摘要:

The report consists of two parts: First it is shown that the initial momentum anisotropy of a PKA of 3 keV is modulated into near isotropy during the collisional phase of displacement cascades using molecular dynamics simulation. Secondly in the case of a PKA of the order of 100 MeV, in which electron-bursts are produced by energetic recoil-atoms, a possible new mechanism of defect-production caused by such electron-bursts is proposed.

ISSN:1042-0150    

DOI:10.1080/10420159408228881

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:1042-0150    

DOI:10.1080/10420159408228882

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We employ molecular statics and molecular dynamics computer simulation methods to study structural relaxation of small (⟨10) vacancy and interstitial clusters in Cu. Vacancy clusters whose sizes are below four do not relax much, but clusters larger than five were found to relax appreciably, often into a stacking fault tetrahedron and an octahedral void. It was found that stacking fault tetrahedra of hexa-vacancies relax to a void. Interstitials were introduced into bcc positions. A di-interstitial was found to relax to two parallel ⟨110⟩ split interstitials and tri- and tetra-interstitials relaxed to composite clusters of ⟨100⟩ split interstitials and a bcc interstitial. Penta- and hexa-interstitials form agglomerates of parallel ⟨110⟩ crowdions whose central portions are not on a single (111) plane. Such structures allow easy motion of these clusters along ⟨110⟩ directions under stress. Such movement of interstitial clusters has been observed by electron microscopy in neutron-irradiated Au and Cu.

ISSN:1042-0150    

DOI:10.1080/10420159408228883

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In the present paper, important results of our recent computer simulation of radiation-induced amorphization in the ordered compounds CuTi and Cu4Ti3are summarized. The energetic, structural, thermodynamic and mechanical responses of these intermetallics during chemical disordering, point-defect production and heating were simulated, using molecular dynamics and embedded-atom potentials. From the atomistic details obtained, the critical role of radiation-induced structural disorder in driving the crystalline-to-amorphous phase transformation is discussed.

ISSN:1042-0150    

DOI:10.1080/10420159408228884

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An analysis of experimental observations on irradiation-induced amorphization has been used to establish a phenomenological basis for developing a theory on the atomistic mechanisms responsible for this transition. Once the mechanisms are formulated, modeling can be done using various complementary mathematical approaches, viz., rate theory, to describe the kinetics, and atomistic simulations of defective systems through static relaxations and molecular dynamics. Results of rate theory and static relaxations are summarized here.

ISSN:1042-0150    

DOI:10.1080/10420159408228885

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We present two aspects of the thermal behaviour of cascades, related to the mechanisms of heat transport. The first aspect concerns the PKA energy range where subcascades are produced and discusses the thermal interaction between them. For this description we couple the results of the Binary Collision Approximation (BCA) to a simplified solution of the heat equation. Comparison with Molecular Dynamics (MD) results when available supports this approach. However this analysis only considers lattice conductivity, neglecting the possible effects of electronic transport. In the second part of this presentation we consider the effects of the electronic energy loss on the dynamics of thermal spikes in Cu. This study is based on a simple model of the stopping power and the electron phonon interaction in the framework of the Embedded Atom Model (EAM) for MD. This approach is only valid for weak-coupling systems, like Cu, where we obtain quantitative information on the effect.

ISSN:1042-0150    

DOI:10.1080/10420159408228886

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The processes of radiation damage, from initial defect production to microstructure evolution, occur over a wide spectrum of time and size scales. An understanding of the fundamental aspects of these processes requires a spectrum of theoretical models, each applicable in its own time and distance scales. As elements of this spectrum of models, molecular dynamics and binary collision simulations play complementary roles in the characterization of the primary damage state of high energy collision cascades. Molecular dynamics is needed to describe the individual point defects in the primary damage state with the requisite physical reality. The binary collision approximation is needed to model the gross structure of statistically significant numbers of high energy cascades. Information provided by both models is needed for connecting the defect production in the primary damage state with the appropriate models of defect diffusion and interaction describing the microstructure evolution.

ISSN:1042-0150    

DOI:10.1080/10420159408228887

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The dynamics of point defect production in β-SiC is studied using the Molecular Dynamics (MD) technique. A hybrid pair/three-body potential developed by E. Pearsonet al.10is used to model interatomic forces. The bulk displacement energies are found for Si and C atoms along selected crystallographic directions within the ⟨111⟩ tetrahedral gaps. It is found that Si atoms have higher displacement energies than C atoms for all directions. Si displacement energy is found to be ∼52 eV, while that of C is only ∼10 eV through the ⟨111⟩ gap. Focused cascades along the close-packed [111] direction contribute to displacements in β-SiC but, replacement collision sequences are not likely to occur. Displaced atoms come to equilibrium in hexagonal interstitial sites between the (111) planes in most cases. Also, trivacancies tend to occur on the (111) carbon planes. The equilibrium cascade configurations are observed to be highly non-stoichiometric with the majority of displacements being of C type.

ISSN:1042-0150    

DOI:10.1080/10420159408228888

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Molecular dynamics (MD) calculations of the bulk threshold displacement energies in single crystal silicon are carried out using the Tersoff potential. The threshold values are angularly dependent and typically vary from 10 to 20 eV for initial primary recoil momentum vectors near open directions in the lattice. An analytic representation of the angular dependence of the threshold values about the ⟨1 0 0⟩ and ⟨1 1 1⟩ is developed to facilitate comparison with experiment.

ISSN:1042-0150    

DOI:10.1080/10420159408228889

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor