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					International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
    INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 6, September – October (2013), © IAEME
               ENGINEERING AND TECHNOLOGY (IJARET)

ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online)
                                                                          IJARET
Volume 4, Issue 6, September – October 2013, pp. 222-228
© IAEME: www.iaeme.com/ijaret.asp                                         ©IAEME
Journal Impact Factor (2013): 5.8376 (Calculated by GISI)
www.jifactor.com




         AN EXPERIMENTAL STUDY OF WEAR RESISTANCE OF AL – SIC
                    COATINGS ON STEEL SUBSTRATE

                   Dalip Kumar1, Antariksha Verma2, Sankalp Kulshrestha3
     1
      (Department of Mechanical Engineering, Delhi College of Engineering / Delhi Technological
                              University, Main Bawana Road -Delhi India)
     2, 3
          (Department of Mechanical Engineering, Jodhpur Engineering College & Research Centre /
                         Jodhpur National University Jodhpur – Rajasthan, India)


ABSTRACT

       Al and Al–SiC composites coatings were prepared by oxyacetylene flame spraying process
on steel substrate. Coatings with controlled reinforcement rate were obtained by spraying mixtures
containing aluminum powder with 20 vol. %, 30 vol.%, and 50 vol.% SiC particles. The wear
behavior of these coatings has been tested using the Pin-on-Disc technique under dry sliding
conditions. The wear resistance of the aluminum coatings was greatly enhanced by the incorporation
of the SiC reinforcement. The wear rate of the coating was found increased with increase in load.
The co-efficient of coating was found decreased with increased SiC particle. The worn surfaces were
examined using SEM (Scanning Electron Microscope), and it was found that the main wear
mechanism was due to adhesion, abrasion and deformation.

KEYWORDS: Al-SiC, Thermal Spray Coating, Wear Rate, Wear Mechanism.

1.        INTRODUCTION

        Many kinds of surface modification processes are applied to improve the wear resistance of
Al alloy [1]. Among coating processes, thermal spraying is superior one, capable of coating a thick
layer in short operating time. Taking the weight saving effect into consideration, Al-base material is
beneficial as a coating material. However, there is little research on the combination of the Al alloy
substrate and the coating materials of Al alloy [2–4], including Al-base metal matrix composite with
SiC, TiC, Al2O3 or FeO+TiO2 as reinforcement as the coating material [2–3]. B. Torres et. al [5]
investigated that Aluminum matrix composite coatings reinforced with more than 20vol.% of SiC
particles, wear resistance of the aluminum coatings was greatly enhanced by the incorporation of the
SiC reinforcement which delayed the transition from mild to severe wear.Due to the refined silicon
particle size and high volume fraction of silicon, thewear resistance is improved by this type of

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International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 6, September – October (2013), © IAEME

surface treatment. Precipitation of iron aluminides with high volume fraction in aluminum matrix
makes a composite surface layer to increase the hardness and wear resistance. High Si- and Fe-
bearing modified layers have low toughness so that cracking is easy to occur in operation.
Anodizing, deposition and vacuum arc technologies [6]are also useful to yield thick aluminumoxide
protective layer.Al and Al–SiC composites coatings were prepared by oxyacetylene flame spraying
on ZE41 magnesiumalloy substrates. Coatings with controlled reinforcement rate of up to 23 vol. %
were obtained by sprayingmixtures containing aluminum powder with up to 50 vol.% SiC particles.
The coatings were sprayed onthe magnesium alloy with minor degradation of its microstructure or
mechanical properties. Thecoatings were compacted to improve their microstructure and protective
behavior. The wear behavior of these coatings has been tested using the pin-on-disk technique and
the reinforced coatings provided85% more wear resistance than uncoated ZE41 and 400% more than
pure Al coatings [7].
In this work, aluminum matrix composite coatings reinforced with 20 vol. %, 30 vol. % & 50 vol. %
of SiC particles have been deposited using oxyacetylene flame spraying on steel substrates. The wear
behaviourof these coatings has been tested using the pin-on-disk technique under dry sliding
conditions.

2.     EXPERIMENTAL PROCEDURE

2.1     Materials
        Aluminum matrix composite coatings reinforced with 20 vol. %, 30 vol. % & 50 vol. % of
SiC particles have been deposited using oxyacetylene flame spraying on steel substrates. To improve
the adhesion of the sprayed coatings, the substrates were sand blasted by abrasives of about 1 mm
diameter to obtain surface with an average roughness of 10.5±0.7 mm. The samples were cleaned in
ultrasonic wave in acetone and dried with air to avoid that any grease from the grinding system
would reduce the adhesion of the coatings.The aluminum powder was mixed with SiC particles with
an average size of 50 mmusing a conventional rotating ball milling machine with alumina balls for
40 min in dry conditions. Mixtures containing 20 vol. %, 30 vol. % and 50 vol. % of SiC particles
were directly fed into the thermal spray gun for their simultaneous spraying. The spraying was
carried out with an oxyacetylene thermal spray.The material feeding rate was 2.0 g/s, approximately,
and the spray gun was passed twice over each sample to obtain coatings with thicknesses in the 400–
450 mm range.

2.2     Wear test
        Wear tests were carried out under dry sliding condition using a Pin-on-Disc (Wear and
friction monitor, DTU, Delhi) set up. The counter body was a 6 mm diameter alumina pin.Specimen
andcounter body surfaces were cleaned with acetone to avoid the presence of humidity and non-
desirable deposits. The tests were performed in ordinary laboratory environment at RH30% and20°C.
The wear test was carried out with 10N, 20N and 30 N load and 200 rpm sliding speed. Specimens
were also weighted before and after the tests with a 0.00001 g balance to measure the mass loss. The
coefficient of friction was obtained by means of a torquetransducer. The wear rate is determined in
terms of mass loss in g per 70 meter of sliding distance.

3. RESULTS & DISCUSSION

3.1    Micro structural characterization of sprayed coatings
       The porosity of the coating was very low (Fig. 1a). As a result of morphology, the actual
porosity measured on the transversal section of the coatings was 2.9%.The morphology of the
coatings was the usual one of thermally sprayed ones; the coating was formed by the accumulation of

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International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 6, September – October (2013), © IAEME

splats and the presence of localized defects between them was the main cause for the apparition of
porosity (Fig. 1 b). The splats at the substrate-coating interface deformed and followed the substrate
topography without leaving voids (Fig. 2a). The substrate microstructure did not seem to be modified
by thespraying procedure (Fig. 2b).The mean porosity of the coatingwas 4.1% throughout the
spraying procedure.




 Fig. 1 (a) Microstructure of sprayed aluminum alloy coating at 100X (b) Microstructure of Al-20%
                               SiC particles composite coating at 100X




 Fig. 2 (a) Microstructure of Al-30% SiC particles composite coating at 100X (b)Microstructure of
                          Al-50% SiC particles composite coating at 100X


3.2     Wear rate
        The wear rate versus normal load, for the different coatings analyzed are shown in Fig. 3 As
it can be observed in the figure, the wear rate of Al/SiCp composites increased with normal load. In
addition, the wear resistance of thealuminumcoatingswasgreatly reduces by the use of SiCp.



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International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 6, September – October (2013), © IAEME



             Load (N)                             10              20              30
                                                                           Weight Loss
            Material                     Weight Loss (g)
           Al (Pure)          0.017             0.025        0.032
          Al+20%SiC           0.012             0.018        0.023
          Al+30%SiC           0.009             0.013        0.015
          Al+50%SiC           0.005             0.009        0.011
   Table 1 Weight Loss in g at constant speed of 200rpm and weight of 10, 20 & 30 N at70 Meter
                                          Sliding Distance


                                    0.035
                                     0.03
                    Wear Rate (g)




                                    0.025
                                                                                            Al
                                     0.02
                                                                                            Al+20%SiC
                                    0.015
                                                                                            Al+30%SiC
                                     0.01
                                                                                            Al+50%SiC
                                    0.005
                                       0
                                            0           10       20        30          40
                                                               Load (N)
                                                Fig. 3 Variation of Wear Rate with Load

       The addition of SiC particle to thecoating reduced the wear rates by a strong amount. With
the addition of load there is increase in wear rate. The wear rate was high in case of pure aluminum,
but with the addition of SiC particle the wear rate was found decreased [8].

3.3 Co- efficient of Friction
        Friction coefficients were similarin all the tests; they increased slightly with the incorporation
of the pure aluminum coating and reduced with the incorporation ofSiC particles into the coatings.
The coefficient of friction is high for pure aluminum because of adhesion between aluminum coating
and counter body. This was also favoured by the higher plastic deformation of the aluminum coating
as a result of its lower hardness.The presence of SiC particles reduced the adhesion between the ball
and the coatings and also reduced the deformation of thecoatings. There is negligible effect of load
on the co-efficient of friction.

             Load (N)                             10              20              30             Co-efficient
                                                                                                 of Friction
            Material                 Co-efficient of Friction (µ)                                    (µ)
           Al (Pure)            0.46             0.45             0.47
          Al+20%SiC             0.54             0.53             0.54
          Al+30%SiC             0.71             0.72             0.73
          Al+50%SiC             0.88             0.87             0.89
   Table 2 Co-efficient of Friction at constant speed of 200rpm and weight of 10, 20 & 30 N at70
                                        Meter Sliding Distance


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International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 6, September – October (2013), © IAEME


                                                    1




                       Co-efficient of Friction
                                                  0.9
                                                  0.8
                                                  0.7
                                                  0.6                             Al
                                                  0.5                             Al+20%SiC
                                                  0.4
                                                                                  Al+30%SiC
                                                  0.3
                                                  0.2                             Al+50%SiC
                                                  0.1
                                                    0
                                                        0   10   20     30   40
                                                     Load (N)
                                 Fig. 4 Variation of Co-efficient of friction with Load


3.4    Wear Mechanism
       In order to determine the main wear mechanism, the worn surfaces of Al and SiC particles
composites were observed by SEM.The presence of voids and cracks along the wear path in the
surface of the worn as-sprayed aluminum coating, apart from thedrag lines, evidenced the
simultaneous action of abrasive, adhesive and delaminating wear mechanisms. However, the
contribution of delaminating and adhesive wear to the total degradation of the samples seemed to be
higher than the effect of abrasion. The roleplayed by adhesion was also confirmed by the irregular
shape ofthe sides of the wear path (Fig. 5a).Big substrate cracks appear indicating that delamination
wear took place.




      Fig. 5 (a) Microstructure of worn surface of sprayed pure aluminum coating at 100X (b)

         Microstructure of worn surfaces of Al-20% SiC particles composite coating at 100X
The worn coatings reinforced with the low SiC particle content,observed at higher
magnificationsshowed evidence ofabrasion and adhesion. The cracks does not propagate into
surface, it shows that delamination wear did not take place (Fig. 5b).The adhesion mechanisms were
less important than in the pure aluminum coating becausefewer voidswere observed.



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International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 6, September – October (2013), © IAEME




     Fig. 6(a) Microstructure of worn surfaces of Al-30% SiC particles composite coating at 100X (b)
            Microstructure of worn surfaces of Al-50% SiC particles composite coating at 100X

        As SiC particles increased to 30 vol. % as shown in Fig. 6a, the adhesion was observed very
less after the wear test. The sprayed coating with highest reinforcement 50% SiC, was less affected
by adhesive failure (Fig. 6b). The high density of SiC particles seems to control the propagation of
crack growth. Finally, the presence of SiC particles reduced the mechanical deformation of the
coating, limiting the integration of the different splats, but transferring the loads to the substrate
coating interface, favouring the delamination of the coating.

4.        CONCLUSIONS

1. Aluminum and aluminum matrix composite coatings reinforced with 20 vol.% SiCp, 30 vol. %
   SiCp and 50 vol. % SiCp have been successfully prepared oxy-acetylene thermal spraying
   process on steel substrates.
2. The wear rate was found increased with increase in load.
3. The wear rate was greatly reduced with the addition of SiC particles reinforcement.
4. The Co-efficient of friction of the coating was found decreased with increase in SiC particles
   reinforcement.
5. There was no effect of increase of load on co-efficient of friction.
6. The addition of SiCparticles reduced plastic deformation and increased the wear resistance of the
   coating.
7. The wear mechanism with pure aluminum coating was due to adhesion, Abrasion and
   deformation. With high SiC particle reinforcement the wear mechanism was due to abrasion and
   deformation.

REFERENCES

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 2. Z. Mutasim, L. Hsu, Proceedings of the Seventh NTSC, June1994, Boston, MA, 85–91.
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 4. K. Nakata, M. Ushio, Surf. Coat. Technol. 142–144(2001)277–282.

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