Observations on interdiffusion in planar copper/tin-nickel/gold tricouples

Many of the basic properties of the electrodeposited tin-nickel (Sn-Ni) alloy have been investigated, but two previously unreported aspects are interdiffusion behavior in the Cu/Sn-Ni/Au system and the thermal stability of Sn-Ni when associated with gold. Planar couples were aged at temperatures between 100 and 500°C for times to one year and evaluated by scanning electron microscopy, electron probe microanalysis, and Auger electron spectroscopy. Results show that above 250°C the layer disintegrates into fine particles and the gold and copper interdiffuse as if the Sn-Ni layer were never present. At lower temperatures, the disintegration of the layer is not detectable by the techniques used or within the time period studied. However, tin is still released from the layer and diffuses very rapidly, even through thick gold, to the surface where it is oxidized. The thicker the tin-nickel layer, the greater the amount of surface oxide which is produced for a fixed aging condition. Thus some quantities of tin-oxide can be expected to form on the surface of gold in times of just a few years for application temperatures between 100°C and room temperature.     

An electrochemical study on the dissolution of gold and copper from gold/copper alloys

The dissolution behavior of gold and copper from their elemental states and from gold/copper alloys in cyanide solutions has been investigated using a rotating-disc electrode. The anodic and cathodic reactions were studied separately, and the resulting polarization curves were combined to examine the overall dissolution reactions. The dissolution rate of pure gold in the aerated cyanide solutions was inhibited by the anodic passivation on the gold surface, whereas the dissolution rate of pure copper was found to be mass-transfer controlled. On the other hand, the dissolution of gold and copper from the alloys was partially controlled by electrochemical reaction and largely by mass transfer.     

Predicting diffusion paths and interface motion in γ/γ + β, Ni-Cr-Al diffusion couples

A simplified model has been developed to predict β recession and diffusion paths in ternary γ/γ + β diffusion couples (γ: fcc, β: NiAl structure). The model was tested by predicting β recession and diffusion paths for four γ/γ + β, Ni-Cr-Al couples annealed for 100 hours at 1200 °C. The model predicted β recession within 20 pct of that measured for each of the couples. The model also predicted shifts in the concentration of the y phase at the γ/γ + β interface within 2 at. pct Al and 6 at. pct Cr of that measured in each of the couples. A qualitative explanation based on simple kinetic and mass balance arguments has been given which demonstrates the necessity for diffusion in the two-phaseregion of certain γ/γ + β, Ni-Cr-Al couples.     

On the formation of the ordered phases CuAu and Cu3Au at a copper/gold planar interface

The formation of the ordered compounds, CusAu and CuAu, has been observed in a study primarily aimed at determining the rate of interdiffusion in the gold-copper system. In the planar diffusion couples aged at temperatures from 50°C to 400°C and for times to 4 years, the compounds were observed to form as layers at the goId/copper interface for temperatures under 400°C. The layers were visible in the scanning electron microscope backscattered image of polished cross-sections, and their compositions were determined by the corresponding plateaus observed in the electron microprobe X-ray intensity profiles. Kirkendall type porosity was also observed to form in the copper-rich zone adjacent to the ordered compound layers. These results are compared and contrasted to the findings of several other studies which have considered this reaction and its practical implications to device performance.     

Room-temperature diffusion in Cu/Ag thin-film couples caused by anodic dissolution

Thin, 100-nm films of first silver and then copper were deposited consecutively onto inert substrates by magnetron sputter deposition. Constant anodic current densities were applied at room temperature to dissolve the outer copper film to varying depths. The 50Cu/50Ag interface, derived from the auger electron spectroscopic concentration-depth profile, initially moved into the copper toward the outer dissolving surface, indicating enhanced diffusion of copper into silver. After longer times at all anodic current densities, the interface reversed and moved back toward the underlying silver-rich layer, indicating that eventually diffusion of silver into copper predominated. The reversal time was inversely proportional to the anodic current density. These effects are explained by anodic formation of subsurface vacancies which migrate as divacancies to the copper/silver interface where they affect interface movements by the well-known Kirkendall mechanism. Calculated diffusivities up to 10⁻¹² cm²/s at maximum anodic current densities of 900 μA/cm² are dramatically above any that are normally observed at room temperature.     

Pressure effects in multiphase binary diffusion couples

A systematic study has been carried out of the effect of pressure upon growth kinetics of intermediate phases formed in diffusion couples in the binary systems Ni-Al, U-A1, and U-Cu. Even though applied pressures greater than 100 MPa and long times were investigated little or no pressure effect was observed, in disagreement with previous literature reports. The magnitude of observed pressure effects falls within that expected by closure of Kirkendall porosity.     

Room-temperature diffusion in Cu/Ag thin-film couples caused by anodic dissolution

Thin, 100-nm films of first silver and then copper were deposited consecutively onto inert substrates by magnetron sputter deposition. Constant anodic current densities were applied at room temperature to dissolve the outer copper film to varying depths. The 50Cu/50Ag interface, derived from the auger electron spectroscopic concentration-depth profile, initially moved into the copper toward the outer dissolving surface, indicating enhanced diffusion of copper into silver. After longer times at all anodic current densities, the interface reversed and moved back toward the underlying silver-rich layer, indicating that eventually diffusion of silver into copper predominated. The reversal time was inversely proportional to the anodic current density. These effects are explained by anodic formation of subsurface vacancies which migrate as divacancies to the copper/silver interface where they affect interface movements by the well-known Kirkendall mechanism. Calculated diffusivities up to 10⁻¹² cm²/s at maximum anodic current densities of 900 μA/cm² are dramatically above any that are normally observed at room temperature.     

Qualitative observations on the diffusion of copper and gold through a nickel barrier

To retard failure of gold plated copper parts by diffusion of copper to the gold surface, a layer of nickel is frequently used between the copper and gold as a diffusion barrier. To evaluate the mechanisms whereby the nickel retards the motion of copper atoms to the gold surface, planar tri-couples of Cu/Ni/Au were prepared by electroplating nickel and gold layers on OFHC copper coupons. Diffusion anneals were carried out at temperatures from 150 to 750°C. A qualitative evaluation of diffusion behavior was provided by an electron microprobe utilizing X-ray wavelength dispersive analysis on polished cross sections. Results demonstrate that the nickel layer retards but does not block the transport of copper to the gold surface. Possible mechanisms for the anomalous buildup of copper at the gold/nickel interface and gold at thecopper/nickel interface are discussed.     

Qualitative observations on the diffusion of copper and gold through a nickel barrier

To retard failure of gold plated copper parts by diffusion of copper to the gold surface, a layer of nickel is frequently used between the copper and gold as a diffusion barrier. To evaluate the mechanisms whereby the nickel retards the motion of copper atoms to the gold surface, planar tri-couples of Cu/Ni/Au were prepared by electroplating nickel and gold layers on OFHC copper coupons. Diffusion anneals were carried out at temperatures from 150 to 750°C. A qualitative evaluation of diffusion behavior was provided by an electron microprobe utilizing X-ray wavelength dispersive analysis on polished cross sections. Results demonstrate that the nickel layer retards but does not block the transport of copper to the gold surface. Possible mechanisms for the anomalous buildup of copper at the gold/nickel interface and gold at the copper/nickel interface are discussed.     

Lateral diffusion in planar lipid bilayers

Direct measurements by fluorescence correlation spectroscopy of lateral diffusion coefficients of fluorescent lipid analogs in lipid bilaryer membranes indicate self-diffusion coefficients D greater than 10(-7) square centimeters per second for various lipid systems above their reported transition temperatures. Cholesterol in egg lecithin at mole ratio of 1 : 2 reduces D by about twofold, while retained hydrocarbon solvent can increase it by two- to threefold.     

含铜金精矿金铜分离浮选试验研究

针对某黄金冶炼厂现有工艺流程对入选金精矿的要求,进行了金精矿金铜分离浮选试验研究。通过试验研究,确定了合理的金铜分选工艺流程及条件,使高铜金精矿、金精矿达到了现有生产工艺要求。     

Analysis of low-temperature intermetallic growth in copper-tin diffusion couples

A multiphase diffusion model was constructed and used to analyze the growth of the ε- and η-phase intermetallic layers at a plane Cu-Sn interface in a semi-infinite diffusion couple. Experimental measurements of intermetallic layer growth were used to compute the interdiffusivities in theε andη phases and the positions of the interfaces as a function of time. The results suggest that interdiffusion in the ε phase(≈D _ε) is well fit by an Arrhenius expression with D₀ = 5.48 × 10⁻⁹ m²/s andQ = 61.9 kJ/mole, while that in the η phase (≈D_η) has D₀ = 1.84 × 10⁻⁹ m²/s andQ = 53.9 kJ/mole. These values are in reasonable numerical agreement with previous results. The higher interdiffusivity in theη phase has the consequence that theη phase predominates in the intermetallic bilayer. However, the lower activation energy for interdiffusion in theη phase has the result that theε phase fills an increasing fraction of the intermetallic layer at higher temperature: at 20 °C, the predicted ε-phase thickness is ≈10 pct of that ofη, while at 200 °C, its thickness is 66 pct of that ofη. In the absence of a strong Kirkendall effect, the original Cu-Sn interface is located within theη-phase layer after diffusion. It lies near the midpoint of theη-phase layer at higher temperature (220 °C) and, hence, appears to shift toward the Sn side of the couple. The results are compared to experimental observations on intermetallic growth at solder-Cu interfaces.     

The early stage of Ni3AI layer growth in NiAI/Ni diffusion couples

The growth kinetics and morphology of the Ni₃Al intermediate phase present in NiAI/Ni diffusion couples have been studied for short times ranging from a few minutes, or less, to a few hours at 1100 °C. Despite high heating rates (<240 seconds to reach 1100 °C), a significant portion of the Ni₃Al layer forms upon heating such that the layer growth which occurs during heating is approximately equal to that which occurs during the first hour of isothermal interdiffusion. TEM studies indicate that the irregular interfaces present at both interphase boundaries are associated with grain boundaries within the Ni₃Al phase. A qualitative model accounting for enhanced layer growth by a grain boundary contribution to diffusion within the Ni₃Al layer is described. formerly with the Department of Metallurgy and Materials Engineering, Lehigh University, Bethlehem, PA,.     

Strain-induced grain evolution in polycrystalline copper during warm deformation

The evolution mechanisms of dislocation microstructures and new grains at high strains of above 4 were studied by means of multiple compression of a polycrystalline copper (99.99 pct). Deformation was carried out by multipass compression with changing of the loading direction in 90 deg in each pass at temperatures of 473 K to 573 K (0.35 to 0.42 T _m ) under a strain rate of 10⁻³ s⁻¹. The flow stresses increase to a peak followed by a work softening accompanied mainly by dynamic recrystallization (DRX) at 523 K to 573 K. In contrast, the steady-state-like flow appears at 473K accompanied with the development of fine grains at strains as high as 4.2. The relationship of flow stress to the new grain size evolved can be expressed by a power law function with a grain size exponent of about −0.35, which is different from −0.75 for high-temperature DRX at above 0.5 T _m . At 473 K, misorientations of deformation-induced dislocation subboundaries increase with increasing strain, finally leading to the evolution of new grains. It is concluded that the dynamic grain formation at 473 K cannot result from DRX, but from the evolution of deformation-induced dislocation subboundaries with high misorientations and, concurrently, the operation of dynamic recovery.     

Irregular growth of AlSb in solid aluminum-solid antimony diffusion couples

An investigation was made of the growth of the intermediate phase aluminum antimonide (AlSb) in solid aluminum-solid antimony diffusion couples, AlSb being the only intermediate phase present in the equilibrum phase diagram. Most diffusion couples were assembled from polycrystalline aluminum and antimony, but a few were made from single crystals; the diffusion couple surfaces were prepared in a variety of ways and the couples were isothermally annealed at temperatures between 450° and 615°C. It was found in all cases that AlSb nucleates at the original interface and after sufficient time coalesces into a highly irregular layer, irrespective of the details of the surface treatment. In several cases in which limited nucleation of AlSb took place, the morphology of the crystals was such as to suggest that the observed anisotropic growth was related to the zinc-blende crystal structure of the AlSb. Formerly Graduate Student, Department of Physical and Engineering Metallurgy, Polytechnic Institute of Brooklyn, Brooklyn, N. Y. Formerly Graduate Student, Department of Physical and Engineering Metallurgy, Polytechnic Institute of Brooklyn.