NSUF 24-4889: Study of the behavior under ion irradiation of amorphous oxide protective coatings developed for lead fast reactors

The outstanding properties of a-Al2O3 coatings are strictly related to their integrity in any case. The latter is, in turn, linked to the stability of the amorphous microstructure of the coating. Indeed, crystallization of the a-Al2O3 coating occurs above 600°C, and phase transformation might lead to densification. This can also turn into crack formation and loss of adhesion and coating integrity, thus exposing the underlying substrate to corrosive environments. This issue is exacerbated when the coating is working under a radiation field because it can even accelerate the crystallization process. Understanding the radiation-enhanced/induced crystallisations is therefore crucial. Radiation-induced crystallization was elucidated for the PLD a-Al2O3 case thanks to two different experimental campaigns at the IVEM tandem facility: grain growth was found to occur at a lower temperature than that at which crystallization occurs in absence of a radiation field (600°C) Then It was also shown thanks to another NSUF campaign that the addition of 3% wt. Yttria dopant exhibits a positive impact on the crystallization process, as it significantly retards the onset of nucleation of the crystalline phase and slows down the grain growth kinetics. However, the doping concentration considered cannot prevent crystallization at higher radiation doses, even at the lowest temperature analyzed (400°C). For this reason, increasing the doping concentration to retard further the crystallization was explored. Indeed, the Y2O3 doping concentration effect on the crystallization temperature was investigated by IIT since the last RTE. A combination of vacuum annealing to promote temperature-induced crystallization, X-ray Diffraction measurement to assess the crystalline phases, and SEM micrography to check the coating integrity were exploited. We have successfully determined the optimal dopant concentration that facilitates the structural stability of Al2O3- based coatings. XRD measurements confirmed the optimum composition possesses an amorphous structure with a remarkably temperature-induced crystallization threshold of above 950°C. The present study investigates the retarding effect of varying dopant concentrations on the radiation-induced crystallization of amorphous alumina coatings.

Additional Info

Field	Value
Award Announced Date	2024-02-02T12:36:25.103
Awarded Institution	Istituto Italiano di Tecnologia
Facility Tech Lead	Wei-Ying Chen
Irradiation Facility
PI	Fabio Di Fonzo
PI Email	[email protected]
Project Type	RTE
RTE Number	None