Lu, Yu. Predict the mechanical behavior of irradiated cast stainless steels based on the microstructures and measured properties from nanoindentation

Principal Investigator
First Name:
Yu
Last Name:
Lu
Institution:
University of Florida
Title:
Graduate student
Team Members:
Name: Institution: Expertise: Status:
Yiren Chen Argonne National Laboratory Nuclear Materials Other
Yong Yang University of Florida Radiation Damage Faculty
Experiment Details:
Experiment Title:
Predict the mechanical behavior of irradiated cast stainless steels based on the microstructures and measured properties from nanoindentation
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 specimens are all in the shape of 3 mm discs (~120 um in thickness) and were irradiated in the Halden reactor at 310°C to the dose of 3 dpa. The discs will be electro-polished prior to shipping to CAES for removing any loose contaminations and to expose fresh materials for FIB lift out. For the microstructure characterization, the anticipated nano-sized precipitates and fine dislocation loops structure will be analyzed using Transmission Electron Microscope (TEM), while the elemental analysis of the ultrafine precipitates will be studied using Atom Probe Tomography (APT). The phase of nano-sized precipitates will be identified using TEM Diffraction, while the composition and size distribution will be quantified using APT. It was speculated that this low temperature irradiation will only induce ultra-fine precipitates if any and the radiation induced elemental segregation should also be very minimum. All the sample preparations will be performed using a Focus Ion Beam (FIB). For the nanoindentation test, the sample will be prepared before it sends to the CAES. Both the ferrite and austenite phase in each specimen will be tested. Five indents will be performed on both phase for each specimen. Load-controlled nanoindentation testing will be performed employing a calibrated TI 950 TriboIndenter with diamond Berkovich tip. A nanoindentation recipe (the 40 s total indentation time was divided into three segments consisting of 15 s loading time, 10 s holding time, and 15 s unloading time) will be used for the experiment. Since the result can be easily affected by bluntness and indentation size effect, a loading range (1000 μN to 12,000 μN) will be chosen to find out the optimal load to acquire the accurate modulus for both phases.
Technical Abstract
The work is planned to systemically characterize the neutron irradiated CF3 and CF8 cast stainless steels irradiated to 3 dpa at 310°C. The study is aimed to complete the study of irradiation effect on the microstructural evolution in the ferrite phase of cast stainless steels and to predict their mechanical behaviors. Both the transmission electron microscope and atom probe tomography will be used to study the irradiated induced nano-sized features including dislocation, phase separation and precipitates. The nanoindentation will be applied to obtain yield strength and Young’s modulus of ferrite and austenite phases, separately. The output from the execution of proposed study will provide a more systematic study at an atomic level on the neutron irradiation effects in the LWRs internal structural materials at LWRs relevant conditions, and will help to predict their mechanical behavior through finite element modeling (FEM) using the parameters obtained from microstructural characterization and nanoindentation. This proposed research will provide a fundamental understanding on the response of cast stainless steels during the designed 40 years reactor life, and more relevantly, predicting their mechanical property for the extended life of 60 years and beyond.