《复合材料 Composites》课程教学资源（学习资料）第五章 陶瓷基复合材料_High toughness in laminated SiC ceramics from aqueous tape casting

Availableonlineatwww.sciencedirect.com SCE區 DIRECT G ta materialia ELSEVIER Scripta Materialia 52(2005)381-385 www.actamat-journals.com High toughness in laminated Sic ceramics from aqueous tape casting Jingxian Zhang, Rong huang, Hui Gu, dongliang Jiang Qingling Lin, Zhengren Huang The State Key Laboratory of High Performance Ceramics and Superfine Structure, Shanghai Institute of Ceramics, Received 15 July 2004: accepted 20 October 2004 Available online ll november 2004 Abstract Toughness as high as 9.5 MPa m was achieved in a Sic material prepared from aqueous tape casting, laminating and hot pressing. The increased toughness is related to the formation of second phase at triple pockets, YAlO,, which was different from the composition of sintering additives Al2O3 and Y2O3 (Y3Al5O12). The extra Al2O3 was found at thin amorphous films covering most grain boundaries where Y2O3 was absent. A similar difference between the initial additive composition and the final second phase was found in another Sic material with lower toughness. It is proposed that the presence of thermal residual stress at second phase is responsible for the improvement in fracture toughness o 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Tape casting: Toughness: Silicon carbide 1. Introduction to build parts from engineering materials such as struc tural ceramics and composites LOM is one of the rapid Tape casting is the common process for the prepara- prototyping and manufacturing techniques where a part tion of multilayered composite materials[1-3]. Tradition- is built sequentially from layers of paper, green sheets of lly organic solvents were used to prepare concentrated ceramics, sheets of metal, etc. This technique is espe- suspensions due to their low boiling point and surface ten- cially suitable for producing geometrically complex ob- sion. Recently, aqueous tape casting processes have jects, and for operating with a high degree of received more attention due to environmental and health automation [6-10]. However, the preparation of ceramic onsiderations [4]. To increase the strength and the frac- composites from green sheets has rarely been studied ture toughness, lamination was often employed to create In the present work, the feasibility of preparing SiC residual stress, and/or to align the anisotropic grains [ 3, 5]. laminates by aqueous tape casting and hot pressing However, multilayered composites without residual was studied. To lower the sintering temperature, we used stress or component design also showed an increase Al,O3 and Y,O3 as sintering additives. The correlation toughness 51 between microstructure and the mechanical properties Recently, many scholars show their interest in apply- of SiC laminates was investigated g laminated object manufacturing(LOM) technology 2. Experimental procedures Corresponding author. Tel. +81 727519785: fax: +81 727519 The material was prepared from commercially avail E-mailaddress:jx_zh@yahoo.com(.Zhang able a-SiC powder(FCP-15, Norton Co. ) 5 wt% Al2O 1359-6462/S- see front matter 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved doi: 10. 1016/j-scriptamat 2004.10.026

High toughness in laminated SiC ceramics from aqueous tape casting Jingxian Zhang *, Rong Huang, Hui Gu, Dongliang Jiang, Qingling Lin, Zhengren Huang The State Key Laboratory of High Performance Ceramics and Superfine Structure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China Received 15 July 2004; accepted 20 October 2004 Available online 11 November 2004 Abstract Toughness as high as 9.5 MPa Æ m1/2 was achieved in a SiC material prepared from aqueous tape casting, laminating and hot pressing. The increased toughness is related to the formation of second phase at triple pockets, YAlO3, which was different from the composition of sintering additives Al2O3 and Y2O3 (Y3Al5O12). The extra Al2O3 was found at thin amorphous films covering most grain boundaries where Y2O3 was absent. A similar difference between the initial additive composition and the final second phase was found in another SiC material with lower toughness. It is proposed that the presence of thermal residual stress at second phase is responsible for the improvement in fracture toughness.
2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Tape casting; Toughness; Silicon carbide 1. Introduction Tape casting is the common process for the prepara￾tion of multilayered composite materials[1–3]. Tradition￾ally organic solvents were used to prepare concentrated suspensions due to their low boiling point and surface ten￾sion. Recently, aqueous tape casting processes have received more attention due to environmental and health considerations [4]. To increase the strength and the frac￾ture toughness, lamination was often employed to create residual stress, and/or to align the anisotropic grains[3,5]. However, multilayered composites without residual stress or component design also showed an increase in toughness [5]. Recently, many scholars show their interest in apply￾ing laminated object manufacturing (LOM) technology to build parts from engineering materials such as struc￾tural ceramics and composites. LOM is one of the rapid prototyping and manufacturing techniques where a part is built sequentially from layers of paper, green sheets of ceramics, sheets of metal, etc. This technique is espe￾cially suitable for producing geometrically complex ob￾jects, and for operating with a high degree of automation [6–10]. However, the preparation of ceramic composites from green sheets has rarely been studied. In the present work, the feasibility of preparing SiC laminates by aqueous tape casting and hot pressing was studied. To lower the sintering temperature, we used Al2O3 and Y2O3 as sintering additives. The correlation between microstructure and the mechanical properties of SiC laminates was investigated. 2. Experimental procedures The material was prepared from commercially avail￾able a-SiC powder (FCP-15, Norton Co.). 5 wt% Al2O3 1359-6462/$ - see front matter
2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.scriptamat.2004.10.026 * Corresponding author. Tel.: +81 727 519 785; fax: +81 727 519 631. E-mail address: jx_zh@yahoo.com (J. Zhang). www.actamat-journals.com Scripta Materialia 52 (2005) 381–385

J. Zhang et al Scripta Materialia 52 (2005)381-385 and Y,O3 was used with the molar ratio of Y2O3: Al,O3 as 3: 5. The dispersant was a secondary polyamine, pol ethylene imine(PEl, Acros Organics, M. W. 50-60000 The binder and the plasticizer were Polyvinyl alcohol 1788(Qidong Chemical Plant, China) and glycerol SiC (Analytical, Shanghai Chemical Reagent Corporation, China), respectively. Details about the tape casting proc- ess were reported in previous papers [11, 12 The green sheets were cut into a rectangular size (40 x 50 mm) and stacked in a graphite die. Binder re- moval was carried out under an argon atmosphere Samples were hot pressed at 1850C and 35 MPa in 303540455055606569 Ar atmosphere for 0.5 h Monolithic samples were also prepared by hot pressing and pressureless sintering for companson Tests of flexural strength were performed by three point bending from speci 36 Fracture toughness was determined by single-edge- notched beam(SENB) method at room temperature The microstructure of the specimen was investigated by SEM and TEM. Energy dispersive X-ray(EDX) spectroscopy was also used to determine local compo- nents at the grain boundary 3. Results and discussions Fig. I(a) XRD patterns of as sintered Sic samples with initial 3. Microstructure characterization Y2O3: Al2O3 ratio as 3: 5 and(b) TEM micrograph showing morpho XRD analysis of the resultant SiC samples showed hat YAlO3, other than Y3AlsO1 is formed as the sec ond phase after sintering although the initial Y2O3: Al_O3 molar ratio was 3: 5(Fig. la). TEM obser- vation confirmed the presence of YAlO3 at triple and multiple-grain junctions(Fig. Ib). The microstructures do not manifest any evidences of elongated grain growth Thin amorphous films were found at grain bounda ries by TEM observation. Spatially-resolved EDS anal ysis detected a strong segregation of aluminum cations to grain boundary, as revealed in Fig. 2. Like this boundary, most grain boundaries have Al-rich amor- phous film, where little or no yttrium element was found. Such amorphous phase may contain also Sio in addition to Al2O3[13-15]. This observation indicates a preferential diffusion of Al,O3 to grain boundary, in eement with the formation of YAlO3 at triple To confirm the departure of second phase from the designed composition, another Sic sample with the additive Y203: Al2O3 molar ratio as 3: 7 was prepared Distance fom grain boundary (nm under the same procedure. According to the mechanism for the diffusion of AlO3, Y3AlsO12 phase should form 15Eem】ev at the intergranular regions. XRD characterization did find this phase as the second phase in the new material gin boundary n sice a d n l ispibusion of dl y eleme nts across as seen in Fig. 3

and Y2O3 was used with the molar ratio of Y2O3:Al2O3 as 3:5. The dispersant was a secondary polyamine, poly￾ethylene imine (PEI, Acros Organics, M.W. 50-60000). The binder and the plasticizer were Polyvinyl alcohol 1788 (Qidong Chemical Plant, China) and glycerol (Analytical, Shanghai Chemical Reagent Corporation, China), respectively. Details about the tape casting proc￾ess were reported in previous papers [11,12]. The green sheets were cut into a rectangular size (40 · 50 mm) and stacked in a graphite die. Binder re￾moval was carried out under an argon atmosphere. Samples were hot pressed at 1850 C and 35 MPa in Ar atmosphere for 0.5 h. Monolithic samples were also prepared by hot pressing and pressureless sintering for comparison. Tests of flexural strength were performed by three point bending from specimens of size 3 · 4 · 36 mm. Fracture toughness was determined by single-edge￾notched beam (SENB) method at room temperature. The microstructure of the specimen was investigated by SEM and TEM. Energy dispersive X-ray (EDX) spectroscopy was also used to determine local compo￾nents at the grain boundary. 3. Results and discussions 3.1. Microstructure characterization XRD analysis of the resultant SiC samples showed that YAlO3, other than Y3Al5O12 is formed as the sec￾ond phase after sintering although the initial Y2O3:Al2O3 molar ratio was 3:5 (Fig. 1a). TEM obser￾vation confirmed the presence of YAlO3 at triple and multiple-grain junctions (Fig. 1b). The microstructures do not manifest any evidences of elongated grain growth. Thin amorphous films were found at grain bounda￾ries by TEM observation. Spatially-resolved EDS anal￾ysis detected a strong segregation of aluminum cations to grain boundary, as revealed in Fig. 2. Like this boundary, most grain boundaries have Al-rich amor￾phous film, where little or no yttrium element was found. Such amorphous phase may contain also SiO2 in addition to Al2O3 [13–15]. This observation indicates a preferential diffusion of Al2O3 to grain boundary, in agreement with the formation of YAlO3 at triple pockets. To confirm the departure of second phase from the designed composition, another SiC sample with the additive Y2O3:Al2O3 molar ratio as 3:7 was prepared under the same procedure. According to the mechanism for the diffusion of Al2O3, Y3Al5O12 phase should form at the intergranular regions. XRD characterization did find this phase as the second phase in the new material, as seen in Fig. 3. Fig. 1. (a) XRD patterns of as sintered SiC samples with initial Y2O3:Al2O3 ratio as 3:5 and (b) TEM micrograph showing morphol￾ogy of the second phase. Fig. 2. (a) TEM image of an amorphous film about 2.5 nm thick at a grain boundary in SiC and (b) distribution of Al, Y elements across this boundary. 382 J. Zhang et al. / Scripta Materialia 52 (2005) 381–385

J. Zhang et al. Scripta Materialia 52(2005) Table l Sic Mechanical properties of monolithic and multilayered SiC samples Bulk sic Pressureless Hot Y2O3: Al2O3 3:7 Relative density (%)99.5 98 99 Strength(MPa) 754±47650±54724±31662±4I Toughne 4.5±1.06.8±1.29.5±1.17.58±1.1 (MPa·m-) 10203040如670 tion are also listed for comparison. Our samples with Fig.3. XRD patterns of as sintered SiC samples with initial Al,O3 and Y,O3 molar ratio as 3: 5 really show a high Y2O3: Al2O3 ratio as 3: 7. fracture toughness of 9.5 MPa m 2. There are two explanations for the improved mechanical properties 3. 2. Thermal residual stress Perovskite-like YAlO3 has an orthorhombic crystal tructure, its thermal expansion coefficients are .5×10-°/C,43×10-6°Cand10.8×10-°/Cale the a, b or c axis, respectively [16]. Since this value is al ways larger than that of SiC(4.5 x 10/C), a residual tensile stress is expected between a YAlO3 particle and surrounding matrix on cooling The radial matrix stress (omr) and the tangential matrix stress(ome=-omr2)are based on the hydrostatic stress ah developed surround the YAlO3 grain. It can be estimated from the followi equation [171 (x-xm)△T where ap, am, Vp, Vm, Ep and Em are the thermal expan sion coefficient. Poisson s ratio and youngs modulus of YAlO3 and SiC, respectively. Due to the lack of both ”1:6 elastic modulus and Poissons ratio for YAlO3, we calcu late instead the stress generated by YAG particle in Sic Fig 4. Micrographs of the fracture surface. matrix as a reference. Using 8x 10-6/C and 4.5 x 10-6/ C[18] for ap (YAG)and am(SiC), 333 GPa [19] and 440 GPa [17 for Ep and Em, and 0.30 and 0.25 [20]for SEM micrographs of the fracture surface of SiC sam- Vp and Vm, respectively, we find that the substantial ma ples are shown in Fig 4. From the microstructure of the trix stress can be developed as high as me =-668 MPa laminates, it was difficult to determine the interface be- in compression and omr =1335 MPa in tension for ATof tween the adjacent SiC layers. It is worth noting in 1000C. The existence of such a large stress may weaken Fig. 4 that the Al2O3/Y203 doped Sic ceramics exhibit the inter-phase boundaries, leading to a fracture along a predominantly intergranular fracture mode, Most of such boundaries [19]. Fig. 5 shows that the cracks prop- the grains are uniform and equiaxed. The existence of agated along the grain boundary and the interface be- thermal residue stress may weaken the interphase tween second phase and Sic matrix. It indicates that a boundaries, leading to intergranular fracture behavior. relatively weak interface comes from the amorphous grain boundary films and the thermal mismatch stress 3.2. Mechanical properties at hetero phase boundaries, which facilitated the inter granular fracture The effect of additive composition on various Based on the calculation above it is postulated that mechanical properties of Sic laminates is demonstrated the thermal expansion mismatch may result in micro- in Table 1. The properties of hot pressed and pressure- cracking at the SiC-YAlO3 boundary ahead of a pri less sintered monolithic samples with the same composi mary propagating crack, similar to that in SiC-Ti

SEM micrographs of the fracture surface of SiC sam￾ples are shown in Fig. 4. From the microstructure of the laminates, it was difficult to determine the interface be￾tween the adjacent SiC layers. It is worth noting in Fig. 4 that the Al2O3/Y2O3 doped SiC ceramics exhibit a predominantly intergranular fracture mode, Most of the grains are uniform and equiaxed. The existence of thermal residue stress may weaken the interphase boundaries, leading to intergranular fracture behavior. 3.2. Mechanical properties The effect of additive composition on various mechanical properties of SiC laminates is demonstrated in Table 1. The properties of hot pressed and pressure￾less sintered monolithic samples with the same composi￾tion are also listed for comparison. Our samples with Al2O3 and Y2O3 molar ratio as 3:5 really show a high fracture toughness of 9.5 MPa Æ m1/2. There are two explanations for the improved mechanical properties. 3.2.1. Thermal residual stress Perovskite-like YAlO3 has an orthorhombic crystal structure, its thermal expansion coefficients are 9.5 · 10
6 /C, 4.3 · 10
6 /C and 10.8 · 10
6 /C along the a, b or c axis, respectively [16]. Since this value is al￾ways larger than that of SiC (4.5 · 10
6 /C), a residual tensile stress is expected between a YAlO3 particle and surrounding matrix on cooling. The radial matrix stress (rmr) and the tangential matrix stress (rmh =
rmr/2) are based on the hydrostatic stress rh developed surround the YAlO3 grain. It can be estimated from the following equation [17]: rmr ¼ rh ¼ ap
am
DT ½ð Þ 1 þ mm =2Emþ½ 1
2mp
=Ep ð1Þ where ap, am, mp, mm, Ep and Em are the thermal expan￾sion coefficient, Poisson
s ratio and Young
s modulus of YAlO3 and SiC, respectively. Due to the lack of both elastic modulus and Poisson
s ratio for YAlO3, we calcu￾late instead the stress generated by YAG particle in SiC matrix as a reference. Using 8 · 10
6 /C and 4.5 · 10
6 / C [18] for ap (YAG) and am (SiC), 333 GPa [19] and 440 GPa [17] for Ep and Em, and 0.30 and 0.25 [20] for mp and mm, respectively, we find that the substantial ma￾trix stress can be developed as high as rmh =
668 MPa in compression and rmr = 1335 MPa in tension for DT of 1000 C. The existence of such a large stress may weaken the inter-phase boundaries, leading to a fracture along such boundaries [19]. Fig. 5 shows that the cracks prop￾agated along the grain boundary and the interface be￾tween second phase and SiC matrix. It indicates that a relatively weak interface comes from the amorphous grain boundary films and the thermal mismatch stress at hetero phase boundaries, which facilitated the inter￾granular fracture. Based on the calculation above, it is postulated that the thermal expansion mismatch may result in micro￾cracking at the SiC–YAlO3 boundary ahead of a pri￾mary propagating crack, similar to that in SiC–TiB2 Fig. 4. Micrographs of the fracture surface. Table 1 Mechanical properties of monolithic and multilayered SiC samples Sintering process Bulk SiC Laminated SiC Hot pressed Pressureless sintering Hot pressed Y2O3:Al2O3 3:7 3:7 3:5 3:7 Relative density (%) 99.5 98 99 99.1 Strength (MPa) 754 ± 47 650 ± 54 724 ± 31 662 ± 41 Toughness (MPa Æ m1/2) 4.5 ± 1.0 6.8 ± 1.2 9.5 ± 1.1 7.58 ± 1.1 Fig. 3. XRD patterns of as sintered SiC samples with initial Y2O3:Al2O3 ratio as 3:7. J. Zhang et al. / Scripta Materialia 52 (2005) 381–385 383

J. Zhang et al Scripta Materialia 52 (2005)381-385 4. conclusions Sic laminates prepared by aqueous tape casting showed an improvement in fracture toughness. The com- position of sintering additives influenced the formation of second phase as well as the final properties of SiC lam inates. The resultant development of microstructure can be well understood and controlled. It is inferred that the presence of residual stress might be the main reason for the improvement in fracture toughness of Sic laminates Acknowledgment 500nm The authors are grateful to the Science and Technol- ogy Committee of Shanghai for providing support under Fig. 5. The crack propagated along the grain boundary and the phase the contract number of 02DJ14065 and 0159nm075 References systems [21]. These microcracks can dissipate the strain energy and shield the main cracks, leading to further in [1 Mistler RE Tape casting, past, present, potential Am Ceram Soc crease in fracture toughness [18, 22]. These thermal resid Bul1998;78(2:82-6 2 Mianxue Wu, Messing GL. Fabrication of oriented Sic-whisker ual stress induced energy-absorbing mechanism is well reinforced mullite matrix composites by tape casting. J Am Ceram documented in literature, i.e. TIC, YAG and TiB2 parti Soc1994:77(10):2586-92 cle reinforced Sic composites [17, 23, 24 3 Kiyoshi Hirao, Masay The thermal expansion coefficient for YAlO3 is even Processing strategy for astrophic silicon nitride. J Am Ceram 687-90 higher than Y3Al5O12. A relatively higher thermal resid ual stress was generated with Y AlO3 as the second phase 14 Hotza D. Greil P. Review: ac ape casting of ceramic owders. Mater Sci Eng A 1995: 202: 206-1 assuming its elastic constant and poissons ratio are the [5] Philippe Boch, Thierry Chartier, Muriel Huttepain. Tape casting same as that for Y3 AlsO1. In this case, more energy is OyzrO2 laminated composites. J Am Ceram Soc dissipated in Sic composites and higher fracture tough 1986:69(8)cl9l-2. ness results. For particulate-reinforced composites, the [6 Xuemin Cui, Shixi Ouyang, Zhiyong Yu, Changan Wang, Yong thermal residual stress was considered a major contrib. casting processing. Mater Lett 2003: 57: 1300-4 utor to the toughing of ceramics [17]. This might be [7 Anirban Das, Giridhar Madras, Niladri Dasgupta, Umarji AM the reason for the difference in fracture toughness for Binder removal studies in ceramic thick shapes made by laminated the two laminated materials, as given in Table 1 bject manufacturing. J Eur Ceram Soc 2003: 23: 1013-7 [8 Yumin Zhang, Xiaodong He, Jiecai Han, Shanyi Du. Ceramic 3. 2.2. Colloidal processing technique green tape extrusion for laminated object manufacturing. Mate Lett1999:40:275-9 Colloidal processes could help to produce very homo-[9] Donald Klosterman, Richard Chartoff, George Graves,Nora geneous green sheets with limited flaws [25]. Rosaura Osborne. Brian Priore. Interfacial characteristics of composites Ham-Su [26 showed that lamination process could fabricated by laminated object manufacturing. Composites A modify faws to a more forgiving morphology and re- (10J Yumin Zhang Jiecai Han, Xinghong Zhiqiang Li, Shanyi Du. Rapid protot d combustion had been observed in laminated AlO3 fabricated by synthesis of TiC: Ni functionally grader Mater Sci Eng non-aqueous tape casting though such improvement A2001;299:218-24. was quite limited [5]. For hot pressed bulk SiC, larger [11 Zhang JX, Jiang DL, Tan SH, Gui LH, Ruan ML. Aqueous defects are inevitably trapped during powder compac rocessing of Sic Green Sheets I. Dispersant. J Mater Res 2002;17(11):2012-8 tion [4]. These defects will reduce the thermal residual 12]Zhang JX, Jiang DL, Tan SH, Gui LH, Ruan ML. Aqueous stress and therefore lower the fracture toughness processing of Sic Green Sheets Il Binder and plasticizer. J Mater [27, 28]. In comparison with laminated SiC samples, Res2002;17(11):2018-25 hot pressed bulk SiC exhibits a low fracture toughness 3] Aksay IA, Pask JA. Stable and metastable In light of these discussions, the formation of YAlO SiO -AlO3. J Am Ceram Soc 1975: 58: 507 is likely to be the main reason for the improvement of [14] Mulla MA, Krstic VD. Low temperature pressureless sintering of silicon carbide with aluminum oxide and yttrium oxide addi- mechanical properties in Sic samples tions. Ceram Bull 1991; 70(3): 439-43

systems [21]. These microcracks can dissipate the strain energy and shield the main cracks, leading to further in￾crease in fracture toughness [18,22]. These thermal resid￾ual stress induced energy-absorbing mechanism is well documented in literature, i.e. TiC, YAG and TiB2 parti￾cle reinforced SiC composites [17,23,24]. The thermal expansion coefficient for YAlO3 is even higher than Y3Al5O12. A relatively higher thermal resid￾ual stress was generated with YAlO3 as the second phase assuming its elastic constant and Poisson
s ratio are the same as that for Y3Al5O12. In this case, more energy is dissipated in SiC composites and higher fracture tough￾ness results. For particulate-reinforced composites, the thermal residual stress was considered a major contrib￾utor to the toughing of ceramics [17]. This might be the reason for the difference in fracture toughness for the two laminated materials, as given in Table 1. 3.2.2. Colloidal processing technique Colloidal processes could help to produce very homo￾geneous green sheets with limited flaws [25]. Rosaura Ham-Su [26] showed that lamination process could modify flaws to a more forgiving morphology and re￾duce the severity of void-tape flaws. This kind of effect had been observed in laminated Al2O3 fabricated by non-aqueous tape casting though such improvement was quite limited [5]. For hot pressed bulk SiC, larger defects are inevitably trapped during powder compac￾tion [4]. These defects will reduce the thermal residual stress and therefore lower the fracture toughness [27,28]. In comparison with laminated SiC samples, hot pressed bulk SiC exhibits a low fracture toughness. In light of these discussions, the formation of YAlO3 is likely to be the main reason for the improvement of mechanical properties in SiC samples. 4. Conclusions SiC laminates prepared by aqueous tape casting showed an improvement in fracture toughness. The com￾position of sintering additives influenced the formation of second phase as well as the final properties of SiC lam￾inates. The resultant development of microstructure can be well understood and controlled. It is inferred that the presence of residual stress might be the main reason for the improvement in fracture toughness of SiC laminates. Acknowledgment The authors are grateful to the Science and Technol￾ogy Committee of Shanghai for providing support under the contract number of 02DJ14065 and 0159nm075. References [1] Mistler RE. Tape casting, past, present, potential. Am Ceram Soc Bull 1998;78(2):82–6. [2] Mianxue Wu, Messing GL. Fabrication of oriented SiC-whisker￾reinforced mullite matrix composites by tape casting. J Am Ceram Soc 1994;77(10):2586–92. [3] Kiyoshi Hirao, Masayoshi Ohashi, Brito ME, Shuzu Kanzaki. Processing strategy for producing highly antistrophic silicon nitride. J Am Ceram Soc 1995;78(6):1687–90. [4] Hotza D, Greil P. Review: aqueous tape casting of ceramic powders. Mater Sci Eng A 1995;202:206–17. [5] Philippe Boch, Thierry Chartier, Muriel Huttepain. Tape casting of Al2O3/ZrO2 laminated composites. J Am Ceram Soc 1986;69(8):c191–2. [6] Xuemin Cui, Shixi Ouyang, Zhiyong Yu, Changan Wang, Yong Huang. A study on green tapes for LOM with water-based tape casting processing. Mater Lett 2003;57:1300–4. [7] Anirban Das, Giridhar Madras, Niladri Dasgupta, Umarji AM. Binder removal studies in ceramic thick shapes made by laminated object manufacturing. J Eur Ceram Soc 2003;23:1013–7. [8] Yumin Zhang, Xiaodong He, Jiecai Han, Shanyi Du. Ceramic green tape extrusion for laminated object manufacturing. Mater Lett 1999;40:275–9. [9] Donald Klosterman, Richard Chartoff, George Graves, Nora Osborne, Brian Priore. Interfacial characteristics of composites fabricated by laminated object manufacturing. Composites A 1998;29:1165–74. [10] Yumin Zhang, Jiecai Han, Xinghong Zhang, Xiaodong He, Zhiqiang Li, Shanyi Du. Rapid prototyping and combustion synthesis of TiC:Ni functionally gradient materials. Mater Sci Eng A 2001;299:218–24. [11] Zhang JX, Jiang DL, Tan SH, Gui LH, Ruan ML. Aqueous processing of SiC Green Sheets I. Dispersant. J Mater Res 2002;17(11):2012–8. [12] Zhang JX, Jiang DL, Tan SH, Gui LH, Ruan ML. Aqueous processing of SiC Green Sheets II. Binder and plasticizer. J Mater Res 2002;17(11):2018–25. [13] Aksay IA, Pask JA. Stable and metastable equilibria in system SiO2–Al2O3. J Am Ceram Soc 1975;58:507. [14] Mulla MA, Krstic VD. Low temperature pressureless sintering of b-silicon carbide with aluminum oxide and yttrium oxide addi￾tions. Ceram Bull 1991;70(3):439–43. Fig. 5. The crack propagated along the grain boundary and the phase boundary. 384 J. Zhang et al. / Scripta Materialia 52 (2005) 381–385

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