CAREER: Precipitation Pathways and Deformation Micromechanisms of Refractory Superalloys (RSAs)

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). PART 1: NON-TECHNICAL SUMMARY

The disruptive potential of a superior class of high-temperature structural materials is immense, and would revolutionize the energy sector and aerospace industry while advancing our military technologies. For example, such materials would enable stationary gas turbines (which produce 40% of all U.S. electricity) and aerospace gas turbines (which account for 5% of man-made global warming) to operate at higher temperatures.

Higher engine temperatures provide greater engine efficiency and boost power output from powerplants and aviation, contributing to a stronger economy while reducing greenhouse gas emissions and enabling tactical superiority for military aircraft. The recent discovery of refractory high entropy superalloys (RSAs) that possess excellent combinations of high strength and ductility at room-temperature and elevated temperature is extremely promising, especially as normal refractory alloys are typically brittle under ambient conditions.

The proposed research identifies knowledge-gaps regarding deformation mechanisms, microstructure stability at high temperatures and addresses these gaps through advanced materials characterization, mechanical testing and simulation, including National Laboratory facilities. Such analysis and understanding are critical for accelerated materials development to realize next-generation powerplants and aerospace engines.

This project not only meets demands for advanced materials but synergistically reduces talent gaps in science and engineering. The University of Miami College of Engineering is collaborating with the Phillip and Patricia Frost Museum of Science, which receives approximately 700,000 visitors annually. The collaboration serves to increase awareness and interest in metallurgy, and its impact on lowering CO2 and energy footprints of air travel and electricity production, through integration of ongoing research and education initiatives.

PART 2: TECHNICAL SUMMARY

The project goal is to study the precipitation, strengthening and deformation mechanisms of refractory high entropy superalloys (RSA) by specifically testing the hypotheses that (i) the precipitation formed on quenching is due to spinodal decomposition, which raises concerns regarding long-term stability of the two-phase microstructure, and that (ii) the excellent mechanical properties are due to co-deformation of both phases via activation of the a<111> slip system, given the preferred a<001>{001} mechanism does not satisfy the criterion for polycrystalline ductility. The application of in-situ small-angle x-ray and neutron scattering to determine the time dependent Fourier transform of the composition variation, and thereby directly test for spinodal decomposition, while simultaneously monitoring for phase transformations in a wide-angle detector, significantly contributes to the understanding of precipitation pathways in alloys.

In-situ neutron diffraction during elastic loading provides fundamental data (such as phase stiffnesses) necessary for phase field simulations regarding microstructure evolution. In-situ diffraction during plastic deformation combined with TEM dislocation analysis probes the deformation micromechanics and reveals why RSAs exhibit a combination of strength and ductility, whereas refractory (single-phase) alloys are typically brittle at ambient temperature.

The fundamental research regarding phase evolution, spinodal decomposition and slip systems within body-centered cubic alloys is significant across multiple alloy systems, essential for the development of RSAs, and necessary to advance high-temperature metallurgy. The STEM talent gap is addressed through a tight integration of research and education.

The development of an undergraduate course that offers an educational opportunity to perform research alongside faculty and industry engineers enhances materials education in South Florida. The lack of diversity in STEM is addressed through a multi-step program, where U. Miami is ideally located in a majority-minority city and educates a highly diverse student body.

Significant awareness and understanding in metallurgy is generated through partnership with the Frost Science Museum, where statistical surveys monitor success of these education and outreach activities.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.