INTRODUCTION

Fulfilling customer needs are essential for business success. The activities of

an automobile manufacturer have to be oriented towards the customer’s expectation

and customers delight. Nowadays, needs like functionality, comfort, safety, reliability,

as well as high level of quality are taken for granted. Design, material quality and

their perception are reflected. Correct material selection is essential in order to

guarantee functionality or grace fullness of the multitude components of an

automobile. The piston, cylinder liner and valves are the important parts of the

internal combustion engine to be given more attention.

In baseline engine, the liner undergoes a severe wear at high temperatures of

combustion which results in seizure of the liner. Due to heat losses through the

cylinder walls, the thermal efficiency of the engine decreases. Reduction of emissions

from diesel engine is becoming increasingly important, because of promulgation of

stringent emissions legislation. Particulate and NOx emission are the primary concern

for diesel engine owing to the nature of the compression ignition process and diesel

fuel consumption. The challenging problems occurring are due to the presence of

solid particulates in the exhaust, in addition to gas phase pollutants. In order to

minimize these pollutants, it is necessary to go for an alternate method to design

engine cylinder and its combustion chamber components. The rapid increase in fuel

expenses, the decreasing supply of high grade fuels in the market and environmental

concerns stimulated research for more efficient engines.

To increase wear resistance, thermal efficiency, and minimize pollutants in the

exhaust of the engine, a thermal barrier and wear resistant coating is applied to inner

walls of the cylinder which replaces conventional liner.

Thermal barrier Coating (TBC), a new technique used at present scenario. TBC is a

thin layer of ceramic coating applied to combustion chamber components, mainly for piston

crown, valves, cylinder cover and cylinder walls. By using this technique, the present

problems could be solved to some extent.

Thermal barrier coatings becoming increasingly important in providing thermal

insulation for heat engine components. Thermal insulation reduces in-cylinder heat

transfer from the engine combustion chamber and also components structural

temperature. Containment of heat also contributes to increase in cylinder work and offers

higher exact temperature for energy recovery. Lower component structural temperature

will result in greater durability.

The problem faced by gas turbine engineers was the failure of components

exposed to not combustion gases. This problem was exacerbated by oxidizing

components of combustion gas (C02 and O2), high pressure (4 MPa) and the very high

loads experienced by gas turbine blades. Common causes of failure in hot end of

component even to date are creep, oxidation and thermo-mechanical fatigue.

There have been three major engineering advances in dealing with problem:

1. The development of the super alloys( 1950 to 1980)

2. The development of air cooling system( 1960 to present)

3. The development of durable thermal barrier coatings (1980 to present).

The gains in gas temperatures obtained were of the order of about 2000 c for the

development of super alloys, 5000C for air cooled system and 3000C for thermal barrier

coatings. Hence in the hot end of modem gas turbine engines most components are

made of super alloys with air cooled system and an increased number of components

now have thermal barrier coatings.

Modem TBCs are required not only to limit the heat transfer through the coating

but also to protect the engine components from oxidation and corrosion. No single

coating composition appears to satisfy these multifunctional requirements. As a result, a

"coating system" needs to be evolved. Research in the last 20 years have led to a

preferred coating system, consisting of three separate layers to achieve long term

effectiveness in the high temperature, oxidative and corrosive environment in which

they are to function.

First, a thermally protective TBC layer with a low thermal conductivity is

required to maximize thermal drop across the thickness of coating. This coating is likely

to have a thermal expansion co-efficient which differs from that of the component

material. This layer should therefore have a high in-plane compliance to accommodate

the thermal expansion mismatch between the TBC and the underlying super alloy

component. In addition to this it should be able to retain this property and its low

thermal conductivity during prolonged environmental exposure. A porous, columnar,

100-200µm thick, yttria stabilized zirconia (YSZ) layer is currently preferred for this

function.

Second, an oxidation and hot corrosion resistant layer is required to protect the

underlying component from environmental degradation. This layer is required to remain

relatively stress free during long term exposure and remain adherent to the substrate to

avoid

Thermal mismatch which mainly occurs due to improper adhesion and difference in

thermal expansion, coefficients between bond coat and cylinder material. TBC must also

withstand wear and tear. There is a need to over come these problems for employing TBC to

engine cylinder as a liner. In present work an attempt has been made to develop a TBC which

is also a wear resistant coating to be used in IC engine as a liner.

For last 100 years, engineers have searched for the best materials for

cylinder, pistons and rings. In the early years of automotive engines. the choice of

materials was cast iron. Engineers used cast iron in pistons, rings and cylinders. Cast

iron worked fine for cylinders and rings, but pistons made of cast iron were heavy, Cast

iron pistons were replaced by aluminum pistons due to the lower density of the

aluminum alloy. Due to the combination of cast iron cylinders and rings, aluminum

pistons are still in use in most automotive engines today. In the present investigations,

Aluminium-6061 (AI-606J) and Cast Iron are selected as engine cylinder materials.

These are also called as substrates of TBC system developed in the present work. Bond

coating is an intermediate layer of the TBC system. It is mainly used to bond a

subsequent over coat design for a particular function. The bond materials are specially

designed to provide optimal properties for both adherence of the top coating and

integrity of the interfacing substrate. Grading the TBC system from the bond coat to top

ceramic coat by incorporating one or more intermediate layers into the coating system

can minimize ceramic metal thermal expansion coefficient. The bond coat materials are

selected considering coincidence of thermal expansion coefficient values of the coating

and the relative elastic moduli, good wettability of the coating material at the surface of

support during its applications, suitable chemical affinity between the two systems. In

the present work, commercially available three bond coat materials, viz., Al25Fe7Cr5Ni

(Metco 446 metal powder), Ni9Cr3Si (Metco 451) and Fe38NilOAl (Metco 452, metal

powder) are selected. On AI-6061 substrate, two coating systems are developed. The

first coating system consists of two bond layers (A125Fe7Cr5Ni as Bond coat I-BCI and

Ni9Cr3Si as Bond Coat 2-BC2) and a top coat. The second coating system consists of

one bond coat (BC I) and a top coat. Similarly, two more coating systems are developed

on cast iron substrate. In this, the first coating system consists of two bond layers

(Fe38Ni10Al as bond coat l and Ni9Cr3Si as bond coat 2) and a top coat. The second

coating system consists of one bond coat and a top coat.

The performance of a TBC system as a liner in IC engine mainly depends on top

coat. Top coat should have characteristics of high wear and erosion resistance, low

thermal conductivity and high expansion coefficient. A significant amount of research

activities have been carried out on coating systems which utilizes alumina (Al2O3) and

Zirconia as top coats. The survey of the published literature shows that alumina is used

as a wear and erosion resistant coating where as Zirconia is used as thermal barrier

coating to minimize heat loss. The thermal conductivity of alumina is significantly high

compared to that of Al-6061. Also alumina has high hardness. Due to this, alumina can

be used as thermal barrier as well as wear resistant coating with AI-606 I substrate. The

addition of CaO, MgO, Y2O3 to zirconia decreases both the cubic to tetragonal and

tetragonal to monoclinic transformation temperatures. Thus, with sufficient additions of

various oxides to zirconia, the cubic phase can be stabilized. At concentrations less than

this limit, partial stabilization occurs, and all three phases i.e. cubic, tetragonal and

monoclinic can be retained on cooling to room temperature. The resulting ceramic is

referred as Partially Stabilized Zirconia (PSZ). The thermal shock resistance of PSZ has

been found to be superior to that of a fully stabilized and pure zr02. Thus partially

stabilized zirconia can be used as thermal barrier coating in both AI-6061 and cast iron

engine cylinders. In the present work, commercially available two materials viz.,

alumina (Metco 105SFP) and ZrO225CeO2 (Metco 205 NS) are selected as top coat

materials. The first coating system of AI-606 I and cast iron consists of alumina as a top

coat and second systems consists ZrO225CeO2 as top coat. The top coat thickness in all

the coating systems is varied as 100 ,200 and 300.

The performance of TBC coating system depends upon top layer morphology as

well as the coating technique. A manifest of this is seen when TBC top layers are

deposited using Atmospheric Plasma Spray ( APS) or Electron Beam-Physical Vapour

Deposition (EBPVD)Techniques. Coatings produced by APS have a thermal

conductivity in the range of 0.8-1.0 W/mK at 25°C. This is significantly lower than the

1.5-1.9 W/mK reported for EBPVD coatings at 25°C and as a result, the APS coatings

provide superior thermal protection. However the spallation resistance of these layers

is less than that of EB-PVD TBC layers (S to 10 time's shorter spallation lifetimes).

This arises because of the superior in-plane compliance of EB-PVD coating. As a

result, EB-PVD TBC layers are preferred for aerospace gas turbine applications. But

thicker TBCs are applied using plasma spraying technique. Plasma spraying can be

used to deposit a wide range of ceramics and metals and any combinations of these. It

is possible to deposit alloys and mixed ceramics with components of widely differing

vapor pressures without significant changes in composition. Very homogenous

coatings can be formed that display no significant changes of composition with

thickness. High deposition rates are possible without extreme investments in capital

equipment. Plasma spraying can be carried out in virtually any environment, air,

encoded inter low and high-pressure environment (relative to ambient) or underwater.

Thus in the present investigation, atmospheric plasma spraying method is selected for

coating the materials on substrate.

LITERATURE SURVEY

2.1 Coating Techniques

The following block diagram gives the different techniques used for depositing metal, cermet

and ceramic non-metallic powders.

Fig: 2.1 Classifications of Coating Techniques

2.1.1 Chemical Vapor Deposition (CVD)

CVD method ensures dense coating deposits on the materials due to the

decomposition of relatively high pressure gases. Gaseous compounds of the materials to

be deposited are transported to the substrate surface to achieve deposition due to thermal

reaction process. Reaction byproducts are then exhausted out of the system. It is a very

versatile process to produce varieties of coatings, powders, fibers and monolithic parts. It

is possible to produce almost all types of metallic or non-metallic elements, including

carbon and silicon, as well as compounds such as carbides, nitrides, borides, oxides,

intermetallics and many others using this technique.

Specific advantage of this process is attributed to the reactants which are gases

with wide type of characteristics. CVD is not a line-of-sight process as is the case with

other plating/coating techniques. Coatings can be made on porous bodies, blind holes,

large L/D tubes, etc. The various advantages this process are versatility of the process,

high levels of purity and density of the coatings, deposition occurring below the melting

point of the deposits, economical operation to cite a few.

2.1. 2 Physical Vapor Deposition (PVD)

It is functionally, a vaporization coating technique, involving transfer of material

at an atomic level.

The process involves the following four stages.

Evaporation: The material to be deposited is bombarded by a high-energy source such

as beam of electrons or ions dislodging the atoms from the surface of the target before

vaporizing them.

Transport: The movement of vaporized atoms from the target to the substrate to be

coated.

Reaction: Coatings of metal oxides, nitrides, carbides new metal targets. The metal

atoms react with appropriate gases during the transportation stage.

Deposition: Coating build up on the substrate surface.

Fig: 2.2 PVD Process

2.1.3 Flame Spraying Process

Combustion flame is the heat source to melt the coating material, which may

either be in rod, wire or powder form. In case of the wire and rod systems, a feed

mechanism drives the stock material into the combustion chamber where the flame melts

and propels (due to the high flow rates of the gases) the particles as a spray deposit. It is

possible that the powder used carried by an additional gas (generally nitrogen) from a

hopper unit to the gun for combustion and deposition.

Fig: 2.3 Flame Spraying

2.1.4 Spray and Fuse Process

This process is a modification of the powder flame spraying process explained in

the previous section. The process is a combination of two steps, where the coating

material is firstly sprayed by a flame spray gun (or a plasma spray gun) and

immediately after spraying, fused by an oxy-acetylene torch, induction heating or heat

treatment in a furnace (which is generally held under a reducing atmosphere or in a

vacuum). The fusion temperature is high, often up to 1300 0C, but can produce thicker

coatings up to 2000 μm with a high hardness The advantages of this process is the

production of fully dense microstructure and high bond strength between the coating and

the substrate. The major disadvantage is due to the high temperatures experienced by

the substrate during the fusion step.

2.1.5 HVOF Thermal Spray Process

HVOF (High Velocity Oxy-Fuel) thermal spray process is another variant of

form of the flame spraying process. The coating material is in the powder form. The

process can be categorized as Detonation Gun (pulse) HVOF system and Continuous

Combustion HVOF system. The difference between the two systems is related to type of

fuel gases and cooling systems employed in the process. Further, in detonation gun

system, combustion is maintained by a timed spark which is used to detonate the particle

and gas mixtures.

(A) Detonation-Gun Spraying

The process consists of a gas mixture, generally a mixture of oxygen and acetylene,

which is ignited by a spark plug to ensure a controlled detonation (or explosion) wave

(which heats the individual particles to temperatures of 4500 0C) which would accelerate

the particles and subjects them at subsonic speeds of 800 mS-1. Fig. 2.4 shows the

schematic of a typical detonation-gun system. A uniform, closely packed, laminar type of

structure of a coating can be obtained from the process due to the high temperature and

kinetic energy of the particles, which would also ensure higher hardness, density and

bond strengths of the coatings in comparison with those of plasma spray coatings.

Coatings up to 0.5 mm thickness can be produced by multiple detonations, but high

sound levels of 150 decibels are also produced. Double walled sound-proofing is

essential and the process is controlled from outside this housing.

Fig: 2.4 TAFA TJ-4000 HVOF Detonation Gun-Schematic

(B) Diamond Jet HVOF Thermal Spraying is a flame deposition technique wherein

powder material is melted by the combustion of oxygen with a fuel gas and it is propelled

at a high velocity with the help of compressed air, towards surface to be coated. In the

combustion zone, the powder material enters the flame, where it becomes molten or

semi-molten, depending upon the melting temperature and the feed rate of the material.

The flame temperature for the HVOF process is about 2300 – 3000 0C. The molten or

semi-molten particles are then propelled out of the gun nozzle at supersonic velocities,

exceeding 1350 mS-1 towards the substrate or forming die.

Fig: 2.5 Diamond Jet Spray Gun-Schematic

In comparison with other thermal spraying techniques such as plasma spraying,

this process allows very low thermal residual stress, thus enabling the deposition of

higher thicknesses of coatings. The DJ HVOF system exhibits the highest bond strengths

and lowest porosity of all the other thermal spraying processes, due to the high kinetic

energy experienced by the impinging particles.

2.2 Plasma Spray Coating Technique

2.2.1 Process Characteristics

Plasma, often called as the fourth state of matter, consists of neutral atoms,

positive ions and free electrons. Plasma is generated when sufficient energy is transferred

to a gas, which is capable of ionizing it, thus making the electrons and ions to act

independently of one another. It has been estimated that 98 % of visible universe exists in

the form of plasma. Natural plasma occurs in earth as the aurora borealis and lighting.

Examples for common man made plasma include neon and fluorescent tubes and bulbs.

Thermal plasma is a state wherein energy levels of electrons, heavy particles and

ions are similar. Higher levels of ion transfer significantly enhances the kinetic energy of

the gas in comparison with that observed during electron collisions. Higher electron

temperature plasma though energetic, is found to be not enabling higher levels of energy

transfer which is attributable to their lower mass particles. Energy sources for the creation

of thermal plasma used in the thermal screen devices are usually electric arcs, DC or RF

discharges. Thermal plasma can also be generated using micro waves, gamma radiation

and electric arcs based on alternating current.

In plasma arc spraying process also known as plasma spraying process, the

thermal energy of an electric arc (40 kW or 80kW) together with a plasma forming gas,

which would be either nitrogen or argon, are utilized in melting and propelling of the

deposit material at high velocities (600 mS-1) onto a substrate. This process is capable of

generating very high temperature, exceeding 16,000 C, which can be gainfully employed

in the deposition of materials with high melting points. The deposited material is

generally in a powder form and requires a carrier gas to feed it into the combustion

chamber. The process enables discharging high bond strengths of the coatings due to the

very high propulsion velocities of the impinging particles.

In a DC plasma arc process, gas heating is enough to generate core plasma

temperatures exceeding 20000 °C depending upon the properties of gas and its electrical

break down characteristics. Enthalpy of the gas is an indicator of its heating potential

while it is getting translated to plasma state.

The basic components of a DC plasma arc gun is shown in Fig. 2.6

It consists of an axially aligned cathode and an anode. Tungsten is used as the

cathode because of its high melting point and good thermionic emittance as well. The

thoriated tungsten tip is found to operate around its melting point due to high current

densities which locally heats tip of the cathode. The water cooled copper anode

constricts and spatially stabilizes the arc and accelerates the expanding heated gases.

Cathode relies on conduction and the high melting point of tungsten to survive the high

temperature of the arc since they are not directly water cooled. Direct current plasma arc

guns are intensely water cooled not only to prevent melting but also to minimize the

erosion of cathode and nozzle.

In working, plasma forming gases are introduced through the rear region of the gun.

They enter the arc chamber through a gas rim that imparts a spin or vortex to the gas

flow. The arc is stabilized at the cathode tip which in the low pressure region of the

vortex and rotates the arc attachment or arc route at the anode. Rotation of the anode arc

attachment minimizes its erosion. The heated gases expand radially and axially,

accelerating as they expand before exiting through the nozzle. Depending upon the

pressure ratio between the upstream arc region and the down stream nozzle exit of the

gun the gases either expand sub-sonically or super sonically. Many gun designs employ a

converging/diverging type of nozzle to achieve super sonic expansion which in turn

increases particle velocity.

Fig: 2.6 Plasma Spray Gun

2.2.2 Plasma Spraying Equipments

Plasma arc spray systems are made up of components similar to other thermal spray

systems.

Direct current plasma arc spray systems are the most complex and the most flexible

of all thermal spray processes. Plasma guns are designed for 144 to 720 MJ input power.

Water cooling is essential because of high temperature and enthalpies. Pressure of water

exceeding 1MPa is needed to suppress the localized film boiling in the gun which would

reduce the component life and coating contamination. This necessitates the use of high

pressure co-rings seals and passage ways inside the gun. Ceramic gas injectors and high

temperature insulators are required to separate the electrodes. The high power density of

DC plasma arc can produce relatively high erosion rates of the anode and the cathode.

Gun design is a significant factor in determining the component life. Designs that use a

closely coupled anode and cathode possess shorter life than those that employ wide

spacing and a flow nozzle. Operational procedures particularly start up and shut down

sequences shall significantly affect the electrode life. Mono atomic gases are also found

to extend the electrode life due to their lower enthalpy. Arc erosion of anode and erosion

of powder ports and powder feed tube are the factors to be considered while deciding

about the anode replacement. The cathode is generally replaced after effecting nozzle

changes about 2-5 times and is governed by its geometry and current density.

Powder ports contribute significantly to ensure consistency in coating process. Adjustable

and removable powder ports need to be monitored and controlled. Alignment tools

should be used to ensure precise and repeatable positioning when powder ports installed

replaced or adjusted.

2.2.3 Special Features of Plasma Spraying Technique

The following are some of the unique features of the plasma spraying process.

The technique can be used to deposit a wide range of ceramics and metals and

their combinations as well.

It is possible to deposit alloys and mixed ceramics with components of widely

differing vapor pressures without significant changes in composition.

Homogenous coatings can be formed for any composition while maintaining

uniformity in their thickness.

Fine microstructures with equiaxed grains and without any type of columnar defects

are the characteristics of this process.

High deposition rates are possible without huge investments on capital equipment.

The process can be carried out virtually in any environment such as air, encoded

inert low and high-pressure environments, or underwater.\

2.3 Plasma Sprayed Ceramic Coatings

Ceramic coatings can be readily formed employing a wide variety of techniques

(e.g. sputtering, electron-beam deposition). The technique being used since the middle of

previous century, to form metal alloys, ceramic and cermet coatings on a range of

metallic substrates. These types of coatings mostly greater than 50 µm in thickness are

used for varieties of engineering applications to realize enhances, wear/erosion and

corrosion resistance of thermal barriers; electrical magnetic components and so on.

Plasma spraying technique has been playing a significant role in depositing a

variety of ceramic materials on conventional metallic substrates. These coatings are

generally employed to realize enhances wear resistance of abradable seals as well as

thermal barriers, thus permitting hot sections of gas turbine engines to function at

increased operating temperatures in aircraft industries. Plasma sprayed refractory ceramic

coatings are also used in handling liquid metals and in electrically insulated metal

substrates in the automotive electronics industry.

A number of inter dependent parameters are found to describe the characteristics

of the plasma sprayed ceramic coating process. Some of them are gas type, pressure and

flow rate, spray distance to cite a few. The physical features of the feed stock powder

appear to influence the quality of the coating. Particle size, shape and its distribution, and

the level of chemical uniformity of the constituents in a mixed oxide are the parameters

but to be neglected in this analysis. Particle size influences the meltability whereas its

shape determines the extent of flowability of the powder into the flame.

The microstructure and phase distribution of plasma sprayed coatings are

dissimilar in composition with that of the substrate. Material properties of the coating

such as thermal diffusivity, mechanical strength in tension and shear and wear

characteristics are found to be different in comparison with that of bulk material.

2.4 Thermal Barrier Coatings for Internal Combustion Engines

Chrome plated cylinder liners were used in Internal Combustion (IC) Engines till

70s. Hard chromium was electroplated directly on to the bore of the aluminum cylinder.

Honda cars of late 70s exclusively used this process. Kawasaki employs a process referred to

as electro-fusion for the said purpose. Leading auto manufacturers such as Yamaha, Honda,

and KTM utilize a technique wherein the Nikasil material is applied directly on the aluminum

bore. On the liner Suzuki employs a boron composite material for the purpose. These

processes are found to enable the designers to reduce the clearance between the piston and

cylinder which results in enhanced power from the engine.

A Poeton Max Power, Wiscons [1] in is considered to be the leader in the technologies

related to engine cylinder plating and coatings. The company has devised a system to coat

cylinders, pistons, rings and combustion chambers of IC engines with a Nickel composite

loaded with ceramic particles. The process was first developed for its application in aircraft

industries but later on made its way into automotive environments.

Y.Miyairi [2] has investigated the performance and exhaust emission characteristics

of a thermally insulated single cylinder diesel engine. The cylinder head and piston crown are

thermally insulated with sintered silicon nitride (SSN) whereas the upper part of the cylinder

liner with Partially Stabilized Zirconia (PSZ). He has shown that volumetric efficiency of

engine with insulated cylinder head and liner is higher in comparison with the engine which

has an insulated piston cavity. It is also examined that the gas temperature in the cylinder

with insulated piston crown, cylinder head and cylinder liner is much higher than that of

other types of engines such as baseline engine, engine insulated with piston crown, engine

with insulated cylinder head and cylinder liner which is mainly due to formation of Nitrogen

Oxide in large amount. Local insulation of combustion chamber walls with ceramics has

resulted in improved engine performance with decreased volumetric efficiency. Insulation of

the piston cavity, cylinder head and cylinder liner upper part together is found to reduce the

emission of hydrocarbons under natural aspirated conditions at low speeds. On the other, a

reduction in Brake Specific Fuel Consumption (BSFC) is reported under both naturally

aspirated and turbo charged condition when the cylinder head and liner upper parts were

thermally insulated with ceramics. Further insulation of the piston cavity has contributed the

increased in BSFC partly due to the increase in the reciprocating mass.

Osawa [3] has conducted tests on coatings made on small aluminium bore of an air

cooled diesel engine. He has reported that coatings possessing high thermal insulation and

low friction characteristics perform best albeit with a 10% reduction in fuel consumption.

Morel [4] has analyzed that a significant part of the retained heat is directly converted

to positive work. He has also examined that a typical highway truck engine with a practical

zirconia coating able to achieve a 5% performance benefit over that of an engine cooled

baseline at rated conditions.

Wong [5] has considered different combinations of coatings with different thermal

characteristics and coating thicknesses to predict the pattern of fuel consumption in IC

engines. The simulation model developed by him considers the influence of transient heat

transfer into and out of the combustion chamber surface throughout the entire engine

operating cycle. The simulation also included an advanced liner friction model which

accounts for the effects of liner surface temperatures and lubricating oil viscosity. Results of

the analysis showed that all thermal barrier coating materials provided a performance benefit

that is strongly dependent on the coating thickness. Most coatings for the piston and head

face surfaces provided a maximum benefit at a coating thickness of 0.1mm. The predicted

maximum benefit in thermal performance is found to range from 1 to 2%. It is predicted that

a coating thickness of 0.5 mm in the liner would provide an optimum oil viscosity and a

reduced friction with a 5% increase in performance.

Dennis Assanis and Kevin Wiese [6] have carried out work on zirconia band TBC coated

on to the piston of diesel engine with a coating thickness of thickness of 0.5 mm and 1mm.

They have compared the performance and exhaust emission of coated piston engine with that

of base line piston engine. They have found that 0.5mm thick ceramic coated piston engine

has in comparison with that of the metal piston engine. On the other, the thermal efficiency of

1mm thick ceramic coated piston was only 4% higher than that of base line engine piston.

Due to more complete combustion in the insulated configuration, exhaust CO levels are

found to be 30 to 60% lower than that of base line engines. Similarly unburned hydrocarbon

levels were 35 to 40% lower than that of baseline engine. The NOx concentration is also

found to 10 to 30% lower than that of baseline engine due to the changes in the nature of

combustion. The variation in thermal efficiency and BSFC as a function of engine speed is

shown in Fig. 2.7.

Fig: 2.7 Thermal Efficiency and BSFC as a Function of Speed for Baseline and Ceramic Coated Engines [6]

Hideo Kawamura [7] has worked on Si3N4 monolithic ceramic coatings which are

applied to combustion chamber walls. A combustion chamber with thermos structure made

of sintered Si3N4 was used for this purpose. He has reported that the pre-combustion

chamber exhibits a good potential for LHR (Low Heat Rejection) engine due to capability of

combustion chamber wall temperature resulting in improved fuel consumption and

controlling of exhaust emission. The NOx emissions are also found to be low due the

presence of rich mixture in the pre-chamber in spite of the prevalent high temperature. It is

mainly due to the diffusion of air and fuel mixture near the cylinder wall which reduces the

temperature of the combustion gas. The fuel consumption in case of new type of energy

recovery system is found to be 180 g/kWh or less for 2 liters cylinder light duty diesel engine

with the proposed new combustion chamber. The LHR engine consisting of a thermos

structure having good heat insulation layer is found to eliminate the need for cooling system,

and found to improve the heat insulation ratio upto 75% or more.

Masaki Tanaka [8] has conducted experiments on Cr2O3+Mo coated piston and

cylinder liners and found that that the ceramic coated piston rings and cylinder liner

possesses superior wear resistant characteristics.

F.Rastegar [9] has worked on High Velocity Oxygen Fuel (HVOF) cermet coatings

employed in high horse power diesel engines. He has used Cr3C2/NiCr as the coating

material. He has found that the highly dense chrome carbide based HVOF coatings develop

crack resistance during their service life. The liner wear is found to be almost three times

higher in comparison with chrome under severe service conditions.

Roy Kamo [10] had carried out work on TBC for improving the engine performance

considering three engine configurations such as Metal base line builds, coated cylinder liner

builds and fully insulated builds wherein the cylinder liner, piston top and cylinder head faces

were coated with thin layers of thermal barrier ceramic composite materials. He has used

Zirconia slurry and chrome oxide for piston and head face coatings, Zirconia for cylinder

liner post densified with chrome oxide using plasma spraying technique with the thickness of

coatings as 0.127 mm and 0.508 mm for piston and liner respectively. He has reported that

the coated liner build exhibits about 1% improvement in performance over that of the metal

base line while the fully insulated configuration would produce about 2% loss in fuel

consumption. Heat rejection results indicate that the coated liner did not produce any

significant reductions while the fully insulated configuration produced a full load reduction

of 10% at 1400 rpm and no reduction at all with the increase in engine speed.

M.Vittal [11] had studied emission characteristics of indirect diesel engines with TBC

applied to their combustion chamber. The piston crown, cylinder head and valves were given

a thin thermal barrier coating (thickness 300 m). The parts were given a bond coat of

NiCoCrAly followed by top coat of Yttria stabilized Zirconia. He had reported that the

thermal barrier coatings minimize the CO emissions marginally, increase the exhaust

temperature, and decrease specific fuel consumption, decreases with the air fuel ratio with

reduced particulate emissions. Further, thermal analysis of the particulate matter had

demonstrated that the ceramic coated engine shifts the composition of the particulate matter

towards more dry soot and less volatile content (Fig. 2.8).

Fig: 2.8 Compositional Differences between Exhaust Particulates from the Baseline and Ceramic Coated

Engine Configurations

Hejwowski [12] has suggested that TBC with NiCrAl bond coat and Alumina –

Titania or yttria partially stabilized ZrO2 can be used to constitute a durable and efficient

thermal barrier coating on gasoline and diesel engine piston crowns. An optimum thickness

for TBC is slightly below 0.5 mm according to him. Further, he has also found that, that the

Specific Fuel Consumption (SFC) is lowered by 15 to 20 % with the use of coated piston

crown with 8% increase in power (Fig. 2.9). TBC with alumina –titania shows good

resistance to conditions prevailing in a gasoline engine combustion chamber. The fuel

consumption of a modified engine is found to reduce by 4.2 % at a speed of 1100 rpm, 11.7

% at 4000 rpm and 20.7% at 2500 rpm. Temperatures of cooling water and oil are slightly

higher in a modified engine.

Fig: 2.9 Variation of Brake Power and BSFC with Speed (1) Baseline Engine (2) Ceramic Coated Engine

Computer aided modeling and analysis carried out by Melvin Woods [13] has shown

that the conventional thermal spray coatings (slurry densified Zirconia) experience thermal

fatigue and does not provide the desired durability. He has also reported that a coating

thickness of 1.25 mm of zirconia can produce same insulation level that of 2.5 mm thick

coating by changing the piston material to titanium alloy.

Prasad and Ravindra [14] have carried out an investigation on heat transfer in an oil

cooled piston with and without ceramic insulation on crown face. A 2 mm thick oxide based

ceramic insulation material is coated on the piston crown of diesel engine. They have

predicted the isothermal distribution in the piston body and the heat flow rate through the

different cooling media at different engine loads for both the cases with and without

insulation coating and found that there is a reduction in heat loss of 12 to 30% for the piston

with insulation coating, assuming that both the heat transfer and temperature of the

combustion products remain unchanged.

Kulkarni and Jagdish. R [15] has indicated that ceramics, a family of heat resistant

super tough materials, contribute to energy savings. Cylinder head liners, valve train

components and exhaust ports with ceramic coatings are form to retain heat and eliminate the

need for cooling systems.

Poola and Ramesh. B [16] have characterized the TBCs that are applicable to SI

engines. Improving the fuel economy while reducing the exhaust emissions of a conventional

carbureted two stroke spark ignition engine was the main thrust of their investigations. An in

cylinder catalyst in the form of coating is found to provide a moderate thermal insulation in

the combustion chamber by deposition of thin ceramic material.

Ashok Kumar [17] has evaluated the performance of aluminum-titanate coated piston

crown of a CI engine. The insulating piston crown is found to increase the temperature of

cylinder wall which in turn contributes to reduction in volumetric efficiency which has a

significant impact on the power developed. The aluminum-titanate coating is found to

increase the temperature of combustion chamber, reducing the amount of lubrication and an

increase in friction. He has also proposed that the increase in the energy content of the

exhaust gases can be effectively utilized for turbo compounding.

2.5 Surface Texture of Plasma Sprayed Coatings

Earlier research activities on TBCs are most related to surface topography

charactertion at micrometric and nanometric scales to address the issues related to the

evaluation of quantitative parameters over profile and surface data points, which can be

acquired by means of roughness measurement instruments and/or atomic force

microscopes [18]. Quantitative parameters are typically designed to be representative of

mean properties of a surface topography; Ra, the arithmetic mean roughness of a profile,

or its 3D equivalent, Sa, one .he well known examples of such an approach. The wear

and friction performance of ceramics haw been studied by earlier investigators [23, 24].

It has been found that low wear rates can sometimes be obtained at low surface

roughness of materials, but with high friction coefficients which is in contrary with the

general view that the friction coefficients are low because of their high hardness.

2.6 Effect of Surface Roughness and Chemistry of Bond Coat on

Surface Roughness of Coatings

Effect of bond coat roughness by subjecting it to different treatments before

spraying of the top coat has been investigated [19]. It has been found that roughening of

the bond coat raises the fracture energy of the bond coat/top coat interface up to a certain

level of roughness beyond which a plateau is reached. Study of the crack paths followed

in different cases indicated that, while cracking occurs largely within the interface when

it is relatively smooth, it tends to occur within the top coat, close to the interface, at

higher roughness levels of the interface.

The effect of creep in the bond coat has also been studied . It is anticipated that

some systematic work on the role of bond coat creep could be undertaken using

proprietary Sulzer powders with high creep resistance, but no decision has yet been taken

on the provision of powder for this purpose.

The roughness [20] on the surface of work pieces increases with the thickness of

the inial oxide layer. It is maximum at the final removal of oxide layer. The bonding or

adhesive strentgth of the sprayed surface also is maximum in such a condition. Bonding

strength increases with the arithmetical mean height of the surface roughness due to the

thickness of the initial oxide layer. Further, when the arithmetical mean height of the

surface which is pre-treated by the cathode spots is the same, bonding strength is also

increases which are due to the narrow mean spacing of profile irregularities.

O. Sarikaya [21] has reported that the increase in the roughness of substrate

surface also increases the porosity and roughness of coatings. Higher hardness, lowest

porosity and the lowest coating roughness has been obtained by him at a substrate

roughness of 3.28IJm. Roughness of the coating also increases with enhanced thickness

of the coating. He has examined the coatings prepared at 500°C substrate temperature and

found that their microhardness increased at 28% level, where as porosity and coating

roughness decreased at 86 and 36% levels respectively. It has also been reported that the

thicker top coat is mechanically weakened with the increase in volume of pores and

magnitude of residual stresses.

Z. Liu [22] has reported that plasma sprayed Zr02 8%Y203 coatings on mild

steel substrate possess surface roughness of 4.51Jm in as-sprayed condition. The

surface quality is found to improve upon laser treatment. He has shown the roughness

of the coating increases with the increase in traverse speed of the laser beam, where as

the roughness decreases with the increase in the pulsing frequency. Further there is a

marginal increase in the roughness levels with the increase in the fluence. This is

attributed to simultaneous occurrence of ablation and thermal effects during the

sealing process of an excimer laser

C. Batista [23] has carried out an investigation on surface topography of

plasma sprayed and laser assisted zr02 thermal barrier coatings using triangulation

technique. He has found that there is a significant decrease in surface roughness of the

coatings upon laser treatment which is due to the increase in crack density which is a

function of both scanning speed and over lap of the beam.

R. Krishnan et.al. [24] Have examined the surface texture of as-sprayed and

CO2 infra red laser treated alumina air plasma sprayed coatings on copper substrate.

They have reported that the surface roughness of as-sprayed coatings is about 5µm

The surface roughness is found to 2.5 µm at 50 W powers and minimum at l.0 µm at

100 Wand increases to 1.3 µm at 150W power. The reduction in surface roughness of

laser treated coatings is mainly due to the transformation of γ-AL2O3 to α-Al2O3 and

densification through elimination of pores.

2.7 Porosity of Plasma Sprayed Coatings

Porosity is one of the disadvantages of plasma sprayed ceramic coatings. It

occurs in ceramic coatings due to i. Retrained gases with in the splats which introduce

spherical porosity ii. Early solidification or incomplete melting resulting n irregular

pores iii. Incomplete filling of interstices between previously deposited particles

resulting in fine planar pores which are observable between individual splats and at

locations of incomplete contact between lamellae.

Porosity can be classified into three distinctive groups such as; oblate, oriented

with high aspect ratios and volumetric pores. The oblate pores originate from incomplete

contact locations of adjacent splats due to insufficient wetting. These voids are generally

flat with high aspect ratios and their dominant orientation is parallel to the substrate.

Vertically oriented voids are present between horizontally (i.e. parallel to the substrate

surface) adjacent splats. The oblate pores mainly contribute to the inner surface area

porosity but they are only a small fraction of the total porosity . Due to their high aspect

ratios, these voids have a major effect on the elastic constants of the coatings since they

effectively decrease the crosssectional area of the coatings . Volumetric or globular pores

are fonned not only because of trapped gases but also due to incomplete filling of surface

pits and gaps left by solidified splats. It has been found that their contribution to the inner

surface area is small but they contribute up to 30% of the total porosity . The aspect ratio

of the pores is small and there is no preferred orientation for them. Globular pores are

found to decrease the Young's modulus of the coatings in small volume fraction .

Depending upon the spray conditions, some fraction of the pores can be surface-

connected. Network pore structure is found to reduce the elastic modulus. Factors such

as speed and temperature of the particles have a strong influence on all aspects of the

porosity .

Residual stress in coatings is an important issue since it enables the coating to get

debonded from the substrate . Residual stresses are introduced in the coatings during the

impact quenching of the molten particles causing a difference in the magnitudes of

coefficients of thermal expansion between the coating and the substrate. Pore structure

also contributes to the residual stresses since they are influenced by elastic modulus and .

The strains mainly determined by the thermal conditions during the deposition process.

Portinha [25] has carried out the characterization of plasma sprayed thermal

barrier coatings possessing porosity gradients while using Zr02+8%Y203 as top coat and

NiCoCrAlY bond coat on Nickel super alloy inconel 738 LC substrate. Samples are

initially annealed at 11000 C for 100hurs in air and are subjected to a thermal shock

heating at 10000 C and cooling in water, for 100 cycles. The as-sprayed coatings are

found to exhibit a porous and lamellar structure with porosity in the range of 12 to 15%.

Upon annealing in air, all coatings present a sintered structure with reduction in their

porosity levels. The porosity of sintered coatings is found to be in the range of 7 to 8%.

The sintering effects are found to increase the thermal conductivity, elastic modulus with

a loss in their strain tolerant behavior. Thermally shocked coated samples showed no

spallation and only exhibited some densification at the surface with the appearance of

small cracks which are perpendicular to the coating plane found to enhance the strain

accommodation. The porosity is found to increase from the bond coat interface towards

the surface of the top coat. In as-sprayed condition, the absolute porosity is found to vary

from 3 to 5% from interface to top coat surface and in annealed condition is from 1 to

2%. The reduction is due to the sintering effects at high temperature. Porosity is also

found to depend on deposition parameter. It increases with increase in the working

distance and decreases significantly at higher powers of the plasma gun. It is mainly due

to the reduced velocity of the melted particles in the first case when they reach to the

coating in growth and in the second case the particles have more velocity at higher

temperatures.

2.8 Bond strength of sprayed coatings

Bond strength (adhesive bonding) is one of the important properties of plasma

sprayed coatings. The main mechanism of adhesion can be described as mechanical

keying, physical, diffusive and chemical in natur. According to sobolav et al. [26]

Mechanical interlocking, due to rughness of the substrete surface, high pressures

developed on the droplet impact and soldification of the lower part of the splat is found

to be prominent mechanism for introducing the bond strength.

Compostion of the substrate and that of the bond coat as well are found to affect

the adhesion of alumina formed during the oxidation of bond. With the spalling of

alumina, zirconia layer is found to disintegrate contributing the failure of TECs.

Migration, segregation and stress generation are key issues of concern in the thermally

grown oxide regions. Migration of aluminum ions from bond coat to metal alloy substrate

occurs due to a concentration gradient. Similarly, migration from both the substrate and

bond coat into the thermally grown oxide region also happens. It appears that limited

yttrium ion migration to the alumina improves adhesion; however, contaminants in the

alumina generally lead to additional stresses, which decrease the adhesion during thermal

expansion process. High temperature diffusion of bulk yttria ions to the YSZ surface is

found to destabilize the top coat enabling the transformation of zirconia phase to

monoclinic resulting in an undesirable volume expansion which may contribute to

spallation. It has also been suggested by earlier researchers that both neutral and ionic

aluminum diffusion into the YSZ layer induces spallation . Diffusion controlled

migration in the TEC is found to promote h harmful phase transitions besides enhancing

the thermal stresses. Though a concentration gradient is found to enable the migration via

diffusion, the oxygen chemical potential gradient, occurring during oxidation is found to

supply another driving force. Studies have also shown that, this chemical potential

gradient is found to penetrate the top coat, bond coat and the metal substrate. It also

affects the oxygen reactive species in all these layers, including those which were

initially in the form of stable oxides, nitrides, carbides and sulphides . For example,

sulfur is found to segregate the interface, which can prove to be detrimental to the life of

TBC. The interfacial sulfur is found to increase the thickness of the oxidation layer,

decrease the adhesion of the oxide layer to the metal, besides enhancing the

transformation of metastable alumina to the alpha phase and hence pore formation at the

interface and also within the oxide layer. It also increases interfacial roughening and

formation of voids. The formation of voids is found to be problematic since they act as

stress concentration sites within the oxidation layer .

2.9 Parameters Affecting the Wear Rate of Plasma Spray Coatings

a) Effect of Intra-Lamellar Microcracking

The vertical cracks present in the plasma sprayed ceramic coatings playa

significant role in the formation of wear debris . The presence of pre-existing cracks

within the individual splats provides low energy pathways for the crack growth during

the abrasive processes including scratching and erosion.

b) Effect of Material Hardness

It is established that the wear resistance of a material is closely related to its micro

hardness, toughness, microstructure, defect content and the ratio of its hardness to the

hardness of the abrasive. Hardness has a large effect on the wear of materials through

the mechanisms of plastic deformation, while fracture toughness is a dominant factor in

wear involving brittle fracture. In case of plasma sprayed coatings, better correlations are

found between the hardness of the worn material and the modes of wear where plastic

deformation is a major mechanism. the relationship between hardness and wear is in the

form of W=k/Hn where W is the wear rate, k and n are constants and H is the hardness of

the surface. Exponent n is varied form 2.8 for adrasion and 1.6 foe small particle and low

angle erosion. Many studies have suggested that a high hardness is desirable for both

brittle and ductile materials, while a brittle material benefits father from a high

toughness there is no simple relationship between the abrasive wear resistance and

hardness of the coating. The abrasive wear mechanism of the coating IS found to be not

only .dependent on coating hardness and density, but also on particle size, type of

powder used, coating microstructure, as well as micro structural changes occurring

during the process of wear. The wear resistance of alumina coatings can be changed

significantly by selecting different powder process methods or by adding different

additives, even if the hardness is almost similar.

c) Effect of Fracture Toughness

Fracture mechanics concepts have been used to explain and predict the wear of

brittle materials[27]. The models are based on ideal brittle materials such as glasses,

single crystals such as sapphire with an assumption about the formation of lateral and

radial crack systems. However, when these models are applied to more typical

polycrystalline materials such as coarser grained alumina, where lateral cracking does

not always occur, the model predictions are found to be inaccurate. These models suffer

from the simplifying assumptions and are applicable to either ideal or brittle materials

and only one type of wear mechanism operates at a time viz. plastic deformation or

brittle fraction. However engineering materials are rarely ideal and it has been

demonstrated clearly that the wear of ceramic plasma sprayed coatings by hard particles

usually involves both plastic flow and brittle fracture occurring at the same time. The

effect of fracture toughness on the wear resistance of brittle materials is usually related

to hardness.

d) Effect of Load

Load or the contact stress is the most obvious and easily monitored parameter that

can affect wear. The magnitude of the normal load or the contact stress is important since

it increases both the area of contact and the depth below the surface at which the

maximum shear stress occur as well as the elastic or plastic deformation states.

e) Effect of Residual Stress

Wear behavior of APS and VPS coatings have been found to be dependent on the

levels of residual stress in the coatings. The resistance of materials to abrasive wear has

often been correlated with hardness and the levels of residual stress in thin films have

also been correlated with hardness, clearly indicating that the resistance of the coating to

deformation process must play an important role in the wear tests. The wear resistance of

plasma sprayed alumina increases with the increase in levels of compressive residual

stress in the coatings. To obtain the best wear performance it is therefore necessary to

maximize these stresses without compromising on the coating-substrate adhesion.

f) Effect of Microstructure and Grain Size

Wear is acomplex process and many factors are found to influence it. In certain

situations one or more factors will dominate the vwear process of the materials. In

addition to hardness and toughness, the microstruture of cermics especially grain size has

an ammense infuluence on its wear resistance the changes in microstruture are more

vsignificant in the nanostructure coatings than in the conventional coating. It is belived

that the phase transformation has an important effect on the process of wear.

I P.Psyllaki [28] has carried out investigations to examine the wear behavior of

APS and Detonation Gun (DG) sprayed alumina coatings on cast iron and Haste alloy X

substrates having a bond coat of 60Ilm thickness. He has conducted the wear test on both

APS and DG coatings (1ON load and sliding speed 0.1 m/s, 6mm dia. Ab03 ball,

1900HV) in which the friction coefficient at the contact of Al203 coating/sintered Ab03

ball is 0.78 and had remained constant until the coating was totally worn out. He has

reported that the wear has taken place mainly by adhesion mechanism and is enhanced by

the exfoliation of the surface splats. According to exfoliation mechanism, friction can

result in the imitation of crack between two splats of the same lamella. During cyclic

loading of the surface, the crack is propagating along the splat boundary, leading to its

final exfoliation from the worn surface.

In the case of APS Al2O3 coatings, the weak interfaces between the successive

lamellae are found to have failed, leading to the delamination of the coating which is

extended for long distance from the axis of loading. This degradation mechanism is

found to induce the rapid wear of the ceramic coating and hence increased wear rate. In

the DG Al2O3 coating, the stress field developed during sliding led to theinitiation of

cracks perpendicular to the coatings/substrate interface and their propagation through the

coating’s thickness.

Fig: 2.10 Exfoliation Mechanisms during Sliding Friction Testing

3. OBJECTIVES

Thermal barrier coatings(TBC) in internal combustion engine have advantages

such as improved thermal efficiency and combustion, reduction in weight by eliminating

cooling systems, etc. however, practical problems are faced in implementing these

coatings in internal combustion engines, A significant amount of research activities

shows the implementation of TBC to different parts of IC engine. At present TBCs are

applied to combustion components of IC engines, mainly for pistons crow, valves,

cylinder cover, and cylinder liner. However, the extended application of TBC to cylinder

liner has not been explored practically. Cylinder liner is one of the important components

of IC engine which severely under goes wear and tear due to reciprocating motion of

piston. At the same time, linear as subjected to thermal stresses caused by hot gasses of

combustion. TBC in the place of linear has to play very important role in minimizing

wear and tear, heat transfer from cylinder to surroundings. The problem presently faced

in implementing of TBC as engine cylinder is thermal mismatch which mainly occurs

due to improper adhesion and difference in thermal expansion coefficient between bond

coat and cylinder materials. TBC must also withstand wear and tear. There is a need to

overcome these problems for employing TBC to engine cylinder as a liner the present

work is undertaken with the following main objects.

1. To search a proper bond coatings and top coat materials based on

composition of substrates.

2. Selection of proper coatings techniques.

3. Preparation of plasma sprayed coated samples for various tests.

4. To check the microstructure and Topology of coating.

5. To check the surface texture parameter of coating.

6. To determine the bond strength of coating.

7. To determine micro hardness of coating.

8. To determine abrasive wear of coating .

9. To determine erosion wear of coating.

10. To establish the suitability of coatings for its application in internal

combustion Engine as a linear.

REFERENCES

1. Apticote ceramic-2000 system, Poeton max power Inc.,Madison WI53716

2. Y,Miyari,T.Matsuhisa,T.Ozawa, Selective heat insulation of combustion

chamber valves for DI Diesel engine with ceramics,Transaction of SAE 1989.

3. K.Osawa, R.Kamo, E.Valdmanis, Performance of thin thermal barrier

coatings on Small aluminum block diesel engine, SAE Technical paper

910461,1991.

4. T.Morale, Examination of key issues in low heat injection engines SAE

Technical paper, 860316,1986.

5. Wong. V, Assessment of thin thermal barrier coatings for IC Engines, SAE

Technical paper,Vol.950980,1995.

6. Denis Assanis, Kevin Wiese, The effects of ceramic coatings on diesel engine

performance and exhaust emissions, Transactions of SAE,Vol.100 section-3,

1991.

7. Hideo kawamura, Akira Higashino, Combustion and combustion chamber for

a low heat rejection engine, Transactions of SAE, Section-3, 1996

8. Masaki Tanaka, Ceramic metal composite coated piston rings and cylinder

liner of marine low speed diesel engine, Translation from the journal of

MESJ, Vol.27, No.3, 1991, pp 77-85.

9. F. Rajstegar, D.E. Richardson, Alternative to chrome, HVOF Cermet coatings

for high horse power diesel engine, Surface and Coatings Technology, Vol.

90, 1997, pp 156-163.

10. Roy Kamo, Dennis N. Assanis, Walter Bryzik, Thin thermal barrier coatings

for engines, Transactions of SAE, 1989, pp 606-614.

11. M. Vittal, J.A. Borek, D.A. Marks, A.L. Boehman, The effect thermal barrier

coatings on diesel engine emissions, J. of Engg. For Gas Turbines and

Power, Transactions of ASME, Vol. 121, 1999, pp 218-225

12. T. Hejwowski, A. Weronski, thje effect of thermal barrier coating on diesel

engine performance, vacuum, Vol.65, 2002, pp 427-432.

13. Melvin Woods, Paul Glance, Advanced insulted titanium piston for adiabatic

engine, Transaction of SAE, sect.3, Part-2, 1990.

14. Prasad, Ravindra, Sameera. N.K, Investigation of heat transfer in oil cooled

piston with and without ceramic insulation on crown face, Int. Journal

Mechanical Science, Vol.31,no 10, 1989.

15. Kulakarni, Jagadeesh R, Ceramic against fuel consumption, Journal of

Institution of Engineers India, Vol. 66, 1985.

16. Poola, Nagesh B, Nagalingam B, Gopalakrishna K. V, Devices to improve the

performance of a conventional two stroke spark ignition engine, Conference

paper, Transactions of ASME, 1995.

17. M. Ashok kumar, P. Ramareddy, Effect of aluminum-Titaniate Coatings on

Piston Crown on Performance of CI engines, National conference on “State of

art technologies in mechanical engineering”, 2004

18. W.P. Dong, P.J. Sullivan, K.J. Stout, Comprehensive study of parameters for

characterizing 3D surface topography III: Parameters for characterizing

amplitude and some Functional properties and IV, Wear 178, 1994, pp 29-60.

19. T.W. Clyne, C.J. Humphreys, Improvements in plasma sprayed TBC for Use

in Advanced Gas Turbines, Department of Material Science and Metrology,

University of Cambridge, Cambridge CB2 3QZ.

20. Y. Kubo, Satrou Maezono, Pre-treatment on metal surface of plasma sprayed

with cathode spots of low pressure, Surf., Coat. And Technol., 190, 2005, pp

1168-1172.

21. O. Sarikaya, Effect of some Parameters on Micro-structure and Hardness of

alumina coatings prepared by the air plasma spraying process. Surf.,Coat, and

Technol. 190, 2005, pp 388-393.

22. Z. Liu, Crack free surface sealing of plasma sprayed ceramic coatings on

excimer laser, Applied Surface Science , 186, 2002, pp 135-139.

23. C. Batista, A. Portinha, Surface laser glazing of plasma sprayed thermal

barrier coatings, Applied Surface Science, 247, 2005, pp 313-319.

24. R.Krishnan, R. Keshavamurthy, C. Babu rao, Laser surface modification and

characterization of air plasma sprayed alumina coatings, Surf., Coat., Technol,

200,2006, pp 2791-2799.

25. A. Portinha, Charecterization of thermal barrier coatings with a gradient in

porosity, Surf., Coat., Technol,195, 2005, pp 245-251.

26. V.V Sobolev, J. Nutteng ,Int. Mater. Rev. 42(3), 1997 pp 117

27. M.A Moore, F.S King, Abrasive wear of brittle solids, Wear 60, 1980, pp 123-

140.

28. P.P.Psyllaki, M. Jendin, Microstructure and wear mechanism of thermal

sprayed alumina coatings, Material letters, 47, 2000, pp 77-82.