NSUF 19-1694: In-situ irradiation study of carbides/nitrides/carbo-nitrides in additively manufactured ferritic-martensitic steels.
Ferritic-martensitic (F-M) steels are promising structural material candidates for Generation IV fast reactor concepts, and are gaining increased attention for fabrication using additive manufacturing (AM) , demonstrating a paradigm shift in reactor designing. In these alloys, the in-reactor performance depends on the stability of the various non-metallic precipitate families such as M23C6, M7C3, M2X and MX carbides/nitrides. However, despite decades of research, the fundamental question of how irradiation damage propagates and looks like in nanoprecipitates such as those in F-M steels is not answered yet. This is partly due to the nanoscale precipitates being embedded in the steel matrix, which makes characterization using electron microscopy techniques tedious to perform. Recently, it is has been shown that precipitates in F-M steels can be efficiently studied with unprecedented statistics using the extraction replica samples and modern microscopy tools. To improve our understanding of F-M steel degradation processes in iradiation environments, this study underscores the need for an independent investigation of the irradiation behaviour of steel precipitates using in-situ irradiations.To accomplish our goal of studying irradiation damage within differing F-M steel precipitates such as M23C6, M7C3 and MX phases, this proposed work will perform in-situ ion irradiations inside a transmission electron microscope (TEM) at IVEM, using 1 MeV Fe ions up to 10 dpa using dose rate of ~10-3 dpa/s on extraction replica samples from a 9%Cr-1%Mo based T91 steel manufactured using AM. The irradiations will be performed at room temperature and 300 °C, to study the effect of temperature on defect evolution, precipitate amorphization etc. Performing irradiations on extracted precipitates has the advantage of uniquely studying the precipitate behavior without interference of the matrix. For simplicity, the irradiations will firstly focus on the microstructure evolution within the relatively coarser carbides such as M23C6 and M7C3, and then irradiation behavior of MX carbides will be explored. It is well-known that electronic energy deposited by electron beams can affect the irradiation damage phenomenon within non-metals. To account for this issue, two batches of experiments will be performed: (i) one with electron beam on, i.e. in-situ mode and (ii) without electron beam, which becomes an ex-situ mode. Following the irradiations, we will perform state-of-art post-irradiation characterization using conventional TEM, high-resolution TEM, EDX mapping in scanning TEM to characterize the irradiation induced defect microstructure and chemistry evolution within the precipitates. In addition, transmission Kikuchi diffraction (TKD) in a FEG-SEM will be performed to evaluate irradiation induced phase transformations, if any, occurring within the precipitates. Post-irradiation characterization does not require NSUF support. Performing ion irradiation on replica samples is also not a technical issue because insitu irradiations on carbon-based supports have been performed at numerous insitu accelerator labs across the globe where it is well-known that carbon supports stay stable under irradiation and high temperatures.These experiments will provide crucial fundamental knowledge of how non-metallic precipitates can evolve under irradiation and thereby help better predict the irradiation behavior of F-M steels.
Additional Info
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| Abstract | Ferritic-martensitic (F-M) steels are promising structural material candidates for Generation IV fast reactor concepts, and are gaining increased attention for fabrication using additive manufacturing (AM) , demonstrating a paradigm shift in reactor designing. In these alloys, the in-reactor performance depends on the stability of the various non-metallic precipitate families such as M23C6, M7C3, M2X and MX carbides/nitrides. However, despite decades of research, the fundamental question of how irradiation damage propagates and looks like in nanoprecipitates such as those in F-M steels is not answered yet. This is partly due to the nanoscale precipitates being embedded in the steel matrix, which makes characterization using electron microscopy techniques tedious to perform. Recently, it is has been shown that precipitates in F-M steels can be efficiently studied with unprecedented statistics using the extraction replica samples and modern microscopy tools. To improve our understanding of F-M steel degradation processes in iradiation environments, this study underscores the need for an independent investigation of the irradiation behaviour of steel precipitates using in-situ irradiations.To accomplish our goal of studying irradiation damage within differing F-M steel precipitates such as M23C6, M7C3 and MX phases, this proposed work will perform in-situ ion irradiations inside a transmission electron microscope (TEM) at IVEM, using 1 MeV Fe ions up to 10 dpa using dose rate of ~10-3 dpa/s on extraction replica samples from a 9%Cr-1%Mo based T91 steel manufactured using AM. The irradiations will be performed at room temperature and 300 °C, to study the effect of temperature on defect evolution, precipitate amorphization etc. Performing irradiations on extracted precipitates has the advantage of uniquely studying the precipitate behavior without interference of the matrix. For simplicity, the irradiations will firstly focus on the microstructure evolution within the relatively coarser carbides such as M23C6 and M7C3, and then irradiation behavior of MX carbides will be explored. It is well-known that electronic energy deposited by electron beams can affect the irradiation damage phenomenon within non-metals. To account for this issue, two batches of experiments will be performed: (i) one with electron beam on, i.e. in-situ mode and (ii) without electron beam, which becomes an ex-situ mode. Following the irradiations, we will perform state-of-art post-irradiation characterization using conventional TEM, high-resolution TEM, EDX mapping in scanning TEM to characterize the irradiation induced defect microstructure and chemistry evolution within the precipitates. In addition, transmission Kikuchi diffraction (TKD) in a FEG-SEM will be performed to evaluate irradiation induced phase transformations, if any, occurring within the precipitates. Post-irradiation characterization does not require NSUF support. Performing ion irradiation on replica samples is also not a technical issue because insitu irradiations on carbon-based supports have been performed at numerous insitu accelerator labs across the globe where it is well-known that carbon supports stay stable under irradiation and high temperatures.These experiments will provide crucial fundamental knowledge of how non-metallic precipitates can evolve under irradiation and thereby help better predict the irradiation behavior of F-M steels. |
| Award Announced Date | 2019-02-08T00:00:00 |
| Awarded Institution | Pacific Northwest National Laboratory |
| Facility | Radiochemical Processing Laboratory |
| Facility Tech Lead | Stuart Maloy, Wei-Ying Chen |
| Irradiation Facility | None |
| PI | Shradha Agarwal |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1694 |