CAREER: Assessing Low Temperature Phase Stability through Irradiation

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NON-TECHNICAL DESCRIPTION:Alloys in long-term service at moderately elevated temperatures (200-500°C), fall into a technological gap, where temperature effects are very slow but become significant over time. This temperature range is essential in many important technological industries such as aerospace, energy production and petrochemical plants. Over the period of decades, these materials can degrade and no longer perform as designed, potentially causing safety concerns. Laboratory studies of alloy degradation at these temperatures still take many years to perform and is often impractical. This project proposes to use irradiation as a tool to accelerate low temperature diffusion by creating more defects in the lattice. This method is expected to speed up the phase transformations that degrade properties by several orders of magnitude, which would make laboratory studies feasible. A long term thermal aging experiment will be performed to benchmark the irradiation results and computational simulations of atomic diffusion will be performed to help explain the differences between the two methods. Successful demonstration of the irradiation-enhanced method will allows us to identify the evolution of new, stable low-temperature phases, and to predict the service lifetime of alloys in service. Additionally, we expect to be able to use this knowledge to design new alloys that are better suited to resist long-term thermal degradation. This project is also designed to act as a vehicle for both recruiting and retaining a future generation of engineers and scientists from under-represented groups. By integration with two mentoring programs that bring Oregon high school, undergraduate and graduate students, and the professor together, a pyramid of mentorship in the laboratory is being created. TECHNICAL DESCRIPTION:Alloys in long-term service at temperatures in the range of 200-500°C, fall into a technological gap, where atomistic diffusion is very slow but becomes significant and phase diagrams are, as a consequence of the slow diffusion, usually incomplete. This temperature range is essential in many important technological industries such as aerospace, energy production and petrochemical plants. By using irradiation as a positive tool for materials research we expect to be able to accurately acquire these low-temperature data through irradiation-enhanced phase transformations. Successful demonstration of the validity of this method will allow the identification of new, stable low-temperature phases, and to validate kinetic transformation models within a practical timeframe. A parallel computational study will be used to explain differences between thermal and irradiation-assisted phase transformation and give fundamental insight into the mechanisms that control the transformation in the Ni-Cr-Fe system. In turn, the design of new alloys better suited to meet forthcoming technological needs can be expected to become possible. The research components of this project advance work of the scientific community by generating an improved thermodynamic database for the Ni-Cr-Fe system and implementing it within a commercial software package. This project supports the broader goal of training the future materials workforce by arming them with state-of-the-art experimental methods and theoretical approaches for studying phase transformations. Additionally, this project will help to increase diversity in STEM fields through research opportunities for under-represented high school and undergraduate student groups through two different outreach programs. These research opportunities and a newly-developed didactic class will encourage students to explore opportunities in materials science, specifically metallurgy.