NSUF 22-4453: Effect of neutron irradiation on the microstructure of NF616 (Grade 92) as a function of dose and temperature
NF616 (Grade 92) is being considered as a candidate structural material for advanced reactors, due to their superior resistance to radiation induced void swelling, microstructural stability, and thermal properties. Based upon elevated temperature creep-rupture strength and impact toughness, HT-9 has significant weakness when compared with NF616. Although elevated-temperature mechanical properties favor NF616, neutron irradiation data is very limited. Hence, to get a comprehensive understanding of the mechanical behavior under neutron irradiation, it is essential to study neutron irradiated samples at various doses and temperatures. The progressive change in the microstructure with irradiation dose and temperature includes void formation, increases in dislocation density, second phase formation, and other changes that can lead to swelling, hardening, and embrittlement. The strongest hardening and embrittlement occur at temperatures below ~425°C in F-M steels due to strong increases in dislocation density and the formation of several different populations of second phases that all act to reduce dislocation mobility. The extreme hardening and low fracture toughness that occur for irradiation temperatures below 425°C is a serious issue for the use of NF616 because many reactor concepts call for core components to see temperatures as low as 320°C. To address the issue of low-temperature neutron irradiation hardening and embrittlement, systematic investigations on the mechanical behavior and microstructure of NF616 are needed over a range of doses and temperatures. As a part of the UW-Madison Irradiation Experiment, NF616 was neutron irradiated in the ATR (387-469C; 3-8 dpa).
Our team recently won a RTE (#2879) award and performed mechanical characterization of irradiated NF616 as a function of doses and temperatures at PNNL to evaluate the degree of low-temperature (~425°C) neutron irradiation hardening. Our team also won a RTE (#4259) award and efforts are currently ongoing at PNNL to perform TEM characterization of few irradiated NF616 samples. Maximum impact of this work will be obtained by performing fractographic (failed tensile specimens) and microstructural characterization (SEM and EBSD) of these neutron irradiated NF616 samples present at PNNL. Hence, the goal of the proposed RTE project is to utilize SEM and EBSD to evaluate the control and irradiated samples and determine the failure mode (fractography), general grain structure, prior austenite grain size, martensite packet, lath structure and primary carbide structure as a function of irradiation doses and temperatures, since these parameters can significantly affect the mechanical behavior and radiation resistance of NF616. The results obtained from the proposed RTE project (fractography and microstructural characterization using SEM and EBSD) would be extremely beneficial to get a complete understanding on the effect of neutron irradiation on NF616 and thus enable us to obtain properties-microstructure-temperature-dose correlations. The results of the proposed work could be extended beyond NF616, and it would be relevant to many F-M steels. Thus, the proposed work will have substantial implications for the deployment of next-generation advanced reactors.
The project performance (sample preparation, imaging, and analysis) is expected to take place during July-September 2022 and will result in one conference presentation and one journal article publication.
Additional Info
| Field | Value |
|---|---|
| Abstract | NF616 (Grade 92) is being considered as a candidate structural material for advanced reactors, due to their superior resistance to radiation induced void swelling, microstructural stability, and thermal properties. Based upon elevated temperature creep-rupture strength and impact toughness, HT-9 has significant weakness when compared with NF616. Although elevated-temperature mechanical properties favor NF616, neutron irradiation data is very limited. Hence, to get a comprehensive understanding of the mechanical behavior under neutron irradiation, it is essential to study neutron irradiated samples at various doses and temperatures. The progressive change in the microstructure with irradiation dose and temperature includes void formation, increases in dislocation density, second phase formation, and other changes that can lead to swelling, hardening, and embrittlement. The strongest hardening and embrittlement occur at temperatures below ~425°C in F-M steels due to strong increases in dislocation density and the formation of several different populations of second phases that all act to reduce dislocation mobility. The extreme hardening and low fracture toughness that occur for irradiation temperatures below 425°C is a serious issue for the use of NF616 because many reactor concepts call for core components to see temperatures as low as 320°C. To address the issue of low-temperature neutron irradiation hardening and embrittlement, systematic investigations on the mechanical behavior and microstructure of NF616 are needed over a range of doses and temperatures. As a part of the UW-Madison Irradiation Experiment, NF616 was neutron irradiated in the ATR (387-469C; 3-8 dpa). Our team recently won a RTE (#2879) award and performed mechanical characterization of irradiated NF616 as a function of doses and temperatures at PNNL to evaluate the degree of low-temperature (~425°C) neutron irradiation hardening. Our team also won a RTE (#4259) award and efforts are currently ongoing at PNNL to perform TEM characterization of few irradiated NF616 samples. Maximum impact of this work will be obtained by performing fractographic (failed tensile specimens) and microstructural characterization (SEM and EBSD) of these neutron irradiated NF616 samples present at PNNL. Hence, the goal of the proposed RTE project is to utilize SEM and EBSD to evaluate the control and irradiated samples and determine the failure mode (fractography), general grain structure, prior austenite grain size, martensite packet, lath structure and primary carbide structure as a function of irradiation doses and temperatures, since these parameters can significantly affect the mechanical behavior and radiation resistance of NF616. The results obtained from the proposed RTE project (fractography and microstructural characterization using SEM and EBSD) would be extremely beneficial to get a complete understanding on the effect of neutron irradiation on NF616 and thus enable us to obtain properties-microstructure-temperature-dose correlations. The results of the proposed work could be extended beyond NF616, and it would be relevant to many F-M steels. Thus, the proposed work will have substantial implications for the deployment of next-generation advanced reactors. The project performance (sample preparation, imaging, and analysis) is expected to take place during July-September 2022 and will result in one conference presentation and one journal article publication. |
| Award Announced Date | 2022-06-14T07:20:15.63 |
| Awarded Institution | Idaho National Laboratory |
| Facility | Advanced Test Reactor |
| Facility Tech Lead | Alina Zackrone, Stuart Maloy |
| Irradiation Facility | None |
| PI | Indrajit Charit |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 4453 |