Page 26 - PR 2014 2016 10 Materials and Nanotechnology

302 Materials and Nanotechnology | Progress Report

Coatings and Corrosion of chromium dioxide forming Fe-Cr alloys was
Protection studied. This optimization took into consider-

ation the nature of the RE, RE oxide crystallite
size, RE oxide morphology, ionic radius of the
Hydrotalcite coatings to protect spent RE and the RE oxide coating coverage. In this
Al-clad fuels during wet storage study, the oxidation behavior of three ferritic

stainless steels with varying amounts of Cr
An all-room temperature process was devel- and coated with individual and mixtures of
oped to coat Al alloy surfaces with hydrotalcite nanocrystalline oxides of Ce, La, Nd and Pr in air
(HTC). This process consists of pre-treatment, at 1000 °C was determined. The main criterion
coating with HTC and post-treatment of the for optimization was the extent of addition of
Al alloys. Field tests were carried out in which a trivalent RE oxide to bivalent cerium oxide.
dummy MTR type fuel elements containing Figure 35 shows a mixed RE oxide coating on
uncoated, HTC coated and HTC + Ce coated AISI 409 surface. The CeO + 10% Pr O mixture
2 2 3
plates were exposed for periods of up to 2 years imparted maximum oxidation resistance to
to the spent fuel basin of the IEA-R1 reactor. the steel surface at 1000 °C.
The HTC + Ce coated plates were free from any
form of corrosion compared with the other
plates, revealing marked potential for its use
to protect spent Al-clad fuel elements against
corrosion during extended wet storage. Figure
34 shows HTC coating on an aluminum alloy
surface.

Figure 35: Scanning electron micrograph of CeO + 10% Pr O
2 2 3
mixture on AISI 409 surface.
Localized electrochemical study of welded
Al alloy joined by friction stir welding

Friction stir welding (FSW) is an efficient way
Figure 34: Scanning electron micrographs of RT-HTC coatings to join high strength aluminium alloys. How-
ever, FSW generates different microstructural
Nanocrystalline rare earth oxide coatings areas in contact that may give rise to galvanic
for increased high temperature oxidation couplings and affect the corrosion resistance
resistance of chromia forming alloys of the assembly. In the present work, a local-
ized electrochemical study of the AA7475-T651
Optimization of the use of different rare earth and AA2024-T3 alloys butt-joined by FSW
(RE) oxides as coatings to further enhancement was carried out. Much lower impedances
of the high temperature oxidation resistance were associated to the FSW affected zones

Instituto de Pesquisas Energéticas e Nucleares