Materials Sciences and Applicatio n, 2011, 2, 711-715
doi:10.4236/msa.2011.27098 Published Online July 2011 (http://www.SciRP.org/journal/msa)
711
Study of Corrosion Resistance of Laser Welded
Au-Pd-Ag-In Alloy Using Electrochemical
Techniques
Márcio L. Dos Santos1, Heloísa A. Acciari2, Carla S. Riccardi1, Antonio C. Guastaldi1
1Institute of Chemistry, Universidade Estadual Paulista, Araraquara, Brazil;
2Faculdade de Engenharia de Guaratinguetá, Universidade Estadual Paulista, Guaratinguetá, Brazil.
Received May 22nd, 2010; June 26th, 2010, accepted May 20th, 2011.
ABSTRACT
The aim of this work was to evaluate the corrosion resistance of AuPdAgIn alloy, submitted to laser beam welding, in
0.9% NaCl solution, using electrochemical techniques. Measures of the open circuit potential (OCP) versus time were
applied to electrochemical experiments, as well as potentiodynamic direct scanning (PDS) and electrochemical imped-
ance spectroscopy (EIS) on AuPdAgIn alloy, submitted to la ser beam welding in 0.9% NaCl solution. So me differences
observed in the microstructure can explain the results obtained for corrosion potential, Ecorr, and corrosion resistance,
Rp. EIS spectra have been characterized by distorted capacitive components, presenting linear impedance at low fre-
quencies, including a non-uniform diffusion. The area of the laser weld presented corrosion potential slightly superior
when compared to the one of the base metal. The impedance results suggest the best resistant corrosion behavior for
laser weld than base metal region. This welding process is a promising alternative to dental prostheses casting.
Keywords: Laser Welding, Corrosion, Au-Pd-Ag-In, Electrochemical Techniques
1. Introduction
The metals used in dentistry are in the form of alloys, or
mixtures of one or more metal. Alloys are advantageous
compared with pure metals in physical and mechanical
properties because of engineering the optimum influence
from each constituent [1,2]. The noble dental alloys have
two or three major elemental constituents with the addi-
tion of minor elements to influence specific properties,
such as the melting range, grain formation and corrosion
resistance. In this context, the noble alloys may be con-
sidered in three groups: Au-Ag-Pd, low-gold alloys, in-
cluding Pd-Ag and Pd-Ga, and no-gold alloys as Pd-
Cu-Ga [1]. The Au-Ag-Pd noble alloys are usually single
phase, which may be hardened by solid solution streng-
thening. Likewise, the properties of this alloy group are
generally good with acceptable strength and hardness but
only moderate ductility [2]. Alloys can be joined b y three
similar processes: welding, brazing and soldering [3].
Welding is a joining process in which parent metals fuse
and form the joint with or without a filler alloy [4,5].
Welds in dentistry are often accomplished with a laser.
The area adjacent to the fused metal is known as the
“heat affected zone,” in which partial recrystallization of
the alloy is probable. A decrease in hardness is noted
when measured across a welded joint as a result of re-
crystallization. Minimizing the duration and area of
heating reduces the heat affected zone [1,4].
Data on laser welding of other dental alloys are sparse
and relationship between the microstructure and corro-
sion behavior of Au based dental casting alloys has been
studied. The use of electrochemical techniques in the cor-
rosion study is important for the understanding of its
performance, biocompatibility and biofunctionality, when
clinically applied, for these are con stantly exposed to ag-
gressive environments [6]. Conventional potentiodynamic
direct scanning (PDS) techniques are often used. These
techniques apply polarization potential on the basic cor-
rosion potential over wide potential range. The current
measurements can provide informations about the corro-
sion resistance and susceptibility, such as corrosion rate,
passivation range and breakdown potential [7,8]. These
results should be carefully considered since, with PDS,
the information is not obtained in stationary conditions
[8]. In rather passive systems with relatively low corro-

Study of Corrosion Resistance of Laser Welded Au-Pd-Ag-In Alloy Using Electrochemical Techniques 712
sion rates (application of noble metals or systems with
protective coatings), more reliable information can be
usually gained from electrochemical impedance spec-
troscopy (EIS) measurements [7,8]. Recently, PDS tech-
nique was implemented for the characterization of corro-
sion systems that may exhibit strong non stationary be-
havior, as in pitting corrosion, flow-induced corrosion
and stress-corrosion cracking [9,10]. Electrochemical
impedance spectroscopy applies sinusoidal voltage signal
of relatively small amplitudes (usually few tens of mV),
therefore the conditions of the electrodes are only slight-
ly disturbed [11]. Besides the general corrosion proper-
ties of an investigated system, specific information about
underlying electrochemical mechanisms can also be ob-
tained from the measured impedance spectra [8,11]. The
purpose of this work was investigate the corrosion resis-
tance of AuPdAgIn alloy in 0.9% NaCl solution, simu-
lating the oral environment conditions, before and after
submitted to the laser welding process.
2. Experimental Part
The AuPdAgIn alloy is a specific material applied to
dental purposes, such as the production of implant pros-
thesis and it is classified as extra-solid [12], with chemi-
cal composition of the studied material (weight %), by
wave dispersive spectroscopy (WDS) analysis: 54.00 ±
1.50 Au, 2.10 ± 0.06 Ag, 36.00 ± 1.10 Pd, 8.20 ± 0.77 In.
Cylindrical test specimens, with 0.27 cm diameter and 1
cm length, were submitted to the welding process on butt
joints [13]. The welding equipament, Dentaurum DL
20002S, uses a crystal Nd: YAG as source of laser, and
the beam power was 5.84 kW in 12 milliseconds, origi-
nating a welding energy of, approximately, 70.08 J. The
test specimens were manually placed in the chamber,
with shield atmosphere of argon, and spots of lap weld-
ing, in approximately 2/3 of the surfaces, were applied in
the whole section of the joint, with 60% of beam pene-
tration. A precise cut disc model 15 HC DIAMOND was
used to obtain the test specimens of AuPdAgIn alloy with
area comprehending only the welding area, and a ISO-
MET 1000—BUEHLER machine was used to separate
the base metal from the welding area, after the laser
process. The exposed geometric areas of the welded joint
and of the base metal were 0.057 cm2. The metal-
lographic analysis of the exposed surface of the base
metal and the welding area was obtained with scanning
electronic microscopy (SEM), after polished with 180 to
1000 grade emery papers and alumina with granulations
of 1 m and 0.3 m. It was used nitromuriatic acid as
chemical attack [12,13]. The working electrodes were
prepared from the test specimens used on the metal-
lographic analysis. Measures of the open circuit potential
(OCP) versus time were applied to electrochemical ex-
periments, as well as potentiodynamic direct scanning
(PDS) and electrochemical impedance spectroscopy
(EIS). Electrochemical experiments were performed in a
three-electrode cell containing 0.9% NaCl solution at
room temperature, which are appropriate to simulate
corrosion under oral environment conditions. It was util-
ized as counter electrode Pt foil and reference electrode a
saturated calomel electrode (SCE). Potentiodynamic po-
larization curves were recorded at 1 mV·s–1. Impedance
measurements were done at the open circuit potential,
reached on the steady state, using a Solartron 1255 Fre-
quency Response Analyser coupled to a Solartron 1287
Electrochemical Interface (Solartron Analytical Farn-
borough, UK), using a 10 mV rms perturbation in the
frequency range 100 kHz to 6 mHz, five points per fre-
quency decade and controlled by ZPlot software with
analysis by ZView software (Scribner Associates, Char-
lottesville, USA).
3. Results and Discussion
Figure 1 shows micrographs obtained for Au-Pd-Ag-In
alloy in the regions of the base metal (Figure 1(a)) and
laser weld (Figure 1(b)). It can be observed that area of
Po
Po
Po
20 m
Po
Po
Po
20 m
(a)
10 m10 m
(b)
Figure 1. Light microscopy of the Au-Pd-Ag-In surfaces: (a)
base metal, Po = porosity; (b) laser weld.

Study of Corrosion Resistance of Laser Welded Au-Pd-Ag-In Alloy Using Electrochemical Techniques713
the base metal has a biphasic granular microstructure
containing precipitates of Au. The laser weld presents a
refined dendritical microstructure. The high speedy cool-
ing imposed by the laser weld due to process of located
fusion, followed by a fast cooling (3.02  103˚C·s–1) dur-
ing the welding, which does not allow the microstructure
to return to its initial granular structure.
Figure 2 illustrates the open circuit potential versus
time curves for the base metal and laser weld areas of the
Au-Pd-Ag-In. The stabilization of th e po tential valu e was
observed 3 hours after immersion for both areas. The
corrosion potential in the steady state does not show sig-
nificant differences (0.35 V) for both curves. In the
open circuit potential versus time curves can be observed
an increasing of potential, suggesting the film formation
on the metallic material immersed in electrolyte solution
[14]. Several authors have described an improvement of
corrosion resistance of Au and Pd (>5% content) in
commercial gold-silver alloys i mmersed in chloride solu-
tion. On the contrary, Ag, In and Cu metals suffer pref-
erential attack on this condition [15,16].
0 3 6 91215182124
0,00
0,05
0,10
0,15
0,20
0,25
0,30
0,35
0,40
laser weld
E / V vs. SCE
Time / hour
base metal
Figure 2. Open circuit potential versus time curves obtained
for AuPdAgIn alloy in 0.9% NaCl solution.
-14 -13 -12 -11 -10-9-8-7-6-5-4
-0,6
-0,4
-0,2
0,0
0,2
0,4
0,6
0,8
1,0
laser weld
base metal
E / V vs. SCE
log I / A cm -2
Figure 3. Potentiodynamic polarization curves obtained for
AuPdAgIn alloy in 0.9% NaCl solution.
Figure 3 shows the potentiodynamic polarization
curves of metal base and welding areas. It can be ob-
served a straight electroactive range. An extensive pas-
sivation range of +0.1 to +0.8 V (ECS) with a passive
current variation (0.1 to 1 µA·cm–2) was observed for the
metal base area. A corrosion potential of, app roximately,
+0.1 V was obtained for the welding area. This corrosion
potential value was 50 mV higher than those for metal
base area (+0.053 V). The passivity range was signifi-
cantly ample range for both areas. However, it was ob-
tained a lower passive current (0.01 to 0.1 µA·cm–2), in-
dicating an improvement of corrosion resistance of the
material, probably, due to microstructure of the welding
area. In addition, a low current oscillation could be ob-
served in the welding area from 0.3 to 0.4 V. In the po-
tentiodynamic polarization curves was observed that be-
havior could be associate to an increase of passive layer
thickness probably of AuCl3 and posterior breakdown
and repassivation [14]. For both situations, there was a
breakdown of passive layer around +0.8 V without pit-
ting corrosion. Brugirard, et al. have observed higher Ag
dissolution rate than Pd using gold alloys based on sil-
ver-palladium in artificial saliva [17]. Meyer and Reclaru
have reported the corrosion resistance of noble metal
alloys for dental applications. They have investigated
that the alloys for preparing full-metal crowns and
bridges are somewhat less corrosion resistant than the
newer alloys for the metal-ceramic technique. This dif-
ference is explained by the higher content of noble met-
als in the alloys for ceramic veneering, or by the rela-
tively high content of non-noble metals (silver, copper,
zinc) in the alloys for crowns and bridges. It was also
observed that the presence of cadmium or nickel has a
distinctive (and highly degradative) effect on the corro-
sion behavior, whereas base-metals such as In and Ga do
not affect significantly the resistance to corrosion in the
alloys for metal-ceramic veneering [18]. According to
other studies in literature, alloys with high proportions of
Au were resistant to corrosion due to their high thermo-
dynamic stability. However, many studies found that the
Au ions were released [19].
The complex format of the impedance response ob-
tained for AuPdAgIn alloy presents two distorted semi-
circles within the studied frequency range, Figure 4. The
diameter of each capacitive arc shows that the base metal
area (Figure 4(a)) has a higher corrosion resistance value
than the laser weld joint, Figure 4(b). Both of the im-
pedance spectra were also influenced by a diffusion re-
sponse, which can be observed by a straight line at low
frequencies [6,20,21]. These spectra were fitted using the
model of equivalent electrical circuit with two terms
R(CPE) in series, indicating possible occurrence of at
least two successive electrochemical processes. The non-

Study of Corrosion Resistance of Laser Welded Au-Pd-Ag-In Alloy Using Electrochemical Techniques 714
01020
0
10
20
30
30
012
0
1
2
0.01 Hz
Exp
-Z" / k cm2
320 mV
0.00631 Hz
Calc
Z' / k cm2
1 Hz
0.31623 Hz
0200 400 600
0
200
400
600
0100200
0
100
200
400 mV
1
0.25119
0.15849 Hz
Exp
Calc
-Z" / k cm
Z' / k cm2
10 Hz
1 Hz
Figure 4. Complex plane spectra obtained for AuPdAgIn
alloy in 0.9% NaCl solution at the open circuit potential
reached on the steady state: (a) metal base area; (b) laser
weld.
ideal capacitances were modeled by CPE1 and CPE2, can
be correlated with metallic corrosion and formation of
oxide film, respectively at high and low frequencies.
These values oscillated between 1 - 10 mF·cm–2. The
polarization resistance determined at low frequencies, Rp2
(in parallel with CPE2), was considerably higher for laser
weld area (2 M·cm2) than base metal (5 k·cm2).
Meyer and Reclaru observed that the polarization resis-
tance reached values of order of M, using an alloy with
approximately 40% of Au in its compositions [18,20].
4. Conclusions
The laser weld presented a refined dendritical micro-
structure while the ba se metal showed a biphasic granular
microstructure. The potentiodynamic profiles were con-
siderably similar to both areas observed. However, the
area of the laser weld presented corrosion potential
slightly superior when compared to the one of the base
metal. In both cases, a response of linear impedance was
observed at low frequencies, including a non-uniform
diffusion. The values of Rp by impedance suggest the best
resistant corrosion behavior for laser weld.
5. Acknowledgements
Thanks to the Laboratory VAIAZZI (SP, Brazil) and a
doctoral grant from FAPESP.
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