NSUF 15-539: Post-irradiation Examinations on a Ferritic ODS Steel Irradiated at 450C
Technical Abstract Please describe the project objectives including methods to be employed, and the potential impact to the state-of-the-knowledge if the research is successful. The abstract must also indicate the expected period of performance. The addition of oxide powders such as yttria and alumina during mechanical alloying introduces dense dispersive oxygen-enriched nanoparticles into steel matrices. These nanoparticles can not only significantly enhance the mechanical strength and creep resistance, but also provide extra interfaces, which can behave as sinks of defects under irradiation. Therefore, ODS steels are regarded as promising candidates of the structural materials in advanced nuclear systems, which require excellent mechanical properties and robust radiation tolerance at high temperatures. Previous studies on neutron and ion irradiated MA957 indicate that that dislocation network forms and that the oxygen-enriched nanoparticles remain stable in the high dose regime. However, very limited research has been done for the radiation induced microstructural modifications in neutron-irradiated ODS steels in low dose regime. Meanwhile, it is also valuable to compare these alterations in microstructures in MA957 with those in model alloys and non-ODS commercial alloys. All the knowledge helps understand the radiation resistance mechanisms of ODS steels and provides insight into the development of prospective ODS or nanostructured advanced alloys. To realize these objectives, three MA957 specimens irradiated in ATR at 450C with three dose conditions (0.01dpa, 0.1dpa and 1dpa) are proposed to be investigated by a series of advanced characterization techniques including atom probe tomography (APT) and transmission electron microscopy (TEM). 450C irradiation temperature was chosen since high-temperature performance is crucial for ODS alloys. Also, previous PIE results of Fe-Cr base alloys indicate that the responses of the materials are quite different between 300C and 450C irradiation temperatures. As the PIE of the MA957 samples irradiated at 300C with the same dose condition will be supported by another project, it is relevant to investigate the 450C neutron-irradiated MA957 specimens. Focused ion beam (FIB) will be utilized to prepare tip specimens for successive atom probe experiments since it does not involve any preferential corrosion as electropolishing does. APT will be used to retrieve the 3D element distribution in the samples. Then we will measure the variations in chemical composition and size distribution of the small-scale oxygen-enriched nanoparticles (5nm). Thus, a comprehensive understanding of radiation-induced microstructural modifications in MA957 at 450C and within the low-dose regime will be established due to the accomplishment of this proposed PIE project. FIB preparation will take 3 days; TEM investigation will take 4 days; APT investigation will take another 3 days. The total time is within the RTE proposal limitation.
Additional Info
| Field | Value |
|---|---|
| Abstract | Technical Abstract Please describe the project objectives including methods to be employed, and the potential impact to the state-of-the-knowledge if the research is successful. The abstract must also indicate the expected period of performance. The addition of oxide powders such as yttria and alumina during mechanical alloying introduces dense dispersive oxygen-enriched nanoparticles into steel matrices. These nanoparticles can not only significantly enhance the mechanical strength and creep resistance, but also provide extra interfaces, which can behave as sinks of defects under irradiation. Therefore, ODS steels are regarded as promising candidates of the structural materials in advanced nuclear systems, which require excellent mechanical properties and robust radiation tolerance at high temperatures. Previous studies on neutron and ion irradiated MA957 indicate that that dislocation network forms and that the oxygen-enriched nanoparticles remain stable in the high dose regime. However, very limited research has been done for the radiation induced microstructural modifications in neutron-irradiated ODS steels in low dose regime. Meanwhile, it is also valuable to compare these alterations in microstructures in MA957 with those in model alloys and non-ODS commercial alloys. All the knowledge helps understand the radiation resistance mechanisms of ODS steels and provides insight into the development of prospective ODS or nanostructured advanced alloys. To realize these objectives, three MA957 specimens irradiated in ATR at 450C with three dose conditions (0.01dpa, 0.1dpa and 1dpa) are proposed to be investigated by a series of advanced characterization techniques including atom probe tomography (APT) and transmission electron microscopy (TEM). 450C irradiation temperature was chosen since high-temperature performance is crucial for ODS alloys. Also, previous PIE results of Fe-Cr base alloys indicate that the responses of the materials are quite different between 300C and 450C irradiation temperatures. As the PIE of the MA957 samples irradiated at 300C with the same dose condition will be supported by another project, it is relevant to investigate the 450C neutron-irradiated MA957 specimens. Focused ion beam (FIB) will be utilized to prepare tip specimens for successive atom probe experiments since it does not involve any preferential corrosion as electropolishing does. APT will be used to retrieve the 3D element distribution in the samples. Then we will measure the variations in chemical composition and size distribution of the small-scale oxygen-enriched nanoparticles (<5nm) in order to examine the stability of them under both high temperature and irradiation conditions. Meanwhile, alpha-alpha’ phase separation is prominent for Fe-14Cr system such as MA957. It is relevant to have data of alpha’ precipitation of a Fe-14Cr alloy at this temperature so that the Fe-Cr phase diagram can be further perfected. Hence, APT data will also be used to study this phenomenon using the frequency distribution method. The radiation-induced segregation near grain boundaries and matrix-nanoparticle interfaces will be investigated according to the APT data too. TEM will be utilized to characterize the evolution of dislocation loops and voids/bubbles using conventional diffraction contrast images with analysis techniques such as b•g, inside-outside contrast and underfocus-overfocus method. STEM HAADF images, along with EELS and EDS, will be employed to examine the stability of medium and large nanoparticles (>5nm). Thus, a comprehensive understanding of radiation-induced microstructural modifications in MA957 at 450C and within the low-dose regime will be established due to the accomplishment of this proposed PIE project. FIB preparation will take 3 days; TEM investigation will take 4 days; APT investigation will take another 3 days. The total time is within the RTE proposal limitation. |
| Award Announced Date | 2014-12-04T00:00:00 |
| Awarded Institution | Illinois Institute of Technology |
| Facility | Materials Research Collaborative Access Team (MRCAT) |
| Facility Tech Lead | Jeff Terry, Yaqiao Wu |
| Irradiation Facility | None |
| PI | James Stubbins |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 539 |