NSUF 17-938: Nanoindentation testing of neutron irradiated 304 stainless steels hex-blocks

Investigation on neutron-induced changes in properties of reactor structural materials is necessary to predict lifetime limits for LWR applications. Additionally, the LWR industry is preparing for in-vessel welding of cracked structural components. The major structural steel is 304 stainless steel, but it is difficult to extract large test samples from operating reactors. To reduce cost and exposure, small-scale testing on mini-specimens has been used to conduct mechanical tests. It is now possible to further reduce specimen size using micro-scale mechanical testing. TEM disks cut from the EBR-II 304 SS hex-blocks are perfect for this purpose and the required examination facilities are available at INL. Most importantly, this work will strongly benefit from comparison with extensive published research on identical specimens. Density change, microstructure and microchemistry have already been examined and documented using densitometry, ultrasonic measurements, TEM, SEM and APT. Macroscopic mechanical properties were also determined by shear punch and mini-tensile testing. This will allow comparison of the new micro-mechanical measurements with the published macro-mechanical values. After optimizing the test parameters on unirradiated and neutron-irradiated specimens, these techniques will be used to evaluate identical specimens that were cut from specimens that are welded using low-energy input laser welding to mitigate the frequently observed helium-induced cracking, in order to assess changes in mechanical properties across the weld cross section. Nanoindentation tests will be performed to study the local mechanical properties of unirradiated, irradiated, and irradiated plus welded specimens, the latter especially measured across the weld boundaries. Pre-mapping and post-deformation mapping of near-surface voids using backscatter electron imaging will allow a nondestructive image of the deformation distribution using the deformation of the voids as a local strain monitor. Particular attention will be paid to areas where helium-induced cracking has occurred.

Additional Info

Field	Value
Abstract	Investigation on neutron-induced changes in properties of reactor structural materials is necessary to predict lifetime limits for LWR applications. Additionally, the LWR industry is preparing for in-vessel welding of cracked structural components. The major structural steel is 304 stainless steel, but it is difficult to extract large test samples from operating reactors. To reduce cost and exposure, small-scale testing on mini-specimens has been used to conduct mechanical tests. It is now possible to further reduce specimen size using micro-scale mechanical testing. TEM disks cut from the EBR-II 304 SS hex-blocks are perfect for this purpose and the required examination facilities are available at INL. Most importantly, this work will strongly benefit from comparison with extensive published research on identical specimens. Density change, microstructure and microchemistry have already been examined and documented using densitometry, ultrasonic measurements, TEM, SEM and APT. Macroscopic mechanical properties were also determined by shear punch and mini-tensile testing. This will allow comparison of the new micro-mechanical measurements with the published macro-mechanical values. After optimizing the test parameters on unirradiated and neutron-irradiated specimens, these techniques will be used to evaluate identical specimens that were cut from specimens that are welded using low-energy input laser welding to mitigate the frequently observed helium-induced cracking, in order to assess changes in mechanical properties across the weld cross section. Nanoindentation tests will be performed to study the local mechanical properties of unirradiated, irradiated, and irradiated plus welded specimens, the latter especially measured across the weld boundaries. Pre-mapping and post-deformation mapping of near-surface voids using backscatter electron imaging will allow a nondestructive image of the deformation distribution using the deformation of the voids as a local strain monitor. Particular attention will be paid to areas where helium-induced cracking has occurred.
Award Announced Date	2017-04-26T10:09:11.827
Awarded Institution	Center for Advanced Energy Studies
Facility	Microscopy and Characterization Suite
Facility Tech Lead	Yaqiao Wu
Irradiation Facility	None
PI	Cheng Sun
PI Email	[email protected]
Project Type	RTE
RTE Number	938