Modeling microstructure evolution of binary systems subjected to irradiation and mechanical loading

We study a change in mechanical properties of binary systems subjected to irradiation influence described by ballistic flux of atomic mixing having regular and stochastic contributions. By using numerical modeling based on the phase field approach we study dynamics of deformation fields in a previously irradiated system and in the binary system deformed during irradiation. An influence of both deterministic and stochastic components of ballistic flux onto both yield strength and ultimate strength is studied. We have found that degradation of mechanical properties relates to the formation of percolating clusters of shear bands. Considering a hardening coefficient we analyze stages of plastic deformation of both initially irradiated alloy and alloy subjected to sustained irradiation. Stability of binary alloy under mechanical loading in the form of shear strain with a constant rate and cyclic deformation is discussed.     

Modeling self-organization of nano-size vacancy clusters in stochastic systems subjected to irradiation

We study the self-organization of vacancy clusters in irradiated materials under reactor and accelerator conditions. Using a continuum stochastic model we take into account dynamics of point defects and their sinks with elastic interactions of vacancies. Dynamics of vacancy clusters formation is studied analytically and numerically. We have shown a difference in patterning dynamics at irradiation under reactor and accelerator conditions. The external noise influence related to fluctuation in a defect production rate is studied in detail. Applying our approach to pure nickel irradiated under different conditions we have shown that vacancy clusters having a linear size ～eq 6 nm can arrange in a statistical periodic structure with nano-meter range. We have found that the linear size of vacancy clusters at accelerator conditions decreases down to 20%, whereas a period of vacancy clusters reduces to 6.5%.     

Ultra-precision machining induced phase decomposition at surface of Zn-Al based alloy

The microstructural changes and phase transformation of an ultra-precision machined Zn-Al based alloy were examined using X-ray diffraction and back-scattered electron microscopy techniques. Decomposition of the Zn-rich η phase and the related changes in crystal orientation was detected at the surface of the ultra-precision machined alloy specimen. The effects of the machining parameters, such as cutting speed and depth of cut, on the phase decomposition were discussed in comparison with the tensile and rolling induced microstrucutural changes and phase decomposition.     

Computer simulation study of phase separation in a binary mixture with a glass-forming component

We present a computer simulation study of spinodal decomposition with one of the two phases freezing in a glassy state during phase separation. As a model we used the Cahn-Hilliard equation with a concentration-dependent mobility coefficient which decreases rapidly with increasing concentration of the glass-forming component. We solved the Cahn-Hilliard equation numerically for two dimensions. The domain growth depends crucially on the volume fraction of the glassy phase. For high volume fractions, when the glassy phase forms a percolating matrix, a novel coarsening mechanism is discovered, which arises from the migration and coalescence of liquid droplets within the glassy matrix. Various quantities characterizing the time-dependent domain pattern, like droplet size distribution, one- and two-point distribution function and structure factor of the concentration field, are computed. We checked the validity of the dynamic scaling hypothesis.     

Radiation damage in triglycine sulphate due to fast neutron irradiation

Abstract

The change in electrical properties of TGS crystals due to induced defects created by fast neutron irradiation of two different energies (2 and 14 MeV) and different integrated neutron fluxes have been studied in the vicinity of phase transition. It is observed that the electrical conductivity increases with increase of neutron fluence up to 1.7 × 10¹⁰ n · cm^?2 and the values of the relative change of electrical conductivity in case of 2 MeV are higher than that of 14 MeV neutrons at the same neutron fluence (φ)     

The neutron spin phase imaging technique applied to dia- and paramagnetic samples

We report on a novel application of the Neutron Spin Phase Imaging technique, by performing polarised neutron radiography on dia- and paramagnetic samples. In order to achieve the necessary sensitivity we employed a 2.5 T Ramsey apparatus which was used in a previous experiment to measure the spin-dependent neutron scattering length of the deuteron. First successful results on aluminium, lead, titanium and heavy water (D₂O) samples are presented. They are in good quantitative agreement with expected values deduced from susceptibility measurements.     

水平滚筒内二元颗粒体系径向分离模式的数值模拟研究

发展了考虑法向接触力、切向接触力和力矩、以及滚动摩擦力矩的三维三方程线性弹性-阻尼离散单元模型及计算程序，对薄滚筒内二元S型颗粒体系进行了数值模拟，发现采用本文的数学模型可以准确地预测出滚筒内二元S型颗粒流的分层现象.分析了影响滚筒内颗粒分层的因素，讨论了滚筒转速、颗粒装载率等参数对分层的影响，当转速较高时，滚筒内形成大颗粒在外、小颗粒在内、具有圆形界面的月亮模式，当转速较低时形成具有波浪形界面的花瓣模式，并且随着滚筒转速的逐渐降低，花瓣的数量逐渐增加，数值模拟结果与实验完全符合.模拟还得到了花瓣模式的形     

水平滚筒内二元颗粒体系径向分离模式的数值模拟研究

发展了考虑法向接触力、切向接触力和力矩、以及滚动摩擦力矩的三维三方程线性弹性-阻尼离散单元模型及计算程序,对薄滚筒内二元S型颗粒体系进行了数值模拟,发现采用本文的数学模型可以准确地预测出滚筒内二元S型颗粒流的分层现象.分析了影响滚筒内颗粒分层的因素,讨论了滚筒转速、颗粒装载率等参数对分层的影响,当转速较高时,滚筒内形成大颗粒在外、小颗粒在内、具有圆形界面的月亮模式,当转速较低时形成具有波浪形界面的花瓣模式,并且随着滚筒转速的逐渐降低,花瓣的数量逐渐增加,数值模拟结果与实验完全符合.模拟还得到了花瓣模式的形 关键词： 分层 滚筒 模式形成 离散单元方法     

Change in Raman scattering spectrum with polymorphic transformation of α-SiO2 subjected to neutron irradiation

The changes in Raman scattering spectra in polymorphic transformation of α-SiO₂ crystals subjected to various fluences of fast neutrons are considered. Regularities in the radiative change of the spectral characteristics of a number of bands are established. A preliminary model of radiative modification of the structure of a crystal is developed within the framework of the “vapor” theory. Institute of Nuclear Physics, Academy of Sciences of the Republic of Uzbekistan, Tashkent, Ulugbek Settlement, 702132, Uzbekistan. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 582–585, September–October, 1997.     

Asymmetric angular dependence of Jc in coated conductors prior to and after fast neutron irradiation

Angular dependent measurements of J_c were performed on a commercial coated conductor (SuperPower) consisting of a 1 μm thick YBCO layer grown on a MgO IBAD buffer layer. An asymmetric behavior of the angular dependence of J_c (J_c(Ф)) was found with a changing distance between the two peaks at different temperatures and applied magnetic fields. One peak always occurs when the field is oriented parallel to the tape surface, the other smaller peak is located in the perpendicular orientation at high fields, but slightly shifted (by up to 10°) at 77 K and low magnetic fields. This peak shift, the overall J_c(Ф) asymmetry and the influence of fast neutron irradiation on J_c(Ф) are discussed. The spherical defects, introduced by collisions of fast neutrons with the lattice atoms, are randomly distributed, add to the as-grown defect structure and change the critical current anisotropy by altering both peaks.     

Continual deformation analysis with scanning phase method and time sequence phase method in temporal speckle pattern interferometry

If a laser beam illuminates a continual deformation object surface, it will lead to a temporal speckle pattern on the observation plane. Recording this time-dependent speckle pattern the deformation of the surface of an object can be obtained. Two methods, scanning phase method (SPM) and time sequence phase method (TSPM), have been introduced for measuring the displacement caused by the deformation in temporal speckle pattern interferometry (TSPI). Their principle is that by capturing a series of speckle interference patterns related to the object deformations, the fluctuations in the intensity of the interference patterns can be obtained. Through scanning these fluctuations and estimating both the average intensity and modulation of the temporal speckle interference patterns, the phase maps for whole-field displacements are calculated. In this way one is capable of quantitatively measuring continual displacements simply using a conventional electronic speckle pattern interferometry (ESPI) system without phase shifting or a carrier. The elaboration on the new methods is given in this paper and experiments are performed to demonstrate their performance with a conventional ESPI system.     

Pulse trains propagating through excitable media subjected to external noise

We study the propagation of periodic pulse trains in excitable media exposed to external spatio-temporal noise using the light-sensitive Belousov-Zhabotinsky reaction with the underlying Oregonator model as representative example. In the weak noise approximation we find noise-induced transitions in the dispersion relation of pulse trains. We discuss noise-enhanced propagation of pulse trains within a certain wave-length range caused by external noise of moderate strength.     

Transient dynamical behavior and phase transitions in magnetic systems

It was recently suggested that transient dynamical properties were of some use to predict equilibrium critical properties of 2D and 3D models of statistical mechanics on the lattice. We investigate such dynamical properties for three related models with competitive interactions, namely the ANNNI model, the brickwork model, and the BNNNI model. In spite of known differences in their equilibrium phase diagrams, our simulations display similar transient dynamical behaviors for all three models. The reliability of this method for probing equilibrium properties seems therefore questionable even for rather simple magnetic models without any structural disorder.On leave from Centre de Physique Théorique, Ecole Polytechnique, 91128, Palaiseau Cedex, France.     

Static and time-dependent properties of polymer gels around the volume phase transition

Recent progress in the study of the volume phase transition of polymer gels is reviewed. The phenomenological theories of swelling equilibrium and phase transition of gels are summarized, and some basic experimental results on poly-N-isopropylacrylamide (NIPA) gels are compared with the prediction from these theories. Special attention is paid to the elastic properties of the gel network near the volume phase transition. The effect of external stresses on the swelling and the phase transition is analyzed. Some anomalous and unique characteristics revealed in NIPA gels such as shape- and size-dependent swelling and phase transition properties, curious phase coexistence, and domain structure are presented. Experimental results on some time-dependent phenomena such as phase separation, spinodal decomposition, and pattern formation are also presented and discussed. Some problems inherent to gels from biological bodies are briefly discussed.     

Displacement damage and transmutations in metals under neutron and proton irradiation

The knowledge of the defect and impurity generation rates, as well as the defect spatial distribution, is the corner stone for the understanding of the evolution of material properties under irradiation. This knowledge is also an essential element for comprehensive experimental simulations of the behavior of irradiated materials.In this article the interaction of neutron and proton irradiation with metals is discussed with respect to displacement damage production. Charged particle irradiation is also briefly illustrated. After discussion of the primary interaction of projectiles (neutrons, charged particles in general, and protons in particular) with target atoms/nuclei, we describe the interaction of a recoil atom with other target atoms resulting in the slowing down of the projectile, displacement damage, impurity atom production due to nuclear reactions, and the creation of atomic displacement cascades. Then the further evolution of defect structure is discussed. The next section, devoted to subcascade formation, is divided into two parts. The first experimental evidence of subcascade formation under neutron and charged particle irradiation is presented. Then the models of subcascade formation are described. Finally we review the models for the calculation of displacement damage and show how these models can be applied to displacement damage calculation under neutron irradiation with a demonstration of a real application of the methods discussed to several nuclear facilities. To cite this article: P. Vladimirov, S. Bouffard, C. R. Physique 9 (2008).     

Thermodynamics and phase transitions in two-dimensional Yukawa systems

The results of numerical simulations of strongly-coupled two-dimensional dissipative Yukawa systems are presented. The thermodynamic characteristics of these systems were studied, namely the internal energy, the specific heat and the entropy. For the first time, it is discovered that the considered characteristics have two singular points on the melting line; one of these points corresponds to the first-order phase transition from crystal to the hexatic phase, and another point corresponds to the second-order phase transition from the hexatic phase to the isotropic liquid. The obtained results are compared to the existing numerical and analytical data.     

The formation of an ultrafine-grained structure in long-range order metals and alloys subjected to phase transformations and irradiation

The generation of an ultrafine-grained structure in long-range order metals and alloys by phase transformations and ion irradiation is studied. It is shown that the structure of pure iridium can be significantly refined under certain regimes of ion irradiation, and a microduplex structure possessing high mechanical properties can be produced in binary and ternary alloys, combining the processes of atomic ordering, aging, and phase recrystallization.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 81–89, August, 2004.     

Preparation of (5.0%)Er3+:Y3Al5O12/Pt-(TiO2-Ta2O5) nanocatalysts and application in sonocatalytic decomposition of ametryn in aqueous solution

(5.0%)Er³⁺:Y₃Al₅O₁₂/Pt-(TiO₂-Ta₂O₅) powder, as a high effective sonocatalyst, was prepared using sol-gel and calcination method. Then it was characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). In order to evaluate the sonocatalytic activity of the prepared (5.0%)Er³⁺:Y₃Al₅O₁₂/Pt-(TiO₂-Ta₂O₅) powder, the sonocatalytic decomposition of ametryn was studied. In addition, some influencing factors such as different Ti/Ta molar ratios on the sonocatalytic activity of the prepared (5.0%)Er³⁺:Y₃Al₅O₁₂/Pt-(TiO₂-Ta₂O₅) powder, catalyst added amount with ultrasonic irradiation time and used times on the sonocatalytic decomposition efficiency were examined by using ion chromatogram determination. The experimental results showed that the best sonocatalytic decomposition ratio of ametryn were 77.50% based on the N atom calculation and 95.00% based on the S atom calculation, respectively, when the conditions of 10.00 mg/L initial concentration, 1.00 g/L prepared (5.0%)Er³⁺:Y₃Al₅O₁₂/Pt-(TiO₂-Ta₂O₅) powder (Ti/Ta = 1.00:0.25 heat-treated at 550 °C for 3.0 h) added amount, 150 min ultrasonic irradiation (40 kHz frequency and 300 W output power), 100 mL total volume and 25–28 °C temperature were adopted. Therefore, the (5.0%)Er³⁺:Y₃Al₅O₁₂/Pt-(TiO₂-Ta₂O₅) composite nanoparticles could be considered as an effective sonocatalyst for decomposition of ametryn in aqueous solution.