# Introduction he ceramic coatings on metallic materials have shown significant improvements since 1970. For the aim of the thermal barrier coatings, thermal expansion, thermal conductivity, wear properties, creep and corrosion resistance are important properties. The flame spray and plasma spray techniques are the two main coating techniques used these days. The application of ceramic for thermal barrier coating in adiabatic engines started from 1980. First of all gas turbine wings were used in the area, and then piston, cylinder liner, valve, piston crown surface were used for ceramic coatings. The experimental bonding strength values of ceramic coatings given by some researchers [1][2][3][4] show clear changes. Literature data on the bonding strength of ceramic coatings demonstrated that the plasmasprayed ceramic coatings have a higher bonding strength than flame-sprayed coatings do [5]. Eichhorn F et al. [6] has shown that a bonding strength value of pure alumina was less than the bonding strength of stabilized alumina. The bonding strength of a ceramic coatingwith a bonding coating is higher than that of Authors ? ? : Mechanical Engineering Department, National Institute of Technology, Hamirpur (H.P.), India. e-mail: rajsharmanith@gmail.com without bonding coating. The work of Unger R H andGates et al. [7,8] shows that the adhesion strength between the substrate and the ceramic coating could be improved by a NiAl bonding coating. Few researchers have shown that within the coating materials zirconia ceramics as wear resistance material have been extensively considered for engineering applications [9][10][11]. Latest works expose that microstructure and mechanical properties, such as grain size [12][13][14][15][16], porosity [17], hardness [18,19], fracture toughness [20], have strong effect on abrasive sliding wear resistance of bulk ceramics and coatings under dry or lubrication circumstances. Due to reduction in the grain size of ceramics their mechanical properties would be improved [21,22], which is helpful in improving the abrasive sliding wear resistance of bulk ceramics and coatings [23][24][25]. # II. # Plasma Spraying Technique The plasma powder is getting through plasma gas and sprayed on substrate, this phenomenon is known to be plasma spraying technique. At plasma spray technique, the coating powder can be sent by a plasma gas. Between two electrodes plasma is formed and powder is deposited in plasma arc. The plasma gas is usually argon or nitrogen. At plasma spraying technique, when argon, hydrogen or nitrogen gases are used, oxidation problem is minimized. For this reason, plasma spraying techniques have found useful application. One of the advantages of plasma spraying is that it makes possible to coat with high melting point materials. # III. # Experimental Studies a) Thermal Torch Experiment (Flame Punching Experiment) In this experiment for application to certain area, thermal barrier coatings are exposed to flame. In this area, some deformation is observed and lower working temperature is required. Thermal torch experiment is applied to measure the strength of coating layer to hot flame. In the experiment work of some researchers [5][6][7] T # Global Journal of Researches in Engineering Volume XIII Issue X Version I 39 ( ) A Year flame is applied with a distance of 10mm using an oxyacetylene torch. Pressure of acetylene is kept 100 kPa. Heat is directly applied to sample and punching times are measured. The sample dimensions are chosen according to ASTM standard to be as 100x50x1.5 mm. # a) Thermal Shock Experiment There are many applications areas of thermal barrier coating and one of them is used in high temperature requirement area. In this area samples are exposed to thermal cycling. Thermal shock experiment is aimed to find the place in which the sample destroyed. The thermal shock experiment is applied according to ASTM C 385-58 standard. During the experiment, samples are heated at certain temperature and waited for uniform distribution of temperature and are put immediately into water to provide thermal shock. IV. # Results and Discussions a) Thermal Resistance In the work of Serdar et al. [26] the test results were evaluated on the basis of the time required for drilling a hole through the coated specimens. Results are shown in table 1. As it can be seen from table 2 ceramic coating greatly enhances the life of the complete composite structure. It can also be seen from table 1 that zirconia with NiAl bonding coating supplied the maximum performance (deforming in 47 s) and chromium-oxide with NiAl bonding coating illustrated the second performance (with 37 s) and finally alumina with NiAl bonding coating was deformed within 31 s giving the weakest performance. Figs. 1-4 show the view of deformed samples with/without bonding coating. During the flame tests on thermal barrier coatings resistance to high temperatures is observed as these ceramics extend the life of composite structure. The life of base materials definitely increases with the application of ceramic coating. b) Thermal Shock Properties Table 2 shows the test results of thermal shock experiment shown by Serdar et al. [26]. In this test zirconia coated samples deformed at 1040 oC after 37 s and this is the best result in the experiment. Then chromium-oxide coated specimens performed the second thermal shock resistance and they are deformed at 960 oC after 33 s, and finally the alumina coated samples are deformed at 920 oC in 31 s. After thermal shock experiment it can be seen that vertical cracks are initiated in all samples and the reason for the formation of vertical cracks can be explained by thermal shock due to high cooling rate of the tests. In alumina and zirconia coated samples, the cracks are formed in much less quantity compared to other coated samples [11,[27][28][29]. Thermal shock tests are applied to the coated specimens in order to observe their mechanical behaviour under the stresses due to thermal expansion mismatch between the coating and the substrate. It has been shown that coatings are resistance to rapid changes in temperature in spite of the difference in their thermal expansion coefficients. # Conclusions Thermal barrier coated samples are directly exposed to flame (for example combustion rooms in rocket and gas turbines). The view of flame application area shows significant deformation. For this reason, lower working temperature is chosen and figure of merit is decreased. There are many different usage areas of thermal barrier coatings. One of them is the high temperature area. The coating is exposed to thermal cycling. The time of cycling is lower in engine with piston. In literature, piston crown surface, cylinder cover and valve parts are coated with ceramics. Beside these, piston rings and cylinder liner are coated with ceramics. With the thermal shock and the thermal torch experiments, it is shown that the coated materials have higher resistance to high temperatures. Zirconia coating has the best properties in thermal shock and thermal punching experiments. With zirconia coating the figure of merit of engine part will be increased. 1![Figure 1 : Deformed Cr2O3 (Chromium-oxide) sample without bonding coating after flame torch experiment [26]](image-2.png "Figure 1 :") 2![Figure 2 : Deformed Cr2O3 (Chromium-oxide) sample with bonding coating after flame torch experiment[26] ](image-3.png "Figure 2 :") 3![Figure 3 : Deformed Al2O3 (Alumina) sample withoutbonding coating after flame torch experiment[26] ](image-4.png "Figure 3 :") 4![Figure 4 : Deformed Al2O3 (Alumina) sample with bonding coating after flame torch experiment[26] ](image-5.png "Figure 4 :") 1 3CoatingSubstrateDeformedDeformedmaterialstime (s)temperature( o C)WithZirconiabonding371040(ZrO 2 )coatingWithout351000bondingcoatingWithAluminabonding31920(Al 2 O 3 )coatingWithout20700bondingcoatingWithChromium-bonding33960oxidecoating(Cr 2 O 3 )Without21720bondingcoatingV. © 2013 Global Journals Inc. (US) . Strafford KN, Datta PK, Gray JS. Surface engineering practice processes, fundamentals and * AAmbroz KasparJZvaranie 1982 10 363 * AMatt?ng BDelventhal Metalloberflache 1966 20 424 * MDem?rc? 1994 Istanbul Marmara University M.Sc Thesis * Plasma-sprayed oxide ceramics on steel substrates MVural SZeytin AHUcisik Surf Coat Technol 97 1997 * Plasma Spray coating. Department of MaterialsEngineering CCBerndt 1985 Clayton, Victoria: Monash University * FE?chhorn JMetzler Metalloberflache 1968 22 225 * RHUnger Proceedings of the National Thermal SprayConference the National Thermal SprayConferenceOrlando, FL 1987 * WDGates AMD?az SajAqu?l?no Prosthetic Dent 69 12 1993 * Wear and friction characteristics of ion-implanted zirconia ceramics GBStachowiak GWStachowiak PEvans Wear 241 2000 * Unlubrication friction and wear behaviour of zirconia ceramics YSun BLi DYang TWang YSasaki KIShii Wear 215 1998 * Friction and wear of partially stabilized zirconia: basic science and practical applications RhjHannink MJMurray HGScott Wear 100 1984 * Vander varstPGTh, de With B. Grain-size dependence of sliding wear in tetragonal zirconia polycrystals YHe LWinnubst AJBurggraaf HVerweij J Am Ceram Soc 79 12 1996 * Effect of grain size on friction and sliding wear of oxide ceramics KHZumgahr WBundschuh BZimmerlin Wear 1993 * Abrasive Wear of tetragonal zirconia polycrystal ceramics DWang ZMao J Chin Ceram Soc 23 5 1995 * Effects of material properties and testing parameters on wear properties of fine-grain zirconia (TZP) CTYang WJWei Wear 242 2000 * Microstructural effects on the friction and wear of zirconia films in unlubricated sliding contact SCMoulzolf RJLad PJBlau Thin Solid Films 347 1999 * Influence of porosity on friction and wear of tetragonal zirconia polycrystal YHe LWinnubst AJBurggraaf HVerweij VanderVarstpgth J Am Ceram Soc 80 2 1997 de With B * WestSussex 1990 * Tribological properties of nanostructured and conventional WC-Co coatings deposited by plasma spraying YZhu KYukimura CDing PZhang Thin Solid Films 388 2001 * Influence of fracture toughness on the wear resistance of yttriadoped zirconium oxide TEFischer MPAnderson SJahanmir J Am Ceram Soc 72 2 1989 * Mechanical properties of ultra-fine grained zirconia ceramics GsamTheunissen JSBouma AjaWinnubst AJBurggraag J Mater Sci 27 14 1992 * Enhanced mechanical properties by grain boundary strengthening in ultra-fine grained TZP ceramics YJHe AJWinnubst CDSagel-Ransijn AJBurggraaf HVerweij J Eur Ceram Soc 16 6 1996 * Abrasive wearbehaviour of conventional and nanocomposite HVOF-sprayed WC-Co coatings DAStewart PHShipway DGMccartney Wear 1999 * Friction and wear behaviour of implanted AISI316LSS and comparison with a substrate HDogan FFindik OMorgul Mater Des 23 7 2002 * Comparative study of wear mechanism of surface treated AISI 316L stainless steel HDogan FFindik AOztarhan IndLubrTribol 55 2-3 2003 * An investigation of different ceramic coating thermal properties SSalman RKose LUrtekin FFindik Materials and Design 27 2006 * Stud ies of the correlation between wear behaviour and bonding strength in two types of ceramic coating SSalman Cizmeciog J Mater Sci 33 1998 * SSalman 1995 YildizTehnical University Ph.D Thesis * LUrtekin 2001 Kutahya Dumlupinar University M.Sc Thesis