Physics of Metals and Metallography (v.115, #6)

Interaction of surface of ribbons of amorphous soft-magnetic iron-based alloys with vapor by N. A. Skulkina; O. A. Ivanov; I. O. Pavlova; O. A. Minina (529-537).
The interaction with water vapor of the surface of ribbons of amorphous soft-magnetic iron-based alloys with positive saturation magnetostriction and an effect of the interaction on the magnetization distribution and magnetic properties have been investigated. The results of the investigation showed that, during in-air heat treatment, the interaction of the surface of ribbons of amorphous soft-magnetic alloys with water vapor upon the heating of samples and at the initial stage of isothermal holding exerts a substantial effect on the magnetization distribution and the level of magnetic properties formed. Preliminary room-temperature treatment of the ribbon surface in the as-quenched state with water vapor favors an increase in pseudo-uniaxial tensile stresses along the ribbon axis because, during annealing, the enhanced concentration of hydrogen and oxygen atoms introduced into the ribbon surface is formed in this direction. When certain regimes of heat treatment are used, this leads to an increase in the volume of domains with magnetization oriented along the axis of the ribbon in its plane and allows a significant enhancement in the efficiency of the in-air heat treatment.
Keywords: magnetic permeability; magnetization; amorphous soft-magnetic alloys; heat treatment; cooling rate; isothermal-holding temperature

Structure and stability of superconducting core of single-core MgB2/Cu,Nb tube composite with a high critical current by T. P. Krinitsina; E. I. Kuznetsova; Yu. V. Blinova; D. N. Rakov; Yu. N. Belotelova; S. V. Sudareva; M. V. Degtyarev; E. P. Romanov (538-546).
The core of a single-core MgB2/Cu,Nb composite, which has been prepared by the ex-situ technique and exhibits a high critical current equal to 427 A (at 0 T and 4.2 K, j c ≥ 105 A/cm2), has been studied using various structural methods. Two kinds of MgB2 crystals were observed; those of the first kind is large, highly dense crystals characterized by a low oxygen content (2–8 at %) and the others are fine, weakly coupled crystallites characterized by high oxygen content (4–21 at %). To perform a comparative analysis of the structures, we have also studied an MgB2 bulk sample synthesized at 1000°C. It was found that two phases with the same lattice are formed; they differ in the magnesium and boron contents (within the homogeneity range), impurity oxygen content and microstructure as well but differ slightly in the lattice parameters. The two-phase state of MgB2 bulk sample is due to the mechanism of its formation, which includes the melting of magnesium, the dissolution of solid boron in it, and the crystallization of MgB2 from the melt with the formation of dendrite-like structure characterized by corresponding redistribution of components and impurities. To a certain degree, the two-phase structure of MgB2 bulk sample is inherited by the MgB2/Cu,Nd composite prepared by ex-situ technique (annealing of composite at 700°C). It was shown that oxygen in the MgB2 compound is the destabilizing factor and leads to the transformation of the superconductor into MgO.
Keywords: composites; microstructure; superconductors

Interaction of perovskite-like compounds based on transition-metal oxides with gas phase at T = 200–400°C by N. A. Zyuzeva; I. B. Bobylev; S. V. Naumov; E. P. Romanov (547-556).
The effect of the chemical composition of some perovskite-like cuprates, manganites, and cobaltite on their reactivity for oxygen and water vapor that are present in the annealing atmosphere, at 200–400°C has been studied. The partial substitution and alloying of LnBa2Cu3O y compounds lead to the increase in their stability with respect to aggressive components of gas phase (H2O, CO2). It was found that only compounds with structures characterized by several kinds of oxygen vacancies can absorb oxygen and water from the annealing atmosphere.
Keywords: perovskites; ceramics; heat treatment; effect of water; structure; electrophysical properties

Dynamic equilibria of phases in the processes of the mechanosynthesis of an alloy with composition Fe72.6C24.5O1.1N1.8 by V. A. Volkov; I. A. El’kin; A. V. Zagainov; A. V. Protasov; E. P. Elsukov (557-565).
X-ray diffraction, Mössbauer spectroscopy, and measurements of the dynamic magnetic susceptibility have been used to investigate phase states of the Fe72.6C24.5O1.1N1.8 alloy at different stages of the mechanosynthesis (MS) in a planetary ball mill. The introduction of impurities of O and N into an Fe75C25-based alloy changes the sequence of the formation of phases during MS: instead of Fe3C, the Fe7C3 carbide is first to be formed. The processes of phase formation in the alloy preliminarily subjected to MS have unidirectional nature upon the continuation of the MS and upon annealings and are determined by the interaction of the alloy components with one another under the effect of the accumulated excess energy. The phase compositions of the MS alloys depend on the conditions of the dynamic equilibrium between the crystalline and amorphous phases.
Keywords: phase transformations; mechanical alloying; amorphous alloys; structure; metallic alloys; carbides

Small-angle neutron scattering investigation of the substructure of nickel irradiated with fast neutrons by S. G. Bogdanov; B. N. Goshchitskii; V. D. Parkhomenko (566-569).
The method of small-angle neutron scattering has been used to investigate the samples of pure nickel before and after irradiation with fast neutron fluences of Φ = 1018, 1019, and 1020 cm−2 (E n ≥ 0.1 MeV). It has been found that the substructure of the samples consists of vacancy clusters with two characteristic sizes of 2.5–4 and ∼7 nm. The sizes of precipitates weakly depend on fast neutron fluence. The magnitude of their density is on the order of 1022 and 1019 m−3, respectively, and increases by three to ten times as the fluence grows.
Keywords: small-angle scattering; vacancy clusters; fast-neutron irradiation

This work discloses the evolution of a two-dimensional nanocrystalline aggregate in the process of shear deformation under the conditions of hydrostatic compression of the material in the deformation-temperature range T = 0.5–0.7T m. It has been shown that grain growth by the mechanism of mutual rotation with subsequent coalescence is characteristic of deformation temperatures T = 0.6T m and below, whereas at T = 0.65 and 0.7T m one of grains with predominant orientation grows at the expense of other grains. In all instances, the growth of the degree of shear deformation leads to the disappearance of all grain boundaries in the calculated cell under consideration.
Keywords: severe plastic deformation; nanomaterial; polycrystal; grain growth; molecular dynamics; deformation temperature

Temperature investigations of mechanosynthesized cementite by V. A. Barinov; V. A. Kazantsev; V. T. Surikov (576-585).
Methods of differential thermal analysis and Mössbauer spectroscopy (57Fe) have been used to study the process of the formation of cementite in α-Fe upon the low-temperature mechanosynthesis (T < 375 K) in the medium of liquid hydrocarbons. It has been established that this process occurs in the absence of austenite and corresponds to a two-stage model suggested previously for describing the mechanism of the decomposition of the quench martensite α″-(Fe)C with the precipitation of the θ phase in the process of aging or tempering. Upon dilatometric studies of the single-phase samples of cementite in the range of 750 ≤ T ≤ 925 K, a significant increase was revealed in the linear elongation Δl/l 0 and linear thermal expansion coefficient (LTEC). It has been assumed that this increase is not connected with the localization of carbon atoms in the positions C(4a) and C(4b), but rather is determined by the anomalously high concentration of equilibrium carbon vacancies V C in the unit cell of cementite. The concentration of this type of vacancies can be sufficient for the growth of a graphite component of the carbon layer on the surface of the particles of the mechanosynthesized cementite (θ phase).
Keywords: iron carbides; mechanosynthesis; phase transition, Curie temperature, Mössbauer studies; differential thermal analysis (DTA), dilatometry of cementite compacts

Acoustic detection of stress-corrosion cracking of nitrogen austenitic steels by Yu. I. Filippov; V. V. Sagaradze; V. A. Zavalishin; N. L. Pecherkina; N. V. Kataeva; S. Yu. Mushnikova; S. K. Kostin; G. Yu. Kalinin (586-599).
Structural changes and resistance to the stress-corrosion cracking of the nitrogen-bearing austenitic steels 04Kh20N6G11M2AFB and 09Kh20N6G11M2AFB (with 0.04 and 0.09 wt % C, respectively) after different treatments, including thermomechanical action, quenching from 1200°C, and aging at 700°C for 2 and 10 h, have been studied. It has been shown that aging at 700°C of the air-melted austenitic steel 09Kh20N6G11M2AFB leads to a decrease in the strength of samples with an induced crack upon the cantilever bending in air and in a 3.5% aqueous solution of NaCl as compared to the strength of the steel 04Kh20N6G11M2AFB-EShP with a smaller carbon content after high-temperature mechanical treatment or quenching from 1200°C. The smallest resistance to stress-corrosion cracking is observed in the samples of 09Kh20N6G11M2AFB steel after 10 h of aging, which is accompanied by the most intense acoustic emission and by brittle intergranular fracture. This is explained by the high rate of the anodic dissolution of the metal near chromium-depleted grain boundaries due to the formation of continuous chains of grain-boundary chromium-containing precipitates of carbides and nitrides.
Keywords: corrosion cracking; nitrogen-bearing austenitic steel; electron microscopy; acoustic emission

The criteria for the optimization of chemical composition of Ti-Zr-Nb alloys have been selected that allow for obtaining materials with low elastic moduli and which have been used to melt alloys 50Ti-(50 − x) Zr-xNb, at 15 < x < 20 at %. Transmission electron microscopy and X-ray diffraction analysis have been used to study the phase composition of the as-cast alloys and alloys after homogenizing annealing. The minimum elastic modulus (69 GPa) and minimum microhardness (2440 MPa) have been found in the almost single-β-phase alloy with a maximum niobium content (17.1 at %). An increase in the volume fraction of α″ phase in the alloys with a lower niobium content (to 15 at %) promotes the growth of values of these properties. The phase transformations that occur during the continuous heating of homogenized alloys have been studied. The dependence of the temperature of the polymorphic (α + β)-β transformation on the ratio of the alloying elements in the studied alloys have been shown.
Keywords: low-modulus alloys; Ti-Zr-Nb alloys; structure; phase composition; properties

Effect of reverse bending on texture, structure, and mechanical properties of sheets of magnesium alloys with zinc and zirconium by N. M. Shkatulyak; V. V. Usov; N. A. Volchok; A. A. Bryukhanov; S. V. San’kova; M. Rodman; M. Shaper; C. Klose (609-616).
Effect of low-cycle room-temperature reverse bending on the crystallographic texture, metallo-graphic structure, and mechanical properties of sheets of ZE10 magnesium alloy after hot rolling and annealing has been studied. The initial texture is characterized by a wide scatter of basal poles in the transverse direction. In the process of reverse bending, the changes in the initial texture and structure (which is represented by equiaxed grains containing twins) lead to regular changes in the anisotropy of mechanical properties.
Keywords: ZE10 magnesium alloy; hot rolling; reverse bending; structure; texture; twins; anisotropy; mechanical properties

The effect of the initial microstructure of low-alloy tube steel 13KhFA on its mechanical properties after quenching from the intercritical temperature range (ICR) has been studied. It has been established that the maximum impact toughness KCV-80 is achieved in the case of the initial quenched structure, and the lowest values correspond to the initial annealing. The dependences of the KCV-80 on the temperature of the second quenching for these initial states are fundamentally different as well.
Keywords: structure; low-carbon steel; bainite; martensite; intercritical range; quenching; impact toughness; embrittlement

The microstructure of samples of cladding tubes made of steel 0.07C-16Cr-19Ni-2Mo-2Mn-Ti-Si-V-P-B (EK164) irradiated to different damaging doses (up to 77 dpa) in the BN-600 reactor at temperatures from 440 to 600°C has been investigated. Characteristics of radiation porosity formed during irradiation in different temperature intervals have been determined. The dependences of the porosity characteristics on the rate of generation of atomic displacements and temperature of neutron irradiation have been established.
Keywords: austenitic steel; neutron irradiation; rate of generation of atomic displacements; swelling; porosity characteristics