W Dressler R. riedel The temperature dependent three-point erties of various sintered silicon nitrides includ bending strength of a B-SiAION-ceramics with ing two commercially available products and a z=0. 5 is shown in Fig. 9. 9 The strength of SiAlON-ceramics are summarized in Table 3 about 830 MPa remains constant up to 1300.C pointing out that nearly no softening of grain 4.2 Silicon carbide ceramics boundaries occurs. The effect of crystalli the amorphous grain boundary phase of a 4.2. 1 Sintering of Sic-ceramics Y203/Al2O doped Si,N, ceramics on the high In order to densify Sic ceramics various sinter temperature strength is depicted in Fig. 10. The ing methods like pressureless sintering, hot increase of mellilite(Y Si,O, NA) crystallized in pressing, HIPing and sinter HIPing are used the grain boundary from 20 to 90% results in an Except for pressureless sintering these methods increase of high temperature strength from 650 have the disadvantage of being cost intensive to 1020 MPa. 7 The thermo-mechanical prop- 1400 1000 800 a.1000 乏 800 600 600 400 400 200H·sAN(2=0.5) 90 Mellilite 0 0200400600800100012001400 0200400600800100012001400 Temperature [c] Temperature [c] Fig. 10. Influence of secondary phase crystallization ig.9. Temperature dependent three-point-bending (metllilite: YSi, O, N, )on high temperature strength of strength of B-sis.sALsOI-SN Y2OvAl,O doped si, N,-ceram Table 3 processes materials S(SN-SA8, of thermo-mechanical properties of Si N,and SiAIon ceramics produced by different densification to Komeya and Matsui. 2 As a comparison the properties of two industrially produced Si, N NGK Insulators Ltd, Nagoya, Japan; New Material, Kyocera Corp, Kyoto, Japan)are given Property Silicon nitride SiAION Reaction Pressureless or Hot SN-88, New material NGK Kyocera Thermal conductivity(Wm K 2 6-20 29-35 29-3·5 3-4 13-18 23-30 3·0-35 thermal expansion Young’ s modulus(GPa) Poissons ratio 024-0-26 320323 Bending strength(MPa) 150 400-1000800-1050 1000°C 23 350-1000 800-1000 770 1200°C 170-307 250-800 250-950 770 703 760 606 Fracture toughness 4-7 Critical thermal 350-600 400-800 800-900 500-600 shock temperature (C: ATo Oxidation resistance(mg cm 0-5,1400°C,014,1500°C 1000h 100h24 W. Dressier, R. Riedel The temperature dependent three-point bending strength of a //-SiAlON-ceramics with z=0.5 is shown in Fig. 9. '0° The strength of about 830 MPa remains constant up to 1300°C pointing out that nearly no softening of grain boundaries occurs. The effect of crystallizing the amorphous grain boundary phase of a Y203/m1203 doped Si3N4 ceramics on the high temperature strength is depicted in Fig. 10. The increase of mellilite (Y2Si303N4) crystallized in the grain boundary from 20 to 90% results in an increase of high temperature strength from 650 to 1020 MPa."'7 The thermo-mechanical prop- 1000 800 t~ Q. 600 t-- t- 400 ,o 09 200 Fig. 9. iIIiIIIIIIllllIIIIIIIIIIIIIIIl~ q --o--SiAION (z = 0.5) I , I I I I I 0 200 400 600 800 1000 1200 1400 Temperature [°C] Temperature dependent three-point-bending strength of/~-Sis.~AI,,~O,,~N7 ~.'" erties of various sintered silicon nitrides includ￾ing two commercially available products and a SiAION-ceramics are summarized in Table 3.' '" 4.2 Silicon carbide ceramics 4.2.1 Sintering of SiC-ceramics In order to densify SiC ceramics various sinter￾ing methods like pressureless sintering, hot pressing, HIPing and sinter HIPing are used. Except for pressureless sintering these methods have the disadvantage of being cost intensive 1400 1200 t~ 1000 800 t- ¢- 600 ,= ",- 400 CO mIim ~||II|||II |||II|~ ~ --e--20 % Mellilite I 200 ~90 % Mellilite 0 I I I I I I 0 200 400 600 800 1000 1200 1400 Temperature [°C] Fig. 10. Influence of secondary phase crystallization (metllilite: Y2Si303N4) on high temperature strength of Y203/AI203 doped Si3Nn-ceramics."'7 Table 3. Range of thermo-mechanical properties of SigN4- and SiAION ceramics produced by different densification processes according to Komeya and Matsui. ''2 As a comparison the properties of two industrially produced Si3Nn￾materials (SN-88, NGK Insulators Ltd, Nagoya, Japan; New Material, Kyocera Corp., Kyoto, Japan) are given Property Silicon nitride SiAION Reaction Pressureless or Hot SN-88, New material, sintering gas-pressure pressing NGK Kyocera sintering Density (g cm 3) Thermal conductivity (W m Coefficient of (10 "°C ') thermal expansion Young's modulus (GPa) Poisson's ratio Bending strength (MPa) RT 1000°C 1200°C 1400°C Fracture toughness (MPa.m'/2) Critical thermal shock temperature (°C: AT,.) Oxidation resistance (mg cm 2) 2' 1-2"6 2'9-3 "5 2"9-3"5 3 "5 3 "4 3"0-3" 15 K ') 2"6-20 13-18 29-32 70 59 -- 2'3-3"0 3'0-3"5 3"1-3"3 3"4 3"0 2'5-3"0 100-200 240-330 320 300 318 230 0"24-0"26 0"24-0"28 0'26 0"26 0"28 0"29 150-295 400-1000 800-1050 790 861 360-800 160-300 350-1000 800-1000 770 801 350-800 170-307 250-800 250-950 770 703 -- -- -- -- 760 606 300-800 3-4 4-7 6-7 7 6 2-4 350-600 400-800 800-900 1200 -- 500-600 0'5, 1400°C, 0"14, 1500°C, 1000 h 100 h