Yeom, Hwasung. Microstructural Investigation of Radiation Stability of Cold Spray Manufactured Oxide Dispersion Strengthened (ODS) Steel

Principal Investigator
First Name:
Hwasung
Last Name:
Yeom
Institution:
University of Wisconsin
Title:
Assistant Scientist
Team Members:
Name: Institution: Expertise: Status:
Mia Lenling University of Wisconsin-Madison Manufacturing ODS steel materials, ion-irradiation experiment Graduate Student
Kumar Sridharan University of Wisconsin-Madison A technical lead on fabrication of ODS steel samples by cold spray process and conventional mechanical alloying Faculty
Xiang Liu Idaho National Laboratory Advanced characterization including S/TEM and HRTEM Post Doc
Mukesh Bachhav Idaho National Laboratory An INL lead for the material characterization Other
Experiment Details:
Experiment Title:
Microstructural Investigation of Radiation Stability of Cold Spray Manufactured Oxide Dispersion Strengthened (ODS) Steel
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.):
In the proposed RTE, instrument time is requested on Transmission Electron Microscopy (TEM) to study the radiation stability (more specifically, size and size distribution and composition) of the oxide nanoparticles and evolution of radiation-induced defects in ODS steel cladding tubes produced by the cold spray process. A total of six samples will be investigated in the proposed RTE. Three samples (two cold spray produced samples and one conventionally produced sample) will be in the un-irradiated condition and will serve as the baseline for this study. The two cold spray samples will be (i) as-deposited and (ii) post-deposition heat treated samples, and one ODS steel sample produced by the conventional method. The other three samples will be irradiated counter parts of these samples. Irradiation for the latter three samples will be performed using 3.7 MeV Fe+2 ions to a maximum damage level of 110 dpa at 500 °C. We are requesting six days of use on the TEM instrument to analyze all samples along with four days of time on the Focused Ion Beam (FIB) for TEM sample preparation. Irradiations will be completed by August 2019.
Technical Abstract
The goal of the proposed rapid turnaround experiment (RTE) led by the University of Wisconsin, Madison (UW) is to perform comparative microstructural study on irradiation response of ODS steel produced by two distinct manufacturing routes using advanced TEM examination. The proposed research would provide extended data showing the stability of oxide nanoclusters in the cold spray produced ODS steel materials with regards to the number density, size, and composition under heavy ion irradiation as compared to ODS steel materials fabricated by conventional mechanical alloying methods. In the proposal, six days of instrument time is requested on the TEM characterization and four days of associated FIB time at the Irradiated Materials Characterization Laboratory (IMCL) in Idaho National Laboratory (INL). During the cold spray process, pre-alloyed 14YWT powder particles containing oxide nanoparticles are propelled at supersonic velocities through a converging-diverging nozzle system by pre-heated, pressurized gas onto a substrate to form a deposit. The particle temperature is low and deposition occurs by severe plastic deformation. While UW has successfully demonstrated a manufacturing route for ODS steel cladding tubes using the cold spray process under an ongoing NEET project, comprehensive microstructural analysis using the TEM is required to quantify the evolution of the nano-oxide particles and radiation-induced defects in the irradiated ODS steel materials. The size, size distribution, number density, and the composition of the oxide nanoparticles, which dictate the high temperature strength of ODS steels, as well as a radiation sink strength of the oxide nanoparticles will be evaluated. The first question this RTE will seek to answer is about evaluation of the stability of oxide nanoparticles during the cold spray process and their reprecipitation during ion-irradiation. It is hypothesized that the high velocity impact of the oxide nanoparticles in the powder particle during the cold spray process results in oxide particle dissolution into the ferritic steel matrix, analogous to the high energy ball milling process used in the conventional methods of preparing ODS. Subsequent heavy ion irradiation of the supersaturated solid-solution matrix can potentially lead to reprecipitation of the oxide nanoparticles. Investigation of this hypothesis requires TEM examination of as-deposited ODS steel and its ion-irradiated counterpart. The second question this RTE will seek to answer is how cold spray manufactured ODS steel behaves under radiation as compared to conventionally manufactured ODS steel with respect to distribution of radiation-induced defects and characteristics of the oxide nanoparticles. Both the above scientific questions in our opinion are most conclusively addressed by the state-of-the-art TEM facility at the Idaho National Laboratory. Supporting work (outside RTE proposal): (i) Ion irradiation of cold spray produced ODS steel samples performed at UW’s accelerator facilities using 3.7 MeV Fe+2 ions to a maximum damage level of 110 dpa. (ii) Continued SEM characterization of oxide nanoparticles in the ODS steels (produced by both cold spray and conventional methods) at the UW’s Materials Science Center.