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@PHDTHESIS{Aarab:996219,
author = {Aarab, Fadoua},
othercontributors = {Schwaiger, Ruth and Zander, Brita Daniela},
title = {{E}ntwicklung und {C}harakterisierung
salzkorrosionsresistenter ferritischer {E}delstähle zur
{A}nwendung in solarthermischen {K}raftwerken},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2024-10454},
pages = {1 Online-Ressource : Illustrationen},
year = {2024},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University 2025; Dissertation, Rheinisch-Westfälische
Technische Hochschule Aachen, 2024},
abstract = {The aim of the present work is the development and
characterization of salt corrosion resistant, cost-effective
steels for application in solar thermal power plants. The
base of the alloy development is the fully ferritic
high-performance steel called HiperFer (High performance
Ferrite) developed at Forschungszentrum Jülich (IEK-2),
which is known for its good thermomechanical fatigue
strength, steam oxidation resistance and creep resistance.
Concentrating solar power (CSP) and thermal energy storage
(TES) based on molten salts are still not economically
feasible, with material investment costs being a major
drawback. Ferritic stainless steels are a comparatively
inexpensive class of materials that can contribute
significantly to cost reduction. The addition of aluminium
to ferritic stainless steel can lead to self-passivation by
formation of a compact Al2O3 top layer, which has
significantly higher corrosion resistance to solar salt
compared to the Cr2O3 top layers that typically form on
expensive structural alloys (like austenitic steels and
Ni-base alloys) for CSP and TES. Cyclic salt corrosion tests
under flowing synthetic air were performed on ferritic
experimental alloys (17Cr2-14Al0.6-1Nb2.6-4W0.25Si) using
solar salt (60 $wt.-\%$ NaNO3 and 40 $wt.-\%$ KNO3). The Al
content of the steel was varied to investigate potentially
hazardous effects on precipitation strengthening Laves phase
particles as well as the effect on the formation of
protective Al oxide top layers. The W and Nb contents of the
alloys were increased to study their influence on the
precipitation of the Laves phase. The salt corrosion
experiments showed that in novel ferritic HiperFerSCR (Salt
Corrosion Resistant) steels, simultaneous self-passivation
against molten salt attack and mechanical strengthening by
precipitation of fine Laves phase particles are possible.
The microstructural investigation revealed the formation of
a compact, continuous Al2O3 layer on the surface of the
model alloys with Al contents of at least 5 $wt.-\%.$ Due to
the formation of the protective Al2O3 layer, low corrosion
rates comparable to the corrosion rates of expensive,
alumina forming Ni-based alloys are achieved. In addition, a
stable distribution of fine strengthening Laves phase
precipitates in the metal matrix has been achieved,
resulting in a combination of salt corrosion resistance and
potentially high mechanical strength through a combination
of solid solution and precipitation strengthening. In
addition to adjusting the chemical composition, salt
corrosion resistance can be further optimized by suitable
surface treatment. It has been shown that a roughened
surface promotes the formation of a protective Al2O3 layer.
These results show that high-strength ferritic alloys are
promising candidates for use in CSP and TES applications. In
this work, the Laves phase evolution at higher temperatures
was also investigated. It was shown that the chemical
composition as well as the thermal pre-treatment affects the
mechanical properties and the microstructure especially by
change in Laves phase precipitation. The addition of
aluminium leads to incorporation of Al into a
(Fe,Cr,Al,Si)2(Nb,W) Laves Phase. Thus, the strengthening of
the HiperFerSCR ferritic alloy concept occurs by solid
solution and precipitation strengthening mechanisms.
Accordingly, suitable heat treatment parameters are
necessary to achieve an optimum particle size distribution.
Considering the Laves phase stability, oxide film formation
and corrosion rates, the model alloy with an Al content of 5
wt. $\%$ prove to be a promising future material for CSP and
TES applications.},
cin = {527110 / 522710 / 520000},
ddc = {620},
cid = {$I:(DE-82)527110_20191118$ / $I:(DE-82)522710_20140620$ /
$I:(DE-82)520000_20140620$},
pnm = {Verbundvorhaben STERN: Steigerung der Kosteneffizienz von
Flüssigsalzreceivern; Teilvorhaben: Entwicklung und
Qualifizierung von Werkstoffen für Solarreceiver
(03EE5048D)},
pid = {G:(BMWi)03EE5048D},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2024-10454},
url = {https://publications.rwth-aachen.de/record/996219},
}
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