Journal of Minerals & Materials Characterization & Engineering, Vol. 10, No.5, pp.445-453, 2011 Printed in the USA. All rights reserved
Slurry Erosive Wear Behavior of Plasma Sprayed Inconel-718 Coatings on
Al6061 Alloy
C.S. Ramesh1*, Suresh Kumar2, D.S. Devaraj1, R. Keshavamurthy1
1Department of Mechanical Engineering, PES Institute of Technology, Bangalore, Karnataka,
2Department of Mechanical Engineering, SBMJCE, Ramanagaram District., Karnataka, India
* Corresponding Author:
Plasma Sprayed coatings provide protection against corrosion, erosion and wear. Inconel- 718
is a metallic coating which has good wear and erosion resistance. This is plasma sprayed on to
Al6061 substrate and then subjected to slurry erosive wear tests. It is observed that the slurry
wear rates of Al6061 decreased on coating the substrate material with Inconel- 718.
Keywords: Plasma spray, Inconel- 718, Al6061, Erosion.
Out of many surface modification techniques, plasma spraying stands out as one of the most
versatile and technologically sophisticated thermal spraying technique [10]. Plasma spraying is
gaining extensive attention in the research fraternity as it has the advantage of applying coatings
using different materials such as ceramic, metallic and composite coatings with possibility of
controlling the thickness from few microns to few millimeters. Thus produced coatings improve
hardness and hence reduce wear.
Al6061 has found many applications in the field of aeronautics, automobiles and other
fabrication processes due to its high strength to weight ratio and excellent formability and
corrosion resistance. However, its wear resistance is poor. Hence, an attempt has been made in
the present work to develop metallic coatings using Inconel-718 to overcome the above
446 C.S. Ramesh, Suresh Kumar, D.S. Devaraj, R. Keshavamurthy Vol.10, No.5
In the recent past, many studies have been reported in the literature on wear behavior of different
coatings on different substrates produced by plasma spray technique. Chang-Jiu Li etal [1] have
reported that the erosion of plasma-sprayed ceramic coating was inversely proportional to the
mean lamellar bonding ratio. The erosion resistance of a thermally sprayed ceramic coating was
controlled by the fracture toughness of the coatings. Da-Wei Zhang et al [2] have concluded that
the erosive–corrosive wear rate of stainless steel substrate reduced by about 50% by laser-clad
Ni–Cr3C2 composite coating in acidic slurry of quartz sand. Diana Lopez et al [3] have reported
the formation of cracks in the coating and plastic deformation in both the substrate and the
coating, especially when the mean impact velocity exceeded a critical value between 6.9 and 8.6
ms1. Hoppel et al [4] have coated different combinations of Co/WC and NiCr/Cr3C2 on different
alloy substrates of Ni, Cr and Mo combinations and have reported that the slurry erosive wear
resistance of coated specimens are greater in comparison to the un-coated substrate. Wang et al
[5] have concluded that the slurry erosion resistances of the Ti N coatings were significantly
higher than that of the uncoated mild steel and the AISI 304 stainless steel. They have observed
that increase of particle erosion speed had no significant effect on the erosion of coatings. Jari
Knuuttila et al [6] have reported that aluminum phosphate sealing gives the best improvement in
slurry erosive wear resistance of alumina and chromia coatings when the wear is dominated by
brittle fracture and the contact conditions are relatively rough. However, if tribochemical wear is
encountered, sealing with aluminum phosphate has no effect.
Rutherford et al [7] have reported that use of polymer films on steels have resulted in improved
slurry erosion wear resistance. Hadad [8] have reported that WC–Cr–Co coatings deposited
by thermal spray methods on steel substrate exhibited improvement in slurry erosive wear
resistance. Abou El-Khair et al [9] have concluded that use of nickel coating on aluminum
based composites by electrochemical deposition have exhibited high hardness, corrosion and
wear resistance against slurry erosion. However, meager information is available as regards the
study on Inconel coatings on Al6061 substrate.
In the light of the above, this work focuses on development of plasma sprayed Inconel-718
coatings on Al6061 substrate and to investigate the slurry erosive wear behavior of the developed
2.1 Materials
2.1.1 Coating material: Inconel-718
Inconel-718 is chosen as the coating material. It is nickel based super alloy having excellent wear
and corrosion resistance coupled with high strength at ambient temperature. This alloy finds
Vol.10, No.5 Slurry Erosive Wear Behavior 447
variety of applications like gas turbines, jet engines, steam generators, fission and fusion reactor
structures. Table 1 gives the chemical composition of Inconel-718 used in the present work.
The size of the particles of Inconel-718 alloy powder used ranged between 20 to 50 µm.
Table 1: Chemical composition of Incone l - 71 8
Element Weight %
Carbon 0.08
Manganese 0.35
Silicon 0.35
Phosphorus 0.015
Sulfur 0.015
Nickel + Cobalt 55.0
Chromium 21.0
Cobalt 1.00
Aluminum 0.80
Molybdenum 3.30
Titanium 1.15
Boron 0.006
Copper 0.15
Cb + Ta 5.50
Iron Balance
2.1.2 Substrate material: Al6061 alloy
Al6061 is selected as substrate material. Table 2 gives the chemical composition of Al6061
substrate used in the present work. Al6061 plates were cut to produce specimen of size
22mmx25mmx8mm. These samples were thoroughly cleaned using acetone followed by grit
Table 2: Chemical composition of Al6061 (Major elements)
Element Weight %
Al 97.9
Si 0.60
Cu 0.28
Mg 1.0
Cr 0.20
448 C.S. Ramesh, Suresh Kumar, D.S. Devaraj, R. Keshavamurthy Vol.10, No.5
2.2 Coating Procedure
Air Plasma Spray (APS) coating was carried out at M/S Metallizing Equipment Company Pvt.
Ltd. Jodhpur, India. SG-100 torch mounted on a computer controlled KUGA robot is used for
plasma spraying Inconel-718 alloy powder on grit blasted Al6061substrate. Hydrogen and argon
gases are used as inert gases during the coating process. Table 3 gives the plasma spray
parameters adopted in the present work to develop coatings of thicknesses 200 and 250µm. A
constant stand off distance of 5” was adopted.
Table 3: Plasma spray parameters
Voltage 40 volts
Current 800 amps
Primary Inert gas – Argon gas
Secondary Inert– hydrogen
40 LPM
0.4 LPM
Carrier gas – Argon gas
32 Kw
INCONEL718 powder
Powder feed rate
100 gm/min
33 grams / min
2.3 Slurry Erosion Test
Wear of Inconel-718 coated on Al6061 specimens were studied using standard slurry erosive
wear tester as shown in Fig.1. Prior to the tests, the samples were thoroughly cleaned with
acetone and its initial weight was measured using an electronic balance of accuracy 0.01mg. The
specimens were then fixed to the spindle of the tester with the samples fully immersed in slurry
media of 3.5%NaCl and silica sand of particular grit size. Tests were conducted for various
slurry concentrations and coating thicknesses. The particle size of sand particles was 600 µm
while the speed of rotation and time period were maintained at 500rpm and 15hrs respectively.
After the test, the specimens were cleaned with acetone and its weight is measured to assess the
slurry erosion wear loss of the samples.
Vol.10, No.5 Slurry Erosive Wear Behavior 449
Fig. 1 Photograph of slurry erosion wear tester
3.1 Microstructure
Fig. 2 shows the SEM of cross section of the coatings. Further, coating thickness of 200µm can
be observed. A good bond between the coating and the substrate do exist indicating that the
adopted coating process parameters are optimal. It is observed that there exist several layers of
deformed particles with typical lamellar structure. No visible cracks are being observed in both
the coating and the substrate. A dense and uniform coating can be observed.
Fig. 3a shows the SEM photograph of uncoated Al6061 substrate. The rough surfaces observed
on the substrate is due to grit blasting. Fig.3b shows the SEM of the coated specimen. The
surface morphology of the coatings clearly indicates that the obtained coating is uniform and
450 C.S. Ramesh, Suresh Kumar, D.S. Devaraj, R. Keshavamurthy Vol.10, No.5
Fig. 2 SEM of cross sectional micrograph of Inconel-718 on Al6061 alloy
(a) Grit blast Al6061 substrate (b) Inconel 718 coatings on Al6061 substrate
Fig. 3(a-b) SEM of uncoated and coated Al6061 alloy surfaces
3.2 Slurry Erosion Test
3.2.1 Effect of slu r r y c on c e n t r at i o n
Fig. 4 shows the effect of slurry concentration on erosive wear of uncoated and Inconel-718
coated Al6061. It can be observed that the mass loss of uncoated Al6061increases steeply with
increase in slurry concentration. However, a marginal increase in mass loss is observed in case of
the developed coatings. An excessive material removal is observed in case of uncoated
Al6061samples at all the slurry concentrations. This can be attributed mainly to its lower
hardness and poor erosion resistance. Further, increased coating thickness results in reduced
slurry erosive wear loss for all the slurry concentration studied.
The improvement in the slurry erosion resistance of the coatings can be attributed to the
following reasons.
Vol.10, No.5 Slurry Erosive Wear Behavior 451
Rotati onal Speed: 500r pm,
Test duration: 15hr s,
Imping part i cl es size : 600 µm
50100 150
Weight loss
uncoated Al6061 al l oy
Inconel- 718 CO ATED
Fig.4 Effect of slurry concentration on slurry erosive wear of Inconel-718 coatings
Increase in hardness and strength of Inconel-718, higher toughness of the coatings, excellent
corrosion resistance of Inconel 718 as it contains higher proportions of alloying elements such as
nickel, cobalt and chromium. These alloying elements favors the formation of stable oxide films
which are corrosion protective in nature thereby enhancing the slurry erosion resistance of the
coatings. However, the increased mass loss with increase in slurry concentration of all the
studied materials can be attributed to fact that, increased abrasive particle concentration in the
slurry enhances the probability of more impingements on the surfaces leading to increased
deterioration of material from its surfaces.
3.2.2 Effect of coating thickness
Fig.5 shows slurry erosive wear loss of uncoated and Inconel-718 coated Al6061 with increase in
coating thickness for a given slurry concentration. It can be observed increase in the coating
thickness results in better slurry erosion resistance of the coatings. This can be mainly attributed
to the higher extent of corrosion protection of the surfaces with increased coating thickness.
Increased coating thickness results in porosity reduction which is a major factor affecting
corrosion. Presence of porosity leads to higher extent of localized pitting which accelerates the
material removal process during slurry erosion tests where the primary mechanism of material
removal is corrosion.
452 C.S. Ramesh, Suresh Kumar, D.S. Devaraj, R. Keshavamurthy Vol.10, No.5
Im pinging p articl e size: 600µm, Speed of slurry
rot ation: 50 0 rpm, Test dur ation : 15hrs
Uncoated Al6061
alloy Inconel-718
coating (200 µm)Inconel-718
coating (250µ m)
Fig. 5: Effect of coating thickness on slurry wear loss at slurry concentration of 100 g/litre
Plasma sprayed Inconel 718 coatings have significantly improved the slurry erosion resistance of
Al6061 substrate in 3.5%NaCl sand slurry.
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