Availableonlineatwww.sciencedirect.com Part B: engineering ELSEVIER Composites: Part B 37(2006)509-514 www.elsevier.com/locate/compositesb Oxide laminated composites with aluminum phosphate(AlPO4)and alumina platelets as crack deflecting materials Dong-Kyu Kim, Waltraud M. Riven Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, 1304 w. Green Street, Urbana, IL 61801, USA Received 5 February 2005: received in revised form 14 September 2005: accepted 15 September 2005 Available online 3 April 2006 Abstract Oxide-oxide laminated composites with aluminum phosphate(AlPO4)and alumina platelets as crack deflecting interphases were developed the tape casting method. Dense bodies of Al2O3, mullite, 50 vol% Al2O3 50 vol% YAG in situ composite, and 3Y-TZP were sintered and characterized. Tape casting formulations for different oxides with solid contents of 25.1 and 30 vol%, respectively, were developed. XRD indicated compatibility between alumina, mullite, zirconia and AlPO4 Laminated, matrix-interphase composite systems consisting of AlO3- AlPO4, mullite-AlPO4, 50 vol% Al,O3 50 vol% YAG in situ composite-AlPO4, and 50 vol% Al2O3 50 vol% YAG in situ composite-alumina platelets were made. The 50 vol% Al2O3 50 vol% YAG in situ matrix-alumina platelet composite showed quasi-elastic load-displacement behavior under the conditions of fabrication, and had a 3-point bending strength and work of fracture of 188+8 MPa and 0.65+0.02 kJ/m respectively. The 3Y-TZP-AlPO4 laminated composite could not be made because of delamination due to thermal expansion mismatch. C 2006 Elsevier Ltd. All rights reserved Keywords: Laminated composites; Aluminum phosphate; Alumina platelets; Tape casting: Bending strength 1. Introduction kinds of AlO3AlO3-ZrO2 laminates, and measured their mechanical properties in 3-point bending, obtaining 335 To overcome the brittleness and increase the toughness of 560 MPa strengths and fracture toughness of 4.6-8.0 MPa m"2 ceramics, laminated composites have been made. Laminated Morgan et al. [9, 34] suggested that the monazite (LapO4)- ceramic composites have been fabricated by tape casting [1, 2, alumina interface was weak enough to produce interfacial slip casting [3, 4, electrophoretic deposition [5,6], die debonding when a crack approached the interface, and that this pressing [7], sequential centrifuging [8, 9), rolling [10, 11], weak interface was maintained after 200 h at 1600"C Mawdsley and co-extrusion [12]. Some laminated, ceramic composite et al. [ 16] fabricated alumina/monazite laminates consisting of systems reported in the literature are AlO3/ZrO2[13, 14], 44-54 alternating layers of alumina and monazite after hot Al2O,LaPO4 [15-21], YPO4/Y3Al5O12[22], TiO /MgSiO, pressing at 1400"C for 1-1.5 h under a pressure of 30 MPa. The Al2O/ Al2TiO5 [24, Al,O,/MoSi2+Mo, Bs[25], Al,O/ thicknesses of the alumina and monazite layers after hot-pressing AL2O3 platelets [26], Al20 /fluoromica [27 Al2O,/mullite of the laminates were 150 and 125 um, respectively. Their 4-point [28], SiC [29], SiC/C [10, 11], Si3N4 [30], and Si3N /bn bend strengths ranged between 172.9 and 252.5 MPa.The laminated composites had works of fracture in the range of 0.08- Crack deflection in AlO /Zr02 laminated composites is 0.6 kJ/m". Liu et al. [31] hot-pressed SiN//BN laminates at attributed to residual stress at the interface [33]. Sarkar et al. [51 1750"C/1.5 h under a pressure of 30 MPa. Their average bend fabricated 80 alternating layers of alumina and zirconia of strength and work of fracture were 430 MPa and 6.5kJ/m2 1.5 mm total thickness by electrophoretic deposition. The respectively. Clegg et al. [10] produced SiC/graphite laminated thicknesses of the densified alumina and zirconia layers were 2 composites by sintering at 2040"C for 30 min in an argon and 12 um, respectively. Chartier et al. [13] made five different atmosphere. They reported that the composites had an average bend strength of 633 MPa and works of fracture in the range of 4.66.7kJm orresponding author. +1 217 333 5258: fax: +1 217 333 2736 In this study, oxide/oxide laminated composite systems E-mail address: kriven@uiuc.edu(W.M. Riven) were fabricated by the tape casting method. Tape casting 1359-8368/S- see front matter 2006 Elsevier Ltd. All rights reserved. formulations for different oxides were developed. Alumina, doi: 10. 1016/ mullite. zirconia and a 50 vol%o alumina. 50 vol% YAG in situ
Oxide laminated composites with aluminum phosphate (AlPO4) and alumina platelets as crack deflecting materials Dong-Kyu Kim, Waltraud M. Kriven * Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, 1304 W. Green Street, Urbana, IL 61801, USA Received 5 February 2005; received in revised form 14 September 2005; accepted 15 September 2005 Available online 3 April 2006 Abstract Oxide–oxide laminated composites with aluminum phosphate (AlPO4) and alumina platelets as crack deflecting interphases were developed by the tape casting method. Dense bodies of Al2O3, mullite, 50 vol% Al2O3$50 vol% YAG in situ composite, and 3Y-TZP were sintered and characterized. Tape casting formulations for different oxides with solid contents of 25.1 and 30 vol%, respectively, were developed. XRD indicated compatibility between alumina, mullite, zirconia and AlPO4. Laminated, matrix-interphase composite systems consisting of Al2O3– AlPO4, mullite-AlPO4, 50 vol% Al2O3$50 vol% YAG in situ composite-AlPO4, and 50 vol% Al2O3$50 vol% YAG in situ composite-alumina platelets were made. The 50 vol% Al2O3$50 vol% YAG in situ matrix-alumina platelet composite showed ‘quasi-elastic’ load–displacement behavior under the conditions of fabrication, and had a 3-point bending strength and work of fracture of 188G8 MPa and 0.65G0.02 kJ/m2 , respectively. The 3Y-TZP–AlPO4 laminated composite could not be made because of delamination due to thermal expansion mismatch. q 2006 Elsevier Ltd. All rights reserved. Keywords: Laminated composites; Aluminum phosphate; Alumina platelets; Tape casting; Bending strength 1. Introduction To overcome the brittleness and increase the toughness of ceramics, laminated composites have been made. Laminated ceramic composites have been fabricated by tape casting [1,2], slip casting [3,4], electrophoretic deposition [5,6], die pressing [7], sequential centrifuging [8,9], rolling [10,11], and co-extrusion [12]. Some laminated, ceramic composite systems reported in the literature are Al2O3/ZrO2 [13,14], Al2O3/LaPO4 [15–21], YPO4/Y3Al5O12 [22], TiO2/MgSiO3 [23], Al2O3/Al2TiO5 [24], Al2O3/MoSi2CMo2B5 [25], Al2O3/ Al2O3 platelets [26], Al2O3/fluoromica [27], Al2O3/mullite [28], SiC [29], SiC/C [10,11], Si3N4 [30], and Si3N4/BN [31,32], etc. Crack deflection in Al2O3/ZrO2 laminated composites is attributed to residual stress at the interface [33]. Sarkar et al. [5] fabricated 80 alternating layers of alumina and zirconia of w1.5 mm total thickness by electrophoretic deposition. The thicknesses of the densified alumina and zirconia layers were 2 and 12 mm, respectively. Chartier et al. [13] made five different kinds of Al2O3/Al2O3–ZrO2 laminates, and measured their mechanical properties in 3-point bending, obtaining 335– 560 MPa strengths and fracture toughness of 4.6–8.0 MPa m1/2. Morgan et al. [9,34] suggested that the monazite (LaPO4)– alumina interface was weak enough to produce interfacial debonding when a crack approached the interface, and that this weak interface was maintained after 200 h at 1600 8C. Mawdsley et al. [16] fabricated alumina/monazite laminates consisting of 44–54 alternating layers of alumina and monazite after hotpressing at 1400 8C for 1–1.5 h under a pressure of 30 MPa. The thicknesses of the alumina and monazite layers after hot-pressing ofthelaminates were 150 and 125 mm, respectively. Their 4-point bend strengths ranged between 172.9 and 252.5 MPa. The laminated composites had works of fracture in the range of 0.08– 0.6 kJ/m2 . Liu et al. [31] hot-pressed Si3N4/BN laminates at 1750 8C/1.5 h under a pressure of 30 MPa. Their average bend strength and work of fracture were 430 MPa and 6.5 kJ/m2 , respectively. Clegg et al. [10] produced SiC/graphite laminated composites by sintering at 2040 8C for 30 min in an argon atmosphere. They reported that the composites had an average bend strength of 633 MPa and works of fracture in the range of 4.6–6.7 kJ/m2 . In this study, oxide/oxide laminated composite systems were fabricated by the tape casting method. Tape casting formulations for different oxides were developed. Alumina, mullite, zirconia, and a 50 vol% alumina$50 vol% YAG in situ Composites: Part B 37 (2006) 509–514 www.elsevier.com/locate/compositesb 1359-8368/$ - see front matter q 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.compositesb.2006.02.003 * Corresponding author. C1 217 333 5258; fax: C1 217 333 2736. E-mail address: kriven@uiuc.edu (W.M. Kriven)
D-K. Kim, W.M. Kriven / Composites: Part B 37(2006)509-514 composite were fabricated as strong matrix phases. Aluminum Solvent phosphate(AlPO4) and alumina platelets were investigated as temperature mechanical properties of the laminated composites were characterized and evaluated for each of the laminated Solvent+ plasticizer 2. Experimental procedures Binde (24h ball milling) Commercial alumina(Alcoa, A16 SG), mullite(Kyoritsu KM 101), zirconia(Tosoh, 3Y-TZP), and alumina platelet (Atochem, Pierre-Benite, France, 5-10 um) powders were used. Aluminum phosphate and a 50 vol% alumina- 50 vol% Tape casting YAG in situ composite powder were synthesized by a steric entra apment synthesis method [35-46]. To synthesize AlPO4 aluminum nitrate nonahydrate [Al(NO3)3 9H2O, Aldrich Chemical Inc, 98+% purity] and ammonium phosphate Laminating dibasic compound [(NH4)2. HPO4. Fisher Scientific] were used as Al and P sources, respectively. Appropriate amounts of aluminum nitrate nonahydrate and yttrium nitrate hexahy drate [Y(NO3)3 6H2O, Aldrich Chemical Inc,99.9% purity ere mixed as Al+and Y to make a 50 vol% Binder removal alumina. 50 vol% YAG in situ composite matrix phase. The nitrates were first dissolved in distilled water. After 30 min of 5 wt%o Pva solutio followed by another 50 min of mixing. The solution was then CIP and Sintering heated at 200C and then 400C to remove the water. The partially dehydrated cake was dried at 150C overnight ground in a mortar and pestle, and finally calcined. Fig 1 Schematic flow chart for making oxide-oxide laminated composites by The solvent for the tape cast laminates was a mixture of tape casting 60 wt% ethanol(AAPER ALCOL and Chemical, ethyl alcohol USP)and 40 wt% methyl ethyl ketone(99.8% purity, Fisher Scientific, Fair Lawn, NJ). Phosphate ester hos PS-21A Table 1 The tape casting formulations used for the different ceramic material Solvent asticizer Comments (PVG) Eth(60%)MEK(40%) Mullite 6 5.7 Al,O3 Delamina tion after removal 50%Al2O3 5.7 50%6YAG in situ composit 3Y-TZP 5 1.3×2 5.7 30% sol- ent→30% tion and too olvent(1st high vis. all milling) 576 5.7 30%o solver Too Al]O3 platelets 30 576 8.6 300% sol- Difficult to vent→2h problem Note: All ingredients are in vol%, Eth, ethanol (Ethyl Alcol USP, AAPER ALCOL and chemical): MEK, methyl ethyl ketone (99.8%, Fisher Scientific); PS phosphate ester(Emphos PS-21A, Witco): PVB, polyvinylbutyral( Butvar B90, Solutia): PG, polyethyleneglycol (300NF, FCC Grade, Union Carbide): DP, dibutylphthalate(99%o, Aldrich Chemical)
composite were fabricated as strong matrix phases. Aluminum phosphate (AlPO4) and alumina platelets were investigated as crack deflecting interphases. The microstructure and room temperature mechanical properties of the laminated composites were characterized and evaluated for each of the laminated systems fabricated. 2. Experimental procedures Commercial alumina (Alcoa, A16 SG), mullite (Kyoritsu, KM 101), zirconia (Tosoh, 3Y-TZP), and alumina platelet (Atochem, Pierre-Benite, France, 5–10 mm) powders were used. Aluminum phosphate and a 50 vol% alumina$50 vol% YAG in situ composite powder were synthesized by a steric entrapment synthesis method [35–46]. To synthesize AlPO4, aluminum nitrate nonahydrate [Al(NO3)3$9H2O, Aldrich Chemical Inc., 98C% purity] and ammonium phosphate dibasic compound [(NH4)2$HPO4, Fisher Scientific] were used as Al and P sources, respectively. Appropriate amounts of aluminum nitrate nonahydrate and yttrium nitrate hexahydrate [Y(NO3)3$6H2O, Aldrich Chemical Inc., 99.9% purity] were mixed as Al3C and Y3C sources, to make a 50 vol% alumina$50 vol% YAG in situ composite matrix phase. The nitrates were first dissolved in distilled water. After 30 min of mixing, 5 wt% PVA solution was added to the solution, followed by another 50 min of mixing. The solution was then heated at 200 8C and then 400 8C to remove the water. The partially dehydrated cake was dried at 150 8C overnight, ground in a mortar and pestle, and finally calcined. The solvent for the tape cast laminates was a mixture of 60 wt% ethanol (AAPER ALCOL and Chemical, ethyl alcohol USP) and 40 wt% methyl ethyl ketone (99.8% purity, Fisher Scientific, Fair Lawn, NJ). Phosphate ester (Emphos PS-21A, Fig. 1. Schematic flow chart for making oxide–oxide laminated composites by tape casting. Table 1 The tape casting formulations used for the different ceramic materials Powder Solvent Dispersant (PS) Binder (PVG) Plasticizer Extra additions Comments Eth (60%) MEK (40%) PG DP Mullite 25.1 57.6 1.3 5.7 4.7 5.6 – – Al2O3 25.1 57.6 1.3 3.7 5.6 6.7 – Delamination after binder removal 50%Al2O3– 50%YAG in situ composite 25.1 57.6 1.3 5.7 4.7 5.6 – – 3Y-TZP 25.1 57.6 1.3!2 5.7 4.7 5.6 30% solvent/30% solvent (1st ball milling) Agglomeration and too high viscosity AlPO4 25.1 57.6 1.3 5.7 4.7 5.6 30% solvent Too highviscosity Al2O3 platelets 30 57.6 1.3 8.6 1.0 1.5 300% solvent/2 h evaporation Difficult to form and processing problem Note: All ingredients are in vol%, Eth, ethanol (Ethyl Alcol USP, AAPER ALCOL and chemical); MEK, methyl ethyl ketone (99.8%, Fisher Scientific); PS, phosphate ester (Emphos PS-21A, Witco); PVB, polyvinylbutyral (Butvar B90, Solutia); PG, polyethyleneglycol (300NF, FCC Grade, Union Carbide); DP, dibutylphthalate (99%, Aldrich Chemical). 510 D.-K. Kim, W.M. Kriven / Composites: Part B 37 (2006) 509–514
D.-K. Kim, W.M. Kriven/ Composites: Part B 37(2006)509-514 511 paper. The work of fracture of each sample was obtained from the calculation of the area under the load-displacement curve 3. Results and discussion Table I summarizes the tape cast mixing formulations for the different oxides. The amount of powder was 25.1 vol% except for the alumina platelets, in which case 30 vol% of powder was used. For the alumina matrix, a lower amount of binder of 3.7 vol% and higher amounts of plasticizers, i.e 5.6 vol% of polyethylene glycol and 6.7 vol% of dibutyl pthalate, were used, because of delamination after binder removal For the 3Y-TZP matrix. 30 vol% excess solvent was Fig2 SEM micrograph of the 5-10 um alumina platelets having thickness of added, before and after the first ball milling, respectively, to lower the viscosity. The viscosity of the AlPO4 formulation was lowered by adding 30 vol% excess solvent before the first Witco Chemicals, Houston, TX)was used as a dispersant. The ball milling. To prevent possible change of their shape by binder was polyvinyl butyral( Butvar B90, Solutia Chemicals, breaking during mixing, alumina platelets were mixed with Louis,MS). Dibutyl phthalate(99% purity, Aldrich polymers by stirring without balls. The alumina platelets Chemical Inc, Milwaukee, wI) and polyethylene glycol 300 vol excess solvent, and dispersant were mixed by stirring 300NF, FCC grade, Union Carbide, Danbury, CT) were for 12 h. Another 12 h mixing was carried out afte er adding the used as plasticizers. A conventional tape casting machine with plasticizers and binder into solution. The excess solvent was double doctor blades was used. The first doctor blade openings evaporated before tape casting for the strong matrix materials and crack deflecting materials The morphology of the alumina platelets is seen in the SEM were 600 and 75 um, respectively. The second doctor blade micrograph of Fig. 2. TI hey had a hexagonal platelet shape, an openings were 1200 and 150 um, respectively. The speed of approximate thickness of I um, and size of 5-10 um. The XR casting was I cm/s. The procedures for making laminated results indicated compatibility between the oxide matrix opposites are shown in the flow chart of Fig. 1. De-airing was materials and AlPO4, and are schematically summarized in ig. 3. The mixtures of Al,O3, mullite, 50 vol% alumina. 50 speed. The laminated composite was thermo-compressed into a vol% YAG in situ composite, 3Y-TZP and AlPOA were 80C. The binder removal was achieved by increasing the 1650C/10 h, and 1550C/I h, respectively. The aluminum temperature from room temperature to 150C at a ramp rate of phosphate was compatible with alumina, mullite, and zirconia 1C/min, then from 150 to 600C at a ramp rate of 0.1C/min, However, AlPO4 was not compatible with the 50 vol% and finally by maintaining the sample at 600C for 2 h. Cold alumina. 50 vol% YAG in situ composite matrix. AlPO4 isostatic pressing ( CIP) was carried out at 413.7 MPa. The reacted with YAG in the composite, and formed yttrium sintering conditions differed depending on the particular phosphate (YPO4) materials The bulk density of sintered pellets was measured by Archimedes method(ASTM C373). To study the chemical bility between oxide matrix materials Rigaku X-ray diffractometer (Model D-Max automated diffractometer, Rigaku/USA, Danvers, MA)was used. Two powders were mixed by 24 h ball milling, sintered, and 1600c/0h analyzed for any co-existing phases by XRD. The microstruc- L"""" tures of the laminated composites were studied by scannin 1650c/0h electron microscopy(SEM, Model S-530, Hitachi, Osaka, Japan). A screw-driven universal testing machine (Model 人xs 4502, Instron Corp, Canton, MA)was used to measure flexural 1550c/h strengths in 3-point bend testing. The cross-head speed was 0. 1 mm/min, the supporting span was 30 mm, and the specimen sIze was3mm(H)×4mm(W)×40mm①L).The 2 Theta flexural strength and work of fracture data were determined by Fig 3. X-ray diffraction profiles indicating the compatibility between the four testing 3-5 samples. The final surface polishing of specimens oxide matrix materials and AIPO4(temperature/time represents the sintering for bend testing were conducted by 600 grit SiC polishing condition)
Witco Chemicals, Houston, TX) was used as a dispersant. The binder was polyvinyl butyral (Butvar B90, Solutia Chemicals, St Louis, MS). Dibutyl phthalate (99% purity, Aldrich Chemical Inc., Milwaukee, WI) and polyethylene glycol (300NF, FCC grade, Union Carbide, Danbury, CT) were used as plasticizers. A conventional tape casting machine with double doctor blades was used. The first doctor blade openings for the strong matrix materials and crack deflecting materials were 600 and 75 mm, respectively. The second doctor blade openings were 1200 and 150 mm, respectively. The speed of casting was 1 cm/s. The procedures for making laminated composites are shown in the flow chart of Fig. 1. De-airing was carried out by rotating a ball-free suspension at a very slow speed. The laminated composite was thermo-compressed into a rectangular pellet at 34.5 MPa after being maintained for 1 h at 80 8C. The binder removal was achieved by increasing the temperature from room temperature to 150 8C at a ramp rate of 1 8C/min, then from 150 to 600 8C at a ramp rate of 0.1 8C/min, and finally by maintaining the sample at 600 8C for 2 h. Cold isostatic pressing (CIP) was carried out at 413.7 MPa. The sintering conditions differed depending on the particular materials. The bulk density of sintered pellets was measured by Archimedes’ method (ASTM C373). To study the chemical compatibility between oxide matrix materials and AlPO4, a Rigaku X-ray diffractometer (Model D-Max automated diffractometer, Rigaku/USA, Danvers, MA) was used. Two powders were mixed by 24 h ball milling, sintered, and analyzed for any co-existing phases by XRD. The microstructures of the laminated composites were studied by scanning electron microscopy (SEM, Model S-530, Hitachi, Osaka, Japan). A screw-driven universal testing machine (Model 4502, Instron Corp., Canton, MA) was used to measure flexural strengths in 3-point bend testing. The cross-head speed was 0.1 mm/min, the supporting span was 30 mm, and the specimen size was 3 mm (H)!4 mm (W)!40 mm (L). The flexural strength and work of fracture data were determined by testing 3–5 samples. The final surface polishing of specimens for bend testing were conducted by 600 grit SiC polishing paper. The work of fracture of each sample was obtained from the calculation of the area under the load–displacement curve from bend testing. 3. Results and discussion Table 1 summarizes the tape cast mixing formulations for the different oxides. The amount of powder was 25.1 vol%, except for the alumina platelets, in which case 30 vol% of powder was used. For the alumina matrix, a lower amount of binder of 3.7 vol% and higher amounts of plasticizers, i.e. 5.6 vol% of polyethylene glycol and 6.7 vol% of dibutyl pthalate, were used, because of delamination after binder removal. For the 3Y-TZP matrix, 30 vol% excess solvent was added, before and after the first ball milling, respectively, to lower the viscosity. The viscosity of the AlPO4 formulation was lowered by adding 30 vol% excess solvent before the first ball milling. To prevent possible change of their shape by breaking during mixing, alumina platelets were mixed with polymers by stirring without balls. The alumina platelets, 300 vol% excess solvent, and dispersant were mixed by stirring for 12 h. Another 12 h mixing was carried out after adding the plasticizers and binder into solution. The excess solvent was evaporated before tape casting. The morphology of the alumina platelets is seen in the SEM micrograph of Fig. 2. They had a hexagonal platelet shape, an approximate thickness of 1 mm, and size of 5–10 mm. The XRD results indicated compatibility between the oxide matrix materials and AlPO4, and are schematically summarized in Fig. 3. The mixtures of Al2O3, mullite, 50 vol% alumina$50 - vol% YAG in situ composite, 3Y-TZP and AlPO4 were sintered under the conditions of 1600 8C/3 h, 1600 8C/10 h, 1650 8C/10 h, and 1550 8C/1 h, respectively. The aluminum phosphate was compatible with alumina, mullite, and zirconia. However, AlPO4 was not compatible with the 50 vol% alumina$50 vol% YAG in situ composite matrix. AlPO4 reacted with YAG in the composite, and formed yttrium phosphate (YPO4). Fig. 2. SEM micrograph of the 5–10 mm alumina platelets having thickness of w1 mm. Fig. 3. X-ray diffraction profiles indicating the compatibility between the four oxide matrix materials and AlPO4 (temperature/time represents the sintering condition). D.-K. Kim, W.M. Kriven / Composites: Part B 37 (2006) 509–514 511
D.-K. Kim, W.M. Kriven/Composites: Part B 37(2006)509-514 Mechanical prope Bending strength(MPa) Fracture toughness(MPa Creep properties C 25° 1000℃C AlO[471 380(100% 350092%) 280(74%) 3.3(100%) 2.5(76%) 24(73%) c-Axis sapphire: best creep Mullite [491 240(100% 240(100%) 250(104%)23(100%) 2.5(109%) 2.8(122%) Approximately an order rate than that of 02[5 Zro 1511 790(100% 200(25%) 7(100% 2(29%) YAG 52 230(100%) 210(91%) 200(87%) 1.5(100%)1.3(87%) 14093%) [110 and [1l1] YAG has higher creep resistance to c-axis sapphire [531 Alumina Yag 420(100% 4.3(100%) 4.1(95%) .9091%) The creep resistance is eutectic composi better than that of poly- 54,55 rystalline YAG and that The variations of the mechanical properties of the oxide deflecting phases, are summarized in Table 4. The Al2O3- matrix materials as a function of temperature were gathered AlPO4 laminated composite showed non-brittle fracture and from the literatures and the results are summarized in Table 2. had a bending strength and work of fracture of 161+ 15, and Alumina had a bending strength of 380 MPa at room 0.47+0.05 kJ/m, respectively. The 50 vol% alumina. 50 temperature, and held 74% of its room temperature strength vol% YAG in situ composite matrix-AlPOA laminated at 1300C. Mullite had a higher strength and work of fracture composite also showed brittle fracture and had a bend strength at 1300C than at room temperature. The mullite had 250 and and work of fracture of 181+10 MPa and 0.26+0.06 kJ/m 2. 8 MPa m values for bending strength and fracture respectively. The reason for this behavior is attributed to the toughness, respectively, at 1300C. The 3Y-TZP had the Table 3 The Al2O3 YAG eutectic composite had 420 and 4.3 MPa m2 ysical and mechanical properties of the four matrix materials used in this temperature, but the values decreased dramatically at 1000C of bending strength and fracture toughness, respectively, at Sintering 3-Point bend Average ondition (g/cm) grain slz room temperature. The composite retained 100 and 91% of its (um) room temperature bending strength and fracture toughness, Al-o 1600°/h3.40098%)437±13229 respectively, at 1300C [54,55]. The mullite, YAG,andMullite 600°C/10h3.13098% 308±11 Al2O3 YAG eutectic composites all possessed good reported 50 vol% Al2. 1700"C/5 h 61±19Al2O32.14, creep propertie 50 vol%c YAG:2.37 The oxide matrix materials were sintered at different composite temperatures, and their physical and mechanical properties 3Y-TZP 1550°/h6.03(99%)1073±46 0.52 were studied. Table 3 presents the results. The densities of the sintered Al,O3, mullite, and 3Y-TZP were 98, 98, and 99%o of theoretical density, respectively. The 3-point bending strengths of the alumina. mullite. 50 vol%o alumina. 50 vol% YAg in situ omposite matrix, and 3Y-TZP were 437+13, 308+11. 361+19, and 1073+46 MPa, respectively. The average grain sizes after sintering of Al,O3, mullite, and 3Y-TZP ere 2.3, 1.4 and 0.5 um, respectively. In the case of the 60 vol%o alumina 50 vol%o mullite in situ composite matrix, the average grain sizes of the alumina and YAG phases were 2.1 nd 2.4 um, respectively. A SEM micrograph of the Al2O3-AlPO4 laminated composite is shown in Fig. 4. The alumina layer was dense, the aluminum phosphate layer was porous, and interphase between the two materials indicated no delamination. The results of the 3-point bending tests for the laminated composites with mullite, alumina, zirconia, and 50 vol% alumina.50 vol% YAG in situ composite as matrix materials Fig 4. The SEM micrograph platelets
The variations of the mechanical properties of the oxide matrix materials as a function of temperature were gathered from the literatures and the results are summarized in Table 2. Alumina had a bending strength of 380 MPa at room temperature, and held 74% of its room temperature strength at 1300 8C. Mullite had a higher strength and work of fracture at 1300 8C than at room temperature. The mullite had 250 and 2.8 MPa m1/2 values for bending strength and fracture toughness, respectively, at 1300 8C. The 3Y-TZP had the highest bending strength and fracture toughness at room temperature, but the values decreased dramatically at 1000 8C. The Al2O3$YAG eutectic composite had 420 and 4.3 MPa m1/2 of bending strength and fracture toughness, respectively, at room temperature. The composite retained 100 and 91% of its room temperature bending strength and fracture toughness, respectively, at 1300 8C [54,55]. The mullite, YAG, and Al2O3$YAG eutectic composites all possessed good reported creep properties. The oxide matrix materials were sintered at different temperatures, and their physical and mechanical properties were studied. Table 3 presents the results. The densities of the sintered Al2O3, mullite, and 3Y-TZP were 98, 98, and 99% of theoretical density, respectively. The 3-point bending strengths of the alumina, mullite, 50 vol% alumina$50 vol% YAG in situ composite matrix, and 3Y-TZP were 437G13, 308G11, 361G19, and 1073G46 MPa, respectively. The average grain sizes after sintering of Al2O3, mullite, and 3Y-TZP were 2.3, 1.4 and 0.5 mm, respectively. In the case of the 50 vol% alumina$50 vol% mullite in situ composite matrix, the average grain sizes of the alumina and YAG phases were 2.1 and 2.4 mm, respectively. A SEM micrograph of the Al2O3–AlPO4 laminated composite is shown in Fig. 4. The alumina layer was dense, the aluminum phosphate layer was porous, and interphase between the two materials indicated no delamination. The results of the 3-point bending tests for the laminated composites with mullite, alumina, zirconia, and 50 vol% alumina$50 vol% YAG in situ composite as matrix materials and aluminum phosphate and alumina platelets as crack deflecting phases, are summarized in Table 4. The Al2O3– AlPO4 laminated composite showed non-brittle fracture and had a bending strength and work of fracture of 161G15, and 0.47G0.05 kJ/m2 , respectively. The 50 vol% alumina$50 - vol% YAG in situ composite matrix-AlPO4 laminated composite also showed brittle fracture and had a bend strength and work of fracture of 181G10 MPa and 0.26G0.06 kJ/m2 , respectively. The reason for this behavior is attributed to the Table 2 Mechanical properties of six oxide ceramics Bending strength (MPa) Fracture toughness (MPa$m1/2) Creep properties 25 8C 1000 8C 1300 8C 25 8C 1000 8C 1300 8C Al2O3 [47] 380 (100%) 350 (92%) 280 (74%) 3.3 (100%) 2.5 (76%) 2.4 (73%) c-Axis sapphire: best creep resistant [48] Mullite [49] 240 (100%) 240 (100%) 250 (104%) 2.3 (100%) 2.5 (109%) 2.8 (122%) Approximately an order less creep rate than that of Al2O3 [50] ZrO2 [51] 790 (100%) 200 (25%) – 7 (100%) 2 (29%) 2 (29%) – YAG [52] 230 (100%) 210 (91%) 200 (87%) 1.5 (100%) 1.3 (87%) 1.4 (93%) [110] and [111] YAG has higher creep resistance to c-axis sapphire [53] Alumina YAG eutectic composite [54,55] 420 (100%) 420 (100%) 420 (100%) 4.3 (100%) 4.1 (95%) 3.9 (91%) The creep resistance is better than that of polycrystalline YAG and that of a-axis sapphire [56] Fig. 4. The SEM micrograph of the as-fabricated Al2O3–AlPO4 laminated composite. Table 3 The physical and mechanical properties of the four matrix materials used in this study Sintering condition Density (g/cm3 ) 3-Point bend strength (MPa) Average grain size (mm) Al2O3 1600 8C/3 h 3.40 (98%) 437G13 2.29 Mullite 1600 8C/10 h 3.13 (98%) 308G11 1.44 50 vol% Al2- O3$50 vol% YAG in situ composite 1700 8C/5 h – 361G19 Al2O3:2.14, YAG:2.37 3Y-TZP 1550 8C/1 h 6.03 (99%) 1073G46 0.52 512 D.-K. Kim, W.M. Kriven / Composites: Part B 37 (2006) 509–514
D.-K. Kim, W.M. Kriven/ Composites: Part B 37(2006)509-514 Table 4 delamination after sintering. The thermal expansion coeffi The strength and work of fracture of oxide laminated composites cients of3Y- TZP and alpo4are10.2and2.3×10-°°C, Work of respectively, [57]. The reason for delamination of the MPa) fracture composite is attributed to the large thermal expansion ( k/m) coefficient mismatch. Fig. 5 shows the load vs displacement 157±16 0.46+0.03 curve from bend testing of the 50 vol% alumina 50 vol% YAG Al2O3(600 um)-AlPO4(75 um) 161±15 50 vol% Al,O3. 50 vol% YAG in situ 181±10 0. 26+0.06 in situ composite matrix-alumina platelet interphase, indicating omposite(600 um)-AIPO4(75 um) quasi-elastic'load vs displacement behavior. The composite 50 vol% Al,O3. 50 vol% YAG in situ 188±8 065±0.02 underwent almost 0.35 mm of displacement. The SEM composite(600 um)-alumina platelets micrograph of the 3-point, bend-tested, 50 vol% alumina. 50 (75m) vol% YAG in situ composite matrix-alumina platelet 3Y-TZP(600 um)-AIPO4(75 um) Delamination laminated composite is shown in Fig. 6. The crack was deflected along the alumina platelet interphase layer and 4. Conclusions Various oxide-oxide laminated composites were fabricated having porous AlPO4 or alumina platelets as crack deflecting terphases. Tape casting formulations for oxide materials with powder loadings of 25.1 vol%, were developed. In the case of loading of 30 vol%o was used. The AlPO. was chemically compatible with alumina, mullite and zirconia during various high-temperature annealing conditions between 1550 and 1600C. However, AlPOa 00.050.10.15020250.30.35 reacted with YAg in the 50 vol%o alumina 50 vol% YAG in situ composite matrix, forming YPO4. The 50 vol%o alumina- 50 vol% YAG in situ composite matrix itself had an Fig. 5. The load vs displacement curve for the 3-point bending test of 50 vol% average 361+19 MPa 3-point bending strength, in which the ol% YAG in situ matrix-AlPOa laminated composite. grain sizes of the alumina and YAG were 2.1 and 2. 4 um, reaction of the AlPO4 to form YPOa at the interface, so that the respectively, after sintering at 1700C for 5 h. Alumina- AlPO4 could no longer function as a weak, porous, crack. AlPO4, mullite-AlPO4, 50 vol% alumina 50 vol% YAG in situ composite matrix-alumina platelet laminated composites deflecting interphase. The 50 vol% alumina. 50 vol% YAG showed some graceful failure and had works of fracture of exhibited non-brittle fracture, and had a strength and a work of 0.46+0.03, 0.47+0.05, and 0.65+0.02 kJ/m, respectively The 50 vol%o alumina. 50 vol%YAG in situ composite matrix fracture of 188+8 MPa and 0.65+0.02 kJ/m, respectively. AlPO4 laminated composite showed brittle fracture because of The 3Y-TZP-AlPO4 laminated composite showed reaction of AlPO, to form YPO 4 within the interphase. The 3Y TZP-AlPOA laminated composite was delaminated because of too large a mismatch in the thermal expansion coefficients. References 50% ALOs in situ composite [1] Boch P, Chartier T, Huttepain M. J Am Ceram Soc 1986: 69: C191 [2 Plucknett KP, Caceres CH, Hughes C, Willinson DS. J Am Ceram Soc 1994;77:214 [3] Requena J, Moreno R, Moya JS. J Am Ceram Soc 1989: 72: 1511 [4] Takebe H, Morgana K. Yogoyo Kyokaishi 1988: 96: 1149 [5] Sarkar P, Haung X, Nicholson PS. J Am Ceram Soc 1992: 75: 290 [6] Whitehead M, Sarkar P, Nicholson PS. Ceram Eng Sci Proc 1994: 15 1110. [7 Wang H, Hu X J Am Ceram Soc 1996: 79: 553 18 Marshall DB, Ratto JJ. J Am Ceram Soc 1991: 74: 2979 [91 Morgan PED, Marshall DB. J Am Ceram Soc 1995: 78: 1553 Fig. 6. Crack deflection along alumina platelet interphases in the laminate 1 Clegg WJ. Acta Metall Mater 1992: 40: 3085 composed of 50 vol% Al2O3. 50 vol% YAG in situ composite matrix and [12] Shannon T, Blackburn S Ceram Eng Sci Proc 1995: 16: 1115. alumina platelets(corresponding to the specimen in Fig. 5). [13 Chartier T, Merle D, Besson JL. J Eur Ceram Soc 1995; 15: 101
reaction of the AlPO4 to form YPO4 at the interface, so that the AlPO4 could no longer function as a weak, porous, crackdeflecting interphase. The 50 vol% alumina$50 vol% YAG in situ composite matrix-alumina platelet laminated composite exhibited non-brittle fracture, and had a strength and a work of fracture of 188G8 MPa and 0.65G0.02 kJ/m2 , respectively. The 3Y-TZP–AlPO4 laminated composite showed delamination after sintering. The thermal expansion coeffi- cients of 3Y-TZP and AlPO4 are 10.2 and 2.3!10K6 /8C, respectively, [57]. The reason for delamination of the composite is attributed to the large thermal expansion coefficient mismatch. Fig. 5 shows the load vs displacement curve from bend testing of the 50 vol% alumina$50 vol% YAG in situ composite matrix-alumina platelet interphase, indicating ‘quasi-elastic’ load vs displacement behavior. The composite underwent almost 0.35 mm of displacement. The SEM micrograph of the 3-point, bend-tested, 50 vol% alumina$50 - vol% YAG in situ composite matrix-alumina platelet, laminated composite is shown in Fig. 6. The crack was deflected along the alumina platelet interphase layer and showed a complicated crack path. 4. Conclusions Various oxide–oxide laminated composites were fabricated having porous AlPO4 or alumina platelets as crack deflecting interphases. Tape casting formulations for oxide materials with powder loadings of 25.1 vol%, were developed. In the case of tape casting of alumina platelets, a solid loading of 30 vol% was used. The AlPO4 was chemically compatible with alumina, mullite and zirconia during various high-temperature annealing conditions between 1550 and 1600 8C. However, AlPO4 reacted with YAG in the 50 vol% alumina$50 vol% YAG in situ composite matrix, forming YPO4. The 50 vol% alumina$50 vol% YAG in situ composite matrix itself had an average 361G19 MPa 3-point bending strength, in which the grain sizes of the alumina and YAG were 2.1 and 2.4 mm, respectively, after sintering at 1700 8C for 5 h. Alumina– AlPO4, mullite-AlPO4, 50 vol% alumina$50 vol% YAG in situ composite matrix-alumina platelet laminated composites showed some graceful failure and had works of fracture of 0.46G0.03, 0.47G0.05, and 0.65G0.02 kJ/m2 , respectively. The 50 vol% alumina$50 vol% YAG in situ composite matrixAlPO4 laminated composite showed brittle fracture because of reaction of AlPO4 to form YPO4 within the interphase. The 3YTZP–AlPO4 laminated composite was delaminated because of too large a mismatch in the thermal expansion coefficients. References [1] Boch P, Chartier T, Huttepain M. J Am Ceram Soc 1986;69:C191. [2] Plucknett KP, Caceres CH, Hughes C, Willinson DS. J Am Ceram Soc 1994;77:2145. [3] Requena J, Moreno R, Moya JS. J Am Ceram Soc 1989;72:1511. [4] Takebe H, Morigana K. Yogoyo Kyokaishi 1988;96:1149. [5] Sarkar P, Haung X, Nicholson PS. J Am Ceram Soc 1992;75:2907. [6] Whitehead M, Sarkar P, Nicholson PS. Ceram Eng Sci Proc 1994;15: 1110. [7] Wang H, Hu X. J Am Ceram Soc 1996;79:553. [8] Marshall DB, Ratto JJ. J Am Ceram Soc 1991;74:2979. [9] Morgan PED, Marshall DB. J Am Ceram Soc 1995;78:1553. [10] Clegg WJ, Kendall K, Alford NM, Button TW, Birchall JD. Nature 1990; 347:455. [11] Clegg WJ. Acta Metall Mater 1992;40:3085. [12] Shannon T, Blackburn S. Ceram Eng Sci Proc 1995;16:1115. [13] Chartier T, Merle D, Besson JL. J Eur Ceram Soc 1995;15:101. Table 4 The strength and work of fracture of oxide laminated composites Strengh (MPa) Work of fracture (kJ/m2 ) Mullite (600 mm)–AlPO4 (75 mm) 157G16 0.46G0.03 Al2O3 (600 mm)–AlPO4 (75 mm) 161G15 0.47G0.05 50 vol% Al2O3$50 vol% YAG in situ composite (600 mm)–AlPO4 (75 mm) 181G10 0.26G0.06 50 vol% Al2O3$50 vol% YAG in situ composite (600 mm)–alumina platelets (75 mm) 188G8 0.65G0.02 3Y-TZP (600 mm)–AlPO4 (75 mm) Delamination Fig. 5. The load vs displacement curve for the 3-point bending test of 50 vol% Al2O3$50 vol% YAG in situ matrix-AlPO4 laminated composite. Fig. 6. Crack deflection along alumina platelet interphases in the laminate composed of 50 vol% Al2O3$50 vol% YAG in situ composite matrix and alumina platelets (corresponding to the specimen in Fig. 5). D.-K. Kim, W.M. Kriven / Composites: Part B 37 (2006) 509–514 513
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