Development of Self-Passivating, High-Strength Ferritic Alloys for Concentrating Solar Power (CSP) and Thermal Energy Storage (TES) Applications

Fadoua Aarab () and Bernd Kuhn
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Fadoua Aarab: Institute of Energy and Climate Research (IEK), Structure and Function of Materials (IEK-2), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
Bernd Kuhn: Institute of Energy and Climate Research (IEK), Structure and Function of Materials (IEK-2), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany

Energies, 2023, vol. 16, issue 10, 1-12

Abstract: Concentrating solar power (CSP) and thermal energy storage (TES) based on molten salts still lacks economic feasibility, with the material investment costs being a major drawback. Ferritic stainless steels are a comparatively cheap class of materials that could significantly contribute to cost reductions. The addition of aluminum to ferritic steel can result in self-passivation by forming a compact Al 2 O 3 top layer, which exhibits significantly higher corrosion resistance to solar salt compared to the Cr 2 O 3 surface layers typically formed on expensive structural alloys for CSP and TES, such as austenitic stainless steels and Ni-base super alloys. However, to date, no ferritic stainless steel combining Al 2 O 3 formation and sufficient structural strength is available. For this reason, cyclic salt corrosion tests under flowing synthetic air were carried out on seven Laves phase-forming, ferritic model alloys (17Cr2-14Al0.6-1Nb2.6-4W0.25Si), using “solar salt” (60 wt. % NaNO 3 and 40 wt. % KNO 3 ). The Al content was varied to investigate the influence on the precipitation of the mechanically strengthening Laves phase, as well as the impact on the formation of the Al-oxide top layer. The W and Nb contents of the alloys were increased to examine their influence on the precipitation of the Laves phase. The salt corrosion experiments demonstrated that simultaneous self-passivation against a molten salt attack and mechanical strengthening by precipitation of fine Laves phase particles is possible in novel ferritic HiperFer SCR (salt corrosion-resistant) steel. Microstructural examination unveiled the formation of a compact, continuous Al 2 O 3 layer on the surface of the model alloys with Al contents of 5 wt. % and higher. Furthermore, a stable distribution of fine, strengthening Laves phase precipitates was achieved in the metal matrix, resulting in a combination of molten salt corrosion resistance and potentially high mechanical strength by a combination of solid solution and precipitation strengthening. These results show that high-strength ferritic alloys are suitable for use in CSP applications.

Keywords: thermal energy storage; concentrating solar power; protective Al 2 O 3 scale; salt corrosion resistance; strengthening Laves phase precipitation (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2023
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