Creep Behaviour of Fe-Mn Binary Alloys

Tensile creep behaviour of fine-grained Fe-Mn binary alloys containing 0.42-1.21 wt. % Mn has been investigated in the temperature range from room temperature to 475K under 10-50 MPa. Tensile tests are carried out with a constant cross-head speed under uniaxial load at a strain rate 10^-4s^-1. Stress exponent and activation energy are determined to clarify deformation mechanism. The obtained variation of steady state creep rate with respect to the applied stress for Fe-Mn binary alloys exhibits two distinct regimes at about 20 MPa, indicating a possible change in creep mechanism. The average stress exponent is approximately 2.2, which is a characteristic of grain boundary sliding in the alloys. The activation energy for plastic flow varies from 135 to 92k J/mol, depending on the Mn content.     

Hydrogen Solubility in Zirconium Alloys

Physics of Atomic Nuclei - Analysis of the published to date results for hydrogen solubility in zirconium alloys—core structural materials of water-cooled nuclear reactors is presented. Data...     

Calorimetry of Crystallization Processes in Binary Alloys

Physics of the Solid State - Using high-performance differential scanning calorimetry, crystallization processes in pure metals and some binary alloys on their basis have been investigated. Heat...     

Phonon Dispersion in Equiatomic Li-Based Binary Alloys

The computations of the phonon dispersion curves （PDC） of four equiatomic Li-based binary alloys, namely Li0.5Na0.5, Li0.5K0.5, Li0.5Rb0.5 and Li0.5Cs0.5, to second order in the local model potential is discussed in terms of the real-space sum of Born von Karman central force constants. Instead of the concentration average of the force constants of metallic Li, Na, K, Rb and Cs, the pseudo-alloy atom （PAA） is adopted to compute directly the force constants of four equiatomic Li-based binary alloys. The exchange and correlation functions due to Hartree （H） and Ichimaru-Utsumi （IU） are used to investigate the influence of screening effects. The phonon frequencies of four equiatomic Li-based binary alloys in the longitudinal branch are more sensitive to the exchange and correlation effects in comparison with the transverse branches. However, the frequencies in the longitudinal branch are suppressed due to IU-screening function than the frequencies due to static H-screening function.     

Precipitation Kinetics in Binary Alloys near Grain Boundaries

Based on the method of the free energy density functional, the effect of grain boundaries on the precipitation process in binary alloys is considered. A comparative analysis of precipitation kinetics has been carried out for a single-crystal fragment of a solid solution and for a fragment containing a part of the boundary between two grains. We have found the influence of grain boundaries on the kinetics of the average radius of precipitates, their concentration, and nucleation rate for several compositions of the alloy.

     

Hydrogen Release and Room Temperature Creep for Vanadium Alloys Containing Hydrogen

Vanadium alloy has been taken as one of the candidate structural materials for fusion reactors because of its excellent high-temperature mecha nical performances, high thermal stress factor and low radioactivity. It is a kind of potential materials for hydrogen storage as well. Because operated in an environment conta!ning hydrogen and its isotopes or the neutron irradiation resulting transmutation product of H, the problem that H induced degradation of mechanical properties and hydrogen embrittlement has been being one of the key issues for the application for vanadium alloys.     

Chemisorption on supported-metal catalysts

A Gree-function formalism is developed to describe the electronic and chemisorption properties of a supported-metal composite substrate. Within the framework of the tight-binding approximation, the metal catalyst is represented by a finite chain of d-orbitals, while the semi-infinite semiconductor support is characterized by a linear chain of alternating s- and p-orbitals. The Anderson-Newns model is used to calculate the chemisorption energy and adatom charge transfer for hydrogen chemisorption on the Ni/ZnO composite system.     

二元合金表面偏析的Monte Carlo方法模拟

详细介绍了二元合金表面偏析的Monte Carlo模拟方法,并应用改进的分析型嵌入原子模型结合Monte Carlo方法模拟研究了Pd-Au合金表面成分及其剖面成分分布,发现Au在表面偏析,并同已有实验结果进行了比较.     

Chemisorption on a quantum dot

The quantum kinetic equations for a “quantum dot-adatom” system are derived. It is demonstrated that the inclusion of the interaction between a quantum dot and an adatom leads to an increase in the quantum dot radius. The perturbations of the electron density of the quantum dot and the adatom upon chemisorption are calculated.     

Chemisorption on a model insulator

The adsorption both of a single atom and a monolayer of atoms on the (001) surface of a model two-band crystal with the CsCI structure is investigated using the Green's function formalism and the phase shift technique. The electronic structure of the surface is described within the Linear Combination of Atomic Orbitals (LCAO) scheme and the Tight Binding (TB) approximation. Each adatom is represented by a single non-degenerate energy level. The adatoms are placed on the surface in both the on-site and the centered fourfold-site configuration. The change in the density of electronic states upon chemisorption is found, and comparison is made with similar results on a metal surface. It is shown that many, but not all, of the qualitative features in chemisorption on metallic surfaces can be transferred to the case of an insulating surface. In addition, it is shown that there are systematic variations in the density of states with adatom coverage which depend upon the absorption site.     

Modeling of Nucleation in Binary Alloys on the Basis of the Free-Energy Density Functional

Physics of the Solid State - An approach based on the method of the free-energy density functional for calculating the nucleation rate of the second-phase precipitates has been developed. The...     

Chemisorption theory

The aim of chemisorption theory is to achieve for any adsorbateladsorbent system complete quantum predictions of the equilibrium positions of all the nuclei, the ground-state (electronically adiabatic) potential energy surface, the electronic excitation spectrum, and the response of the system to external probes. We are still a very long way from this goal, but some simplified models can now be explored in depth. Serious quantitative work begins with Toya,^1,2 and my review ends with the work of Appelbaum and Hamann³ These works provide examples of two of the three approaches to chemisorption theory. Toya's is a configuration interaction (CI) approach, using the states of the noninteracting adsorbate/solid system as basis states; Appelbaum and Hamann try to integrate Schrodinger's equation directly. The third approach is the linear combination of atomic orbitals molecular orbital (LCAO-MO) theory, and I begin with it because it is generally familiar in its simpler forms through its widespread use in molecular quantum mechanics. However, I remark at this stage that the direct integration of Schrodinger's equation may be more economical in computer time than the traditional quantum chemistry approach; it is certainly more economical if the nonlocal Hartree-Fock exchange potential is replaced by a local approximation to it.     

Screening-Dependent Study of Superconductivity in 3d-Transition Metals Binary Alloys Superconductors

In the present article, we report the screening-dependent study of the superconducting state parameters （SSPs）, viz. electron-phonon coupling strength A, Coulomb pseudopotential μ^＊, transition temperature TC, isotope effect exponent a, and effective interaction strength No V of 3d-band transition metals binary alloys superconductors have been made extensively in the present work using a model potential formalism and employing the pseudo-alloy-atom （PAA） model for the first time. Five local field correction functions proposed by Hartree （H）, Taylor （T）, Ichimaru-Utsumi （IU）, Farid et al. （F） and Sarkar et al. （S） are used in the present investigation to study the screening influence on the aforesaid properties. The present results of the SSPs obtained from H-screening are found in qualitative agreement with the available experimental data wherever exist.     

Chemisorption on a quantum-well wire

The specific features of chemisorption on a quantum-well wire are studied. It is shown that the energy of an electron of an adatom chemisorbed on the quantum-well wire changes jumpwise with variations in the wire radius.     

Chemisorption of water on nickel surfaces

Magnetic and volumetric measurements associated with neutron inelastic spectroscopy demonstrate that water is dissociatively adsorbed on nickel. In the case of Raney nickel, for low coverages, the oxygen is fixed on surface aluminium atoms and hydrogen occupies two nickel sites. At high coverage, the water molecule is fixed via oxygen bonding to the hydrogen covered nickel. On nickel prepared from its hydroxide, adsorption is reversible, the water molecule occupying six metal sites.     

Interfacial Stress,Interfacial Energy,and Phase Equilibria in Binary Alloys

A simple model is presented in order to explore the influence of interfacial stress, interfacial energy, and surface stress on the characteristics of phase equilibria in stressed, two-phase binary alloys. Two different system geometries are employed: concentric spheres and thin plates. The conditions for thermodynamic equilibrium are solved and equations of state for each geometry are obtained in terms of the phase fraction, alloy composition, system dimension, and several dimensionless materials parameters. Elastic stress introduces new equilibrium states that are further modified by the interfacial quantities. Those conditions for which interfacial quantities can induce significant changes in the equilibrium phase fraction and phase compositions are identified.     

Chemisorption of oxygen on aluminum surfaces

A critical review of the oxygen—aluminum system is presented. The primary emphasis concerns the electronic properties of aluminum surfaces exposed to oxygen. The chemisorption and oxidation aspects are considered. Cluster and slab model calculations are discussed fully and the results are related to relevant experimental data. Some of the unresolved issues are listed. A comprehensive guide to the oxygen—aluminum literature is provided.     

Study of Disordered Fe2Cr(1−x)Mn x Al Alloys

Hyperfine Interactions - A series of ferromagnetic alloys Fe2Cr(1?x)Mn x Al were prepared by arc melting for x=0 to 0.05. The alloys are single phased, but disordered with B2 type structure....     

Dependence of Dynamic Yield Stress of Binary Alloys on the Dislocation Density under High-Energy Impacts

Physics of the Solid State - The above-barrier glide of edge dislocations in binary alloys containing Guinier–Preston zones under high-energy impacts was theoretically analyzed. It was shown...