and phases of the interface was studied in details. Finally, the mechanical and electrochemical properties of the interface processed under optimum process parameters are reported.

Effects of bulk and interface scattering on giant magnetoresistance in the Co/Cu multilayer systems

The evolution of the giant magnetoresistance (GMR) effect in thin film multilayers based on (Co/Cu) n has been investigated by using semi-classical approach of the two spin channel currents developed by Hood, Falicov and Penn. The in plane MR of Co/Cu multilayers is calculated for correlated quasiperiodic interfaces. The numerical results show important influence of interface roughness on the behaviour of MR. The variation of MR with phenomenological parameters S ↑ and S ↓ for two directions of spin and relaxation time is reported. This interface roughness has been successfully included in our GMR simulation using a semi-classical description to analyse the experimental results giving the variation of MR with the thickness of the copper interlayer.

Electron beam welding of Ti-15-3 titanium alloy to 304 stainless steel with copper interlayer sheet

Electron beam welding of Ti-15-3 titanium alloy to 304 stainless steel with a copper sheet as interlayer was carried out. Microstructures of the joint were studied by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffractometry (XRD). In addition, the mechanical properties of the joint were evaluated by tensile test and the microhardness was measured. These two alloys were successfully welded by adding copper transition layer into the weld. Solid solution with a certain thickness was located at the interfaces between weld and base metal in both sides. Regions inside the weld and near the stainless steel were characterized by solid solution of copper with TiFe 2 intermetallics dispersedly distributed in it. While weld near titanium alloy contained Ti-Cu and Ti-Fe-Cu intermetallics layer, in which the hardness of weld came to the highest value. Brittle fracture occurred in the intermetallics layer when the joint was stretched.

In situ complexation of thiourea in the interlayer space of copper(II)-montmorillonite

Intercalation of thiourea into the interlayer space of Cu(II)-montmorillonite was performed by solid–solid reaction at room temperature. The successful intercalation was proved by powder X-ray diffraction data and spectroscopic results. The basal spacing of the intercalation compound at the molar ratio 1:6 for copper(II) ion to thiourea was ca. 1.7 nm and the value was larger than that of the starting host material. The absence of the electron spin resonance signal of the product indicated that the copper(II) interlayer cation was reduced to copper(I) cation which remained in the interlayer space as a copper(I) thiourea complex. Both elemental (CHN) and thermogravimetry analyses, as well as Raman and infrared spectroscopy of the intercalation compound supported the presence of the copper(I) thiourea complex in the interlayer space montmorillonite.