Download or read book Dynamics of Radiation induced Amorphization in Intermetallic Compounds written by and published by . This book was released on 1992 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Dynamics of Radiation induced Amorphization in Intermetallic Compounds written by and published by . This book was released on 1992 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent progress in molecular-dynamics simulations of radiation-induced crystalline-to-amorphous transition in intermetallic compounds and the relationship between amorphization and melting are discussed. By focusing on the mean-square static displacement, which provides a generic measure of energy stored in the lattice in the forms of chemical and topological disorder, a unified description of solid-state amorphization as a disorder-induced, isothermal melting process can be developed within the framework of a generalized Lindemann criterion.
Download or read book Radiation induced Amorphization of Intermetallic Compounds written by and published by . This book was released on 1991 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the present paper, important results of our recent computer simulation of radiation-induced amorphization in the ordered compounds CuTi and Cu4Ti3 are 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. 25 refs., 4 figs.
Download or read book Radiation induced Amorphization of Intermetallic Compounds written by and published by . This book was released on 1991 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Atomistic Simulation of Radiation induced Amorphization of the B2 Ordered Intermetallic Compound NiTi written by and published by . This book was released on 1990 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: Amorphization of the B2 intermetallic compound NiTi under electron irradiation has been investigated using molecular dynamics. The effect of irradiation was simulated using two processes: (1) Ni and Ti atoms were exchanged, resulting in chemical disorder, and (2) Frenkel pairs were introduced, leading to the formation of stable point defects and also chemical disorder upon mutual recombination of interstitials and vacancies. After (approximately)0.4 exchanges per atom, the first process resulted in an energy increase of approximately 0.11 eV/atom and a volume increase of 1.91%. On the other hand, after introducing (approximately)0.5 Frenkel pairs per atom, the second process led to smaller increases of 0.092 eV/atom in energy and 1.43% in volume. The calculated radial distribution functions (RDFs) were essentially identical to each other and to the calculated RDF of a quenched liquid. The structure factor, however, showed that long-range order was still present after atom exchanges, while the introduction of Frenkel pairs resulted in the loss of long-range order. It was concluded that point defects are necessary for amorphization to occur in NiTi, although chemical disorder alone is capable of storing enough energy to make the transition possible. 18 refs., 3 figs.
Download or read book Radiation induced Crystalline to amorphous Transition in Intermetallic Compounds of the Cu Ti Alloy System written by and published by . This book was released on 1992 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent progress in molecular-dynamics studies of radiation-induced crystalline-to-amorphous transition in the ordered intermetallic compounds of the Cu-Ti system is discussed. The effect of irradiation was simulated by the generation of Frenkel pairs, which resulted in both the formation of stable point defects and chemical disorder upon defect recombination. The thermodynamic, structural and mechanical responses of the compounds during irradiation were determined by monitoring changes in the system potential energy, volume expansion, pair correlation function, diffraction patterns, and elastic constants. It was found that the intermetallics Cu4Ti3, CuTi, and CuTi2 could be rendered amorphous by the creation of Frenkel pairs, but Cu4Ti could not, consistent with experimental observations during electron irradiation. However, the simulations showed that Cu4Ti did become amorphous when clusters of Frenkel pairs were introduced, indicating that this compound may be susceptible to amorphization by heavy-ion bombardment. A generalization of the Lindemann criterion was used to develop a thermodynamic description of solid-state amorphization as a disorder- induced melting process.
Download or read book Atomistic simulation of radiation induced amorphization of intermetallic compounds written by Ramaswami Devanathan and published by . This book was released on 1993 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Statics and Dynamics of Alloy Phase Transformations written by Patrice E.A. Turchi and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 725 pages. Available in PDF, EPUB and Kindle. Book excerpt: The study of phase transformations in substitutional alloys, including order disorder phenomena and structural transformations, plays a crucial role in understanding the physical and mechanical properties of materials, and in designing alloys with desired technologically important characteristics. Indeed, most of the physical properties, including equilibrium properties, transport, magnetic, vibrational as well as mechanical properties of alloys are often controlled by and are highly sensitive to the existence of ordered compounds and to the occurrence of structural transformations. Correspondingly, the alloy designer facing the task of processing new high-performance materials with properties that meet specific industrial applications must answer the following question: What is the crystalline structure and the atomic configuration that an alloy may exhibit at given temperature and concentration? Usually the answer is sought in the phase-diagram of a relevant system that is often determined experimentally and does not provide insight to the underlying mechanisms driving phase stability. Because of the rather tedious and highly risky nature of developing new materials through conventional metallurgical techniques, a great deal of effort has been expended in devising methods for understanding the mechanisms contrOlling phase transformations at the microscopic level. These efforts have been bolstered through the development of fully ab initio, accurate theoretical models, coupled with the advent of new experimental methods and of powerful supercomputer capabilities.
Download or read book Irradiation induced Amorphization and Elastic Shear Instability in Intermetallic Compounds written by and published by . This book was released on 1989 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: Previously we reported a substantial ((approximately)50%) decrease in shear modulus prior to amorphization in Kr irradiated Zr3Al, and proposed that amorphization is triggered when the crystalline lattice becomes unstable against shear stress. In the present work, the relation between amorphization and shear elastic instability has been investigated in two additional compounds (FeTi and NiAl) during room temperature irradiation with 1.7-MeV Kr. A shear modulus was measured using Brillouin scattering; structural information was obtained in situ in a high voltage electron microscope interfaced to a tandem accelerator. During irradiation of FeTi, chemical disordering and a large ((approximately)40%) decrease of shear modulus were observed, and an amorphous phase developed subsequently. In contrast, NiAl remained crystalline and chemically ordered during irradiation, and exhibited only a (approximately)10% decrease in shear modulus. Hence, these two results provide further support that a shear instability triggers irradiation-induced amorphization. The shear instability mechanism may also apply to other solid-state amorphization techniques, e.g., hydrogen charging and mechanical deformation. 22 refs., 3 figs.
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 488 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Download or read book Disorder induced Amorphization written by and published by . This book was released on 1997 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt: Many crystalline materials undergo a crystalline-to-amorphous (c-a) phase transition when subjected to energetic particle irradiation at low temperatures. By focusing on the mean-square static atomic displacement as a generic measure of chemical and topological disorder, we are led quite naturally to a generalized version of the Lindemann melting criterion as a conceptual framework for a unified thermodynamic approach to solid-state amorphizing transformations. In its simplest form, the generalized Lindemann criterion assumes that the sum of the static and dynamic mean-square atomic displacements is constant along the polymorphous melting curve so that c-a transformations can be understood simply as melting of a critically-disordered crystal at temperatures below the glass transition temperature where the supercooled liquid can persist indefinitely in a configurationally-frozen state. Evidence in support of the generalized Lindemann melting criterion for amorphization is provided by a large variety of experimental observations and by molecular dynamics simulations of heat-induced melting and of defect-induced amorphization of intermetallic compounds.
Download or read book Energy Research Abstracts written by and published by . This book was released on 1994-02 with total page 484 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Disorder driven Nonequilibrium Melting Studied by Electron Diffraction Brillouis Scattering and Molecular Dynamics written by and published by . This book was released on 1999 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the present paper, a brief overview of the electron diffraction, Brillouin scattering and molecular dynamics studies of radiation-induced amorphization of ordered intermetallic compounds is presented. In these studies, measured changes in the velocity of surface acoustic phonons, lattice constant, and the Bragg-Williams long-range order parameter induced by irradiation were compared with the results of computer simulations of defect-induced amorphization. The results indicate that progressive chemical disordering of the superlattice structure during irradiation is accompanied by an expansion of the lattice and a large change in sound velocity corresponding to a (approximately) 50% decrease in the average shear modulus. The onset of amorphization occurs when the average shear modulus of the crystalline compound becomes equal to that of the amorphous phase. This elastic softening criterion for the onset of amorphization and the dependence of the average shear modulus on the long-range-order parameter are in excellent agreement with molecular dynamics simulations. Both the experimental observations and computer simulations confirm the predictions of the generalized Lindemann melting criterion which stipulates that thermodynamic melting of a defective crystal occurs when the sum of the dynamic and static mean-square atomic displacements reaches a critical value identical to that for melting of the defect-free crystal. In this broader view of melting, the crystal-to-glass transformation is a disorder-driven nonequilibrium melting process occurring at temperatures below the Kauzmann isentropic glass-transition temperature.
Download or read book Issues in Materials and Manufacturing Research 2011 Edition written by and published by ScholarlyEditions. This book was released on 2012-01-09 with total page 7150 pages. Available in PDF, EPUB and Kindle. Book excerpt: Issues in Materials and Manufacturing Research: 2011 Edition is a ScholarlyEditions™ eBook that delivers timely, authoritative, and comprehensive information about Materials and Manufacturing Research. The editors have built Issues in Materials and Manufacturing Research: 2011 Edition on the vast information databases of ScholarlyNews.™ You can expect the information about Materials and Manufacturing Research in this eBook to be deeper than what you can access anywhere else, as well as consistently reliable, authoritative, informed, and relevant. The content of Issues in Materials and Manufacturing Research: 2011 Edition has been produced by the world’s leading scientists, engineers, analysts, research institutions, and companies. All of the content is from peer-reviewed sources, and all of it is written, assembled, and edited by the editors at ScholarlyEditions™ and available exclusively from us. You now have a source you can cite with authority, confidence, and credibility. More information is available at http://www.ScholarlyEditions.com/.
Download or read book Metals Abstracts written by and published by . This book was released on 1996 with total page 1628 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Materials Transactions JIM written by and published by . This book was released on 2004 with total page 1016 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Materials Transactions written by and published by . This book was released on 2004 with total page 1012 pages. Available in PDF, EPUB and Kindle. Book excerpt:
