Generation IV Lead-Cooled Fast Reactors (LFRs) represent one of the best solutions for a safe and sustainable energy future. However, their extreme operating conditions require the development of new materials. Ceramic coatings, particularly amorphous yttria-doped alumina thin films with an AY 7030 composition, deposited via Pulsed Laser Deposition (PLD), offer a valid response to the liquid metal-induced corrosion of structural steels. The mechanical characterization of these films is complex, as conventional analytical methods for nanoindentation prove to be inadequate for micrometric thicknesses. This study aims to accurately identify the mechanical properties of AY 7030 films, specifically Young's modulus and yield stress. A methodology which combines experimental nanoindentation tests and finite element modeling was adopted. The experimental setup was replicated in Abaqus using a two-dimensional axisymmetric model, calibrated by considering the real blunting of the indenter tip. Python-developed algorithms allowed for parameter estimation through inverse analysis, utilizing a deterministic least-squares approach and, subsequently, a Bayesian formulation based on the Extended Kalman Filter (EKF), which also enables the estimation of confidence intervals. The results demonstrate the effectiveness of this hybrid approach for the characterization of thin coatings. For a comprehensive mechanical validation, further investigations are required. In particular, studies regarding the film's sensitivity to hydrostatic pressure via the Drucker-Prager criterion, coupling nanoindentation with uniaxial compression test on micropillars. Furthermore, the integration of a study of the residual imprint and the use of a 3D model could further improve the accuracy of the results.
I reattori nucleari di quarta generazione raffreddati a piombo rappresentano una delle migliori soluzioni per un futuro energetico sicuro e sostenibile. Tuttavia, le loro estreme condizioni operative richiedono lo sviluppo di nuovi materiali. I rivestimenti ceramici, in particolare i film sottili amorfi in allumina drogata con ittria di composizione AY 7030, depositati mediante deposizione laser pulsata (PLD), offrono una valida risposta alla corrosione degli acciai strutturali indotta dal metallo liquido. La caratterizzazione meccanica di questi film è complessa poiché i metodi analitici convenzionali per la nanoindentazione risultano inadeguati per spessori micrometrici. Questo studio mira a identificare con precisione le proprietà meccaniche dei film AY 7030, in particolare il modulo di Young e la tensione di snervamento. È stata adottata una metodologia che combina prove sperimentali di nanoindentazione e modellazione agli elementi finiti. Il setup sperimentale è stato riprodotto in Abaqus mediante un modello bidimensionale assialsimmetrico, calibrato considerando il reale arrotondamento della punta dell'indentatore. Gli algoritmi sviluppati in Python hanno permesso di stimare i parametri mediante analisi inversa, utilizzando un approccio deterministico ai minimi quadrati e, successivamente, una formulazione bayesiana basata sull'Extended Kalman Filter (EKF), che consente di stimare anche gli intervalli di confidenza. I risultati dimostrano l’efficacia di questo approccio ibrido per la caratterizzazione di rivestimenti sottili. Per una completa validazione meccanica, sono necessari ulteriori approfondimenti. In particolare, studi riguardanti la sensibilità del film alla pressione idrostatica tramite il criterio di Drucker-Prager, accoppiando la nanoindentazione alla compressione uniassiale su micropillar. Inoltre, l'integrazione di uno studio approfondito dell'impronta residua e l'utilizzo di un modello 3D potrebbero migliorare ulteriormente l'accuratezza dei risultati.
Experimental and numerical analysis for mechanical characterization of Alumina-Yttria films in lead-cooled fast fission reactors
GUGLIELMETTI, LAURA
2025/2026
Abstract
Generation IV Lead-Cooled Fast Reactors (LFRs) represent one of the best solutions for a safe and sustainable energy future. However, their extreme operating conditions require the development of new materials. Ceramic coatings, particularly amorphous yttria-doped alumina thin films with an AY 7030 composition, deposited via Pulsed Laser Deposition (PLD), offer a valid response to the liquid metal-induced corrosion of structural steels. The mechanical characterization of these films is complex, as conventional analytical methods for nanoindentation prove to be inadequate for micrometric thicknesses. This study aims to accurately identify the mechanical properties of AY 7030 films, specifically Young's modulus and yield stress. A methodology which combines experimental nanoindentation tests and finite element modeling was adopted. The experimental setup was replicated in Abaqus using a two-dimensional axisymmetric model, calibrated by considering the real blunting of the indenter tip. Python-developed algorithms allowed for parameter estimation through inverse analysis, utilizing a deterministic least-squares approach and, subsequently, a Bayesian formulation based on the Extended Kalman Filter (EKF), which also enables the estimation of confidence intervals. The results demonstrate the effectiveness of this hybrid approach for the characterization of thin coatings. For a comprehensive mechanical validation, further investigations are required. In particular, studies regarding the film's sensitivity to hydrostatic pressure via the Drucker-Prager criterion, coupling nanoindentation with uniaxial compression test on micropillars. Furthermore, the integration of a study of the residual imprint and the use of a 3D model could further improve the accuracy of the results.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/260322