Physics of Metals and Metallography (v.118, #9)
On the calculation of the energies of dissociation, cohesion, vacancy formation, electron attachment, and the ionization potential of small metallic clusters containing a monovacancy by V. V. Pogosov; V. I. Reva (827-838).
In terms of the model of stable jellium, self-consistent calculations of spatial distributions of electrons and potentials, as well as of energies of dissociation, cohesion, vacancy formation, electron attachment, and ionization potentials of solid clusters of Mg N , Li N (with N ≤ 254 ) and of clusters containing a vacancy (N ≥ 12) have been performed. The contribution of a monovacancy to the energy of the cluster and size dependences of its characteristics and of asymptotics have been discussed. Calculations have been performed using a SKIT-3 cluster at Glushkov Institute of Cybernetics, National Academy of Sciences, Ukraine (Rpeak = 7.4 Tflops).
Keywords: metallic clusters; vacancy; cohesion energy; vacancy-formation energy; ionization potential; model of stable jellium
X-ray diffraction line broadening analysis of nanostructured nickel powder by M. Bahramyan; S. Hossein Nedjad (839-845).
X-ray diffraction peak profile analysis is a powerful method for investigation of the microstructural characteristics of nanocrystalline materials produced by severe plastic deformation. Williamson–Hall method, its modification, and Fourier transform methods like Warren–Averbach and its modification are used to extract microstructural information based on integral breadth and Fourier coefficients of the peak profiles. In this work, pure nickel powders were milled for 2, 5, 20, and 40 h to clarify the microstructural variations for this metal with FCC atomic structure. By using the Williamson–Hall and Warren–Averbach methods and their modifications, crystallite size, microstrain, dislocation density, and character of dislocation were extracted. It was obtained that the fraction of edge-type dislocation decreased with milling time (above 50%), while after prolonged milling, the fraction of screw-type dislocations decreased, so that 50%-edge-to 50%-screw ratio was obtained. It was also found that the values of the crystallite size obtained from classical Warren–Averbach and modified Warren–Averbach (area-average) were closed.
Keywords: X-ray diffraction pattern; nanostructure; dislocation structure; ball milling; nickel
Radiation-induced atomic redistribution in Aging Fe–Ni alloys upon neutron irradiation by V. A. Shabashov; V. V. Sagaradze; A. E. Zamatovskii; K. A. Kozlov; N. V. Kataeva (846-856).
The structural and phase transformations and atomic redistribution induced by neutron irradiation have been investigated in aging fcc Fe–Ni alloys using special alloying with elements M (Si, Ti, Al, Zr) that form intermetallic compounds. It has been established that the mechanism and kinetics of disturbance of regions of Ni–M atomic order in atomic displacement cascades upon neutron irradiation are linked to the chemical activity and diffusion mobility of alloying elements. Comparison with the laws of the deformationinduced dissolution of intermetallic compounds has been conducted.
Keywords: Fe–Ni; intermetallic compounds; neutron irradiation; Mössbauer spectroscopy
Effect of heat treatment on the crystal structure of deformed samples of chromium–manganese steel by D. S. Chezganov; O. A. Chikova; M. A. Borovykh (857-863).
Results of studying microstructures and the crystal structure of samples of 35KhGF steel (0.31–0.38 wt % С, 0.17–0.37 wt % Si, 0.95–1.25 wt % Mn, 1.0–1.3 wt % Cr, 0.06–0.12 wt % V, and the remainder was Fe) have been presented. The samples have been selected from hot-rolled pipes subjected to different heat treatments. A study has been carried out in order to explain the choice of the heat-treatment regime based on determining the structure–properties relationship that provides an increase in the corrosion resistance of pipes to the effect of hydrocarbons. Methods of the energy-dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) have been used. In the microstructure of samples, oxide inclusions and discontinuities with sizes of 1–50 μm that presumably consist of the scale were detected. The ferrite grain size and the orientations of crystals were determined; the data on the local mechanical stresses in the Taylor orientation- factor maps were obtained. The grain refinement; the increase in the fraction of the low-angle boundaries; and the decrease in the local mechanical stresses and, therefore, the highest corrosion resistance to the effect of hydrocarbons is achieved by normalizing at 910°С.
Keywords: chromium–manganese steel; microstructure; crystal structure; heat treatment; EBSD analysis
Evolution of the structure of tin bronze under dynamic channel-angular pressing by V. V. Popov; A. V. Stolbovsky; E. N. Popova; R. M. Falahutdinov; E. V. Shorohov (864-871).
The study of the evolution of the structure of tin bronze under dynamic channel-angular pressing (DCAP) has been performed. For comparison, the evolution of the structure of commercial copper subjected to the same treatment has been investigated. A comparison of the microhardness of copper and bronze has been carried out after one and two DCAP passes
Keywords: severe plastic deformation; dynamic channel-angular pressing; grain–subgrain structure; electron backscatter diffraction; electron microscopy
On diffusion theory in inhomogeneous media: Thin-film source of diffusant by A. G. Kesarev; V. V. Kondrat’ev; I. L. Lomaev (872-878).
Using asymptotic methods in the theory of differential equations, the original solution of the atomic diffusion problem in the semi-infinite inhomogeneous medium has been obtained for the thin-film (instantaneous) source of diffusant and arbitrary coordinate dependence of the diffusion coefficient. We have mathematically estimated the applicability of this solution and compared it numerically with the known exact solution for a particular case of the exponential coordinate dependence of the diffusion coefficient and a trivial case of the constant diffusion coefficient. Based on our analysis, the ranges of annealing times and depths of diffusant penetration for which the suggested approach proves to be correct have been established.
Keywords: diffusion; thin-film/instantaneous source; nonlinear diffusion equation; spatial dependence; diffusion coefficient
Effect of abrasive water jet on the structure of the surface layer of Al–Mg alloy by T. I. Tabatchikova; N. A. Tereshchenko; I. L. Yakovleva; N. Z. Gudnev (879-889).
Optical, scanning, and transmission electron microscopy methods, and X-ray diffraction analysis have been used to study the changes in the structure and the microhardness in the surface layer of the Al–Mg (5.8–6.8 wt %) alloy after water jet cutting. The dislocation density, the sizes of coherent scattering regions, and microdistortions have been determined. The transformation of the fine structure has been revealed in the displacement from the alloy volume to the abrasive-waterjet cutting surface.
Keywords: abrasive waterjet cutting; AMg6 alloy; structure
Electrocontact material based on silver dispersion-strengthened by nickel, titanium, and zinc oxides by G. M. Zeer; E. G. Zelenkova; O. V. Belousov; V. V. Beletskii; S. V. Nikolaev; O. N. Ledyaeva (890-895).
Samples of a composite electrocontact material based on silver strengthened by the dispersed phases of zinc and titanium oxides have been investigated by the electron microscopy and energy dispersive X-ray spectroscopy. A uniform distribution of the oxide phases containing 2 wt % zinc oxide in the initial charge has been revealed. The increase in the amount of zinc oxide leads to an increase of the size of the oxide phases. It has been shown that at the zinc oxide content of 2 wt %, the minimum wear is observed in the process of electroerosion tests; at 3 wt %, an overheating and welding of the contacts are observed.
Keywords: electrocontact material; nanopowders; silver; nickel; zinc oxide; titanium dioxide; tin oxide; microstructure
Formation of the structure of thin-sheet rolled product from a high-strength sparingly alloyed aluminum alloy “nikalin” by P. K. Shurkin; N. A. Belov; T. K. Akopyan; A. N. Alabin; A. S. Aleshchenko; N. N. Avxentieva (896-904).
The regime of thermomechanical treatment of flat ingots of a high-strength sparingly alloyed alloy based on the Al–Zn–Mg–Ni–Fe system upon the production of thin-sheet rolled products with a reduction of more than 97% has been substantiated. Using experimental and calculated methods, the structure and phase composition of the experimental alloy in the as cast and deformed state and after heat treatment including quenching with subsequent aging have been studied. It has been found that the structure of the wrought semi-finished products after aging according to Т and Т1 regimes consists of the precipitation-hardened aluminum matrix and uniformly distributed isolated particles of Al9FeNi with a size of 1–2 μm, which provides a combination of high strength and satisfactory plasticity at the level of standard high-strength aluminum alloys of the Аl–Zn–Mg–Cu system. The fractographic analysis confirmed that the tested samples underwent a ductile fracture.
Keywords: high-strength aluminum alloys; microstructure; phase composition; thin-sheet rolled product; heat treatment
Quantitative description of the flow-stress dependence of aluminum alloys at the stage of steady flow upon hot deformation on the Zener–Hollomon parameter by A. Yu. Churyumov; V. V. Teleshov (905-912).
The deformation behavior of a 1981 aluminum alloy has been studied using a complex for simulating thermomechanical processes in the temperature range of 200–400°C at a deformation rate in the range of 0.001–10 s–1. The models of the relationships between the flow stress, temperature, and deformation rate have been constructed using a power-law dependence, exponential dependence, and hyperbolic-sine function on the Zener–Hollomon parameter (Z). In the calculations according to the power-law and exponential equations, discrepancies between the calculated and experimental values of the Zener–Hollomon parameter have been revealed at low and high values. These discrepancies are caused by the fact that the experimentally obtained dependences of the flow stress on the Z parameter over the entire range of its change with a single magnitude of the effective activation energy of the plastic deformation consist of two linear parts that correspond to the hot and warm deformation and have different magnitudes of the effective activation energy of plastic deformation with a lower value of the activation energy for hot deformation.
Keywords: Zener–Hollomon parameter; hot deformation; aluminum alloys; flow stress
High-strain-rate superplasticity of the Al–Zn–Mg–Cu alloys with Fe and Ni additions by A. D. Kotov; A. V. Mikhaylovskaya; A. A. Borisov; O. A. Yakovtseva; V. K. Portnoy (913-921).
During high-strain-rate superplastic deformation, superplasticity indices, and the microstructure of two Al–Zn–Mg–Cu–Zr alloys with additions of nickel and iron, which contain equal volume fractions of eutectic particles of Al3Ni or Al9FeNi, have been compared. It has been shown that the alloys exhibit superplasticity with 300–800% elongations at the strain rates of 1 × 10–2–1 × 10–1 s–1. The differences in the kinetics of alloy recrystallization in the course of heating and deformation at different temperatures and rates of the superplastic deformation, which are related to the various parameters of the particles of the eutectic phases, have been found. At strain rates higher than 4 × 10–2, in the alloy with Fe and Ni, a partially nonrecrystallized structure is retained up to material failure and, in the alloy with Ni, a completely recrystallized structure is formed at rates of up to 1 × 10–1 s–1.
Keywords: aluminum alloys; eutectic particles; porosity; superplasticity indices; fine-grained structure
Experimental determination of Poisson’s ratio of a single crystal nickel heat-resistant alloy in the temperature range of 20–1000°C by S. A. Golynets; V. N. Toloraiya; S. N. Nekrasov; K. K. Khvatskii (922-927).
This work is devoted to the experimental determination of Poisson’s ratio at temperatures of 20–1000°C, which was carried out on cylindrical samples of a single-crystal heat-resistant nickel alloy with crystallographic orientations of (CGOs) , , and . The modulus of elasticity for the samples of these orientations has also been determined. It has been established that, in samples of heat-resistant nickel singlecrystal alloy with CGO , Poisson’s ratio can vary from negative to positive values depending on the azimuthal orientation, i.e., on the crystallographic directions that lie in the plane perpendicular to the longitudinal axis of the sample. To control the azimuthal CGO of cylindrical samples , a special metallographic procedure was developed based on the determination of the dendritic structure on the butt ends of these samples using etching. The data on the azimuthal orientation were subsequently used to place a sensor in order to determine the transverse deformation in these directions.
Keywords: heat-resistant nickel alloy; mechanical properties; Poisson’s ratio; modulus of elasticity; crystallographic orientation