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

这项设计材料以革命和工程我们的未来（DMREF）合作研究基金的目标是确定能够预测镁合金失效的基本验证的平均场和全场模型。这是开发材料设计概念的关键步骤，以使轻质镁合金能够用于安全关键应用或开发变形加工策略。 在理解镁合金变形方面的一个关键的、根本的差距涉及位错-位错、位错-孪晶、孪晶-孪晶和孪晶-晶界（GB）相互作用及其对应变硬化和损伤引发的影响。现在理解的是，（i）孪晶变体之间的相互作用，例如“自孪晶”和双孪晶，催化宏观剪切局部化，以及（ii）裂纹成核发生在孪晶-GB和孪晶-孪晶相交处。预测和减轻这些行为的能力滞后。除非这些问题得到解决，否则镁合金将被降级为非安全关键应用中的铸造部件。 需要多尺度方法，因为关键机制在不同的长度尺度上操作：1。原子的（位错核与其他位错、孪晶边界的相互作用以及退粘）; 2.微观（位错-位错、位错-孪晶和孪晶-孪晶相互作用）; 3.介观（导致背应力和裂纹起始的孪晶母颗粒和颗粒-颗粒相容性相互作用）;以及4.宏观（应用于成形模拟或结合剪切局部化的性能预测设计）。合作伙伴将采用TEM、原位SEM和电子背散射衍射（EBSD）系列成像技术，以及基于中子和同步辐射X射线的表征，指导和验证相应长度尺度下的行为模型。这些模型将极大地帮助实现轻质镁合金的“可成形”和“可压碎”，从而使社会能够利用性能和效率优势。这将有助于减少潜在的有害温室气体排放，因为轻质镁合金在交通运输领域的广泛应用。此外，开发中的多尺度建模概念可以修改以应用于许多其他材料，这些材料通过类似的孪晶或马氏体相变机制变形：例如Be，Co，Ti，U和Zr合金，高级高强度钢（例如TTRIP和TRIP）和形状记忆合金。最后，该合作旨在培养年轻的科学家和工程师，经过培训，在尖端的研究环境中工作，为他们未来的工业或学术研究提供良好的准备，这越来越需要理论和实验的工作知识。

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.