Ag Solid Solution Research Articles

Influence of synthesis conditions on the nanostructure of immiscible copper–silver alloy thin films

Far from equilibrium, immiscible nanocrystalline Cu–Ag alloy thin films of nominal composition Cu–30(±5) at.% Ag were deposited by co-sputtering. While films deposited at ∼300 K exhibit a two-phase mixture of face-centered cubic (fcc) Ag + fcc Cu, those deposited either at ∼100 K or at low power (∼40 W) exhibit an fcc Cu–25 at.% Ag solid solution, excess fcc Ag and small fractions of a metastable hexagonal (4H) Cu–Ag phase. Increasing the sputtering gas pressure leads to phase separation into fcc Cu, fcc Ag and metastable 4H Cu–Ag.

Serrated flow in cast ZE43 alloy

Plastic deformation of solid solutions is occasionally accompanied by plastic instabilities, i.e. serrated flow or the Partevin-Le Chatelier (PLC) effect. The PLC effect has been observed and investigated in various kinds of aluminum alloys [1–5]. For most aluminum alloys, this effect is observed at ambient temperature. The dynamic interaction between mobile dislocations and diffusing solute atoms, known as dynamic strain aging (DSA), is commonly accepted to account for the observed phenomena [6–11]. Compared to the extensive investigations on serrated flow of aluminum alloys, only a few papers have been concerned with the serrated flow in magnesium alloys. Couling [12] briefly reported the anomalous yielding effect in a Mg–0.5%Th alloy at testing temperatures from 373 K to 663 K. Chaturvedi et al. [13, 14] reported serrated flow in an Mg–10 wt.%Ag solid solution at temperatures between 326 K and 397 K. Zhu et al. [15] recently observed serrated flow in a 16-h-aged Mg–5Y–4Nd alloy and Corby et al. [16–19] found serrations in a AZ91 alloy when tested at room temperature. There seems no other reported work on serrated flow in magnesium alloys. The present paper reports our observations on serrated flow in a cast ZE43 alloy (Mg–4 wt.%Zn– 3 wt.%RE, here RE refers to misch metal). Specimens prepared from the cast ZE43 alloy were annealed at 798 K for 10 h, and quenched from 798 k into hot water (353 K), then taken out to room temperature (T4 treatment). In addition, Half of the hot-water quenched specimens were aged at 523 K for18 h (T6 treatment). Tensile tests were conducted on a screwdriven Instron testing machine at various initial strain rates at temperatures ranging from room temperature to 573 K. Serrations on the stress–strain curves of the specimens in both T4 and T6 conditions were observed in a temperature range from 393 K to 513 K. Outside this temperature range, smooth flow curves were obtained. Figure 1 Shows segments of the flow curves of the specimens in both T4 and T6 conditions at a strain rate of 2.4 · 10s and a temperature of 473 K, where the serrations were most pronounced. It can be seen that periodical serrations develop after about a 1% critical strain, ec. The serrations start to appear as a sequence of small yield points, and with increasing strain, the magnitude (stress drop) of the serrations becomes larger. The higher flow stress for the specimens in T6 condition indicates a precipitation strengthening effect. The power law model r 1⁄4 ke was used to fit the stress–strain curves, giving work hardening exponent n for the two heat treatment conditions a value of 0.31. The specimens in T6 condition develop serrations later than that in T4 condition, but the stress drops seem larger. The possible reason for the higher stress drops of the specimens in T6 condition is due to the effect of C. Y. Wang (&) Department of Materials Engineering, Bohai Shipbuilding Vocational College, Huludao 125000, P.R. China e-mail: cywang1969@yahoo.com.cn

Structures and magnetic moments of Co–Ag alloy films prepared by ion beam assisted deposition at various ion incidence angles

Alloy films in the immiscible Co–Ag system are prepared by ion beam assisted deposition (IBAD) at various ion incident angles. Metastable structures containing Co and Ag solid solutions and amorphous structures are obtained. The size of these components is within 5 nm. The atomic magnetic moments (AMM) of Co are studied by X-ray magnetic circular dichroism (XMCD). The orbit moments are found to increase much. The orbit/spin ratio arrives to 0.27–0.38. The total AM varies in a wide range. The possible mechanism for the high orbit/spin ratios and variation of AMM are discussed on the base of crystalline structure, cluster size and interface.

ITO–Ag alloy–ITO film with stable and high conductivity depending on the control of atomically flat interface

The conductivity of ITO–Ag–ITO films declines with the deposition temperature increased above 200 °C, because the surfaces of Ag layers become rough that scatter the conduction carriers. The solid-solution Ag–Ti alloy and Ag–Ti–Cu alloy are developed to improve the stability of the surface morphology of Ag layers. This research proves that the Ag–Ti film can keep a smooth surface at an even higher deposition temperature. This leads ITO–AgTi–ITO films to have low resistivity at high deposition temperatures. However, further addition of Cu atoms into Ag–Ti films causes several spikes formed on the surfaces probably relative to the relaxation of strain energy. The conductivity of the ITO–AgTiCu–ITO film will decline when a large amount of spikes is formed on the surface of Ag–Ti–Cu layer at a high deposition temperature.

Phase constitution and solidification characteristics of undercooled Ag-Cu-Ge ternary eutectic alloy

Liquid Ag38.5Cu33.4Ge28.1 ternary eutectic alloy was undercooled by a great degree up to 175 K(0.22 TE). X-ray diffraction analysis reveals that its rapidly solidified microstructure is composed of (Ag) solid solution phase, (Ge) semiconducting phase and η(Cu3Ge) intermetallic compound phase. With the increase of undercooling, there occurs a transition from the cooperative growth of three eutectic phases to the preferential nucleation and growth of (Ge) phase. The (Ag) and η phases usually grow to form pseudobinary lamellar eutectic structure. When the undercooling exceeds 80 K, the structural morphology of primary (Ge) phase transfers from faceted blocks to branched dendrites. Some (Ge) dendrites look like flowers, which usually have 5—8 lobes. In addition, the number of lobes tends to increase as undercooling increases. The crystal surfaces of the flower-like (Ge) dendrite are {111} planes and the dendrite grows along the 〈100〉 preferred growth direction.

Fcc solid solution alloy films formed in immiscible Fe–Ag system and their mechanical behaviors

Fe–Ag alloy films were deposited by magnetron sputtering. Fe K edge X-ray absorption near-edge structure (XANES) was performed by synchrotron radiation to evidence the structure of the films. Annealing experiments were carried out to study their stability. The hardness and elastic modulus were measured by nanoindentation. The experimental and calculated XANES spectra both reveal that Fe atoms replace part of Ag atoms and supersaturated fcc Ag (Fe) solid solution alloy films are formed up to 38 at.% Fe. The solid solutions are stable and begin to precipitate at 400 °C The elastic modulus increases with the increase of Fe concentration and satisfies the rule of mixtures. The hardness of the as-deposited alloy film is larger than that calculated based on the rule of mixtures. The mechanism responsible for the enhancement of the hardness is discussed in terms of Labusch model of solid solution hardening.

Precipitation of a metastable Fe(Ag) solid solution upon annealing of supersaturated Fe(Ag) thin film prepared by pulsed laser deposition

Upon annealing, a single-phase, bcc Fe1-xAgx (x=1.8 or 3.2 at. %) thin film, prepared by pulsed laser deposition, simultaneously undergoes grain growth and precipitation of a bcc Fe(Ag,9-10 at. %) solid solution at the grain boundaries. At a high annealing temperature or after a long annealing time the metastable state transforms to the equilibrium state, pure Fe and pure Ag. A quantitative kinetic growth model has been proposed to explain that this non-equilibrium phenomenon results from surface diffusion.

Microstructure and strength of brazed joints of Ti3Al base alloy with AgCuZn filler metal

Brazing Ti3Al alloys with filler metal Ag–Cu34–Zn16 was carried out at 1073–1173 K for 60–1200 s. The relationship between brazing parameters and shear strength of the joints was investigated, and optimum brazing parameters obtained as follows: brazing temperature 1073–1083 K, brazing time 250–300 s. The maximum shear strength obtained for joints was 160–170 MPa. The reaction products and the interface structure of the joints were investigated by SEM, EPMA, and XRD. Three kinds of reaction product were observed to have formed during the brazing of Ti3Al alloys with Ag–Cu34–Zn16 filler metal: namely Ti(Cu, Al)2+TiCu intermetallic compounds formed close to the Ti3Al alloy, and Ag solid solution formed in the middle of the joint. The interfacial structure of brazed Ti3Al alloy joints with Ag–Cu34–Zn16 filler metal was Ti3Al/Ti(Cu, Al)2+TiCu/Ag solid solution/Ti(Cu, Al)2+TiCu /Ti3Al, and this structure does not change with brazing time once it forms. The formation of intermetallic compounds Ti(Cu, Al)2+TiCu results in embrittlement of the joint and poor joint properties. The thickness of Ti(Cu, Al)2+TiCu intermetallic compounds increases with brazing time according to a parabolic law. The activation energy Q and the growth velocity K0 of the Ti(Cu, Al)2+TiCu reaction layer in the brazed joints of Ti3 Al alloys with Ag–Cu34–Zn16 filler metal were 170 kJ mol–1 and 2·31 × 10−5 m2 s−1 respectively. The growth formula was y2=2·13 × 10−5exp(−20447.44/T)t. Careful control of the growth of the reaction layer Ti(Cu, Al)2+TiCu can influence the final joint strength.

Formation and Phase Transition of Argyrodite Type Ag7TaSe6xS6(1‐x) Solid Solution.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Drastic changes for segregation and wetting between flat and vicinal surfaces of binary alloys

Segregation for the (3 1 0) surface in Cu(Ag) solid solution is studied by Monte Carlo simulations in conjunction with an N-body interatomic potential. Three stages occur according to the bulk concentration of Ag. At low concentration, only the surface plane is enriched by Ag atoms and no structural change is observed. In a second stage, three Ag planes form at the surface. These planes are strongly disordered due to the large size-mismatch between Ag and Cu atoms. Finally, a third stage occurs, in which a thick Ag film grows at the surface. This wetting behaviour is accompanied by a structural change, the Ag film becoming well ordered and growing along the 〈1 1 2〉 direction. Comparison is drawn up with segregation for the flat (0 0 1) surface on one hand and for the Σ=5(3 1 0)〈0 0 1〉 tilt grain boundary on the other hand.

Effect of Cu-substitution on the conductivity of Ag-rich AgI–CuI solid solutions

The ionic conductivity of the silver rich solid solutions Ag 1− x Cu x I (0< x<0.25) was measured using complex impedance spectroscopy over the frequency range 100 Hz–15 MHz and in the temperature range 25–250 °C. As observed in undoped AgI, two conducting regions (above and below T c) are found in these solid solutions also. Despite the large size difference in the ionic radii of Ag + and Cu + ions, the bigger sized Ag + ion dominates the overall conductivity of the system. Arrhenius plots of the dc conductivity demonstrates clearly the enhanced defect concentration and grain boundary effects in the low temperature phase as well as the smallness of the observed activation energy along with the softening of the AgI lattice in the high temperature phase. The pertinent effect of Cu doping in AgI is discussed in terms of the recent experimental and theoretical facts. A plausible conduction mechanism is being worked out.

Multilayer properties of superficial and intergranular segregation isotherms: A mean-field approach

Segregation is studied at the (001) and (310) surfaces, as well as for the $\ensuremath{\Sigma}=5$ (310) [001] tilt grain boundary (GB), in the Cu(Ag) system. Based on an effective Ising model with energetic parameters obtained from an N-body interatomic potential, we compare the segregation driving forces for the three interfaces in this system, which presents a strong tendency toward phase separation in the bulk. Within mean-field theory, we derive segregation isotherms, and we find an essential difference between the flat (001) surface and the open (310) surface. For the first one, the isotherm is characterized by a succession of monolayer phase transitions, whereas the isotherm of the (310) surface exhibits a multilayer phase transition, all these transitions occurring well within the domain of the Cu(Ag) solid solution. The segregation isotherm for the (310) [001] tilt grain boundary is similar to the (310) surface one, with the presence of a multilayer phase transition too. The behavior of the GB plane itself is rather intricate, a multireentrant phase transition being predicted. A ground-state analysis and a simple bilayer model allows us to detail the conditions for the existence of an interfacial multilayer phase transition, as a function of both the energetic and crystallographic parameters and the temperature.

Phase transition induced by superficial segregation: the respective role of the size mismatch and of the chemistry

Segregation at the (0 0 1) surface in Cu(Ag) alloys has been studied using Monte Carlo (MC) simulations in conjunction with a semi-empirical N-body potential. The simulations show that the surface undergoes a first order phase transition at 600 K. This phase transition corresponds to a discontinuous increase of the surface concentration of Ag from 0.3 to 0.9 for a critical value of the bulk concentration well within the domain of existence of the bulk Cu(Ag) solid solution. This chemical transition is coupled with a change of the surface structure. The Ag-rich phase presents a pseudo-hexagonal c(10×2) structure, in complete agreement with experiments. This structural transition requires that some of the surface atoms are squeezed out into adatom positions. We present also a matching of the MC results on a lattice gas model consistent with the N-body interatomic potential used in the simulations. This matching allows us to determine the segregation driving forces and to detail their dependence on the surface structure. Surprisingly, the presence of the superstructure does not change the main driving forces for the surface plane but has a large influence for the first underlayer. In addition, the matching allows a discussion on the respective role of the structure and of the chemistry for the occurrence of the surface phase transition.

Wetting and structural transition induced by segregation at grain boundaries: a monte carlo study.

Wetting of the Sigma = 5 (310) <001> symmetrical tilt grain boundary (GB) close to the solubility limit in the Cu(Ag) solid solution has been observed by means of Monte Carlo simulations at T = 600 K. More precisely, a finite thickness film almost pure in Ag, separating the two initial Cu(Ag) grains, can be obtained from a critical intergranular germ induced by the strong segregation of Ag in the GB. As this film is actually a single crystal, this implies a complete rearrangement of the GB core structure. Thus the initial GB is replaced by two Cu(Ag)/Ag(Cu) interfaces. Evidence is presented for the increase of the film thickness when approaching the solubility limit, as expected in wetting phenomena.

Structural phase transition induced by interfacial segregation: a comparison between surface and grain boundary

The coupling between interfacial segregation and structural phase transition is studied in dilute Cu–Ag alloys using Monte Carlo modelling. Both the (0 0 1) surface and the Σ=5 (3 1 0) 〈0 0 1〉 tilt grain boundary (GB) are considered. The simulations show that the (0 0 1) surface plane undergoes a first order phase transition from a Cu-rich phase to a Ag-rich phase at T=600 K when varying the bulk concentration within the domain of existence of the Cu(Ag) solid solution. This chemical transition is accompanied by a structural one, the Ag-rich phase having a pseudohexagonal c(10×2) structure, in good agreement with experiments. For the GB, two segregation modes are established. For low Ag concentration in bulk, only the GB plane is enriched in Ag and the crystallographic structure of the GB is not modified by the Ag enrichment. At higher bulk concentration, an intergranular wetting is observed: a thin film almost pure in Ag is formed in the region where the GB was initially present. Surprisingly, the Ag film is monocrystalline, indicating that the atomic structure of the GB has disappeared, even if the Cu grains retain their mutual disorientation. The thickness of the Ag film increases when the bulk concentration comes near to the bulk solubility limit. We discuss the possibility of a similar wetting for the (0 0 1) surface and we compare the configurations obtained by equilibrium surface segregation in Cu(Ag) (0 0 1) and by depositing Ag/Cu (0 0 1).

Single domain textured (YBa 2Cu 3O 7−δ) 1− x(Ag 2O) x samples

The effect of the Ag doping on the structural and superconducting parameters was investigated in two series of melted and highly textured samples of the system (YBa 2Cu 3O 7−δ) 1− x (Ag 2O) x . The x concentration level of the first series range from 0 to 10 wt % and the second ones from 0 to 3.6 wt %. The optimal AgO 0.5 level doping found by means of the SQUID magnetization measurements ranged about 1.6–2.8 wt %. From the secondary precipitated CuO phase and from the appearance of Ag component the solubility limit of Ag in solid solution (SS) YBa 2Cu 3− y Ag y O 7− y/2−δ was found.

Palladium catalysts in the selective hydrogenation of hexa-1,5-diene and hexa-1,3-diene in the liquid phase. Effect of tin and silver addition Part 1. Preparation and characterization: from the precursor species to the final phases

Palladium, palladium–tin and palladium–silver catalysts, supported on two alumina samples with different acidity, have been prepared by diffusional impregnation for use in the selective hydrogenation of hexa-1,5-diene and hexa-1,3-diene in the liquid phase. UV–VIS–NIR (transmission and diffuse reflectance) studies of the palladium starting solutions and of the solids obtained during all preparation stages (impregnation, drying, calcination) show that the nature of the supported precursor species depends on the acidity of the alumina. Palladium tetrachloropalladate (strongly bound anionic species) are predominant on the more acidic alumina while the more basic one favours the formation of weakly bound neutral complexes through exchange of chloride ligands with hydroxy groups and water. The nature of these species influences not only the particle size of monometallic Pd samples (the stronger the interaction, the smaller the metal particle size), but also the nature of the final bimetallic Pd–Ag catalysts; a Pd–Ag solid solution is observed on the bimetallic catalyst prepared by interaction of a cationic Ag precursor withsupported PdCl42-, whereas interaction with neutral Pd species leads to separate metal phases. The interaction of Sn precursor solutions with supported PdII species induces the formation of heteronuclear species which decompose upon drying; Pd2Sn or Pd3Sn phases are detected on the final catalysts, depending on the initial Pd/Sn ratio and on the nature of the Sn precursor solvent (using ethanol favours the formation of Pd3Sn).

Study of the local atomic structure of a silver aluminum alloy by the method of extended electron energy loss fine structure (EELFS)

Extended energy loss fine structure spectra are obtained for electrons at the Al K and Ag M4,5 edges for an Al-20 wt %Ag solid solution after high-temperature aging, as well as for the pure alloy components. The analysis layer depth was ∼20 A. Radial distribution functions for the atoms are determined by Fourier transforming these spectra with a correction for the phase shift and the method of regularization. For pure aluminum and silver it is found that the position of the first coordinate spheres does not differ from bulk interatomic distances. For the binary alloy it was shown that the state of the sample corresponds to a decomposed solid solution with inclusions of a phase enriched with silver against an aluminum host background. The interatomic Al-Al distances in the binary alloy correspond to the length of a pure aluminum bond. The partial distances to the first two coordination spheres for the pairs Ag-Ag, Ag-Al are the same and equal the interatomic distances of the γ-phase Ag2Al.

Mechanical alloying of immiscible elements: Experimental results on Ag‒Cu and Co‒Cu

Abstract Equimolar solid solutions of Ag[sbnd]Cu and Co[sbnd]Cu were prepared by mechanical milling of the elements. The structure and the thermodynamic properties of the resulting phases were analysed by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. Large mixing enthalpies (ΔH = 6–8kJg-atom−1 and ΔH = 4–8kJg-atom−1 for Ag-Cu and Co-Cu respectively) were measured in the alloyed phases. It is clear that the solid solution forms through a process of grain refinement down to the nanometre scale and is assisted by an atomic-scale dissolution. The possible role played by coherent interfaces in substantially increasing the energy of the solid solutions is discussed.

In-situ X-ray diffraction examination of nanocrystalline Ag 37Cu 63 powders synthesized by mechanical alloying

Nanocrystalline Ag 37Cu 63 powders have been synthesized by a mechanical alloying method although Ag and Cu are almost immiscible to each other. The microstructure changes of the as-synthesized powders with increasing temperature have been examined by XRD and TEM. Below 200 °C, the specimen is composed of an amorphous phase and a supersurated CuAg solid solution with the starting composition. The Cu-8 at.% Ag solid solution is formed at 200 °C, so that an amorphous phase and two CuAg solid solutions with different compositions are coexistent in the specimen. On further heating of the specimen to 300 °C and above, the amorphous phase and two CuAg solid solutions vanish completely and transform into Cu- and Ag-phase.