Understanding Precipitation and the Mechanical Properties of Novel Laves Phase-Strengthened Austenitic Steels for Energy Applications

本项目旨在了解变形对Laves相强化奥氏体钢中析出过程的影响，包括确定NiAl共析出的机制，以及这两种析出物如何影响随后的变形过程。因此，本研究将通过对这些材料进行不同时间和温度的退火研究，包括事先冷轧和不冷轧，以及室温拉伸试验和高温蠕变试验，以及事后TEM检查，来确定析出机制和滑动位错与这些析出物的相互作用。断裂行为也将通过在扫描电子显微镜下进行不同温度下的原位应变研究来检查。将利用电子衍射仔细研究各种热处理和蠕变变形后相之间的取向关系，同时利用透射电镜和原子探针层析成像中的能量色散光谱确定微化学性质。在不同温度下，分别进行原位退火研究和原位应变研究，进一步阐明析出过程和变形机制。这项工作将由一名博士生和几名本科生完成。限制发电厂在高温下运行的关键因素是缺乏坚固、耐腐蚀和经济上可行的材料。在高温下运行可以使能量转换效率达到50%，这不仅可以降低运行成本，还可以延长化石燃料的使用寿命和/或减少工厂的碳足迹。不幸的是，目前使用的钢不能满足更高工作温度的这些要求。该项目旨在确定新型不锈钢的最佳加工条件和机械性能，这些不锈钢采用新型颗粒增强，并与铝合金结合以提高抗氧化性。一名博士生和几名本科生正在进行这项工作。

TECHNICAL SUMMARYThis project aims to understand both the effects of deformation on the precipitation processes in Laves phase-strengthened austenitic steels, including determining the mechanism of NiAl co-precipitation, and how these two kinds of precipitates affect subsequent deformation processes. Thus, the proposed work will determine both the precipitation mechanisms and the interaction of gliding dislocations with these precipitates by performing annealing studies for a variety of times and temperatures, both with and without prior cold rolling, and both room-temperature tensile tests and elevated-temperature creep tests on these materials followed by post-mortem TEM examination. The fracture behavior will also be examined by performing in-situ straining studies at a variety of temperature in a scanning electron microscope. The orientation relationships between the phases both after various thermo-mechanical treatments and after creep deformation will be carefully studied using electron diffraction, while the microchemistry will be determined using both energy dispersive spectroscopy in the TEM and atom probe tomography. The precipitation processes and the deformation mechanisms will be further elucidated by performing in situ annealing studies and in situ straining studies in the TEM, respectively, at a variety of temperatures. The work will be performed by a Ph.D. student and several undergraduates.NON-TECHNICAL SUMMARYThe critical factor limiting the operation of power generation plants at higher temperatures is the lack of materials that are strong, corrosion resistant and economically viable. Operation at high temperature can lead to energy conversion efficiencies of 50%, which not only reduces running costs, but can also extend the lifetime of fossil fuels and/or reduce the carbon footprint of the plants. Unfortunately, currently-used steels cannot satisfy these requirements for higher operating temperatures. This project aims to determine the optimum processing condition and mechanical properties in new class of stainless steels strengthened with novel particles, and alloyed with aluminum for improved oxidation resistance. A Ph.D. student and several undergraduates are performing the work.