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Vol. 8. Issue 6.
Pages 6125-6133 (November - December 2019)
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Vol. 8. Issue 6.
Pages 6125-6133 (November - December 2019)
Original Article
DOI: 10.1016/j.jmrt.2019.10.007
Open Access
Experimental investigation on the effect of ceramic coating on the wear resistance of Al6061 substrate
Suresh Chinnusamya,
Corresponding author

Corresponding author.
, Venkatachalam Ramasamyb, Subburam Venkatajalapathya, Gobinath Velu Kaliyannanc, Sathish Kumar Palaniappand
a Department of Mechanical Engineering, Paavai Engineering College, Namakkal, Tamil Nadu, 637018 India
b Department of Mechanical Engineering, K.S.R. College of Engineering, Tiruchengode, Tamil Nadu, 637209 India
c Department of Mechanical Engineering, Kongu Engineering College, Erode, Tamil Nadu, 638060 India
d Department of Mining Engineering, Indian Institute of Technology, Kharagpur, West Bengal, 721302 India
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Figures (11)
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Tables (4)
Table 1. Chemical composition of Al 6061.
Table 2. Process parameters used for plasma spray coating.
Table 3. Different weight percentage combinations of Al2O3 / Cr2O3 / SiC for top coats.
Table 4. Different weight percentage combinations of Al2O3 / ZrO2/ TiO2 for top coats.
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In the present research work, various ceramic materials such as Al2O3 - Cr2O3 - SiC, and Al2O3 - ZrO2 - TiO2 were developed for the analysis of wear performance and hardness. The specimens were coated using plasma spray coating technique. A bond coat of 50μm thickness was applied on the substrate using NiCrAlY for good adhesion before laying the top coat. The wear behaviour and hardness of the samples were investigated by wear and hardness tests. The Energy Dispersive X-ray Analysis (EDAX) was performed to analyse the chemical composition of the samples. The Field Emission Scanning Electron Microscope (FE-SEM) was used to analyse the surface and cross-section of the samples. X-ray diffraction (XRD) studies are carried out to understand the structural and crystallographic information. The performances of the coated and uncoated samples were compared and investigated. It was observed that the specimen with Al2O3 (60%) + ZrO2 (20%) + TiO2 (20%) coating produced best results for wear rate (0.03612mm3/Nm) and Coefficient of friction (0.357). The proposed ceramic coating composition could be recommended for automobile components that require good wear and heat resistance to improve the service life.

Aluminium alloy 6061
Plasma spray coating
Wear rate
Coefficient friction
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Aluminium alloys offer a wide range of desirable properties and find applications in the fabrication of engineering structures. The 6000 series aluminium alloys are utilized in the production of cylinder blocks, crankcases and pistons as considerable amount of weight savings can be effected. Especially, Al6061 alloy possesses many favourable characteristics like heat-treatability, good toughness, corrosion resistance along with mechanical strength which make it suitable to cater medium and high strength structural applications. The internal combustion (IC) engine components such as piston and cylinder liner are generally produced using steel, cast iron, and aluminium alloys. These parts experience wear regularly due to friction as they involve continuous movements during IC engine operations. Moreover, these components require hard exterior structure to endure wear and soft interior to absorb energy. Hence, various types of coating materials are attempted on IC engine components to get high hardness and wear resistance thereby longer operating life. Among various coatings, ceramic coatings are normally preferred for wear resistant and thermal load bearing characteristics.

Guilmard et al., [1] performed wear tests using pin-on disc setup by applying a range of loads between 5N and 300N with a speed range between 3 and 10.7m/s to find material combinations that result in lower wear and coefficient of friction. Krishnamurthy et al. [2], plasma coated the Al6061 plates with ceramic oxides such as Al2O3 and ZrO25CaO to test their wear resistance through pin-on-disc as per ASTM G99. Wear characteristics, porosity, microhardness, surface roughness and microstructure were investigated and observed that the wear rate was influenced by applied load, porosity, splats and microhardness of the coated material. The effectiveness of plasma coating was analysed through SEM microstructures. Krishnamurthy et al., [3] carried out a study to investigate the wear performance of Al6061 substrate coated with alumina and Y2O3 stabilized Zirconia composite.

The SEM observations revealed that micro-cracks were formed on the coating as the substrate was exposed to plasma flame and also the porosity and surface roughness of the coating were likely to increase to certain extent with the increase in coating thickness. The investigation further reveals that the wear mechanism is primarily because of abrasion and when bond coat is exposed, the material lost by adhesion in the pin-on-disc test. Rastegar et al., [4] investigated different type of thermal spray coatings on piston rings to reduce material loss by wear. Ahn et al. [5], reported that the sliding action of plasma sprayed, self-mated ZrO2-8% Y2O3 (partially stabilized zirconia) enhanced the wear-performance compared to sliding against a metallic substrate. Paul, Peirz, and Matthew et al., [6–8] used Zirconia as a major ceramic material for thermal barrier coating to apply on diesel engine components. Huadong et al., [9] suggested the cast iron with low phosphorous content as a tribological material to match with Al2O3 - 40% ZrO2 plasma sprayed ceramic coatings under oil lubricated conditions as the wear resistance of lower and higher phosphorous containing cast iron which was much better than that of medium phosphorous containing cast iron. Ahad et al., [10] investigated the spark-plasma-sintered Ti and TiB2 composite specimens for the mechanical and physical properties. It was reported that TiB2 mainly enhances the mechanical properties by refinement of matrix grains.

Hyo-Sok et al., [11] carried out studies to investigate the various properties of composite powders by applying nanostructured Al2O3, TiO2 and ZrO2 composite powders through plasma spraying. In addition, these characteristics were compared with the conventional Al2O3 - 13wt. % TiO2 coating. Habig et al., [12] applied piston crown by plasma spraying technique which showed increase in thermal efficiency by 13.95%, reduction in mass fuel consumption by 6.02% and reduction in brake specific fuel consumption by 9.84% when compared to uncoated engine. Zum Gahr et al., [13] studied the tribological studies of ceramic materials by focussing on the ceramic-steel couples under different conditions. Shrirao et al., [14] compared a coating of 500μm thickness of mullite (Al2O3 - 60% and SiO2 - 40%) over a 150μm thickness of an NiCrAlY bond layer on diesel engine components like piston crown, cylinder head and valves for performance with the standard engine in the same air fuel ratio and found that there was 1.07% decrease in SFC value, 16% decrease in heat amount to coolant and 22% increase on heat amount to exhaust. Ramachandran et al., [15] tested the performances of plasma spray coatings with various powder combinations for abrasive wear resistance. The electrical resistivity of alumina and titania – alumina coatings with different particle sizes were investigated and alumina-titania coatings exhibited better results.

Abdullah Uzun et al., [16] suggested that the ceramics with low thermal conductivity can be utilized structurally to control temperature distribution and heat flow for better performance. Ramaswamy et al., [17] found that the thermal cycling life of mullite coating above 1273K is much shorter compared to Yttria (Y2O3) stabilized zirconia. You Wang and Pantelis et al., [18,19] were observed the coefficient of friction of ceramic compound coatings to remain higher or at least equal to that of cast iron when tested under dry and reciprocating sliding conditions for a chrome-plated counter face material. Batory et al. [20], analysed mechanical and tribological properties of gradient coating and reported the better performance. Hejwowski et al. [21], reported that the better wear characteristics of ceramics and the lower level of heat rejection from combustion chamber through thermally insulated components results in availability of increased heat energy that would increase the in-cylinder work and the amount of energy carried by the exhaust gases, which could be effectively utilized. Ourong Liu et al. [22], were observe the coating blends of Al2O3 + ZrO2, ZrO2 + 20% Y2O3 and ZrO2 + 8%Y2O3 to have excellent wear-resistance than that of cast-iron which is currently used for liners.

Samadi et al., [23] reported that the mullite has excellent thermo-mechanical characteristics and its low coefficient of thermal expansion would cause mismatch with the bonding substrate. For instance, mullite coating crystallizes at the range of 1023–1273 K causing cracking and de-bonding due to its volume contraction. Andre Skopp et al., [24] reported that the formation of titanium di-oxide makes materials containing titanium a good wear resistant material which is used for cylinder liner coatings in the place of uncoated grey cast iron liner materials that offer low wear resistance and also friction coefficient gets reduced by 10–20% of system wear. Babu Rao et al., [25] investigated the sliding wear behaviour of fly ash reinforcement particles on AA2024 composite and reported that the composites had better wear resistance than base matrix. Yong Yang et al., [26] prepared a nanostructured Al2O3 / TiO2 / ZrO2 composite powder for plasma spraying. The density, flowability and adhesion of the powders for good bonding were investigated and selected the best particle size for powder combination.

Deivasigamani et al. [27], found that the Boron Carbide particle reinforced Al359 composite sample possesses increased hardness compared with the base material. This is due to the presence of ceramic phase coefficient of friction that can be increased up to 20% wt. addition. There is considerable increment in the wear resistance of Boron Carbide reinforced composite. Thankam Srekumar Rajesh et al. [28], added TiO2 in lower ranges to Al2O3 in the application of ceramic coatings through thermal spray method. Addition of titanium di-oxide offers some favourable properties like reduction of porosity and increase in fracture toughness of the coating composition. Kandeva et al., [29] presented the results for the wear characteristics of electroless nickel-phosphorus composite coatings with and without diamond nanoparticles with dimensions of 4, 40, 100, 200 and 250nm and reported that the heat treatment of all coatings with and without diamond nanoparticles leads to increased abrasion resistance.

From the available literatures it is found that not much attempts have been made to study the wear characteristics of Al6061 alloy coated with different ceramic oxides at various proportions. This work attempts to apply two different set of ceramic coatings on Al6061 alloy to analyse the change in properties.

2Experimental details2.1Materials

The chemical composition of the Al6061 alloy is given in Table 1. The presence of magnesium and silicon provides good mechanical properties like machinability, weldability formability and corrosion resistance to Al6061 alloy which has moderate strength.

Table 1.

Chemical composition of Al 6061.

Constituent  Al  Mg  Si  Fe  Cu  Zn  Mn  Cr  Others 
Wt.%  Bal  0.956  0.562  0.532  0.236  0.202  0.102  0.046  0.864 
2.2Plasma spraying

Al6061 alloy is normally used for the fabrication of IC engine parts like piston, cylinder liner etc. Hence, Al6061 plates of 30×3×3mm dimensions are fabricated and provided with different ceramic coatings for investigation. The specimen (substrate material) is inspected for accuracy of dimensions, surface quality and cleaned from dust and other depositions. The ceramic coating materials selected in this work can endure high temperature and hence a suitable material having similar chemical properties. The micro-geometry of the base material is required to be used as interlayer between the metal alloy and the ceramics. The interlayer, called as bond coat would compensate for the differences in thermal coefficients of coating materials and improve resistance to thermal shock. The bond coat material is selected based on the matching factors with the base material like coefficient of thermal expansion, wettability, chemical-affinity and adhesion characteristics. The ceramic compounds are used as thermal barrier coatings due to their low conductivity and relatively high coefficients of thermal expansion which reduce the detrimental interfacial stresses. The process flow schematic representation of plasma spray coating method as shown in Fig. 1. The material used for bond coat is NiCrAlY composite (METCO 430 NS powder) of 50μm thickness applied on the substrate of 100μm to enhance adhesion between top coat and the substrate.

Fig. 1.

The pictographic representation of spray coating process.


The bond coatings and top coatings are done on specimen plates of Al6061 using a METCO 3MB plasma spraying machine with the selected combinations of ceramic powders as per the spray parameters shown in Table 2. Functionally graded coatings are produced by plasma spray technique for a thickness of 150μm comprising 50μm of a bond coat (NiCrAlY) and 100μm of top coat (with selected ceramic compositions).

Table 2.

Process parameters used for plasma spray coating.

Material  Primary gas (Argon) pressure (kpa)  Secondary gas (Hydrogen) pressure (kpa)  Carrier gas flow argon flow rate (Ipm)  Current (A)  Voltage (V)  Spray distance (mm)  Feed rate (g/min) 
TC1  120  50  90  500  70  50–80  45 
TC2  120  50  90  500  70  50–80  45 
BC  100  40  80  450  65  45–80  40 
2.3Characteristics of ceramic coating powders

Alumina (Al2O3) is commercially used ceramic material with wide applications for increasing hardness. Alumina (Al2O3) possesses high hardness, chemical inertness that is suitable for making a coating material [30]. Also, limited addition of Al2O3 on coating material improves bonding strength without affecting the ductility. Its thermal characteristics like high thermal conductivity and low thermal expansion may produce micro cracks during melting and solidification cycles. Silicon carbide (SiC) is known for its lightness, hardness, good thermal conductivity and low thermal expansion apart from being resistant to acids. It is used for high hardness and high temperature enduring applications such as abrasives, refractories etc. These qualities of SiC make it as competent material for coating purposes. Chromium oxide (Cr2O3) has very good self – healing and anti-galling (corrosion resistance) properties. The material can offer good wear – resistance, abrasion resistance, chemical resistance and hence served as a good coating material. The coatings consisting of Al2O3/Cr2O3/SiC combinations are commonly referred as Group-A and the sub-groups of different weight proportions are represented as A1, A2 and A3 as shown in Table 3.

Table 3.

Different weight percentage combinations of Al2O3 / Cr2O3 / SiC for top coats.

SampleWeight (%)
Al2O3  CrO2  SiC 
A1  60  20  20 
A2  60  40 
A3  60  40 

Zirconium oxide (ZrO2) or Zirconia is a hard ceramic used to form protective coatings and offers excellent mechanical, thermal and electrical properties. It undergoes phase changes when heated which can be eliminated by doping it with small quantities of other materials. The low thermal conductivity of zirconia has made it an appropriate material for thermal barrier coatings (TBC) [31]. Titanium di-oxide (TiO2) is chemically inert and protects the base substance from embrittlement, fading and cracking as it can absorb ultraviolet light radiations [32]. TiO2 is used in most of the surfaces which are white in colour and no health concerns are associated with it. The coatings consisting of Al2O3/ZrO2/TiO2 combinations are commonly referred as Group-B and the sub-groups of different weight proportions are represented as B1, B2 and B3 as shown in Table 4.

Table 4.

Different weight percentage combinations of Al2O3 / ZrO2/ TiO2 for top coats.

SampleWeight (%)
Al2O3  ZrO2  TiO2 
B1  60  20  20 
B2  60  40 
B3  60  40 

X-ray diffraction (XRD) peaks of ceramic coated samples were recorded with a D8 Advanced Bruker Diffractometer in the range of 20°C–80°C. The surface morphology of uncoated and ceramic powder coated specimen were analysed using field emission scanning electron microscope (FE-SEM) on a Tescan, Mira 3 FE-SEM. The energy dispersive X-ray spectroscopy (EDAX) was used to identify the composition of uncoated and ceramic coated specimens. Hardness of the uncoated and coated samples was examined through Banbros Rockwell tester. Friction and wear tests are carried out on the uncoated and coated specimen using DUCONES Pin-on- disc Tribometer as per ASTM G99 standard with @WINDUCOM.

2.5Hardness measurement

The hardness is measured along with the total thickness of both top and bond coatings. Hardness measurements are taken at three different locations on the transverse section of the coated and uncoated samples and the average value is calculated for each.

2.6Abrasive wear test

Friction and wear tests are carried out on the coated specimen using Pin-on- disc. A wear testing machine with A60 grit, Al2O3 abrasive wheel is used as disc. All the seven samples are tested under a cycle of 15N constant load. A track diameter of 80mm and a speed of 240rpm, trial timing of 330s under dry atmospheric conditions are used for the test trials. For each applied load, wear and friction force are obtained from the testing machine. The wear rate and the coefficient of friction of the test samples are calculated using standard formulae.

3Results and discussion

The objective of this research is to investigate the effectiveness of ceramic coating systems for enhancing mechanical properties of IC engine components like piston and cylinder liner for improving their service life.

X-ray diffraction (XRD) studies are carried out to understand the structural and crystallographic information of the prepared samples. Fig. 2 shows the XRD spectra of the uncoated, coated A1 and coated B1 samples. The XRD spectrum of the uncoated sample exhibited various high intense peaks corresponding to the Al only. The XRD spectrum of the coated A1 sample exhibited various peaks corresponding to the Al2O3, Cr2O3 and SiC. Whereas, the XRD spectrum of the coated B1 sample exhibited high intense peaks corresponding to the Al2O3, ZrO2 and TiO2. No other impurity peaks observed in the spectra indicates the structural integrity. The high intense peaks indicate that the synthesized sample is in crystalline nature.

Fig. 2.

XRD spectra of uncoated, coated A1 and coated B1 samples.


Scanning Electron Microscopic (SEM) images along with EDAX spectrum for the samples of uncoated (Fig. 3a), coated A1 (Fig. 3b) and coated B1 (Fig. 3c) are shown. All the SEM images are taken after conducting wear tests on the samples. The micrographs of uncoated specimen show the surface of the base alloy with irregularities like cracks, groove and other uneven patterns caused during fabrication process and further aggravated by the wear test process.

Fig. 3.

(a) SEM images of uncoated Al-6061 substrate with corresponding EDAX. (b) SEM images of A1 coated Al-6061 substrate with corresponding EDAX. (c) SEM images of B1 coated Al-6061 substrate with corresponding EDAX.


The plasma spray technique used for producing the coatings involves high impact force and melting of the spray powders at high temperatures. The powders are melted as a bulk and it contains different range of melt conditions like entirely melted, partially melted and completely unmelted particles. Such a mix of various levels of melted particles leads to porous coating on the substrate and also the rapid solidification of the coating results in micro-cracks. The application of heat during coating process also causes thermal stress due to difference in solidification rate of various layers which again leads to the formation of cracks and other irregularities. The micrographs of the coated A1 and coated B1 also show voids at some places which are caused by various factors such as sudden solidification, different levels of melted particles, different rates of solidification and layers of thermal stress that may form irregularities on the surface

Fig. 3(a) shows the EDAX spectrum of uncoated sample which clearly shows the presence of aluminium as the only predominant element of the base alloy used. Fig. 3(b) provides the proportionate peaks of aluminium, chromium, carbon, silicon and oxygen that are the predominant peak elements present in the coated sample A1. The existence of silicon and carbon in silicon carbide enhances the wear resistance. The presence of carbon in SiC compound adds a self-lubricant property to the composite. Fig. 3(c) confirms the presence of oxygen, aluminium, zirconium and titanium elements which constitute as the major elements of coated sample B1.

Fig. 4 shows the cross-sectional FE-SEM image of the bond coat and top coat applied on one of the test specimen. It clearly shows that the thickness of the bond coat and ceramic top coat which are applied on the substrate and bond coat through plasma spray coating are 50μm and 100μm, respectively. It is clearly observed that the coating thickness is even throughout the specimen.

Fig. 4.

Cross sectional FE-SEM images of B1 top coat.


The coated and uncoated samples are tested for their hardness under Rockwell hardness testing machine. The observations shows that the specimens containing ZrO2 and TiO2 (B1 to B3) have given a HRB range of 90–95 whereas the hardness range of specimens with Cr2O3 and SiC is only 72–75 Hardness. These are comparatively higher than that of uncoated specimen’s hardness range of 57–60 HRB. The hardness values obtained for each coated specimen is depicted along with their wear rate in Fig. 5. The uncoated specimen has shown higher wear rate and lesser hardness compared to ceramic coated specimens. On comparison, the samples containing Al2O3 + ZrO2 + TiO2 have higher hardness and lower wear rate than the samples containing Al2O3+Cr2O3+SiC ceramic compounds. Among the different compositions of Al2O3+ ZrO2 + TiO2, the sample B1 containing Al2O3 (60%) + ZrO2 (20%) + TiO2 (20%) has given the best results in terms of wear rate (0.03612 mm3/Nm) and hardness (94). The analysis shows that the wear rate decreases when hardness increases. If wear caused by plastic deformation, the hardness of the material significantly influences the wear rate. Thus wear and hardness are co-related, particularly in plasma spray coatings where plastic deformation could be a mode of wear.

Fig. 5.

Top coat hardness and wear rate variations of the tested samples.


Two different coating combinations of different proportions (A1 to A3 & B1 to B3) are investigated in this study. Both coating systems exhibited better results compared to uncoated material. Hence, both these systems of ceramic coating could be applied for increasing the service life of the piston and cylinder liner components of IC engines. The specific compositions of system B1 could be applied as coating for getting maximum benefit among the tested sample proportions.

Wear test is carried out with 15N constant load to find the coefficient of friction for three different materials and time duration of the test is 330s. The values obtained for coefficient of friction lie in between the 0.1352 (minimum) and 0.1648 (maximum). The contact area and depth of contact are the important factors that decide the contact stress. Figs. 6–8 represents the coefficient of friction attained for the three material systems against different time periods from 0 to 330s. It is found from Fig. 6 that the composition of A1 has less coefficient of friction than other two combinations. The composition of A1 containing Al2O3 (60%) +Cr2O3 (20%) + SiC (20%) provides a consistent smooth curve with little reduction in coefficient of friction from the start to till the end of 330s. But, the other two systems (A2 and A3) which contain Cr2O3 and SiC in higher percentages show a zig-zag curve with substantial variations in their coefficient of friction.

Fig. 6.

Comparison plot for average coefficient of friction for system A samples at 15N load.

Fig. 7.

Comparison plot for average coefficient of friction for system B samples at 15N load.

Fig. 8.

Comparison plot for average coefficient of friction of the best samples from A, B & uncoated systems at 15N load.


The Fig. 7 shows the coefficient of friction for the second material system (B) which contains three different combinations B1, B2 and B3. From the analysis, it is observed that the composition of B1 had sudden increment in coefficient of friction from 0 to 83s and then starts to come down slightly till 186s after which shows a steady trend without much variations in the coefficient of friction. The composition B2 shows decreasing trend from 0 to 41s time period and then shows an increasing trend with very little increments. But B2 shows higher coefficient of friction compared to B1 for all time intervals. The composition B3 shows high coefficient of friction compared to B1 and B2. The graph of B3 composition shows an ‘up –and –down’ trend without much variations from the start to the end and the variation is within the range of 0.0152 to 0.1332. The study shows that when the percentage level of ceramic material increased, the coefficient of friction increases appreciably after crossing optimum percentage. It can be noted that in both A1 and B1 systems, the compositions containing 60% of Al2O3 exhibited better results.

Fig. 8 compares the results obtained for coefficient of friction of uncoated, A1 (best among the first set of compositions) and B1 (best among the second set of compositions) specimens. From the analysis, it is found that the uncoated material shows highest coefficient of friction compared to other systems. Its coefficient of friction is high at the start and shows up-and-down trend till the end. It is evident from the graph that B1 gives the lowest coefficient of friction compared to A1 and the uncoated systems.

The wear rate for the three material systems (Uncoated, A & B) involved in this investigation is shown in Fig. 9–11. The Fig. 9 shows the wear of the three different compositions of system A, namely A1, A2 and A3. The wear of A1 is more at start compared to A2 and A3. After the initial period of 21s, A1 and A2 follows same trend of increment in wear till the end. But A3 shows a sudden increment at the start itself up to 21s after which it follows almost the trend of A1 and A2 till it attains 268s. Now, the trends of the three systems show a change and the system A1 provides the lowest wear for the consecutive time periods compared to A2 and A3 systems. From the graph, it is found that A1 shows the lowest wear rate as the other two material systems are not consistent at the initial and final periods, depicting considerable variations in wear.

Fig. 9.

Comparison plot for average wear of the samples of system A at 15N load.


The Fig. 10 shows the wear rate for different selected compositions of system B, namely B1, B2 and B3. The wear rate of B1 depicts rapid increment at the initial period of 21s to 103s (0.00856mm3/Nm to 0.03467mm3/Nm) and then shows a very slow and gradual increment in wear up to the end of the cycle (maximum 0.04898mm3/Nm). In case of B2, the wear jumps to a sudden increment for the first interval of 21s to 41s (0.015 mm3/Nm–0.030 mm3/Nm) and the pattern shows a consistently gradual increment in wear till the end of the cycle (maximum 0.079 mm3/Nm). The B2 composition shows, a higher wear compared to B1 from starting of the cycle to till the end for all time intervals. The B3 composition shows an abrupt increment in wear for the first period of 21s–41s (0.03317mm3/Nm–0.06612mm3/Nm) and then shows a very gradual increment for every period till the end of cycle (maximum 0.1197mm3/Nm). The B1 composition is considered as the best among B1, B2 & B3 as it shows lesser wear than the other two compositions.

Fig. 10.

Comparison plot for average wear of the samples of system B at 15N load.


The Fig. 11 shows the wear rate of the three material compositions selected for final comparison. The composition includes uncoated system, A1 (best among the first set of compositions) and B1 (best among the second set of compositions). It is clear and obvious that the uncoated specimen exhibit very high wear rate (from 0.05865mm3/Nm to 0.23116 mm3/Nm). From this it is inferred that ceramic coatings improve the hardness of the surface of working components and help to reduce wear caused by friction. It can be noted from general analysis that the ceramic coatings show high wear at initial periods as the surface of the specimen is rough. With continuous friction, the surface becomes comparatively smooth and wear rate tends to decrease. This being the common trend for ceramic materials, however, individual ceramic material differs in their wear rate depending on their mechanical properties and mixing of different compounds at different proportions which influence the wear. Among the best compositions selected from the two coating systems, namely A1 (60% Al2O3 + 20% CrO2 + 20% SiC) and B1 (60% Al2O3 + 20% ZrO2 + 20% TiO2), the specimen B1 had lesser wear comparatively.

Fig. 11.

Comparison plot for average wear of the samples of uncoated specimen, A1 (best in system A) and B1 (best in system B) at 15N load.


The first system of coating which contains CrO2 + SiC also shows low wear rate. However, it is comparatively higher than the second system because of the presence of CrO2 which has a tendency to lower the hardness of the composition. In second coating system, the presence of ZrO2 has a tendency to resist wear as it is a very hard ceramic material. Also, the TiO2 compound provides good binding to alumina particles. This particular composition has the highest hardness among all compositions tested and shows lowest wear rate which reveals that this composition has the optimum blend among the coating compositions tested.


The Al6061 material used for fabricating piston and cylinder liner of an IC engine is tested for its wear properties to compare with new proposed ceramic coatings. The specimens made of Al6061 material are coated with Al2O3 - Cr2O3 - SiC (Coating system A, namely A1, A2 and A3) and Al2O3 - ZrO2 - TiO2 (Coating system B, namely B1, B2 and B3) ceramics to carry out wear tests and to analyse their wear resistance capability. The results show that the coated specimens of both systems A and B possess better wear resistance than the uncoated specimen. The performance of the samples further analysed by hardness test and SEM micrographs. The XRD results further confirmed the structural purity of the synthesized samples. The following conclusions are derived upon completing the research work.

  • 1

    A bond layer of NiCrAlY is coated on the substrate to ensure better bonding between the substrate and blend of ceramic powders and then the base alloy (Al6061) is pre-heated by blasting and coated as top coating.

  • 2

    The uncoated and coated specimens are undergone wear test and their wear resistance is compared. The coated specimens show better endurance to wear compared to the uncoated Al6061 specimen.

  • 3

    The uncoated specimen shows a wear rate of 0.2311 mm3/Nm. Among the Al2O3 - Cr2O3 - SiC coating compositions, A1 exhibited the best result of 0.1297mm3/Nm whereas in the Al2O3 - ZrO2 - TiO2 group, the B1 composition exhibited the best result of 0.0489 mm3/Nm. The wear rate is tested and calculated for a constant period of 330s for all the specimens. Among the seven specimens tested, B1 (60% Al2O3 + 20% ZrO2 + 20% TiO2) exhibited the least wear rate.

  • 4

    It is observed that the wear rate is high at the beginning stage and the material removal is taken place by abrasion when it reaches the bond layer. The wear rate slows down when the removal is by adhesion. It is clear from the experimental conditions of applied load and time; the pin is not penetrated into the substrate for the coated specimens tested. If the pin is penetrated down to the base alloy substrate, the material removal rate is high, that is revealed in the uncoated specimen.

  • 5

    The Rockwell hardness test revealed that the sample B1 has the highest hardness of 94 HRB and least wear rate of 0.03612mm3/Nm.

Conflict of interest

The author (s) provides no conflict of interest for publishing this manuscript.

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Journal of Materials Research and Technology

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