NSUF 24-5078: In-situ TEM Heating Investigation of M23C6 Stability in Neutron Irradiated HT9

HT9 is the leading structure materials for various advanced reactor systems as it manifests high thermal conductivity, low thermal expansion coefficient, good high temperature strength, very low void swelling rate under neutron irradiations. HT9 also manifest high temperature strength which highly relies on the stability of tempered microstructure features including lath boundary and pre-excising M23C6 precipitates. However, under extreme conditions, particularly high temperature (>600°C), significant microstructural changes could occur in HT9, causing deleterious effects on the long-term performance of HT9 steel for high temperature applications. There is a great need to improve understanding the stability of pre-existing M23C6 precipitate (typically ~150nm) stability under extreme irradiation conditions as M23C6 plays a governing role in strengthening the lath boundaries and mitigating the gliding of mobile dislocations, therefore strongly affecting the high temperature strength of HT9 steel. This Super RTR is aiming to fill this knowledge gap by performing in-situ TEM heating study of one fresh HT9 and seven neutron-irradiated HT9 samples which are all available for this work. The accomplishment of this project will harvest a quantitative data set of microstructure features for neutron-irradiated HT9 at temperature of 540-680℃ with achieved dose of 9-79dpa. The microstructure data set include 1) a quantitative measurement of microstructure features, including the size, distribution, and number density of precipitate, matrix composition, dislocation microstructure, and lath boundary; and 2) the relationship of M23C6 stability in terms of initial size, dpa, and heating temperature (650 and 800℃ holding up to 2hr); and 3) potentially dynamic evolution of lath boundary and dislocations during heating study. The results are believed to be valuable asset to improve the mechanical properties of HT9 cladding for high temperature application in advanced reactors. The results will be reported in the final report and published in a journal manuscript (aiming at Journal of Nuclear Materials).

Additional Info

Field	Value
Award Announced Date	2024-08-15T09:39:40.39
Awarded Institution	Idaho National Laboratory
Facility Tech Lead	Alina Montrose
Irradiation Facility
PI	Yachun Wang
PI Email	[email protected]
Project Type	RTE
RTE Number	None