Copper Segregation Research Articles

Diffusion and segregation of substrate copper in electrodeposited Ni–Fe thin films

The Cu surface segregation is investigated in the electrodeposited Ni–Fe layers using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS) and atomic force microscopy (AFM). The results indicate that Cu segregation and accumulation take place in areated and deareated baths and the amount of segregated copper increases after air exposure. This phenomenon is explained by lower interfacial tension of the Cu in comparison with Ni and Fe. Our results reveal more surface segregation in the electrodeposit than vacuum reported results. This should be due to interface charging and higher surface diffusion in applied potential. The effect of interface charging on the interfacial tension is discussed based on Lippmann equation. Increasing of the Cu accumulation after air exposure is related to selective oxidation in alloys and higher tendency of Cu to surface oxidation.

The roles of macrosegregation and of dendritic array spacings on the electrochemical behavior of an Al–4.5 wt.% Cu alloy

The microstructural pattern and the solute redistribution of as-cast aluminum alloys play an important role on the resulting corrosion behavior. However, of the main aluminum alloys, Al–Cu alloys have the lowest negative corrosion potential. The purpose of this work was to evaluate the electrochemical behavior of an Al–4.5 wt.% Cu alloy solidified under unsteady-state heat flow conditions. This evaluation was carried out through the analysis of both potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) tests in a 0.5 M NaCl solution at 25 °C. The experimental segregation profile obtained in the solidification experiment was characterized by positive and negative copper content regions at the bottom and the top of the casting, respectively. Likewise, in conventional foundry practice, in a same casting both positive and negative copper segregation regions may occur. Such casting can exhibit different corrosion responses at different locations. The influences of solute redistribution during solidification, the magnitude of dendritic spacing and hence of the Al-rich phase and of Al 2Cu particles distribution along the casting on the corrosion resistance, were examined in samples collected along the casting length. The corrosion rate and impedance parameters (obtained from an equivalent circuit analysis) are also discussed.

Effect of Solidification Rate and Composition on Segregation in Al-Li-Cu-Zr Alloys

In the present study, solidification and segregation of Al-Li-Cu-Zr alloys have been investigated. Results show that shape of ingots and amount of lithium can change solidification essence. Increasing solidification rate, not only eliminates grain-refining effect of zirconium but also causes coarse segregation of copper in grain boundaries (negative segregation). Increasing amount of lithium in Al-Cu-Li-Zr alloys can change the solubility of other alloying elements (Cu, Zr) and increase solidification range and microsegregation of copper in structure.

Structure and composition of the segregated Cu in V 2O 5/Cu system

We have investigated segregation of copper at the surface of V 2O 5 films deposited onto Cu substrate by employing surface analysis techniques. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) confirmed that the Cu is segregated at the surface and its chemical state is Cu 2O. According to secondary ion mass spectroscopy (SIMS) and glow discharge spectroscopy (GDS), the Cu concentration inside the deposited V 2O 5 layer is low. Ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling spectroscopy (STS) revealed the segregation alters the surface local density of states. Surface analysis of deposited samples in ultra high vacuum (UHV) condition verified that the segregation occurs during the deposition. We have extended kinetic tight binding Ising model (KTBIM) to explain the surface segregation during the deposition. Simulation data approve the possibility of surface segregation during room temperature deposition. These results point out that on pure Cu substrate, oxidation occurs during the segregation and low surface energy of Cu 2O is the original cause of the segregation.

Oxygen induced segregation of copper to Ag/Cu(1 0 0) surface

We have studied oxygen induced segregation of copper on Ag/Cu(1 0 0) surface using DFT methods. We calculated the energetics for the ideal and reconstructed copper surfaces having a layer of silver in different depths of the slab with different oxygen coverages. With no oxygen present, the preferred location of silver atoms was the topmost layer. At the coverage 0.5 ML and higher our results support the experimental observation of Hirsimäki et al. that copper replaces silver in the topmost layer of the surface when the surface is in contact with oxygen [M. Hirsimäki, M. Lampimäki, K. Lahtonen, I. Chorkendorff, M. Valden, Surf. Sci. 583 (2005) 157].

Oxidation-induced copper segregation in Cu60Zr30Ti10 bulk metallic glass

Copper segregation in a subsurface layer during annealing of Cu60Zr30Ti10 bulk metallic glass at 773 K under oxygen atmosphere has been investigated by x-ray diffraction, Auger electron spectroscopy, x-ray photoelectron spectroscopy, and scanning electron microscopy. The formation of metallic copper is strongly dependent on the annealing environment. Various oxides with metallic copper are formed after annealing in oxygen atmosphere, but only crystalline intermetallic phases are found under vacuum annealing. Besides, surface characterization results show that the sample annealed in oxygen and vacuum result in enrichment and depletion of Cu on the surface region, respectively.

The Surface Segregation of Copper in Non-oriented Electrical Steels

The surface segregation of copper was investigated in laboratory and industrial non-oriented electrical steel sheets containing copper. The cold-rolled samples of Fe–Si–Al alloys were annealed in the temperature range 320–1 120 K in the ultra-high-vacuum chamber of a field-emission Auger electron spectrometer, and subsequently characterized by Auger electron spectroscopy (AES).The Cu segregation rate was estimated based on the surface concentration of Cu after annealing at a given temperature. Not surprisingly, the AES analysis showed that the intensity of the surface segregation of copper increased with increasing annealing temperature. However, thermal desorption spectroscopy (TDS) showed that above 770 K the desorption of Cu started to reduce the surface concentration of Cu, thus making a reliable estimation of the segregation rate impossible.During the annealings, in addition to the surface segregation of copper, the surface segregation of alloying and impurity elements was observed as well. Moreover, it appeared that some of these constituents compete for available surface sites. For example, it could be concluded that the surface segregation of copper hindered the surface segregation of carbon in the Fe–Si–Al alloys.

Improving mechanical properties of 2219 aluminium alloy GTA welds by scandium addition

The effect of scandium additions to 2219 aluminium alloy weld metal has been investigated. At low levels (0·16%) of scandium, in spite of grain refinement in the weld metal, improvement in the mechanical properties has been nominal. At higher levels of scandium (0·37%), a substantial improvement in the tensile properties has been obtained. Further improvement in mechanical properties has been achieved by adding small amounts of magnesium. Transmission electron microscopy revealed the presence of fine precipitate particles in the scandium containing weld metals. Electron probe microanalysis (EPMA) and SEM–EDX revealed extensive copper segregation to grain and subgrain boundaries. The presence of scandium reduces the severity of segregation by producing fine equiaxed grains in the weld metals and also by refining the grain substructure. The morphology and size of the high copper eutectic phase at grain boundaries and sub-boundaries have been found to be finer and well distributed in the case of scandium containing weld metals. EPMA linescans and quantitative analyses proved that the depletion of copper in the matrix is minimised as a result of the fine grained structure.

Catalytic combustion of methane on novel catalysts derived from Cu-Mg/Al-hydrotalcites

Novel Cu-Mg/Al mixed oxides (designated as i-CMAO-800) were prepared by calcinations of Cu-Mg/Al hydrotalcites [(Cu2+ +Mg2+)/Al3+= 3] at 800 °C. Their performance for the catalytic combustion of methane was investigated. The oxides and their precursors were characterized by XRD, TG-DSC, TPR and N2 adsorption/desorption techniques. The results showed that BET surface areas and the stability of the resultant oxides were greatly influenced by the copper contents in hydrotalcite precursors, bringing about difference in their activities for methane catalytic combustion. XRD results indicated that Cu was highly dispersed in hydrotalcite precursors in case of low copper contents, (Cu 40 wt%). For higher Cu contents, Cu(OH)2 was formed, and, consequently, a separate phase of CuO was detected in the oxide catalysts after calcination. As indicated by the TG-DSC results, different decomposition behaviors were observed for various hydrotalcites. Thermal calcination promoted the formation of copper aluminates and segregation of CuO from the bulk phases. TPR results showed 15CMAO-800 has the highest reduction rate, and the catalytic activities of iCMAO-800 mixed oxides depend on both the reduction rates and the amounts of copper ions in mixed oxides. The catalyst 15-CMAO-800 showed the best performance.

Copper Segregation to the 5 (310)/[001] Symmetric Tilt Grain Boundary in Aluminum

New insight into the atomic segregation of copper to an aluminum grain boundary has been obtained using multiple, complementary atomic resolution electron microscopy techniques coupled with ab-initio electronic structure calculations. The copper segregation is site specific and changes the structure of the boundary by occupying interstitial sites. Minor elemental constituents in materials can have profound effects on their engineering performance. This change in structure can be associated with these strong effects. The observed structural change will alter the mass transport behavior of the boundary and has implications for the understanding of electromigration mechanisms.

A New Cleaning Technique for Corrosion Protection in Aluminum Metallization

AbstractA new cleaning technique using gas dissolved water has been found to be effective in protecting against corrosion in aluminum metallization, which is also useful in post-cleaning of Cu CMP as already reported. Corrosion can be a significant concern in aluminum as well as in copper metallization. In Al CMP process, corrosion often occurs in contact with DIWbecause of the big potential difference between Al and the barrier metal. In this study, it has been confirmed that gas dissolved water is able to change the potential of various metal films, and that following Al CMP, post-cleaning using gas dissolved water instead of DIW can successfully protect against corrosion.Furthermore this technique is also effective in the post-cleaning process of Al wiring formed by RIE, which contains a slight amount of Cu. Because segregation of copper at the side-wall of wiring often occurs during RIE and the following processes, Al-Cu wiring is easily corroded during the DIW rinsing step in wet cleaning, which may cause killer defects. Gas dissolved water can remarkably decrease the potential difference between Al-Cu alloy and segregated Cu, as well as Al-Cu alloy and the Ti/TiN used as a barrier metal. Moreover, because it seems that a reaction occurs between cathode water and Ti/TiN, where electrons may be supplied there to corrosive sites, corrosion can be prevented.

Local pressurization during solidification of Al-Si-Cu alloys

Local pressurization is a squeeze method for eliminating the shrinkage porosity. In this study, local pressurization was carried out with a specially designed permanent mold to examine the effect of pressurization on the shrinkage porosity through the investigation of macrostructure, partial density variation under the pin tip for two types of aluminium alloys of hypoeutectic (AC4B) and eutectic (ADC12). Then copper concentration at the different positions in AC4B casting was analysed in order to investigate segregation. And in order to estimate the flow of liquid or solid-liquid zone by local pressurization, the ratio of flowing volume of two alloys was measured with varied pressurization timing and different pressures. The solid fraction of flowing zone was calculated by the use of both the solidification simulation and the characteristic macrostructure change of flowing zone. The solid fraction indicates the fraction within which the present pressurization can induce interdendritic liquid flow.The results showed that the partial density of two alloys cannot be affected within the certain limits of pressurization timing for a given pressure and pressurizing speed, and does not increase obviously even if pressure increases, such as 64 to 128MPa for ADC12 casting. It was also found that the negative segregation of copper in AC4B casting occurred under the pin tip. The concentration of copper varied with distance from the pin tip. The degree of segregation was severe in the position 15mm distant from the pin tip. Opposite to the negative segregation, the positive segregation occurred in the upper zone around the pin. From the simulation, the maximum solid fraction of flowing zone, where interdendritic liquid moves, is shown to be about 0.46 and 0.53 for AC4B casting with pressure of 32 and 64Mpa, respectively.

Effects of electrochemical hydrogenation of Zr-based alloys with high glass-forming ability

Zr–(Ti)–Cu–Al–Ni metallic glasses exhibit a high thermal stability corresponding to a wide undercooled liquid region. Depending on their composition, the formation of metastable intermediate phases, e.g. a quasicrystalline phase is possible. The combination of early and late transition metals makes these alloys very interesting regarding their interaction with hydrogen. Amorphous Zr55Cu30Al10Ni5, Zr65Cu17.5Al7.5Ni10 and Zr59Ti3Cu20Al10Ni8 ribbons were prepared by melt spinning and their microstructure and thermal behaviour was checked by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. The cathodic reactivity of alloy samples at different microstructural states and after pre-etching in 1 vol.-% HF was investigated in 0.1 M NaOH by applying potentiodynamic polarisation techniques. Galvanostatically hydrogenated samples were characterised by XRD, DSC, TEM and thermal desorption analysis (TDA). For amorphous Zr59Ti3Cu20Al10Ni8 samples an increase in electrochemical surface capacity by two orders of magnitude is observed after pre-etching. Compared to the quasicrystalline and crystalline alloy, the hydrogen reduction takes place at significantly lower overpotentials. Zr-based alloys cathodically absorb hydrogen up to H/M=1.65 while keeping the amorphous structure. Already small amounts of hydrogen cause a significant decrease of the thermal stability and changes in the crystallisation sequence. The hydrogen desorption is a two-stage process: (T<623 K) hydrogen desorption from high interstitial-site energy levels and (T>623 K) zirconium hydride formation and subsequent transformation under hydrogen effusion. Hydrogen suppresses the oxygen-triggered formation of metastable phases upon heating and supports primary copper segregation. At very high H/M ratios, severe zirconium hydride formation causes the crystallisation of new compounds.

Upgrade of operating range for SULTAN test facility

The German SUpraLeiterTest ANlage (SULTAN) test facility at the Centre de Recherches en Physique des Plasma (CRPP), Villigen, is a worldwide unique tool to test high current superconductors over a broad range of operating conditions. The key component of the facility is a set of forced flow superconducting coils to generate a background field up to 11 T. A flux pump supplies the test sample with current up to 100 kA. A set of pulsed coils generates a transverse, time varying field, with amplitude up to 4 T and field rate up to 65 T/s. The instrumentation and the data acquisition system allow accurate measurements of the dc behavior, ac losses, transient stability, current distribution. A clear definition of the interface between facility and users gives flexible and easy access to external scientists with minimum time requirement for sample replacement. The experiments from the last five years of operation contributed to the progress in understanding design issues for large cable-in-conduit conductors, including quench propagation, copper segregation, coupling loss, joint, stability, and cyclic load.

The Influence of Temperature on the Wear Mode and Deterioration of Coatings Used For Titanium Aircraft Engine Components

The interface between titanium compressor blades and rotors of jet engines was studied to determine the mechanisms responsible for problematic deteriorations of protective Cu-Ni-In coatings. Results indicated that at operational temperatures of 221 °C, titanium from the uncoated disk was transferred to the softer Cu-Ni-In coating on the blade. This in turn created titanium on titanium contact and resulted in fretting wear. At higher temperatures of 454 °C, copper segregation appears to be the dominant deterioration mechanism. In order to simulate these wear modes and evaluate candidate coatings, a unique testing procedure was developed that included a range of gross-slip scale displacements. Cobalt, molybdenum, tungsten carbide, and Nickel-based coatings were evaluated by this testing procedure that first involved a low-cycle series of gross-slip displacements (125μm), followed by a higher cycle series in a reduced (25μm) gross-slip regime. Results of the study revealed that an unlubricated pure-cobalt coating could protect the blade without damaging the disk at elevated temperatures. While no coatings performed exceptionally at lower temperatures, pure molybdenum exhibited some promise.

Phase and Morphology in Mixed CuO-WO3 Films for Chemical Sensing

ABSTRACTSemiconducting metal oxide (SMO) chemiresistive sensors are highly sensitive toward a broad range of hydrocarbons. To develop a gas phase sensor with selectivity toward organophosphorus compounds, such as chemical warfare agents and pesticides, we have developed dosimeters based upon a poisoning mechanism. Here, we report the growth and characterization of WO3 thin films, modified with Cu2O. XPS data show that exposure to phosphonate compounds leads to accumulation of phosphate on the surface, together with dramatic changes in the surface segregation of copper. We present XRD and XPS results to characterize the phase changes following growth, annealing, and exposure to phosphonate compounds. The correlation between sensor response and phosphorous accumulation shows that the highest activity occurs at intermediate coverages of Cu2O, in the15–25 Å range, on 500 Å WO3 films.

Preparation and Characterization of Copper/Yttria Titania Zirconia Cermets for Use as Possible Solid Oxide Fuel Cell Anodes

The potential of a new anode cermet based on Cu and titania doped yttria stabilized zirconia (YZT) for high temperature fuel cells was examined. Cermets were prepared by a standard solid-state reaction using Y0.2Ti0.18Zr0.62O1.9 and CuO as starting materials. Green pellets were sintered at 1000 °C for 10 hours resulting in sound pellets. These were successfully reduced in 5 % H2 in Argon again yielding sound pellets with a porosity of 50 %. These were characterized by SEM, XRD and TGA methods and their conductivity measured by ac impedance and the 4 point DC method as a function of both temperature and oxygen partial pressure. On sintering there was evidence of a small amount of reaction between CuO and YZT. This resulted in a slight tetragonal distortion of YZT; however, most of the copper oxide was not incorporated into the zirconia. The cermet was successfully redox cycled and percolation was achieved when the copper composition exceeded 33 % of the volume. Conductivity remains high under a wide range of oxygen partial pressures from the most reducing conditions up to 10–4 atm O2. Electrochemical testing performed using three-electrode geometry showed good performance for hydrogen oxidation for temperatures up to 800 °C. At higher temperatures up to 1000 °C copper was observed to be very mobile with considerable agglomeration of metallic copper particles. Indeed in some instances there was a total segregation of copper from YZT resulting in a copper layer forming at the electrolyte interface with the outer layer of the electrode being essentially YZT. This agglomeration and migration of Cu led to a significant degradation in electrochemical performance with large increases in the series resistance and polarization resistance, especially under anodic bias. Due to these segregation problems copper based cermets produced in this manner are not thought to be good candidates for fuel cell electrodes operating at 1000 °C.

Influence of the initial step density on the growth mechanisms of the Fe/Cu( [formula omitted]) interface

We report on a scanning tunnelling microscopy study of the Fe/Cu(1 0 0) interface formation at room temperature (RT). From detailed studies of Fe film morphology for coverages<4 ML, we show the influence of the morphology of the initial surface on the growth mechanisms. Under iron deposition a step edge erosion occurs and intensifies with coverage leading to an unexpected flux of Cu atoms from step edges to the growing islands on the terraces. Two-dimensional heterogeneous Cu–Fe islands are formed on the surface with large amount of Cu at least for the two first atomic layers. In the case of a Cu(1 0 0) substrate with a high density of steps, the resulting growth mode is more complex than the layer by layer or bilayer ones, usually proposed in the literature. The excess of Cu atoms in the first growing planes allows a copper segregation at RT for thickness up to 4 ML. The tensile stress in the Cu surface plane, induced by initial iron inclusions, can be responsible for such a behaviour.

Investigation of the interplay of nickel dissolution and copper segregation in Ni/Cu( [formula omitted]) system

The effect of segregation on the dissolution of a thin Ni layer (3–14 equivalent-monolayers (eq-ML)) into a semi-infinite Cu substrate has been investigated at different temperatures (600–730 K) by Auger electron spectroscopy. Computer simulations have also been carried out to understand the details of the dissolution and a sophisticated method is proposed to analyse the experimental kinetics. The simulations indicated a step-wise character of dissolution and an interesting interference between segregation and dissolution. Because of the strong concentration dependence (there is a fast diffusion in Cu and there is practically no diffusion into Ni), the interface remains sharp and shifts proportionally with time until it does not reach the next-to-the-last Ni layer. Then the dissolution continues by the saturation of Cu in the topmost layer, according to the segregation isotherm. After the complete coverage of the surface by Cu, the final homogenisation takes place by the total dissolution of the next-to-the-last layer. According to these results, it was possible to separate the dissolution from the segregation and to determine the average speed of the interface shift, which is proportional to the intrinsic diffusion coefficient.

Roles of Copper and Nickel in 13%Cr Stainless Steel for Improvement of Wet Carbon Dioxide Corrosion Resistance

Abstract Resistance to hydrogen sulfide (H2S) and carbon dioxide (CO2) corrosion in 13%Cr stainless steel (SS) has been studied to develop a new material in an application field of oil country tubular goods (OCTG). Recently, the combined addition of copper and nickel was found to increase the corrosion resistance of 13%Cr SS under wet, high-temperature, and CO2 environments. The purpose of the present work was to make clear the role of such copper and nickel elements as additive elements to the 13%Cr SS. With the increase in the addition of copper and nickel to the steel, a thickness of corrosion film growing in the immersion test decreased drastically, and the corrosion rate reached < 0.1 mm/y, even at 200°C. The transmission electron microscope analysis revealed that the thin corrosion film was an amorphous phase, and that the addition of copper caused the change of the corrosion film structure from a spinel crystalline to the amorphous one. Nano-ordered segregation of copper at the interface between th...