Chemical interaction of the In-Ga eutectic with Al and Al-base alloys

Article abstract of DOI:10.1134/S0020168506030083

The chemical interaction of the indium-gallium eutectic with Al and Al-base alloys is studied by x-ray diffraction, optical microscopy, and electron microscopy. Experimental data are presented that shed light on the reaction mechanism and the diffusion processes responsible for the subsequent disintegration of the material and its dissolution in water. Mechanical tests show that the activation of aluminum leads to a transition from plastic to brittle fracture. Pleiades Publishing, Inc., 2006.

Full text of DOI:10.1134/S0020168506030083

ISSN 0020-1685, Inorganic Materials, 2006, Vol. 42, No. 3, pp. 256–260. © Pleiades Publishing, Inc., 2006.
Original Russian Text © M.V. Trenikhin, A.V. Bubnov, A.I. Nizovskii, V.K. Duplyakin, 2006, published in Neorganicheskie Materialy, 2006, Vol. 42, No. 3, pp. 298–303.
Chemical Interaction of the In–Ga Eutectic
with Al and Al-Base Alloys
M. V. Trenikhin*, A. V. Bubnov*, A. I. Nizovskii**, and V. K. Duplyakin*
* Institute of Hydrocarbon Processing Problems, Siberian Division, Russian Academy of Sciences,
Neftezavodskaya ul. 54, Omsk, 644040 Russia
** Boreskov Institute of Catalysis, Siberian Division, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 5, Novosibirsk, 630090 Russia
e-mail: tremv@yandex.ru
Received May 11, 2005
Abstract—The chemical interaction of the indium–gallium eutectic with Al and Al-base alloys is studied by
x-ray diffraction, optical microscopy, and electron microscopy. Experimental data are presented that shed light
on the reaction mechanism and the diffusion processes responsible for the subsequent disintegration of the
material and its dissolution in water. Mechanical tests show that the activation of aluminum leads to a transition
from plastic to brittle fracture.
DOI: 10.1134/S0020168506030083
INTRODUCTION
series of in situ experiments in order to assess the
dynamics of the interaction between the liquid In–Ga
alloy and the surface of aluminum granules. To this end,
an In–Ga drop (ꢀ3 mm3) was spread over the surface of
an Al granule precleaned with ethanol, and changes in
the surface morphology of the granule were followed
using electron microscopy after holding in the vacuum
lock of the SEM at a pressure of ꢀ1 Pa or atmospheric
pressure and 20°C for different lengths of time.
The morphology of the products of reaction
between activated aluminum and water was examined
on an EM-125 transmission electron microscope
(TEM).
A sample of the AK5M-2 alloy (Cu 1.7, Si 4.57, Fe
0.95, Mg 0.58, Mn 0.27, Ti 0.05, Zn 0.7 wt %, the bal-
ance being Al; RF State Standard GOST 1583-93) pre-
pared via crucible melting followed by natural cooling
was examined by optical microscopy (MBI-15 micro-
scope). To reveal the grain structure, the sample surface
was polished, etched in the mixture of acids recom-
mended in [8], and then degreased with ethanol. The
sample ranged in grain size from 50 to 100 µm.
There is now ample evidence that a liquid metal in
contact with a solid metal diffuses into it [1, 2]. Al–Ga
is known to be among the most convenient test systems
for studying this effect [3, 4]. In particular, the rate of
liquid gallium penetration into aluminum along its
grain boundaries was reported to be as high as 0.55–
8.7 µm/s [5, 6].
Similar processes take place when aluminum is in
contact with an indium–gallium alloy, but this system
has been studied in less detail.
The purpose of this work was to study chemical
interaction of the indium–gallium eutectic with Al and
Al-base alloys using a number of physicochemical
characterization techniques with the aim of gaining
information about the mechanism of this interaction
and the processes responsible for the subsequent disin-
tegration of the material and its dissolution in water
with the formation of hydroxides.
EXPERIMENTAL
We studied interaction of 7- to 10-mm-diameter
pure-grade aluminum granules and 5 × 10 × 15-mm
plates of Al, Al–Ti, Al–Si, Al–Cu, and other aluminum
alloys with the In–Ga eutectic (24 wt % In, melting
point of 16°C [7]) in the liquid state (in what follows,
this process will be called activation).
To assess the effect of liquid In–Ga on the plasticity
of bulk aluminum, activated aluminum specimens were
tested in tension on an R-10 tensile testing machine.
RESULTS AND DISCUSSION
The phase composition of activated aluminum and
SEM examination. In examining the variation in
the products of its reaction with water was determined the surface morphology of aluminum in response to
by x-ray diffraction (XRD) with DRON-3 and HZG- activation, we took advantage of the fact that the back-
4/A powder diffractometers. The surface morphology scattered electron signal in SEM depends on the con-
of the materials was examined on a Tesla BS-350 scan- ductivity of the material: lower conductivity areas on
ning electron microscope (SEM). We carried out a the specimen surface backscatter more electrons [9]. In
256

CHEMICAL INTERACTION OF THE In–Ga EUTECTIC WITH Al AND Al-BASE ALLOYS
257
SEM images, such areas appear lighter (Fig. 1). This
allowed us to more accurately interpret our results for
the multiphase system Al–In–Ga.
Electron-microscopic examination of the surface
morphology of activated aluminum after holding in the
vacuum lock of the SEM at low pressure for different
lengths of time, up to 36 h, revealed no evidence of
interaction between aluminum and liquid In–Ga.
After holding at atmospheric pressure, there were
clear indications of interaction:
1. The surface of the In–Ga drop became rougher.
2. Areas that appeared bright when exposed to the
electron beam were observed on the specimen surface.
10 µm
3. The apparent specimen volume decreased sub-
stantially.
Fig. 1. Surface microstructure of aluminum after holding in
the vacuum lock of the SEM at atmospheric pressure for
60 min; 600×.
4. Both dark and light areas (compared to the unaf-
fected surface) appeared on the aluminum surface near
the In–Ga drop.
The first changes in surface morphology were
observed 20–30 min after the drop had been applied to
the granule. The changes became more pronounced
with increasing holding time.After 20–25 h, the surface
of the aluminum specimen was seen to have a loose
microstructure.
Detailed analysis of SEM micrographs revealed a
number of regular trends. In particular, with increasing
holding time the fraction of light areas increased on
both the aluminum and drop surfaces, as did the rough-
ness of the drop surface. Some of the light areas on the
aluminum surface were surrounded by darker areas. As
mentioned above, the light areas in SEM micrographs
are due to locally reduced conductivity. An interesting
feature in the arrangement of the light areas is that they
do not form a continuous zone near the In–Ga drop and
often coincide with grains of the parent aluminum spec-
imen. In the peripheral parts of the grains, we also
observed narrow light areas, whereas the grain bound-
aries had relatively high conductivity, i.e., absorbed the
electron beam better than the grain bulk (Fig. 2). Con-
sequently, the In–Ga alloy forms an intergranular film,
which seems to be responsible for the broadening of
grain boundaries during activation, as observed in SEM
micrographs.
10 µm
Fig. 2. Liquid In–Ga film between aluminum grains (center)
and the product of surface reaction between aluminum and
liquid In–Ga, presumably, pseudoboehmite (left).
Thus, XRD results support the assumption that the
liquid In–Ga alloy penetrates into the bulk of aluminum
along grain boundaries, without changing its structure.
In subsequent experiments, activated aluminum was
immersed in distilled water maintained at 20°C, which
led to aluminum dissolution, the formation of alumi-
num hydroxides, and hydrogen release.
XRD examination. Comparison of XRD data for
aluminum activated with liquid In–Ga for 5 min and the
XRD pattern of the parent aluminum specimen indi-
cated that
The XRD patterns of the samples prepared by react-
ing activated aluminum with water, followed by drying
at 110°C, showed only reflections from aluminum
hydroxides (pseudoboehmite and small amounts of
bayerite and nordstrandite) and metallic indium (Fig. 3,
scan 3). The likely reason is that indium is nonreactive
with water [10], while gallium is oxidized by water and
is probably then incorporated into the aluminum
(1) the lattice parameter of aluminum (0.405 nm)
remained unaffected by the reaction between aluminum
and liquid In–Ga to within ꢀ0.05%;
(2) the width of XRD peaks from activated alumi-
num was equal to the instrumental broadening (∆2θ ꢀ
0.10°);
(3) no reflections from additional phases emerged,
except for a broad, weak line of the liquid In–Ga alloy. hydroxide lattice.
INORGANIC MATERIALS Vol. 42 No. 3 2006

258
TRENIKHIN et al.
PB
550°C, XRD patterns showed peaks from γ−Al2O3 and
PB
PB
PB
Al
SiO2 (quartz).
In
The Al50Cu50 alloy activated as described above dif-
fered markedly in reaction with water from the activa-
tion products in the Al–Ti and Al–Si systems. The alloy
consisted of the intermetallic phase CuAl2 and a trace
amount of aluminum metal. Reacting the activation
product with water, we obtained a dark, fine-particle
precipitate. After drying, the precipitate consisted of
the intermetallic phase CuAl2 and small amounts of
aluminum hydroxides.
3
2
PB
In
Al
Al
Characterization by optical microscopy. The
reaction between the activated aluminum alloy AK5M-
2 and liquid In–Ga led to the formation of dark areas on
the surface ofAK5M-2.After 50–60 min, the dark areas
extended 2–3 mm from the boundary of the liquid
In−Ga alloy (Fig. 4). In addition, there were light areas
corresponding to grain-boundaries and dark rounded
particles less than 20 µm in size. Similar results were
obtained by examining the reaction between aluminum
and liquid In–Ga by SEM and TEM (Fig. 5).
PB
PB
In
1
30
40
50 2θ, deg
Fig. 3. XRD patterns of the samples prepared by reacting
activated aluminum with water for (1) 1, (2) 3, and
(3) 5 min, followed by drying at 110°C; PB = pseudoboeh-
mite, In = metallic In, Al = metallic Al.
After 24 h of reaction, dark areas appeared on the
surface, which had a dendritic microstructure. The
reaction extended 10–15 mm into the alloy. The dark
areas typically corresponded to grain surfaces, whereas
the grain boundaries remained light. There were, how-
ever, zones where the reaction was more pronounced at
grain boundaries and adjacent regions. Grain-boundary
and near-boundary contrast changes also prevailed in
the zone 18–20 mm from the liquid In–Ga alloy, but the
reaction front did not reach the zone where the morpho-
logical changes in question occurred. Characteristi-
cally, the surface of the liquid In–Ga alloy changed
from lustrous metallic to dull dark brown in appearance
and became rougher, and the volume of the drop
decreased by as much as 30–40%.
As mentioned above, we also activated several alu-
minum alloys, in particular the Al–2.5% Ti alloy, con-
taining the intermetallic compound TiAl3. The activa-
tion process was accompanied by no significant anom-
alies. After subsequent reaction with water, XRD
patterns showed reflections from TiAl3, pseudoboeh-
mite (AlOOH), and bayerite (Al(OH)3).
Silumin (11.04% Si) was activated by a standard
procedure. The activation product reacted rapidly with
water. XRD patterns showed only weak reflections
from Al, with no peaks from any silicon-containing
compounds. After subsequent calcination in air at
Fig. 4. Surface morphology of the AK5M-2 alloy after
60 min of reaction with the liquid In–Ga alloy; the dark area
represents the reaction front; 220×.
Fig. 5. TEM micrograph showing the products of reaction
between water and aluminum activated with liquid In–Ga;
80000×.
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CHEMICAL INTERACTION OF THE In–Ga EUTECTIC WITH Al AND Al-BASE ALLOYS
259
Holding for an additional five days under the same
conditions produced no changes in the surface mor-
phology of the sample.
If the In–Ga drop applied to the aluminum surface
was not specially deformed, it did not wet the surface,
even after holding for 3–5 days between 20 and 60°C.
18
16
14
12
10
8
Unprocessed Al
Activated Al
In an earlier study [11], gallium was also assumed to
be incorporated into the aluminum lattice in the course
of diffusion. This accounts for the absence of diffrac-
tion peaks from gallium or its compounds in XRD pat-
terns of the products of reaction between aluminum and
liquid In–Ga. In addition to reflections from aluminum
hydroxide, the XRD patterns showed only peaks from
metallic indium. These findings can be interpreted in
terms of the Hume-Rothery rule [12], according to
which the solid solubility of two metals is limited if
they differ in atomic radius by more than 14–15%.
Using the atomic volumes Ω reported by Barrett and
Massalski [13] for different elements and the formula
rΩ = (0.75Ω/π)1/3, where rΩ is the Seitz radius, we
obtain rΩ = 0.158, 0.164, and 0.184 nm for aluminum,
gallium, and indium, respectively. Pilipenko [14] also
gives the atomic radii of these elements, taken from
three different sources. The average radii (in the same
6
4
2
0
17
25
Activation temperature, °C
35
Fig. 6. Tensile strength of aluminum as a function of activa-
tion temperature.
vated with liquid In–Ga had a well-defined plastic zone.
The regions of subsequent rupture were found to suffer
a tensile strain, without cracking. The plastic strain of
activated aluminum was substantially lower. In that
case, the fracture surface was cracked and textured in a
direction normal to the loading axis.
We also examined the tensile strength of aluminum
order as above) are 0.137, 0.130, and 0.164 nm. The as a function of activation temperature. In all instances,
considerable difference in atomic radius between In the activation time was 5 min. The results indicate that
andAl (on average more than 15%) seems to be respon- the diffusion rate decreases with decreasing tempera-
sible for the insignificant indium solubility in alumi- ture. The tensile strength of parent aluminum was
num, which is below 0.01 wt % according to Goldstein 166 MPa, and that of aluminum activated at 17°C was
et al. [9].At the same time, the gallium solubility in alu- 109 MPa. Raising the activation temperature to 25–
minum amounts to 21 wt % [15], in line with the small 35°C reduced the tensile strength of aluminum to 50–
difference in atomic radius between these metals. The 60 MPa (Fig. 6). Similar results were reported by Lar-
natural assumption that the particles seen in Fig. 4 con- ikov et al. [19], who observed an increase in intrinsic
sist of indium lends indirect support to the incorpora- stress as the temperature of reaction between aluminum
tion of gallium into the aluminum lattice and the forma- and liquid gallium was raised.
tion of metallic indium.
The light areas seen along grain boundaries after the
reaction with the liquid In–Ga alloy seem to represent
CONCLUSIONS
The observed reaction between a liquid In–Ga alloy
and aluminum, accompanied by changes in the surface
morphology of aluminum, is associated with surface,
grain-boundary, and volume diffusion. The relatively
fast rate of reaction propagation is primarily due to sur-
face and grain-boundary diffusion.
At low pressure, aluminum did not react with
indium or gallium; at atmospheric pressure, we
observed the formation of dielectric products, presum-
ably aluminum hydroxides.
In the case of alloys containing an intermetallic
phase (TiAl3 or CuAl2), this phase did not react with
water after activation and retained aluminum.
Mechanical tests showed that the activation of alu-
minum led to a transition from plastic to brittle fracture.
Our results provide clear evidence for two forms of
embrittlement by the liquid alloy: a low-temperature
effect, related directly to the reduction in the surface
microinhomogeneities due to additional phases consist-
ing of foreign atoms that do not react with the alloy.
In the systems studied, the equilibrium angle θ
between the solid–liquid and liquid–vapor interfaces
(contact angle) was close to 180°, attesting to a high
surface tension at the interface between the solid and
liquid metals and a nearly perfect nonwetting condition
[16]. Spreading the In–Ga drop over the aluminum sur-
face reduced the contact angle. For θ approaching zero,
the liquid must penetrate into the bulk of the solid metal
along grain boundaries [17]. Moreover, according to
Nikitin [2] embrittlement develops most frequently if
the solubility of a liquid metal in a solid one is very low,
which corresponds to indium dissolution in aluminum.
In addition, the atomic volume of solid gallium is
known to be 3.2% greater than that of liquid gallium
[18], which may also contribute to the disintegration of
aluminum and its alloys.
Mechanical tests. We carried out tensile strength energy of the solid metal in the presence of a molten
tests on aluminum plates. Specimens that were not acti- coating, and an effect due to the diffusion-induced
INORGANIC MATERIALS Vol. 42 No. 3 2006

260
TRENIKHIN et al.
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changes in the composition and, accordingly, mechani-
cal properties of the solid material. The latter effect
becomes more important at higher temperatures.
The activation of aluminum seems to be due to the
disruption of the surface oxide layer under the action of
the liquid alloy, leading to an increase in the effective
reaction surface. Subsequent grain-boundary and vol-
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alloys gives rise to the embrittlement of the material
and drastically increases its reactivity with water.
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