High energy x-ray diffraction microstructural analysis of oxide dispersion strengthened steel for advanced nuclear systems

Oxide dispersion strengthened (ODS) steel exhibits exceptional radiation resistance and high-temperature creep strength when compared to traditional ferritic and martensitic steels. ODS steel has been considered one of most promising structural materials for advanced nuclear systems. In this study, we applied the high-energy synchrotron radiation technique to investigate the fundamental deformation process of a 9Cr ODS steel. The 9Cr ODS steel was fabricated by mechanical alloying, hot isostatic pressing followed by thermal treatments to encourage better mechanical properties. During the mechanical and thermal treatments, the Ti (~0.5%) and Y2O3 (~0.35%) existing in the raw materials developed into complex oxide nanoparticles consisting primarily of Y2TI2O7, which allowed for significant strengthening of the steel. The in-situ tensile tests measured with high-energy X-ray diffraction were carried out at the 1-ID beamline of the Advanced Photon Source at Argonne National Laboratory. The specimen was subjected to increasing uniaxial tensile stresses up to failure, with a total of nine axial scans for each of the stress/strain states. The wide range of scans allowed the direct measurement of material responses from both necking and un-necked parts of the specimens. From the X-ray measurement, the load partitioning between the ferritic matrix and the nanoparticles was found to occur during the yielding process. The nanoparticles experienced a dramatic loading process, and the internal stress on the nanoparticles increased to 3.5 GPa before sample necking. In contrast, the ferritic matrix slightly relaxed during early yielding, and slowly strained until necking. However, the load partitioning processes reversed during sample necking, causing the internal stress placed on the nanoparticles to rapidly decrease and this indicated a debonding of the particles from the matrix. This debonding led to a decrease in the partial capacity of the particles to carry load. The load then transferred to the matrix, which then exhibited an increased lattice-strain rate during necking. This study developed a comprehensive understanding of loading behaviors for various phases in the ODS steel. It also showed that high-energy synchrotron X-ray radiation, as a non-destructive technique for in-situ measurement, is a useful tool for studying materials performance for advanced nuclear systems applications.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Nuclear, Plasma, and Radiological Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Rytych, Carl

Contributors dc:contributor

• Stubbins, James F.

• Nuclear
• Materials
• Oxide Dispersion Strengthened (ODS)
• Y2O3

Statement dc:rights

• Copyright 2013 Carl Rytych

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/46613

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/46613