Journal of Minerals & Materials Characterization & Engineering, Vol. 8, No. 9, pp 693-700, 2009
jmmce.org Printed in the USA. All rights reserved
693
Corrosion Behavior of Nanostructured TiAlN and AlCrN Hard Coatings
on Superfer 800H Superalloy in Simulated Marine Environment
Vikas Chawlaa*, D. Puria, S. Prakasha and Buta Singh Sidhub
a Metallurgical & Materials Engineering Department, I.I.T. Roorkee, Roorkee-247667, India
b Mechanical Engineering Department, Y.C.E., Talwandi Saboo-151302,India
*Corresponding author: ,
Phone: [phone], Fax: [phone]
ABSTRACT
In this work, TiAlN and AlCrN coatings were deposited on Superfer 800H superalloy using
Balzer’s rapid coating system (RCS) machine (make Oerlikon Balzers, Swiss) under a reactive
nitrogen atmosphere. The corrosion resistance of the substrate, TiAlN and AlCrN coated
samples in a 5 wt% NaCl solution was evaluated and compared by salt fog (spray) test for 24
hrs, 48 hrs and 72 hrs. The samples were monitored and analyzed by using weight loss
measurement, XRD and SEM/EDAX techniques. There was no weight loss observed for coated
as well as uncoated specimens in all test conditions.
Keywords: Salt fog test, Physical vapor deposition, Corrosion, Nanostructured coatings,
Pitting
1. INTRODUCTION
Superalloys are extensively used in turbine blades of industrial gas turbines and jet engines [1].
Corrosion of iron /steel and superalloys is affected by the environment to which these are
exposed [2]. In a wide variety of applications, for example, in aero and thermal power plants,
mechanical components especially turbine engines have to operate under severe conditions, such
as high load, speed, temperature and hostile chemical environment [3]. Mostly Cr and Al are
added in Fe and Ni-based superalloys to enhance the oxidation resistance. When the superalloys
were employed in jet engines, the resistance to pitting corrosion was another property, which can
also influence the serving life of engines as it rested on seaside [1]. Besides the oxidation
resistance of superalloys at high temperature, the resistance to pitting corrosion at normal
temperature is another important performance of these materials.
The atmospheric sulfate and chloride pollutants can enhance conductivity of the wet film on the
metal surface, leading to the metal deterioration process [2, 4]. Chloride ions present in sea
aerosol can be considered as a natural pollutant [2, 4]. Chloride ions serve as the catalyzer in
accelerating the corrosion process. Dobrzanski et al., [5] reported that the chloride-rich seawater

694 V. Chawla, D. Puri, S. Prakash and B. S. Sidhu Vol.8, No.9
is a harsh environment that can attack the materials by causing pitting and crevice corrosion. The
maximum corrosion rate occurs near 3.5%wt NaCl-the approximate salt concentration of
seawater. Although numerous studies in the literature reported the high temperature corrosion
behavior of bulk alloys and metallic coatings on boiler steels, behavior of corrosion occurring at
room temperature in marine environment, is scarce in the literature.
In recent years, corrosion performance of nanostructured materials/coatings is a hot topic in
corrosion field. As reported by Chawla et al. [6], in the past decade, attractive properties
associated with a nanostructure have been documented for bulk materials, where most of the
research in the field of nanomaterials has been focused. Nanostructured materials indeed behave
differently than their microscopic counterparts because their characteristic sizes are smaller than
the characteristic length scales of physical phenomenon occurring in bulk materials [7].
This work has been focused to compare the corrosion behavior of nanostructured thin (by
physical vapor deposition process) TiAlN and AlCrN coatings deposited on Superfer 800H
(INCOLOY 800 H) substrate, by salt spray (Fog) tests.
2. EXPERIMENTAL DETAILS
2.1 Development of Coatings
TiAlN and AlCrN coatings; with a thickness around 4µm, were deposited on Fe-based Superfer
800H superalloy, which was procured in the form of rolled sheets from Mishra Dhatu Nigham
Ltd, Hyderabad (India).. The selected superalloy is widely used for steam boilers, furnace
equipment and piping in the chemical industry, baffle plates/tubes in fertilizer plants. The actual
chemical composition of the substrate steel analyzed with the help of Optical Emission
Spectrometer of Thermo Jarrel Ash (TJA 181/81), USA make. The actual chemical composition
of the Superfer 800H superalloy has been analyzed with the help of Optical Emission
Spectrometer of Thrmo Jarrel Ash (TJA181/81), U.S.A make. Normal and actual chemical
composition is reported in Table 1.
Table 1: Chemical composition (wt %) of Superfer 800H (INCOLOY 800 H)
Elements C Mn Si Cr Ni Ti Al Fe
Nominal 0.10 1.0 0.6 19.5 30.8 0.44 0.34 Bal.
Actual 0.10 1.5 1.0 21.0 32.0 0.30 0.30 Bal.
Specimens with dimensions of approximately 20mm x 15mm x 5mm were cut from the alloy
sheet. Polished using emery papers of 220, 400, 600 grit sizes and subsequently on 1/0, 2/0, 3/0,
and 4/0 grades, and then mirror polished using cloth polishing wheel machine with 1μm

Vol.8, No.9 Corrosion Behavior of Nanostructured TiAlN and AlCrN 695
lavigated alumina powder suspension. The specimens were prepared manually and all care was
taken to avoid any structural changes in the specimens.
The nanostructured thin TiAlN and AlCrN coatings; with a thickness around 4µm, were
deposited on the substrates at Oerlikon Balzers Coatings India Limited, Gurgaon, India. A front-
loading Balzer’s rapid coating system (RCS) machine (make Oerlikon Balzers, Swiss) was used
for the deposition of the coatings. The grain size of the thin films was estimated by Scherrer
formula from XRD diffractogram and by Atomic force microscopy (AFM; Model: NTEGRA,
NT-MDT, Ireland). The grain size for TiAlN and AlCrN coatings was found 09 nm and 22 nm
respectively. The details of the coating parameters and coating characterization have been
reported in another paper (communicated).
2.2 Salt Spray (Fog) Testing and Analysis of the Corroded Specimens
The ASTM B117 Salt Fog test was used to evaluate the performance of the uncoated and
nanostructured thin TiAlN and AlCrN coatings. The salt fog test is an accelerated corrosion test
by which samples exposed to the same conditions can be compared. In the B117 test, the samples
are exposed to a salt fog generated from a 5% sodium chloride solution with a pH between 6.5
and 7.2 in salt fog testing set up (HSK 1000, Heraeus Votsch, Germini) as shown in Figure 1.
The salt solution employed was prepared with NaCl analytical grade reagent with minimum
assay 99.9 % supplied by Qualigens Fine Chemicals, Mumbai, India and deionised water.
All the samples were placed in the salt fog chamber for 24 Hrs, 48 Hrs and 72 Hrs. Photographs
were taken before and subsequent to exposure to document the surface conditions. Initial weight
and dimensions were measured. The uncoated as well as the coated specimens were polished
down to 1μm alumina wheel cloth polishing to obtain similar condition on all the samples before
salt fog testing.
Figure 1. Experimental set-up for Salt spray (Fog) testing (a) Salt fog testing set up, (b) Salt fog
chamber, (c) Interior view of chamber
(a)(b)
(c)
SaltFogChamber
ControlUnit
SaltFogChamber
InteriorViewSaltFog
Chamber
Samples

696 V. Chawla, D. Puri, S. Prakash and B. S. Sidhu Vol.8, No.9
2.3 Analysis of the Corroded Specimens
After exposure; samples were monitored and analyzed by using XRD and SEM/EDAX
techniques. Visual examination was made after the completion of the tests and the macrographs
of the corroded specimens were taken. Surface SEM analysis of the corroded specimens was
conducted using Field emission scanning electron microscope (FEI Company, Quanta 200F) with
EDAX attachment. EDAX analysis at few points of interest was taken. XRD analysis was carried
out for the as coated specimens to identify the various phases present on their surfaces. The X-ray
diffraction patterns were obtained by a Bruker AXS D-8 Advance Diffractometer (Germany) with
CuKα radiation and nickel filter at 30 mA under a voltage of 40 kV. The specimens were scanned
with a scanning speed of 2o/min in 2θ range of 20o to 120o and the intensities were recorded.
Before salt fog testing; the samples were cleaned in acetone, dried, weighed to an accuracy of
1×10-5 g using an electronic balance. After exposure; samples were monitored and analyzed by
using XRD and SEM/EDAX techniques. Then all the samples were cleaned in running water not
warmer than 38°C to remove salt deposits from the surface and then immediately dried with
compressed air. The final weight was measured and then the weight loss per unit area was
calculated.
3. RESULTS AND DISCUSSION
The ASTM B117 Salt Fog test was used to evaluate the performance of the uncoated and
nanostructured thin TiAlN and AlCrN coated Superfer 800H superalloy. The salt fog test is an
accelerated corrosion test by which samples exposed to the same conditions can be compared. In
the B117 test, the samples are exposed to a salt fog generated from a 5% sodium chloride
solution with a pH between 6.5 and 7.2. All the samples were placed in the salt fog chamber for
24 Hrs, 48 Hrs and 72 Hrs. Photographs were taken before and subsequent to exposure to
document the surface conditions. Initial weight and dimensions were measured. After exposure;
samples were monitored and analyzed by using XRD and SEM/EDAX techniques. Then all the
samples were cleaned in running water not warmer than 38°C to remove salt deposits from the
surface and then immediately dried with compressed air.
The macro morphologies of the uncoated and nanostructured thin TiAlN and AlCrN coated
superalloy exposed to salt fog test for 24 Hrs, 48 Hrs and 72 Hrs; are depicted in Figure 2. No
signs of corrosion have been observed in case of uncoated and coated Superfer 800H superalloy
subjected to salt fog tests for different durations. The surface appearance of all the samples
remains untouched. Figure 2 shows the surface SEM images of uncoated and nanostructured
TiAlN and AlCrN coated superalloy exposed to salt fog test for 72 Hrs. The SEM/EDAX
analysis of the samples exposed to 24 Hrs, 48 Hrs and 72 Hrs salt fog tests have shown similar
results i.e. no corrosion products have been found on the surface. So, the SEM/EDAX analysis in
case of salt for tests for 72 Hrs (maximum duration in present test) has been presented here.

Vol.8, No.9 Corrosion Behavior of Nanostructured TiAlN and AlCrN 697
Figure 2. Surface macrographs of uncoated and coated Superfer 800H superalloy subjected to
salt-fog testing (5% NaCl) : (a), (b) and (c) Uncoated Superfer 800H subjected to
24hrs, 48hrs and 72 hrs testing, respectively; (d), (e) and (f) Nanostructured TiAlN
coating subjected to 24hrs, 48hrs and 72 hrs testing, respectively; (g), (h) and (i)
Nanostructured AlCrN coating subjected to 24hrs, 48hrs and 72 hrs testing,
respectively
As can be seen in Figure 3; no corrosion product has been found on the surface of any sample.
The EDAX point analysis at some points of interest points out the presence of Fe, Ni and Cr in
case of uncoated superalloy (Point 1 and 2 in Figure 3). In case of nanostructured thin TiAlN and
AlCrN coatings; no corrosion products were seen (Figure 3. b & c). The EDAX point analysis
(Point 3 to 6 in Figure 3) revealed the presence of the coating elements only. So, in case of 72
Hrs test conditions; the uncoated and nanostructured thin coatings have performed well in salt
fog tests.
XRD diffractograms for coated and uncoated Superfer 800H superalloy subjected to salt fog tests
for 24 Hrs, 48 Hrs and 72 Hr; are depicted in Figure 4 on reduced scale. As indicated by the
diffractograms in Figure 4: Fe, Ni and Cr are the main phases present in case of uncoated
(a) (d) (g)
(c)
(h)
(e)
(b)
(f) (i)
24 hrs
48 hrs
72 hrs
5mm
5mm 5mm
5mm
5mm
5mm 5mm
5mm
5mm

698 V. Chawla, D. Puri, S. Prakash and B. S. Sidhu Vol.8, No.9
superalloy. In nanostructured TiAlN coating, AlN and TiN are the main phases revealed by
EDAX analysis. Further, the main phases identified for the nanostructured AlCrN coating are
CrN and AlN.









Figure 3. Surface macrographs of uncoated and coated Superfer 800H superalloy subjected to
salt-fog testing (5% NaCl) for 72 hrs: (a) Uncoated Superfer 800H superalloy (b)
Nanostructured TiAlN coating (c) Nanostructured AlCrN coating.
The weight loss measurements were carried out for the uncoated and nanaostructured thin TiAlN
and AlCrN coated Superfer 800H supealloy exposed to the salt fog tests for 24 Hrs, 48 Hrs and
72 Hrs. No weight change was observed in any case. It can be mentioned based on the present
investigation that uncoated Superfer 800H and nanostructured thin TiAlN and AlCrN coatings
can provide a very good corrosion resistance when exposed to the simulated marine environment
i.e. salt fog test.
(a)
(c)
(b)
POINT 1 POINT 2
POINT 3 POINT 4
POINT 5 POINT 6
300 µm
300 µm
300 µm
44.16 % Fe
27.58 % Ni
19.06 % Cr
03.76 % C
00.99 % Na
01.35 % Al
01.52 % Si
00.67 % Mn
00.72 % Fe
55.01 % Ti
27.23 % Al
13.79 % N
02.56 % C
05.45 % Fe
36.65 % Al
34.11 % Cr
03.54 % Ni
13.74 % N
05.30 % C
45.04 % Fe
27.11 % Ni
18.62 % Cr
02.60 % C
01.04 % Na
01.04 % Al
01.75 % Si
01.51 % Mn
00.70 % Fe
52.11 % Ti
25.72 % Al
13.98 % N
03.30 % C
05.22 % Fe
38.08 % Al
32.25 % Cr
02.89 % Ni
12.93 % N
05.81 % C

Vol.8, No.9 Corrosion Behavior of Nanostructured TiAlN and AlCrN 699
20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
Intensity (arbi tra ry u ni ts)
Diffraction angle (2-Theta)
λ
σ
σ
λλ
λ
σ
δδ
δλ
δ
λ
δ
δ
β
α
β
α
α
ε
β
α Ni β F e ε C r
δ TiN λ AlN σ CrN
C
B
72 H rs
72 H rs
72 Hrs
48 Hrs
48 H rs
48 H rs
24 Hrs
24 H rs
24 H rs
A
Figure 4. X-Ray Diffraction pattern of uncoated and coated Superfer 800H superalloy
subjected to salt-fog testing (5% NaCl): (A) Uncoated Superfer 800H superalloy,
(B) Nanostructured TiAlN coating, (C) Nanostructured AlCrN coating.
4. CONCLUSIONS
The corrosion behavior of the nanostructured thin (by physical vapor deposition process) TiAlN
and AlCrN coatings on Superfer 800H superalloy; has been analyzed by salt spray (Fog) tests
(5.0 wt% NaCl). The following conclusions can be made:
1. In salt spray tests; the uncoated as well as nanostructured TiAlN and AlCrN coated
Superfer 800H superalloy have performed very well. The uncoated as well as coated
samples have shown no weight change during exposure for 24 Hrs, 48 Hrs and 72 Hrs to
salt fog tests and fully protected the substrate material.
2. It can be mentioned based on the present investigation that uncoated Superfer 800H and
nanostructured thin TiAlN and AlCrN coatings have shown a very good corrosion
resistance when exposed to the simulated marine environment i.e. salt fog test.

700 V. Chawla, D. Puri, S. Prakash and B. S. Sidhu Vol.8, No.9
ACKNOWLEDGEMENT
The authors wish to thank All India Council for Technical Education (A.I.C.T.E.), New Delhi,
India for providing National Doctoral Fellowship (NDF) to Mr. Vikas Chawla (corresponding
author) and grant under Nationally Coordinated Project (NCP).
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