Some aspects of deformation in Al-Zn alloys

Creep resistance investigations of the Al-40 wt % Zn alloy at room temperature have been performed and revealed some creep compliance. Additions of Cu and Si decrease considerably the preliminary creep compliance in the alloy which then turn to be dimensionally stable and resistant to creep. Tensile test investigations performed at different deformation rates have not revealed the existance of the superplastic deformation mechanism.Presented at the 4^th International Symposium on Plasticity of Metals and Alloys, September 711, 1987, Srni, Czechoslovakia.     

K-absorption spectrum of aging Al-Zn alloys

The K-absorption spectra of aging Al-Zn alloys experience a systematic shift of the main edge during natural aging toward the short wavelength side. This is apparently due to filling of the 4S–4P shells of the zinc atoms by electrons at the expense of the aluminum atoms. Additions of Mg and Sn lead to a more intense redistribution of the outer electrons. The early zone stage of aging of Al alloys exhibits an electronic character.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 7, pp. 18–22, July, 1971.In conclusion the authors wish to thank Prof. A. E. Bryukhanov and docent V. I. Kotlyat for constant interst shown in the study and valuable comments made while discussing the results.     

Electronic topological transitions and phase stability in the fcc Al-Zn alloys

We report on a detailed investigation of the phase equilibria and the Fermi surface in the Al-Zn system. Our calculation are based on the density functional theory and we use the linear muffin-tin orbital method and the Green's function technique. The calculated free energies of alloy formation exhibit the existence of a miscibility gap between the alloys containing approximately 10 and 55 at.% of Zn, in agreement with the phase diagram of the Al-Zn system. Seven electronic topological transitions (ETT) were found in Al-Zn system within the stability range of the fcc solid solution. A relation between these ETT and the phase stability of the fcc Al-Zn solid solutions is established. We show that extremum points on the concentration dependencies of the thermodynamic properties of Al-Zn alloys can be explained by band-filling effects. Received 6 February 2002 Published online 19 November 2002     

Quantitative analysis of Al-Zn alloys in the early stage of decomposition

The method of low-angle x-ray scattering is used to perform a detailed analysis of the early stage of decomposition of Al-Zn alloys with 4.41 and 9.41 at. % Zn quenched at different homogenization temperatures. The parameters that characterize the post-quench state of the alloys are determined. It is found that a reduction in the quenching temperature is accompanied by a reduction in the size of the Guinier-Preston (GP) zones and their content of the dissolved element. Here, the density of the zones also decreases. An attempt is made to establish a connection between the parameters of the GP zones and the regions containing closely-spaced lamina formed in the alloys at the homogenization temperature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 29–34, August, 1989.We thank A. N. Bekrenev and L. A. Naumov for their advice on conducting the experiment.     

Calculation of concentrational dependence of equilibrium lattice parameters for the alloys Al-Cu and Al-Ag

We fit the Animalu model potential by using the crystal equation of state. We give the fitted parameters for 25 metals that have a cubic lattice. We calculate the concentrational dependence of the lattice parameters for the alloys Al-Cu and Al-Ag. The derivative da/dc in these alloys agrees well with the experimental data.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 30–34, June, 1986.     

Solvus line of the metastable rhombohedral phase in the Al-Zn system for Al-rich alloys

The X-ray diffraction on single crystals and on coarse-grained foils of Al-Zn alloys was used to determine the solvus temperatures of the metastable rhombohedral α′ _R -phase. The dissolution of α′ _R -phase was studied simultaneously by application of DTA technique. Results obtained from different heat-treatments of the investigated alloys were critically interpreted in terms of the nucleation theory. The dissolution of large α′ _R -particles was necessary to obtain the correct α′ _R -solvus line unaffected by the reversion of the solid solution below the solvus temperatures.     

Atomic configuration of antiphase boundaries in alloys

Computer simulation methods in the approximation of pairwise interatomic Morse potentials are used to calculate the atomic configurations and the energy of formation of 1/2 <110> {111} antiphase boundaries in ordered Cu₃Au and Ni₃Fe alloys. Atomic displacements result in considerable smearing of the first five planes closest to an antiphase boundary and a slip of atomic planes. These effects substantially reduce the energy of formation of antiphase boundaries. The influence of the size factor on the atomic configuration on the antiphase boundaries is discussed.Translated from Izvestiya Vysshykh Uchebnykh Zavedenii, Fizika, No. 2, pp. 43–47, February, 1985.In conclusion, the authors express their thanks to A. I. Tsaregorodtsev for useful discussion of this work.     

Volume of formation and electronic configuration in dilute alloys

A method is presented to relate the volume of formation to the electronic configuration of impurities in metals. The electronic configuration determines the effective size of the impurity through a modified ThomasFermi-Dirac model combined with elasticity theory. The size of the impurity determines the macroscopic volume change in the crystal, and the electronic configuration can be varied to fit the experimental volume of formation. Alloys of mainly transition metals are studied. The general conclusion of the work is that the charge transfer deduced from the changes in electronic configuration agrees with the expectations of the electronegativity scales, except for a few exceptions. For most of the alloys studied the changes consist of reoccupation of d and non-d levels at each site, maintaining the local neutrality. Only in a few cases were ionic configurations found, and the degree of ionicity was very small.     

The X-ray diffraction and electron microscopic investigation of stable and metastable equilibria in Al-rich Al-Zn alloys

The solvus line for the metastable cubic α′-phase and for the stable α- and α′-solubility limit for Al-Zn alloys with zinc content from 15 to 50 wt.% were determined. X-ray diffraction on single crystals was used to study the structures of phases developed during the applied heat-treatments. The dissolution of α′-phase at temperatures close below and above the determined solvus temperatures was observed by the transmission electron microscopy. The shift of the known (α+α′)-phase boundary to lower temperatures of about 8 °C was found. Similarly, small changes were obtained in the shape of the curve giving the solid solubility limit of Zn in Al.     

Energy of an excited atomic configuration in alloys

We investigate a model relating the excitation caused by ion bombardment of a metal substrate to the formation of an additional energy minimum relative to the equilibrium state for the excited atomic configuration. We present an explanation of the effects of changing the boundaries of solid solutions during ion implantation. V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 37–40, July, 1996.     

The influence of tensile stress on grain and cell boundary precipitation in supersaturated Al-Zn alloys during creep

The results are presented of the optical microscopic and X-ray diffraction study of the stress-induced nucleation and growth of (Zn) precipitates at grain and cell boundaries (GB's and CB's) during uniaxial creep at 200 °C of supersaturated AlZn20 and AlZn30 alloys. The rate of precipitation is increased mainly owing to the modifying effect of tensile stress on diffusion processes in alloy samples during their anneal. The diffusion of Zn atoms toward GB's and CB's from adjacent regions of grains is accompanied during creep by diffusive flux of Zn along boundaries parallel or nearly parallel to the tensile creep axis toward boundaries with near to normal orientation to that axis. Enhanced precipitation of results then preferentially at the latter and is supressed at the former boundaries where even the dissolution of preexisting has been found during a later application of tensile stress. The stress-induced precipitation of at GB's gradually ceases with prolonged creep exposures due to the lengthening of duffusion paths of Zn atoms from grain interior to GB's.Dissolution of lamellae by their regress toward GB's and CB's is assisted with the stress-induced diffusion of Zn along epitaxial / lamellar interfaces. Copious precipitation of at the parts of GB's and/or CB's with near to normal orientation to the creep axis is then observed on account of Zn from dissolved lamellae. Creep strain also leads to the fragmentation of lamellae and thus also to breaking down of the paths for diffusion of Zn along / interfaces. Spheroidization of fragmented parts of lamellae is then observed. Spheroids of remain embedded within the former lamellar regions.Large creep strains and high strain rates observed on fine-grained alloy samples may be associated with an enhanced viscous GB sliding due to the stress-dependent flow of Zn along GB's and/or CB's.     

Atomic configuration of microtwins in alloys having Ll2 superstructure

In the approximation of paired interatomic potentials of the Morse type, modeling is done on the atomic configuration and energy of formation of superstructure stacking faults and superstructure twinning stacking faults in the ordered alloys Cu₃Au and Ni₃Fe, and also in the intermetallide Ni₃Al. Features are observed in the local deformation of the crystal lattice defects near equilibrium (in terms of internal energy), and the principle difference in the state of the atomic surroundings of the examined plane defects is shown. In alloys of Cu₃Au and Ni₃Fe, calculations are done for different values of the long-range order parameter. A difference is detected in the variation of the energy of formation of superstructure twinning stacking faults in alloys of Cu₃Au and Ni₃Fe with the long-range order parameter. This difference correlates with experimental observation of the properties when varying the temperature in the alloys.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 31–36, November, 1987.     

Growth kinetics of precipitate-free zones near grain boundaries in Cu-Al-Co alloys

Transmission electron microscopy was used to study the growth kinetics of precipitate-free zones in aging Cu-Al-Co alloys. The formation of zones was associated with the precipitation of the CoAl intermetallic compound at grain boundaries and dissolution of metastable cobalt precipitates near the boundary. The growth of the zone width was found to be of a two-stage character. The activation energy of the zone growth process was determined and proved to be identical in both stages. The first stage is associated with the presence of a supersaturated solid solution of cobalt. The zone growth kinetics in the second stage at 600 and 650°C is nearly linearly dependent on time.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 75–80, April, 1979.     

Thermal vibrations of atoms in equilibrium Al-Ag solid solutions

An expression is derived for the effective mean square amplitude of thermal vibrations of atoms in a crystal lattice for the case of a binary, substitutional, metallic solid solution. All the possible configurations in the first coordination shell are respected. The dependence of on the Ag content is measured at 525°C for an equilibrium solid solution of Ag in Al from X-ray data. The results show that the values of increase for both the Al and Ag atoms as unequal neighbours are added to the first coordination shell. The relation between the force constant and is also derived. By using this relation for our measurements it was shown that the force constants decrease in both Al and Ag atoms as the number of nearest neighbours of different kinds increases; it thus follows that the bonding forces between different kinds of atoms are smaller than between atoms of the same kind. We therefore suppose that this describes the tendency of the equilibrium solid solution to form local regions with increased concentration of identical atoms.In conclusion the author thanks Ing. J. Laek C. Sc. for very carefully carrying out the chemical analysis of the Al-Ag alloys and J. Bedná for exact measurements of the density in order to determine the homogeneity of the alloys. She also thanks Z. iký for help in the X-ray diffraction measurements.     

Phonon dispersion relation of aluminum-copper with the Guinier-Preston zone formation

The phonon dispersion relation of ζ00 T branch of Al-1.8 at.% Cu has been measured by means of neutron inelastic scattering. A single crystal specimen aged at room temperature between 17 and 72 hr. after quenching from 550°C shows a strong resonance mode at the energy of about 2.5 THz. This resonance mode cannot be explained by the calculation based on the simple mass-defect model, and may be attributed to the formation of the Guinier- Preston zone.     

On the electronic relaxation in substitutional alloys

The many-electron system in a single-band model is perturbed by intruding an additional planewave particle. The time dependence of the momentum density matrix is shown to be related to the one-particle correlation function, both of them being determined by the spectral weight function. In some cases, the system shows an oscillatory approach to equilibrium.Ke Karlovu 3, Praha 2, Czechoslovakia.The authors are much indebted to Dr. B. Velický, CSc, for many valuable discussions regarding the work. Helpful comments of several other colleagues are also acknowledged.     

On the magnetoresistance in dilute magnetic alloys

Many-particle contributions to extended Suhl equations are considered to derive a magnetoresistance, which saturates for nonzero magnetic fields below the unitatarity limit in agreement with experiments.     

On the Tc of dilute alloys

The equation for the critical temperature T_c, of a dilute superconducting alloy due to Markowitz and Kadanoff (MK) is generalized to include renormalization effects due to the electron-phonon interaction. Such corrections constitute a 50% effect in weak coupling superconductors like aluminum while in strong coupling systems like lead this correction gives a factor of 2.5. The mean square anisotropy parameter appearing in the T_c equation is also generalized to remove the separability assumption of the electron-phonon interaction. Some consequences of these two corrections to the analysis and systematization of data for dilute superconducting alloys is discussed.