Material design of ceramic coating by plasma spray method

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<ul><li><p>Fusion Engineering and Design 41 (1998) 143147</p><p>Material design of ceramic coating by plasma spray method</p><p>Masaru Nakamichi a,*, Takeshi Takabatake b, Hiroshi Kawamura a</p><p>a Japan Atomic Energy Research Institute, Oarai Research Establishment, 3607 Narita-cho, Oarai-machi, Higashi Ibaraki-gun,Ibaraki-ken 311-13, Japan</p><p>b Tocalo Company Limited, 4-13-4 Fukae Kita-machi, Higashi Nada-ku, Kobe-shi, Hyogo-ken 658, Japan</p><p>Abstract</p><p>In the ceramic coating on substrate, cracking and peeling occur due to the difference of thermal expansion betweensubstrate material and coating material. For evaluation of peeling property of plasma sprayed coating, it is demandedthat thermal properties of plasma sprayed coating are estimated in detail. In this study, the results of comparison ofthermal properties between bulk material and plasma sprayed material are investigated to design the ceramic coatingquantitatively. Thermal conductivity of plasma sprayed MgOAl2O3 is decreased by approximately 50% to that ofsintered MgOAl2O3. Thermal conductivity of plasma sprayed 410SS agreed well with the calculation results ofrelation between porosity and thermal conductivity of iron sintered material. Thermal expansions of atmosphericplasma sprayed MgOAl2O3 and bulk 410SS, respectively. Therefore, as to material design on ceramic coating, it wasmade clear that thermal conductivity is more important than thermal expansion. 1998 Elsevier Science S.A. Allrights reserved.</p><p>1. Introduction</p><p>In fusion reactor, ceramic coating on the sur-face of structural materials such as 316SS hasbeen considered for electrical insulator and tri-tium permeation barrier in fusion reactor [16].On the other hand, in general industrial fields,ceramic and metal coatings are useful as heatresisting coating and anti-corrosion coating. Inparticular, plasma spraying coating is used widely,because this method is able to apply variousmaterials to coating, in particular to thick coat-ing. In the ceramic coating on substrate, crackingand peeling occur due to the difference of thermal</p><p>expansion between substrate material and coatingmaterial. Therefore, for material design for ce-ramic coating, it is necessary to put an undercoat-ing between substrate and coating to prevent thecracking and peeling of coating by thermal stress.However, in the present situation, the quantitativematerial design in ceramic coating cannot be de-termined due to the lack of material data base ofceramic coating. For evaluation of peeling prop-erty of plasma sprayed coating, it is demandedthat thermal properties of plasma sprayed coatingare estimated in detail. Thermal conductivity andthermal expansion are the most importantparameters for evaluation of thermal stress [710]. From this point, the results of comparison ofthermal properties between bulk material andplasma sprayed material are reported to design</p><p>* Corresponding author. Tel.: 81 29 2648417; fax: 8129 2648480; e-mail: masaru@jmtr.oarai.jaeri.go.jp</p><p>0920-3796:98:$19.00 1998 Elsevier Science S.A. All rights reserved.</p><p>PII S0920-3796(98)00245-2</p></li><li><p>M. Nakamichi et al. : Fusion Engineering and Design 41 (1998) 143147144</p><p>Table 1Spraying conditions of MgOAl2O3</p><p>Spraying apparatus PLASMA-TECHNIK AG A-3000S</p><p>Particle size 1045 mm</p><p>Plasma gasesAr 6.7104 m3:s</p><p>2.2104 m3:sH2</p><p>Plasma current 630 A</p><p>Plasma voltage 74 V</p><p>Spray distance 120 mm</p><p>Table 2Spraying conditions of 410SS</p><p>Spraying apparatus PLASMA-TECHNIK AG A-2000V</p><p>Particle size 1045 mm</p><p>Plasma gasesAr 7.5104 m3:s</p><p>1.3104 m3:sH2</p><p>Plasma current 685 A</p><p>64 VPlasma voltage</p><p>275 mmSpray distance</p><p>Pressure chamber 5.9 kPa</p><p>the ceramic coating quantitatively. In this study,MgOAl2O3 was selected as a coating material.MgOAl2O3 is one of most promising coatingmaterials due to its high electrical resistivity. Asthe undercoating, 410SS was selected becausethermal expansion coefficient of 410SS is close tothat of MgOAl2O3.</p><p>2. Specimens and measurements</p><p>MgOAl2O3 specimens of plasma sprayed ma-terial by atmospheric plasma spray method andsintered material are used for measurement ofthermal conductivity and thermal expansion.410SS specimens of plasma sprayed material byvacuum plasma spray method and bulk materialare used for measurement of thermal conductivityand thermal expansion. The spraying conditionsof MgOAl2O3 and 410SS are shown in Tables 1and 2, respectively. The particle size ofMgOAl2O3 powder (MgOAl2O3: 99wt.%) and410SS (Fe12wt.% Cr) powder is from 10 to 45mm. The porosity of plasma sprayed MgO Al2O3and plasma sprayed 410SS is 11 and 9%, respec-tively. The size of each plasma sprayed specimen</p><p>was w10110 t2 mm. The three kinds of sin-tered MgOAl2O3 (MgOAl2O3: \99.9wt.%)were used. The porosity of sintered MgOAl2O3were 2, 5 and 12%. The MgOAl2O3 specimen ofthe porosity of 2% was fabricated by slip castmethod and the one of the porosity of 5 and 12%were fabricated by cold press method. The fabri-cation conditions of the three kinds of sinteredMgOAl2O3 are shown in Table 3. The size ofeach sintered MgOAl2O3 was w10110 t1 mm.The porosity of bulk material of 410SS (Fe12wt.% Cr) was 0%. The size of bulk material of410SS was w10110 t2 mm. The SEM photo-graphs of cross section of plasma sprayedMgOAl2O3 (porosity: 11%), sinteredMgOAl2O3 (porosity: 5%) and plasma sprayed410SS (porosity 9%) were shown in Fig. 1.</p><p>The thermal conductivity was measured by laserflash method. The laser flash thermal constantsanalyser TC7000 made by SINKU-RIKO, wasused for the measurement of thermal conductivity.The laser interferometry type thermal expansionmeter LIX-1 made by SINKU-RIKO, was fromroom temperature 973 K in 5103 Pa.</p><p>Table 3Fabrication conditions of sintered MgOAl2O3</p><p>Fabrication method Sintering temperature Sintering timePorosity</p><p>1800CSlip cast2% 7200 sCold press 1700C 7200 s5%Cold press 1650C10% 7200 s</p></li><li><p>M. Nakamichi et al. : Fusion Engineering and Design 41 (1998) 143147 145</p><p>Fig. 1. SEM photographs of cross section of materials.</p><p>Fig. 2. Thermal conductivity of MgOAl2O3 materials.</p><p>sintered MgOAl2O3. However, this rule was notapplied to plasma sprayed MgOAl2O3. The rea-son for this phenomena is considered to be thedifference of pores. The pores of sinteredMgOAl2O3 were distributed uniformly, but thepores in plasma sprayed MgOAl2O3 had thelayered structure (see Fig. 1).</p><p>The results of thermal conductivity measure-ment of 410SS materials was shown in Fig. 4.</p><p>The relation between porosity and thermal con-ductivity for 410SS materials is shown in Fig. 5.The distribution of pores in plasma sprayed410SS is similar to that of sintered material.Therefore, thermal conductivity of plasmasprayed 410SS agreed well with the calculationresults of relation between porosity and thermalconductivity of iron sintered material. The equa-tion of this relation reported by T. Nakamura etal. [11,12] is shown as follows.</p><p>3. Results and discussion of thermal conductivitymeasurement</p><p>The results of thermal conductivity measure-ment of MgOAl2O3 materials are shown in Fig.2.</p><p>Thermal conductivity of sintered MgOAl2O3(porosity: 12%) and atmospheric plasma sprayedMgOAl2O3 (porosity: 11%) at room temperatureare 8 and 4 W:m:K, respectively (see Fig. 2).Thermal conductivity of plasma sprayedMgOAl2O3 decreased by approximately 50%from that of sintered MgOAl2O3. The relationbetween porosity and thermal conductivity withtemperature MgOAl2O3 materials was shown inFig. 3. Thermal conductivity of sinteredMgOAl2O3 was in proportion to porosity of</p><p>Fig. 3. Relation between porosity and thermal conductivity ofMgOAl2O3 materials.</p></li><li><p>M. Nakamichi et al. : Fusion Engineering and Design 41 (1998) 143147146</p><p>Fig. 4. Thermal conductivity of 410SS materials.</p><p>Fig. 6. Thermal expansion of MgO Al2O3 materials.</p><p>similar to that of bulk 410SS (see Fig. 7).From these results, thermal expansions of at-</p><p>mospheric plasma sprayed MgOAl2O3 and vac-uum plasma sprayed 410SS are similar to that ofsintered MgOAl2O3 and bulk 410SS,respectively.</p><p>5. Conclusion</p><p>Thermal conductivity of plasma sprayedMgOAl2O3 is decreased by approximately 50%from that of sintered MgOAl2O3. The reason forthis phenomena is considered to be the differenceof distribution of pores in sintered MgOAl2O3and pores in plasma sprayed MgOAl2O3. On theother hand, the distribution of pores in plasmasprayed 410SS is similar to that of sintered mate-rial. Therefore, thermal conductivity of plasmasprayed 410SS agreed well with the calculationresults of relation between porosity and thermalconductivity of iron sintered material.</p><p>In the thermal shock test, MgOAl2O3 coatingon 316SS substrate with 410SS undercoating was</p><p>K:K01o P</p><p>where: K, Thermal conductivity of sintered mate-rial; K0, Thermal conductivity of bulk material; o,Constant (o2.12.2 for iron sintered material);and P, Porosity of sintered material.</p><p>4. Results and discussion of thermal expansionmeasurement</p><p>The results of thermal expansion measurementof MgOAl2O3 materials and 410SS materials areshown in Figs. 6 and 7, respectively.</p><p>From the results of thermal expansion measure-ment of MgOAl2O3 materials, it was obviousthat thermal expansion of sintered MgO Al2O3was not affected by the porosity of sinteredMgOAl2O3 (see Fig. 6). It was obvious thatthermal expansion of plasma sprayed 410SS was</p><p>Fig. 5. Relation between porosity and thermal conductivity of410SS materials. Fig. 7. Thermal expansion of 410SS materials.</p></li><li><p>M. Nakamichi et al. : Fusion Engineering and Design 41 (1998) 143147 147</p><p>Fig. 8. The temperature difference between surface side andback side with thermal flux.</p><p>coating, it was made clear that thermal conductiv-ity of sintered ceramics could not be used due tothe difference of distribution of pores, but thermalexpansion of bulk and sintered material could beused.</p><p>References</p><p>[1] M. Nakamichi, H. Kawamura, K. Miyajima, Y. Harada,M. Saito, Trial fabrication and preliminary characteriza-tion of Y2O3 film as electrical insulator in liquid metalblanket, Fusion Technol. 2 (1994) 1217.</p><p>[2] M. Nakamichi, H. Kawamura, R. Oyamada, Trial fabri-cation and preliminary characterization of electrical insu-lator for liquid metal system, JAERI-Tech 95-009, 1995.</p><p>[3] M. Nakamichi, H. Kawamura, R. Oyamada, K. Miya-jima, Y. Harada, Trial fabrication of Y2O3 coating on316SS, Therm. Spray. 2 (1995) 1027.</p><p>[4] M. Nakamichi, H. Kawamura, R. Oyamada, K. Miya-jima, Y. Harada, Effect of undercoating on properties ofY2O3, Therm. Spray. 2 (1995) 815.</p><p>[5] T. Terai, T. Yoneoka, H. Tanaka, A. Suzuki, S. Tanaka,M. Nakamichi, H. Kawamura, K. Miyajima, Y. Harada,Compatibility of yttria (Y2O3) with liquid lithium, J.Nucl. Mater. 233237 (1996) 1421.</p><p>[6] M. Nakamichi, H. Kawamura, K. Miyajima, Y. Harada,R. Oyamada, Trial fabrication and preliminary character-ization of MgOAl2O3 coating, J. Nucl. Mater. 233237(1996) 14271430.</p><p>[7] K. Tani, K. Miyajima, Y. Harada, H. Nakahira, Thermaland elastic anistropy of thermally sprayed coatings,Mater. Trans. Jim. 33 (6) (1992) 618.</p><p>[8] R. Bandt, Thermal diffusivity measurements on plasma-sprayed CaO-stabilized ZrO2, High Temp. High Pressures13 (1976) 79.</p><p>[9] J.L. Weeks, R.L. Seifert, Apparatus for the measurementof the thermal conductivity of solids, Rev. Sci. Instrum.24 (11) (1953) 1054.</p><p>[10] R. Taylor, An investigation of the heat pulse method formeasuring thermal diffusivity, Br. J. Appl. Phys. 16 (1965)509.</p><p>[11] T. Nakamura, Ceramics and Heat, Gihode, 3 (1985).[12] W.D. Kingery, J. Francl, R.L. Coble, T. Vasilos, Thermal</p><p>conductivity: X, Data for several pure oxide materialscorrected to zero porosity, J. Am. Ceram. Soc. 37 (2)(1954) 107.</p><p>.</p><p>sound 30 times at 700C [6]. Thermal shock testwas carried out by water quenching from 500,600, 700 and 800C. The peeling of MgOAl2O3coating occurred at temperatures above 700C. Asthe preliminary evaluation of the peeling ofMgOAl2O3 coating, the difference of tempera-ture between surface side and back side withthermal flux was calculated (see Fig. 8). The re-sults of the preliminary evaluation, that theMgOAl2O3 coating was 200 mm thickness wassound at 2 MW:m2 thermal flux.</p><p>From these results, thermal expansions of at-mospheric plasma sprayed MgOAl2O3 and vac-uum plasma sprayed 410SS are similar to that ofsintered MgOAl2O3 and bulk 410SS,respectively.</p><p>Therefore, as to material design of ceramic</p></li></ul>

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