Physics of Metals and Metallography (v.109, #4)

The distribution of an ac magnetic field in a conducting fiber composite of a finite length with components differing in their magnetic and electrical properties has been found. The geometry of the skin layer has been determined, and the degree of homogeneity of the magnetic field in samples representing a system of fibers regularly arranged in the matrix has been evaluated. The specific features of the distribution of the magnetic field and eddy currents caused by the presence of interfaces between unlike materials, magnetic properties, dimensions, and the mutual location of inclusions have been analyzed.
Keywords: fiber composite; skin layer; magnetic; conducting; eddy current; numerical calculations

The process of grain-boundary segregation (GBS) has been considered under an assumption that the formation of associates (atomic complexes with a composition that corresponds to the nearest chemical composition in the phase diagram) is possible in a grain boundary (GB). The grain boundary is considered as a two-component mixture of A and B atoms, which can exist both in free and bound states (bound in a complex). The formation of complexes with an arbitrary composition and complexes of an AB type have been considered. It has been shown that, even in the absence of segregation (b = 1), the interactions of atoms in a GB that induce the formation of complexes leads to an enrichment of GBs in impurity atoms. It has been demonstrated that under certain conditions, a GBS isotherm can exhibit saturation corresponding to the chemical composition of the complex.
Keywords: grain-boundary segregation; grain-boundary segregation isotherm; atomic complexes

The values of the thermodynamic parameters of second-order interaction in dilute binary substitutional solid solutions have been estimated for twenty seven systems on the basis of experimental thermodynamic data. The possibilities are outlined of using these data for checking the results of the first-principles calculations of the electronic theory of alloys. It has been established that for the majority of the systems examined the sign of the parameter of second-order interaction is opposite to that of the Wagner parameter of interaction. For the solid solutions of molybdenum in chromium at a temperature of 1471 K the values of the thermodynamic parameter of the second-order interaction and first-order enthalpy parameter are connected with the value of the Wagner parameter of interaction via formulas, which correspond to the model in which three-particle interaction is absent and the radius of pairwise interaction corresponds to the nearest coordination shell. The potential of pairwise interaction is temperature-independent. For the solid solutions of platinum in cobalt at a temperature of 1273 K, the value of the Wagner parameter of interaction calculated in the approximation of an Ising Hamiltonian with the use of effective pairwise interactions evaluated in the literature by the methods of the electronic theory of alloys agree in sign and in order of magnitude with the experimental value.
Keywords: interaction parameters; enthalpy parameter; first-principles calculations; functional-density theory; generalized perturbation method; three-particle potential; coordination shell

To the theory of grain-boundary diffusion in nanostructured materials by A. G. Kesarev; V. V. Kondrat’ev; I. L. Lomaev (329-336).
Using an asymptotic method of solving diffusion equations and a Laplace transform, the theory of grain-boundary diffusion is extended to the case of a coefficient of bulk diffusion strongly changing near the structural boundaries of grains under the conditions of annealing corresponding to regime C in usual polycrystals. An analysis of the layer activity measured in the diffusion experiment was performed and, on the example of copper, its radical difference from the case of equilibrium boundaries was shown. Results of numerical calculations and qualitative estimates are presented, which make it possible to establish the field of the applicability of the approach suggested.
Keywords: nanostructured materials; diffusion; nonequilibrium boundaries

Effect of alloying with iron on the electronic properties adnd structure of the Cu3Pd alloy by N. I. Kourov; V. G. Pushin; L. N. Buinova; A. V. Korolev; M. A. Korotin; Yu. V. Knyazev; N. G. Gokhfel’d (337-346).
Variation of electrical and magnetic properties in atomically ordered Cu3Pd alloy as a result of a one-percent addition of iron atoms has been investigated. The rearrangement of the electronic structure upon transition from the binary Cu3Pd to a ternary alloy of composition Cu74.25Pd24.75Fe1 has been considered using energy-band calculations and measurements of optical properties. The characterization of the micro-structural state was carried out by the methods of transmission electron diffraction microscopy.
Keywords: electronic structure; optical properties; electrical and magnetic properties

In this work, we theoretically and experimentally established the common feature of the evolution of the efficiency of the electromagnetic generation of acoustic waves near the temperatures of second-order magnetic phase transitions characteristic of both the “order-disorder” (Curie point in isotropic ferromagnets) and “order-order” (easy-axis-angular-phase and angular-phase-easy-plane) transitions in uniaxial magnets, which consists in the fact that the peak of efficiency corresponds precisely to these temperatures at any values of the magnetic field even if in a magnetic field these temperatures cease to be the points of phase transitions.
Keywords: electromagnetoacoustic transformation; magnetic phase transitions

Kink effect upon the electromagnetic generation of ultrasound in isotropic ferromagnets by M. A. Borovkova; R. S. Il’yasov; N. V. Fedorova (354-357).
The influence of the shape anisotropy on the field dependences of double electromagnetic-acoustic conversion in samples of an Invar alloy 29NK in the high-temperature range below the Curie point is experementally studied. It is shown that at a constant temperature the value of the polarizing field in which a jumplike generation of ultrasound occurs is determined by the demagnetizing factor of the sample, and the observed anomaly of the electromagnetic-acoustic conversion is caused by the kink effect.
Keywords: electromagnetic-acoustic conversion; shape anisotropy; kink effect

The structure and magnetic properties of the PrNi5 − x Cu x alloys have been studied in a composition range of 2.5 ≤ x ≤ 5. Single-phase solid solutions with a hexagonal structure of the CaCu5 type have been shown to be realized within this composition range. It has been found that upon the introduction of nickel into the Van Vleck paramagnet PrCu5 the ground state of the alloys with x ≤ 4.3 becomes ferromagnetic. All the compositions under study exhibit high magnetocrystalline anisotropy of the “easy-basal-plane” type. With allowance for the literature data available, a complete magnetic phase diagram of the PrNi5 − x Cu x system was constructed; it is characterized by two maxima in the compositional dependence of the Curie temperature. The earlier suggested model of the effect of local random crystal fields on the magnetic state of Pr3+ ions in alloys with low copper contents was shown to be applicable also for the explanation of magnetic properties of alloys with low nickel contents. The results of this study confirm the hypothesis about the determining role of local irregular crystal fields in the formation of the magnetic properties of the pseudobinary PrNi5 − x Cu x intermetallic compounds.
Keywords: paramagnetism; ferromagnetism; crystal field

A study by the method of thermal-desorption spectroscopy has revealed an effective diffusion of Sm atoms into Ir(111), which is stimulated by a graphite monolayer on the iridium surface. It is shown that the diffusion efficiency is greater by a factor of ∼106–107 in the presence of a graphite monolayer on iridium than in the absence of this layer. The energy of activation for the diffusion of Sm atoms into and from iridium has been found to be E = 5.5 eV and E = 6.3 eV, respectively. Iridium strips with a samarium-saturated nearsurface layer can be used as efficient sources of Sm ions (or Sm atoms), with the flux density varying in the range of 4 × 109 cm−2 s−1 〈 ν 〈 3 × 1011 cm−2 s−1 as the temperature of the strip varied from 1830 to 2110 K. If the temperature of the strip remains unchanged, the flux of Sm is maintained constant for many hours. After contact with the ambient atmosphere and evacuation of air, the samarium-saturated iridium strip is still serviceable as a source of samarium.
Keywords: emission; surface ionization; monolayer; diffusion

Grain refinement in small-size ingots of intermetallic alloys Ti-46Al-8Nb and Ti-46Al-8Ta with the use of a massive transformation by V. M. Imayev; T. I. Oleneva; T. G. Khismatullin; R. M. Imayev; R. Valiev; H. -J. Fecht (369-375).
An estimation of the efficiency of the refinement of colonies/grains of the as-cast structure of ingots of size Ø13 × 150 mm in the Ti-46Al-8Nb and Ti-46Al-8Ta (at %) alloys with the aid of a heat treatment including massive transformation has been performed. It is shown that the initial coarse-grained as-cast structure of these alloys can be refined using massive transformation without the use of a labor-consuming procedure of hot working. The method proposed is efficient for the alloys containing alloying elements that retard diffusion in the alloys, which makes it possible to obtain massive γ m phase at moderate cooling rates. It is shown by X-ray diffraction that the massive γ m phase is characterized by a reduced parameter of tetragonality, which can be restored via subsequent high-temperature aging.
Keywords: gamma titanium aluminides; grain refinement; massive transformation

Influence of the temperature and rate of generation of point defects on the processes of deformation-induced segregation in the Fe-Cr-Ni alloy by S. A. Starikov; A. R. Kuznetsov; V. V. Sagaradze; V. A. Pechenkin; I. A. Stepanov (376-382).
The process of nickel segregation at grain boundaries in the Fe-Cr-Ni alloy upon severe plastic deformation has been investigated depending on the temperature. The kinetics of the formation of segregates has been studied by numerically solving diffusion equations that take into account the generation and absorption of point defects and their mutual recombination. It has been shown that the Ni concentration at grain boundaries is reduced with increasing temperature and at T ≥ 600 K no segregates are formed, which agrees with the experiment. The dependence of the degree of Ni segregation on the rate of generation of point defects is nonmonotonic, with a maximum in the range of medium rates of generation, which qualitatively corresponds to the analogous dependence observed upon radiation-induced segregation of nickel in this alloy.
Keywords: deformation; Fe-Cr-Ni alloy; grain boundaries; segregation

X-ray diffraction and electron microscopy have been used to investigate structural states of the material of compacts and sheets of an aluminum-copper-lithium alloy with a lithium content corresponding to the field of equilibrium of a solid solution with the phase T 1 (Al2CuLi). In pressed strips, there arises a multicomponent texture (Bs “110”〈112〉, Cu “211”〈111〉, S “123”〈hkl〉) typical of pressed articles of aluminum-lithium alloys. Their microstructure was characterized by the presence of slip bands oriented in the rolling direction. The formation of lamellar precipitates of the T 1 phase at slip-band boundaries in the process of deformation is supposedly stimulated by Shockley partial dislocations. In hot-rolled sheets, there arose an unusually intense nearly single-component texture of the Ex 1 “011”〈111〉 type, whose appearance is mainly caused by the cross rolling of the sheets. The reduced strength characteristics of the sheets examined are connected with a sharply oriented character of the structure of both the matrix phase and the strengthening T 1 phase. A quasicrystalline phase T 2 present in the material and the precipitates of the δ′ phase exert no marked effect on the level of mechanical properties.
Keywords: texture; microstructure; orientation-distribution function; electron microscopy; aluminum-lithium alloys

Transmission electron microscopy was used to investigate structural and phase transformations and defects of the icosahedral (ι) phase that is formed upon isothermal annealings (T ann = 550–700°C) of quenched quasicrystal-forming alloys Al61Cu26Fe13 and Al63Cu25Fe12 (β solid solution + ι phase). It has been established that in the Al63Cu25Fe12 alloy there occurs a reversible ι-R-approximant transformation, whereas in the Al61Cu26Fe13 alloy there is formed a single-phase ι structure with regions with a high density of randomly distributed planar defects (T ann = 550°C), which are partially annealed at 650°C. The observed defects are, mainly, ultrathin interlayers (“intergrowths” to 3–5 nm in thickness) on quasicrystal planes with A5ι axes with an imperfect decagonal structure. As the basic mechanism, the growth mechanism of the formation of defects during the β → i transformation is proposed. The role of the alloy composition and low-temperature β → 3C-phase transformation in the realization of this mechanism is discussed.
Keywords: quasicrystal-forming alloys; icosahedral phase; crystal ↔ quasicrystal transformation; β solid solution; defects; transmission electron microscopy

This work is devoted to the estimation of the technological plasticity of binary and alloyed γ titanium aluminides by conducting compression tests at T = 1000°C. The technological plasticity was shown to grow with decreasing size of grains and grain colonies and with increasing amount of β-stabilizing elements in the alloys. The best technological properties are characteristic of the alloys that solidify completely through the β phase, containing β-stabilizing additions of niobium and molybdenum and microadditions of boron. These alloys are characterized by a small size of crystallites in the cast state; the use of special heat treatments makes it possible to substantially decrease the fraction of the lamellar component and to increase the content of the β(B2) phase in them. For the most technological alloy, tensile tests in the cast state have been carried out. In the temperature range of T = 900–1100°C, superplastic elongations have been achieved.
Keywords: titanium aluminides; microstructure; mechanical properties; technological plasticity

Effect of isochronal annealing on the magnetic and mechanical properties of Ti-Al-Co and Ti-Al composites by F. Kh. Akopov; I. V. Chkhartishvili; M. V. Galustashvili; D. G. Driaev; V. M. Gabuniya; S. Dzh. Tsakadze (411-414).
Ti-Al and Ti-Al-Co metal composites have been produced by shock-wave compaction using hexogen and ammonite explosives. The microstructure, microhardness, and temperature spectra of the real part of the complex magnetic susceptibility χ′(T) have been studied. The measurements have been performed in the course of isochronal annealings of the samples at temperatures progressively increasing in steps of 50 K. The values of χ′, which correspond to the isothermal sections of the spectra at 140 K and 400 K, as a function of the isochronal annealing temperature, χ′(T), have the form of asymmetrical bell-shaped curves. The maxima of these curves are in the region of the temperature of the α → β polymorphic transformation of cobalt. Possible reasons for this behavior of χ′ have been discussed.
Keywords: metal composite; shock wave; magnetic susceptibility; isochronal annealing