Journal of Minerals & Materials Characterization & Engineering, Vol. 9, No.7, pp.653-670, 2010 Printed in the USA. All rights reserved
Improvement of High Temperature Wear Resistance of AISI 316 ASS
through NiCrBSiCFe Plasma Spray Coating
N. L .Parthasarathi, Muthukannan Duraiselvam*
Department of Production Engineering, National Institute of Technology, Tiruchirappalli-620
015, Tamil Nadu, INDIA
*Corresponding author:
In this work, the microstructural description, mechanical properties and dry sliding wear
features of NiCrBSiCFe plasma sprayed on AISI 316 austenitic stain l ess steel (ASS ) s ubstra te
were examined. Defect-free metallurgically bonded coatings were obtained. Wear tests were
carried out at 2 m/s sliding velocity under the load of 20N for 2000 m sliding distance at
various conditions like room temperature (35°C), 150°C, 250°C and 350°C using a EN-8
medium carbon steel pin as a counterface material. The properties namely coating density,
micro hardness, coefficient of fri ction (CoF) and wear resistan ce of the coating were studied.
NiCrBSiCFe plasma sp ray coated st eel subs trate showed superior wear resistance properties
than the uncoated steel substrate in all the temperatures. The sliding wear resistance was
improved up to 4.5 times than that of the uncoated material. In wear test carried out at
350ºC, the coated substrates showed relatively lesser wear than in other temperatures due to
the oxide formation, which acted as a protective layer. In addition, the shallow ploughing
mode of wear reduced the severity of material removal at 350°C. Using scanning electron
microscope (SEM) pictures, the wear properties of the coated steel substrate were evaluated
in terms of plastic deformation, material transfer and abrasion.
Keywords: AISI 316 ASS; NiCrBSiCFe; Plasma spraying; Abrasion; Wear.
AISI 316 austenitic stainless steel (ASS) is a frequently used engineering material employed
in high temperature applications because of its excellent corrosion resistance. Due to the low
hardness of the AISI 316 ASS, continual attempts were made to enhance hardness thereby to
improve the wear resistance. A detailed study on sliding-wear evaluation of nitrided
austenitic alloys was carried out. During the contact with themselves or other materials, ASS
654 N. L .Parthasarathi, Muthukannan Duraiselvam Vol.9, No.7
frequently suffers severe metallic wear, due to the formation of strong adhesion junctions
between the contact surfaces [1].
The wear of AISI 316 ASS was studied in a variety of gaseous atmospheres at constant load
and sliding speed under reciprocating conditions. The environments such as air, CO2, argon
and partial vacuum were investigated. The wear debris in all cases was essentially metallic
and its rate of production per unit length was constant with sliding distance [2].
In austenitic and martensitic steels, the load and sliding speed dependencies of the coefficient
of friction (CoF) and temperature was studied. It was shown that severe adhesive wear
(seizure) conditions result in formation of 20 to 40µm thick layer with the fine-crystalline
microstructure [3]. Room temperature tests on air and vacuum plasma-sprayed TiC-NiCrBSi
coatings using a pin-on-disc tribometer at various loads and sliding speed have been
performed in order to understand the effects of the parameters on the coating wear and
friction behaviour. Results have shown that load, sliding speed and the plasma spray process
affect the wear resistance and the friction behaviour of thermally sprayed coatings. Higher
loads during sliding led to higher wear rates for both air and vacuum plasma sprayed coatings
[4]. NiCrAlY and CoNiCrAlY powders were thermal-sprayed using the high frequency pulse
detonation method (HFPD) onto AISI 310 ASS samples to obtain dense, adherent, high
temperature oxidation resistant coatings.
The oxidation kinetics of both coatings was characterized by parabolic rate constants, which
are very close to those for the formation of aluminium oxide on nickel or cobalt based alloys
[5]. The plasma carburized layers prevented surface plastic deformation and improved the
wear resistance of the steel during the early stages of the wear process. Subsurface plastic
deformation occurs beneath the layer, leading to the catastrophic failure of the layer and a
transition in the wear rate after a limited duration of testing.
Three carburized layers with varying thickness, ranging from 15 to 40 µm were tested and the
thickest layer tested produced the best wear performance under the rolling-sliding test
conditions. [6]. The dry sliding behaviour of an austenitic stainless steel and a duplex 2205
austenitic-ferritic stainless steel was investigated. The evolution of wear was characterised by
the existence of a sliding distance transition. In particular, wear passed from delamination to
tribo-oxidation, with a reduction in wear rate [7].
A low temperature plasma carburising technique was developed to engineer the surfaces of
austenitic stainless steels to achieve combined improvement in wear and corrosion resistance.
The resultant carburised layer was free from carbide precipitates and contained a single
austenite phase supersaturated with carbon. The results showed that the hard and corrosion
resistant carburised layers are effective in preventing surface plastic deformation, eliminating
adhesive and severe abrasive wear [8]. Tribological reactions on the friction and wear of
quasicrystalline materials (Al-Ni-Co-Si) and coatings with two alloy compositions have been
prepared by plasma and high velocity oxy fuel (HVOF) spraying techniques. The tribolayers
were characterised by the formation of a transfer film on the counterface and densification of
Vol.9, No.7 Improvement of High Temperature Wear Resistance 655
the coating subsurface. The wear rate appeared to be controlled by the thickness of the pore-
free region formed within the coating surface zone [9].
A modified NiCr coating was thermal-sprayed using different procedures (flame, plasma,
HVOF and HFPD) onto stainless steel specimens. The microstructures, porosities, oxide
contents and microhardness of the coatings were determined [10]. Plasma-sprayed nickel
coatings on stainless steel and cobalt alloy coupons heated to temperatures ranging from
room temperature to 650°C. Heating the substrate removes surface moisture and other
volatile contaminants, delays solidification of droplets, helps to penetrate the surface cavities,
and promotes diffusion between the coating and substrate. All these mechanisms enhance
coating adhesion [11].
A study on the effect of relative humidity and applied load range on the friction and wear of
AISI 304 austenitic stainless steel were characterized by two different grain sizes of 2.5 and
40 µm. At loads of 2 N, using a standard ball-on-disc tribometer, severe wear was evident at
low humidity, while relatively lower wear was observed at high humidity indicating a
lubricating effect of water [12]. For the protection of the surfaces against degradation, the
HVOF spraying with high strength, hardness, low porosity (less than 1%), high erosion-
corrosion and wear resistances were employed. The role of some HVOF coatings in the
protection of metals and alloys against degradation at high temperatures in various media was
studied [13]. The effect of localised laser melting of plasma sprayed NiCrBSi coatings, on the
corrosion behaviour was investigated. The microstructure of the coatings was analysed by
SEM and energy dispersive spectroscopy (EDS) analysis [14]. The plasma spraying
technique was used to get the solid lubrication iron sulfide coating on the 1045 steel. The
friction test of the FeS coatings, tested on a ring-on-block tester, showed that the plasma
spraying FeS coatings possessed the remarkable friction-reduction performance. The worn
failure mechanism of the coatings was flaking off [15].
The wear behavior of the coating was evaluated using a pin on disc wear system against SiC
abrasive medium of 120 and 600 grades at 5, 10, 15, and 20 N normal load. Results revealed
that the influence of normal load on wear is governed by the microstructure, hardness and
abrasive grit size. The heat treatment increased average microhardness of the coating [16].
The effect of nitrogen ion implantation with energy of 125 keV on such tribological
characteristics of AISI316L ASS as the friction coefficient, wear resistance, and
microhardness was studied. An increase in the abrasion resistance after implantation was
detected, which was different for various media. The largest increase in the wear resistance
was observed during testing in air. The largest decrease in the CoF was observed for all
implanted samples in argon atmosphere [17].
Friction and wear characteristics of Al–SiC composites have been investigated under dry
sliding conditions and compared with those observed in pure aluminium. Dry sliding wear
tests have been carried out using pin-on-disc wear test rate normal loads of 5, 7, 9 and 11 Kgf
656 N. L .Parthasarathi, Muthukannan Duraiselvam Vol.9, No.7
and at constant sliding velocity of 1.0 m/s. The best results have been obtained at 20% weight
fraction of 320 grit size SiC particles for minimum wear [18].
Glow discharge (GD) nitro carburizing, at low carbon content and different working
temperatures, was performed on AISI 316L and AISI 304 stainless steels. At working
temperatures higher than 400°C, roughness increased and wear was limited to asperity
compaction. Wear was reduced by up to a factor of 5 in treated steels [19]. NiCrBSi has been
deposited onto 0Cr13Ni5Mo stainless steel using the activated combustion high velocity air
fuel (AC-HVAF) technique. The structure and morphologies of the Ni-based coatings were
investigated by XRD, SEM and EDS [20]. In the above studies, the influence of temperature
in the tribological properties was not highlighted.
The existing studies did not focus on the working conditions of the sliding wear and the worn
tracks of the coatings were not characterised with respect to the temperatures. In this work,
the NiCrBSiCFe was plasma sprayed on AISI 316 ASS and the tribological properties were
evaluated at different temperatures such as room temperature (35°C), 150°C, 250°C and
350°C using a pin-on-disc tribometer. The influence of microstructure and hardness of the
coating on the wear resistance was explained. The wear mechanism was identified by
correlating SEM and XRD analysis.
2.1. Materials and Plasma Spraying Process
The as-received AISI 316 ASS sheets were machined into a disc of 100 mm diameter and
4mm thickness. Acetone was used for degreasing. The substrates were grit blasted to improve
the surface roughness to a Ra value of 10 µm. Micro- Melt® B-60 NiCrBSiCFe alloy powder
supplied by Carpenter Powder Products Inc., U.S.A. was used as a raw material. The
morphology of NiCrBSiCFe powder particles was analysed by SEM. The powder consists of
gas atomised spherically shaped particle as is shown in Figure 1. The mean particle size of
the feedstock powder used in the present study was identified as 63.72 µm. An EN-8 medium
carbon steel pin was used as a counterface material. The chemical composition of substrate,
powder and counterbody is shown in Table 1. During plasma spraying, the spray gun (Sulzer
Metco SST-24) was stationary and the specimen was mounted on a rotating table. The
coating feedstock material was injected vertically into the plasma jet by argon (Ar) carrier gas
for primary flow and hydrogen gas (H2) for secondary flow. The plasma coating was
performed up to 500 µm thickness. The selected spray parameters are given in Table 2.
Vol.9, No.7 Improvement of High Temperature Wear Resistance 657
Figure 1. SEM morphology of NiCrBSiCFe powder
Table 1. Chemical composition (wt. %) of spray powders and the counterbody
Elements Ni Cr B Si C Fe S Mn Mo
AISI 316
Substrate 14 18 -- 1.0 0.08 Bal. 0.03 2.00 3.00 0.045
Powder Bal. 13.3 3.1 3.9 0.5 3.7 -- -- -- --
counterbody -- -- -- 0.15 0.35 Bal. -- 0.6 -- 0.04
Table 2. Selected Processing Parameters.
Spray parameter Value
Substrate AISI 316 ASS
D.C. Current (A) 480
D.C. Volts ( v) 70
Primary gas flow rate (SLPM) Argon 150
Feedstock carrier gas flow rate (SLPM) Argon 37
Powder flow rate (g/min) 120
Stand-off spray distance ( mm) 125
Scanning velocity (mm/sec) 6
Coating thickness (µm) 500
658 N. L .Parthasarathi, Muthukannan Duraiselvam Vol.9, No.7
2.2. Wear Test
Wear tests were carried out under dry sliding condition on a DUCOM pin-on-disc tribometer,
model TR-20-M-106 as shown in Figure 2. The linear variable differential transducer
(LVDT) probe was positioned on the weights to measure displacement and the load cell to
sense the tangential force. ASTM G99-05 [21], the standard test method for wear testing
with a pin-on-disc apparatus was slightly deviated by having plasma sprayed steel disc as a
specimen for characterising the coating. The counterface material, EN-8 medium carbon
steel, was prepared in the form of pin with a dimension of 31 mm height and 6mm diameter.
The pin was made to slide on the coated steel disc at 2.0 m/s sliding speed under the load 20
N for 2000 m sliding distance.
The NiCrBSiCFe plasma coated samples were polished by surface grinding to attain the
surface roughness value Ra~1 µm. The wear tests were conducted at temperatures such as
room temperature (35°C), 150°C, 250°C and 350°C. Before and after test, the plasma sprayed
disc substrates were ultrasonically cleaned, dried and weighed using an electronic analytical
balance to an accuracy of 0.1 mg. By using the data acquisition system, the depth of wear and
the frictional force were recorded automatically with respect to time. Using the mass loss,
the volume loss was computed using equation 1. The wear resistance was calculated using
equation 4. The measured frictional force from the data acquisition system was used to
compute CoF using equation 5.
Where, ρ1 is the density of water (1 g/cm3 at room temperature), ma is the weight of the
plasma coating in air (g) and m1 is the weight of plasma coating in water (g).The wear rate
and wear resistance was calculated by the following equations:
Where, F is the Frictional force in N, N is normal applied load in N.
Vol.9, No.7 Improvement of High Temperature Wear Resistance 659
Figure 2. Experimental setup for pin-on disc
2.3. Coating Characterisation
The following methods were used to characterise the coatings.
2.3.1. Microstructural and XRD characterisation
The plasma sprayed AISI 316 ASS samples were sectioned, polished and etched with Nital.
The etched specimens were studied by optical microscopy (OM). The micrograph of EN-8
medium carbon steel was also analysed. The worn tracks of the plasma sprayed specimens
were analysed using SEM (HITACHI S 3000H) to identify the mode of material loss during
sliding at different temperatures. The phase constitution of uncoated and as-sprayed AISI 316
ASS specimens was evaluated by XRD analysis with CuKα radiation source (D/MAX
ULTIMA III, Rigaku Corporation, Japan) operating at 30 mA and 40 kV. The set scanning
speed and the scanning range are 2°/min and 10–80°, respectively.
2.3.2. Characterisation of NiCrBSiCFe as-sprayed coated surface
The concept of splat formation due to the impact of spherical powder on the substrate during
plasma spraying is schematically shown in Figure 3(a).The as-sprayed NiCrBSiCFe plasma
coated surface is shown in Figure 3(b). The splat formed due to the impact of the molten
spherical powder on the substrate was clearly captured by SEM. These splats aided the
lamellar microstructure formation, which offered higher hardness and wear resistance. The
coated surface when analysed by SEM revealed the presence of small voids. The as-sprayed
surface also showed sparsely distributed unmelted spherical particles. These unmelted
spherical powder particles were visible due to the high flight in velocity of the particle.
660 N. L .Parthasarathi, Muthukannan Duraiselvam Vol.9, No.7
(a) (b)
Figure 3. (a) Splat formation after the impact of the spherical powder during spraying
(b) As-sprayed NiCrBSiCFe plasma coated surface
2.3.3. Microhardness and density measurement
The microhardness was measured using Zwick MHT Vickers hardness tester at a load of 300
g for 20 seconds. Using the molecular formula, the theoretical density of the NiCrBSiCFe
plasma sprayed coating was calculated as 8.146 g/cm3. In order to determine the actual
density, the NiCrBSiCFe coating was mechanically peeled off from the substrate and
measured using Archimedes principle as per equation 2. The average actual density of the
coating was 8.116 g/cm3.
3.1. Coating Microstructure
The cross-sectional microstructures of NiCrBSiCFe plasma sprayed coatings are shown in
Figure 4(a) and (b). The improved roughness by grit blasting was explicitly visible as
undulations on the interface region aided for a good metallurgical boding. The micrograph
indicated that the physical bonding between the coating and the interface was sound. Absence
of pores in the interface region substantiated that the bonding was intact. The microstructure
of the coatings showed elongated splats (explained in section 3.5) of molten powder forming
a lamellar structure. This structure was responsible for the higher hardness, which offered
superior wear resistance. The absence of microcracks showed that the processing parameters
selected in this study have ensured a good quality of plasma sprayed coatings. The
microstructure of the substrate, AISI 316 ASS is shown in Figure 3(c). The austenitic
structures were clearly visible. The microstructure of the counterbody, EN-8 medium carbon
steel pin is shown in Figure 3(d). The structure was "body-centered tetragonal" (BCT) and
Vol.9, No.7 Improvement of High Temperature Wear Resistance 661
was classed as a hard ferro-magnetic group. The presence of frequent carbides in the
microstructure was responsible for the higher hardness.
(a) (b)
(c) (d)
Figure 4.Cross-sectional micrographs: (a) interface and coating, (b) lamellar structure of the
as-sprayed structure of the NiCrBSiCFe plasma sprayed coating, (c) AISI 316 ASS substrate
(d) EN-8 medium carbon steel counterbody
3.2. Microhardness Characterisation
The Vickers hardness of AISI 316 ASS substrate and EN-8 medium carbon steel pin was 223
HV0.3 and 302 HV0.3, respectively. Three distinct regions were distinguished in the hardness
profile namely plasma sprayed coating, interface and substrate. The microhardness of the
cross section of the NiCrBSiCFe coatings as a function of distance from the coating substrate
is shown in Figure 5. The microhardness of the NiCrBSiCFe plasma coating is found to vary
with the distance from the coating-substrate interface. Coating microhardness values were
found to be in the range of 730–918 HV0.3. The maximum value of about 918 HV0.3 was
obtained in the top of the coating, which may be the point of the carbide or boride formed
during plasma spraying. The average microhardness value is 822 HV0.3.The interface region
showed an intermediate hardness values ranging 294-398 HV0.3. The increase of hardness of
662 N. L .Parthasarathi, Muthukannan Duraiselvam Vol.9, No.7
AISI 316 ASS substrates due to the plasma sprayed coating was responsible for the superior
wear resistance.
Figure 5. Microhardness variation of the NiCrBSiCFe coatings as a function of the distance
from the surface
3.3. Friction and Wear Behaviour
The consolidated wear with respect to time at different temperatures is shown in Figure 6.
The wear was primarily dominated by plastic deformation. In uncoated AISI 316 ASS
substrate, it was inferred that the wear at 250°C was higher than that of the rest of the
temperatures. The wear rate at 350°C was initially found to be higher, but as time proceeds,
the oxide layer formations considerably reduced the wear. The hard oxide layers formed
might have induced slipping in sliding wear. Except in 350°C, the uncoated AISI 316 ASS
showed severe wear in all operating temperatures. In contrast, the NiCrBSiCFe coated
samples showed very less wear in all temperatures. Relative sliding between the contacting
surfaces leads to the rupture of these junctions and subsequent material transfer from one
surface to the other, in addition to the production of debris and material loss. The presence of
a lubricating oxide film reduces the tendency for adhesive wear occurrence [22].
Notably in 350°C, the wear rate was marginally lesser than the rest of the temperatures due to
the initiation of oxide layers, which was also substantiated by SEM analysis (Figure 10 (d)
and 11 (d)). The CoF for the uncoated AISI 316 ASS varies between 0.4 and 0.5 in all the
temperatures and is shown in Figure 7. In NiCrBSiCFe coated discs, the CoF was found to be
Vol.9, No.7 Improvement of High Temperature Wear Resistance 663
relatively lesser and was ranging from 0.2 to 0.4 in all temperatures. In coated samples worn
at 350°C, the CoF was in the lower optimum range of 0.2 to 0.3. This optimum value might
be due to the oxide formations in the interface at 350°C. The oxide formations were
explained in detail in section 3.6. The wear resistances of the uncoated and plasma sprayed
steel substrates are shown in Figure 8. The highest wear resistance of 693.92 m/mm3 was
recorded for the plasma sprayed steel substrate at 350°C.
Figure 6. Variation of wear with respect to time and temperature.
664 N. L .Parthasarathi, Muthukannan Duraiselvam Vol.9, No.7
Figure 7. Variation of coefficient of friction with respect to time and temperature
Figure 8. Comparison of wear resistances of uncoated and NiCrBSiCFe coated samples with
respect to temperature
Vol.9, No.7 Improvement of High Temperature Wear Resistance 665
3.4. Phase Identification by XRD
The consolidated XRD patterns of the uncoated and NiCrBSiCFe coated AISI 316 ASS
substrates were shown in Figure 9. It reveals the peaks having the phases of γ-Iron (FCC) in
all operating temperatures. The peaks reveal the presence of certain intermetallics namely
Fe3B [20], Cr1.12Ni2.88 and Ni3B [14]. Si and Cr peaks were also present in smaller intensities.
It is also clear that there are no new phases formed in the coating during the thermal spray
process. The major intermetallic found in the coated surface was Cr1.12Ni2.88 in all operating
temperatures. The formation of the intermetallics was also responsible for the higher hardness
and superior wear resistance in the NiCrBSiCFe coated AISI 316 ASS.
Figure 9. XRD pattern showing phases of uncoated and NiCrBSiCFe coated AISI 316 ASS
3.6. Worn Surface Characterisation by SEM
Dry sliding leads to high local pressure between contacting asperities, which results in plastic
deformation, adhesion and the consequent formation of junctions locally. The worn surface of
the uncoated AISI 316 ASS substrates at room temperature is shown in Figure 10(a). Wear
debris was sparsely present in the worn surface. The mode of material removal in room
temperature was delamination. A grey dense plateau-like region was present in the worn
surface of the uncoated AISI 316 ASS at 150°C is shown in Figure 10(b). A cleavage was
seen in the worn surface along with small amount of debris. The multilayered material
removal exposing the subsurface for subsequent removal was seen in the SEM analysis.
666 N. L .Parthasarathi, Muthukannan Duraiselvam Vol.9, No.7
Figure 10(c) shows the worn surface of the uncoated AISI 316 ASS substrate. The deep prow
justified the considerable amount of material loss during sliding. Subsurface was visible due
to the subsequent removal of material. A comparatively deeper valley was noticed and it was
due to the excess material removed by the sliding wear. The worn surface of the uncoated
AISI 316 ASS at 250°C is shown in Figure 10(c). Multilayered flake formations with more
debris were prominently visible. These debris acts as an abrasive medium resulting in the
excessive material removal during sliding [22]. Figure 10(d) shows the worn surface of the
uncoated AISI 316 ASS at 350°C. The oxide formations which acted as a protective layer
eliminated the chances of severe material loss. In contrast, the worn track formed by sliding
wear of the coated samples had a very smooth and shiny appearance.
A distinct discipline in the mode of wear was attributed in the NiCrBSiCFe coated samples.
The worn tracks were mostly characterized by score lines parallel to the sliding direction,
which was sign of superior wear resistance. The surface morphology of NiCrBSiCFe coated
specimen worn at room temperature is shown in Figure 11(a). The worn track exhibited
microcracks with very few amount of scabs and debris. Plough markings were shown parallel
to the sliding direction. As the time progresses, the delaminated layer may peel off and lead
to considerable material loss. The worn surface morphology of the NiCrBSiCFe coated
sample at 150°C is shown in Figure 11(b). The mode of wear was found to be delamination
with prow formation. Prow formation was just initiated at 150°C. Scabs were sparsely seen
eliminating the chances of more abrasive wear. The mode of material removal at 250°C was
ploughing. The advanced stage in plough mode of material removal is prow formations. The
deeper prow formations were the end result of frequent ploughings on the same instance. This
mode leads to relatively more material loss which is evident from Figure 11(c).
The central core of a prow had undergone flattening and lateral spreading, which remains
adherent to the base metal. The worn surface morphology of NiCrBSiCFe coated sample at
350°C is shown in Figure 11(d). The initiation of oxide layer formation was visible in the
SEM analysis. The score lines, which run always parallel to the sliding direction, were seen.
The interesting phenomenon happened in the interface of the counterbody and the coated
substrate is oxide formation. The oxide formation is visible in SEM. These oxide layers could
be of Fe3O4 and CrO3. Oxide films formed during the contact play a protective part,
eliminating the chances of excessive material loss. This lubrication property of the oxides
reduced the severity of wear. Dry sliding wear leads to the removal of material from the
surface by the formation of chips, shavings and fragments called debris. The geometry of the
worn surface and a groove formed depends on the size and shape of the worn debris (abrasive
particle). It was clearly noticed from the SEM observations that that the worn asperities seen
on the worn surfaces of the coated surfaces are relatively finer, which was responsible for
superior wear resistance [22].
Vol.9, No.7 Improvement of High Temperature Wear Resistance 667
(a) (b)
(c) (d)
Figure 10. SEM picture of the uncoated AISI 316 ASS worn surfaces: (a) worn surface at
room temperature (b) worn surface at 150°C (c) worn surface at 250°C (d) worn surface at
668 N. L .Parthasarathi, Muthukannan Duraiselvam Vol.9, No.7
(a) (b)
(c) (d)
Figure 11. SEM picture of the NiCrBSiCFe coated surfaces: (a) worn surface at room
temperature (b) worn surface at 150°C (c) worn surface at 250°C (d) worn surface at 350°C
From the experiments conducted on uncoated and NiCrBSiCFe plasma sprayed AISI 316
ASS substrates at various operating temperatures, the following conclusions can be drawn.
The NiCrBSiCFe was plasma sprayed on AISI 316 ASS to a thickness of up to 500
µm. The coatings produced were physically bonded to the substrate and free from
The improvement in hardness up to an average value of 822 HV0.3 of AISI 316 ASS
from 223 HV0.3 was achieved by NiCrBSiCFe plasma spraying primarily contributed
to the improvement of wear resistance.
The plasma sprayed NiCrBSiCFe coating exhibited up to 4.5 times increase in wear
resistance compared to the uncoated AISI 316 ASS substrates.
Vol.9, No.7 Improvement of High Temperature Wear Resistance 669
The superior wear resistance of the NiCrBSiCFe coated samples in the operating
temperature 350°C justifies the applicability of the coating for high temperature
applications involving sliding contact.
The molten splats formed during plasma spraying leading to the lamellar
microstructure were responsible for the higher hardness and higher wear resistance in
coated AISI 316 ASS substrates.
The worn surface morphology analysed by SEM revealed the presence of oxide
formations at 350°C. This was a minimal material removing mode which excluded the
chance of more material loss.
The SEM analysis of the worn tracks concluded that more plastic deformation and
material loss had been incurred by the uncoated substrates than the NiCrBSiCFe
plasma sprayed AISI 316 ASS.
The geometry of the worn asperities of the NiCrBSiCFe plasma spayed coating was
finer compared to the uncoated specimens. This property reduced the intensity of wear
rate in coated specimens. The SEM results were found to be in accordance with the
sliding wear test results.
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