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.     

Exact electronic spectra and inverse localization lengths in one-dimensional random systems : I. Random alloy, liquid metal and liquid alloy

Analytic continuations into the complex energy plane of Dyson-Schmidt type of equations for the calculation of the density of states are constructed for a random alloy model, a liquid metal and for a liquid alloy. In all these models the characteristic function follows from the solution of this equation. Its imaginary part yields the accumulated density of states and its real part is a measure for the inverse of the localization length of the eigenfunctions. The equations have been solved exactly for some distributions of the random variables. In the random alloy case the strengths of the delta-potentials have an exponential distribution. They may also have finite, exponentially distributed values with probability 0 p 1 and be infinite with probability q = 1 −p. In the liquid metal the liquid particles are assumed to behave like hard rods. This implies an exponential distribution of the distances between the particles. The common electronic potential may be arbitrary, but is assumed to vanish outside the rods. In the one-dimensional liquid alloy there is, apart from positional randomness of the liquid particles, a distribution of the strengths of the electronic delta-potentials. For Cauchy distributions an argument of Lloyd is extended to obtain the characteristic function from the one in the model with equal strengths. For the case of a liquid of point particles a three parameter class of distributions of the strengths is shown to yield a solution in the form of known functions of the equation mentioned above. For several cases numerical calculations of the density of states and the inverse localization length of the eigenfunctions are presented and discussed.

New results are found: exponential decay of the density of states near special energies in the random alloy and liquid metal; divergence of the density of states at certain energies with non-classical exponent 1/3 in the random alloy if the average of the potential strengths vanishes; exponentially small broadening of the bound-state levels for low concentrations of the liquid particles; peak in the localization length at the bound-state energies, which becomes exponentially narrow for low concentrations; different exponent in the decay of the inverse localization length at large energies for delta potentials and square-well potentials. Further an expression for the grand potential is given, involving a sum over the characteristic function at certain points and divergence of the zero-point energy is found for Cauchy distributions of the delta potential strengths.     

Analysis of the results of investigation of the kinetics of ordering in alloys of different systems by the methods of formal chemical kinetics

Several different alloy systems are used as examples to show that the experimental dependences of the degree of long-range order on the time of isothermal annealing can be approximated by the equations of formal chemical kinetics. It was found that there are functions-linear for actual processes-which can conditionally be used as a criterion of the accuracy of models of processes. The results obtained regarding the kinetics of the alloy Ni₂Cr are compared with calculations based on an ordering model in terms of the theory of absolute reaction rates.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 55–60, June, 1988.     

Densities,molar volumes,and surface tensions of Na-K-Cs ternary alloys along the two sections containing the eutectic alloy

The densities, molar volumes, and surface tensions of 21 ternary alloys of the Na-K-Cs system have been determined in the temperature range 293–453 K for the two sections directed to the Cs and K vertices and containing the eutectic alloy. The polytherms of these parameters for the Na_0.129K_0.435Cs_0.436 eutectic alloy in the temperature range 200–460 K are described by linear equations and their values at 373 K are determined to be 1406 kg m^?3, 54.62 × 10^?6 m³ mol^?1, and 77.0 mN m^?1, respectively. The isotherms of molar volumes of the ternary alloys in both sections obey the additivity rule; in the low-concentration range, cesium exhibits high surface activity.     

Order-disorder transformation theory in ternary alloys with face-centred cubic lattice-I.: Equilibrium equations

The atomic ordering of the L 1₂ binary superstructure type in a ternary alloy is investigated. The equilibrium equations of the alloy are given according to the Kikuchi approximation with the account of the atomic interaction energy and the correlation in the first coordination sphere.     

Fast crystallization of structural steel during laser processing of the surface

The size, shape, and structure of the molten zone appearing on the surface of Fe-C multicomponent alloy upon laser recrystallization are studied. The laser scan rate varies between 0.01 to 0.167 m/s. A set of equations for the temperature and concentration fields is derived within a model of locally nonequilibrium crystallization. The use of the hypothesis for marginal stability, as applied to crystal growth, makes it possible to find the characteristic size of the crystal structure. The mathematical simulation of recrystallization upon laser processing is in good agreement with experimental data. The results of the simulation can be used for predicting the mechanical properties in the molten zone as a function of the energy parameters of the radiation and thermophysical properties of the alloy.     

Nonlinear theory for epitaxial growth of semiconductor alloys on vicinal surfaces

A set of coupled nonlinear diffusion equations is derived for describing the epitaxial growth of semiconductor alloys on vicinal surfaces. The equations include diffusion and a quadratic interaction term to account for incipient island formation. A criterion is obtained for determining the temperature T_c at which growth becomes dominated by step advancement as a function of alloy composition, substrate temperature, and growth rate. The sensitivity of T_c to variations in the interaction parameters is briefly discussed.     

Effects of enhanced diffusion on preferred sputtering of homogeneous alloy surfaces

The effects of enhanced diffusion caused by sputter damage on the kinetics of preferred sputtering of alloy surfaces have been analyzed. The diffusion flux is specifically included in considering the mass balance within the altered layer and on the sputtered surface. An analytical solution has been derived by solving the two mass-balance equations simultaneously under certain conditions. The solution is used as the basis of an interative method to obtain exact numerical solutions as a function of sputtering time. The analysis enables one to define an altered layer with respect to the steady state and to express its thickness in terms of the sputter yields and the diffusivity. Illustrative results showing the evolution of the altered layer during sputtering are given for a typical binary alloy surface. Implications of this analysis and possible future experiments are discussed.     

Fe-Ni殷钢的穆斯堡尔谱研究

用穆斯堡尔谱研究了Fe-Ni殷钢的磁性特征,证实合金中存在两种不同磁态的Fe原子,并依此解释了殷钢效应。提出了测定合金中两种状态Fe原子磁矩的公式。报道了Fe-Ni合金在Ni32wt%附近的一些反常现象。 关键词：     

Self-consistent alloy treatment of the periodic anderson model: Susceptibility and specific heat of intermediate valence compounds

To describe the electronic properties of mixed valence compounds we study the periodic Anderson model within the frame of the alloy analog approximation. In this approach the model Hamiltonian is replaced by the sum of two single-particle alloy Hamiltonians the parameters of which have to be determined self-consistently. The alloy problem is solved within the coherent potential approximation. In contrast to other treatments of the periodic Anderson model this approximation scheme is exact in both trivially solvable limits of vanishing hybridization and Coulomb repulsion, respectively. For model parameters corresponding to a mixed valence situation only nonmagnetic solutions of the self-consistency equations exist. After discussing the limit of small hybridization analytically we numerically calculate the magnetic susceptibility and the electronic specific heat as a function of temperature for realistic values of the hybridization and Coulomb repulsion. The results are in very good qualitative agreement with experimental data.Work performed within the research program of the Sonderforschungsbereich 125 Aachen/Jülich/Köln     

Nonlinear surface processes under nonequilibrium TiNi activation by a pulsed electron beam

Nonlinear processes involved in oxygen diffusion from the adsorption layer into the bulk of an alloy exposed to a low-energy high-current pulsed electron beam are investigated in the framework of a mathematical model accounting for nonequilibrium activation and melting of the irradiated material. An example is a TiNi alloy. The model includes heat, diffusion, and kinetic equations, with initial and boundary conditions corresponding to electron-beam treatment of the alloy. Kinetic parameters are estimated. The time and space distributions of the TiNi temperature and oxygen concentration for a varying maximum pulse power density and pulse duration are calculated. The heating and diffusion depths are determined. The results obtained with and without regard to the activation effect are compared. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 8–15, March 2007.     

InGaN: An overview of the growth kinetics,physical properties and emission mechanisms

This article reviews the fundamental properties of InGaN materials. The growth kinetics associated with the growth parameters, such as growth temperatures, V/III ratios, and growth rates which influence the quality of the InGaN epilayers, are briefly described. An overview of the properties of the InGaN alloys, such as the optical, structural and electrical characteristics, is presented. The design and fabrication of novel optoelectronic device structures require an accurate knowledge of the band gap as a function of alloy composition; therefore, attention is paid to Vegard’s law and the bowing parameter; in addition, the major factors leading to the uncertainties of the bowing parameter of InGaN are addressed. Apart from that, the determination of indium composition by X-ray diffraction (XRD) using different assumptions and various equations are summarized. The erroneous measurements of the indium composition by using this technique are also described. Finally, different emission mechanisms of the strained InGaN quantum wells proposed by different groups of researchers are also discussed.     

Nonlocal conserved quantities,balance laws,and equations of motion

A formalism is developed whereby balance laws are directly obtained from nonlocal (integrodifferential) linear second-order equations of motion for systems described by several dependent variables. These laws augment the equations of motion as further useful information about the physical system and, under certain conditions, are shown to reduce to conservation laws. The formalism can be applied to physical systems whose equations of motion may be relativistic and either classical or quantum. It is shown to facilitate obtaining global conservation laws for quantities which include energy and momentum. Applications of the formalism are given for a nonlocal Schrödinger equation and for a system of local relativistic equations of motion describing particles of arbitrary integral spin.     

直读光谱测试法研究铅基合金中铝,砷,钙,铜,硫,锑,硒,锡等元？…

采用直读光谱分析法分析,研究铅基合金中铝,砷,钙,铜,硫,锑,硒,锡等元素的分布,找出了分布规律,总结了最佳测试取样方法。     

液体钾、钠及其合金NaK的密度

我们用膨胀计方法,在温度0—300℃的范围内,测定了液体金属钠、钾以及它们的合金NaK三种样品的密度。所用金属的纯度约在三个九以上,结果表明,所测液体金属及其合金的密度可作为温度的线性函数来表示,但NaK合金的(d,t)直线在接近冰点地方偏离直线上翘。     

Near-eutectic Zn-Mg alloys: Interrelations of solidification thermal parameters,microstructure length scale and tensile/corrosion properties

Zn-Mg alloys are considered to have potential application in bone implants, since both metals are biocompatible and have biodegradable characteristics. Adding Mg to Zn can boost mechanical and corrosion resistances. However, the literature is very limited on quantifying the interrelation of solidification parameters, microstructural features and mechanical/corrosion properties of Zn-Mg alloys. The present study examines the interrelations of alloy Mg content, macrosegregation effects, morphology and scale of the matrix and eutectic phases, nature of intermetallics and tensile and corrosion properties of near-eutectic Zn-Mg alloys. The alloys samples are obtained by unsteady-state directional solidification resulting in a wide range of solidification thermal parameters and microstructures. We examine microstructural features of both dendritic and complex regular eutectic phases. It is shown that the eutectic exhibits a bimodal pattern with neighboring areas of coarse and fine lamellae. Experimental growth laws relating the primary, secondary and eutectic spacings to the solidification cooling rate and growth rate are proposed. Hall-Petch type equations are derived expressing tensile strength and elongation to dendritic and eutectic spacings. Electrochemical parameters determined by polarization curves during corrosion tests and SEM analyses of corroded areas have shown that the alloy having an essentially eutectic microstructure is associated with better corrosion resistance.     

Explicit model for ultrasonic attenuation in equiaxial hexagonal polycrystalline materials

Attenuation coefficients for longitudinal and transverse ultrasonic waves are obtained in explicit form for untextured hexagonal polycrystalline materials. The equations obtained are easy to use for interpretation and evaluation of experimental results for ultrasonic characterization of microstructures. The attenuation coefficients are separated into two terms, corresponding to incident wave scattering into longitudinal and transverse waves. It is shown that the general expressions for attenuation coefficients in the long wavelength (Rayleigh) and short wavelength (stochastic) regimes transit to the known classical asymptotics. Simple equations to estimate the frequency range of the transition from the Rayleigh to stochastic regimes are also given. An example of experimental measurements in Ti alloy is provided to illustrate application of the model; the results show reasonable agreement between the experiment and the model with no adjustable parameters.     

Theory of the residual electrical resistivity of binary actinide alloys

A system of self-consistent equations has been proposed for the coherent potential approximation of the multiband conductivity model for the case of conduction electron scattering from chaotic electric fields of ions of disordered binary alloy components at zero temperature. It has been qualitatively demonstrated that the deviation of the concentration dependence of the residual electrical resistivity of actinide alloys with multiband conductivity from the Nordheim rule is caused by the explicit dependence of the electrical resistivity of the alloy on the magnitude and sign of the real part of the Green’s function at the Fermi level. The derived system of equations for the multiband coherent potential approximation has been used to calculate the concentration dependence of the density of states and the residual electrical resistivity of the alloys of neptunium and plutonium. The results of the calculations have been compared with the available experimental data.     

振动盘式粘度计及R403B和R413A气相粘度的实验测量

建立了国内第一台振动盘式粘度计测量气体的粘度，扭丝采用钛镍合金丝．得到了测量的工作方程．在利用测量的ＨＣＦＣ２２的气相粘度进行校核的基础上测量了Ｒ４０３Ｂ在温度３０３－３６３Ｋ，压力０．１～２．１４ＭＰａ 内的气相粘度，及Ｒ４１３Ａ在温度３０５～３６３Ｋ，压力０．１～１．８２ ＭＰａ 内的气相粘度，并回归了其粘度计算方程．