Physics of Metals and Metallography (v.119, #10)

Effect of Selective Thermomagnetic Treatment on Unidirectional Magnetic Anisotropy in FeNi/TbCo Films by K. G. Balymov; N. A. Kulesh; A. S. Bolyachkin; A. P. Turygin; V. O. Vas’kovskiy; O. A. Adanakova; E. V. Kudyukov (923-926).
The effect of selective thermomagnetic treatment on the exchange interaction between magnetic layers in Fe11Ni89/Tb30Co70/Ti films has been investigated. Dependencies of the exchange bias field induced in the Fe11Ni89 layer on the annealing temperature have been obtained and interpreted. We consider structural modifications of the interface and stress-relaxation processes in the Fe11Ni89 layer to be the main reasons for the observed modifications of hysteresis properties.

In the current work, a diffusion model was suggested to estimate the boron activation energies for FeB and Fe2B layers on the gas-borided Armco iron at temperatures of 1073, 1173, and 1273 K for a treatment time varying between 1.33 and 4 h. This model takes into account the effect of boride incubation times during the formation of the FeB and Fe2B phases. The mass balance equations were reformulated to describe the evolution of boride layers after applying the diffusion annealing process. In addition, the time needed to completely dissolve the FeB phase in the boride layer was also predicted. This predicted time was influenced by the boriding parameters during the diffusion annealing process.
Keywords: borides; growth kinetics; diffusion model; incubation times; annealing diffusion process

Thermoelastic Martensite Transformations and the Properties of Ultrafine-Grained Ni54Mn20Fe1Ga25 Alloys Obtained by Melt Quenching by E. B. Marchenkova; V. G. Pushin; V. A. Kazantsev; A. V. Korolev; N. I. Kourov; A. V. Pushin (936-945).
Studies of structural and phase transformations in the cast and melt-quenched ferromagnetic four-component alloy Ni54Mn20Fe1Ga25 were performed using transmission and scanning electron microscopy and X-ray diffraction, The obtained data have been compared with the results of studies of physical characteristics (electrical resistance, thermopower, magnetic susceptibility, magnetization, and temperature coefficients of linear expansion and relative elongation ΔL/L measured by the method of dilatometry) in the temperature range of 2–870 K. This work has established the effects of quenching on the microstructure, magnetic state, critical temperatures, and specific features of thermoelastic martensitic transformations in the alloy.
Keywords: structure; martensitic transformations; physical properties; reversible deformation; quenching from the melt; fine-grained state

Structure and Properties of Cu/Mg Composites Produced by Hydrostatic Extrusion by A. Yu. Volkov; A. A. Kalonov; D. A. Komkova; A. V. Glukhov (946-955).
Two Cu/Mg-composite rods of different content of components were produced by hydrostatic extrusion. The volume proportion of the copper sheath and magnesium core was almost equal in one of the two composite samples. Seven thin magnesium fibers were located in the copper matrix of another composite. Estimate calculations of the strength properties and electrical resistance of deformed composites were carried out and compared with the experimental results. The influence of anneals on the microstructure and electrical and mechanical properties of composites was also studied. This work has shown that a temperature rise causes sequential formation of the intermetallic compounds CuMg2 and Cu2Mg at the Cu/Mg interface, which, according to the phase diagram, results in eutectic reactions. The results of this work can be used in the development of high-strength composite conductors.
Keywords: metallic composites, copper; magnesium alloys, eutectic decomposition, mechanical properties, resistometry

Structural Aspect of Isothermal Bainitic Transformation in High-Carbon Manganese–Silicon Steel by I. L. Yakovleva; N. A. Tereshchenko; D. A. Mirzaev; I. V. Buldashev (956-961).
Transmission and scanning electron microscopy and X-ray diffraction analysis were used to compare the structural states of high-carbon manganese–silicon steel which underwent low-temperature isothermal bainitic and martensitic transformations. It was shown that bainite consisting of thin α-phase plates and residual austenite interlayers forms during isothermal holding at 300°С. As the isothermal holding time increases, fine carbide particles precipitate within the bainite α-phase.
Keywords: high-carbon manganese–silicon steel; low-temperature bainitic transformation; structure; martensite; bainite; residual austenite; fine carbide particles

X-ray diffraction analysis was used to study the martensite structure of the Ni47Mn42In11 alloy. This study shows that the martensitic transformation in the alloy occurs with the formation of modulated martensite. Using a new cell prototype, this work determined the parameters of basic cell of the modulated martensite structure and the modulation direction and lattice-modulation period. Orientation relationships between the high-temperature austenite and martensite structures were also determined. A comparative analysis of the new and previous results was performed. The new basic cell indicates the martensite crystal symmetry.
Keywords: martensitic transformation; orientation relationships; lattice distortion; prototype; basic cell; modulated structure; modulation period

Annealing of the submicrocrystalline (SMC) structure of niobium obtained by high pressure torsion to e = 7 at the temperature of liquid nitrogen was carried out. The influence of the annealing temperature in the range of 100–1100°C on the recrystallization of the SMC structure and the formation of texture was investigated. This paper discusses the role of static recovery and thermoactivated formation of recrystallization nuclei. The submicrograined recrystallized structure characterized by an average grain size of 0.8 μm, by a high homogeneity, and by the lack of the texture has been obtained. The sharpest recrystallization texture is formed as a result of annealing at 900°C; the average grain size is 10 μm in this case.
Keywords: niobium; cryogenic deformation; submicrocrystalline structure; recrystallization; texture; grain boundaries; EBSD analysis

In the present study, the Chou’s general solution model (GSM) has been used to predict the excess Gibbs enthalpy of the liquid Co–Sb–Sn ternary alloys with three selected sections x Sb/x Sn = 1/3, x Co/x Sb = 1/5, and x Co/x Sn = 1/4, of Ag10–In80–Pd–Sn10, Ag20–In60–Pd–Sn20, and Ag–In40–Pd20–Sn40 quaternary alloys and the excess Gibbs energy of Ni–Cr–Co–Al–Mo–Ti–Cu with seven component alloys with selected sections, namely, x Ni = x Cu, x Cr = x Ti, x Co = x Ti, x Al = x Ti, x Mo = rx Ti, x Ti = (1 – x Cu)/(r + 5), and r = 0.1 at temperatures 1273, 1173, and 2000 K, respectively. However, any information in the literature regarding the application of GSM to the alloys mentioned above could not be found, the other geometric models such as Kohler, Muggianu, and Toop are also included in present calculations. Using standard deviation formula, it is seen that some reasonable agreements exist between the results of the geometric models and those of related experiments.
Keywords: the excess Gibbs enthalpy of mixing; the excess Gibbs energy of mixing; multicomponent alloys; Geometric models; Redlich–Kister parameters

Simulation of the Effect of Ultrasound on the Dislocation Structure of Deformed Polycrystals by R. T. Murzaev; D. V. Bachurin; A. A. Nazarov (993-1003).
Computer simulation was used to study the relaxation of disordered systems of dislocations in the stress field of nonequilibrium grain boundaries upon ultrasonic treatment (UST). The effect of ultrasound is simulated by an oscillatory shear stress applied to the crystal. Edge dislocations in a model grain with three nonparallel slip systems located at an angle of 60° to each other were examined. The nonequilibrium state of grain boundaries is simulated with the aid of a quadrupole of wedge disclinations located at its junctions. This study showed that the UST caused a rearrangement of the dislocation structure and led to a reduction of internal stresses. The amplitude of ultrasound and the degree of the nonequilibrium state of grain boundaries (strength of the disclination quadrupole) significantly affect the relaxation of the dislocation structure. There are optimum values of the UST amplitude, at which a maximum reduction of the internal stresses is achieved. This study also investigated the dependence of the degree of relaxation of internal stresses on the amount of dislocations in the grain.
Keywords: discrete dislocation simulation; disordered dislocation structures; nonequilibrium grain boundaries; disclination quadrupole; ultrasonic treatment

The Strength and Fracture Mechanism of Unalloyed Medium-Carbon Steel with Ultrafine-Grained Structure under Single Loads by G. V. Klevtsov; R. Z. Valiev; N. A. Klevtsova; I. N. Pigaleva; E. D. Merson; M. L. Linderov; A. V. Ganeev (1004-1012).
This work is devoted to the study of the tensile strength, static crack resistance (К 1С ), and impact toughness of unalloyed medium-carbon (0.45% C) steel with ultrafine-grained (UFG) structure obtained by equal-channel angular pressing (ECAP) in comparison with coarse-grained (CG) steel after quenching and high tempering. The ECAP was carried out in the following regime: austenitization for 1 hour at 800°C + quenching in water + medium tempering (350°C) + ECAP at 350°C (Bc route, n = 6, φ = 120°). Our work shows that the K 1С of steel in the UFG state is 53 MPa m1/2 and, in the CG state, 69 MPa m1/2. The static failure of steel samples in the CG- and UFG states occurred under conditions of planar deformation. The relation between the depth of the plastic zone below the surface of the fractures in the region of crack propagation and the static crack resistance of steel in the CG- and UFG states is described by the equations h y = 1/12π(K 1C 0.2)2 and h y = 1/8π(K 1C 0.2)2. After ECAP, a narrowing of the ductile–brittle transition interval of steel and its shift towards low temperatures by 70–80°C can be observed. Moreover, the temperature dependence of the size of the shear lips at the surface of the fractures correlates with the temperature dependence of the impact toughness of the steel. The dominant fracture mechanism of CG steel in the lower and middle regions of the ductile–brittle transition is a cleavage, and that of UFG steels, a quasi-cleavage. In the upper region of the ductile–brittle transition, the steel under study fractures with the formation of a pit microrelief.
Keywords: steel; ultrafine-grained structure; coarse-grained structure; equal-channel angular pressing; strength; fracture mechanism; static crack resistance; impact toughness; depth of plastic zone under the fracture surface; planar deformation

This paper presents the results of our study of the contact endurance of laser-clad chromium–nickel coatings of the NiCrBSi system with different contents of chromium, boron, and carbon (PG-SR2, containing 0.48% C, 14.8% Cr, 2.1% B wt %; and PG-10N-01, containing 0.92% C, 18.2% Cr, 3.3% B wt %) and with additions of carbides of titanium TiC (15 and 25 wt %) and chromium Cr3C2 (15 wt %) upon contact fatigue loading according to the scheme of the pulsing non-impact “sphere-to-surface” contact. It has been established that the contact endurance of chromium–nickel coatings with different chemical compositions and different dispersity of structure is determined by their ability to resist plastic deformation under the conditions of repeated elastic–plastic deformation upon the mechanical non-impact contact action. This study has shown that composite coatings can be created, which contain large (50–150 μm) particles of the strengthening phases, whose contact endurance will not be substantially inferior to the contact endurance of coatings with fine (1–10 μm) strengthening phases. An estimation of the ability of the surface of the coatings to resist the mechanical contact action was made with the use of the data on microindentation. It has been shown that the method of microindentation (single loading) can be used for determining the ability of chromium–nickel coatings to withstand repeated contact loadings.
Keywords: laser cladding; chromium–nickel coatings; structure; phase composition; microindentation; contact fatigue

X-ray diffraction analysis, optical metallography examination, and microhardness measurements were used to investigate a copper single crystal sphere 34 mm in diameter after loading by spherically converging shock waves. It has been established that the deformation structure formed after shock loading depends on both the direction of shock wave propagation in the initial single crystal and the depth of the layer location in the sphere. This study found that high-rate plastic deformation of the copper single crystal under the studied loading conditions occurs mainly by slipping. In addition, “noncrystallographic” slip bands and localized deformation bands were observed in middle and deep layers. Shear bands were shown to nucleate both on the loading surface and inside the single crystal during shock wave propagation. No adiabatic shear bands were observed.
Keywords: shock waves; high-rate plastic deformation; copper; single crystal; structure