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

这一建议解决了晶体-晶体相变和非晶化的新现象，这种现象可以通过在显著低于熔化温度(1000K)的温度下进行虚拟熔化来发生。一些迹象表明，虚拟熔化可以作为各种结构变化的机制：金属和金属纳米线在高应变率加载下的塑性流动、断裂和升华。本项目的目标是发展多种理论和计算方法(结合实验)来研究虚拟熔化的主要特征，并探索这些现象在各种应用中的共性。将发展一般的连续介质热力学和动力学理论，以及相场理论和定量模型，并应用于相变、高应变率加载下的塑性流动、断裂和虚拟熔化升华的模拟。将对相同的现象和材料进行分子动力学模拟。与虚拟熔化相关的新机制有望在各种材料系统中应用，例如用于HMX炸药、医药和商业非线性光学介质中的相变，以及用于地质、电子和超硬材料的高压非晶化。理解基于机制的动力学将导致能够控制转换并寻找需要访问(或避免)的隐藏阶段。一名研究生将接受培训。将开展密切的跨学科合作。国际和平研究所将开设一门新的关于相变多尺度建模的研究生课程(可通过远程学习获得)，并将组织专门讨论相变问题的研讨会。

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.