NSUF 17-1080: Post-irradiation analysis of hybrid metallic coatings on SiC after neutron irradiation 290-330°C
The objective of the project is to examine and understand the post-irradiation microstructure of metallic coatings on SiC. This will determine whether said coatings would be successful in light water and advanced reactor environments. The first phase of the investigation eliminates the effects of coolant by irradiating in inert gas. The project would use a simple but rigorous post-irradiation examination (PIE) of the coating/coupons. First, optical inspection of the coupons can show gross compressive or tensile stresses. Mismatch stresses by thermal expansion were in the order of 0.1% (0.001) but the linear radiation swelling was expected to be ~5 x 10-3 (0.5%). For ceramic coatings, imposed strain of this order can quickly show in optical inspection, and is easily detected after cross-sectioning. A key part of the PIE is conventional Bragg-Brentano X-ray Diffraction (2? direction) with supporting NIST standards, zero-background holders and contamination control. This would obtain phase transformations, and changes in microstrain, crystallite size and lattice parameters. The coating compositions are unique in chemistry and are materials that were selected for corrosion resistance. Therefore, lattice parameters would be an early indication of radiation stability of the microstructure at this temperature. Secondly, these are unique materials in the sense that they have a unique stress state not typically found in bulk materials and further X-ray analysis is possible by collecting on the ?-direction to determine texture, residual stress, grain size and epitaxial relations. The coupons are designed for multipurpose use, and adhesion pull-off tests are considered for coatings that show no visible damage. This is conducted using a commercial pull-stub/epoxy system that attempts to remove parts of the coating to determine the debonding strength. The final step of mounting for FIB foil extraction and TEM is the most crucial. The FIB extraction also provides SEM, which can confirm whether a tensile or compressive stress state likely existed in the coating, and whether the interface between SiC and the coating was maintained. TEM of the coating will show the defect cluster configuration, density and chemical composition changes. This is the de facto method for defect characterization. This will provide insight into what type of defects are present, correlated to other data such as lattice parameter swelling and crystallite size to determine whether the coating material is undergoing point defect or void swelling. The benefits of this research are two-fold. First, optical microscopy, cross-sectioning and mechanical testing should validate or devalidate the concept of coatings for SiC fuel cladding, and addresses a significant gap that will provide fundamental principles to barrier coating designs in core environments. Secondly, several coatings (Ni2Si, TiN, ZrSi2, Cr2N and CrN) are compounds that have little to no irradiation history, and the microstructures produced by TEM are of fundamental to comprehensive understanding of radiation defects in the relatively few ceramics that have been irradiated. At least one peer-reviewed publication and two short communications are expected from this study.
Additional Info
| Field | Value |
|---|---|
| Abstract | The objective of the project is to examine and understand the post-irradiation microstructure of metallic coatings on SiC. This will determine whether said coatings would be successful in light water and advanced reactor environments. The first phase of the investigation eliminates the effects of coolant by irradiating in inert gas. The project would use a simple but rigorous post-irradiation examination (PIE) of the coating/coupons. First, optical inspection of the coupons can show gross compressive or tensile stresses. Mismatch stresses by thermal expansion were in the order of 0.1% (0.001) but the linear radiation swelling was expected to be ~5 x 10-3 (0.5%). For ceramic coatings, imposed strain of this order can quickly show in optical inspection, and is easily detected after cross-sectioning. A key part of the PIE is conventional Bragg-Brentano X-ray Diffraction (2? direction) with supporting NIST standards, zero-background holders and contamination control. This would obtain phase transformations, and changes in microstrain, crystallite size and lattice parameters. The coating compositions are unique in chemistry and are materials that were selected for corrosion resistance. Therefore, lattice parameters would be an early indication of radiation stability of the microstructure at this temperature. Secondly, these are unique materials in the sense that they have a unique stress state not typically found in bulk materials and further X-ray analysis is possible by collecting on the ?-direction to determine texture, residual stress, grain size and epitaxial relations. The coupons are designed for multipurpose use, and adhesion pull-off tests are considered for coatings that show no visible damage. This is conducted using a commercial pull-stub/epoxy system that attempts to remove parts of the coating to determine the debonding strength. The final step of mounting for FIB foil extraction and TEM is the most crucial. The FIB extraction also provides SEM, which can confirm whether a tensile or compressive stress state likely existed in the coating, and whether the interface between SiC and the coating was maintained. TEM of the coating will show the defect cluster configuration, density and chemical composition changes. This is the de facto method for defect characterization. This will provide insight into what type of defects are present, correlated to other data such as lattice parameter swelling and crystallite size to determine whether the coating material is undergoing point defect or void swelling. The benefits of this research are two-fold. First, optical microscopy, cross-sectioning and mechanical testing should validate or devalidate the concept of coatings for SiC fuel cladding, and addresses a significant gap that will provide fundamental principles to barrier coating designs in core environments. Secondly, several coatings (Ni2Si, TiN, ZrSi2, Cr2N and CrN) are compounds that have little to no irradiation history, and the microstructures produced by TEM are of fundamental to comprehensive understanding of radiation defects in the relatively few ceramics that have been irradiated. At least one peer-reviewed publication and two short communications are expected from this study. |
| Award Announced Date | 2017-09-20T12:31:43.24 |
| Awarded Institution | Center for Advanced Energy Studies |
| Facility | Microscopy and Characterization Suite |
| Facility Tech Lead | Kory Linton, Yaqiao Wu |
| Irradiation Facility | None |
| PI | David Carpenter |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1080 |