NSUF 19-1632: On Surprising Dose Rate Effects in Neutron Irradiated Fe-Cr Alloys: A TEM Study of Composition Effects at DPA Rates that Vary by Only a Factor of 4
It is essential to be able to replicate the neutron damage expected within structural materials used in commercial reactors. Although a fission materials-testing reactor is the closest analogue to a power-producing reactor, the higher neutron flux in such facilities could lead to inaccurate predictions of the irradiation hardening and embrittlement these materials experience due to the dose-rate effect. This work will study microstructural damage by Transmission Electron Microscopy (TEM) and electron energy-loss spectroscopy (EELS) of neutron-irradiated FeCr alloys, and compare these with the same alloys irradiated with neutrons to the same dose and at the same temperature, but faster dose-rate. This comparison is important towards the understanding of dose-rate effects, defect homogeneities, and chromium dependencies. We request 6 days on the active-materials dual-beam FIB microscope at CAES to produce TEM foils from two neutron-irradiated FeCr binary alloys; Fe3Cr and Fe12Cr. These alloys originate from capsule 1A of the UCSB-1 ATR experiment and will be compared with the equivalent alloys irradiated at a higher dose-rate (capsule 6A). We have already compared two sets of Fe6Cr and Fe9Cr alloys irradiated with neutrons, where the sets differ in dose-rate by a factor of 4. Our findings show there is a significant difference in the dislocation loop homogeneity, and a factor of 8 difference in the density of chromium α’-phases. These differences can only be attributed to the dose-rate effect. We studied alloys from the slower dose-rate experiment (capsule 1A), while other authors have conducted microstructural and microchemical analysis of the high dose-rate alloys. We propose to expand our investigation to include the slow dose-rate capsule 1A Fe3Cr and Fe12Cr alloys in order to gain a better understanding of the role chromium has on the dose-rate effect. Furthermore, we intend to retrieve the equivalent alloys from the capsule 6A experiment so that nanoindentation can be carried out on all high dose-rate and low dose-rate alloys in the range of 3-12Cr (alloys Fe6Cr and Fe9Cr from both capsules are already in the UK). Since TEM foils are very delicate and easily damaged or oxidised, it is important the final thinning process is conducted immediately prior to study in the TEM (within ~24 hours). For this reason, foils will only be prepared at CAES as far as being ready for the final lift-out and thinning process. These final steps of the foil preparation will be conducted at the Culham Centre for Fusion Energy (CCFE) (funded outside of this proposal). Nanoindentation will also be conducted at CCFE. Prior to FIB work, the neutron-irradiated materials will require polishing to obtain a high quality finish (suitable for EBSD) which is essential for quality FIB work and near surface mechanical testing (nanoindentation). A typical polishing procedure for this type of work would be with mechanical polishing down to ~1µm diamond, and final electropolish to remove residual surface deformation. For a previous RTE, this step was conducted by staff at INL prior to the samples’ shipment to CAES. We request the samples be prepared in the same manner for this work.
Допълнителна информация
| Поле | Стойност |
|---|---|
| Abstract | It is essential to be able to replicate the neutron damage expected within structural materials used in commercial reactors. Although a fission materials-testing reactor is the closest analogue to a power-producing reactor, the higher neutron flux in such facilities could lead to inaccurate predictions of the irradiation hardening and embrittlement these materials experience due to the dose-rate effect. This work will study microstructural damage by Transmission Electron Microscopy (TEM) and electron energy-loss spectroscopy (EELS) of neutron-irradiated FeCr alloys, and compare these with the same alloys irradiated with neutrons to the same dose and at the same temperature, but faster dose-rate. This comparison is important towards the understanding of dose-rate effects, defect homogeneities, and chromium dependencies. We request 6 days on the active-materials dual-beam FIB microscope at CAES to produce TEM foils from two neutron-irradiated FeCr binary alloys; Fe3Cr and Fe12Cr. These alloys originate from capsule 1A of the UCSB-1 ATR experiment and will be compared with the equivalent alloys irradiated at a higher dose-rate (capsule 6A). We have already compared two sets of Fe6Cr and Fe9Cr alloys irradiated with neutrons, where the sets differ in dose-rate by a factor of 4. Our findings show there is a significant difference in the dislocation loop homogeneity, and a factor of 8 difference in the density of chromium α’-phases. These differences can only be attributed to the dose-rate effect. We studied alloys from the slower dose-rate experiment (capsule 1A), while other authors have conducted microstructural and microchemical analysis of the high dose-rate alloys. We propose to expand our investigation to include the slow dose-rate capsule 1A Fe3Cr and Fe12Cr alloys in order to gain a better understanding of the role chromium has on the dose-rate effect. Furthermore, we intend to retrieve the equivalent alloys from the capsule 6A experiment so that nanoindentation can be carried out on all high dose-rate and low dose-rate alloys in the range of 3-12Cr (alloys Fe6Cr and Fe9Cr from both capsules are already in the UK). Since TEM foils are very delicate and easily damaged or oxidised, it is important the final thinning process is conducted immediately prior to study in the TEM (within ~24 hours). For this reason, foils will only be prepared at CAES as far as being ready for the final lift-out and thinning process. These final steps of the foil preparation will be conducted at the Culham Centre for Fusion Energy (CCFE) (funded outside of this proposal). Nanoindentation will also be conducted at CCFE. Prior to FIB work, the neutron-irradiated materials will require polishing to obtain a high quality finish (suitable for EBSD) which is essential for quality FIB work and near surface mechanical testing (nanoindentation). A typical polishing procedure for this type of work would be with mechanical polishing down to ~1µm diamond, and final electropolish to remove residual surface deformation. For a previous RTE, this step was conducted by staff at INL prior to the samples’ shipment to CAES. We request the samples be prepared in the same manner for this work. |
| Award Announced Date | 2019-02-08T00:00:00 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Yaqiao Wu |
| Irradiation Facility | None |
| PI | Jack Haley |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1632 |