Physics of Metals and Metallography (v.110, #1)

Magnetic properties of Ni3Al x Mn1 − x alloys by N. I. Kourov; S. Z. Nazarova; A. V. Korolev; Yu. A. Dorofeev; N. V. Volkova; E. V. Belozerov (1-4).
Paramagnetic susceptibility of alloys Ni3Al x Mn1 − x in the field of the transition between the ferromagnets described in the band theory (Ni3Al) and in the spin-localized (Ni3Mn) model of magnetic moments has been investigated. The concentration dependences of the paramagnetic Curie temperature, effective magnetic moment, and temperature-independent component of magnetic susceptibility have been determined.
Keywords: paramagnetic susceptibility; intermetallic compound; atomic ordering; itinerant-electron magnetism; spin-localized model

Heat release in magnetic nanoparticles in AC magnetic fields by V. A. Sharapova; M. A. Uimin; A. A. Mysik; A. E. Ermakov (5-12).
Using the method of gas-phase synthesis, nanocrystalline powders on the basis of iron oxides (defect magnetite Fe3O4), with an average size of 16, 21, 30, and 44 nm, and nanocomposites on the basis of iron and cobalt encapsulated into carbon, with an average size less than 10 nm have been prepared. The nano-particles placed into a buffer solution were subjected to the action of an ac (rotating and axial) magnetic field. The rotating field ensures higher values of heat release as compared to the axial field in media with a comparatively low viscosity. The greatest values of heat liberation in the axial field at frequencies to 100 kHz are observed for the iron-oxide particles with an average size on the order of 16 nm (up to 20 W/g). For the nano-composite on the basis of Fe@C and Co@C, the specific heat losses in rotating fields are greater than for the axial field (10 and 26 W/g, respectively).
Keywords: nanoparticle; iron oxide; carbon-containing nanocomposites; magnetic properties; axial field; rotating field; specific heat losses

Phase composition and magnetic properties of nanocrystalline SmFe11 − x Ga x C1.25 (2 ≤ x ≤ 5) alloys by A. G. Popov; D. I. Gorbunov; V. S. Gaviko; L. A. Stashkova; N. N. Shchegoleva; G. M. Makarova; A. S. Volegov (13-23).
As-cast and rapidly quenched alloys (RQAs) SmFe11 − x Ga x C1.25 (2 ≤ x ≤ 5) have been studied. The RQAs were prepared by melt spinning on a steel wheel rotating at a velocity V = 10−40 m/s. Fragments of the RQAs were annealed in a vacuum at T ann = 500−850°C. The as-cast alloys are multiphase; the maximum volume fraction in them corresponds to the Sm2(Fe, Ga)17C compound with a rhombohedral structure. The rapid quenching leads to the formation of the Sm(Fe, Ga)11C compound (1: 11) with a tetragonal BaCd11-type structure; the maximum volume fraction of the compound is reached in the alloy with x = 3 quenched to a wheel rotating at V = 30 m/s. The melt spinnins of the alloys with x = 2−4 at V = 40 m/s is accompanied by their substantial amorphization. During annealing, the amorphous phase crystallizes mainly with the formation of the 1: 11 phase. A nonequilibrium phase diagram of the alloys quenched at V = 40 m/s and annealed at T ann = 500−850°C has been constructed. The 1: 11 compound has a single-phase region near x = 3 at T ann ≥ 600°C. As the volume fraction of the 1:11 phase increases, the coercive force H c of nanocrystalline RQAs increases. The maximum coercive force is observed for the SmFe8Ga3C1.25 alloy quenched at V = 40m/s and subsequently annealed at 700°C; it is 0.8 and 12 kOe at 293 and 50 K, respectively. The high coercive force obtained indicates that the Sm(Fe, Ga)11C phase is magnetically uniaxial and has a high magnetic anisotropy energy. The magnetic anisotropy constant K 1 of the compound at T = 50 K was estimated to be 3.1 × 107 erg/cm3.
Keywords: Sm-Fe-Ga-C alloys; compound with a tetragonal BaCd11-type structure; phase composition; magnetic hysteretic properties; uniaxial magnetic anisotropy

The electron-microscopic examination of the CuAu alloy subjected to rapid quenching from temperatures below T C revealed in its structure the presence of a phase, whose structure is close (in terms of the lattice parameters) to the L10 structure, but is characterized by the presence of uncommon extra reflections in the electron diffraction patterns at distances 1/3〈201〉*, 1/5〈203〉*, 1/7〈304〉*, etc., in the coordinates of the L10 structure, and by the simultaneous presence of superlattice reflections of two types in their electron diffraction patterns. A crystallographic analysis showed that the extra reflections observed cannot correspond to the points of the reciprocal lattice of the long-period Z phase [4] or any other phase. The arrangement of these reflections is explained well by the punctures of the plane of diffraction by a set of [ $$ ar 1 $$ 01]* parallel streaks passing through fundamental and superlattice reflections. These streaks are parallel to the (101) plane and to the plates of the phase revealed.
Keywords: CuAu alloy; ordering; L10 structure; electron microscopy; diffraction methods; crystallographic analysis; crystal lattice

Effect of a glass shell on the crystallization of Fe- and Co-based amorphous microwires by G. E. Abrosimova; A. S. Aronin; N. N. Holstinina (36-41).
Crystallization of amorphous Fe73.9B13.2Si10.9C2 and Co73.6B11.2Si13C2 microwires in a glass isolation (shell) upon heating has been studied by X-ray diffraction. Crystallization of the core of an amorphous microwire starts at temperatures above 400°C. No noticeable effect of the glass shell on the crystallization of the Fe-based microwire was observed. The crystallization of the Co-based microwires with a glass shell begins at a lower temperature than the crystallization of those without a shell. There has been observed a difference in the effect of the glass shell on the crystallization of microwires of different chemical compositions.
Keywords: microwire; X-ray diffraction analysis; crystallization

Structure and critical currents of multiple-filament composite superconductors Bi,Pb-2223/Ag by T. P. Krinitsina; E. I. Kuznetsova; D. V. Surnin; Yu. V. Blinova; S. V. Sudarev; E. P. Romanov; D. N. Rakov; Yu. N. Belotelova (42-51).
X-ray diffraction, transmission electron microscopy, and scanning electron microscopy with microanalysis have been used to study filamentary superconducting composites Bi,Pb-2223/Ag with different values of the critical current (54 and 89 A), prepared by the same method. It is shown that the lowered values of the critical current are connected with decreasing diffusion flow of Ag atoms from the sheath into the ceramics and with a decrease in the oxygen content in the superconducting 2223 phase. This, in turn, is caused by a weakening of the diffusion contact between the Ag sheath and the ceramics. At the Ag-ceramics boundaries, small aggregates of carbon and, sometimes, oxygen atoms are revealed. For explaining the origin of these aggregates, the initial composites (without heat treatment) were investigated by the method of Auger spectroscopy. It has been found that in the composites which upon subsequent annealing exhibit bubbling (disturbance of the contact between the Ag sheath and the ceramics), there is present a noticeable quantity of bound oxygen (water vapors) with an admixture of carbon dioxide.
Keywords: HTSC composites; structure; superconductivity; bubbling of Ag sheath

A critical analysis of available thermodynamic data for the Fe-Nb-C, Fe-Nb-N, and Fe-Nb-C-N systems has been performed. Based on this analysis, self-consistent thermodynamic descriptions of these systems have been selected and refined using the CALPHAD method. With the use of the thermodynamic descriptions constructed, phase equilibria in these systems have been calculated. On the basis of these calculations, the solubility of carbides, nitrides, and carbonitrides in the Fe-Nb-C, Fe-Nb-N, and Fe-Nb-C-N systems has been analyzed and some laws governing the effect of composition and temperature on the phase composition of niobium-containing steels have been considered.
Keywords: thermodynamics; phase equilibria; solubility; niobium carbonitrides

Structure and microhardness of nanocrystalline composite alloys on the basis of Al and Ti by N. I. Noskova; R. V. Churbayev; N. F. Vil’danova; O. A. Elkina; L. A. Zemnukhova (62-69).
A nanotechnology for production of layered composite nanocrystalline Al-Si, Al(1Hf + 0.2Nb + 0.2Sn, wt %)-Si, Al(0.5Ce + 0.5Re + 0.1Zr, wt %)-Si, and Ti-Si alloys has been suggested. The structure of the nanocrystalline composites obtained has been studied by the methods of optical microscopy and scanning and transmission electron microscopy. Experimental data on the microhardness of layered composite nanocrystalline alloys on the basis of aluminum and titanium are given. The microhardness of the nanocrystalline two-layered Al-Si composite in comparison with submicrocrystalline aluminum increased by a factor of three. In the nanocrystalline two-layered Ti-Si composite (compacted from powders), the microhardness also increased by a factor of almost six in comparison with nanocrystalline titanium. In the nanocrystalline two-layered composite alloys of aluminum, the increase in microhardness in the case of the Al(Hf,Nb,Sn)-Si alloy was up to 45% as compared to the composite on the basis of the metallic foil and by a factor of two as compared to the powder-compact composite; and in the case of the Al(Ce, Re,Zr)-Si alloy, by a factor of 1.6 and 2.7, respectively. An increase in the number of layers in the composites had no significant effect on the level of microhardness.
Keywords: nanotechnology; nanocrystalline composites; structure; microhardness

Kinetic-simulation methods were used to investigate the mechanisms of deformation of ultrafine-grained copper produced by equal-channel angular pressing. The study was based on the modernized Estrin-Tóth dislocation model, which takes into account, besides the slip of dislocations, the possibility of their non-conservative motion, which is connected with the presence of a large quantity of vacancies in the materials subjected to severe plastic deformation. Furthermore, apart from an analysis of the evolution of the total dislocation density, the evolution of the forest dislocations in the walls of cells (grains) was taken into account, which made it possible to calculate the change in the misorientation angles between the adjacent cells (grains) in the course of plastic deformation. As the experimental data, the true tensile stress-strain curves of ultrafine-grained Cu obtained at temperatures of 77 and 298 K were used. To investigate the effect of grain size on the kinetics of plastic deformation at the above temperatures, analogous calculations were carried out for the case of coarse-grained Cu.
Keywords: kinetic simulation; mechanisms of deformation; severe plastic deformation; grain size; temperature; nonconservative movement of dislocations; concentration of deformation vacancies; misorientation angles

Orientation dependence of superelasticity in ferromagnetic single crystals Co49Ni21Ga30 by I. V. Kireeva; Yu. I. Chumlyakov; Z. V. Pobedennaya; I. V. Kretinina; E. Cesari; S. B. Kustov; C. Picornell; J. Pons; I. Karaman (78-90).
Dependence of the amount of reversible deformation on the orientation of the crystal axis and testing temperature has been studied using [001] and [ $$ ar 1 $$ 24] single crystals of the Co49Ni21Ga30 (at %) alloy upon compression. It has been shown that in the [001] crystals with TM s (M s is the temperature of the onset of the forward martensitic transformation upon cooling) the reversible deformation is equal to 5.5–6.5% and consists of the deformation connected with the shape-memory effect (SME) equal to 4–4.2%, and of “ferroelastic” deformation equal to 1.5–2.2%, which is reversible upon unloading. The total reversible deformation exceeds the lattice deformation ɛ0 observed upon the B2-L10 martensitic transformation, which is equal to 4.5%. At T > A f (A f is the finish temperature of the reverse martensitic transformation upon heating), the reversible deformation in [001] crystals is equal to 6.5%. It has been shown electron-microscopically that the reversible deformation equal to 1.5–2.2% in the temperatures range of T = 77−300 K is connected with the development of mechanical twinning in the L10 martensite on (110) L10 planes, which proves to be reversible in the [001] crystals and can be partly irreversible in the [ $$ ar 1 $$ 24] crystals. Upon heating, the (110) L10 twins of the stabilized L10 martensite pass into the ( $$ ar 1 $$ 12) B2 twins of the B2 phase.
Keywords: ferromagnetic single crystals; thermoelastic martensitic transformations; shape-memory effect; superelasticity; twinning

Wear resistance and structural transformations upon abrasive and adhesive wear of titanium nickelide Ti49.4Ni50.6 in microcrystalline (MC) and submicrocrystalline (SMC) states have been investigated. It has been shown that the abrasive wear resistance of this alloy exceeds that of the steel 12Kh18N9 by a factor of about 2, that of the steel 110G13 (Hadfield steel), by a factor of 1.3, and is close to that of the steel 95Kh18. Upon adhesive wear in a testing-temperature range from −50 to +300°C, the Ti49.4Ni50.6 alloy, as compared to the steel 12Kh18N9, is characterized by the wear rate that is tens of times smaller and by a reduced (1.5–2.0 times) friction coefficient. The enhanced wear resistance of the Ti49.4Ni50.6 alloy is due to the development of intense strain hardening in it and to a high fracture toughness, which is a consequence of effective relaxation of high contact stresses arising in the surface layer of the alloy. The SMC state produced in the alloy with the help of equal-channel angular pressing (ECAP) has no effect on the abrasive wear resistance of the alloy. The favorable effect of ECAP on the wear resistance of the Ti49.4Ni50.6 alloy takes place under conditions of its adhesive wear at temperatures from −25 to +70°C. The electron-microscopic investigation showed that under conditions of wear at negative and room temperatures in the surface layer (1–5 μm thick) of titanium nickelide there arises a mixed structure consisting of an amorphous phase and nanocrystals of supposedly austenite and martensite. Upon friction at 200–300°C, a nanocrystalline structure of the B2 phase arises near the alloy surface, which, as is the case with the amorphous-nanocrystalline structure, is characterized by significant effective strength and wear resistance.
Keywords: alloy Ti49.4Ni50.6; structural transformations upon wear; strain hardening; toughness; tribological properties

Method of in situ measuring surface tension of a solid-gas interface by E. I. Gershman; S. N. Zhevnenko (102-107).
A method of in situ measuring surface tension of a solid-gas interface is described theoretically and is realized experimentally. The method is based on the Udin technique, which reduces to the determination of the load of zero creep, i.e., the load on a sample at which no deformation of the sample occurs at a high temperature. It is assumed that the load of zero creep balances the force of surface tension. This load is found by a linear interpolation of the strain-rate dependence on the load to the zero strain. A method is described which makes it possible to directly find the load of zero creep in the process of experiment, i.e., an “in situ” method. An installation was designed and preliminary experiments were performed, which show the correctness of the theoretical calculations and the experimental procedure. The experiments were carried out in a hydrogen atmosphere at 960°C. The possibility is shown of finding the load of zero creep by the method of the straightening of the experimental strain-rate dependence on stress in the process of the experiments carried out in the work.
Keywords: surface tension; method of zero creep; solid-gas interface