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

镁（Mg）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，不仅提高了国家的能源效率，还减少了温室气体的排放。然而，镁及其合金在变形时容易断裂，这严重限制了镁的市场渗透。然而，镁合金的变形机制，特别是原子水平的变形机制，至今仍不清楚，这阻碍了对镁合金变形行为和性能进行有效控制的研究。本项目旨在研究镁合金的变形机制，并建立一个可靠的多尺度模型，将这些机制整合在一起，然后使用该模型来预测镁及其合金的变形行为。这项研究将加速开发轻质和韧性镁合金，以取代汽车和航空航天工业中的传统钢和铝合金，从而产生深远的社会影响。该项目还将在里诺的内华达州大学（UNR）为K-12学生和教师提供有关金属和变形行为的创新教育，包括实验室图尔斯参观、科学演示和工程游戏。Mg的变形主要由原子尺度的位错滑移和孪生控制。然而，如何孪生启动，演变，并与其他孪生模式或位错的相互作用至今仍然难以捉摸。因此，该项目的总体目标是开发高保真多尺度变形模型来描述和预测镁及其合金的变形行为，这将指导汽车和航空航天工业开发更具延展性的镁合金。这就需要在原子尺度和介观尺度上更深入地理解和改进变形机制的建模，并且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）使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级成核条件; 2）在连续级晶体塑性建模中实现这些原子级变形机制，以验证实验数据。该项目的成功完成将推进镁的形变孪晶的知识水平，并实现镁的高保真形变建模，从而加速镁合金的研究和开发。该奖项反映了NSF的法定使命，通过使用基金会的智力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.