Virtual Melting and Amorphization as Mechanisms of Plastic Flow, Fracture, and Phase Transformations

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This proposal addresses the new phenomenon of crystal-crystal phase transformation and amorphization that can occur through virtual melting at temperatures significantly below (1000K) the melting temperature. Some indications were found that virtual melting may serve as mechanisms of various structural changes: plastic flow under high strain rate loading of metals and metallic nanowires, fracturing, and sublimation. The objective of this project is to develop multiple theoretical and computational approaches (coupled to experiment) to study the main features of virtual melting, and to explore the generality of the phenomena in various applications. General continuum thermodynamic and kinetic theories, as well as phase field theory and quantitative models, will be developed and applied to simulations of phase transformations, plastic flow under high strain-rate loading, fracture, and sublimation via virtual melting. Molecular dynamics simulations for the same phenomena and materials will be performed. New mechanisms related to virtual melting are expected in various material systems, e.g., for phase transformation in HMX explosive, pharmaceuticals, and commercial nonlinear optical media and for high-pressure amorphization in geological, electronic, and superhard materials. Understanding the mechanism-based kinetics will lead to ability to control the transformations and look for hidden phases that need to be accessed (or avoided). One graduate student will be trained. Intense interdisciplinary collaboration will be developed. The PI will develop a new graduate course on multiscale modeling of phase transformations (available via distance learning) and will organize symposia devoted to the phase transformations.