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

Dartmouth College, Hanover NH

Investigators

Abstract

TECHNICAL SUMMARY This 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 SUMMARY The 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.