NSUF 24-5033: Deciphering the role of nitrogen on the performance of ferritic-martensitic steels under high-dose irradiation using N-15 isotope doping

This project aims to investigate the role of nitrogen (N) in suppressing void formation and stabilizing nanosized nitride precipitates in ferritic-martensitic (FM) steels at high-dose irradiation. FM steels are promising candidates for advanced reactors due to their mature fabrication techniques and excellent radiation resistance. However, these materials face significant challenges, including creep at elevated temperatures (> 500 °C) and swelling at high doses. While oxide dispersion strengthening (ODS) has been proven effective in addressing these issues, scaling ODS steel fabrication economically remains a challenge. Tailoring intrinsic nanosized nitride precipitates offers a promising alternative for enhancing both the mechanical properties and radiation resistance of FM steels. Achieving this, however, requires a deeper understanding of how N solutes impact precipitate stability and void formation. A key challenge lies in characterizing the distribution of N within FM steels. While Energy Dispersive X-ray Spectroscopy (EDS) in Transmission Electron Microscopy (TEM) and Atom Probe Tomography (APT) can measure local element concentrations at the nanoscale, N's characteristic X-rays are heavily absorbed by nearby materials, complicating its quantification when its concentration is less than 1 at%. APT offers ultrahigh sensitivity for almost all elements, but overlaps between the Si28 +2 peak and the main N peak (14N+1) at mass/charge ratio=14 obscure N's detection in FM steels with high Si content. Doping FM steels with N-15, a stable isotope that does not overlap with major Si peaks, offers a unique opportunity to monitor N distribution and the stability of MX nitride precipitates. By characterizing the distribution of N and MX nitride precipitates in N15-doped FM samples, this project seeks to uncover mechanisms by which N solute atoms suppress void formation and stabilize MX precipitates under high-dose irradiation, providing a foundation for optimizing N concentrations to enhance FM steels' mechanical properties and resistance to swelling. Two key hypotheses are tested: (I) Increasing N concentration suppresses void growth by reducing dislocation bias through N segregation to dislocations, and (II) increasing N concentration stabilizes MX precipitates by enhancing N back diffusion. To achieve these objectives, dual-ion beam irradiation using Fe and He ions will simulate high-dose neutron damage. APT and TEM characterization will be used to investigate radiation-induced defects, including dislocation loops, cavities, and precipitates, as well as N segregation to these microscale features. In-situ ion irradiation in TEM will directly monitor the dissolution of MX precipitates, examining their stability at very high doses (~70 dpa). This comprehensive study provides valuable insights into improving FM steels for advanced reactor applications.

Additional Info

Field	Value
Award Announced Date	2024-08-15T09:37:00.193
Awarded Institution	Pennsylvania State University
Facility Tech Lead	Kevin Field, Kory Linton, Yaqiao Wu
Irradiation Facility	Michigan Ion Beam Laboratory
PI	Xing Wang
PI Email	[email protected]
Project Type	RTE
RTE Number	None