Journal of Minerals & Materials Characterization & Engineering, Vol. 8, No. 9, pp 715-727, 2009
jmmce.org Printed in the USA. All rights reserved
715
Characterization and Comparison of Corrosion Behavior of Nanostructured
TiAlN and AlCrN Coatings on Superfer 800H (INCOLOY 800 H) Substrate
Vikas Chawlaa*, D. Puria, S. Prakasha, Amita Chawlab, and Buta Singh Sidhuc
a Metallurgical & Materials Engineering Department, I.I.T. Roorkee, Roorkee-247667, India
b Chemistry Department, Government Brijindra College, Faridkot -151203, India
c Mechanical Engineering Department, Y.C.E., Talwandi Saboo-151302,India
*Corresponding author: ,
Phone: [phone], Fax: [phone]
ABSTRACT
Nitrided coatings have been used to increase hardness and to improve the wear and corrosion
resistance of structural materials. In this work, TiAlN and AlCrN coatings were deposited on
Superfer 800H (INCOLOY 800 H) substrate by using Balzer’s rapid coating system (RCS)
machine (make Oerlikon Balzers, Swiss) under a reactive nitrogen atmosphere. The coated
samples were subjected to optical microscopy (OM), XRD analysis, Field emission scanning
electron microscope (FESEM with EDAX attachment), AFM analysis. The corrosion resistance
of the substrate, TiAlN-coated and AlCrN-coated samples in a 3 wt% NaCl solution was
evaluated and compared by electrochemical potentiodynamic polarization method. It was found
that the AlCrN-coating exhibited better corrosion resistance.
Keywords: Polarization, Tafel slope, Hard coatings, Corrosion, Physical vapour deposition.
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

716 V. Chawla, D. Puri, S. Prakash, A. Chawla and B. S. Sidhu Vol.8, No.9
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.
Recent studies show that 80% of the total cost for the protection of metals is related to coating
application [5]. Plasma assisted physical vapour deposition processes (PAPVD) allow the
deposition of metals, alloys, ceramic and polymer thin films onto a wide range of substrate
materials. 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].
In this work, nanostructured titanium aluminum nitride (TiAlN) and aluminum chromium nitride
(AlCrN) coatings were deposited on Superfer 800H (INCOLOY 800 H) substrate by using
Balzer’s rapid coating system (RCS) machine (make Oerlikon Balzers, Swiss) under a reactive
nitrogen atmosphere at Oerlikon Balzers’ Coatings, Gurgaon, India. The corrosion behavior of
the as deposited coatings and substrate in a 3%wt NaCl solution was tested and compared by an
electrochemical method i.e. linear polarization resistance (LPR) and potentiodynamic
polarization tests. The emphasis is put on the influence of nanostructured coatings on the
corrosion behavior of Fe-based superalloy.
2. EXPERIMENTAL DETAILS
2.1. Development of Coatings
AlCrN and TiAlN coatings were deposited on superfer 800H (INCOLOY 800 H) substrate, with
a thickness around 4µm. The actual chemical composition of the substrate has been analyzed
with the help of Optical Emission Spectrometer of Thermo Jarrel Ash (TJA 181/81), USA make.
The nominal and actual chemical composition of the substrate is as reported in Table 1.
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
lavigated alumina powder suspension.

Vol.8, No.9 Characterization and Comparison of Corrosion Behavior 717
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.
A front-loading Balzer’s rapid coating system (RCS) machine was used for the deposition of the
coatings (Figure 1). The machine is equipped with 6 cathodic arc sources. Two of the six sources
were used to deposit a thin, 0.3 μm thick TiN sub-layer to improve adhesion of coating. The
remaining four sources were employed to deposit the main layer of the coatings, which was
obtained using customized sintered targets.
Figure 1. Schematic illustration of the coating device used for the film deposition [11].
The compositions of the targets used, coating thickness and the summary of the process
parameters are presented in Table 2. For all coatings argon (Ar) and pure nitrogen atmosphere
was used during deposition. Prior to deposition all the substrates were cleaned in two steps:
firstly with Ultrasonic Pre-Cleaner (Imeco, Pune, India) and secondly with Ultrasonic Cleaning
Machine with 9 Tanks including hot air dryer (Oerlikon Balzers Ltd. India) for 1.5 Hrs.
2.2 Characterization of the Coatings
A Zeiss Axiovert 200 MAT inverted optical microscope, fitted with image software Zeiss
Axiovision Release 4.1, was used for optical microscopy. The porosity measurements were made
with image analyser, having software of Dewinter Materials Plus 1.01 based on ASTM B276.

718 V. Chawla, D. Puri, S. Prakash, A. Chawla and B. S. Sidhu Vol.8, No.9
Table 2. Summary of coating deposition parameters
Machine used Standard balzers rapid coating system (RCS) machine
Make Oerlikon Balzers, Swiss
Targets composition for TiAlN coating: Ti, Ti 50Al50
AlCrN coating: Al70Cr30
Number of targets Ti (02), Ti 50Al50 (04) and Al70Cr30 (06)
Targets power: 3.5 kW
Reactive gas Nitrogen
Nitrogen deposition 3.5 Pa
pressure
Substrate bias voltage -40V to -170V
Substrate temperature 450°C ± 10°C
Coating Thickness 4 µm ± 1 µm

A PMP3 inverted metallurgical microscope was used to obtain the images. The surface
morphology (2D and 3D) of the thin films was characterized by AFM (Model: NTEGRA, NT-
MDT, Ireland) to calculate the surface roughness and particle size. The coated specimens were
subjected to XRD analysis using Bruker AXS D-8 advance diffractometer (Germany) with Cu
Kα radiation. The scan rate used was 2°/min and the scan range was from 20° to 120°. The grain
size of the thin films was estimated from Scherrer formula, as given in Eq. (1). In this
expression, the grain size D is along the surface normal direction, which is also the direction of
the XRD diffraction vector.
D=0.9λ / B cosθ (1)
Where B is the corrected full-width at half maximum (FWHM) of a Bragg peak, λ is the X-ray
wavelength, and θ is the Bragg angle. B is obtained from the equation B2=B2r-B2strain-C2, where
Br is the FWHM of a measured Bragg peak, B strain= ε tan θ is the lattice broadening from the
residual strain ε measured by XRD using the cos2α sin2ψ method, and C is the instrumental line
broadening. Jayaganthan et al. [8] have also reported the particle size measurement by Scherrer
formula. Field emission scanning electron microscope (FESEM, FEI, Quanta 200F Company)
with EDAX Genesis software attachment (made in Czech Republic) is used to characterize the
surface morphology of the coatings. SEM micrographs along with EDS spectrum were taken
with an electron beam energy of 20keV.

Vol.8, No.9 Characterization and Comparison of Corrosion Behavior 719
2.3 Electrochemical Test
In order to evaluate the corrosion behavior of the substrate and coatings, electrochemical
methods i.e. linear polarization resistance (LPR) and potentiodynamic polarization tests were
conducted in an aerated 3 wt% NaCl solution at room temperature. The linear polarization
technique was preferred over Tafel polarization technique for monitoring corrosion current. The
primary reason was that linear polarization scans were conducted in very small potential range (-
20mV to + 20mV vs Open Circuit Potential), which does not damage the surface of the sample,
unlike Tafel scans, which require scanning over a longer potential range [9].
The electrolyte employed was prepared with NaCl analytical grade reagent with minimum assay
99.9 % (Art. No. 15915) supplied by Qualigens Fine Chemicals, Mumbai, India and deionised
water. The potentiodynamic polarization test was carried out using EG&G PAR model 273A
potentiostat. The test cell used was having the provisions in the form of circular openings of
different sizes to permit the introduction of the two high purity graphite counter electrodes, the
working electrode (test specimen) and the Luggin probe capillary tube, which housed the
saturated calomel reference electrode (SCE). The tip of the Luggin probe capillary was placed
near the sample.
The exposed surface area of all specimens was 1 cm2 and the remaining portion except the
exposed area was painted with good quality nail-paint in order to prevent the initiation of
corrosion. Before the electrochemical measurements, samples were allowed to stabilize at their
open circuit potential for 30 min. Potentiodynamic polarization measurements were carried out
starting from -250 mVOCP to 1600 mVSCE with a scan rate of 0.5 mV/s. The potentiodynamic
polarization plots were interpreted using SoftcorrTM III Corrosion Measurement software Version
2.30 provided by EG&G Instruments INC. All the experiments were repeated two times.
3. RESULTS & DISCUSSION
3.1 Microstructural Properties
The TiAlN and AlCrN coatings have been formulated successfully by PAPVD technique on
Superfer 800H (INCOLOY 800 H) substrate. Figure 2 shows the macrographs for TiAlN and
AlCrN coatings. The surface appearance of AlCrN coating is light grey in color and violet grey
in case of TiAlN coating. The optical micrographs of the substrate and thin coatings are depicted
in Figure 3. The coatings have uniform microstructure. It is evident from the microstructure that
the coatings contain some pores and inclusions. The porosity for as coated TiAlN and AlCrN
coatings is 0.41 % and 0.48 % respectively and reported in Table 3.

720 V. Chawla, D. Puri, S. Prakash, A. Chawla and B. S. Sidhu Vol.8, No.9
Figure 2. Surface macrographs of (a) TiAlN and (b) AlCrN coatings on Superfer 800H
(INCOLOY 800 H) substrate.
Figure 3. Optical micrograph (200X) of the surface of (a) Substrate, (b) TiAlN coating and (c)
AlCrN coating.
(
a
)
5mm
(
b
)
5mm
(c)
(b
50µm
50µm 50µm
(a)

Vol.8, No.9 Characterization and Comparison of Corrosion Behavior 721
Table 3. Micro structural and mechanical properties of the coatings
Coating Surface Hardness* Particle Size (nm) Porosity Friction Coating
Roughness (HV 0.05) Scherrer AFM (%) coefficient color
(nm) Formula Analysis against steel (dry) *
TiAlN 02.62 3300 09 10 0.41 0.30-0.35 violet-grey
AlCrN 05.99 3200 22 25 0.48 0.35 light-grey
*Data supplied by at Oerlikon Balzers’ Coatings, Gurgaon, India.
XRD diffractograms for each coating are depicted in Figure 4 on reduced scale. XRD analysis
for AlCrN coating confirmed the presence of CrN and AlN phases. Further, in case of TiAlN
coating the prominent phases are a large percentage of Ti2N along with AlN. From the XRD
diffractograms, the grain size of the thin coatings was estimated from Scherrer formula as given
in Eq. (1), and reported in Table 3. The grain size in case of TiAlN coatings (09 nm) is less than
that of AlCrN coating (22 nm). Oerlikon Balzers Ltd. India provided the data regarding hardness
and the friction coefficient against steel (dry), along with the coating parameters (Table 3). The
coated layer on the steel substrate has provided higher hardness as compared to the substrate.
TiAlN coating showed higher hardness value than AlCrN coating as reported in Table 3.
35 40 45 505560 6570 7580 85
TiAlN coating
AlCrN Coating
α CrN
β AlN
ε Ti N β
β
α
β
ε
ε
β
α
ε
β
ε
α
β
Intensity (arbitrary units)
Diffraction angle (2-Theta)
Figure 4: X-ray diffraction pattern for TiAlN and AlCrN coatings on Superfer 800H

722 V. Chawla, D. Puri, S. Prakash, A. Chawla and B. S. Sidhu Vol.8, No.9
SEM micrographs along with EDAX analysis for as coated TiAlN and AlCrN coatings are
shown in Figure 5. In case of TiAlN coating, the EDAX point analysis (Figure 5.a) shows the
presence of Ti (45.53 %) as the main phase along with Al (23.35 %) and N (25.10 %). A very
small amount of Ni, Fe, Cr and C is present, which may be due to the micro voids or pores
present in the coating. Further in case of AlCrN coating, Cr (30.72 %), N (21.86 %) and Al
(36.61 %) are the main phases along with small amount of Fe, C, Ni and Ti as indicated by the
EDAX analysis (Figure 5.b).
Figure 6 (a, b, c and d) shows the AFM surface morphology (2D and 3D) of the TiAlN and
AlCrN coatings deposited on superfer 800H (INCOLOY 800 H) substrate. The difference in the
morphology between the two coatings can be inferred by comparing the 2D images in Figure 6
(a) and (c); however a clearer comparison of the coatings is afforded by viewing 3D images in
Figure 6 (b) and (d). As the axis scale indicates the overall roughness of the TiAlN coating,
Figure 6 (b) is less than that of AlCrN coating, Figure 6 (d). The particle size in the coatings was
also provided by AFM Analysis, which is reported in Table 3. The TiAlN coating is having
lesser particle size (10 nm) as compared to AlCrN coating (25 nm).
3.2 Electrochemical Properties
The initial corrosion current density and LPR (Rp) was measured by LPR test. The corrosion
parameters obtained in LPR test are shown in Table 4. The corrosion current densities of the
films were found much lower than that of the substrate. The TiAlN coating has performed very
well and showed best corrosion resistance on the basis of corrosion current density and
polarization resistance. So, initial stage corrosion protection is provided by the coatings.
The corrosion rate ( icorr ) of the specimens was obtained using the Stern-Geary equation [9].
1
2.303  ac  a  c   
Where βa = anodic Tafel slope, βc = cathodic Tafel slope, Rp = polarization resistance and, Z is a
function of the Tafel slopes.
Potentiodynamic polarization curves of the substrate and each film are shown in Figure 7 and the
corrosion parameters in Table 5. The corrosion current density and the corrosion potential were
obtained by the intersection of the extrapolation of anodic and cathodic Tafel curves. The
corrosion current densities of the substrate and the films were found much lower as compared to
the LPR test (at initial stage) results. As the substrate having composition (reported in Table 1)
with higher percentage of Cr (approx. 20%) and Ni (approx. 30%), a protective oxide layer may
have formed which has blocked further corrosion.
(2)

Vol.8, No.9 Characterization and Comparison of Corrosion Behavior 723
Figure 5: SEM/EDAX analysis along with EDS spectrum for (a) TiAlN (X 200); (b) AlCrN
coatings (X 200) on Superfer 800H (INCOLOY 800 H).
(b)
45.53% Ti
23.35% Al
25.10% N
00.88% Ni
02.58% Fe
01.93% C
00.63 % Cr
30.72% Cr
36.61% Al
21.86% N
03.25% Ni
03.43% Fe
03.74 % C
00.39% Ti
(b)
(a)
(a)
500µm
500µm

724 V. Chawla, D. Puri, S. Prakash, A. Chawla and B. S. Sidhu Vol.8, No.9
Figure 6: 2D and 3D AFM images of TiAlN [(a) & (b)] and AlCrN [(c) & (d)] coatings on
Superfer 800H (INCOLOY 800 H).


Table 4. Results of Linear polarization resistance tests
Specimen Ecorr icorr Rp βa βc
(mV) (µA/cm2) (kΩ-cm2 ) (V/decade) (V/decade)
Substrate -204.2 05.37 4.042 0.1 0.1
TiAlN -284.4 0.338 64.14 0.1 0.1
AlCrN -416.9 0.474 45.73 0.1 0.1


(a) (b)
(c) (d)

Vol.8, No.9 Characterization and Comparison of Corrosion Behavior 725
Table 5. Results of potentiodynamic polarization tests
Specimen Ecorr icorr βa βc Rp Pi
(mV) ( µA/cm2) (V/decade) (V/decade) (kΩ-cm2 ) (%)
Substrate -97.33 0.058 0.2022 0.128 0586.89 --
TiAlN -220.9 0.068 0.0923 0.172 0383.55 Not Protecting
AlCrN -194.7 0.021 0.0971 0.109 1049.52 63.79
-500
-450
-400
-350
-300
-250
-200
-150
-100
-50
0
50
-14-13-12-11-10-9-8-7-6-5-4-3-2
Substrate
TiAlN Coating
AlCrN Coating
E (mV)
I{ log(A/cm2)}
Figure 7. Potentiodynamic Polarization Curves
The corrosion product formed may have reduced the passage of the electrolyte to attack the
samples, and hence providing protection. The AlCrN coating has performed very well and
showed best corrosion resistance on the basis of corrosion current density and polarization
resistance (Table 5).

726 V. Chawla, D. Puri, S. Prakash, A. Chawla and B. S. Sidhu Vol.8, No.9
From polarization test results, the protective efficiency, Pi (%) of the films can be calculated by
Eq. (3):
 %1
° 100
Where icorr and iocorr indicate the corrosion current density of the film and substrate, respectively
[10]. The calculated protective efficiencies and polarization resistances are presented in Figure 8.
The AlCrN film showed the highest protective efficiency of 63.79% caused by lowest corrosion
current density of 0.021 µA/cm2. The observed protection by the TiAlN and AlCrN coatings in
an aerated 3 wt% NaCl solution at room temperature, are almost in agreement with the findings
of Xing-zhao et al. [11].The current density in case of TiAlN coating is also very low, but
slightly more than that of the substrate. So, TiAlN coating is not providing the necessary
protection to the substrate for longer duration. Liu et al. [1] reported the superior resistance of
Ni-based superalloy nanocrystalline coating by sputtering to pitting corrosion in NaCl solution.
Ye et al. [12] found that sputtered 309 SS nanocrystalline coating had a higher pitting resistance
in comparison with its bulk material.
Figure 8: Protective efficiency and Polarization resistance of TiAlN and AlCrN coatings on
Superfer 800H (INCOLOY 800 H).
4. CONCLUSION
The nanostructured TiAlN and AlCrN coatings were deposited successfully on superfer 800H
(INCOLOY 800 H) by using Balzer’s rapid coating system (RCS) machine. The microstructural
586.89
1049.52
383.55
300
400
500
600
700
800
900
1000
1100
20
30
40
50
60
70
80
90
100
Substrate AlCrNCoating TiAlNCoating
PolarizationResistance((kΩ‐cm2)
ProtectiveEfficiency(%)
ProtectiveEfficiency
(%)
PolarizationResistance
((kΩ‐cm2)
(3)

Vol.8, No.9 Characterization and Comparison of Corrosion Behavior 727
morphologies and electrochemical properties of the coatings were investigated in the present
work. Both the coatings have been found to possess low porosity. The XRD and SEM/EDAX
analysis confirmed the formation of the requisite composition of the coatings. The AFM studies
revealed that the overall roughness and particle size of TiAlN coating is less than that of AlCrN
coating. At the initial stage (LPR test), the corrosion current densities of the films in an aerated 3
wt% NaCl solution at room temperature were found much lower than that of the substrate steel.
The coatings are providing necessary protection to the substrate initially. But, in longer run i.e.
potentiodynamic polarization test, the AlCrN coating has performed very well and showed best
corrosion resistance as evident from corrosion current density and polarization resistance.
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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