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

设计材料革新和设计我们的未来(DMREF)合作研究基金的目标是确定能够预测镁合金失效的基础上经过验证的平均场和全场模型。这是开发材料设计概念的关键一步，使轻质镁合金能够在安全关键应用或变形处理策略的开发中使用。理解镁合金变形的一个关键的基本差距涉及位错-位错、位错-孪晶、孪晶-孪晶和孪晶晶界(GB)的相互作用及其对应变硬化和损伤萌生的影响。现在可以理解的是：(I)孪生变体之间的相互作用，如“自孪生”和双孪生，催化宏观剪切局部化；(Ii)裂纹形核发生在孪生-GB和孪生-孪生交叉处。预测和缓解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。需要一种多尺度的方法，因为关键机制在不同的长度尺度上运行：1.原子(位错核与其他位错以及与孪晶界的相互作用和脱粘)；2.微观(位错-位错、位错-孪晶和孪晶-孪晶相互作用)；3.细观(孪晶母晶和晶-晶相容相互作用导致背应力和裂纹萌生)；以及4.宏观(应用于考虑剪切局部化的成形模拟或性能预测设计)。合作伙伴将使用透射电子显微镜、原位扫描电子显微镜和电子背散射衍射(EBSD)系列成像技术，以及基于中子和同步加速器X射线的表征来指导和验证相应长度尺度上的行为模型。这些模型将极大地帮助努力使轻质镁合金“可成形”和“可压碎”，从而使社会能够发挥性能和效率的好处。这可能有助于通过在交通部门更广泛地应用轻质镁合金来减少潜在有害的温室气体排放。此外，正在开发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生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TWIP和TRIP)和形状记忆合金。最后，合作旨在培养年轻的科学家和工程师，他们接受过在尖端研究环境中工作的培训，为未来的工业或学术研究提供良好的准备，这些研究越来越需要理论和实验方面的实用知识。

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.