Archives
of Materials Science
and Engineering
Volume 45
International Scientific Journal
Issue 1
published monthly by the
September 2010
World Academy of Materials
Pages 56-60
and Manufacturing Engineering
Effect of diffusion on platinum coatings
deposited on the surface of nickel based
superalloy by the electroplating process
M. Yavorska*, J. Sieniawski
R&D Laboratory for Aerospace Materials, Rzeszow University of Technology,
ul. W. Pola 2, 35-959 Rzeszów, Poland
* Corresponding author: E-mail address: [email protected]
Received 15.06.2010; published in revised form 01.09.2010
ABSTRACT
Purpose: In this paper the effect of diffusion on platinum coatings deposited on the surface of nickel based
superalloy was evaluated.
Design/methodology/approach: The platinum coatings with thickness of 3 mm and 7 mm were deposited
by electroplating process on Inconel 713 LC Ni-base superalloy. The heat treatment of electroplating coatings at
the temperature 1050 °C during 2h under argon atmosphere was performed. The microstructure investigations of
the heat treated coatings were conducted by the use of optical microscope (Nikon Epiphot 300) and a scanning
electron microscope (Hitachi S-3400N) equipped with an X-radiation detector EDS (VOYAGER of NORAN
INSTRUMENTS). The phase composition was identified by X-ray (ARL X’TRAX) diffractometer. The surface
roughness parameter - Ra was evaluated by Perthometer S2 MAHR equipment.
Findings: The microstructure of platinum electroplating coating with thickness of 3 µm after diffusion treatment
consists of two phases: γ-Ni and (Al0.25Pt0.75)Ni3. The increase of platinum thickness from 3 µm to 7 µm does
not influence the phase composition of heat treated coatings. Heat treatment of platinum electroplating coatings
causes the increase of surface roughness parameter as a result of unequal mass flow of platinum and nickel.
Research limitations/implications: The results will be used in the future investigations to explain the
mechanism of reaction of platinum as a modifier in aluminide coatings.
Practical implications: The platinum electroplating coatings after diffusion treatment and aluminizing process
are widely used as coatings for turbine blades of aircraft engines.
Originality/value: The paper includes the results of microstructure and surface roughness investigations of
platinum electroplating coatings with 3 mm and 7 µm thickness after diffusion treatment.
Keywords: Inconel 713 LC; Platinum electroplating; Diffusion treatment; Surface roughness
Reference to this paper should be given in the following way:
M. Yavorska, J. Sieniawski, Effect of diffusion on platinum coatings deposited on the surface of nickel based
superalloy by the electroplating process, Archives of Materials Science and Engineering 45/1 (2010) 56-60.
SHORT PAPER
1.Introduction
1.
Introduction
Nickel-based superalloys are used as materials for the hot
components of aeroengines, land based and marine gas turbines
56
56
[1-4]. These superalloys have a good mechanical properties but
low oxidation resistance at high temperature and environments of
aggressive gases.
© Copyright by International OCSCO World Press. All rights reserved. 2010
Therefore to improve the lifetime it is necessary to protect
superalloys against heat, oxidation and corrosion degradation. An
aluminde coating deposited on nickel-based superalloy provides
excellent oxidation and corrosion resistance of elements. Several
studies showed that platinum additions improve the properties of
both alloy and aluminide coating [5-15]. Pt-modified aluminide
coatings affirm the protection of nickel-base superalloys from
oxidative gases even at gas temperature above 1400ºC [11].
Platinum improves the oxide scale adherence [12]. Authors of
[14] showed that platinum reduces void formation at the interface
of metal/oxide. Other studies showed that platinum accelerates
aluminium diffusion, then reduces the vacancies flux from the
metal to the surface and inhibits vacancy coalescence and internal
void formation. Authors [10] reported that platinum decreases
the diffusive flux of alloying elements to the coating, promotes a
selective alumina scale formation and accelerates healing after
spallation. Pt slightly accelerates an alumina scale growth and
delays transformation of metastable alumina oxides to Į-Al2O3.
The addition of platinum to an aluminide coatings improves the
stability of ß-NiAl phase and delays the transformation of ß-NiAl
to the J’-Ni3Al phase.
The important factor of platinum coatings after electroplating
is the diffusion treatment. The application of diffusion treatment
of platinum coatings provides their good adherence.
In this paper the effect of diffusion on platinum coatings
deposited on the nickel based superalloys was investigated. The
influence of platinum coating thickness on the depth and
microstructure of heat treated coating was analyzed.
2.
Experimental procedure
2. Experimental
procedure
The alloy used in this study was Inconel 713LC. Chemical
composition of the used melt is given in Table 1.
Table 1.
Chemical composition of the Inconel 713LC Ni-base superalloy
Elements content, % mass
Ni
Cr
C
Mo Nb Al Ti
Co
Fe
S
74.7 12 0.05 4.6 1.96 5.7 0.7 0.08 0.19 0.02
Process of platinum electroplating was made in WSK
“PZL-Rzeszów”. The material surface preparation for platinum
electroplating process includes four basic operation. These are, in
the usual order of execution: surface degreasing, surface etching,
rinsing in cold water, surface activation.
The electrochemical degreasing was carried out in gluconate
electrolyte at the temperature of 50ºC. The electrolyte contained
180-240 g/dm3 sodium gluconate - C6H11NaO7 and 18-240 g/dm3
sodium hydroxide - NaOH. The rinsing in a heat water was
carried out in order to clean samples surface from C6H11NaO7 and
NaOH. The samples surface activation was carried out by etching
in the mixture of: 90 g/dm3 HF + 530 g/dm3 HNO3
Platinum electroplating process included the activation and
appropriate electroplating. The activation electroplating was
performed during 1h by means of tetraamineplatinum (II)
composite bath - Pt(NH3)2(NO2)2 15 g/dm3, which enables the
rapid growth of an adherent and relatively homogeneous coating.
The current density during the activation electroplating process
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was about of 10 A/dm2. Titanium was used as an anode to
electroplating. The appropriate electroplating was done with the
current density of 0.1 A/dm2. The thickness value of 3 µm and
7 µm were used to investigate the influence of Pt coating
thickness on depth and microstructure of the heat treated coatings.
The samples after electroplating were heat treated at the
temperature of 1050ºC for 2 h under argon atmosphere (Fig. 1).
Fig. 1. Samples after platinum electroplating
The platinum electroplating samples after diffusion treatment
were cut study the cross-section. Polished sections were etched by
the use of reagent with chemical composition as follows: 100 ml
HNO3, 7 ml HF, 11 ml H2O. Microstructure investigations of
samples after diffusion treatment were performed by the use of
light microscope Nikon 300 and scanning electron microscope
(SEM) HITACHI S-3400N equipped with EDS spectrometer.
Evaluation of phase composition of the investigated coatings was
made using ARL X’TRAX-ray diffractometer, equipped with
filtered copper lamp with the voltage of 45 kV and heater current
of 40 mA. Measurements were made in the range of 15 to 140º.
The surface roughness parameter - Ra was evaluated by
Perthometer S2 MAHR. The average value of surface roughness
parameter and standard deviation were calculated.
3.
Results and
3. Results
and discussion
discussion
Coating surfaces after platinum electroplating with thickness
of 3 and 7 µm had a closely spaced “cauliflowers” appearance.
The cauliflower morphology of the coatings depends on process,
such as current density and potential [8].
The diffusion annealing of platinum electroplating coating
with thickness of 3 Pm at 1050ºC for 2 h causes the formation of
diffusion zone at the cross-section of the coating (Fig. 2). The
thickness and morphology of the microstructure components were
investigated. The depth of diffusion zone is approximately 16 µm.
Analysis of the chemical composition on the cross-section
proved the interdiffusion of platinum and substrate elements.
Platinum diffused into the substrate and substrate elements, e.g.
Ni diffused into the platinum layer as a result of diffusion zone
formation (Fig. 2). The original surface of the substrate can be
identified by adjusting the contrast of spots that are surrounding
the pores. The microstructure of the cross-section of heat treated
coatings consisted of two phases. The white phase (%at:
14Al-8Cr-60Ni-17Pt) has a higher Pt and Al content and lower Cr
concentration in comparison to the surrounding substrate (%at:
5Al-14Cr-80Ni) (Table 2, point 1,3) .
57
M. Yavorska, J. Sieniawski
Pt diffusion zone
3
Interface after
heat treatment
Fig. 2. Cross-section image of platinum electroplating coating
with thickness of 3 µm after heat treatment process; a two-phase
microstructure
Table 2.
The results of EDS analysis from on area presented in Fig. 2
Al, %
Cr, %
Ni, %
Pt, %
Point
at
wt
at
wt
at
wt
at
wt
1
14.09 4.98 8.53 5.80 60.7 46.64 16.68 42.58
2
6.06 2.63 12.34 10.33 77.07 72.83 4.53 14.21
3
5.84 3.34 13.67 15.10 80.49 81.56
Surface morphology characterized a fine-grain structure with
a typical grain size about 3-5 µm. The high content of aluminium
nickel and platinum was observed on the surface of platinum
coating after diffusion treatment (Figs. 3a,b).
a)
The chemical composition on the cross-section of platinum
coating after heat treatment showed outward diffusion of nickel,
chromium and aluminium elements and inward diffusion of
platinum (Fig. 4).
Elements content, % at
1
2
90
80
70
60
Pt
Al
Ni
Cr
50
40
30
20
10
0
3
5
7
9
11
13
15
17
Distance from the surface, Pm
Fig. 4. Chemical composition on the cross-section of platinum
electroplating coating with thickness of 3 µm after heat treatment
process
X-ray diffraction of the phase analysis samples with a 3 µmthick platinum coating after heat treatment revealed a two-phase
Ȗ-Ni and (Al0.25Pt0.75)Ni3 structure (Fig. 5). The authors [11]
proved, that phase composition of heat treated coating do not
seem to change with the annealing time.
Intensity, imp/s
b)
Fig. 5. X-ray diffraction results of platinum electroplating coating
with thickness of 3 µm after heat treatment process
Energy, keV
Fig. 3. Microstructure (a) and EDS analysis results (b) of the
surface of platinum electroplating coating with thickness of 3 µm
after heat treatment process: showing a fine grain structure
58
58
The heat treatment of platinum electroplating coating with
thickness of 7 µm causes the formation of diffusion zone. The
depth of diffusion zone is about 18 µm (Fig. 6). The coating
consists of two phases: white phase contains 25.83% at and
15.56% at platinum and a grey one which contains nickel
approximately 81% at and 0% at platinum (Table 3).
Archives of Materials Science and Engineering
Effect of diffusion on platinum coatings deposited on the surface of nickel based superalloy by the electroplating process
Table 4.
Elemental composition from EDS analysis of the area showed in Fig. 7
Point
X1
X2
Al, %
at
wt
Cr, %
at
wt
Ni, %
at
wt
Pt, %
at
wt
14.86 7.82 6.69 6.78 68.44 47.32 10.01 38.08
4.88 1.65 12.40 8.09 61.95 39.39 20.77 50.87
Fig. 6. Cross-section image of platinum electroplating coating
with thickness of 7 µm after heat treatment process: showing a
two-phase microstructure
Table 3.
Elemental composition from EDS analysis of the area showed in Fig. 6
Al, %
Cr, %
Ni, %
Pt, %
Point
at
wt
at
wt
at
wt
at
wt
1
8.44 2.51 9.72 5.58 56.01 36.30 25.83 55.61
2
6.73 2.36 12.50 8.45 65.21 49.75 15.56 39.44
4
5.73 3.29 13.10 14.49 81.17 82.22
A fine grained structure with the grain size of 5-7 µm is
formed on the surface of the treated sample. The surface is
enriched in platinum, nickel, chromium and aluminium
(Pt 10-20%at, Ni 66-68%at, Cr 6-12%at, Al 4-15%at).
The chemical composition on the cross-section of 7 µm-thick
platinum coating after diffusion treatment showed outward
diffusion of nickel, chromium and aluminium elements and
inward diffusion of platinum. This phenomena is similar to the
platinum coating with thickness of 3 µm.
X2
X1
Fig. 8. Diffraction results of platinum electroplating coating with
thickness of 7 µm after heat treatment process
The surface roughness parameter of specimens decreases with
the increase of platinum deposition thickness (Table 5). Heat
treatment of platinum electroplating causes the increase of surface
roughness with the increase of platinum thickness. This
phenomena is a result of unequal mass flow and internal stresses
release caused by interdiffusion of platinum and nickel [15].
Table 5.
Values of surface roughness parameter after platinum
electroplating and diffusion treatment
Nickel alloy
Ra
Platinum
Diffusion
Inconel
electroplating
treatment
0 Pm
713 LC
3 Pm
7 Pm
3 Pm
7 Pm
Average
1.080
0.664
0.605
2.623
2.971
value
Standard
0.0144
0.047
0.003
0.167
0.051
deviation
4.
Conclusions
4. Conclusions
Fig. 7. Morphology of the surface of platinum electroplating
coating with thickness of 7 µm after heat treatment process
The phases of Ȗ and Ȗ’(Al0.25Pt0.75)Ni3 were determined in the
platinum electroplating coating with thickness of 7 µm after heat
treatment process (Fig. 8).
Volume 45
Issue 1 September 2010
Platinum coatings with thickness of 3 and 7 Pm were
produced by electroplating method. Electroplating samples were
heat treated at the temperature 1050 ºC during 2 h under argon
atmosphere. Heat treated coatings with thickness of 3 µm had
16 µm depth. The increase of coating thickness from 3 to 7 µm
leds to the increase of coating depth from 16 to 18 µm. Diffusion
59
zone was obtained after heat treatment of platinum coatings with
3 µm and 7 µm thickness. It was found that platinum coatings
both with 3 µm and 7 µm thickness consist of the two phases Ȗ-Ni and (Al0.25Pt0.75)Ni3. The chemical composition on the crosssection of platinum coating after diffusion treatment showed
outward diffusion of nickel, chromium and aluminium elements
and inward diffusion of platinum. Heat treatment of platinum
electroplating causes the increase of surface roughness parameter
with the increase of platinum thickness as a result of unequal
mass flow of platinum and nickel.
[6]
[7]
[8]
[9]
Acknowledgements
Acknowledgements
The present work was supported by the Polish Ministry of
Education and Science under research project U-8072/G.
[10]
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