Yu, Zefeng. High resolution (S)TEM/EDS characterization of neutron irradiated commercial Zr-Nb alloys

Principal Investigator
First Name:
Zefeng
Last Name:
Yu
Institution:
University of Wisconsin
Title:
Graduate Research Assistant
Team Members:
Name: Institution: Expertise: Status:
Zefeng Yu University of Wisconsin Sample preparation for TEM; SEM; EDS; APT; characterization on irradiated mateirals; Zr based alloys Graduate Student
Lingfeng He Idaho National Laboratory Nuclear Fuels, TEM, radiation effects, Ceramics Other
Xiang Liu Idaho National Laboratory TEM, ODS, nanoindentation, x-ray diffraction, APT, austenitic, dislocation loops, zircaloy, irradiation embrittlement, irradiated microstructure, ferritic martensitic steels, EDS, advanced alloys, Post-Irradiation Examination, radiation-induced segregation Post Doc
Adrien Couet University of Wisconsin Nuclear Materials, Corrosion, synchrotron, Irradiation, Alloys, electrochemistry, oxide Faculty
Experiment Details:
Experiment Title:
High resolution (S)TEM/EDS characterization of neutron irradiated commercial Zr-Nb alloys
Describe the work that you are proposing in detail. Please include as many specifics as possible (e.g., dose, dose rate, ion energy, types of ions, beam line x-ray energy, irradiation temperature, analysis temperature, atmosphere, etc.):
The major focus of this proposal is to use high resolution (S)TEM/EDS to study microstructure and microchemistry in metal and oxide of neutron irradiated ZIRLO® and X2®. Table 1 shows detailed bulk composition and irradiation condition of neutron irradiated samples, which are currently located at INL. For the characterization of irradiation induced platelets (IIP) and dislocation loops in the metal, it is necessary to prepare 3mm disc TEM samples at Irradiated Materials Characterization Laboratory (IMCL). To study the stability of irradiation induced platelets in the oxide, shielded FEI Helios dual-beam SEM-plasma FIB at IMCL will be used to fabricate totally 4 TEM lamella from hot samples. Both native precipitates and IIPs will be characterized by STEM/EDS. For STEM/EDS characterization, Titan Themis 200 S/TEM with Super-X EDS at IMCL will be suitable to acquire not only high-quality images of IIPs but also effectively mapping the composition of both native precipitates and IIPs. The imaging condition would be likely g = <0002> at different zone axis to thoroughly investigate the size, shape, and orientation of IIPs. EDS line scan over precipitates will directly provide chemical evidence to support that they are indeed Nb-rich platelets. Conventional TEM will be used to study the size and density of dislocation loops. Subsequently, precipitate density and volume fraction will be calculated to compare with literature and correlation between dislocation loops and IIPs will be assessed. Totally, we are requesting 1 week of PFIB time and 1 week of Titan time at IMCL to complete this RTE project.
Technical Abstract
We propose to use scanning transmission electron microscopy ((S)TEM) with Super-X EDS to study the evolution of microstructure and microchemistry of neutron irradiated ZIRLO® and AXIOM X2® alloys at different irradiation doses (1 cycle and 4 cycles). The major research objective of this study is to provide knowledge on neutron irradiation induced Nb redistribution in Zr-Nb alloys and its correlation with irradiation induced dislocation loops. The overall research program aims at precisely characterizing the size, density, microchemistry and crystallography of irradiation induced platelets (IIPs) and the density of dislocation loops of neutron irradiated samples, to better understand the in-reactor irradiation induced growth (IIG) and corrosion behavior of Zr-Nb alloys. The two main hypothesis tested here are that (i) reduced irradiation induced growth of Zr-Nb alloys is due to the precipitation of IIPs that prevents the nucleation of <c> loops by lattice compression, and (ii) the precipitation of Nb-rich IIPs, and the associated decrease in Nb solute concentration, is responsible for the low corrosion rates experienced by Zr-Nb alloys. Our recently published paper on proton irradiated Zr-Nb alloys has, to some extent, proved the second hypothesis. The next step is to examine the microstructure and microchemistry of neutron irradiated Zr-Nb alloys using (S)TEM/EDS. This study will primarily use Titan Themis 200 with Super-X Energy Dispersive Spectroscopy (EDS) at Irradiated Materials Characterization Laboratory (IMCL) to perform (S)TEM/EDS characterization. To effectively study the precipitates and dislocation loops in the metal and to avoid ZrH contamination from FIB milling, electropolished 3mm disc of neutron irradiated samples will be prepared from the metallic region of the fuel rod at IMCL. To characterize the precipitates in the oxidized region of neutron irradiated samples, shielded Plasma-FIB will be used to prepare TEM lamella in a much faster pace than using conventional gallium source FIB. The primary focus of (S)TEM/EDS is to investigate size, microchemistry, and crystallography of irradiation induced Nb-rich platelets in both metal and oxide neutron irradiated samples. The characterization of dislocation loops using the 3mm disc will be performed under TEM mode using specific g vectors. Since Titan Themis 200 is equipped with EELS, the thickness of each imaging area will be measured to compute the precipitate and loop density.
Book / Journal Publications
Name Title
Zefeng Yu Nb redistribution in proton irradiated Zr1.0Nb
Conference Publications
Name Title
Zefeng Yu Precipitation mechanism of irradiation induced Nb-rich particles in ZrNb alloys
Zefeng Yu Nb redistribution in proton irradiated Zr1.0Nb