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

Board Of Regents, Nshe, Obo University Of Nevada, Reno, Reno NV

Investigators

Abstract

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.