Page 310 - 00. Complete Version - Progress Report IPEN 2014-2016

310 Materials and Nanotechnology | Progress Report

Coatings and Corrosion Protection

Hydrotalcite coatings to protect spent ation the nature of the RE, RE oxide crystallite
Al-clad fuels during wet storage size, RE oxide morphology, ionic radius of the
RE and the RE oxide coating coverage. In this
An all-room temperature process was devel- study, the oxidation behavior of three ferrit-
oped to coat Al alloy surfaces with hydrotal- ic stainless steels with varying amounts of Cr
cite (HTC). This process consists of pre-treat- and coated with individual and mixtures of
ment, coating with HTC and post-treatment nanocrystalline oxides of Ce, La, Nd and Pr in
of the Al alloys. Field tests were carried out in air at 1000 °C was determined. The main cri-
which dummy MTR type fuel elements con- terion for optimization was the extent of ad-
taining uncoated, HTC coated and HTC + Ce dition of a trivalent RE oxide to bivalent ceri-
coated plates were exposed for periods of up um oxide. Figure 35 shows a mixed RE oxide
to 2 years to the spent fuel basin of the IEA-R1 coating on AISI 409 surface. The CeO2 + 10%
reactor. The HTC + Ce coated plates were free Pr2O3 mixture imparted maximum oxida-
from any form of corrosion compared with the tion resistance to the steel surface at 1000 °C.
other plates, revealing marked potential for
its use to protect spent Al-clad fuel elements
against corrosion during extended wet stor-
age. Figure 34 shows HTC coating on an alu-
minum alloy surface.

Figure 35: Scanning electron micrograph of CeO2
+ 10% Pr2O3 mixture on AISI 409 surface.

Localized electrochemical study of welded
Al alloy joined by friction stir welding

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

Instituto de Pesquisas Energéticas e Nucleares