Impact of grain boundary character on the radiation-induced segregation morphology in proton-irradiated 316L austenitic stainless steel

Radiation-induced segregation (RIS) is a non-equilibrium kinetic phenomenon that occurs as a result of radiation damage and leads to the local depletion or enrichment of atoms at point-defect sinks such as grain boundaries and dislocation loops in metallic alloys. This segregation can be so strong that it leads to radiation-induced precipitation at these sinks. Segregation and precipitation at these microstructural features can result in the degradation of structural materials' properties. Large research efforts have been dedicated to understanding and controlling these undesirable microstructural evolutions. RIS has been rationalized via the diffusion of the point defects generated during the radiation bombardment, their coupling to the solute atoms in the alloy, and their subsequent migration and elimination at point defect sinks. Throughout the past literature dedicated to RIS, it has frequently been assumed, explicitly or implicitly, that grain boundaries and their corresponding point defect absorption efficiency remain unaffected by the accumulation of radiation damage. This is most relevant to coherent 3 twin boundaries, which are assumed to be poor point defect sinks owing to their well-ordered local structure, and therefore free of RIS. As a result, grain boundary engineering of steels with high fractions of twin boundaries has been proposed as a way to prevent the formation of segregated GB networks. There are, however, publications that report non-negligible RIS at twin boundaries. This thesis explores experimentally the impact of grain boundary character on the development of radiation-induced segregation (RIS) in 316L austenitic steel irradiated with 2 MeV protons at 360C and focuses on ascertaining the validity of the aforementioned assumption regarding a GB’s radiation-independent defect absorption efficiency. Electron backscatter diffraction is employed to select grain boundaries, and an additional pole figure analysis is implemented to select well-aligned 3{111} coherent twin boundaries. The local RIS at captured GBs is characterized in a two-pronged experimental approach utilizing both energy-dispersive spectroscopy in a scanning transmission electron microscope (STEM-EDS) and atom probe tomography (APT). Key STEM-EDS results reveal that RIS can develop at coherent 3 twin boundaries on a similar magnitude as high-angle grain boundaries, and further APT analysis demonstrates that the morphology of RIS at coherent twin boundaries is heterogeneous, in contrast to the homogeneous segregation observed at high-angle grain boundaries. The ensemble of these results supports the hypothesis that grain boundary sink efficiency can evolve under irradiation through damage accumulation at and near coherent twin boundaries. This may have important implications for intergranular stress corrosion cracking studies, grain boundary engineering proposals, and future predictive studies on the microstructural evolution in irradiated alloys.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Materials Science & Engr

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Wonner, Sara Katlyn

Contributors dc:contributor

• Bellon, Pascal
• Averback, Robert
• Heuser, Brent
• Charpagne, Marie
• Devaraj, Arun

• Radiation-Induced Segregation
• Proton-Irradiation
• Steel
• Nuclear Materials Science
• Transmission Electron Microscopy
• Atom Probe Tomography

Statement dc:rights

• Copyright 2025 Sara Wonner

Language dc:language

en

Handle dc:identifier

https://hdl.handle.net/2142/132739

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/132739