Excess Vacancy Enabled Transformations in Light Metal Alloys

轻金属合金制造的创新工艺促进了公共福利和国防安全，通过高效生产新材料，在不增加重量的情况下提供强度，应用于从车辆和防护设备到太空探索。该奖项支持有关原子结构如何响应极端温度和应变条件的基础科学研究，这些条件会导致称为空位的缺陷，即金属晶体结构中缺少原子。这项研究促进了对空位为什么以及如何与不同于原生金属的溶质原子聚集在一起的理解，聚集成称为空洞的小气泡，并促进强化颗粒的形成。采用多种实验技术：采用带正电的粒子测量缺陷；原子探针揭示不同元素在晶体结构中的位置；电子显微镜图像显示了更大尺度的特征，如空洞。模拟预测空位、溶质和空隙如何相互作用，以更好地解释实验数据。这些模拟还提供了空洞形成速率如何随温度、空位密度、溶质化学和密度变化的估计。实验数据用于指导仿真的选择和验证仿真的有效性。在此过程中，这项工作提高了仿真能力。该项目吸引了附近一所历史悠久的黑人大学摩根州立大学的本科生，以促进一个新兴项目的成功，该项目提供了该大学目前不提供的工程学位。调查人员还计划举办一个“极端空缺工程”研讨会。技术概述：提出的研究计划旨在通过扩展我们对空位过饱和如何以促进溶质聚集和金属间沉淀的方式改变空位聚集、空位-溶质络合物形成和空洞成核的热力学的基本理解，加速新轻合金和加工路线的发展。在一定范围的成分合金经受淬火和变形，以一种可控的方式提高空位密度。分析使用一种新兴的计算方法，过渡界面采样，加上目标表征使用正电子湮灭光谱，原子探针断层扫描，透射电子显微镜与分子动力学和蒙特卡罗模拟相结合。实验被用来指导模拟，模拟被用来解释实验。这项工作的目的是建立一个热力学的理解，以自由能途径的形式，避开经典的成核理论假设在非平衡系统的关键过程。该研究项目招收来自附近HBCU的摩根州立大学的本科生，以促进新兴的3+2项目的成功，该项目为材料相关工程专业开辟了新的途径。一个关于“极端空缺工程”的研讨会也有望促进一个新兴的材料加工和设计领域。该奖项反映了美国国家科学基金会的法定使命，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 SUMMARYInnovating processes for lightweight metal alloy manufacture advances public welfare and secures the national defense by enabling efficient production of new materials that provide strength without adding weight in applications from vehicles and protective equipment to space exploration. This award supports basic scientific studies regarding how atomic structures respond to extreme conditions of temperature and strain that result in defects called vacancies, where atoms are missing from the metal’s crystal structure. This research advances the understanding of why and how vacancies cluster with solute atoms that differ from the primary metal, gathering into small bubbles called voids and encouraging the formation of strengthening particles.Multiple experimental techniques are used: positively charged particles are used to measure defects; atom probe reveals locations of different elements in the crystal structure; and electron microscopy images show larger scale features such as voids. Simulations predict how vacancies, solute and voids interact to better interpret the experimental data. These simulations also provide estimates of how the rate at which voids form, varies with temperatures, vacancy densities, and solute chemistries and densities. Experimental data are used to guide the choices of simulations and to check the validity of the simulations. In the process, this work advances simulation capabilities.This project engages undergraduates from Morgan State University, a nearby historically Black university, to foster the success of a newly emerging program that provides access to engineering degrees not currently offered at that university. The investigators also are planning to host an “Extreme Vacancy Engineering” workshop.TECHNICAL SUMMARYThe proposed research program aims to accelerate the development of new light alloys and processing routes by expanding our fundamental understanding of how vacancy supersaturation alters the thermodynamics of vacancy clustering, vacancy-solute complex formation, and void nucleation in ways that promote solute clustering and intermetallic precipitation. Alloys over a range of compositions are subjected to quenching and deformation to enhance vacancy densities in a controlled manner. Analysis is performed using an emerging computational methodology, transition interface sampling, coupled with targeted characterization using positron annihilation spectroscopy, atom probe tomography, and transmission electron microscopy in concert with molecular dynamics and Monte Carlo simulation. Experiments are leveraged to guide simulations and simulations to interpret experiments. The work aims to build a thermodynamic understanding for key processes in the form of free energy pathways that eschew classical nucleation theory assumptions in out-of-equilibrium systems.This research program engages undergraduates from Morgan State University, a nearby HBCU, to foster the success of a newly emerging 3+2 program that opens new pathways into materials-related engineering majors. A workshop on “Extreme Vacancy Engineering” is also anticipated to promote an emerging field of materials processing and designThis 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.