Advanced characterization of the early-stage evolution of microstructures and mechanical properties in neutron-irradiated commercial steels

Yan, Huan

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Description

Title

Advanced characterization of the early-stage evolution of microstructures and mechanical properties in neutron-irradiated commercial steels

Author(s)

Yan, Huan

Issue Date

2021-04-21

Director of Research (if dissertation) or Advisor (if thesis)

Stubbins, James F.

Doctoral Committee Chair(s)

Stubbins, James F.

Committee Member(s)

• Heuser, Brent J.
• Trinkle, Dallas R.
• Abbaszadeh, Shiva

Department of Study

Nuclear, Plasma, & Rad Engr

Discipline

Nuclear, Plasma, Radiolgc Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Nuclear Materials
• Ferritic Martensitic Steels
• Neutron Irradiation
• Transmission Electron Microscopy
• Atom Probe Tomography
• Irradiation Hardening

Abstract

In this project, the post-irradiation microstructures and mechanical properties of two types of Fe-Cr ferritic-martensitic (F-M) steels, HT9 and T91, were characterized. The materials were irradiated in the Advanced Test Reactor (ATR) at different temperatures and neutron fluences. Three temperature ranges and four neutron dose levels were investigated in this study. Utilizing transmission electron microscopy (TEM), atom probe tomography (APT) and energy dispersive X-ray spectroscopy (EDS), the nucleation, growth and stability of dislocation loops, G phase, α’ phase, and other precipitates were quantitatively analyzed. The irradiation hardening in these two materials were characterized using nanoindentation technique. The hardening behaviors were carefully analyzed against the observed microstructures using dispersed barrier hardening (DBH) model. In the irradiation conditions investigated in this study, the hardness evolution was dominated by the evolution of dislocation density at relatively high temperatures. Under low-temperature range (below 400°C), the hardening contribution mostly comes from the dispersed defect population. By comparing different irradiation conditions and materials, detailed evolution of microstructures and mechanical properties, and their dependence on Cr content were revealed. In general, it is found that the evolving pattern of microstructural defects and mechanical properties manifests significantly differently beyond certain threshold temperatures. This phenomenon appears to be highly correlated with the mobility of dislocation loops and dislocation lines. High mobility at high irradiation temperature disrupts the stability of the dislocation loop population, which results in decreasing internal sink strength and co-evolution with radiation-induced precipitates.

Graduation Semester

2021-05

Type of Resource

Thesis

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Copyright 2021 Huan Yan

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