NSUF 18-1156: Mechanical characterization of three heats (ORNL, LANL and EBR II) of HT-9 after side-by-side neutron irradiation at LWR and fast reactor relevant temperatures
HT-9 is being considered as a candidate structural material for fast, advanced LWR, and fusion reactors, due to their superior resistance to radiation induced void swelling, microstructural stability, and thermal properties. The neutron-irradiated F-M steels have been studied extensively at various doses and temperatures. The progressive change in the microstructure with the 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 occurs at temperatures below ~425°C in HT-9 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 HT-9 because many reactor concepts call for core components to see temperatures as low as 320°C. Normalized and tempered HT-9 typically exhibit tempered martensitic structure characterized by larger M23C6 (M= Cr, Fe, Mo) carbides formed on lath and prior austenite grain boundaries, and smaller and low-density MC (M = V) carbides formed within the matrix. The heat treatability makes it possible to optimize the material for toughness, ductility and high temperature properties. The heat treatment can affect prior austenite grain size, lath and packet size, precipitate morphology and distribution. The mechanical properties of HT-9 after neutron irradiation varies based upon the manufacturing process, chemical composition, metallurgical conditions, initial microstructure, second phase particles, irradiation dose and temperature. To address the issue of low-temperature neutron irradiation hardening and embrittlement, systematic investigations on the mechanical behavior of HT-9 with slight variations in chemical composition and heat treatment are needed over a range of doses and temperatures. As a part of the UW-Madison NSUF IE, three heats (ORNL, LANL and EBR II) of HT-9 with variations in manufacturing process, chemical composition and heat treatment were side-by-side neutron irradiated (identical temperatures, doses, dose rates and irradiation species) in the ATR (dose 6-8 dpa) at LWR and fast reactor relevant temperatures (300, 400 and 500?C). The proposed project aims to evaluate the mechanical properties (microhardness and tensile) of three heats (ORNL, LANL and EBR II) of neutron irradiated HT-9 as a function of irradiation temperature and processing conditions. Fractography and image analysis (ductility parameters) will be performed to characterize the toughness of samples after thermal aging and irradiation. Very limited low-temperature neutron irradiation studies had been performed to study the variation of manufacturing process, chemical composition and heat treatment on the mechanical behavior of irradiated HT-9. Hence, our team can begin to fill the gap in the literature by successfully completing the proposed work. The mechanical test data and microscopic information obtained from this proposed work would be analyzed to understand the effects of radiation damage on HT-9 heats at the LWR and fast reactor relevant temperatures, and to successfully develop appropriate structure-property-temperature correlations.
Additional Info
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| Abstract | HT-9 is being considered as a candidate structural material for fast, advanced LWR, and fusion reactors, due to their superior resistance to radiation induced void swelling, microstructural stability, and thermal properties. The neutron-irradiated F-M steels have been studied extensively at various doses and temperatures. The progressive change in the microstructure with the 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 occurs at temperatures below ~425°C in HT-9 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 HT-9 because many reactor concepts call for core components to see temperatures as low as 320°C. Normalized and tempered HT-9 typically exhibit tempered martensitic structure characterized by larger M23C6 (M= Cr, Fe, Mo) carbides formed on lath and prior austenite grain boundaries, and smaller and low-density MC (M = V) carbides formed within the matrix. The heat treatability makes it possible to optimize the material for toughness, ductility and high temperature properties. The heat treatment can affect prior austenite grain size, lath and packet size, precipitate morphology and distribution. The mechanical properties of HT-9 after neutron irradiation varies based upon the manufacturing process, chemical composition, metallurgical conditions, initial microstructure, second phase particles, irradiation dose and temperature. To address the issue of low-temperature neutron irradiation hardening and embrittlement, systematic investigations on the mechanical behavior of HT-9 with slight variations in chemical composition and heat treatment are needed over a range of doses and temperatures. As a part of the UW-Madison NSUF IE, three heats (ORNL, LANL and EBR II) of HT-9 with variations in manufacturing process, chemical composition and heat treatment were side-by-side neutron irradiated (identical temperatures, doses, dose rates and irradiation species) in the ATR (dose 6-8 dpa) at LWR and fast reactor relevant temperatures (300, 400 and 500?C). The proposed project aims to evaluate the mechanical properties (microhardness and tensile) of three heats (ORNL, LANL and EBR II) of neutron irradiated HT-9 as a function of irradiation temperature and processing conditions. Fractography and image analysis (ductility parameters) will be performed to characterize the toughness of samples after thermal aging and irradiation. Very limited low-temperature neutron irradiation studies had been performed to study the variation of manufacturing process, chemical composition and heat treatment on the mechanical behavior of irradiated HT-9. Hence, our team can begin to fill the gap in the literature by successfully completing the proposed work. The mechanical test data and microscopic information obtained from this proposed work would be analyzed to understand the effects of radiation damage on HT-9 heats at the LWR and fast reactor relevant temperatures, and to successfully develop appropriate structure-property-temperature correlations. |
| Award Announced Date | 2018-02-01T14:11:15.617 |
| Awarded Institution | Illinois Institute of Technology |
| Facility | Materials Research Collaborative Access Team (MRCAT) |
| Facility Tech Lead | Jeff Terry, Stuart Maloy |
| Irradiation Facility | None |
| PI | Ramprashad Prabhakaran |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1156 |