Ag-based Alloys Research Articles

Prediction of the solid-liquid interface energy of a multicomponent metallic alloy via a solid-liquid interface sublattice model

Despite central roles in solidification and crystal growth, the solid-liquid interface energy σsl of the multicomponent metallic alloys is scarce and scattered because of the experimental complexity in measurements. Moreover, the theoretical prediction of σsl of the metallic alloy has been long suffered from the incomplete understanding of the solid-liquid interface structures. In this paper, the solid-liquid interface of the metallic alloy is reduced to a two-dimensional layer composed of the solid sublattice and liquid sublattice that is further sandwiched by the bulk solid and liquid phases. This enables the well-defined enthalpy and entropy hence the Gibbs energy model of the metallic solid-liquid interface layer. Via a constraint minimization of the solid-liquid interface layer Gibbs energy, the composition- and temperature-dependent σsl of the Al-based and Ag-based alloys are calculated by coupling with the available thermodynamic model parameters of the alloys. The calculation results are validated by the experimental data. It demonstrates that the built interface sublattice model offers a self-consistent framework for the automatic prediction of σsl of the metallic alloys ranging from the binary to a multicomponent system. It thus provides a more compelling solution to the long-standing issue associated with the modeling of the solid-liquid interface thermodynamics of the metallic alloys under both undercooling and equilibrium states.

Composition-dependent electrochemical activity of Ag-based alloy nanotubes for efficient nitrogen reduction under ambient conditions

The composition-activity relationship is highly desirable for electrocatalytic nitrogen reduction reaction (NRR) because it could guide the rational design of efficient NRR catalysts. In this work, the composition effect of Ag-based alloy nanotubes on electrocatalytic NRR activity is systematically investigated. It is found that, among AgAu nanotubes with atomic ratio from 8:1 to 1:2, Ag2Au1 alloy nanotubes achieve the largest enhancement for NRR catalytic activity. Specifically, the NH3 production rate and faradaic efficiency of Ag2Au1 nanotubes are 21.7 μg h−1 mgcat−1 and 3.8% at −0.30 V vs. RHE, respectively, which were 3.0 and 3.6 times higher than those of Ag nanowires. Compared with Ag2Pd1 and Ag2Pt1 nanotubes, Ag2Au1 hollow nanotubes also exhibit a better NRR catalytic activity. Theoretical calculation results indicate that the negative ion characteristic of Au atoms in the Ag2Au1 alloy is favorable for the adsorption and activation of N2. Moreover, Ag2Au1 nanotubes showed stable NH3 yield rate and faradaic efficiency up to 18 h, revealing its great potential for promising NRR electrocatalysis.

Au-induced improvements in the grain stability and mechanical properties of Ag-based alloy wires under electrical current stressing

The evolutions of the surface morphologies, cross-sectional microstructures, and mechanical properties of two types of Ag-based alloy wires with different Au contents under a 105 A/cm2 electrical current density across various times were compared in this study. Ag-based alloy wires that contain 8 wt% Au and 15 wt% Au with 3 wt% Pd were produced via rapid drawing and multiple annealing processes to replace commercial Au-bonded wires in the electronic packaging industry. The surface morphologies of these wires were revealed by scanning electron microscopy (SEM), and cross-sectional microstructures were analyzed by electron back scattering diffraction (EBSD). The SEM observations showed grain- and step-like structures in the Ag–8Au–3Pd and Ag–15Au–3Pd wires after a 5-h treatment, respectively. EBSD results revealed a change in the main preferred orientation from slender grains to equiaxed grains because the high-angle grain boundaries (HAGB) were reduced, and the twin boundaries (TB) were multiplied along the drawing direction. In terms of mechanical properties, Ag–15Au–3Pd wire showed better breaking loads and elongations than Ag–8Au–3Pd wire. The Au effect in Ag-based alloy wires reduced the atomic diffusion to stabilize grain structures and induce a dislocation accumulation, which subsequently improved the mechanical properties by retaining and forming HAGBs, LAGBs, and TBs under high current stressing.

Effect of alloying Au on the microstructural, mechanical and electrical properties of Ag-based alloy wires

In this study, the microstructure and performance of different Ag-based conductive wires were investigated. Ag-based wires that contain 8, 15, 20, and 28 wt% Au were produced by multiple drawing and rapid annealing processes to substitute commercial gold wires in electronic packaging industries. The cross-sectional gain structures observed using focused ion beam showed the formation of a slender granular structure at the center, and the outer portion changed from equiaxed to elongated grains with the increase in Au content. High-resolution transmission electron microscopy showed a remarkable decrease in the twin thickness and stacking defect of 9R structures dissociated from incoherent twin boundaries. Electron backscatter diffraction analysis revealed that slender grains at the center showed strong crystallographic orientation, and the equiaxed grains near the surface were in the preferred orientation. The high Au solute concentration in Ag-based wires induced strong interaction on dislocations, thereby resulting in the formation of low-angle grain boundaries (LAGBs) and nano-twins. Ternary Ag-based alloy wires exhibited high strength and hardness but low conductivity and elongation with the increase in Au content because relatively the high LAGB density and Au solute atoms caused strengthening and electron scattering.

Experimental Thermodynamics and Surface Properties of Ag-Cu-Ge Solder/Braze Alloys

Ag-based alloys have industrial importance in relation to their use as high-temperature solders in jewellery or braze alloys for thermoelectric modules. Good wetting properties and a tarnish-resistance of Ag-Ge and Ag-Cu-Ge alloys together with appropriate mechanical properties make them good candidates for bonding sterling silver (Ag-7.5Cu, in wt.%). The melting temperature and the heat of melting of Ag-Cu, Ag-Ge and Ag-Cu-Ge eutectic alloys have been measured by differential scanning calorimetry. From a technological point of view, particular attention should be paid to the surface tension, a key property of the joining processes. The aim of this study is to correlate the thermodynamic properties of the Ag-Cu-Ge system and its subsystems with their surface properties and to compare the model predicted property values to the data available in the literature.

Pony-Size Silver-Copper and Silver-Iron Alloy Nanoparticles Confined in N-Free Mesoporous Carbon for Efficient Oxygen Electroreduction

Silver-copper (AgCu/tri-OMC) and silver-iron (AgFe/tri-OMC) alloy nanoparticles supported on resols-derived ordered mesoporous carbon were prepared by an impregnation-reduction method. The confinement effect of mesopore channels resulted into the well-dispersed AgCu and AgFe nanoparticles (<10 nm) which were uniformly embedded in the frameworks of nitrogen-free carbons with over 700 m2/g specific surface area. The AgCu/tri-OMC and AgFe/tri-OMC were demonstrated to be the efficient electrocatalysts for oxygen reduction reaction (ORR) in alkaline media. The AgCu/tri-OMC especially exhibited the eminent electrocatalytic performance with onset potential of 1.00 VRHE and half-wave potential of 0.82 VRHE for ORR, intrinsic long-time durability and excellent methanol tolerance, superior to AgFe/tri-OMC catalysts, Pt/C (20 wt%) and other Ag-based alloy catalysts reported in literature. The higher activity of AgCu/tri-OMC originates in the optimum balance between the O-O bond split and desorption of the oxygenated intermediates controlled by energy of the d-band center of Ag in the ORR. The prepared catalytic materials may have broad application prospects and more practical value.

Mechanism of Ag sulfurization resistance improvement by alloying solutes in Ag-based alloy films

The Ag sulfurization resistance of the pure Ag film and four Ag-based alloy films was evaluated by the reflectance decay after the Ag sulfurization test. Among all Ag-based alloy films, the In alloying solute in the Ag-In alloy film shows the best resistance to the Ag sulfurization. Using x-ray photoelectron spectroscopy analysis, the chemical state of the alloying solutes in the Ag-based alloy films was examined. It is found that, with being alloyed in the Ag matrix phase, the 3d5/2 core-level peak positions of the alloying solutes (In, Sn, and Pd) shift toward the lower binding energy region, which is defined as a negative chemical shift. The chemical shifts of In, Sn, and Pd alloying solutes are –0.31 eV, –0.23 eV, and –0.2 eV, respectively. The absolute value of the negative chemical shift represents the tendency of Ag atoms losing valence electrons to the alloying solutes. As the Ag atoms lose valence electrons to the alloying solutes, the Ag atoms have a less tendency to provide the valence electrons to form covalent bonding with S atoms, which suppresses the Ag sulfurization reaction (2Ag + S → Ag2S). Therefore, the larger the absolute value of the negative chemical shift, the higher is the reflectance decay (lesser Ag sulfurization resistance).

Role of cerium in microstructure and corrosion properties of Sn-1.0Ag solder alloys

An alloying element of Sn-1.0Ag-based solder alloy can provide a great opportunity to improve their solder properties and increase its capacity for corrosion resistance. We have developed Sn-1.0Ag-xCe solder alloys consisting of a range of cerium contents from 0 to 0.5 wt% in the production of the refinement and continuation of the precipitates, as well as the reduction in grain size of the alloy microstructures. An increase of cerium addition supported on corrosion resistance exhibited relatively improved pitting potential, film and charge transfer resistances which particularly promoted the formation of passive film, resulting in an improvement of pitting resistance.

Nanoscale Engineering of Efficient Oxygen Reduction Electrocatalysts By Tailoring the Local Chemical Environment of Pt Surface Sites

The oxygen reduction reaction (ORR) is the major source of overpotential loss in low-temperature fuel cells. Expensive, Pt-based materials have been found to be the most effective catalysts, but exploration of alternatives has been hampered by stability constraints at the typical operating conditions of low pH and high potential. I will discuss our studies of elementary mechanism of ORR on various metal electrodes using kinetic and micro-kinetic analysis of reaction pathways and quantum chemical calculations. These studies allowed us to identify the elementary steps and molecular descriptors that govern the rate of ORR. Using these performance descriptors we have been able to identify families of Pt and Ag-based alloys that exhibit superior ORR performance is acid and base respectively. We have synthesized these alloys to demonstrate the superior ORR activity with rotating disk electrode experiments. We have also performed thorough structural characterization of the bulk and surface properties with a combination of cyclic voltammetry, x-ray diffraction, and electron microscopy with spatially resolved energy-dispersive x-ray spectroscopy and electron energy loss spectroscopy. Xin, H.; Linic, S., J. Chem. Phys. 2016 144 (23), 234704Van Cleve T, Moniri, S, Linic, S, 2016, ACS Catalysis 7 (1), 17-24Moniri S., Van Cleve T., Linic S., Journal of Catalysis 345, 1-10Holewinski and Linic. J. Electrochem. Soc. 159, (2012).Adam Holewinski, Juan-Carlos Idrobo, Suljo Linic. Nature Chemistry , 6, 828-834, 2014.

Effect of Post-Braze Heat Treatment on the Microstructure and Shear Strength of Cemented Carbide and Steel Using Ag-Based Alloy

The aim of the present study was to investigate the effect temperature of heat treatment process on the interfacial microstructure and mechanical properties of cemented carbide/carbon steel single lap joint brazed using Ag based alloy filler metal. The brazing process was carried out using torch brazing. Heat treatment process was carried out in induction furnace on the temperature of 700, 725, and 750°C, for 30 minutes. Microstructural examinations and phase analysis were performed using scanning electron microscopy (SEM) equipped with energy dispersion spectrometry (EDS). Shear strength of the joints was measured by the universal testing machine. The results of the microstructural analyses of the brazed area indicate that the increase temperature of treatment lead to the increase of solid solution phase of enrichted Cu. Based on EDS test, the carbon elements spread to all brazed area, which is disseminated by base metals. Shear strength joint is increased with temperature treatment. The highest shear strength of the brazed joint was 214,14 MPa when the heated up at 725°C.

Effects of impurities on double twinning nucleation and grain refinement of Sn-based solder joints

As-solidified Sn3.0Ag0.5Cu + 3.0POSS (polyhedral oligomeric silsesquioxanes), Sn3.0Ag0.5Cu + 0.05CNTs (carbon nanotubes) and Sn3.0Ag3.0Bi3.0In (SABI333) solder joint orientations were quantitatively characterized by electron backscatter diffraction observations. Unlike the typical Sn-based solder joints in which single grains, tricrystals or double tricrystals are normally observed, for the studied joints, the frequency of the single-grained joints was greatly reduced, and the Sn3.0Ag0.5Cu + 3.0POSS and SABI333 solder joints typically consisted of polycrystals. If the Sn dendrites deviated by more than 15° from the preferred [110] and $$[1{\bar{1}}0]$$ directions, then these polycrystals solidified from the Sn–Ag-based melt. Moreover, Bi and In atoms in the Sn–Ag-based alloys could significantly change the preferred [110] and $$[1{\bar{1}}0]$$ directions. In addition, two types of double twinning of tin were observed during reflow in the Pb-free solder joints. Different morphologies were observed between these twinned microstructures. However, the misorientations of the two groups of double twinned orientations ranged from 80° to 90°. In one of the double twinned systems, four Sn grain orientations had the same twin grain with a common [100] or [010] direction; in the other double twinned system, two groups of tricrystals were observed perpendicular to each other.

Recrystallization Behavior in SAC305 and SAC305 + 3.0POSS Solder Joints Under Thermal Shock

Sn-3.0Ag-0.5Cu (SAC305) and SAC305 + 3.0 polyhedral oligomeric silsesquioxanes (POSS) ball grid array (BGA) assemblies have been prepared, observed, and subjected to thermal shock. The microstructure and grain orientation evolution of the solder joints located at the same position of the package were characterized by scanning electron microscopy and electron backscattering diffraction, respectively. The results showed that the microstructure of the solder joints was refined by addition of POSS particles. In addition, compared with the single-grained or tricrystal joints normally observed in SAC305 BGA solder joints, the frequency of single-grained as-reflowed SAC305 + 3.0POSS BGA joints was greatly reduced, and the solder joints were typically composed of multicrystals with orientations separated by high-angle grain boundaries. These multicrystal joints appear to be obtained by dominant tricrystals or double tricrystals with deviation of the preferred [110] and $$[1\bar{1}0]$$ growth directions of Sn dendrites in Sn–Ag-based solder alloys during solidification from the melt. After 928 thermal shock cycles, the SAC305 solder joint had large-area recrystallization and cracks in contrast to the SAC305 + 3.0POSS solder joint located at the same position of the package, indicating that addition of POSS to SAC305 solder joints may contribute to postponement of recrystallization and subsequent crack initiation and propagation along recrystallized grain boundaries by pinning grain boundaries and movement of dislocations. This finding also confirms the double tricrystal solidification twinning nucleation behavior in Pb-free solder joints.

Bifunctional Electrocatalysts for Oxygen Reduction and Borohydride Oxidation Reactions Using Ag3Sn Nanointermetallic for the Ensemble Effect.

Incorporating an oxophilic metal into a noble metal to produce a cost-effective Ag3Sn nanointermetallic catalyst is an emerging approach to enhance the catalytic activity of monometallic Ag in fuel cells, which is different from previous notions that consider a transition metal to increase the catalytic activity of Pt. The Ag3Sn electrocatalyst is prepared by a facile electrodeposition method and exhibits high catalytic performance for the oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR). The Ag3Sn electrocatalyst has an ORR specific activity of 0.246 mA cm-2, 1.3 times greater than the value of commercial Pt/C (0.187 mA cm-2) and a long-term stability with an 11 mV decrement in the half-wave potential and 7.01% loss of the diffusion-limiting current density after 2000 cycles, superior to that of Pt/C. Moreover, the Ag3Sn electrocatalyst delivers a surprisingly higher BOR current density of 11.332 mA cm-2 than most bimetallic Ag alloys. The better ORR catalytic activities of Ag-based alloys may arise from the ensemble effect, in which Sn atoms may promote the oxygen adsorption and Ag atoms may contribute to the removal of reaction products.

Intermediate layer, microstructure and mechanical properties of aluminum alloy/stainless steel butt joint using laser–MIG hybrid welding–brazing method

Butt joining of AA6061 aluminum (Al) alloy and 304 stainless steel of 2-mm thickness was conducted using laser–MIG hybrid welding–brazing method with ER4043 filler metal. To promote the mechanical properties of the welding–brazing joints, two kinds of intermediate layers (Al–Si–Mg alloy and Ag-based alloy) are used to adjust the microstructures of the joints. The brazing interface and the tensile strength of the joints were characterized. The results showed that the brazing interface between Al alloy and stainless steel consisted of double layers of Fe2Al5 (near stainless steel) and Fe4Al[Formula: see text] intermetallic compounds (IMCs) with a total thickness of 3.7 [Formula: see text]m, when using Al–Si–Mg alloy as the intermediate layer. The brazing interface of the joints using Ag-based alloy as intermediate layer also consists of double IMC layers, but the first layer near stainless steel was FeAl2 and the total thickness of these two IMC layers decreased to 3.1 [Formula: see text]m. The tensile strength of the joints using Al–Si–Mg alloy as the intermediate layer was promoted to 149 MPa, which was 63 MPa higher than that of the joints using Al–Si–Mg alloy as the intermediate layer. The fractures occurred in the brazing interface between Al alloy and stainless steel.

Micro structure and mechanical properties of vacuum brazed martensitic stainless steel/tin bronze by Ag-based alloy

A vacuum brazing process using an Ag-based alloy (Ag-28Cu, wt%) as a filler metal was carried out on a dissimilar combination of martensitic stainless steel/tin bronze to understand the material flow characteristic and the influence of micro structure evolution on the shear strength of the brazed joint. A suitable combination of brazing temperature (850°C) and holding time (12min) was found to be beneficial for eliminating internal gaps and voids and providing for a uniform circumferential thickness distribution to satisfy the technical requirements. Cu-based and Ni-based solid solution phases were generated between the filler metal and the Ni layer, which contributed to the shear strength. With the addition of an annealing process, a quantity of Fe from the martensitic stainless steel diffused into the Ni layer, and the intermetallic compound (FeNi3) was generated. Under shear deformation, the brittle intermetallic compound promoted crack initiation, subsequent crack propagation, and final fracture failure, and the shear strength decreased from 260MPa to 180MPa.

Engineering Bimetallic Ag–Cu Nanoalloys for Highly Efficient Oxygen Reduction Catalysts: A Guideline for Designing Ag‐Based Electrocatalysts with Activity Comparable to Pt/C‐20%

Development of highly active and stable Pt-free oxygen reduction reaction catalysts from earth-abundant elements remains a grand challenge for highly demanded metal-air batteries. Ag-based alloys have many advantages over platinum group catalysts due to their low cost, high stability, and acceptable oxygen reduction reaction (ORR) performance in alkaline solutions. Nevertheless, compared to commercial Pt/C-20%, their catalytic activity still cannot meet the demand of commercialization. In this study, a kind of catalysts screening strategy on Agx Cu100-x nanoalloys is reported, containing the surface modification method, studies of activity enhancement mechanism, and applied research on zinc-air batteries. The results exhibit that the role of selective dealloying (DE) or galvanic displacement (GD) is limited by the "parting limitation", and this "parting limitation" determines the surface topography, position of d-band center, and ORR performance of Agx Cu100-x alloys. The GD-Ag55 Cu45 and DE-Ag25 Cu75 catalysts alloys present excellent ORR performance that is comparable to Pt/C-20%. The relationship between electronic perturbation and specific activity demonstrates that positive shift of the d-band center (≈0.12 eV, relative to Ag) for GD-Ag55 Cu45 is beneficial for ORR, which is contrary to Pt-based alloys (negative shift, ≈0.1 eV). Meanwhile, extensive electrochemical and electronic structure characterization indicates that the high work function of GD-Ag55 Cu45 (4.8 eV) is the reason behind their excellent durability for zinc-air batteries.

Activity Trends of Binary Silver Alloy Nanocatalysts for Oxygen Reduction Reaction in Alkaline Media.

The electrocatalytic activity of Pt-based alloys exhibits a strong dependence on their electronic structures, but a relationship between electronic structure and oxygen reduction reaction (ORR) activity in Ag-based alloys is still not clear. Here, a vapor deposition based approach is reported for the preparation of Ag75 M25 (M = Cu, Co, Fe, and In) and Agx Cu100-x (x = 0, 25, 45, 50, 55, 75, 90, and 100) nanocatalysts and their electronic structures are determined by valence band spectra. The relationship of the d-band center and ORR activity exhibits volcano-shape behaviors, where the maximum catalytic activity is obtained for Ag75 Cu25 alloys. The ORR enhancement of Ag75 Cu25 alloys originates from the 0.12 eV upshift in d-band center relative to pure Ag, which is different from the downshift in the d-band center in Pt-based alloys. The activity trend for these Ag75 M25 alloys is in the order of Ag75 Cu25 > Ag75 Fe25 > Ag75 Co25 . These results provide an insight to understand the activity and stability enhancement of Ag75 Cu25 and Ag50 Cu50 catalysts by alloying.

Electrolyte Plasma Modification of Surface of Al- and Ag-Based Alloys at Electro-Hydro-Dynamic Mode of Anodic Process

Electrolyte plasma processes are advanced high-effective and ecological methods of treating the metal surface and can be used as for cleaning and polishing of metal surfaces, as for thermochemical treatment. Previously we showed the possibility to prepare coatings on valve metals at the electro-hydro-dynamic mode and described some patterns of this process. This article is dedicated to the description of coating of both valve and non-valve metals and alloys. Composition, structure and morphology of coatings, which are forming on the Ag- and Al-based alloys surface, were studied depending on parameters of the electrolyte plasma processing.

TEM observations of reactive bonded Ti6Al4V alloy

Ni(V)/Al multilayer covered with Ag-based braze alloy (NanoFoil®) was applied for joining parts made of Ti6Al4V alloy. The reaction of multilayers was started with electric current pulse (0.5A, 9V). The transmission electron microscopy (TEM) observations of joint area, backed by analysis of the electron diffractions, showed that the initial Ni(V)/Al multilayer transformed into fine grain (~150nm) of B2-NiAl intermetallic phase. The silver-based braze alloy layer from top and bottom of Ni(V)/Al multilayer, located itself mostly at the B2-NiAl/Ti6Al4V interface as Ag-rich precipitates, but small amounts out-diffused into B2-NiAl as intergranular veins. The Ti6Al4V close to the B2-NiAl is subject to strain high enough to fill it with platelets of α″-Ti martensite.

Fabrication of (Ba,K)Fe2As2 tapes by ex situ PIT process using Ag-Sn alloy single sheath

Instead of ordinal pure Ag, Ag-based Sn binary alloys (up to 7.5 at%Sn) with higher mechanical strength are used for the sheath material of ex situ powder-in-tube (PIT)-processed (Ba,K)Fe2As2(Ba-122) tapes. We found that the use of the Ag-Sn alloy enhances the densification and texturing of the Ba-122 core, resulting in higher transport, Jc. Moreover, the optimum heat treatment temperature for a high Jc can be lowered by around 100 °C due to the higher packing density of the Ba-122 core prior to the final heat treatment. We also found that the smoothness of the interface between the sheath and Ba-122 core is significantly improved by using the Ag-Sn binary alloy sheaths. These results show that the Ag-Sn alloy is promising as a sheath material in PIT-processed Ba-122 superconducting wires.