Ag Solid Solution Research Articles

Analyses and design for electrochemical migration suppression by alloying indium into silver

Silver electrochemical migration (ECM) is a serious reliability issue for fine pitch as well as power electronic devices that employ silver as interconnection materials. In this study, a method to suppress the ECM behavior of silver was proposed and implemented. Solid solutions of Ag–In and intermetallic compounds were fabricated and their ECM properties were studied through the water drop test (WDT). The WDT was performed on alumina substrate in deionized water at 3 V, where the leakage current was measured. The results show that Ag–In alloy samples have considerably longer lifetime before reaching short circuit than pure silver samples. As indium concentration in Ag–In solid solution increases, the resistance to ECM also increases. The migration process is completely inhibited when the indium concentration reaches 19 at.%. The morphologies of the dendrites and surfaces of the anode and cathode were also investigated. A model was established to explain the anti-ECM mechanism of Ag–In alloys. By forming indium oxide on the surface of the anode under electric field in a humid environment, the anode gets passivated and the silver dissolution path is completely blocked, and thus inhibiting the ECM process. It was discovered that the quality of electrode surfaces is essential in realizing the full potential of the inherent anti-ECM ability of Ag–In alloys. In conclusion, the results of this investigation have shown that Ag–In alloys can be promising and valuable candidates for conductors, metallization, and interconnect materials in fine pitch and high power electronic devices.

Microstructure and Mechanical Properties of a Ag Micro-Alloyed Mg-5Sn Alloy

Effects of 1.5 wt.% Ag addition and solid solution + artificial ageing at 160 °C on the microstructure and mechanical properties of a Mg-5Sn alloy have been studied. The results show that Ag addition has significantly hardened the solution-treated Mg-5Sn alloy. During the ageing process, the hardness increase rate and the strength and ductility of the Mg-5Sn alloy at each state are also improved by Ag addition. The improved strengthening behavior is primarily attributed to the refinement distribution of the Mg2Sn precipitates, the enhanced precipitation process, and the synergistic strengthening effect of Mg2Sn and a metastable plate DO19 phase formed at lower ageing temperature. For each solution-treated alloy, the strength and ductility are higher than the corresponding cast ones. Ageing further enhances the yield strength, and the ductility of the Mg-5Sn-1.5Ag alloy is also increased after ageing. The fracture surfaces of the both peak-aged alloys exhibit the characteristic of a mixture of quasi-cleavage and ductile fracture.

Solid solution softening and enhanced ductility in concentrated FCC silver solid solution alloys

The major adoptions of silver-based bonding wires and silver-sintering methods in the electronic packaging industry have incited the fundamental material properties research on the silver-based alloys. Recently, an abnormal phenomenon, namely, solid solution softening, was observed in stress vs. strain characterization of Ag-In solid solution. In this paper, the mechanical properties of additional concentrated silver solid solution phases with other solute elements, Al, Ga and Sn, have been experimentally determined, with their work hardening behaviors and the corresponding fractography further analyzed. Particularly, the concentrated Ag-Ga solid solution has been discovered to possess the best combination of mechanical properties, namely, lowest yield strength, highest ductility and highest strength, among the concentrated solid solutions of the current study. Microscopically, a clear evidence of narrow twin lamella feature has been observed in the Ag-Ga solid solution, and further identified as the deformation twinning, using high resolution transmission electron microscopy (HRTEM). To explain solid solution softening mechanism in low Peierls potential FCC metals, the authors have proposed a self-contained theoretical interpretation associated with fractional kink-pairs formation, and originally introduced the concept of the short range order (SRO) induced localized homologous temperature (LHT). Furthermore, the mechanism of twinning-induced plasticity (TWIP) can be referred as the underlying reason of the enhanced ductility in the Ag-Ga solid solution alloy. With such excellent mechanical properties, the Ag-Ga solid solution alloy is expected to have a great potential in the development of advanced joining materials for the various applications in electronics industries.

Superior twin stability and radiation resistance of nanotwinned Ag solid solution alloy

Face-centered cubic (FCC) metals are in general vulnerable to high-energy ion irradiation. Twin boundaries have been shown to improve the irradiation tolerance of FCC metals. However, nanotwins in monolithic metals are unstable during irradiation. In this study, we show that Fe solute can drastically improve irradiation stability of twin boundaries in Ag. By adding merely 1 at.% of Fe solute atoms into Ag matrix, ultra-high-density twins with an average twin thickness of ∼3 nm form in Ag. In situ Kr ion irradiation studies show that defect size and density in Ag99Fe1 have been significantly reduced comparing with monolithic coarse-grained Ag and nanotwinned Ag. Furthermore, these extremely fine twins survived heavy ion irradiations. Density function theory calculations suggest that Fe solutes stabilize nanotwins by pinning twin boundaries. The mechanisms of enhanced radiation tolerance enabled by solute-twin boundary networks are discussed.

Photo- and thermally induced property change in Ag diffusion into Ag/As2Se3 thin films

In the present report, we have prepared As2Se3 and bilayer Ag/As2Se3 chalcogenide thin films prepared by thermal evaporation process. The top Ag layer is being diffused into the bottom As2Se3 layer by 532 nm laser irradiation and thermal annealing process. The photo and thermal energy drives the Ag+ ions into the As2Se3 matrix that enhances the formation of As–Se–Ag solid solution which shows the changes of optical properties such as transmission, absorption power, refractive index, and optical band gap. The transmission power drastically decreased for the thermal-induced film than the laser induced one; and the reverse effect is seen for the absorption coefficient. The non-linear refractive index is found to be increased due to the Ag diffusion into As2Se3 film. The indirect allowed optical band gap is being reduced by a significant amount of 0.17 eV (thermal diffusion) and 0.03 eV (photo diffusion) from the Ag/As2Se3 film. The Ag diffusion creates chemical disorderness in the film observed from the two parameters which measures the degree of disorder such as Urbach energy and Tauc parameter. The structural change is not noticed in the studied film as seen from the X-ray diffraction pattern. Scanning electron microscopy and atomic force microscopy investigations showed that the surface morphology was influenced by the diffusion phenomena. The change in optical constants in such type of film can be used in optical waveguides and optical devices.

Ag/Ti3AlC2 composites with high hardness, high strength and high conductivity

Ag/graphite composites, as the most well-known sliding contact material, have short lifetime resulting from its lower hardness and strength. Ti3AlC2 has high conductivity, high hardness and layered structure similar to graphite, which makes it an ideal substitute for graphite. Here, Ag/Ti3AlC2 composites were successfully fabricated via hot pressing technique. In comparison with commercial Ag/graphite composites, the obtained Ag/5 vol% Ti3AlC2 composite exhibited superior mechanical and electrical properties, that is, high hardness of 94.5 ± 0.3 Hv, high tensile strength of 220.0 MPa, and high conductivity of 59.5% IACS (the international annealed copper standard). The formation of Ag (Al) solid solution in interfacial zone, arising from the partial decomposition of Ti3AlC2, greatly enhanced the mechanical properties of Ag/Ti3AlC2 composites.

Dualistic distribution coefficients of trace elements in the system mineral–hydrothermal solution. IV. Platinum and silver in pyrite

The FeS2–Ag–Pt–As system was studied using hydrothermal thermogradient synthesis (with internal sampling) of pyrite crystals at a temperature of 500°C and pressure of 1 kbar in ammonium chloridebased solutions. The modes of occurrence of precious metals (PM) were determined using atomic absorption spectrometry (AAS) in its version of statistical selections of analytical data on single crystals (SSADSC), electron microprobe analysis (EMPA), scanning electron microscopy with energy-dispersive spectrometry (SEM-EDS), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The concentration of Pt in its structural mode in pyrite is as high as 10–11 ppm and is practically not correlated with the As concentration. The dualistic distribution coefficient of Pt between pyrite and hydrothermal solution is 21 ± 7 for the structural mode and 210 ± 80 for the surface-related mode of this element. No inclusions of either any Pt-bearing minerals or Pt itself was detected. Platinum is an element highly compatible with hydrothermal pyrite and is different in this sense from gold, and pyrite is underestimated as a potential concentrator of platinumgroup elements (PGE). The distribution of Ag in pyrite is highly heterogeneous. The likely reason for this is that the Ag solid solution cannot be quenched, and hence, the Ag concentrations broadly vary and are very unsystematically distributed in natural pyrite crystals. Assuming this hypothesis, the limit for Ag accommodation in FeS2 can be estimated using SSADSC at 0.09 ± 0.06 wt % under the experimental parameters, and the distribution coefficient of the structural Ag mode is thereby evaluated at 1400 ± 700. When crystallizing together with FeS2 proustite (Ag3AsS3) near its melting point, forms mixtures with dervillite (Ag2AsS2), in which Ag deficit is counterbalanced by excess divalent As. The limit of As incorporation into pyrite under these conditions is ≤0.1 wt %. SEM-EDS and XPS data indicate that the surface phases are of three types. In the course of crystal growth, practically two-dimensional nonautonomous phases (NP) are aggregated into submicroscopic and micrometer-sized crystalline bodies (mesocrystals) that largely inherit their unusual minor-element composition from NP and are enriched in Ag, Pt, As, and other minor elements. NP and mesocrystals are enriched in Al, which was transferred into them from the Al-bearing Ti alloy of the reaction containers. Silver occur in the volume of the crystals and on their surface as monovalent silver sulfide. Arsenic was detected mostly in the form of di- and trivalent arsenic sulfides. Pentavalent arsenic oxide was identified only on the surface of the crystals and can be easily eliminated by ion milling.

Effect of Ce Addition on the Microstructure and Properties of Ag17CuZnSn Filler Metal

The effect of trace amounts of rare earth element Ce on the wettability, mechanical properties and microstructure of Ag17CuZnSn filler metal was investigated systematically by means of microstructure and spectroscopic characterizations. H62 brass and 304 stainless steel were brazed with Ag17CuZnSn-xCe filler metals. The results indicate that wettability and oxidation resistance of filler metal are remarkably improved with adding trace amount of Ce. The shear strength of brazed joint increases 29% compared to that of brazed joint without adding Ce. Moreover, it is observed that the trace amount of Ce in Ag17CuZnSn filler metal refines the brazed joint matrix microstructure. The elements diffusion is examined during the brazing process. More Ce can diffuse into the stainless steel than that of either Cu or Zn. Compared to the Cu solid solution, Fe prefers to diffuse into the Ag solid solution. When the Ce content is 0.3 wt.%, some bright and brittle Ce-bearing particles appear in the bottom of dimples which deteriorate the shear strength of brazed joint. The results of this study can stimulate the use of low-silver brazing filler metals for various applications.

Nickel–Silver Monotectic in Alumina Crucible for Use with Contact Thermometry

Previously, the authors have published work describing a pure Ni fixed point within alumina crucibles. The success of this study stimulated working with the Ni–Ag monotectic point in alumina crucibles. Similar to eutectic points, the Ni–Ag monotectic temperature is an invariant point but it differs from a eutectic reaction in such a way that the monotectic phase change takes place from Ni–Ag liquid solution to Ni–Ag solid solution and Ag rich Ni–Ag liquid solution. In the phase diagram references, the Ni–Ag monotectic phase transition temperature is assigned to be about 20 $$^{\circ }$$ C below the pure Ni melting/freezing point. As is the case for pure Ni, mechanical stability is one of the concerns. Therefore, proper cell design is necessary to avoid breakage of the alumina crucible. The techniques used for the fabrication and measurement of the pure Ni cell were applied to the Ni–Ag cell as well. The cells have been successfully fabricated and the temperature measurement at the fixed point was carried out for more than 20 thermal cycles in total. A Pt/Pd thermocouple was used to measure the temperature and was calibrated from the tin point to the gold point to measure the ITS-90. Freezing plateaus are realized with the technique of “recurrent offset freezing method with reserved solid”. The duration of each freezing plateau is a minimum of 30 min. The monotectic transformation temperature for the best performed cell is determined as 1428.27 $$^{\circ }$$ C with a combined uncertainty of ±0.06 $$^{\circ }$$ C ( $${k}=1$$ ).

Formation and evolution of nanoporous bimetallic Ag-Cu alloy by electrochemically dealloying Mg-(Ag-Cu)-Y metallic glass

A three-dimensional nanoporous bimetallic Ag-Cu alloy with uniform chemical composition has been fabricated by dealloying Mg65Ag12.5Cu12.5Y10 metallic glass in dilute (0.04M) H2SO4 aqueous solution under free-corrosion conditions. The nanoporous Ag-Cu evolves through two distinct stages. First, ligaments of the nanoporous structure, consisting of supersaturated Ag(Cu) solid solution with a constant Ag/Cu mole ratio of 1:1, are yielded. Second, with excessive immersion, some Cu atoms separate from the metastable nanoporous matrix and form spherical Cu particles on the sample surface. Formation and evolution mechanisms of the nanoporous structure are proposed.

Microstructure and Properties of W–Cu Composite/Fe-Based Powder Alloy Vacuum Brazed Joint with Different Filler Metals

Abstract W–Cu composite and Fe-based powder alloy were brazed with filler metals of Ag–Cu and Cu–Mn–Co alloys in a vacuum furnace. Both of filler metals can join W–Cu composite with Fe-based powder alloy directly in the experiment process. Microstructure, distribution of elements and fracture morphology were observed and analyzed using scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) methods, and phase composition of bonding area was analyzed by X-ray diffraction (XRD). The obtained results indicated that the smooth faying surface and dense microstructure of brazed joint were formed and the primary microstructure of brazing seam were, respectively, Ag(Cu) solid solution and Cu(Mn) solid solution, which ensured forming the stable connection of brazed joint. The bending strength of Ag-based and Cu-based brazed joint can, respectively, reach to 317 and 704 MPa, where fracture showed a typical ductile fracture characteristic. The fracture of Cu-based brazed joint located at brazing seam area, and the fracture of Ag-based brazed joint occurred in Fe-based powder alloy side.

Interfacial Free Energy and Viscosity of Cu(Ag) Solid Solutions

We experimented in direct measurements of interfacial free energies in Cu(Ag) solid solutions. The experiments were performed using the modified zero-creep method in situ at high temperatures in a dry H2 + Ar atmosphere. As a result we obtained temperature dependences of the interfacial free energies of Cu(Ag) alloys and their viscosities. The Ag concentrations were up to the solubility limit. In general, the energy decreases when the Ag concentration rises, but the isotherms have singularities. We suggest that the singularities correspond to the surface transitions which were predicted by calculations and confirmed experimentally. The viscosity increases after adding a small amount of silver (up to about 0.5 at. % of Ag). At relatively high concentrations of silver, the viscosity decreases. At concentrations close to the solubility limit, the viscosity of the alloys has non-Arrhenius temperature dependence. We suggest that all these experimental results can be explained by grain-boundary phase transitions.

The measurement of silver diffusivity in zirconium carbide to study the release behavior of 110mAg in the ZrC TRISO-coated nuclear fuel particle

The tri-structural isotropic (TRISO) coated particle fuel has been developed and used for high temperature gas-cooled reactors (HTGRs). It provides a unique robustness of the first barrier for the fission products. The TRISO fuel particle has typically consisted of a UO2 or UCO kernel, surrounded by successive layers of porous carbon, dense inner pyrocarbon, silicon carbide, and dense outer pyrocarbon. During operation, however, the SiC layer has been known to release radioactive silver 110mAg which makes maintenance more difficult and thus costly. Zirconium carbide has been considered as a promising alternative to the SiC fission product barrier. ZrC exhibits high temperature stability and possibly possesses superior Pd resistance, while the retention properties especially for silver have not been adequately studied.To help elucidate the diffusive behavior of silver in the ZrC coating of the TRISO-coated particle, a new diffusion experimental technique, called the encapsulating source method, has been developed by constructing a constant source diffusion couple between ZrC and Ag gas originated from Zr–Ag solid solution. Scanning electron microscopy (SEM), wavelength-dispersive X-ray spectroscopy (WDS), electron backscatter diffraction (EBSD) and optical methods were used to analyze the diffusion couple annealed at 1500 °C. The resultant diffusion coefficient of Ag in single-crystalline ZrC0.84 at 1500 °C was experimentally determined to be about 2.8 (±1.2) × 10−17 m2/s.

Thermodynamic calculations of AuxAg1−x – Fluid equilibria and their applications for ore-forming conditions

Concentrations of dissolved gold and silver species in hydrothermal fluids equilibrated with Au–Ag solid solutions have been calculated at wide conditions on the well known fO2–pH spaces. Ratios of the total concentrations of dissolved gold and silver species (∑Au/∑Ag) are higher as pH higher and fO2 lower. The ratios are constant at very low and high pH conditions where major dissolved species of both gold and silver are chloride complexes and thio complexes, respectively, while the ratios practically depend only on pH at intermediate pH conditions where Au(HS)2− and AgCl2− are major.The calculated results indicate that the solid solutions of high gold finenesses may precipitate from the fluids of low ratios of the total concentrations of dissolved gold and silver species when the conditions are (1) low pH’s and/or (2) high concentration ratios of dissolved chlorine and sulfur and/or (3) high temperatures.

Preparation and Thermoelectric Properties of n-Type Bi2Te2.7Se0.3:D m

Bismuth chalcogenides such as p-type (Bi,Sb)2Te3 and n-type Bi2(Te,Se)3 are excellent thermoelectric materials near room temperature. They can form homogeneous solid solutions because Bi2Te3, Sb2Te3, and Bi2Se3 have the same class of crystal symmetry. The thermoelectric figure of merit can be improved by increasing the power factor through doping and/or by reducing the thermal conductivity by forming a solid solution. In this study, n-type Bi2Te2.7Se0.3:D m (D: dopant such as I, Cu, Ag) solid solutions were prepared by encapsulated melting and hot pressing. The undoped solid solution had a power factor (PF) of 1.71 mW m−1 K−1 at 323 K and a figure of merit (ZT) of 0.55 at 423 K. The ZT value was improved due to the increased PF by I or Cu doping, and maximum ZT values were obtained as 1.13 for Bi2Te2.7Se0.3:I0.0075 and 0.74 for Bi2Te2.7Se0.3:Cu0.01 at 423 K. However, the thermoelectric properties of Ag-doped Bi2Te2.7Se0.3 solid solutions barely improved.

Deposition of Pd–Ag thin film membranes on ceramic supports for hydrogen purification/separation

Pd–Ag based membranes supported on porous α-Al2O3 (doped with yttria-stabilized zirconia) were studied for hydrogen selective separation. Magnetron sputtering technique was employed for the synthesis of thin film membranes. The hydrogen permeation flux is affected by the membrane columnar structure, which is formed during deposition. From scanning electron microscopy analysis, it was observed that different sputtering deposition pressures lead to distinct columnar structure growth. X-ray diffraction patterns provided evidence of a Pd–Ag solid solution with an average crystallite domain size of 21nm, whose preferential growth can be altered by the deposition pressure. The gas-permeation results have shown that the Pd–Ag membrane supported on porous α-Al2O3 is selective toward H2. For optimized membrane synthesis conditions, the permeance toward N2 is 0.076×10−6molm−2s−1Pa−1 at room temperature, whereas for a pressure difference of 300kPa the H2-flux is of the order of ca. 0.21molm−2s−1, which corresponds to a permeance of 0.71×10−6molm−2s−1Pa−1, yielding a selectivity of α (H2/N2)=10. These findings suggest that the membrane has a reasonable capacity to selectively permeate this gas.

The kinetics of hollowing of Ag–Au core–shell nanowhiskers controlled by short-circuit diffusion

We have grown single-crystalline Ag nanowhiskers on an inert substrate covered by a thin layer of carbon employing a molecular beam epitaxy deposition technique. Subsequent deposition of Au resulted in single-crystalline core–shell Ag–Au nanowhiskers separated by a nanocrystalline thin Au film. Annealing of the core–shell nanowhiskers at the temperature of 170°C resulted in their partial hollowing and formation of Au nanotubes. We found that the hollowing process is accompanied by Ag enrichment in the thin Au film in the vicinity of the nanowhisker, and by the increase in grain size in the film with increasing distance from the nanowhisker root. The Ag enrichment on the surface of the Au film, and at the Au–carbon interface in the vicinity of the nanowhisker, was identified with the aid of analytical transmission electron microscopy. We proposed a kinetic model of hollowing based on the competition between the energy decrease driving the hollowing process (formation of Au–Ag solid solution in the grain boundaries) and the energy increase associated with the creation of new surfaces. The model predicted an inverse dependence of the hollowing rate on the inner radius of the nanowhiskers, in good agreement with the experimental data.

Supersaturation in Ag–Ni alloy by two-step high-pressure torsion processing

Bulk Ag–Ni composites with an ultrafine grained structure were obtained by the use of a new two-step high-pressure torsion consolidation and deformation process after the first processing step. The evolving microstructure in the fully dense composites of 6 and 19 at.% of Ag was investigated by scanning and transmission electron microscopy and X-ray diffraction after applying the first and second deformation step. A deformation-induced formation of single-phase supersaturated solid solution of Ag in nanocrystalline Ni was observed after the second deformation step at the highest degree of deformation independent of the initial composition.

Structural Evolution and Phase Stability of Hume-Rothery Phase in a Mechanically Driven Nanostructured Ag-15 at. pct Sn Alloy

The paper reports phase evolution in mechanically driven Ag-15 at. pct Sn alloy powder starting with elemental powders in order to establish the feasibility of designing nanocomposites of a Ag-Sn solid solution. This alloy lies in the phase field of the hexagonal ζ-phase which is a well-known Hume-Rothery electron compound with an electron-to-atom ratio of about 1.45 and hexagonal crystal structure (a = 0.2966 nm, c = 0.4782 nm). Through a systematic use of X-ray diffraction and transmission electron microscopy, the results establish the formation of the ζ-phase which co-exists with the Ag solid solution during the initial phase of milling. Mechanical milling for long duration (55 hours) destabilizes the ζ-phase. A complete solid solution of Ag with a grain size of ~8 nm could be achieved after 60 hours of milling. Additional milling can induce decomposition of the solid solution that results in a reappearance of ζ-phase. We present a detailed thermodynamic calculation which indicates that complete Ag solid solution of the present alloy composition would be possible if the crystallites size can be reduced below a certain critical size. In particular, we show that both Ag and ζ-phase grain sizes need to be taken into account for determining the metastable equilibrium and the phase change that has been experimentally observed. Finally, we argue that recrystallization processes set a limit to the achievable size of the nanoparticles with metastable Ag solid solution.

Development of Deformation Processed Copper–Refractory Metal Composite Alloys

The strength, electrical conductivity, and substructure of deformation processed Cu-15vol%X alloys have been studied where X included Nb, Ta, and Cr. One alloy of Cu-15Nb was studied in which 2% Ag was added to examine solid solution strengthening of the Cu matrix. The alloys were prepared by consumable arc melting and ingot diameters of 7.6 and 15.2 cm were examined. Deformation was carried out at room temperature by rolling, press forging, and axisymmetric modes. The results show that the strength/conductivity properties of the Nb, Ta, and Cr alloys are essentially the same and are slightly better than the Cu-20vol%Nb alloys previously measured. The Ag alloy was found to be stronger at a given deformation, but the solid solution Ag decreased the conductivity more than it increased strength so that the net effect was to reduce the strength at a given conductivity. TEM studies showed that the substructures of all the alloys were similar to each other and to previous results on Cu-20vol%Nb alloys. Deformation by both press forging and rolling are not as effective at increasing strength as is axisymmetric deformation.