DMREF/Collaborative Research: Multi-Scale Modeling and Characterization of Twinning-Induced Plasticity and Fracture in Magnesium Alloys

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The goal of this Designing Materials to Revolutionize and Engineer our Future (DMREF) collaborative research grant is to identify fundamentally validated mean-field and full-field models capable of predicting failure in Mg alloys. This is a critical step for developing materials design concepts to enable the use of lightweight Mg alloys in safety critical applications or development of deformation processing strategies. A critical, fundamental gap in the understanding of Mg alloy deformation relates to dislocation-dislocation, dislocation-twin, twin-twin, and twin-grain boundary (GB) interactions and their effects on strain hardening and damage initiation. It is now understood that (i) interactions between twin variants, such "autotwinning" and double twinning, catalyze macroscopic shear localization and (ii) crack nucleation takes place at twin-GB and twin-twin intersections. The ability to predict and mitigate these behaviors lags. Unless these issues are solved, Mg alloys will be relegated to cast components in non-safety critical applications. A multi-scale approach is required, because key mechanisms operate at different length scales: 1. atomistic (dislocation core interactions with other dislocations and with twin boundaries, and decohesion); 2. microscopic (dislocation-dislocation, dislocation-twin, and twin-twin interactions); 3. mesoscopic (twin-parent grain and grain-grain compatibility interactions leading to backstress and crack initation); and 4. macroscopic (applications to forming simulation or performance prediction design incorporating shear localization). The partners will employ TEM, in situ SEM and electron backscattered diffraction (EBSD) serial imaging techniques, and neutron and synchrotron X ray-based characterization to guide and validate models of the behavior at the corresponding length scales.These models will greatly aid efforts to render lightweight Mg alloys "formable" and "crushable," so that society can exploit performance and efficiency benefits. This could help reduce potentially harmful greenhouse gas emissions by broader application of lightweight Mg alloys in the transportation sector. Additionally, the multiscale modeling concepts under development can be modified for application to numerous other materials, which deform by similar mechanisms of twinning or martensitic transformation: such as Be, Co, Ti, U, and Zr alloys, Advanced High Strength Steels (e.g. TWIP and TRIP), and shape memory alloys. Finally, the collaboration seeks to develop young scientists and engineers, trained to work in a cutting-edge research environment, providing them with an excellent preparation for future industrial or academic research, which increasingly requires a working knowledge of both theory and experiment.