GOALI: Crack Repair of Irradiated Stainless Steel by Friction Stir Processing

这项学术与工业联络资助机会（GOALI）奖支持基础研究，以揭示搅拌摩擦加工奥氏体不锈钢中sigma相和碳化铬形成的机制。欧拉有限元方法将用于预测搅拌区的温度，应变和应变速率，以便可以预测不同刀具速度和进料速度下的分数再结晶。建模工作将与实验相结合，以验证在避免动态再结晶的条件下进行摩擦搅拌处理可以最大限度地减少或消除sigma相和碳化铬形成的假设。通过电子后向散射衍射和透射电子显微镜对处理后的样品进行相识别，以进行模型验证。在辐照不锈钢上进行的热室实验将验证第二个假设，即摩擦搅拌处理可以在搅拌区域的热影响区不引起氦开裂。本研究将对搅拌摩擦加工奥氏体不锈钢中再结晶对西格玛相和碳化铬形成的作用提供基本的认识。基础研究成果将为修复核部件应力腐蚀裂纹提供新的途径。由于目前的熔焊工艺在修复已经辐照了20年或更长时间的部件时导致氦开裂，这种新方法有可能克服维护我们老化反应堆的主要技术挑战，这对国家能源基础设施和经济至关重要。其他的社会效益还包括教育那些准备为核工业做出贡献的学生，以及与高中教师合作开发新课程的推广项目，旨在鼓励女学生从事科学和工程方面的职业。

This Grant Opportunity for Academic Liaison with Industry (GOALI) award supports fundamental research to uncover the mechanisms of sigma phase and chromium carbide formation in friction stir processed austenitic stainless steel. An Eulerian finite element approach will be used to predict temperatures, strains, and strains rates in the stir zone so that fraction recrystallization can be predicted for different tool speeds and feed rates. The modeling work will be combined with experiments to test the hypothesis that sigma phase and chromium carbide formation can be minimized or eliminated when friction stir processing is done under conditions that avoid dynamic recrystallization. Phase identification will be performed on processed specimens by electron backscatter diffraction and by transmission electron microscopy for model validation. Hot cell experiments on irradiated stainless steel will test a second hypothesis that friction stir processing can be done without causing helium cracking in the heat affected zone of the stirred region. This research will provide fundamental understanding of the role of recrystallization on sigma phase and chromium carbide formation in friction stir processed austenitic stainless steel. A new approach for repairing stress corrosion cracks in nuclear components will emerge from the fundamental research results. As current fusion welding processes cause helium cracking during repair of components that have been irradiated for twenty or more years, this new approach has the potential of overcoming a major technical challenge in maintaining our fleet of aging reactors, which is critical to the national energy infrastructure and the economy. Additional societal benefits include the education of students who will be prepared to contribute to the nuclear industry, and an outreach program working with high school teachers on new curriculum development, aimed at encouraging female students to pursue careers in science and engineering.