Availableonlineatwww.sciencedirect.com journal吖 ScienceDirect nuclear ELSEVIER Journal of Nuclear Materials 367-370(2007)1139-1143 materials www.elsevier.com/locate/jnucmat Coatings and joining for SiC and Sic-composites for nuclear energy systems C.H. Henager Jr. a.,Y. Shin a, Y. Blum b, L A Giannuzzi c B W. Kempshall d S.M. Schwarz d a Pacific Northwest National Laboratory, 902 Battelle Bled, MS P8-15, Richland, WA99352-0999, US.A SRI International Menlo Park. CA 94025. US. FEI Company, 5350 NE Dawson Creek Drive, Hillsboro, OR 97124, USA niversity of Central Florida and Nano Spectre, Inc, Orlando, FL 32826, USA Abstract atings and joining materials for SiC and Sic-based composites for nuclear energy systems are being developed using preceramic polymers filled with reactive and inert powders, and using solid-state reactions. Polymer-filled joints and coat ings start with a poly(hydridomethylsiloxane) precursor, such that mixtures of Al/AlO3/polymer form a hard oxide coat ing, coatings made with Al/SiC mixtures form a mixed oxide-carbide coating, while coatings made with SiC/polymer form a porous, hard carbide coating Joints made from such mixtures have shear strengths range from 15 to 50 MPa depending on the applied pressure and joint composition. The strongest joints were obtained using tape cast ribbons of Si/TiC pow ders such that a solid state displacement reaction at 1473 K and 1673 K using 30 MPa applied pressure resulted in shear trengths of 50 MPa, which exceeds the shear strength of SiC/SiC composite materials. However, the polymer joints are much easier to apply and could be considered for field repair Published by elsevier B.V. 1. Introducti of the fine-grained SiC fibers and of the fiber-matrix interphase material [2]. Further, joining of simple It is widely considered to be a weakness of Sic- shapes into more complex structures is also appar- based composites that they are not fully dense and ently required, particularly for fusion reactor first can, as yet, only be fabricated into simple shapes wall vessels that cannot possibly be made as a single that require development of attachment technolo- section [3]. Thus, a significant effort has gone into gies in order to achieve more complex configura- development and understanding of protective coat- tions. The implication of the lack of full density is ings and joining for SiC/SiC composites [1, 2, 4-12 that external coatings are required, both for herme- The Nano-powder infiltration and transient eutec- ticity considerations [1]and for corrosion protection toid(NITE) process, however, produces a SiC/SiC posite material with high densit Corresponding author. Tel +1 509 376 1442: fax: +1 509 376 ability, and has been used to demonstrate high-per 0418 formance hot-pressed joining [13-15]. The purpose E-mail address. chuck. henager @pnl gov (C.H. Henager Jr.). of this study is to help develop a wider range of 0022-3115/S see front matter Published by elsevier B v doi:10.1016 i-jnucmat2007.03.189
Coatings and joining for SiC and SiC-composites for nuclear energy systems C.H. Henager Jr. a,*, Y. Shin a , Y. Blum b , L.A. Giannuzzi c , B.W. Kempshall d , S.M. Schwarz d a Pacific Northwest National Laboratory, 902 Battelle Blvd., MS P8-15, Richland, WA 99352-0999, USA b SRI, International Menlo Park, CA 94025, USA c FEI Company, 5350 NE Dawson Creek Drive, Hillsboro, OR 97124, USA d University of Central Florida and NanoSpective, Inc., Orlando, FL 32826, USA Abstract Coatings and joining materials for SiC and SiC-based composites for nuclear energy systems are being developed using preceramic polymers filled with reactive and inert powders, and using solid-state reactions. Polymer-filled joints and coatings start with a poly(hydridomethylsiloxane) precursor, such that mixtures of Al/Al2O3/polymer form a hard oxide coating, coatings made with Al/SiC mixtures form a mixed oxide–carbide coating, while coatings made with SiC/polymer form a porous, hard carbide coating. Joints made from such mixtures have shear strengths range from 15 to 50 MPa depending on the applied pressure and joint composition. The strongest joints were obtained using tape cast ribbons of Si/TiC powders such that a solid state displacement reaction at 1473 K and 1673 K using 30 MPa applied pressure resulted in shear strengths of 50 MPa, which exceeds the shear strength of SiC/SiC composite materials. However, the polymer joints are much easier to apply and could be considered for field repair. Published by Elsevier B.V. 1. Introduction It is widely considered to be a weakness of SiCbased composites that they are not fully dense and can, as yet, only be fabricated into simple shapes that require development of attachment technologies in order to achieve more complex configurations. The implication of the lack of full density is that external coatings are required, both for hermeticity considerations [1] and for corrosion protection of the fine-grained SiC fibers and of the fiber–matrix interphase material [2]. Further, joining of simple shapes into more complex structures is also apparently required, particularly for fusion reactor firstwall vessels that cannot possibly be made as a single section [3]. Thus, a significant effort has gone into development and understanding of protective coatings and joining for SiC/SiC composites [1,2,4–12]. The Nano-powder infiltration and transient eutectoid (NITE) process, however, produces a SiC/SiC composite material with high density, low permeability, and has been used to demonstrate high-performance hot-pressed joining [13–15]. The purpose of this study is to help develop a wider range of 0022-3115/$ - see front matter Published by Elsevier B.V. doi:10.1016/j.jnucmat.2007.03.189 * Corresponding author. Tel.: +1 509 376 1442; fax: +1 509 376 0418. E-mail address: chuck.henager@pnl.gov (C.H. Henager Jr.). Journal of Nuclear Materials 367–370 (2007) 1139–1143 www.elsevier.com/locate/jnucmat
C.H. Henager Jr. et al Journal of Nuclear Materials 367-370 (2007)1139-114 coating and joining technologies for fusion. There is with approximate viscosities of less than 10 cP using as either a coating or joining technology for Sic/ Joining was accomplished by slurry application Sic composites and a diverse set of technologies using a dropper with a nominal weight applied may be advantageous at this stage of our efforts in during curing at 423 K in moist air. This was fol- design of fusion power plants. However, a diverse lowed by pyrolysis with a nominal pressure of about set already exists in the form of preceramic poly- 1 MPa in air at 1473 K. One joint was also processed mers,reaction bonding, glass-ceramic seals, and at 1073 K in nitrogen without any applied pressure brazing methods [3]. In this paper we present Coatings were also synthesized using the same slur tional coating and joining methods and technol ries by dip coating onto SiC/SiC composite coupons that have advantages, as well as disadvantages, as well as on 316 stainless steel coupons. Coatings compared to previously developed methods. were pyrolyzed at 1473K for SiC/SiC and at 1073 K for the 316 steel. Joint strengths were tested 2. Coating and joining methods in single-lap shear geometry at ambient temperature Some of the coated steel coupons were exposed up to 2.1. Polysiloxane preceramic polymers 1000 h at 1073 K in air to determine coating integrity and oxidation protection Coated coupons were sec Preceramic polymers, such as polycarbosilanes tioned and examined using an SEM for microstruc and polysiloxanes, with inert and reactive fillers are tural information. Both Hexaloy SiC and SiC/Sic used for SiC/SiC joining technologies [7, 16-18]and coupons were joined and tested in this study have performed adequately as strong joints. Polycar bosilane, which converts to SiC, requires high 2.2. Solid-state displacement reactions temperature processing and inert handling, while polysiloxanes, which convert to Si-O-C, can be Previous research at Pnnl on solid-state dis- pyrolyzed at lower temperatures and can be handled placement reactions demonstrated that the reaction in air. Joints made from such materials exhibit between TiC and Si produced an interwoven struc strengths that range from 5 to 30 MPa when tested in shear. a known difficulty with preceramic poly ture of Ti3 SiC2, TiSi2, and SiC, with the majority phases being the ternary Ti3SiC2 and SiC [24-27 mers is the mass loss, which can exceed 50%, on This reaction was used to make joints from tape cast conversion to a ceramic phase. A slightly different approach uses a linear chain of polyhydrido. powder mixtures of TiC and Si powders, which were methylsiloxane(PHMS)as a precursor to a highly 99.99% purity having average diameters less than 45 TiC.Si crosslinked polysiloxane, by applying a catalytic 200 um thick and were cut to shape and applied chemistry approach developed at SRI International, between either Hexaloy Sic coupons or CVI SiC that has the advantage of much lower mass loss on ceramic conversion compared to other systems [19 composite coupons. Joints were formed by heating in argon to 573 K at 5 K/min and holding for 2 h 23] and pyrolysis occurs at temperatures as low as for binder burnout with a nominal applie&? 10 K 873K ed by heating to 1473k or 1673K PHMS, which is a low molecular weight low vis- min and holding for I h at 30 MPa applied pressure cosity liquid, is catalytically cured in-situ after its a Joints were tested in shear using a double-notch application and converts on heating in inert envi- shear and sectioned for SEM examination ronments to a silicon oxycarbide phase but can be modified by side group additions to produce a more carbon-rich oxycarbide phase [23]. For the work 3. Results and discussion here, however, PHMS with no side group additions is used and filled with SiC, Al, and Al2O3 powders, 3.1.Joining singly and in combination. The Sic powders are 0.7 um average diameter pure SiC, the Al powders Polymer slurry joints between Hexaloy Sic cou- were in the form of flakes 1-2 um in size, and the ons made with PHMS filled with SiC. Al/Sic Al2O3 powders were submicron diameter. Powder loadings were in the range of 40-60% by volume I Hi-Nicalon Type-S fibers from GE Power Systems with a 2D and were processed in the form of liquid slurries 5-harness satin weave architecture
coating and joining technologies for fusion. There is no single technology that can be applied uniformly as either a coating or joining technology for SiC/ SiC composites and a diverse set of technologies may be advantageous at this stage of our efforts in design of fusion power plants. However, a diverse set already exists in the form of preceramic polymers, reaction bonding, glass–ceramic seals, and brazing methods [3]. In this paper we present additional coating and joining methods and technologies that have advantages, as well as disadvantages, compared to previously developed methods. 2. Coating and joining methods 2.1. Polysiloxane preceramic polymers Preceramic polymers, such as polycarbosilanes and polysiloxanes, with inert and reactive fillers are used for SiC/SiC joining technologies [7,16–18] and have performed adequately as strong joints. Polycarbosilane, which converts to SiC, requires hightemperature processing and inert handling, while polysiloxanes, which convert to Si–O–C, can be pyrolyzed at lower temperatures and can be handled in air. Joints made from such materials exhibit strengths that range from 5 to 30 MPa when tested in shear. A known difficulty with preceramic polymers is the mass loss, which can exceed 50%, on conversion to a ceramic phase. A slightly different approach uses a linear chain of polyhydridomethylsiloxane (PHMS) as a precursor to a highly crosslinked polysiloxane, by applying a catalytic chemistry approach developed at SRI International, that has the advantage of much lower mass loss on ceramic conversion compared to other systems [19– 23] and pyrolysis occurs at temperatures as low as 873 K. PHMS, which is a low molecular weight low viscosity liquid, is catalytically cured in-situ after its a application and converts on heating in inert environments to a silicon oxycarbide phase but can be modified by side group additions to produce a more carbon-rich oxycarbide phase [23]. For the work here, however, PHMS with no side group additions is used and filled with SiC, Al, and Al2O3 powders, singly and in combination. The SiC powders are 0.7 lm average diameter pure SiC, the Al powders were in the form of flakes 1–2 lm in size, and the Al2O3 powders were submicron diameter. Powder loadings were in the range of 40–60% by volume and were processed in the form of liquid slurries with approximate viscosities of less than 10 cP using cyclohexane as a solvent. Joining was accomplished by slurry application using a dropper with a nominal weight applied during curing at 423 K in moist air. This was followed by pyrolysis with a nominal pressure of about 1 MPa in air at 1473 K. One joint was also processed at 1073 K in nitrogen without any applied pressure. Coatings were also synthesized using the same slurries by dip coating onto SiC/SiC composite coupons, as well as on 316 stainless steel coupons. Coatings were pyrolyzed at 1473 K for SiC/SiC and at 1073 K for the 316 steel. Joint strengths were tested in single-lap shear geometry at ambient temperature. Some of the coated steel coupons were exposed up to 1000 h at 1073 K in air to determine coating integrity and oxidation protection. Coated coupons were sectioned and examined using an SEM for microstructural information. Both Hexaloy SiC and SiC/SiC coupons were joined and tested in this study. 2.2. Solid-state displacement reactions Previous research at PNNL on solid-state displacement reactions demonstrated that the reaction between TiC and Si produced an interwoven structure of Ti3SiC2, TiSi2, and SiC, with the majority phases being the ternary Ti3SiC2 and SiC [24–27]. This reaction was used to make joints from tape cast powder mixtures of TiC and Si powders, which were 99.99% purity having average diameters less than 45 lm with a TiC:Si ratio of 3:2. Tapes were about 200 lm thick and were cut to shape and applied between either Hexaloy SiC coupons or CVI SiC composite coupons.1 Joints were formed by heating in argon to 573 K at 5 K/min and holding for 2 h for binder burnout with a nominal applied pressure followed by heating to 1473 K or 1673 K at 10 K/ min and holding for 1 h at 30 MPa applied pressure. Joints were tested in shear using a double-notch shear and sectioned for SEM examination. 3. Results and discussion 3.1. Joining Polymer slurry joints between Hexaloy SiC coupons made with PHMS filled with SiC, Al/SiC, 1 Hi-Nicalon Type-S fibers from GE Power Systems with a 2D 5-harness satin weave architecture. 1140 C.H. Henager Jr. et al. / Journal of Nuclear Materials 367–370 (2007) 1139–1143
C.H. Henager Jr et al Journal of Nuclear Materials 367-370(2007)1139-1143 sure exhibited reasonable strengths pplied pres- creep strength and corrosion resistance depending nd Al/AlO3 at 1473 K using 1 MPa on the structure and amount of free carbon shear testing at ambient temperatures of 21 MPa, [28, 29]. The low strength of the joint processed at 14.5 MPa, and 7 MPa, respectively, as shown in 1073 K in nitrogen suggests that a small amount Fig. 1. SEM micrographs of a Sic-filled PHMs of pressure and higher temperatures are required Hexaloy joint processed at 1473K in air is shown for adequate bonding. in Fig. 2. These joints possess reasonable shear The solid-state reaction joints for Hexaloy Sic strength values and are thin and dense after only between TiC and Si resulted in high strength joints I MPa applied pressure. Compared to similar joint prepared by others, these have the distinction of being slightly stronger and easier to process. Poly carbosilane requires inert handling and higher con version temperatures; however, it does convert to Sic whereas this polymer converts to a silicon oxy- carbide, which may be a disadvantage in terms of 1473K Fig. 3. Comparisons of joint shear strengths for Sic-filled PhMS (single-lap) with solid-state reaction joints of TiC t Si to form Ti,SiC2/SiC joints(double-notch). Solid-state reaction joints are AUSiC SiC (No 30 MPa applied pressure Fig. I. Single-lap shear strength of PhMs j Hexaloy SiC coupons processed in air at 1473K using I MPa pressure or in nitrogen with no applied pressure at 1073K. SiC Ti3SiC Fig. 4. TEM micrograph of joint f hexal Fig. 2. SiC-filled PhMS joints in polished cross-sections showing using the TiC-Si solid-state joining The original SiC clean joint/coupon interfaces and good joint densities for surface is marked with the Hexaloy Sic coupons this interface into the Ti] SiC/SiC joint region
and Al/Al2O3 at 1473 K using 1 MPa applied pressure exhibited reasonable strengths in single-lap shear testing at ambient temperatures of 21 MPa, 14.5 MPa, and 7 MPa, respectively, as shown in Fig. 1. SEM micrographs of a SiC-filled PHMS Hexaloy joint processed at 1473 K in air is shown in Fig. 2. These joints possess reasonable shear strength values and are thin and dense after only 1 MPa applied pressure. Compared to similar joints prepared by others, these have the distinction of being slightly stronger and easier to process. Polycarbosilane requires inert handling and higher conversion temperatures; however, it does convert to SiC whereas this polymer converts to a silicon oxycarbide, which may be a disadvantage in terms of creep strength and corrosion resistance depending on the structure and amount of free carbon [28,29]. The low strength of the joint processed at 1073 K in nitrogen suggests that a small amount of pressure and higher temperatures are required for adequate bonding. The solid-state reaction joints for Hexaloy SiC between TiC and Si resulted in high strength joints, Fig. 1. Single-lap shear strength of PHMS joints between Hexaloy SiC coupons processed in air at 1473 K using 1 MPa pressure or in nitrogen with no applied pressure at 1073 K. Fig. 2. SiC-filled PHMS joints in polished cross-sections showing clean joint/coupon interfaces and good joint densities for Hexaloy SiC coupons. Fig. 3. Comparisons of joint shear strengths for SiC-filled PHMS (single-lap) with solid-state reaction joints of TiC + Si to form Ti3SiC2/SiC joints (double-notch). Solid-state reaction joints are significantly stronger when processed at high temperatures and 30 MPa applied pressure. Fig. 4. TEM micrograph of joint region of Hexaloy coupon using the TiC–Si solid-state joining method. The original SiC surface is marked with the arrows and epitaxy is observed across this interface into the Ti3SiC2/SiC joint region. C.H. Henager Jr. et al. / Journal of Nuclear Materials 367–370 (2007) 1139–1143 1141
1142 C.H. Henager Jr et al Journal of Nuclear Materials 367-370(2007)1139-114. cating very strong bonding. The reason for such strong bonding is that the Sic formed during the solid-state reaction between TiC and Si preferen- tially forms at the existing SiC interface, either the Hexaloy or SiC/SiC composite. This reaction formed Sic is epitaxial with the Hexaloy Sic as shown in Fig. 4. A further consideration is that Ti3SiC, and Sic are reduced-activation materials and there is some evidence of pseudoplasticity in the Ti3 Sic2 phase that might give these joints a mea- sure of fracture resistance that a pure Sic joint would lack. The SEM micrograph of a solid-state TiC-Si joint between SiC/SiC coupons(Hi-Nicalon Type-S fibers)is shown in Fig. 5. Apparent strong bonding at the joint-coupon interface can be seen in this micrograph although the joint does not pear to be fully dense. 20 um b 钱 2BkUx5,日885从m Fig. 5. SEM micrographs of polished cross-sections of TiC-Si solid-state joining of SiC/SiC composite coupons. This joint is not fully dense but exhibits strong bonding at the interface with shear strengths- in excess of 50 MPa, as shown in Fig. 3. Almost more importantly, this shear frac- ure was observed to include some of the Hexaloy Sic and was not restricted to the joint material ind Since the double- notch shear test involves some measure of stress concentration at the notches, it is reasonable to expect that Fig. 6. PHMS-based coatings pyrolyzed at 1073 K in air for 2 h these alues for the solid-state joints s materials including(a)Al/Al203 coatings on SiC/Sic mate of the actual strength. and (b) Al/SiC on SiC/Sic
with shear strengths2 in excess of 50 MPa, as shown in Fig. 3. Almost more importantly, this shear fracture was observed to include some of the Hexaloy SiC and was not restricted to the joint material indicating very strong bonding. The reason for such strong bonding is that the SiC formed during the solid-state reaction between TiC and Si preferentially forms at the existing SiC interface, either the Hexaloy or SiC/SiC composite. This reaction formed SiC is epitaxial with the Hexaloy SiC as shown in Fig. 4. A further consideration is that Ti3SiC2 and SiC are reduced-activation materials and there is some evidence of pseudoplasticity in the Ti3SiC2 phase that might give these joints a measure of fracture resistance that a pure SiC joint would lack. The SEM micrograph of a solid-state TiC–Si joint between SiC/SiC coupons (Hi-Nicalon Type-S fibers) is shown in Fig. 5. Apparent strong bonding at the joint–coupon interface can be seen in this micrograph although the joint does not appear to be fully dense. Fig. 5. SEM micrographs of polished cross-sections of TiC–Si solid-state joining of SiC/SiC composite coupons. This joint is not fully dense but exhibits strong bonding at the interface. Fig. 6. PHMS-based coatings pyrolyzed at 1073 K in air for 2 h on various materials including (a) Al/Al2O3 coatings on SiC/SiC and (b) Al/SiC on SiC/SiC. 2 Since the double-notch shear test involves some measure of stress concentration at the notches, it is reasonable to expect that these measure values for the solid-state joints are an underestimate of the actual strength. 1142 C.H. Henager Jr. et al. / Journal of Nuclear Materials 367–370 (2007) 1139–1143
C.H. Henager Jr et al / Journal of Nuclear Materials 367-370(2007)1139-1143 l143 3. 2. Coating microstructures Nishio, B. Riccardi, M.S. Tillack, Fusion Eng. Des. 55 2001)55 Polymer coatings are made with the same simple 4]S. Sharafat, N. Ghoniem, S. Zinkle, J. Nucl. Mater. 329-333 processing as for the polymer joints. The liquid (2004)1429 5L.L. Snead, T. Inoki, Y Katoh, T. Taguchi, R H. Jones, A slurry is prepared and the coating is applied using Kohyama, N. Igawa, Advances in Science and Technology dip-coating techniques. Pyrolysis is carried out in 33(10th International Ceramics Congress 2002, Part D)129 air, nitrogen, or argon at 973-1473K depending on the substrate. Fig. 6 shows coatings in polished 6J. Sha, A. Kohyama,Y. Katoh, Plasma Sci. Technol. 5(5) 2003)1965 cross-sections after pyrolysis on SiC/SiC coupons [7 C.A. Lewinsohn, M. Singh, C H. Henager Jr, Ceram. Trans. The coatings have varying degrees of porosities that 138(2003)201 are due in part to the mass loss during pyrolysis 8]Y. Katoh, A Kohyama, T Hinoki, L L. Snead, Fusion Sci. The Al/AlO3 coating is fairly dense but the Al/ Technol.44(2003)155 SiC coating is porous. Although such coatings have 9]RH. Jones, Ceramic Engineering and Science Proceedings yet to be studied under fusion relevant conditions it 24(2003)261 [OT Hino, T. Jinushi, Y. Hirohata, M. Hashiba, Y. Yamauchi is apparent that simple processing using PHMS Y Katoh, A Kohyama, Fusion Sci. Technol. 43(2003)184 filled with ceramic particles can be used to synthe- [11]M. Ferraris, P. Appendino, V. Casalegno, F. Smeacetto, M size protective coatings for SiC/SiC composites Salvo, Advances in Science and Technology 33(10th Inter. These coatings are compliant and slightly porous national Ceramics Congress 2002)(2003) but are strongly bonded to the ceramIc surface [12]B. Riccardi, C.A. Nannetti, T. Petrisor, M. Sacchetti, ind can act as thermal barriers. The processing is [13]K. Shimoda, N. Eiza, J.-S. Park, T. Hinoki, A. Kohyama,S extremely simple and robust. Kondo, Mater. Trans. 47(2006)1204 [14]T. Hinoki, A. Kohyama, Annales de Chimie: Science des 4. Conclusions Materiaux 30(2005)659. [5]T. Hino, E. Hayashishita, Y. Yamauchi, M. Hashiba, Y Hirohata, A. Kohyama, Fusion Eng. Des. 73(2005)51 New developments in preceramic polymers have [16]CA. Lewinsohn, R.H. Jones, P. Colombo, B. Riccardi, been introduced to show that simple joints and coat J.NucL. Mater.307-311(2002)1232 ings may be produced using simple materials and [17] C.A. Lewinsohn, R H. Jones, T. Nozawa, M. Kotani, Y. processing. Since fusion engineering is in its infancy Katoh, A. Kohyama, M. Singh, Ceramic Engineering and Science Proceedings 22(2001)621 and no single coating or joining technology is the [18]P Colombo, B Riccardi, A Donato, G. Scarinci, I. Nuc clear favorite at this point, new technologies should Mater.278(2000)12 continue to be developed to allow as much diversity [19]YD. Blum, D.B. MacQueen, Surface Coatings Intern in synthesis and processing as possible. This will tional, Part B: Coatings Transactions 84(2001)27. ensure that many choices are available as required [20J Y.D. Blum, H.P. Chen, D.B. MacQueen, S M.Johnson to meet the needs of fusion projects, such as test (1999)281 blanket modules or future uses of Sic-based materi- [21]Y D Blum, S M. Johnson, M I Gusman, Hydridosiloxanes als. Solid-state joints appear to be very strong and as precursors to ceramic products, U.S. Patent 5,635, 250 in comparison to reaction bonded joints, may have an advantage of reduced glassy phases or residual [22]SM. Johnson, Y D. Blum, C. Kanazawa, H.. Wu, Met. []Y D. Blum, D B MacQueen, H.-J. Kleebe, J. Eur. Ceram. Soc.25(2005)143 References 224]C. Toy, E. Savrun, C. Lewinsohn, C. Henager, Ceram. Trans.103(200056 UT. Hino, Y. Hirohata, Y. Yamauchi, M [25]R. Radhakrishnan, S. Bhaduri, C H. Henager Jr, JOM Y. Katoh. Y. Lee, T. Jinushi, M H. Yoshida, S. Sengoku, K [26] C H. Henager Jr,R H. Jones, Ceram. Trans. 77(1997)117. usama,K. Yamaguchi, T. Muroga, J. Nucl. Mater. 329- 27]R. Radhakrishnan, C H. Henager Jr, J.L. Brimhall, SB 333(2004)673 Bhaduri, Scripta Mater. 34(1996)1809 [2]BA Pint, K.L. More, H M. Meyer, J.R. DiStefano, Fusion [28]S Modena, G.D. Soraru,Y. Blum, R. Raj, J. Am. Ceram. Sci. Technol. 47(2005)851 Soc.88(2005)339 3]AR. Raffray, R. Jones, G. Aiello, M. Billone, L. Giancarli 29]F. Kolar, V. Machovic, J. Svitilova, L. Borecka, Mater. H. Golfier, A. Hasegawa, Y. Katoh, A. Kohyama, Chem.Phys.86(2004)88
3.2. Coating microstructures Polymer coatings are made with the same simple processing as for the polymer joints. The liquid slurry is prepared and the coating is applied using dip-coating techniques. Pyrolysis is carried out in air, nitrogen, or argon at 973–1473 K depending on the substrate. Fig. 6 shows coatings in polished cross-sections after pyrolysis on SiC/SiC coupons. The coatings have varying degrees of porosities that are due in part to the mass loss during pyrolysis. The Al/Al2O3 coating is fairly dense but the Al/ SiC coating is porous. Although such coatings have yet to be studied under fusion relevant conditions it is apparent that simple processing using PHMS filled with ceramic particles can be used to synthesize protective coatings for SiC/SiC composites. These coatings are compliant and slightly porous but are strongly bonded to the ceramic surface and can act as thermal barriers. The processing is extremely simple and robust. 4. Conclusions New developments in preceramic polymers have been introduced to show that simple joints and coatings may be produced using simple materials and processing. Since fusion engineering is in its infancy and no single coating or joining technology is the clear favorite at this point, new technologies should continue to be developed to allow as much diversity in synthesis and processing as possible. This will ensure that many choices are available as required to meet the needs of fusion projects, such as test blanket modules or future uses of SiC-based materials. Solid-state joints appear to be very strong and, in comparison to reaction bonded joints, may have an advantage of reduced glassy phases or residual Si. References [1] T. Hino, Y. Hirohata, Y. Yamauchi, M. Hashiba, A. Kohyama, Y. Katoh, Y. Lee, T. Jinushi, M. Akiba, K. Nakamura, H. Yoshida, S. Sengoku, K. Tsuzuki, Y. Kusama, K. Yamaguchi, T. Muroga, J. Nucl. Mater. 329– 333 (2004) 673. [2] B.A. Pint, K.L. More, H.M. Meyer, J.R. DiStefano, Fusion Sci. Technol. 47 (2005) 851. [3] A.R. Raffray, R. Jones, G. Aiello, M. Billone, L. Giancarli, H. Golfier, A. Hasegawa, Y. Katoh, A. Kohyama, Nishio, B. Riccardi, M.S. Tillack, Fusion Eng. Des. 55 (2001) 55. [4] S. Sharafat, N. Ghoniem, S. Zinkle, J. Nucl. Mater. 329–333 (2004) 1429. [5] L.L. Snead, T. Inoki, Y. Katoh, T. Taguchi, R.H. Jones, A. Kohyama, N. Igawa, Advances in Science and Technology 33 (10th International Ceramics Congress 2002, Part D) 129 (2003). [6] J. Sha, A. Kohyama, Y. Katoh, Plasma Sci. Technol. 5 (5) (2003) 1965. [7] C.A. Lewinsohn, M. Singh, C.H. Henager Jr., Ceram. Trans. 138 (2003) 201. [8] Y. Katoh, A. Kohyama, T. Hinoki, L.L. Snead, Fusion Sci. Technol. 44 (2003) 155. [9] R.H. Jones, Ceramic Engineering and Science Proceedings 24 (2003) 261. [10] T. Hino, T. Jinushi, Y. Hirohata, M. Hashiba, Y. Yamauchi, Y. Katoh, A. Kohyama, Fusion Sci. Technol. 43 (2003) 184. [11] M. Ferraris, P. Appendino, V. Casalegno, F. Smeacetto, M. Salvo, Advances in Science and Technology 33(10th International Ceramics Congress 2002) (2003). [12] B. Riccardi, C.A. Nannetti, T. Petrisor, M. Sacchetti, J. Nucl. Mater. 307–311 (2002) 1237. [13] K. Shimoda, N. Eiza, J.-S. Park, T. Hinoki, A. Kohyama, S. Kondo, Mater. Trans. 47 (2006) 1204. [14] T. Hinoki, A. Kohyama, Annales de Chimie: Science des Materiaux 30 (2005) 659. [15] T. Hino, E. Hayashishita, Y. Yamauchi, M. Hashiba, Y. Hirohata, A. Kohyama, Fusion Eng. Des. 73 (2005) 51. [16] C.A. Lewinsohn, R.H. Jones, P. Colombo, B. Riccardi, J. Nucl. Mater. 307–311 (2002) 1232. [17] C.A. Lewinsohn, R.H. Jones, T. Nozawa, M. Kotani, Y. Katoh, A. Kohyama, M. Singh, Ceramic Engineering and Science Proceedings 22 (2001) 621 . [18] P. Colombo, B. Riccardi, A. Donato, G. Scarinci, J. Nucl. Mater. 278 (2000) 127. [19] Y.D. Blum, D.B. MacQueen, Surface Coatings International, Part B: Coatings Transactions 84 (2001) 27. [20] Y.D. Blum, H.P. Chen, D.B. MacQueen, S.M. Johnson, Materials Research Society Symposium Proceedings 576 (1999) 281. [21] Y.D. Blum, S.M. Johnson, M.I. Gusman, Hydridosiloxanes as precursors to ceramic products, U.S. Patent 5,635,250, June 3, 1997. [22] S.M. Johnson, Y.D. Blum, C. Kanazawa, H.-J. Wu, Met. Mater. 4 (6) (1998) 1119. [23] Y.D. Blum, D.B. MacQueen, H.-J. Kleebe, J. Eur. Ceram. Soc. 25 (2005) 143. [24] C. Toy, E. Savrun, C. Lewinsohn, C. Henager, Ceram. Trans. 103 (2000) 561. [25] R. Radhakrishnan, S. Bhaduri, C.H. Henager Jr., JOM 49 (1997) 41. [26] C.H. Henager Jr., R.H. Jones, Ceram. Trans. 77 (1997) 117. [27] R. Radhakrishnan, C.H. Henager Jr., J.L. Brimhall, S.B. Bhaduri, Scripta Mater. 34 (1996) 1809. [28] S. Modena, G.D. Soraru, Y. Blum, R. Raj, J. Am. Ceram. Soc. 88 (2005) 339. [29] F. Kolar, V. Machovic, J. Svitilova, L. Borecka, Mater. Chem. Phys. 86 (2004) 88. C.H. Henager Jr. et al. / Journal of Nuclear Materials 367–370 (2007) 1139–1143 1143