Ag-Cd Alloys Research Articles

Effect of Ag + ion concentration on the stress corrosion cracking susceptibility of Ag–Cd alloys in AgNO 3 and AgClO 4 aqueous solutions

Silver–cadmium alloys, with compositions ranging from Ag–10Cd (a/o) up to Ag–40Cd (a/o) were found to be susceptible to stress corrosion cracking (SCC) in silver nitrate and in silver perchlorate aqueous solutions, at the equilibrium potential of the reaction: Ag⇌Ag ++e −. The effect of Ag + ion concentration on the stress corrosion cracking propagation rate (CPR) was studied. A linear relation between the logarithm of the CPR and the logarithm of the Ag + concentration was found. The slope of this relation was very close to that reported for the silver exchange current density and the silver ion concentration: (δ log i 0/δ log [ Ag +]) . Most of the cracks found were transgranular, and the crack propagation mechanism was explained through the surface mobility SCC mechanism. In the present work, it is suggested that Ag–Cd alloys could be used as model alloys to study the SCC behaviour of technically more relevant alloys, such as Cu–Zn brasses.

The Main Parameters and Properties of Ag-Cd Alloys Electrodeposited from an Iodide Bath

SUMMARYAg-Cd alloys have been electrodeposited from an iodide bath. The silver content of the bath, metal ratio Cd/Ag, current density and temperature, all affect the silver content of the alloy deposit. The silver content, % in the alloy increases with increase of silver content in the bath and with increase of temperature. On the other hand, silver content % in the alloy increases with decreasing current density or with decreasing metal ratio Cd/Ag in the bath.

Thermal Cycling and Growth of the Martensite Studied by NMR in an Ag-Cd Alloy

113 Cd NMR measurements in two Ag-Cd samples cycled between room temperature and temperatures below M s are presented. The growth curve of the martensite on cooling presents a discontinuity in the cycling temperature region. It is shown that the method of analysis of the NMR data recently developed by us [Phys.Rev.B 46, 10563 (1992)], allows to detect subtle memory effects and the absolute determination of the fraction of the martensite in thermoelastic equilibrium with the parent phase at fixed temperature

High-resolution analytical electron microscopy study of isothermal plate-shaped products in some β-phase alloys

The isothermal plate-shaped products in β-phase Cu-Zn-Al, Cu-Zn-Au, and Ag-Cd alloys have been studied from the viewpoints of morphology, crystal structure, and composition using a high-resolution analytical electron microscope equipped with a field-emission electron gun. It is shown that thin plate-shaped products, at early stages of the isothermal formation, exhibit crystallographic properties characteristic of martensites formed at subzero temperatures but that their compositions were definitely different from those of the surrounding matrices. Therefore, atom diffusion is conceivable to be involved in the plate formation from the nucleation stage and to occur across the coherent plate/matrix interfaces. In order for nucleation of the isothermal transformation to occur, two kinds of reactions should be thermally activated at intermediate temperatures above To for the martensitic transformation: (1) atom diffusion to achieve the observed composition differences between plates and matrices and (2) martensitic transformation in hypothetical alloys with compositions less than those of the original ones by the observed composition differences. The incubation periods experimentally observed should be associated with these two thermal activation processes.

Application of the theory of martensite crystallography to displacive phase transformations in substitutional nonferrous alloys

It has been demonstrated that the theory of martensite crystallography is capable of accounting successfully for the form and crystallography of a range of plate- or lath-shaped transformation products, even when the formation of the product phase involves significant substitutional diffusion. These transformations include the precipitation of metastable hexagonal γ’ (Ag2Al) plates in disordered face-centered cubic (fcc) solid-solution Al-Ag alloys, the formation of ordered AuCu II plates from disordered fcc solid solution in equiatomic Au-Cu alloys, and the formation of metastable9R α 1, plates in ordered(B2) Cu-Zn and Ag-Cd alloys. The application of the theory to these transformations is reviewed critically and the features common to them identified. It is confirmed that, in all three transformations, the product phase produces relief at a free surface consistent with an invariant plane-strain shape change and that the transformations are thus properly described as displacive. The agreement between experimental observations and theoretical predictions of the transformation crystallography is in all cases excellent. It is proposed that successful application of the theory implies a growth mechanism in which the coherent or semicoherent, planar interface between parent and product phases maintains its structural identity during migration and that growth proceeds atom by atom in a manner consistent with the maintenance of a correspondence of lattice sites. In the case of the coherent, planar interfaces associated with γ’ precipitate plates in Al-Ag alloys, there is direct experimental evidence that this is accomplished by the motion of transformation dislocations across the coherent broad faces of the precipitate plates; the transformation dislocations define steps that are two atom layers in height normal to the habit plane and have a Burgers vector at least approximately equivalent to an(α/6)(112) Shockley partial dislocation in the parent fcc structure. However, for AuCu II plates, where the product phase is twinned on a fine scale, and for α1 plates, for which the lattice invariant strain leads to a substructure of finely spaced stacking faults, the structures of the semicoherent interphase boundaries and thus the details of the transformation mechanism remain less clearly defined.

Martensitic transformation in Ag-Cd and Cu-Zn alloys studied by nuclear magnetic resonance.

$^{113}\mathrm{Cd}$, $^{109}\mathrm{Ag}$, and $^{63}\mathrm{Cu}$ nuclear-magnetic-resonance line-shape and Knight-shift measurements are reported for ${\mathrm{Ag}}_{53.5}$${\mathrm{Cd}}_{46.5}$ and ${\mathrm{Cu}}_{61}$${\mathrm{Zn}}_{39}$ over a temperature interval covering the martensitic phase transformation (MPT) displayed by these alloys. The changes observed in the line shape and width are explained in terms of the changes in atomic coordination and crystal symmetry occurring at the MPT. A small but non-negligible temperature dependence of the Knight shift is observed in the austenitic phase with small discontinuous changes at the transformation for all the nuclei investigated. The difference of resonance frequency of $^{113}\mathrm{Cd}$ in the two phases has been utilized to obtain the curve of the percentage of martensite in the Ag-Cd alloy as a function of temperature during the thermoelastic transformation. It is shown that our growth curve reveals details which cannot be seen by dynamical methods such as differential scanning calorimetry.

Surface mobility in the dealloying of Ag-Cd alloys in halide solutions

Dealloying of wire samples of Ag-30Cd and Ag-20Cd alloys was studied, at constant potential, in KCl, KBr and KI solutions. Dealloying was found only at those potentials where the respective silver halides were formed, and could be accelerated by straining the wires. It was concluded that surface mobility was the rate controlling step in the dealloying of these alloys. No evidence of stress corrosion cracking could be detected on the strained samples.

Long range order, antiphase domain structures, and the formation mechanism of α1 (“Bainite”) plates in A CuZnAl alloy

The inheritance of long range order during the β 2 (B2) or β 3 ( L2 1) → α 1 (“Bainite”) transformation in a Cu-26.67Zn-4Al (wt%) alloy has been demonstrated. The associated antiphase domain (APD) structures in the α 1, plates were studied by TEM dark field imaging using both nearest-neighbor (NN) and next-nearest-neighbor (NNN) superlattice reflections. At temperatures below the β 2 → β 3 ordering temperature, both NN and NNN APDs are inherited by the α 1, plates during their initial formation and subsequent early stage plate thickening. NNN order is lost, although NN order and its APD structure are preserved in subsequently thickened layers of the plates. As a result, the α 1 ordered structure is composite, consisting of an 18R central region and an ordered 9R surrounding outer layer. At temperatures above the β 2 → β 3 transition temperature, the parent β 2 possesses only NN order. Similar inheritance of NN order and associated APDs is also found at lower transformation temperatures. The observed evolution of long range order and the APD structure of the α 1 plates strongly suggests that both the initial transformation and early growth stages of the plates involve a shear mechanism. Long range diffusion, which is effectively confined to the NNN sublattice due to the presence of NN order at the interface, eventually takes over and controls subsequent plate thickening. The thickness of the 18R central zone in α 1 plates decreases significantly with increasing transformation temperature, implying that the shear-diffusional transition is shifted to an earlier transformation stage as the transformation temperature becomes increasingly higher than the martensitic transformation temperature, M s . The lifetime of long range order in the α 1, plates also decreases with increasing transformation temperature, as internal diffusion in the plates is enhanced. The implications of these observations are discussed and compared with earlier results on similar transformations in binary CuZn and AgCd alloys. Accordingly, it is believed that, for the first time, an aggregate of substantial documentation has been obtained for the case where a solid state phase transformation begins by a shear mechanism and ends up being dominated by classical diffusion. This behavior can be rationalized in terms of ordering temperatures in relation to the M s temperature of a given alloy. The essential point in this case, is that a “mixed” transformation is clearly involved, the description of which in classical terms, e.g. shear or diffusion controlled, depends upon the time frame of observation during the course of total transformation.

Oxide particle densities in internally oxidised Ag–Cd alloys: Part 1 Effect of heterogeneous nucleation in alloys with high Cd content

It is shown by quantitative evaluation of scanning electron micrographs that there is disagreement between predictions of particle density on the basis of classical theory of internal oxidation and experimental results for Ag–Cd alloys with a medium Cd content at some depth below the surface and with high Cd content over most of the specimen cross-section. It is hypothesised that a transition from homogeneous to heterogeneous nucleation takes place by which the particle density is increased. Nucleation sites are formed by agglomeration of vacancies enriched in front of the oxidation zone because of counterdiffusion of Cd which, in turn, is accelerated by the high defect concentration. Most of the experimental results can be qualitatively explained by considering these effects.MST/900a

Oxide particle densities in internally oxidised Ag-Cd alloys: Part 2 Alloys with ternary additions

The densities of oxide particles are studied as a function of depth below the surface of internally oxidised Ag–9·5 at.-%Cd alloys with additions of ~0·2 or 2 at.-%Al, Mn, Ni, Sn, or Zn. Because of its low diffusivity and low free energy of oxide formation, Ni has no influence on particle density. Tin forms needlelike oxides and reduces the particle density as a result of geometric effects. Zinc has a marked effect on particle shape with platelike precipitates which coalesce during subsequent precipitation of CdO, but does not greatly affect particle density. Both Al and Mn increase particle density up to two orders of magnitude. Planar size distributions are presented which indicate that two types of nucleation site are present in the Mn containing alloys. In the alloy containing 0·15 at.-%Al the Al2O3 particles are too fine to act as nuclei for CdO precipitation; two types of band both with a narrow size distribution of CdO particles, but with slightly different size and largely different density are formed. Heterogeneous nucleation and depletion of the centre region of sample sheets, both of which result from the counterdiffusion of the oxidising elements, are shown to have a great influence on particle density, resulting in a more homogeneous distribution of particle densities over the sample cross-section than that predicted by available theories.MST/900b

Metallurgical study of Ag-Cd and Ag-CdO alloy electrical contacts

Ag-Cd and Ag-CdO contacts, made both by sintering and postoxidation, were evaluated as to their durability by inductive and capacitive overcurrent tests according to the IEC 328 and NBR 6269 standards. Materials transfer during electric tests were monitored at 10000, 20000, 30000, and 40000 switching operations by scanning electron microscopy (SEM), energy-dispersive X-ray analysis, and chemical analysis. Better performance with regard to erosion was found for Ag-CdO postoxidized contacts, compared with sintered ones. Structural changes on the surface of Ag-Cd and Ag-CdO contacts were studied by SEM. The surface of Ag-Cd contacts changed rather uniformly, while Ag-CdO contacts developed considerable inhomogeneity. Sintered and postoxidized contacts also have also different structures. Sintered Ag-CdO contacts show a matrix with pulverized droplets while postoxidized Ag-CdO show very little change. >

Electronic properties of FCC- and BCC-based random AgCd alloys

The electronic structure of FCC- and BCC-based random AgCd alloys is determined within the recently developed tight-binding muffin-tin orbital method in the framework of the single-site approximation. The total and component densities of states and Bloch spectral densities are determined and compared with available experimental data.

Martensite transformation and shape memory effect in Ag-Cd alloys

Martensite transformation and shape memory effect in Ag-Cd alloys

INTERNAL FRICTION OF Ag-Cd ALLOY IN THE BAINITIC TRANSFORMATION

The isothermal internal friction of a Ag-42.3% Cd alloy has been measured by means of a low frequency inverted torsion pendulum apparatus between room temperature and 250℃. The relation between Q-1 and temperature with various heating and cooling rate were determined. Experimental results show that as the bainitic transformation occurs, the Q-1 of Ag-Cd alloy increases rapidly. It may be postulated that there are regions of instability of the parent lattice in the course of nucleation process for the bainitic transformation. The increment of Q-1s is a function of the product of internal friction of the fraction of the lattice localized soft region per volume and the nuclea-tion rate J* of the bainite.

A study on Manufacturing Silver-Metal Oxide Contacts from Oxidized Alloy Powders

Electric contact materials were made from oxidized Ag-Cd and Ag-Sn alloy powders by water atomization. It was found that the oxidation temperature of the Ag-Cd powder affected the morphology of the press-sinter-repressed material and the mechanical properties of the wrought material. Preliminary electrical tests showed that the Ag-CdO material made by this method performed comparably with Ag-CdO material made by more conventional methods.

Underpotential alloy formation in the system Ag( hkl)/Cd 2+

The underpotential deposition (UPD) of Cd on “real” and “quasi-ideal” silver single crystal surfaces of (111) and (100) crystallographic orientation as well as on polycrystalline silver substrate has been investigated in 0.5 M Na 2SO 4 supporting electrolyte solutions. At high underpotentials 100 < Δ E < 350 mV, the UPD is characterized by a quasi-reversible adsorption/desorption of Cd whereas at low underpotentials. Δ E < 50 mV, an increase of the anodic stripping charge with the polarization time is found due to the formation of an AgCd alloy at the substrate surface. The time dependence of this process can be described by a parabolic rate law, the rate constant of which is a function of Δ E and temperature T. Relatively low activation energies of about 70 kJmol −1 were determined from measurements at 293 ⩽ T ⩽ 338 K. The results are discussed in terms of a semi-infinite-linear diffusion model. The alloy formation process is assumed to be initiated by a place exchange between Ag substrate atoms and vacancy sites within a mobile Cd adsorbate layer thus forming the initial stage of a highly distorted AgCd alloy. The further growth will take place by the movement of Ag atoms through the vacancy-rich surface alloy and the simultaneous deposition of Cd at the interface AgCd/Cd 2+.

The nature of special-mode softening and the mechanism of martensitic phase transition in β-phase alloys

Abstract The nature of the special mode in the β1 phases of NiAl and Au—Ag—Cd alloys is studied in detail from the viewpoint of the dynamic mechanism of the martensitic transition. The special mode becomes soft; the softening is responsible far the(112)[111] shear and hence for the formation of close-packed layers in the martensite. The origin of special-mode softening is an increased mode-mode correlation between the C′ and C 44 modes, i.e. an enhanced anharmonicity of the β1 lattice. Based on the results obtained, we propose a model of the transition processes of the β-phase alloys. We also discuss in detail the transition mechanism and show that the special-mode softening is an instability characteristic of the D1 lattice with a two-dimensional property induced by the C′ softening.

Elastic Constants of the β1-AgCd Alloy

The elastic constants of single crystal of β 1 -AgCd alloy with 47.9±0.1 at.%Cd have been measured in a temperature range between 180 K and 360 K, using a ultrasonic pulse-cho overlapping method. It is found that with increasing temperature, the elastic constants C L =( C 11 + C 12 +2 C 44 )/2 and C 44 decrease linearly but C '=( C 11 - C 12 )/2 increases. In addition, this alloy shows a high elastic anisotropy in comparison with other Ag-based β 1 -phase alloys such as AgMg and AgZn.

Electron energy-band structures of some AgCd alloys

Complex energy-band structures of AgCd alloys have been determined by the alloy--Koringa-Kohn-Rostoker-Ziman (KKRZ) method for two different concentrations, and the optical properties estimated from these calculations have been compared with experiment. On the low-concentration side agreement with experiment is found to be excellent, whereas on the higher-concentration end a slight deviation is observed. This is probably due to the fact that the average-T-matrix approximation, which is the basis of the alloy--KKRZ method, is more suited for relatively lower concentrations of the alloying material. An effect of the charge transfer on the higher-concentration alloys has also been investigated. The results show that the disagreement with the experiment can also be accounted for by the charge-transfer effect.

Ag-Cd-Sn合金の内部酸化における酸化物の析出挙動

Ag-Cd and Ag-Cd-Sn alloys containing 10∼17 mass%Cd and 0.5∼1.5 mass%Sn were oxidized at 973 and 1073 K under oxygen pressures of 2.1×104 and 1.0×105 Pa in order to investigate the precipitation behavior of oxides during internal oxidation. Microstructures, distribution of Cd and Sn in oxides, and oxide phases were investigated by optical microscopy, electron probe X-ray microanalysis, and X-ray diffraction, respectively. Oxidation tendency of solute elements were estimated with an EPMA, by utilizing oxide enrichment produced at the oxidation front when oxidation conditions were changed rapidly to higher temperature and lower oxygen pressure.The results obtained are as follows:(1) Massive oxides in Ag-Cd alloys were changed into fine needle-like oxides by addition of Sn. The most remarkable effect was obtained with 0.5%Sn.(2) Oxide phases precipitating at 973 K were identified as CdO, Cd2SnO4, and CdSnO3. CdO and Cd2SnO4 precipitated at 1073 K.(3) SnO2 or composite oxides of CdO and SnO2 precipitated followed by precipitation of CdO on the oxides. It was considered that SnO2 converted into composite oxides by reaction with CdO.