Phase separation in binary systems with competing internal and external multiplicative noises

We have considered phase separation processes in binary stochastic systems with thermal diffusion and ballistic mixing representing irradiation influence. Introducing fluctuations of thermal flux and an external source of atom relocations due to ballistic diffusion into dynamics of a globally conserved field, we have shown that there are two competing mechanisms of phase transitions type of “order-disorder”: thermally assisted diffusion and irradiation induced atomic exchange. We have studied dynamics of the structure function at early stages of decomposition. In the framework of the mean field theory we have derived the effective Fokker-Planck equation to describe phase separation processes. It was shown that the ordering processes can be controlled by both regular and stochastic parts of external source influence. A reentrant behavior of a mean field order parameter versus the external noise intensity and fluctuations correlation radius is found.     

Laser irradiation effects on the surface,structural and mechanical properties of Al–Cu alloy 2024

Laser irradiation effects on surface, structural and mechanical properties of Al–Cu–Mg alloy (Al–Cu alloy 2024) have been investigated. The specimens were irradiated for various fluences ranging from 3.8 to 5.5 J/cm² using an Excimer (KrF) laser (248 nm, 18 ns, 30 Hz) under vacuum environment. The surface and structural modifications of the irradiated targets have been investigated by scanning electron microscope (SEM) and X-ray diffractometer (XRD), respectively. SEM analysis reveals the formation of micro-sized craters along the growth of periodic surface structures (ripples) at their peripheries. The size of the craters initially increases and then decreases by increasing the laser fluence. XRD analysis shows an anomalous trend in the peak intensity and crystallite size of the specimen irradiated for various fluences. A universal tensile testing machine and Vickers microhardness tester were employed in order to investigate the mechanical properties of the irradiated targets. The changes in yield strength, ultimate tensile strength and microhardness were found to be anomalous with increasing laser fluences. The changes in the surface and structural properties of Al–Cu alloy 2024 after laser irradiation have been associated with the changes in mechanical properties.     

非晶纤维的制备和力学行为

将块体材料制备成微纳米纤维时,其力学性能会得到进一步的提高,甚至具备块体材料所没有的力学行为.非晶态材料可经过熔体拉丝一次性成型而得到所需尺寸的均匀纤维,纤维表面质量好,其制备过程相对简单且节能.由于非晶材料短程有序、长程无序的结构,具备优异的力学性能,所以非晶纤维有着广泛的应用前景和基础研究价值.本文对能制备成非晶纤维且有优异力学性能的材料做了简单介绍,对非晶纤维的制备方法及其成型物理机制、非晶纤维的力学行为及其物理机制进行了综述,最后总结了非晶纤维的制备和力学行为的研究中存在的问题,对非晶纤维的发展前景做了展望.     

Pattern selection processes and noise induced pattern-forming transitions in periodic systems with transient dynamics

We apply the phase field crystal method for nonequilibrium patterning to stochastic systems with an external source in which transient dynamics is essential. Considering a prototype model for a one-component periodic system subjected to external influence kind of irradiation we study properties of pattern selection processes and external noise induced pattern-forming transitions. These processes are examined by means of the structure function dynamics analysis. Nonequilibrium pattern-forming transitions are analyzed numerically.     

Phase field modeling precipitation of β-phase and mechanical properties change in Zr–Nb alloys under neutron irradiation

ABSTRACT

We study microstructure transformation in Zr–Nb system under neutron irradiation and its mechanical properties change under mechanical loads in a form of shear deformation by using phase field methodology. The developed phase field approach takes into account defects dynamics based on reaction rate theory and elastic contribution to study mechanical properties change. A numerical modeling is provided in three stages: sample preparation, irradiation of the prepared sample and mechanical loading of the irradiated sample. A precipitation of β-Niobium particles of the size of several nanometers is discussed. Results of phase field modeling indicate that β-Niobium particles grow slowly during irradiation due to point defects rearrangement. Statistical analysis of dynamics of radiation-induced microstructure transformations is provided. Simulation results of shear deformation of pre-irradiated and post-irradiated alloys are discussed. Maps of local distribution of strain and stress and strain–stress curves are obtained. Results are verified with experimental data.     

Modeling phase decomposition and patterning in binary alloy systems subjected to neutron irradiation

We study processes of phase decomposition and patterning in a model of a binary alloy system subjected to sustained irradiation. We exploit the reaction rate theory and generalize the Darken approach of vacancy diffusion to describe generation, recombination, annihilation and spatial interaction of point defects. It is shown that an increase in the defect production rate phase, decomposition processes are replaced by disordering and patterning with vacancy clusters' formation. At elevated damage rates, both phase separation and patterning are accompanied by pattern selection processes. In the framework of numerical simulations, dynamics of phase decomposition and vacancy clusters formation is studied in detail. A change in the morphology of vacancy clusters during irradiation and their statistical properties are discussed.     

External influence on the FINEMET nanocrystals

Mössbauer spectroscopy was used to study the changes induced by preparation, irradiation and mechanical grinding of nanocrystalline Fe-Nb-Cu-Si-B alloy. Mössbauer parameters of the nanocrystalline alloy differed when the sample was prepared in a vacuum or argon atmosphere. Isothermal heating has an influence on the creation of crystalline phase and orientation of net magnetic moment. Neutron irradiation amorphised the crystalline component and modified the amorphous rest. After mechanical grinding, mainly the amorphous rest was modified for irradiated as well as non-irradiated samples. We supposed that in the powdered samples the surface domains play a decisive role by their influence on the reorientation of the magnetic moments.     

Magneto-transport in a binary alloy ring

Magneto-transport properties are investigated in a binary alloy ring subjected to an Aharonov–Bohm (AB) flux ?   within a single-band non-interacting tight-binding framework. In the first part, we expose analytically the behavior of persistent current in an isolated ordered binary alloy ring as functions of electron concentration _Ne$N_e$ and AB flux ?. While, in the second part of the Letter, we discuss electron transport properties through a binary alloy ring attached to two semi-infinite one-dimensional metallic electrodes. The effect of impurities is also analyzed. From our study we propose that under suitable choices of the parameter values the system can act as a p-type or an n-type semiconductor.     

Stochastic ballistic annihilation and coalescence

We study a class of stochastic ballistic annihilation and coalescence models with a binary velocity distribution in one dimension. We obtain an exact solution for the density which reveals a universal phase diagram for the asymptotic density decay. By universal we mean that all models in the class are described by a single phase diagram spanned by two reduced parameters. The phase diagram reveals four regimes, two of which contain the previously studied cases of ballistic annihilation. The two new phases are a direct consequence of the stochasticity. The solution is obtained through a matrix product approach and builds on properties of a q-deformed harmonic oscillator algebra.     

V-Ta合金力学行为的计算与实验研究

用第一性原理方法计算V-Ta合金体系的弹性常数并对其力学性能进行评估.计算得到的杨氏模量、剪切模量、柯西压力及体模量与剪切模量等表明当合金中Ta的含量在10 wt.%左右时,合金具有较高的强度和良好的塑性.为了检验计算结果,合成了V-10 wt.%Ta,V-15 wt.%Ta,V-20 wt.%Ta等不同Ta含量体系,并对其力学性能进行表征,实验所得结果与计算相吻合,为通过计算设计合金提供了一种可行思路.     

Effect of vacuum arc ion beam treatment on the structure and mechanical properties of 30CrMnSiNi2A steel

The paper reports on a study of the structure and mechanical properties of 30CrMnSiNi2A high-strength steel irradiated with a Zr+ ion beam. The effect of irradiation on the steel was assessed by optical, transmission, and scanning electron microscopy as well as by X-ray di ITraction analysis of its irradiated and non-irradiated specimens 1 mm thick under static and cyclic tension, showing an increase in the fatigue life of the steel after irradiation. The deformation behavior and the mechanical properties of the specimens were compared, and the factors responsible for the increase in fatigue life were analyzed.     

晶体塑性有限元方法研究辐照对多晶铜力学性能的影响

将辐照硬化理论与晶体塑性理论结合, 运用ABAQUS有限元分析软件模拟辐照后多晶铜的拉伸过程。分析辐照效应对材料屈服强度、硬化过程、晶体变形等力学性能的影响, 研究位错密度的演化及空间分布规律。数值模拟表明: 辐照效应提高多晶铜的屈服应力, 影响不同阶段的硬化和软化现象; 辐照剂量增大导致位错密度增殖总体变缓, 空间不均匀度增大; 晶体的塑性变形及晶体转动也受到辐照的影响, 在相同的应变条件下, 辐照剂量越大, 晶体塑性变形程度越小, 塑性变形分布不均匀度变大, 同时晶体转动程度及转动角离散度增大。     

非晶物质中的临界现象

非晶态材料有着复杂的原子结构(短程有序、长程无序)和特殊的物理性质,其临界现象和相变问题一直受到学术界关注.非晶合金,又称为金属玻璃,是一种新型的非晶态材料,具有很高的强度和优异的弹性.从微观的角度来看,非晶合金可以看作是一个多粒子系统.临界现象的研究对认识和理解多粒子系统之间的相互作用有深刻的意义.本文主要讨论非晶合金中的临界现象,包括非晶合金从制备过程、微观结构到宏观的力学性能以及磁性方面存在的临界现象,并分析这些临界现象之间的内在联系,进而深入理解非晶合金的微观结构对其宏观性质的影响.这为认识非晶合金的形成本质,提高服役可靠性,探索具有实际应用价值的非晶合金提供理论依据.     

W/Fe/CuCrZr热等静压模块组织及性能分析

为实现面向等离子体材料钨(W)和热沉材料铜铬镐(CuCrZr)合金的可靠连接,对纯铁(Fe)作为W/CuCrZr合金热等静压连接中间层的可行性进行了探索性研究.在850℃/150MPa/135min的热等静压参数下制作了W/Fe/CuCrZr合金的实验模块,分别对连接界面进行了焊接界面、微观形貌、组织成分及剪切力学性能...     

Microstructure,phase transformations,and properties of a Cu<Subscript>3</Subscript>Pd alloy subjected to severe plastic deformation

The structure of a preliminary ordered Cu₃Pd alloy, both with layered and columnar periodic structures, subjected to severe plastic deformation with twist extrusion with subsequent annealing, has been investigated using transmission electron microscopy; X-ray diffraction; and measurements of the resistance, magnetic susceptibility, and microhardness. The purpose of this study is the formation of nano-and submicrocrystalline structures in this alloy in order to improve the strength properties, with conservation of the ordered state determining the high conductivity of the alloy.     

Formation of the composition and topography of surface layers of Cu50Ni50 foils under laser irradiation

The influence of the laser radiation power density on the changes in the composition and mechanical properties of surface layers of Cu₅₀Ni₅₀ foils has been investigated using X-ray photoelectron spectroscopy, scanning probe microscopy, X-ray diffraction, and microhardness measurements. It has been found that, after laser irradiation, the redistribution of elements occurs in the surface layer with a thickness of ～30 nm on the irradiated side of the foil. It has been revealed that there are microdistortions in the crystal lattice of the alloy, microdeformations of grains, and variations in the microhardness of the irradiated surface. The mechanisms explaining the observed changes in the foils after laser irradiation have been proposed.     

The drawing behavior of linear polyethylene: Effect of electron irradiation on drawing and subsequent mechanical behavior of drawn products

Isotropic monofilaments of linear polyethylene were subjected to electron irradiation in different atmospheres at a range of dose levels. It was found that the gel content remained very small up to a dose of about 2.5 Mrad (the gel point), and thereafter increased with irradiation dose in a manner similar to that found by other workers. Drawing of the irradiated filaments was very dependent on dose level, and high draw ratios of 30:1 could not be obtained above the gel point. Although irradiation of the spun monofilaments increased the initial tensile modulus of the drawn material to a small extent, neither the tensile strength nor the shear strength of the monofilaments (the latter measured with a pull-out adhesion technique) was significantly affected. On the other hand, the tensile strain at failure decreased dramatically as the irradiation dose was increased. The results are discussed in terms of our present state of knowledge regarding the structure and properties of highly drawn linear polyethylene, taking into consideration the cross-linking produced by the irradiation.     

Thermally activated deformation in some neutron ibradiated binary nickel alloys

Low temperature deformation behaviour of some neutron irradiated, binary nickel alloye, Ni-1%Ti, Ni-5%Ti and Ni-8%Fe has been investigated in 77–300 X temperature range. The studies have confirmed the irradiation induced defects responsible for both the changes in thermally activated deformation parameters and radiation hardening     

Comparison of the Mechanical Properties and the Ballistic Behavior in Heracron®/Phenol Composite after Plasma Treatment

In this study, aramid, Heracron^®, which was purchased from Kolon Inc., Korea, and phenol composites were prepared by plasma treatment and the influence of this plasma treatment on their mechanical properties and ballistic behavior were ascertained. By measurement of water contact angle and XPS analysis, we find that the plasma treatment may help the incorporation of functional oxygen groups on the surface of the Heracron^® fabrics. Additionally, the surface roughness of Heracron^® fiber may be proportional to the plasma treatment times. By SEM and mechanical tests, it was shown that plasma-treated Heracron^®/phenol composites exhibited higher mechanical properties compared with plasma-untreated Heracron^®/phenol composites. Based on this finding, we can conclude that plasma-treatment can promote the interfacial adhesion between Heracron^® and phenol, resulting in the superior mechanical properties of their composites. However, the ballistic behavior conflicted with the mechanical properties. That is to say, a helmet, manufactured from the plasma-treated Heracron^®/phenol composites, exhibited lower ballistic properties than that of the plasma-untreated Heracron^®/phenol composites. As a result, we demonstrated that for ballistic application, somewhat weak fiber–matrix adhesion leads to the improved ballistic behavior. However, it becomes apparent that the optimum strength condition for the composite interphase depends on the particular application, thus increased fiber–matrix adhesion may be more appropriate.