Peculiarities of α → β transformation in the Pd-In-Ru-H system

A precise X-ray diffractometry method is employed to investigate a Pd-In-Ru alloy foil subjected to electrolytic hydrogenation. It is revealed that an increase in the scattering volume of the sample and its multiphase disintegration are caused by the α → β transformation. The basic characteristics of the given transformation are established.     

Modeling of the γ → α transformation in steels

A mathematical physically based model of the decomposition of undercooled austenite (γ-phase) with the formation of ferrite (α-phase) and pearlite has been developed. The model differs from the currently existing analogs by a new approach to the inclusion of the effect of complex alloying of steels on the nucleation rate of ferrite grains and on the mobility of the α/γ-phase boundary. In the model, the effect of alloying of steels with substitutional elements on the diffusion coefficient of carbon in the bulk of austenite is taken into account. The results of the modeling of the kinetics of austenite decomposition and the calculation of the final ferrite grain size are in good quantitative agreement with the experimental data obtained for a set of steels with a wide range of chemical compositions.     

Molecular dynamics investigation of the size effect upon the β → α transformation in Zr nanocrystals

The stability of the β phase in cubic zirconium nanoparticles has been calculated as a function of the size r (r varies in the range from 2.5 to 11.5 nm) by the molecular dynamics method with the many-body interatomic interaction potential obtained within the embedded-atom model. It has been demonstrated that the temperature T _k at which the cubic cluster of body-centered cubic zirconium becomes structurally unstable depends nonlinearly on the particle size. The curve T _k (r) exhibits a pronounced maximum in the range r ≈ 4.3−4.7 nm. It has been established that the mechanism of the structural transition from the body-centered cubic phase to the hexagonal close-packed phase depends substantially on the particle size. For particles with sizes in the range from 2.5 to 5.0 nm, there exists a temperature range in which the transition from the body-centered cubic phase to the hexagonal close-packed phase remains incomplete for a long time. In this case, two phases coexist and the initial particle undergoes a strong deformation along the habit plane.     

Crystallographic aspects of structure formation under the β → α transformation in oriented cobalt single crystals

The crystallographic parameters of the β → α transformation in oriented cobalt single crystals quenched from 1000°C have been studied by X-ray structure analysis and light microscopy. It is shown that the orientation of martensite crystals of the α phase correspond to the Wasserman orientation relationship.     

Kinetics of the β→α transformation and the hierarchical nature of structure defects in the two-phase state in the Pd-H system

Possible types of time dependences p(t) describing the kinetics of the β→α a transformation in the Pd-H system are presented based on the theory of hierarchical structures. It is shown that one factor influencing the change in the time dependence p(t) is the degree of regularity in the distribution of defects in the hierarchical complexes and the strength of the hierarchical coupling determining the number of hierarchically coupled levels. Analysis of the relations obtained and the experimental data made it possible to distinguish the most likely physical causes for the retardation of the β→α a transformation. Fiz. Tverd. Tela (St. Petersburg) 49, 1621–1626 (September 1999)     

Change in the structural state of the β-phase of TiNi with active precipitation of Ti11Ni14

X-ray diffraction is used to study the phase composition of alloys containing 50.0–53.0 at. % and 60.0 at. % Ni after quenching from the region of homogeneity of the -phase (T_que=1073 K). The change in phase composition after annealing at 773 K over 100 h is also studied. The change in phase composition and the structural state of the -phase in the alloy Ti+51.0 at. % Ni is investigated in relation to temperature and annealing time at 773 K. It is established that the aging of this alloy under conditions of active precipitation of Ti₁₁Ni₁₄, consists of three stages, each of which is characterized by its own phase composition and -phase structural state. The possible effect of these changes in the -phase on martensite transformation characteristics is indicated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 5–9, May, 1989.     

Anomalies in the physical properties of metastable Fe-Ni alloys heated to the temperature interval of the α → γ transformation

Experimental data for the formation sequence of reverted austenite morphologies in the temperature interval of the reverse α → γ transformation in Fe-Ni metastable alloys are analyzed. Emphasis is on the mechanism behind the formation of extended crystals of a new phase, which arise in the middle of the reverse α → γ transformation temperature interval. A correlation between the formation of large extended lamellas and anomalous behavior of the physical properties of metastable Fe-Ni alloys is found.     

Structure of the α-phase of solid methanol

The crystal structure of α-methanol at 15K has been determined from neutron powder diffraction measurements. The structure is orthorhombic, space group P2₁2₁2₁. The molecular geometry is found to be very similar to that in the gas phase, but the methyl group no longer has ideal 3-fold symmetry. The crystal is formed by infinite hydrogen-bonded chains of molecules with adjacent chains ‘pointing’ in opposite directions. The O-H … O hydrogen bonds are almost linear. No phase intermediate between the low temperature α-phase and the high temperature β-phase was found, but a new, metastable phase was discovered.     

High-pressure X-ray diffraction study of the δ-phase in the uranium-neptunium binary system

Abstract

High pressure X-ray diffraction studies were performed at room temperature on a uranium-neptunium binary alloy (U_{0, 40} Np_0.60) using a diamond anvil cell in an energy dispersive facility. The sample maintained its simple cubic phase up to 62 GPa (highest pressure reached in This experiment). The bulk modulus and its pressure derivative were determined to be B₀ = 82 (2) GPa and B₀′ = 9.4 (1.3), from the experimental data in the pressure range 0–20 GPa. The present results are compared with those obtained by the same techniques used for uranium and neptunium.     

Hcp-icosahedron structural transformation induced by the change in Ag concentration during the freezing of （CoAg）561 clusters

The synergy effect of alloy elements in bimetallic clusters can be used to tune the chemical and physical properties. Research on the influences of alloy concentration and distribution on the frozen structure of bimetallic clusters plays a key rolc in exploring new structural materials. In this paper, we study the influence of Ag concentration on the frozen structure of the （AgCo）561 cluster by using molecular dynamics simulation with a general embedded atom method. The results indicate that tt~e structure and chemical ordering of the （AgCo）561 cluster are strongly related to Ag concentration. Hcp-icosahedron structural transformation in the frozen （CoAg）561 cluster can be induced by changing Ag concentration. The chemical ordering also transforms to Janus-like Co Ag from core-shell Co-Ag.     

Phase Transformations α → β → γ → δ → ε in Titanium Hydride TiH x with Increase in Hydrogen Concentration

Structural phase transformations of the hcp bcc fct fcc fct ( ) type in titanium hydrides TiH _x experimentally found to occur with increase in the hydrogen concentration x are studied theoretically. Free energy phases are statistically calculated, and their concentration dependence is determined. Phase transformation temperatures are found from intersection points of free energy curves and from points of common tangents to the curves. The energy parameters of the system are estimated. The calculation results are compared with the experimental data.     

Transition of β to α phase in isotactic polypropylene

In samples of isotactic polypropylene, the influence of the nucleation agent chinacridine permanent red E3B on the crystallization rate and content of α and β modifications and on the rate and mechanism of the β → α transition was investigated using x-ray diffraction, DSC microcalorimetry, and electron microscopy. It was found that, though E3B increases the content of the β phase, it is also a very efficient nucleation agent for the α-phase crystallization. The β → α transition occurring above 140°C could be characterized by a gradual melting and annealing of the β phase, accompanied by a surface crystallization of the α phase on lateral faces of β lamellae by a mechanism similar to cross-branching of α lamellae.     

Phase transformation α → ε in meteoritic Fe–Ni alloy under shock-wave loading

We have studied microstructural deformation-induced changes and phase transformations in the material of the Sikhote-Alin iron meteorite (IIAB) after loading by spherically converging shock waves. The results obtained by the method of electron backscatter diffraction, as well as the data of local chemical analysis unambiguously indicate the presence of regions experiencing polymorphic α → ε and ε → α transitions in the loaded sample.     

Intensity distribution in the bands of the D1 → X1∑+ system of PbO

Relative integrated intensities of the D1 → X¹∑⁺ system of PbO have been measured by heterochromatic photography photometry. The Morse potential has been employed to compute the Franck-Condon factors and r-centroids. The variation of electronic transition moment R_e with internuclear separation r is found to be R_e(r) = const × (0.54 r − 1) in the range 1.957 ⩽ r, Å ⩽ 2.051. Relative band strengths are derived. The effective vibrational temperature of the source was 6199 K.     

Microscopic investigation of electric dipole transitions in the α + 16O system

A microscopic calculation of forbidden E1 transitions is presented in the framework of the generator coordinate method. Isovector and isoscalar origins of E1 transitions are studied in the case of the α + ¹⁶O system. Two-cluster T = 0 and T = 1 configurations are coupled by the exact microscopic Coulomb interaction. The γ- widths of the 1₁⁻ and 3₂⁻, states of ²⁰Ne are fairly reproduced by the model but the anomalous branching ratios observed experimentally remain unexplained. Simplified formulas for the isospin-mixing rates and reduced E1 transition probabilities are compared with the microscopic results and are employed to discuss them. The non-resonant E1 contribution to the ¹⁶O(α, γ)²⁰Ne reaction is shown to be almost negligible at astrophysical energies.     

Determination of the he pressure in bubbles formed during α-implantation of Ni

Abstract

At T?90°C, Ni single crystals were uniformly implanted to a depth of 10 μm with multi-energy He ions (E≤5.2 MeV), to concentrations from 0.06 to 1.1 at.%. From a small-angle X-ray scattering study, helium was found to be trapped in small bubbles with radii of 5.6 to 12 Å. The average distance between bubbles of about 80 Å was found to be independent of the implantation dose. At the higher concentration, CH_c 1.1%, the bubbles were found to be strongly over-pressurized, i.e. the He pressure in the larger bubbles was determined to be as high as 300 kbar with a He atom/vacancy ratio of 2.     

Influence of pressure on the solid state phase transformation of Cu-Al-Bi alloy

The solid state phase transformation of Cu-Al-Bi alloy under high pressure was investigated by x-ray diffraction, energy dispersive spectroscopy and transmission electron microscopy. Experimental results show that the initial crystalline phase in the Cu-Al-Bi alloy annealed at 750℃ under the pressures in the range of 0-6 GPa is α-Cu solid solution (named as α-Cu phase below), and high pressure has a great influence on the crystallisation process of the Cu-Al-Bi alloy. The grain size of the α-Cu phase decreases with increasing pressure as the pressure is below about 3 GPa, and then increases (P 3 GPa). The mechanism for the effects of high pressure on the crystallisation process of the alloy has been discussed.