Deformation of Metals under High Pressure: Multiscale Stress Fields, Plasticity, and Phase Transformations

非技术摘要：涉及高压和塑性变形的过程在材料合成和技术中非常常见，例如高压扭转（或扭转）。这些技术的主要目标是生产具有对工程应用重要的独特物理特性的高压相和纳米结构。然而，缺乏对物理机制的理解以及表征和控制高压下塑性变形、相变和微观结构的同时演化的方法。该项目的目标是进行第一次耦合实验，理论和计算多尺度研究的非均匀应力和应变，塑性流动，相变在几个技术上重要的金属在高压和剪切变形。实验研究将在旋转金刚石砧室中进行，这是一种独特的装置，其中材料被两个金刚石砧压缩到高压，然后扭曲。钻石的透明度允许直接在加载的样品中测量应变和研究各种相变。实验研究将与先进的多尺度建模相结合，从而能够在高压下提取所有变形和转换材料特性。该项目产生的新科学预计将影响现有和未来的纳米颗粒高压相合成技术。由于这项工作的跨学科性质，两名研究生和两名本科生将接受培训，学习，开发和应用尖端的实验和计算技术，以各种复杂的系统。技术摘要：涉及高压和塑性变形的过程是相当常见的材料合成和技术，在自然界（例如在物理学），并在物理实验。高压通常会导致固体的相变，而塑性应变会显著改变相变的微观结构、热力学和动力学。然而，缺乏对高压下位错和相变同时演化的物理机制和方法的理解。该项目的目标是进行第一个耦合的实验，理论和计算的应力和应变场，位错塑性，应变诱导的相变在Zr，Fe，Ce和CeP高压和剪切变形下的多尺度研究。实验研究将在旋转金刚石压砧单元中进行，这是一种独特的装置，其中材料被压缩到高压，然后扭曲，同时提供了现场测量和研究各种相变和应变的机会。分子动力学和纳米级相场的方法将被用来模拟应力场和成核缺陷，耦合到同步X射线显微衍射测量。应变控制相变的动力学将根据相的体积分数来确定。在宏观尺度上，将测量和模拟旋转金刚石对顶砧单元中整个样品内的应力张量、位移、塑性应变和高压相的体积分数的场的演化。因此，所有的变形和转换材料的性能将在高压下确定。Ce和CeP的纯体积相变受塑性剪切影响的假设将被检查。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical abstract:Processes that involve high pressures and plastic deformations are quite common in material synthesis and technologies, e.g. in high-pressure torsion (or twisting). The main objective of these technologies is to produce high-pressure phases and nanostructures that possess unique physical properties important for engineering applications. However, an understanding of the physical mechanisms and ways to characterize and control simultaneous evolution of plastic deformations, phase transformations, and microstructure under high pressure is lacking. The goal of the project is to conduct the first coupled experimental, theoretical, and computational multiscale study of non-uniform stresses and strains, plastic flow, and phase transformations in several technically-important metals under high pressure and shear deformation. The experimental study will be performed in a rotational diamond anvil cell, a unique device in which material is compressed by two diamond anvils to high pressure and then twisted. The transparency of the diamonds allows for measurements of strains and study of various phase transformations directly in the loaded sample. The experimental study will be combined with advanced multiscale modeling, enabling extraction of all deformational and transformational material properties at high pressure. New science produced in the project is expected to impact existing and future technologies for synthesis of the nanograined high-pressure phases. Due to the interdisciplinary nature of the proposed work, two graduate and two undergraduate students will be trained to learn, develop, and apply cutting-edge experimental and computational techniques to a variety of complex systems.Technical abstract:Processes involving high pressures and plastic deformations are quite common in material synthesis and technologies, in nature (e.g. in geophysics), and in physical experiments. High pressure usually causes phase transformations in solids and plastic straining significantly changes the microstructure, thermodynamics, and kinetics of phase transformations. However, an understanding of the physical mechanisms and ways to characterize simultaneous evolution of dislocations and phase transformations under high pressure is lacking. The goal of the project is to conduct the first coupled experimental, theoretical, and computational multiscale study of stress and strain fields, dislocational plasticity, and strain-induced phase transformations in Zr, Fe, Ce, and CeP under high pressure and shear deformation. The experimental study will be performed in a rotational diamond anvil cell, a unique device in which material is compressed to high pressure and then twisted, while providing an opportunity for in situ measurements and study of various phase transformations and strains. Molecular dynamics and a nanoscale phase field approach will be used to model stress-field and nucleation at defects, coupled to the synchrotron X-ray microdiffraction measurements. The kinetics of strain-controlled phase transformations will be determined in terms of volume fraction of phases. At the macroscale, the evolution of the fields of the stress tensor, displacements, plastic strain, and the volume fraction of high-pressure phases within the entire sample in a rotational diamond anvil cell will be measured and simulated. As a result, all deformational and transformational material properties will be determined at high pressure. The hypothesis that the pure volumetric phase transformations in Ce and CeP are affected by plastic shear will be checked.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.