含BCC/B2共格结构多主元合金研究进展

引入共格析出相是强化合金的重要方式。近年来发现在BCC结构多主元合金中引入共格B2相可有效提升其力学性能,形成了一类重要的合金体系。本文综述了含BCC/B2共格结构多主元合金的研究现状,重点讨论这一系列新型合金在成分、组织形貌、结构稳定性以及力学性能等方面的特征,并指出此类合金在宽温域下强度较高、塑性因成分差异而不同的变化特点。目前,这类合金在高于500℃时的结构稳定性较差,无法满足工程应用的需求,而成分设计是解决此问题较为简单易行的方法。本文旨在为含BCC/B2共格结构多主元合金的设计提供参考。     

A criterion for cavitation of two-phase superplastic alloys

Microduplex 60/40 brass and Zn-AI eutectoid were used as models to represent cavitating and non-cavitating classes of the two superplastic alloys, respectively. In addition, a series of alloys were produced to represent the individual phases, over a wide range of temperatures, in these model systems. Hardness, Young's modulus and tensile tests were carried out on all these alloys at temperatures between 20 and 700° C. Analysing the above data, a criterion for the occurrence of cavitation in two-phase superplastic alloys is proposed.[/p]     

A novel Quaternion integration approach for describing the behaviour of non-spherical particles

There are three main frameworks to describe the orientation and rotation of non-spherical particles: Euler angles, rotation matrices and unit Quaternions. Of these methods, the latter seems the most attractive for describing the behaviour of non-spherical particles. However, there are a number of drawbacks when using unit Quaternions: the necessity of applying rotation matrices in conjunction to facilitate the transformation from body space to world space, and the algorithm integrating the Quaternion should inherently conserve the length of the Quaternion. Both drawbacks are addressed in this paper. The present paper derives a new framework to transform vectors and tensors by unit Quaternions, and the requirement of explicitly using rotation matrices is removed altogether. This means that the algorithm derived in this paper can describe the rotation of a non-spherical particle with four parameters only. Moreover, this paper introduces a novel corrector-predictor method to integrate unit Quaternions, which inherently conserves the length of the Quaternion. The novel framework and method are compared to a number of other methods put forward in the literature. All the integration methods are discussed, scrutinised and compared to each other by comparing the results of four test cases, involving a single falling particle, nine falling and interacting particles, a 2D prescribed torque on a sphere and a 3D prescribed torque on a non-spherical particle. Moreover, a convergence study is presented, comparing the rate of convergence of the various methods. All the test cases show a significant improvement of the new framework put forward in this paper over existing algorithms. Moreover, the new method requires less computational memory and fewer operations, due to the complete omission of the rotation matrix in the algorithm.     

A distributed parameter model for particles in the spray drying process

A multicomponent particle drying model has been developed to describe the compositions and temperatures of spray-dried particles using distributed drying kinetics. This means that component migration is expected to occur within the particles, thus temperature and moisture content gradients through the particles are present and might not be uniform. Particles are divided into a number of shells and may be spray dried from a solution of several solutes dissolved in water, such as sugars and proteins. The model simulates the drying kinetics within a concurrent spray dryer and also accounts for the effects of the solubilities of the solids, as well as surface activity of the components. The model has been successfully compared with an analytical solution for evaporation alone, to test the modelling of the external heat and mass-transfer processes. The model has also been compared with an analytical solution for internal diffusion in a sphere, which has tested the modelling of the internal heat and mass-transfer processes.     

Analysis of the influence of temperature and deformation on the stability of the granular structure of alloys containing second-phase particles

Analysis of the influence of thermal, mechanical, and electromagnetic actions on the stability of the granular structure of dispersion-hardened alloys with a uniform distribution of incoherent mobile particles of constant radius has been performed. It has been shown that of all parameters describing the process of interaction between the grain boundary and particles, only the relative mobility μ is a function of temperature. An expression for the relative mobility, universal for all metals, has been obtained in the approximation in which the particles in the crystal matrix participate in the diffusion motion according to the Geguzin model (volume flow mechanism). It has been shown that the influence of the test temperature on the relative mobility μ and, therefore, on the stability of the granular structure is determined by the ratio of the activation energy of grain-boundary migration H to the activation energy of particle motion Q. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 6, pp. 100–105, November–December, 2005.     

Grain growth in the two-phase Al-Cu alloys

Grain and phase growth in the two-phase Al-Cu alloys containing 6, 11, 1 7, 24 and 33 wt % Cu were investigated by annealing at 535 °C for 0.5–100 h. The grain and phase sizes of the phase are seen to be larger than that of the phase. The size of phase decreases whereas the size of phase increases with increasing copper content in the alloy. As such, the phase- and grain-size distributions are broader than the phase- and grain-size distributions, but the size range depends on annealing time and alloy composition. The grain sizes of the ,d , and ,d , phases can be related to the volume fraction of the phase,f , according to the equationd = 0.497d /f .     

Kinetics of the neutralization of static electricity in apparatus containing two-phase systems of gas and solid particles

The mechanisms of neutralization of static electricity of disperse systems when ions of the opposite sign are present in the gaseous medium are discussed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 3, pp. 490–497, March, 1980.     

Circulation model for describing mixing of solid particles in a fluidized bed

We present experimental response curves for the pulsed introduction of labeled (heated) particles into a fluidized system with a noncireulating solid phase, and compare these curves with those calculated by using the circulation and diffusion models.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 46, No. 5, pp. 820–824, May, 1984.     

The shock wave structure in a dense electronegative gas containing conductive particles

The structure of a flat shock wave in an electronegative gas containing a rarified suspension of small metallic particles (macroparticles) is considered. When heated due to thermal electron emission, the particles are ionized in the shock compression that occurs in the carrying gas. The emitted electrons adhere to the electronegative neutral molecules, which gives rise to the formation of a multicomponent gas mixture composed of ions, electrons, neutrals, and positively charged macroparticles. The profiles of the corresponding variables are calculated within the Navier-Stokes approximation. The reaction of sticking is analyzed with the use of chemical kinetics equations. The calculations were performed for the case of air, which assumed by binary mixture of molecules O₂ and N₂. The initial temperature and the Mach number of the oncoming flow are T = 500 K and M = 3.     

A new two-phase system for the preparation of nearly monodisperse silver nanoparticles

Nearly monodisperse silver nanoparticles were prepared in a two-phase water-cyclohexane system. Aqueous silver nitrate was reduced by the product of the reaction of aqueous hydrazine with benzyl aldehyde in cyclohexane to form, in the presence of oleic acid, cyclohexane-soluble silver nanoparticles. The silver nanoparticles were examined by transmission electron microscopy (TEM), UV-visible spectroscopy (UV-vis), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The nanoparticles are relatively monodisperse (diameter less than 6 nm) and have good stability in cyclohexane due to the oleic acid adsorbed on their surfaces. These silver nanoparticles were successfully assembled into a powder with a face-centered-cubic structure by slow evaporation of the solvent. With some change in particle size, these silver nanoparticles could be transferred from cyclohexane to water by the addition of cetyltrimethylammonium bromide.     

A new process for atomization of metal alloys

A laboratory apparatus was constructed to atomize metal alloys by forcing them through sintered ceramic disc filters. The process combines filtration of oxides and/or undesirable second phase particles with atomization. Sintered Al₂O₃ and SiO₂ disc filters with average pore sizes in the range of 36 to 150 m were used. The effectiveness of various filters in removing synthetic inclusions from Al-Ti-B melts was studied. 2 to 10 m size TiB₂ particles were successfully filtered out. Atomization experiments were done with pure aluminium and 7075 aluminium alloy. Spherical powders, 150 to 2000 m in size, of 7075 aluminium alloy with secondary dendrite arm spacings between 4 to 8 m, were cold compacted and extruded into a billet. Room temperature longitudinal properties of the billet in T6 condition were: YS 80×10³ psi, UTS 94.3×10³ psi, elongation 15% and R.A. 42%.     

A new class of quasi-linear models for describing the nonlinear viscoelastic response of materials

In this short note, we develop a new class of “quasi-linear” viscoelastic models wherein the linearized strain is expressed in terms of a nonlinear measure of the stress. The class of models that is developed could be regarded as counterpart to the class of models referred to popularly as “quasi-linear” models, proposed by Fung to describe the response of viscoelastic bodies; however, now the strain is expressed as an integral of a nonlinear measure of the stress. The class of models that are developed can describe response that cannot be described by the class of models proposed by Fung, and moreover, these models are more reasonable from the point of view of causality.     

A new theory describing the hydrogen-assisted intergranular cracking of high-strength steels

A thermodynamic analysis of hydrogen-assisted intergranular brittle fracture of high-strength steels has been made. In this analysis the functional relationship between cohesive energy and hydrogen coverage is derived in the case of solute equilibrium constraint during the decohering process. This relationship is evaluated and discussed in the presence of a triaxial stress field. The variation of threshold-stress intensity, K _th, with hydrogen fugacity is calculated by a criterion for hydrogen-assisted intergranular fracture, and is also considered as it relates to the effects of several material parameters, such as trap-binding energy at a grain boundary, yield strength and work-hardening exponent. In particular the fracture mode transition by hydrogen-assisted cracking is discussed as it relates to the effects of hydrogen on the K _th necessary for the occurrence of the respective fracture modes.     

A new form of accelerator for charged particles

A new form of accelerator is proposed which employs an electric field of constant magnitude rotating in a plane perpendicular to a static magnetic guidance field.     

A numerical model for the dissolution of spherical particles in binary alloys under mixed mode control

A general numerical model is described for the dissolution kinetics of spherical particles in binary systems for any combination of first order reactions at the particle-matrix interface and long distance diffusion within the matrix. The model is applicable to both finite and infinite media and handles both complete and partial particle dissolution. It is shown that interfacial reactions can have a strong effect on the dissolution kinetics, the solute concentration at the particle-matrix interface and the solute concentration profile in the matrix.