New Rules for Coupled Severe Plastic Deformations, Phase Transformations, and Structural Changes in Metals under High Pressure

非技术摘要需要极端拉伸、弯曲和将金属成型为有用部件的工艺通常涉及使用非常高的压力来完成。这些非常高压的方法被广泛用于制造内部和表面具有非常特殊性质的材料。然而，所有这些行动一般都是在事件完成之后进行研究的。该奖项支持对这些过程进行基本的定量研究，并专注于发现与金属的严重拉伸相关的新定律，它们在非常精细的尺度上的演变，人类头发的数量级，以及金属中伴随的变化，称为相变。在该项目中，钛、钛和锆的混合物以及铝-铁-钴-镍-铜合金正在当前和未来材料技术典型的高压和应变率下进行研究。此外，该项目还提供了在材料、高压科学和材料加工领域教育和培训本科生、研究生和博士后的机会。这是通过特殊的课程和研究在PI的机构，实验在一个非常高功率的x射线设施称为“同步加速器”和实验和计算工作之间的相互作用，所有的重点是代表性不足的学生。技术摘要该项目的目标是进行一个基本的原位定量研究，并找到新的规律耦合严重塑性变形，纳米结构的演变，以及Ti、Ti和Zr的混合物以及AlFeCoNiCu高熵合金中的相变。这些金属将在高达65 GPa的压力和10-5-103/s范围内的应变速率下通过广泛的应变程序进行探索。实验将使用动态旋转金刚石压砧单元进行，并从我们的假设的定量检查中得出知识价值，包括：（a）所有相的微晶尺寸和位错密度是否在相变前后获得与压力、应变和应变路径无关的稳态值，这取决于相变过程中的体积分数和/或应变速率吗？(b)对于每个应变率，每个相是否表现得像一个完全塑性的、各向同性的、与应变路径无关的材料？屈服强度与压力和应变率的关系是什么？(c)相变动力学与应变路径无关吗？(d)高应变率是否会因屈服强度增加而促进相变？和（e）由于位错堆积的额外障碍，与单一材料研究相比，钛锆混合物中每种材料的相变是否会得到促进？方法来确定高度不均匀的应力，塑性应变，应变率张量，相的体积分数，微晶尺寸，位错密度，和浓度的物种在动态旋转金刚石对顶砧单元的演变，所有在真实的时间，使用原位X射线衍射和其他诊断的反馈回路。此外，正在开发包括微尺度相场和基于物理的宏观尺度模型以及实验的有限元模拟在内的模拟。正在确定参数识别、机器学习、模型改进和所有材料特性（例如粘塑性、相变演变、微晶尺寸、位错密度），并且也正在最终确定定量模型。为了在技术贡献之外产生更广泛的影响，正在开发一门研究生课程，并为本科生提供研究方面的指导机会，该项目由美国金属和金属纳米结构计划和刺激竞争研究的既定计划（EPSCoR）共同资助该奖项反映了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 ABSTRACTProcesses that require extreme stretching, bending and forming of metals into useful parts typically involve using very high pressures to do so. These very high-pressure methods are used widely to create materials with very specific properties on the inside and at their surface. However, all these operations are generally studied after the events have been completed. This award supports a fundamental quantitative study of these processes while they are occurring and is focused on finding new laws that relate the severe stretching of metal, their evolution at a very fine scale, on the order of a human hair, and the accompanying changes in the metal, called phase transformations. In this project, Titanium, a mixture of Titanium and Zirconium, and an alloy of Aluminum-Iron-Cobalt-Nickel-Copper are being studied under high pressures and strain rates typical of current and future materials technologies. In addition, the project provides opportunities to educate and train undergraduate students, graduate students and a postdoc in the areas of materials, high-pressure sciences and materials processing. This is being accomplished through special courses and research at the PI’s institution, experiments at an extremely high-powered x-ray facility called a “synchrotron” and interaction between experimental and computational efforts, all with an emphasis on underrepresented students.TECHNICAL ABSTRACTThe goal of the project is to perform a fundamental in-situ quantitative study and find new laws for coupled severe plastic deformation, nanostructure evolution, and phase transformations in Ti, a mixture of Ti and Zr, and a AlFeCoNiCu high entropy alloy. These metals will be explored over a broad range of straining programs under pressures up to 65 GPa, and strain rates in the range 10-5-103/s. Experiments will be conducted using a dynamic rotational diamond anvil cell and the intellectual merit will be derived from the quantitative checking of our hypotheses, including: (a) Are crystallite size and dislocation density of all phases getting pressure-, strain- and strain-path-independent, steady-state values before and after phase transformations, and does this depend on the volume fractions during phase transformations and/or the strain rate? (b) Does each phase behave like a perfectly plastic, isotropic, and strain-path-independent material for each strain rate and what is the pressure and strain rate dependence of the yield strength? (c) Are phase transformation kinetics independent of strain path? (d) Does a high strain rate promote phase transformations due to increased yield strength? And (e) Will phase transformations in each material in the Ti-Zr mixture be promoted in comparison to single material studies due to additional obstacles for dislocation pileups?Methods to determine the evolution of highly heterogeneous fields of stress, plastic strain, strain rate tensors, volume fraction of phases, crystallite size, dislocation density, and concentration of species in a dynamic rotational diamond anvil cell will be developed, all in real time, using in-situ X-ray diffraction and other diagnostics in a feedback loop. In addition, simulations including a microscale phase field and physics-based macroscale model as well as a finite-element simulation of the experiments are being developed. Parameter identification, machine learning, model refinement, and all material properties (e.g. viscoplastic, evolution of phase transformations, crystallite size, dislocation density) are being determined, and quantitative models are also being finalized. For broader impacts beyond the technical contributions, a graduate course is being developed, and mentoring opportunities in research for undergraduate students, graduate students and a post-doc are being carried out in conjunction with this project.This project is jointly funded by the Metals and Metallic Nanostructures Program and the Established Program to Stimulate Competitive Research (EPSCoR).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.