Effects of tungsten addition on tensile properties of a refractory Nb−18Si−10Ti−10Mo−<Emphasis Type="Italic">x</Emphasis>W (<Emphasis Type="Italic">x</Emphasis>=0,5, 10 and 15 mol.%)<Emphasis Type="Italic">in-situ</Emphasis> Composites at 1670 K

To investigate the effect of tungsten addition on mechanical properties, we prepared refractory (62−x)Nb−18Si−10Mo−10Ti−xW (x=0, 5, 10 and 15 mol.%)in-situ composites by the conventional arc-casting technique, and then explored the microstructure, hardness and elastic modulus at ambient temperature and tensile properties at 1670 K. The microstructure consists of relatively fine (Nb, Mo, W, Ti)₅Si₃ silicide and a Nb solid solution matrix, and the fine eutectic microstructure becomes predominant at a Si content of around 18 mol.%. The hardness of (Nb, Mo, W, Ti)₅Si₃ silicide in a W-free sample is 1680 GPa, and goes up to 1980 GPa in a W 15 mol.% sample. The hardness, however, of Nb solid solution does not exhibit a remarkable difference when the nominal W content is increased. The elastic modulus shows a similar tendency to the hardness. The optimum tensile properties of the composites investigated are achieved at W 5 mol.% sample, which exhibits a relatively good ultimate strength of 230 MPa and an excellent balance of yield strength of 215 MPa, and an elongation of 3.7%. The SEM fractography generally indicates a ductile fracture in the W-free sample, and a cleavage rupture in W-impregnated ones.     

<Emphasis Type="Italic">J</Emphasis>-<Emphasis Type="Italic">Q</Emphasis> Characterization of Constraint Effects of a Three-Dimensional Cracked Specimen

Failure assessment of the integrity of a ductile flawed structural component is done currently by a one-parameter fracture mechanics approach. The J-integral is the one-parameter used; it has proven to be useful in order to predict ductile crack initiation. However, when tension loading dominates and/or a fully plastic condition develops around the crack, the J-integral alone does not describe completely the crack-tip stress field and a second parameter is needed. In this work, an accurate modeling of the elastic-plastic stress field around a deep crack in a three-dimensional three-point bend specimen is carried out. Numerical results for the crack-tip stress field are used to evaluate a crack-tip constraint parameter Q, in terms of applied loading, from contained plasticity to large-scale yielding. The parameter Q, measures the degree of stress triaxiality and constraint around the crack-tip. In order to obtain the stresses in the near-crack-tip field with high accuracy, a detailed mesh with higher order three-dimensional finite elements is located around the crack front. The modeling of crack-tip blunting deformation is performed by using a small notch radius in the crack-tip. Large-strain and finite-rotation nonlinear behavior effects around the crack-tip are included. The material, an ASTM A 516 steel, is modeled with incremental theory of plasticity. Numerical results of the Q triaxiality parameter are presented for increasing level loads to obtain an extended yield condition. Additional results of J-integral parameter and crack-tip opening displacement, for different load ratios and for different position across the specimen thickness are shown.     

Optical and magnetooptical properties of Heusler alloys <Emphasis Type="Italic">X</Emphasis>MnSb (<Emphasis Type="Italic">X</Emphasis> = Co,Pt)

The ellipsometry method (with photon energies ħω= 0.1–5.0 eV) has been used to study the optical properties of the CoMnSb phase with a structure of the L2₁ type. Infrared-absorption features indicating the existence of a pseudogap in the density of states at the Fermi level N(E _F) have been revealed. The transverse Kerr effect in CoMnSb and PtMnSb has been measured at photon energies ħω = 0.4–4.5 eV. It has been shown that the observed peaks of magnetooptical activity in CoMnSb are due to the off-diagonal component ɛ _ij of the tensor of the complex dielectric constant [^(e)]\hat \varepsilon. Spectral dependences of the magnetooptical effect δ _q quadratic in magnetization M have been studied for the first time for PtMnSb for the s and p polarizations of the light wave. In the region where a giant Kerr effect (ħω ∼ 1.7 eV) is observed in PtMnSb, a sharp increase in the δ _q effect has been revealed caused by the change in the diagonal component ɛ _ii of the tensor] of the dielectric constant in an external magnetic field. Based on the δ _q spectra for the p polarization of the light wave, additions have been calculated to the real and imaginary parts of the diagonal component of the [^(e)]\hat \varepsilon tensor in the magnetic field (Re(Δɛ _ij ) ^p and (Δɛ) _ij ) ^p , respectively). The spectrum of Im(Δε _ij ) ^p has been analyzed in terms of the existing concepts on the electron structure of PtMnSb.     

Formation of ferromagnetism in pseudobinary PrNi<Subscript>5 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> (2.5 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 5) solid solutions

The structure and magnetic properties of the PrNi_{5 − x} Cu _x alloys have been studied in a composition range of 2.5 ≤ x ≤ 5. Single-phase solid solutions with a hexagonal structure of the CaCu₅ type have been shown to be realized within this composition range. It has been found that upon the introduction of nickel into the Van Vleck paramagnet PrCu₅ the ground state of the alloys with x ≤ 4.3 becomes ferromagnetic. All the compositions under study exhibit high magnetocrystalline anisotropy of the “easy-basal-plane” type. With allowance for the literature data available, a complete magnetic phase diagram of the PrNi_{5 − x} Cu _x system was constructed; it is characterized by two maxima in the compositional dependence of the Curie temperature. The earlier suggested model of the effect of local random crystal fields on the magnetic state of Pr³⁺ ions in alloys with low copper contents was shown to be applicable also for the explanation of magnetic properties of alloys with low nickel contents. The results of this study confirm the hypothesis about the determining role of local irregular crystal fields in the formation of the magnetic properties of the pseudobinary PrNi_{5 − x} Cu _x intermetallic compounds.     

Effect of millimeter-range electromagnetic radiation on the biosynthesis of extracellular hydrolytic enzymes in <Emphasis Type="Italic">Aspergillus</Emphasis> and <Emphasis Type="Italic">Penicillium</Emphasis> micromycetes

The influence of the following parameters of millimeter-range electromagnetic radiation on the biosynthesis of extracellular hydrolases and the life cycle of Aspergillus niger 33 and Aspergillus niger 33–19 CNMN FD 02A fungi (producers of amylases) and Penicillium viride CNMN FD 04P fungus (a producer of pectinases) is studied: the wavelength (λ = 4.9, 5.6, and 7.1 mm), the irradiation mode (periodic and continuous), and the duration of exposure (10–60 min). It is established that the efficiency of the irradiation exposure depends on the physical parameters of the radiation and the properties and functional state of the strains. The optimal irradiation conditions allowing the biosynthesis and secretion of extracellular hydrolases to be enhanced by up to 44.4–49.4% as compared with the control groups are established for each particular strain. Moreover, in the case of Aspergillus niger 33–19 CNMN FD 02A micromycetes, the acceleration of the growth cycle by 48 h is observed.     

Structure and Inter-Diffusion Coefficients of Liquid Na<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>K<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> Alloys

Structure and atomic transport properties of liquid Na-K alloys are reported. Inter-diffusion coefficients of liquid Na _x K_1−x , alloys are calculated using scaling law proposed by Samanta et al. following Dzugutov which express the possible relationship between the excess entropy and diffusion coefficient. The interatomic interactions are described from the individual version of the electron-ion potential proposed by Fiolhais et al. The partial pair distribution functions and structure factors are calculated from the solution of Ornstein-Zernike integral equation with Rogers-Young closure. The evaluation with the composition of static structure and inter-diffusion properties are discussed.     

Magnetic properties of Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> nanoparticles in carbon nanotubes

The interlayer coupling in an Fe/Cr/Fe layer system with wedge-type chromium spacers was investigated as a function of the chromium-layer thickness and temperature using Kerr magnetometry. The system with a moderate roughness demonstrates an interlayer coupling that can be well described in the framework of the biquadratic coupling model. The smoother sample shows interlayer coupling that can be described using both the biquadratic coupling and the proximity magnetism model proposed by Slonczewski.     

Influence of ion-plasma treatment on the pitting resistance of 12Kh18N10T steel in a physiological solution

Corrosion-electrochemical studies of 12Kh18N10T steel subjected to ion-plasma treatment by different flow sheets in a 0.9% NaCl physiological solution were carried out. It was found that the combined procedure of ionic nitrogen hardening and arc deposition leads to the most efficient increase in the pitting resistance of the substrate. The advantage of the treated steel increases with respect to the parent steel in proportion to the holding in a corrosive environment.     

Magnetocaloric effect in Ni-Mn-<Emphasis Type="Italic">X</Emphasis> (<Emphasis Type="Italic">X</Emphasis> = Ga,In, Sn,Sb) Heusler alloys

A review is given of experimental and theoretical works concerning the investigation of magnetic and structural phase transitions and of the magnetocaloric effect in Ni-Mn-X (X = Ga, In, Sn, Sb) Heusler alloys possessing unique properties, such as the existence of coupled magnetostructural and metamagneto-structural phase transitions, giant magnetocaloric effect, shape-memory effect in the ferromagnetic state, giant magnetodeformation and magnetoresistance, exchange anisotropy. A conclusion is made that the Heusler alloys, because of their unique properties, are promising for the application in various engineering devices, including technology of magnetic refrigeration.     

Correlation function of one-dimensional <Emphasis Type="Italic">s</Emphasis> = 1 Ising model

The temperature behavior of the Fourier transform of the spin-correlation function has been studied in terms of the one-dimensional Ising model taking into account the interaction between the nearest neighbors in the cases of different signs of exchange interactions, magnetic field, and spin. It has been shown that, in the antiferromagnetic model, in the frustration field, the correlation function has a broad maximum and does not take on the form of a delta function as the temperature approaches zero, which indicates the absence of ordering in the system.     

Structure and principal electrophysical properties of Ge<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>-Si<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> thin films

In the process of thermal treatment of deposited Ge_0.85Si_0.15 films, a number of peculiarities were found related to the character of their conductivity. The films of Ge_0.85Si_0.15 solid solutions are rather resistant to thermal quenching. It was shown experimentally that irradiation with electrons under an accelerating voltage enhances the crystallization in the films and lowers their electric conductivity.     

Electronic structures of Heusler alloy Co2FeAl1-xSix surface

We have calculated the electronic structures of Co2FeAl1-xSix(101) surface using first-principles method based on the density functional theory. Because of the surface effect, the minority spin band gap at the Fermi level disappears at the surface of bulk Co2FeAl1-xSix. However, beneath the surface, the minority spin gap opens at the Fermi level, which indicates that the electronic structures of Co2FeAl1-xSix(101) be-come close to that of bulk phase. Accordingly, the Co2FeAl1-xSix(101) surface is a composite tri-layer structure that corresponds to the weakening of half-metallic property in Co2FeAl1-xSix films. Even though, the spin polarization of Co2FeAl1-xSix(101) surface is still larger than that of Co2FeAl or Co2FeSi materials, making Co2FeAl1-xSix a promising spintronics material.     

Calculating phase diagrams using <Emphasis Type="Italic">PANDAT</Emphasis> and panengine

Knowledge of phase equilibria or phase diagrams and thermodynamic properties is important in alloy design and materials-processing simulation. In principle, stable phase equilibrium is uniquely determined by the thermodynamic properties of the system, such as the Gibbs energy functions of the phases. PANDAT, a new computer software package for multicomponent phase-diagram calculation, was developed under the guidance of this principle. Author’s Note: Trial versions of PANDAT and PanEngine may be downloaded at www.computherm.com. Editor’s Note: A related article, “Our Experience in Teaching Thermodynamics at the University of Wisconsin, Madison,” by Y. Austin Chang and W.A. Oates, is available on-line only at www.tms.org/pubs/journals/JOM/0312/Chang/Chang-0312.html. For more information, contact S.-L. Chen, Compu-Therm LLC, 437 South Yellowstone Drive, Madison, Wisconsin 53719, USA; chen@chorus.net.