NSUF 20-2963: Atom Probe Tomography Study of Elemental Segregation and Precipitation in Ion-Irradiated Advanced Austenitic Alloy A709
This project aims to investigate the dose dependence of elemental segregation and precipitation of advanced Fe-20Cr-25Ni austenitic steel Alloy 709 (A709), that has been irradiated by 3.5 MeV Fe2+ ions to 100, 200, 400 peak dpa, respectively. This project aims to investigate the dose dependence of elemental segregation and precipitation of advanced Fe-20Cr-25Ni austenitic steel Alloy 709 (A709), that has been irradiated by 3.5 MeV Fe2+ ions to 100, 200, 400 peak dpa, respectively. A709 is an advanced austenitic alloy that have been down-selected by the US Advanced Reactor Technologies (ART) Program for structural applications in advanced reactors [1]. A709 shows superior high temperature strength, corrosion resistance, and creep properties, when compared to traditional 316H alloy. This project is a continuing effort of a NEUP program trying to understand the irradiation performance of A709 in a systematic way. Our previous study has investigated the microstructure evolution at relatively lower doses [2] and swelling behavior at higher doses [3]. As shown in a sample result in Fig. 1, we found that after irradiation Ni and Si tend to segregate to dislocation loops and void surfaces, and also form Ni,Si-rich clusters. It is likely that the elemental redistribution can significantly affect the matrix composition and influence the void nucleation, as suggested by earlier work on neutron-irradiated 316 stainless steel [4]. Therefore, it is desired to quantify the dose dependence of the elemental segregation and precipitation behavior, in order to link with other microstructural changes such as void swelling and formation of network dislocations at high doses. Systematic transmission electron microscopy (TEM) characterization has been performed, but only for void characteristics. The proposed atom probe tomography (APT) experiments will provide complementary data to achieve systematic understanding of the irradiation performance of A709. Three irradiated samples and one unirradiated sample will be examined. 5 APT tips will be prepared for each irradiated sample and 3 tips will be prepared for the unirradiated sample. Unlike the traditional 316H austenitic alloy, A709 is a Nb-stabilized 20Cr-25Ni austenitic alloy that contains nano-sized Nb-rich MX precipitates. Although A709 shows superior performance over traditional 316H alloy in a non-radiation environment, it is unknown whether these improved properties will be maintained under irradiation. To quickly assess and understand the irradiation performance of A709, systematic self-ion irradiations have been conducted at various doses levels at fast reactor relevant temperatures (300 °C to 600 °C). The results have identified the peak swelling temperature of A709 to be at ~575 °C, and A709 does show better swelling resistance compared to traditional 316 alloy. Such differences in void swelling behavior could be due to the difference in the vacancy migration energy, a compositionally dependent value. Thus, the need to accurately measure the compositional difference of the matrix at difference doses. The proposed project is critical to understand the radiation-induced segregation and precipitation of A709 alloy and reveal the possible interconnection between elemental segregation and void swelling, which is an important aspect that has not been well studied.
Additional Info
| Field | Value |
|---|---|
| Abstract | This project aims to investigate the dose dependence of elemental segregation and precipitation of advanced Fe-20Cr-25Ni austenitic steel Alloy 709 (A709), that has been irradiated by 3.5 MeV Fe2+ ions to 100, 200, 400 peak dpa, respectively. This project aims to investigate the dose dependence of elemental segregation and precipitation of advanced Fe-20Cr-25Ni austenitic steel Alloy 709 (A709), that has been irradiated by 3.5 MeV Fe2+ ions to 100, 200, 400 peak dpa, respectively. A709 is an advanced austenitic alloy that have been down-selected by the US Advanced Reactor Technologies (ART) Program for structural applications in advanced reactors [1]. A709 shows superior high temperature strength, corrosion resistance, and creep properties, when compared to traditional 316H alloy. This project is a continuing effort of a NEUP program trying to understand the irradiation performance of A709 in a systematic way. Our previous study has investigated the microstructure evolution at relatively lower doses [2] and swelling behavior at higher doses [3]. As shown in a sample result in Fig. 1, we found that after irradiation Ni and Si tend to segregate to dislocation loops and void surfaces, and also form Ni,Si-rich clusters. It is likely that the elemental redistribution can significantly affect the matrix composition and influence the void nucleation, as suggested by earlier work on neutron-irradiated 316 stainless steel [4]. Therefore, it is desired to quantify the dose dependence of the elemental segregation and precipitation behavior, in order to link with other microstructural changes such as void swelling and formation of network dislocations at high doses. Systematic transmission electron microscopy (TEM) characterization has been performed, but only for void characteristics. The proposed atom probe tomography (APT) experiments will provide complementary data to achieve systematic understanding of the irradiation performance of A709. Three irradiated samples and one unirradiated sample will be examined. 5 APT tips will be prepared for each irradiated sample and 3 tips will be prepared for the unirradiated sample. Unlike the traditional 316H austenitic alloy, A709 is a Nb-stabilized 20Cr-25Ni austenitic alloy that contains nano-sized Nb-rich MX precipitates. Although A709 shows superior performance over traditional 316H alloy in a non-radiation environment, it is unknown whether these improved properties will be maintained under irradiation. To quickly assess and understand the irradiation performance of A709, systematic self-ion irradiations have been conducted at various doses levels at fast reactor relevant temperatures (300 °C to 600 °C). The results have identified the peak swelling temperature of A709 to be at ~575 °C, and A709 does show better swelling resistance compared to traditional 316 alloy. Such differences in void swelling behavior could be due to the difference in the vacancy migration energy, a compositionally dependent value. Thus, the need to accurately measure the compositional difference of the matrix at difference doses. The proposed project is critical to understand the radiation-induced segregation and precipitation of A709 alloy and reveal the possible interconnection between elemental segregation and void swelling, which is an important aspect that has not been well studied. |
| Award Announced Date | 2020-02-05T14:19:55.377 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Yaqiao Wu |
| Irradiation Facility | None |
| PI | Dominic Piedmont |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 2963 |