Thermal effects of transformations B2 ⇄ Al in CuPd alloy

We used high-temperature x-ray diffraction and thermography to investigate phase transitions B2 ⇄ Al in alloys Cu-Pd around 40 at. % Pd concentration. In phase transition region B2 → Al in alloy Cu-39.5 at. % Pd, we observed the maxima in the heat capacity curve. Based on structural data, we show that the first maximum is due to structural transition bcc-fcc (B2-Al) and the second is due to a decrease in the atomic long-range order in superlattice B2 and to a continuing bcc-fcc transition. Using structural information, we analyzed the thermograph of the quenched alloy Cu-36 at. % Pd. Structural Engineering Institute, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 35–38, February, 1993.     

Effect of plastic deformation on phase transitions in a Ti50Ni47Fe3 alloy

The results of x-ray structural studies of the effect of previous plastic deformation by rolling on the occurrence of phase transitions in a TiNi(Fe) alloy are presented in the present work. The temperature dependences of the Bragg reflection intensities and half-widths and the dependence of the rhombic angle in the R phase with various degrees of deformation were obtained. Analysis of the results found gave the following rules. Plastic deformation substantially shifts the characteristic temperatures of the martensitic transitions (MT) R-B19′ and B19′-B19″, increases the temperature range of the transformation and can result in a “stepwise” transformation. It was observed that deformation weakly affects the temperature T_R for the B2-R transformation. Tomsk State Architecture and Construction Academy. V. D. Kuznetsov Siberian Physicotechical Institute at Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 11–20, July, 1996.     

Distortion deformations in the B2-R phase transition in titanium nickel alloys

Based on x-ray analysis, we have calculated the lattice distortions in Ti-Ni-Me (Me=Rh, Co, Fe) alloys during the B2-R phase transition. We find that, during the transition, the deformation decreases as the concentration of the alloying component increases in Ti-Ni-Rh and Ti-Ni-Co. No such correlation is observed in the Ti-Ni-Fe alloys. Tomsk State Architecture-Construction Academy. V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 95–100, February, 1997.     

Computer simulation of deformation of two-component compacts under liquid-phase sintering

A model is proposed for predicting the deformation of two-component compacts under diffusion accompanied by phase transformations. The model is based on the movable cellular automata method. Dilatancy effects of a Cu−Al powder mixture under liquid phase sintering are described by means of computer simulations. Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 69–74, March, 1999.     

Structural changes in TiC-TiNi alloys on deformation

The deformation of a composition material with a binding phase of shearing-unstable alloy, namely, titanium nickelide, is considered. X-ray structural analysis and electron—positron annihilation methods are used to investigate the structural changes in the composite material as a function of the degree of deformation. It is shown that the deformation produces the structural phase transition B2 B19, which is confirmed by x-ray structural investigations and electron positron annihilation.Institute of Strength Physics and Materials Science, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Uchebnykh Zavednii, Fizika, No. 4, pp. 100–103, April, 1994.     

Formation of a transition layer during heteroepitaxy of III–V compound semiconductors in gas-phase epitaxy systems

It is known that during gas-phase epitaxy of InP and GaAs the region of the film close to the heteroboundary is formed with altered phase, structural, and electrophysical properties. The main cause for this is formation of a transition layer due to a change in the growth mechanism (transition from nucleational to layer-step growth) and the structure of the growing surface (height and density of growth steps). Tomsk State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 42, No. 1, pp. 18–21, January, 1999.     

Influence of nonhydrostatic stresses on the development of martensitic transformations and inelastic strains at various levels in Ti(Ni-Cu-Fe) polycrystalline intermetallic compounds

The levels of inelastic martensitic strain of polycrystals during a thermoelastic martensitic transformation under a load are discussed. The example ofTi(Ni-Cu-Fe) alloys with the B2 structure was used to study the role of microlevel and mesolevels in inelastic martensitic deformation during cooling of polycrystals under a load and loads in different initial structural states. V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk State University. Institute of Physics of Strength of Materials and Materials Science, Siberian Branch of the Academy of Sciences of the USSR, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, p. 35–46, January, 1998.     

Thermodynamic parameters of diffuse phase transitions in Ag2Te

A differential thermal analysis in vacuum and studies of the coefficients of electrical conductivity and thermal conductivity, and of the thermal emf are made in Ag₂Te in the neighborhood of the structural phase transition. It is shown that these data can be used to calculate the switching factor L(T), determine the region in which the phases coexist within the transition, and calculate the thermodynamic parameters. Prior to and after the main phase transition, additional displacement transitions are observed. It is found that the phase transition takes place roughly according to the scheme α _{385 K}→α′_{405 K}→β′_{420 K}→β _{440 K}. The specific heat C _p, changes in entropy ΔS and transition enthalpy ΔH, as well as the minimum phase fluctuation volume V, and the heat Q of the phase transition are determined. It is shown that excesses of Te and Ag have almost no effect on the transition temperatures T ₀, but have a substantial effect on the thermodynamic parameters. Fiz. Tverd. Tela (St. Petersburg) 40, 1693–1697 (September 1998)     

Calculation of radiative transition probabilities and radiative recombination rate coefficients for H2, OH, H 2+ and OH+ molecules

A method is presented to calculate the radiative transition probabilities and the radiative recombination rate coefficients between electronic molecular states. Total transition probabilities are determined from vibrational transition probabilities without considering the detailed rotational structure of the molecular electronic states. Radiative recombination rate coefficients are obtained from the computation of vibrational photo-ionisation cross sections. Concerning spontaneous emission, Lyman (B → X) and Werner (C → X) band systems of H₂ and Meinel (A → X), (B → A) and (B → X) band systems of OH are investigated. For radiative recombination, transitions between H₂⁺ (X) and H₂(X), and between OH⁺(X, a, A, b, and c) and OH(X) are considered. Transition probabilities and recombination rate coefficients are calculated as a function of temperature in the range 1500–15 000 K.     

The role of structural and nonstructural water in oxyfluoride K<Subscript>2</Subscript>WO<Subscript>2</Subscript>F<Subscript>4</Subscript> · H<Subscript>2</Subscript>O

X-ray structural and polarization optical investigations have been performed, and birefringence and rotation angles of the optical indicatrix φ _b and φ _c of the K₂WO₂F₄ · H₂O crystal have been measured in the temperature range of 100–600 K. The structure and symmetry of compounds at room temperature have been refined. It has been established that the layered crystal K₂WO₂F₄ · H₂O can exist in two states (A and B) depending on the atmospheric humidity and undergoes the sequence of reversible and irreversible phase transformations G ₃ ↔ G ₂ → G ₁ → G ₀. The sequences of changes in the phase symmetry P [`1]\bar 1 ↔ C2/m → P4/nmm for samples A and m ↔ C2/m → P4/nmm for samples B have been found. The second-order proper ferroelastic phase transition (P [`1]\bar 1 ↔ C2/m) at T ₀₃ = 270–290 K (G ₃ ↔ G ₂) is accompanied by twinning and appearance of the shift deformation x ₆. The crystal system of the substance for the B crystals remains invariable after the second-order phase transition G ₃ ↔ G ₂. The irreversible first-order phase transition G ₂ → G ₁ occurs in a temperature range T ₀₂ ≈ 350–380 K; it is accompanied by the loss of the crystallization water, which then is reduced easily from the atmosphere for a day. The substance decomposes at T ₀₁ ≈ 510 K (G ₁ → G ₀). The distinction between the A and B crystals has been explained by the presence or absence of free water in interlayer spacings.     

On the localization of plastic strain at the prefailure stage and the possibility of predicting the site and time of ductile rupture

The localization of macrodeformation during the transition from plastic flow to ductile rupture is studied for a wide class of metals. It is found that the mechanism behind this process is the same as that behind plastic deformation and as such can be described as a change in the type of localized deformation autowave in the following sequence: phase autowave → steady dissipative structure → collapse of autowave or its contraction at the site of ensuing failure. The kinetic characteristics of an autowave collapsing at the prefailure stage, which can be found experimentally, allow one to predict the spatio-temporal coordinates of rupture long before its signs appear.     

Effect of contacts between γ-Fe2O3 nanoparticles on their phase-transition temperature

The effect of mechanical contacts between γ-Fe₂O₃ particles on the temperature of the γ-α structural transition in them is established by magnetic studies and differential thermal analysis (DTA). The sample in which γ-Fe₂O₃ particles had no mechanical contacts with one another remained in the ferromagnetic state up to T _C = 630°C and had two exothermal DTA peaks. The first peak almost coincided with the Curie temperature, while the second peak attributed to the γ → α structural transition corresponded to 760°C. The magnetic transition for particles with a larger number of contacts was shadowed by the γ → α structural transition with a temperature lowered to 550°C.     

Inelastic final-state interactions in B → VV →π K processes

We study the final-state interactions in B →π K decays through B → VV →π K processes where the inelastic rescattering occurs via single pion exchange. The next-to-leading order low-energy effective Hamiltonian and Bauer-Stech-Wirbel (BSW) model are used to evaluate the weak transition matrix elements and final-state interactions. We found that the final-state interaction effects in B →ρ K^*→π K processes are significant. The Fleischer-Mannel relation for the Cabibbo-Kobayashi-Maskawa (CKM) angle γ can be significantly modified. Received: 13 August 1998     

Evolution of the crystal structure during phase working of titanium nickelide

Using x-ray diffraction we have measured the dynamic and static atomic displacements and the unit cell parameters of monoclinic martensite in the intermetallide 50.1 at. %Ti-Ni, during thermal cycling through the interval of the martensitic transition (280 to 400 K). It is shown that along with a change in the sequence of transitions from B2→B19′ to B2→R→B19′, there is also a change in the atomic displacements from predominantly dynamic on the first cycles to static displacements during the later ones. The martensite unit cell has a larger volume on cooling than on heating, and cycling leads to a lowering of its monoclinic angle. Institute of Strength Physics and Materials Production, Siberian Division of the Russian Academy of Sciences.     

Modification of hard alloy WC-steel 110G13 by a pulsed low-energy,high-current electron beam

Using metallography, x-ray diffraction analysis, diffraction electron microscopy, and microhardness measurements we have investigated the results of the action of a pulsed low-energy, high-current electron beam on the phase composition, defect structure, and mechanical properties of the hard alloy WC-30% steel 110G13. We have observed and studied in detail the regions of elevated microhardness (the microhardness of the material in these regions is 1.5–2.0 times greater than the original value) located on the irradiated surface and in the interior of the material. We have shown that the number of zones of elevated microhardness increases with an increase in the number of pulses in the electron beam treatment. We consider the mechanisms for hardening of the material by a low-energy, high-current electron beam. We conclude that the increase in the microhardness of the alloy is due to dispersion of the carbide phase, precipitation of nanometric complex carbide particles, strain hardening, and hardening due to polymorphic transformation (γ→∈) of the binder. Tomsk State Architectural Design Academy; Institute of Physics of Strength and Materials Science, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 104–110, August, 1996.     

Substructural phase transitions during intense plastic deformation of low-carbon ferrite-perlite steel

We have studied the evolution of the defect structure and phase composition of low-carbon ferrite-perlite steel subjected to intense plastic deformation using diffraction electron microscopy. It has been shown that a high degree of deformation is accompanied by disruption of the perlite columns. We have found and described two perlite decay mechanisms: decay of the carbide plates by a path of their granulation due to dislocation slip and dissolution of cementite arising from the outflow of carbon atoms from the carbide phase into ferrite crystal lattice defects. We have described the phenomenon of morphological reconstruction of the cementite-phase particles (a transition from layers to spheres) under plastic deformation conditions. Tomsk State Architectural and Construction University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 63–71, March, 1998.     

Nucleon-nucleon correlations in the reaction of photoelectric production of a Δ isobar on a tensor-polarized deuterium target

Density matrix elements for a Δ isobar produced in the reaction γd→Δp are calculated in a relativistic momentum approximation. A correlation function is obtained for the directions of escape of the spectator proton and the nucleon from the decay Δ→Nπ. The influence of polarization of the target and of the potential of the nucleon-nucleon interaction on the correlation function is considered. Scientific-Research Institute of Nuclear Physics, Tomsk Polytechnic University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 31–39, June, 1998.     

Multiple intermediate valence in plutonium

On the basis of the concepts of an intermediate-valence (IV) regime, an empirical model is proposed that quantitatively describes the magnetic susceptibility, specific heat, and effective atomic volume of the low-temperature α phase and the gallium or aluminum-stabilized face-centered cubic (fcc) δ phase of plutonium metal. The results of the paper allow one to estimate the entropy change associated with the α → δ structural phase transition, the value of this change being very close to the experimental value. According to the model, both phases of plutonium are systems with multiple intermediate valence, whose ground state is a many-particle Kondo singlet, and fluctuations occur between 5f electron configurations with integer valences of 3+, 4+, and 2+.     

Spontaneous parametric transition from periodic motion to chaos in a dynamical system with two degrees of freedom

A study is made of a spontaneous parametric transition to chaos by the disruption of periodic motion in a generating structure with two degrees of freedom. A comparison of the properties of the system examined in this study and the properties of objects with an infinite-dimensional phase space shows the universality of the spontaneous parametric scenario for a loss of stability of periodic motion that leads to randomization of the oscillatory process. Tomsk University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 42, No. 2, pp. 91–95, February, 1999.     

The C (2 Π)→X(2Σ+) transition in thermal emission spectra of the diatomic alkaline earth bromides) transition in thermal emission spectra of the diatomic alkaline earth bromides

The extensive thermal emission spectrum attributed to the diatomic bromides of calcium, strontium and barium has been observed in the visible region at temperatures about 2200–2400° C, using a vacuum graphite furnace. Many new bands,viz., 141 in CaBr, 53 in SrBr and 68 in BaBr, have been recorded and classified. The vibrational constants agree with those determined by earlier workers and involved the ground state in each case. The transition C→X apears in each molecule and consists of two equally intense systems,viz., C₁→X and C₂→X. The general spectroscopic features of the C→X systems of the bromides of the II A sub group of the periodic table have been compared. They exhibit a close structural similarity and furnish a good example of homologous spectra. The system C→X in all these molecules arises from a C² π−X² Σ ⁺ transition where the² π state appears to be intermediate between Hund’s cases (a) and (b).