RII Track-4: NSF: Establish predictive crystal plasticity models with complete deformation twinning mechanisms

镁的密度仅为钢的四分之一，铝的三分之二。由于镁的高强度密度比，用镁合金取代汽车和航空航天工业中的传统结构金属不仅可以提高国家的能源效率，还可以减少温室气体的排放。但Mg及其合金变形后易断裂，严重限制了Mg的市场渗透率。不幸的是，变形机制，特别是在原子水平上，仍然是难以捉摸的，这阻碍了有效策略的发展，以控制镁合金的变形行为和性能。本项目旨在研究镁的变形机制，然后建立一个可靠的多尺度模型，整合这些机制；该模型可用于预测Mg及其合金的变形行为。拟议的研究将通过加速轻量化和延展性镁合金的发展，以取代传统的钢和铝合金，在汽车和航空航天工业产生深远的社会影响。该项目还将在内华达大学里诺分校（UNR）开展创新的K-12金属和变形行为教育，包括实验室参观、科学演示和面向K-12学生和教师的工程游戏。在原子尺度上，Mg的变形主要由位错滑移和孪晶控制。然而，到目前为止，孪生是如何开始、发展和与其他孪生模式或错位相互作用的仍然是难以捉摸的。因此，该项目的首要目标是开发高保真的多尺度变形模型，以描述和预测Mg及其合金的变形行为，这将指导汽车和航空航天工业中更具延展性的Mg合金的开发。这需要在原子尺度和介观尺度上对变形机制有更深的理解和改进的建模，并且需要通过多尺度模型实现两个尺度之间的连贯联系。为了实现这一目标，将追求两个综合研究目标：1)利用最先进的第一性原理计算和基于深度神经网络的分子动力学模拟，建立孪生和位错的原子水平成核条件；2)在连续级晶体塑性建模中实现这些原子级变形机制，并与实验数据进行验证。该项目的成功完成将推进Mg变形孪晶的知识状态，实现Mg的高保真变形建模，从而加快镁合金的研究和开发。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。

The density of magnesium (Mg) is only about one-fourth that of steels and two-thirds that of aluminum. Due to the high strength-to-density ratio of Mg, replacing those conventional structural metals in the automotive and aerospace industries with Mg alloys not only improves the nation’s energy efficiency, but also reduces the emission of greenhouse gases. However, Mg and its alloys tend to break easily upon deformation, which has seriously limited the market penetration of Mg. Unfortunately, the mechanism of deformation, particularly at the atomic level, has remained elusive, which has hampered the development of effective strategies to control the deformation behaviors and properties of Mg alloys. This project aims to investigate the mechanisms of Mg deformation and then develop a reliable multiscale model that integrates those mechanisms; this model can then be used to predict the deformation behaviors of Mg and its alloys. The proposed research will have a profound societal impact by accelerating the development of lightweight and ductile Mg alloys to replace conventional steels and aluminum alloys in the automotive and aerospace industries. This project will also lead to innovative K-12 education on metals and deformation behaviors at the University of Nevada, Reno (UNR), including lab tours, science demos, and engineering games for K-12 students and teachers.Deformation of Mg is mostly governed by dislocation slips and twinning at the atomic scale. However, how twinning initiates, evolves, and interacts with other twinning modes or dislocations has so far remained elusive. Thus, the overarching goal of this project is to develop high-fidelity multiscale deformation models to describe and predict the deformation behaviors of Mg and its alloys that will guide the development of more ductile Mg alloys for the automotive and aerospace industries. This demands a deeper understanding and improved modeling of deformation mechanisms at both the atomic scale and the mesoscopic scale and, furthermore, achieve a coherent connection between the two scales via multiscale models. To achieve this goal, two integrated research objectives will be pursued: 1) establish the atomic-level nucleation conditions of twinning and dislocation using state-of-the-art, first-principles calculations and deep neural network-based molecular dynamics simulations; and 2) implement those atomic-level deformation mechanisms in continuum-level crystal plasticity modeling to validate against experimental data. The successful completion of this project will advance the state of knowledge of deformation twinning in Mg and enable high-fidelity deformation modeling of Mg, which can accelerate research and development of Mg alloys.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.