Materials Science and Engineering A300 (2001) 183 – 189
Hot corrosion of atomized iron aluminides doped with boron and
reinforced with alumina
M.A. Espinosa-Medina
a
, M. Casales
a
, A. Martinez-Villafan ˜e
a
, J. Porcayo-Calderon
b
,
L. Martinez
c,d
, J.G. Gonzalez-Rodriguez
d,e,
*
a
CIMAV, Miguel de Cerantes 120, Complejo Ind. Chihuahua, Chihuahua, Chih., Mexico
b
Instituto de Inestigaciones Ele ´ctricas, Cuernaaca, Mor., Mexico
c
U.N.A.M. Centro de Ciencias Fı ´sicas, Cuernaaca, Mor., Mexico
d
IMP, Eje Central Lazaro Cardenaz 152, Mexico City, Mexico
e
U.A.E.M. Centro de Ind. En Ingenieria y Ciencias Aplicadas, A. Uniersidad 1001, C.P. 62210, Col Chamilpa, Cuernaaca, Morelo, Mexico
Received 22 March 2000; received in revised form 18 August 2000
Abstract
The hot corrosion resistance of sprayed and atomized Fe–40 at.% Al, Fe40Al +0.1B and Fe40Al +0.1B +10Al
2
O
3
intermetal-
lic materials have been evaluated in NaVO
3
at 625 and 700°C using polarization curves and linear polarization resistance
measurements. Also, the results were supported by X-ray diffractometry and electron microscopy studies. The tests lasted 10 days.
At 625°C, the Fe40Al +0.1B +10Al
2
O
3
material exhibited the lowest corrosion rate, whereas the Fe40Al had the highest
corrosion rate. At 700°C the three materials exhibited erratic behavior during the first 100 h, and after this all the intermetallics
had the same corrosion rate. However, the corrosion rate was higher at 625 than at 700°C. The results are discussed in terms of
an electrochemical mechanism, the establishment of an Al
2
O
3
layer, which is more protective in the Al
2
O
3
-containing aluminide
and seems to increase its protectiveness as the temperature increases from 625 to 700°C. © 2001 Elsevier Science B.V. All rights
reserved.
Keywords: Atomised Fe40Al; Hot corrosion; Intermetallics; Linear polarization resistance measurements
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1. Introduction
Corrosion rate is one of the most important parame-
ters in corrosion, particularly in industries where the
damage generated by corrosion can cause catastrophic
failures. This is particularly important in heat exchang-
ers, incinerators and burners, caused mainly by molten
salts. Several alloys in corrosive environments at high
temperature have been evaluated, and the environments
include vanadium pentoxide (V
2
O
5
) [1], sodium sul-
fate +vanadium pentoxide (Na
2
SO
4
+V
2
O
5
) [2], sul-
fates +chlorides and carbonates [3,4]. Intermetallic
materials are formed by the reaction of two elements
that form compounds whose properties and characteris-
tics are different from the original elements. Fe – Al-
based intermetallics have a higher corrosion resistance
in both gases and in molten salts compared with com-
mon alloys [5]. Atomized Fe 40 at.% – Al-based inter-
metallics have been evaluated in a mixture of 20
wt%Na
2
SO
4
+80 wt%V
2
O
5
at 600, 700, 800 and 900°C,
and it is concluded that the aluminum oxide (Al
2
O
3
)
layer has a very important role in its corrosion resis-
tance [6]. Similar results were obtained by Tortorelli [5]
for Fe
3
Al
2
Cr in molten Na
2
SO
4
at 650 and 700°C for
800 h. Corrosion of iron aluminides in molten
NaNO
3
(KNO
3
)–Na
2
O
2
at 650°C proceeds by oxidation
and a low release from an aluminum-rich product layer
into the salt such that the compositions with higher
aluminum concentrations yielded significantly better
corrosion resistance [8]. Preliminary 900°C results from
exposure of FeAl to molten NaCl–Na
2
CO
3
(used as an
oxidizer for waste disposal) showed significantly better
corrosion resistance of this aluminide than Inconel 600
[9].
* Corresponding author. Tel./fax: +52-7-3297084.
E-mail address: ggonzalez@buzom.uaem.mx (J.G. Gonzalez-Ro-
driguez).
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