The problem of heat exhaust is one of the most concerning in the roadmap to the realization of a fusion power plant. The most extreme conditions will have to be endured by the divertor component, currently designed to use tungsten (W) as the plasma facing material. Liquid metals may play a key role in solving the lifetime issues of the solid W divertor design. However, their use may be limited by their strong corrosion action on surrounding materials. To avoid deterioration of thermal and mechanical properties, it is necessary to develop a thin but effective corrosion barrier to protect sensible components. The need for a practical solution in a scarcely investigated field of material science led to the collaboration of Politecnico di Milano and ENEA-Frascati which this thesis work was part of. In this thesis the corrosion of molten tin (Sn) on copper(Cu)-based material has been investigated in order to advance the conceptual divertor design proposed by ENEA. Tungsten (W) was the prime material considered, due to its excellent Sn corrosion resistance in fusion-relevant applications. During this thesis the High Power Impulse Magnetron Sputtering (HiPIMS) technique was used to design and produce dense W coatings with corrosion barrier properties. Morphology, crystallographic structure and film defects were characterized and correlated with substrate properties. Samples were produced and exposed to liquid Sn in order to investigate coatings as corrosion barriers and to gain a better understanding of film failure mechanisms in a liquid metal environment. Exposure to static liquid Sn for up to 10 hours demonstrated that W-based films produced by HiPIMS are promising candidate barrier coatings for future liquid metal divertors. With respect to pure-W films, amorphous-like films obtained by co-deposition of W and Al demonstrated increased corrosion barrier performances, reduced reliability issues and showed resilience against the spreading of Sn corrosion.
Il problema della dissipazione del calore è uno dei principali ostacoli verso la produzione di energia da fusione nucleare. La zona del divertore dovrà sopportare le condizioni più estreme e per questo il tungsteno (W) viene usato come materiale affacciato al plasma. I metalli liquidi possono essere un'alternativa chiave per ridurre i problemi di durabilità del divertore in W solido. Il loro uso è tuttavia limitato dalla forte corrosione che esercitano sui materiali circostanti. Per evitare perdita di proprietà termiche e meccaniche, è necessario sviluppare una barriera anticorrosione sottile ma efficace per proteggere i componenti sensibili. Questo problema è stato affrontato tramite una collaborazione tra il Politecnico di Milano ed ENEA-Frascati, di cui questo lavoro di tesi fa parte. In questa tesi è stata studiata la corrosione dello stagno (Sn) fuso su materiali a base di rame (Cu), al fine di approfondire il design concettuale del divertore proposto da ENEA. Il tungsteno (W) è stato il principale materiale investigato come barriera anticorrosione, grazie a un'alta resistenza alla corrosione da Sn. In questa tesi è stata utilizzata la tecnica HiPIMS (High Power Impulse Magnetron Sputtering) per progettare e produrre rivestimenti in W ad alta densità. La morfologia, la struttura cristallografica e i difetti del film sono stati caratterizzati e correlati alle proprietà del substrato. Svariati campioni sono stati prodotti e testati sperimentalmente tramite esposizione a Sn liquido per valutare l'impiego di tali film come rivestimenti protettivi e per comprendere meglio i meccanismi di rottura del film in un ambiente di metallo liquido. I campioni hanno resistito a Sn a 400°C testato fino a un massimo di 10 ore, dimostrando che i film a base di W prodotti tramite HiPIMS sono candidati promettenti per i futuri divertori a metallo liquido. I film in puro W hanno mostrato però problemi di affidabilità a causa della presenza di difetti causati dal substrato. Film amorfi ottenuti dalla co-deposizione di W e Al hanno dimostrato invece maggiore protezione, ridotto i problemi di affidabilità e mostrato resilienza alla propagazione della corrosione da Sn.
Experimental investigation of thin tungsten films as corrosion barriers for liquid metal divertor conceptual designs
Bugatti, Marco
2022/2023
Abstract
The problem of heat exhaust is one of the most concerning in the roadmap to the realization of a fusion power plant. The most extreme conditions will have to be endured by the divertor component, currently designed to use tungsten (W) as the plasma facing material. Liquid metals may play a key role in solving the lifetime issues of the solid W divertor design. However, their use may be limited by their strong corrosion action on surrounding materials. To avoid deterioration of thermal and mechanical properties, it is necessary to develop a thin but effective corrosion barrier to protect sensible components. The need for a practical solution in a scarcely investigated field of material science led to the collaboration of Politecnico di Milano and ENEA-Frascati which this thesis work was part of. In this thesis the corrosion of molten tin (Sn) on copper(Cu)-based material has been investigated in order to advance the conceptual divertor design proposed by ENEA. Tungsten (W) was the prime material considered, due to its excellent Sn corrosion resistance in fusion-relevant applications. During this thesis the High Power Impulse Magnetron Sputtering (HiPIMS) technique was used to design and produce dense W coatings with corrosion barrier properties. Morphology, crystallographic structure and film defects were characterized and correlated with substrate properties. Samples were produced and exposed to liquid Sn in order to investigate coatings as corrosion barriers and to gain a better understanding of film failure mechanisms in a liquid metal environment. Exposure to static liquid Sn for up to 10 hours demonstrated that W-based films produced by HiPIMS are promising candidate barrier coatings for future liquid metal divertors. With respect to pure-W films, amorphous-like films obtained by co-deposition of W and Al demonstrated increased corrosion barrier performances, reduced reliability issues and showed resilience against the spreading of Sn corrosion.| File | Dimensione | Formato | |
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2023_07_Bugatti_ExecutiveSummary_02.pdf
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2023_07_Bugatti_Tesi_01.pdf
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https://hdl.handle.net/10589/212442