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

需要将金属拉伸、弯曲并成形成有用零件的非技术性工艺通常需要使用非常高的压力来完成这项工作。这些超高压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，所有这些操作通常都是在事件完成后进行研究的。该奖项支持对正在发生的这些过程进行基本的定量研究，并专注于寻找新的定律，这些规律与金属的剧烈拉伸、它们在非常精细的尺度上的演变、在人类头发的量级上以及金属中伴随的变化，称为相变。在这个项目中，钛、钛和锆的混合物以及铝-铁-钴-镍-铜合金将在高压和应变率下进行研究，这是当前和未来材料技术的典型特征。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PI机构的特殊课程和研究、在被称为“同步加速器”的极高功率X射线设备上的实验以及实验和计算工作之间的相互作用来实现的，所有这些都侧重于未被充分代表的学生。技术摘要该项目的目标是进行基本的现场定量研究，并找到钛、钛和锆的混合物以及AlFeCoNiCu高熵合金中耦合严重塑性变形、纳米结构演变和相变的新规律。这些金属将在压力高达65 Gpa，应变率在10-5-103/S范围内的各种应变程序中进行探索。实验将使用动态旋转金刚石顶压室进行，通过对我们的假设进行定量检验，将得出理论上的优点，包括：(A)所有相的微晶尺寸和位错密度在相变前后是否获得与压力、应变和应变路径无关的稳态值，这是否取决于相变过程中的体积分数和/或应变率？(B)对于每个应变率，每个相是否表现为完全塑性、各向同性和与应变路径无关的材料？屈服强度的压力和应变率依赖于什么？(C)相变动力学是否与应变路径无关？(D)高应变率是否由于屈服强度增加而促进相变？以及(E)由于位错堆积的额外障碍，与单一材料的研究相比，钛-锆混合物中每种材料的相变是否会得到促进？将利用现场X射线衍射和反馈回路中的其他诊断方法，实时地确定动态旋转金刚石顶室中高度不均匀的应力场、塑性应变、应变率张量、相体积分数、微晶尺寸、位错密度和物种浓度的演变。此外，正在开发包括微观相场和基于物理的宏观模型的模拟以及实验的有限元模拟。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、相变演化、微晶尺寸、位错密度)，并最终确定定量模型。对于技术贡献以外的更广泛的影响，正在开发一门研究生课程，并与该项目一起为本科生、研究生和博士后提供研究方面的指导机会。该项目由金属和金属纳米结构计划和既定的激励竞争研究计划(EPSCoR)联合资助。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.