NSUF 21-4259: Microstructural characterization of neutron irradiated NF616 (Grade 92) as a function of doses and temperatures
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, in order 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 (387-469°C; 3-8 dpa). We recently won a RTE (#2879; expected completion: Mar 2021) award to perform mechanical characterization of irradiated NF616 as a function of doses and temperatures at PNNL to understand low-temperature (~425°C) neutron irradiation hardening mechanism. Maximum impact of this work will be obtained by performing microstructural characterization of these samples present at PNNL. The proposed project (July-Dec 2021) aims to perform comprehensive TEM microstructural characterization of NF616 as a function of irradiated dose (4-8 dpa) and temperatures (388-452°C). TEM will be employed to study general grain structure, prior austenite grains, martensite packet, lath structure and primary carbide structure, dislocation loops (size and number density), radiation-induced cavities, segregation and phase transformation. Dispersed barrier-hardening model will be utilized to study irradiation hardening mechanism by correlating the microstructural observations from TEM (proposed project) to mechanical property measurements (existing project; tensile and microhardness). Efforts will be made to understand, quantify, and control the contribution of defects to the strength of a material. Efforts will also be made to comprehensively understand the effects of radiation damage on NF616 and to develop appropriate property-structure-temperature-dose correlations. By doing this work, our team can contribute to filling the gap in the literature on understanding irradiation effects on NF616 and F-M steels in general.
추가 정보
| 필드 | 값 |
|---|---|
| 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, in order 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 (387-469°C; 3-8 dpa). We recently won a RTE (#2879; expected completion: Mar 2021) award to perform mechanical characterization of irradiated NF616 as a function of doses and temperatures at PNNL to understand low-temperature (~425°C) neutron irradiation hardening mechanism. Maximum impact of this work will be obtained by performing microstructural characterization of these samples present at PNNL. The proposed project (July-Dec 2021) aims to perform comprehensive TEM microstructural characterization of NF616 as a function of irradiated dose (4-8 dpa) and temperatures (388-452°C). TEM will be employed to study general grain structure, prior austenite grains, martensite packet, lath structure and primary carbide structure, dislocation loops (size and number density), radiation-induced cavities, segregation and phase transformation. Dispersed barrier-hardening model will be utilized to study irradiation hardening mechanism by correlating the microstructural observations from TEM (proposed project) to mechanical property measurements (existing project; tensile and microhardness). Efforts will be made to understand, quantify, and control the contribution of defects to the strength of a material. Efforts will also be made to comprehensively understand the effects of radiation damage on NF616 and to develop appropriate property-structure-temperature-dose correlations. By doing this work, our team can contribute to filling the gap in the literature on understanding irradiation effects on NF616 and F-M steels in general. |
| Award Announced Date | 2021-06-07T16:05:56.78 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Stuart Maloy |
| Irradiation Facility | None |
| PI | Ramprashad Prabhakaran |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 4259 |