Thermal expansion coefficient of BCC defective substitutional alloy AB with interstitial atom C

The analytic expressions for the free energy, the concentration of equilibrium vacancies, the isothermal compressibility, the thermal expansion coefficient and the heat capacities at constant volume and at constant pressure of BCC substitutional alloy AB with interstitial atom C and with vacancy under pressure are derived by the statistical moment method. The theoretical results are applied to the thermal expansion coefficient of alloy FeCrSi in the interval of temperature from 700 K to 1100 K, in the interval of substitutional atom concentration from 0% to 10%, in the interval of interstitial atom concentration from 0% to 5% and in the interval of pressure from 0 GPa to 10 GPa. Our calculated results for main metal Fe are compared with the experimental data.

Crystal Structure and Hydration Characteristics of Tricalcium Silicate Doped with Magnesium Oxide

The research investigates various methods to identify magnesium oxide influences on the crystal structure and hydration properties of tricalcium silicate. The f-CaO content of the clinkers were analyzed by chemical analysis. The complex disordered superstructure of the tricalcium silicate has been studied by a joint XRD, NMR and TEM. The results show that MgO exerts a remarkable influence on the polymorphisms of C3S. Mg is not only substitutional atom but also interstitial atom in the crystal lattice of tricalcium silicate. The HRTEM pattern of C3S doped with MgO is covered by the various irregular lattice. The addition of appropriate amount of MgO in raw meal can change the formation kinetic of C3S, slightly perturb the environment of SiO44- tetrahedral, modify the crystal structure of C3S and affect the hydration activity. Doped with MgO in the raw meal can slow down the hydration rate of alite slightly in early stage.

Determination of Space Site of Vanadium in TiAl(Llo) Intermetallic Compound by ALUCHEMI

The plastic deformation behaviour of the TiAl (Llo type) intermetallic compound is improved by the vanadium macroalloying (1). The knowledge on the space site of V atoms in TiAl is more important for answer what role the vanadium plays during a deformation. By means of ALUCHEMI (Atom Location Using Channeling ―Enhanced Microanalysis) technique (2-3) it has been found that in the gamma phase of the TiAl compound the V atom is dominantly as a substitutional atom to occupy partial positions of Al atoms in this work. In the TiAl the Ti and Al atoms lie on alternate parallel planes (<001>) , four kinds of possible positions of vanadium atoms were estimated; two of which were substitutional atoms to replace the Ti or Al atom, other two were interstitial atoms to occupy the center of an octahedron as marked in Fig. 1 by О and ⊗ respectively. So using ALUCHEMI technique to determine positions of the V atoms two sets of experiment on channeling effect must be carried out.

Theoretical and Experimental Analyses of the Effects of Composition and Strain on Image Contrast in High-Resolution Transmission Electron Microscopy

Although the effects of composition and strain on amplitude-contrast images in the TEM have been thoroughly developed, similar theory does not exist for phase-contrast images and only a few specific situations have been treated. The purpose of this research is to develop a quantitative understanding of the effects of composition and strain on phase-contrast images and to test this theory experimentally. A simple defect which can cause both a local change in composition and strain is a substitutional atom. Hence, this defect is treated first, with the expectation that results from this analysis can be extended to predict image contrast from larger defects under certain imaging conditions.X-ray scattering theory indicates that diffuse scattering from point defects due to composition and strain is linearly additive. For small defect concentrations, the scattered intensity Sdiff(k) is given by:

Peculiar Doping Behavior of Si:Be.

ABSTRACTThe total energies and structures of a number of Be-induced defects in Si are investigated using ab-initio local density calculations. Our primary results are: 1) The geometry of the isoelectronic center is found to correspond to a [111] substitutionalinterstitial pair (SIP); 2) The low energy defect spectrum includes large Be complexes containing at least one substitutional atom; and 3) Simple bonding rules exist for the stability of the different types of bonds in the material. Thus the Si-Be bond is found to be stable for all defect configurations while the Be-Be bond is metastable.

An embedded atom analysis of Au and Pt substitutional atoms in Ni

The Embedded Atom Model (EAM) was utilized to analyze the energy and strain surrounding Au and Pt atoms substituted into a Ni crystal. Au substituted into Ni has a large positive size difference and a positive heat of mixing; Pt substituted into Ni has a large positive size difference and a negative heat of mixing. The EAM predicted highly anisotropic strain fields around the substitutional atom with large positive strains in the [110] direction and small or negative strains in the [100] and [111] directions. This is in contrast to the normal assumption that the strain around a substitution atom is spherically symmetric. The cohesive energy of the atoms around the substitutional atom was found to depend upon the crystallographic direction relative to the substitutional atom in addition to the radial distance from the substitutional atom. The EAM predicted an energy increase for Au substituted into Ni and an energy decrease for Pt substituted into Ni. The EAM results were compared with an elastic analysis.

Carbon analysis in reactor pressure vessel steels

The effect of neutron irradiation on the notch ductility transition temperature (NDTT) of A533B steel is known to be affected by the activity of the carbon atom which would be affected by its nearest neighboring substitutional atom, that is, silicon, manganese, etc. The high carbon activity resulting from increased nickel and silicon promotes the formation of vacancy complexes which produce irradiation hardening and, therefore, higher NDTT shifts.The present study has been undertaken to clarify the role of carbon and impurities in A533-B steel in the mechanism of neutron embrittlement, two specimens of A533-B pressure vessel steels differing in radiation sensitivity have been examined using transmission electron microscopy. The study showed that the carbon-vacancy complex in iron (ferrite) has a carbon atom positioned a finite distance from the vacancy along a <100> line. In some cases martensite was found, in others, a combination of martensite with ferrite.