Ag-Zn Alloys Research Articles

A test of two depth profiling techniques using PIXE

A destructive and a nondestructive technique for depth profiling using PIXE is tested on various concentration profiles of Zn depletion in initially homogeneous Ag 3 at.% Zn alloys. The first consists of measuring the yield of X-rays emerging from thin film targets prepared by deposition of Ag and Zn hydroxides originating from slabs of controlled thickness removed from the analysed sample. The second consists of deconvoluting a set of X-ray yield measurements carried out with various energies. Both techniques are cross-referenced with electron microprobe analysis run on a transverse section of the corresponding specimens, but can also be applied to profiles extending over depths too small for analysis on a transverse section. Internal coherence between the different concentration profiles obtained is checked on the basis of Zn diffusivity in Ag-Zn alloys.

拡散加熱によるＡｇ‐Ｚｎ合金層の形成

Zinc was electrodeposited on pure silver plates 1mm in thickness, which were then annealed at 473K in an argon atmosphere in order to obtain a corrosion resistant Ag-Zn alloy layer.Observasion after annealing revealed a η phase (the solid solution of Ag in Zn), and three intermediate phases, e, γ and ζ. After prolonged annealing the η solid solution layer supplied zinc atoms to the inner intermediate phase layers, thereby becoming porous.When the electrodeposited zinc layer was 10μm in thickness, difficulty of the supply of zinc atoms from the porous layer lying on the specimen surface resulted in disapperance of the e phase layer after 83ks annealing, and of the γ phase layer after 115ks annealing.The porous surface layer was easily removed by buff polishing. The silver plates with zinc deposited layers 200μm in thickness were clamped to prevent void formation and used as a diffusion couple. The interdiffusion coefficient obtained were: 7.9×10-15-3.7×10-16m2/s at 13-30 at% Ag in the e phase, 6.0×10-15-4.0×10-15m2/s at 34.9-37.9 at% Ag in the γ phase and 1.7×10-14-6.8×10-16 m2/s at 46.9-59.0 at% Ag in the ζ phase.

Anomalous small-angle-X-ray scattering on Al–Zn and Al–Zn–Ag alloys

Anomalous small-angle scattering (ASAXS) spectra from Al–Zn and Al–Zn–Ag alloys have been recorded at the Stanford Synchrotron Radiation Laboratory (SSRL). The data were obtained at different energies close to the Zn absorption edge. For the binary alloy, the ASAXS intensities follow quantitatively the variation in the atomic scattering factor of zinc. For the ternary alloys, the anomalous effect decreases when the Zn content decreases. Although only weighted sums of the partial structure functions could be determined, it is shown that the results are consistent with the `two-phase' unmixing model and the direction of tie lines of the metastable miscibility gap has been determined. A new method for analyzing ASAXS data for two absorption edges is proposed.

Determination of anomalous scattering factors for zinc and silver in Al–Zn–Ag alloys

The anomalous scattering factors of zinc and silver in samples of Al-rich Al–Zn–Ag have been measured near their K-absorption edges. EXAFS spectra obtained from the Stanford Synchrotron Radiation Laboratory were converted to the imaginary part of the atomic scattering factor f′′ using the optical theorem. With a knowledge of f′′(E), f′, the real part of the atomic scattering factor, was determined from the Kramers–Kronig dispersion relation.

Pressure-induced phase transformation in AgZn

The effect of pressure on the crystal structure of a solid AgZn alloy has been investigated. X-ray diffraction measurement employing a diamond-anvil cell has shown that the trigonal ζ phase structure is transformed into the cubic CsCl structure at about 3 GPa with a small, but finite, volume discontinuity. A pressure-temperature phase diagram has been constructed on the basis of the results of X-ray diffraction examination, electrical resistance measurement and differential thermal analysis. Discussion is given on the stability of the ζ phase in AgZn.

Elastic Behavior and Phase Stability in the H.C.P. ε-Phase of Ag-Zn Alloy

The elastic constants of ε -phase Ag-Zn alloys in the composition range from about 68 to 84 at.%Zn have been measured using a ultrasonic pulse-echo overlapping method. The elastic constants c 11 , c 44 and c 66 increase lincarly with zinc content. c 33 decreases linearly up to 75 at.%Zn and then fall more rapidly. On the other hand, c 13 increases linearly up to 75 at.%Zn and then rises rapidly. The axial ratio decreases linearly with zinc content, while C = c 11 + c 12 +2 c 33 -4 c 13 which correspond to a strain that change the axial ratio at constant volume, fall more rapidly above 75 at.%Zn. Based on the obtained results, we discuss the relation between the axial ratio change and phase stability, and elastic behavior.

Single and multiple trapping of radiation-induced defects in AgZn alloys

Abstract Experimental results on the recovery spectra of low temperature electron irradiated pure Ag and AgZn alloys in the concentration range 0.018 to 30 at.% of zinc are presented. Their comparison leads to consider two distinct concentration domains. In the low concentration domain he classical model of Corbett, Smith and Walker applies with some modifications. The resistivity ecovery is governed by the combinations and annihilations of point defects. It must be noted hat even in dilute alloys, new kinds of point defects (such as mixed interstitials) arise from the presence of solute atoms. In the high concentration domain, the resistivity recovery is dominated by the setting in of short-range order as a result of the point defect migration: interstitia migration in stage II and, mainly, vacancy migration in stage III. The defect migration, free in he pure metal, is influenced, in the concentrated alloys, by the local environment. The proposed model consistently allows the interpretation of the existi...

Interdiffusion in Solid Solution of the Al–Ag–Zn System at 832 K

Interdiffusion in an α-solid solution of Al–Ag–Zn alloys at 832 K has been investigated. The diffusion profiles have been determined, and then the diffusion paths have been drawn in the ternary composition triangle. The interdiffusion coefficients \ ildeDAgAgAl, \ ildeDAgZnAl, \ ildeDZnAgAl and \ ildeDZnZnAl have been determined by Matano’s method. The four coefficients have been found to be sensitive to the solute concentration. The diffusion profiles and paths have been also calculated by the solution of Fujita et al. and by the finite-difference method using the experimental values of the four interdiffusion coefficients. Good agreements have been found between the experimental and calculated both of them.

Stress-equivalence of solid-solution hardening in concentrated AgAl and AgZn alloys

Stress-equivalence of solid-solution hardening in concentrated AgAl and AgZn alloys

Precipitation in ternary AlZnAg alloys studied by isotopic contrast in neutron small angle scattering

Neutron small angle scattering with isotopic contrast has been used to investigate the solute partitioning and its evolution with time during the decomposition of various AlZnAg ternary alloys. For the first time, the independent partial structure functions S Zn Zn , S Zn Ag and S Ag Ag have been determined from three scattering experiments successively realized with Ag natural, Ag 107 and Ag 109 in Al-5.2at.%Zn-1.5at.%Ag specimens quenched and aged in the same way at room temperature. A comparison is made with a classical two-phase modelling namely spherical Guinier-Preston zones dispersed in a solute depleted matrix. The principal metallurgical features are as follows: Ag slows down the unmixing kinetics as compared with binary AlZn alloys of the same composition; a single type of G.P. zone is formed; when a coarsening stage is reached, the composition of the zones as determined from the scattering data appear to be in agreement with those given by a computation of the metastable phase diagram.

β<SUB>1</SUB>-AgZn合金の弾性的挙動に対する添加元素の影響

β<SUB>1</SUB>-AgZn合金の弾性的挙動に対する添加元素の影響

シアン浴からのＡｇ‐Ｚｎ合金電着物の表面形態に対する電解電流波形の効果

Scanning electron microscopic studies were carried out in connection with the surface appearance of the Ag-Zn alloys electrodeposited from cyanide bath with various kinds of current forms. In the direct current plating, the needle-like deposits were obtained at lower current densities, which changed to granular in shape at higher current densities. In the pulsed current plating at on-time/off-time ratio of 0.25, the surface appearance of the alloys was similar to that obtained with direct current at the same alloy composition. Significant alteration of the current modulation in the pulsed plating resulted in a change in surface appearance, that is, the smoother deposit was obtained by increasing the pulse off-time. In the periodically reversed current plating at a given average cathodic current density, the rounded granular deposits were obtained, regardless of the pulse cycle and duty of anodic current pulse. The displacement reaction and a chemical or electrochemical dissolution of the deposited metals were estimated to bring about the changes in the surface appearance observed in these periodical electrodeposition by measuring the alloy composition, cathode current efficiency and the depositing potential of the alloys.

シアン浴からのＡｇ‐Ｚｎ合金の析出挙動

Direct, pulsed or periodically reversed current was applied to the electrodeposition of Ag-Zn alloys from cyanide baths. In the direct current plating, the electrodeposition behavior of each metal showed the regular type composition in which the deposition of less noble Zn proceed only in the limiting current region of noble Ag. In the pulsed or periodically reversed current plating the reasonable explanation of the trends of change in alloy composition was made by mainly considering the recovery of Ag concentration in the vicinity of the cathode on the basis of above deposition mechanism. In these periodical electrodeposition, the composition of alloys was determined by the average cathodic current density, and it was estimated that the replacement reaction of deposited Zn with Ag ions occurred at the off-time of pulsed current plating and the same amount of deposited Ag and Zn dissolved in the anodic current pulse period of periodically reversed current plating. Further, the effect of pulsed or periodically reversed current on the surface appearance of the alloys was discussed.

The efficiency of displacement cascades for the generation and absorption of self-interstitials and vacancies, in a neutron irradiated AgZn alloy

Abstract Strain relaxation measurements were performed during irradiation with reactor neutrons to monitor the enhancement of the stress-induced directional ordering rate associated with the supersaturated point defect population, in a Ag-24 at. % Zn alloy. The corresponding rate evolution was followed from the first seconds after the initiation of flux until long irradiation periods, directly at temperatures where both self-interstitials and vacancies are mobile. The generation of freely migrating elementary defects by the displacement cascades was found to be characterized by a mean cross-section of 160 barns, if referred to fast neutrons (E>1 MeV) in the reactor spectrum, with a bias of a few per cent. From comparison with the estimated total defect production, it was deduced that only 10% of the initially created point defects undergo random diffusion. The production rate of extra sinks for these defects by cascade collapse was determined also, for irradiation temperatures between 0.3 and 0.4 melting temperature. In fact the measured cross-sections were strongly temperature dependent, as the net result of simultaneous sink formation and anneal during high temperature irradiation.

Assignment of radiation-enhanced ordering to vacancies and self-interstitials, in alpha -AgZn alloys

Discusses the mobility parameters for both vacancies and self-interstitials, in concentrated alpha -AgZn solid solutions. Previous work based on the determination of the radiation enhancement of the ordering rate is reviewed. Some of the available data are reanalysed and interpreted in the light of recent quenching results. Convincing evidence is provided that the self-interstitials are less mobile than the vacancies and that they do contribute to the ordering process under irradiation, for either composition considered, 9 at.% and 30 at.% Zn, contrary to the scheme suggested recently by Schule (1980), namely that ordering occurs entirely by a vacancy mechanism, with the self-interstitials migrating faster than the vacancies in these alloys.

A comment on the previous paper concerning the interpretation of radiation-enhanced ordering in Ag-Zn alloys

For original paper see M. Halbwachs and J. Hillairet, ibid., vol.11, no.11, p.2247 (1981). Some recent developments in the radiation damage field are pointed out. It has been found that the recombination volume between vacancies and self-interstitials is much greater than was generally assumed. In addition, due to an interaction of the high energy particles with lattice atoms during irradiation, the migration energies of the defects decrease. The effect of these factors on the analysis of Halbwachs and Hillairet is discussed.

The role of substitutional solute atmospheres during cyclic deformation

Fatigue experiments under constant torsional strain were carried out on pure aluminium, AlCu, AlMg, AlZn and AlAg alloys. The areas and the shapes of the hysteresis loops after various numbers N of stress cycles were measured; from these the energy loss δE per cycle and the maximum torque T m on the specimen were determined. Both the cyclic hardening T m- N curves and the corresponding energy loss δE-N curves were analysed; different stages of these curves were correlated with the metallographic observations made on the specimen surface during fatigue. It was found that, although the T m- N curves were similar in all cases, the shape of the δE-N curves, the characteristics metallographic changes and the site of crack initiation were condiderably affected by the presence of different solute atoms. The experimental results were explained in terms of the interaction of solute atoms and dislocations.

An investigation of the mobility of vacancies and interstitials in a Ag,-9 at. % Zn alloy by means of high-voltage electron microscopy

Abstract The characteristics of vacancy and self-interstitial clustering behaviour have been studied in a Ag-9 at. ′% Zn alloy during irradiation in an electron microscope operated at 800 or 1000 keV in the temperature range between 250 and 410 K. The salient feature of the observations was that, for irradiation temperatures below 300 K, only stacking-fault tetrahedra were nucleated while, for irradiations above 360 K, all defect agglomerates were faulted dislocation loops of interstitial type. Deeper insight into the mobility of point defects was gained by the realization of two-step irradiations. These have shown that preformed interstitial loops shrank during subsequent re-irradiation below 300 K. This demonstrates, using conventional methods of analysis for the dynamics of the defect populations associated with a fast particle flux, that vacancies migrate faster than selfinterstitials at low temperatures. The present evidence for this unique behaviour of elementary defects in a metal lattice is in agreement with previous anelasticity results obtained in other concentrated AgZn alloys, in which the single vacancy has been identified to be the faster moving defect.

Recombination efficiency of vacancies and self-interstitials in a concentrated AgZn alloy

A novel approach was devised for the determination of the recombination efficiency of vacancies and self-interstitials. It is based on the performance of anelasticity experiments to measure the rate at which directional order is established in ordering alloys. This method applies specifically to concentrated substitutional alloys. It is shown that it enables us to explore a wide temperature region above stage III, a domain in which data are scarce. Application to a Ag-30 at.% Zn solid solution is presented. Experiments were conducted during electron irradiation at a constant flux rate or after flux was suppressed. The recombination reaction constants were measured at a series of temperatures ranging between 200 and 350 K. The inferred capture radius is about six interatomic distances at the highest temperature examined, 340 K. Its variation with temperature is analyzed and discussed.

Elastic Behavior and Phase Stability of the β1-AgZn Alloy

To elucidate the dynamical mechanism of the β 1 to ζ transition the elastic constants of metastable β 1 phase of Ag-Zn alloys containing 46.5 and 48.5 at.% Zn are measured in the range between room temperature and the β 1 to ζ transition temperature using an ultrasonic pulse-echo overlapping method. The elastic constants C L [110]=(C 11 +C 12 +2C 44 )/2 and C 44 decrease linearly with increasing temperature up to 340 K and then fall more rapidly on further heating. On the other hand, C 11 decreases linearly on heating up to 340 K and then increases at higher temperatures. Furthermore, C L [111]=(C 11 +2C 12 +4C 44 )/3 which is mainly related to the β 1 to ζ transition mechanisum decreases rapidly above 340 K. These elastic constants show a characteristic temperature hysteresis with heating and cooling. Based on the obtained results, we discuss the transition mechanism and stability of the β 1 phase.