Understanding the Deformation Mechanisms in Austenitic Iron-Manganese Steels with Changes in Stacking Fault Energy, Strain Rate and Tempeature

为了理解奥氏体铁锰钢所表现出的复杂变形机制，包括相变诱发塑性（TRIP）、孪生诱发塑性（TWIP）和位错滑动，需要系统的力学测试，并将材料表征降至原子尺度。叠层断层能（SFE）随成分和温度的变化强烈影响着主动变形机制。尽管SFE的测定具有挑战性，而且大多数研究都依赖于计算值，但使用部分位错分离的弱光束暗场成像（WBDF）的仔细实验方法可以提供准确的SFE测量。除了成分和变形温度外，重要的显微组织和工艺参数还包括晶粒尺寸和应变速率。SFE与力学行为的相关性是建立对结构-性能-加工关系的基本理解的关键方面，这将允许未来设计新型高锰奥氏体钢的进展。在过去的五年中，与高锰奥氏体钢相关的研究活动显著增加，科学出版物和专利申请的数量都证明了这一点。由于其优异的延展性，应变硬化和韧性，这些钢是需要高成形性和能量吸收的应用的优秀候选者，例如汽车零件的冷冲压。该提案描述了范德比尔特大学、俄亥俄州立大学、德国工业大学和德国马克斯-普朗克研究所（Max-Planck-Institut f<e:2> r Eisenforschung）以及橡树岭国家实验室之间的合作，以解决高锰奥氏体钢未来发展所涉及的基础科学问题。这种国际合作不仅使个人研究人员的专业知识集中在了解这些合金的复杂变形机制上，而且还将促进研究生的教育，他们将从国际经验中受益。通过国际合作，加强学生的教育和培训。这些活动所带来的教育机会将通过范德比尔特-菲斯克桥项目提供给代表性不足的群体。

TECHNICAL SUMMARYTo understand the complex deformation mechanisms exhibited by austenitic iron-manganese steels, which include transformation-induced plasticity (TRIP), twinning-induced plasticity (TWIP), and dislocation glide, requires systematic mechanical testing with materials characterization down to the atomic scale. Changes in stacking-fault energy (SFE) with composition and temperature strongly influence the active deformation mechanism. Although the determination of SFE is challenging and most investigations rely on calculated values, careful experimental methods using weak-beam dark field (WBDF) imaging of partial dislocation separation can provide accurate SFE measurements. In addition to the composition and deformation temperature, important microstructural and processing parameters include grain size and strain rate. Correlation of the SFE with the mechanical behavior is a critical aspect for developing a basic understanding of the structure-property-processing relationships that will allow for future advances in the design of new high-manganese austenitic steels.NON-TECHNICAL SUMMARYIn the last five years, there has been a significant increase in the research activity associated with high-manganese austenitic steels as evidenced by both the number of scientific publications and patent applications. These steels are excellent candidates for applications requiring high formability and energy absorption such as cold-stamping of automotive parts owing to their exceptional ductility, strain-hardening, and toughness. This proposal describes collaboration between Vanderbilt University, the Ohio State University, the RWTH University and the Max-Planck-Institut für Eisenforschung in Germany, and the Oak Ridge National Laboratory to address the basic science involved with the future development of high-manganese austenitic steels. This international collaboration not only allows the combined expertise of the individual investigators to be focused on understanding the complex deformation mechanisms in these alloys, but it will also promote the education of graduate students who will benefit from the international experience. Student education and training will be enhanced through international collaborations. Educational opportunities enabled by these activities will be made available to under-represented groups through the Vanderbilt-Fisk Bridge program.