NSUF 21-4331: Imaging of Irradiation Effects in Tantalum Alloys for Fast-Spectrum Self-Powered Neutron Detectors

Four samples of ASTAR-811C tantalum alloy and three samples of T-111 tantalum alloy were irradiated in the High Flux Isotope Reactor (HFIR) in 2005. All samples were irradiated in the same capsule at 800oC to 0.4 dpa and have undergone tensile strength and electrical resistivity measurements at LAMDA under a previously awarded RTE (20-4166). The results from these efforts indicate significant bulk material changes due to irradiation, a critical concern for detector performance and longevity of the Fast-Spectrum Self-Powered Neutron Detectors (FS-SPNDs) we are currently developing for the Versatile Test Reactor project. A deeper micro-structural investigation will allow us to model the observed macro-scale material changes in these materials, informing our future FS-SPND design efforts.

Because void swelling and dislocation loop evolution in neutron-irradiated tantalum alloys are both likely to occur at the irradiation temperature experienced by these Ta specimens (800oC ~ 0.33TM, where TM is the melting temperature of tantalum), these neutron irradiated specimens provide the added value of being able to map multiple irradiation-induced defects for future comparisons to damage simulated using charged particle irradiations. Radiation-induced void swelling is a critical consideration in the design of future tantalum-based fast-spectrum self-powered neutron detectors as this it could be a source of catastrophic detector failure. All seven tantalum alloy samples are in SS-3 type tensile specimen format. We will perform at least two focused ion beam (FIB) liftouts on one undeformed head section of a representative SS-3 tensile specimen for each alloy. We will then use scanning transmission electron microscopy (STEM) imaging to identify dislocation loop densities in each sample and over/under focus Fresnel contrast imaging to highlight any cavities present in the microstructure. The on-zone STEM imaging will require grains with ideal crystallographic orientations, so FIB liftouts will be informed by electron backscatter diffraction (EBSD) scans across the head of each tensile specimen. We expect all measurements to require 11 days of LAMDA facility time.

Additional Info

Field	Value
Abstract	Four samples of ASTAR-811C tantalum alloy and three samples of T-111 tantalum alloy were irradiated in the High Flux Isotope Reactor (HFIR) in 2005. All samples were irradiated in the same capsule at 800oC to 0.4 dpa and have undergone tensile strength and electrical resistivity measurements at LAMDA under a previously awarded RTE (20-4166). The results from these efforts indicate significant bulk material changes due to irradiation, a critical concern for detector performance and longevity of the Fast-Spectrum Self-Powered Neutron Detectors (FS-SPNDs) we are currently developing for the Versatile Test Reactor project. A deeper micro-structural investigation will allow us to model the observed macro-scale material changes in these materials, informing our future FS-SPND design efforts. Because void swelling and dislocation loop evolution in neutron-irradiated tantalum alloys are both likely to occur at the irradiation temperature experienced by these Ta specimens (800oC ~ 0.33TM, where TM is the melting temperature of tantalum), these neutron irradiated specimens provide the added value of being able to map multiple irradiation-induced defects for future comparisons to damage simulated using charged particle irradiations. Radiation-induced void swelling is a critical consideration in the design of future tantalum-based fast-spectrum self-powered neutron detectors as this it could be a source of catastrophic detector failure. All seven tantalum alloy samples are in SS-3 type tensile specimen format. We will perform at least two focused ion beam (FIB) liftouts on one undeformed head section of a representative SS-3 tensile specimen for each alloy. We will then use scanning transmission electron microscopy (STEM) imaging to identify dislocation loop densities in each sample and over/under focus Fresnel contrast imaging to highlight any cavities present in the microstructure. The on-zone STEM imaging will require grains with ideal crystallographic orientations, so FIB liftouts will be informed by electron backscatter diffraction (EBSD) scans across the head of each tensile specimen. We expect all measurements to require 11 days of LAMDA facility time.
Award Announced Date	2021-06-07T16:14:05.917
Awarded Institution	None
Facility	None
Facility Tech Lead	Kory Linton
Irradiation Facility	None
PI	Kathleen Goetz
PI Email	[email protected]
Project Type	RTE
RTE Number	4331