Silicon -based non-oxide structural ceramics 21 product the starting powders should possess can be analyzed in terms of the pullout mode narrow B-Si3N4 grain size distribution and have developed by becher et al.This model faceted, elongated B-Si3n4 crystals explains the toughening behavior of whisker Ceramics prepared from such Si3N4-powders reinforced ceramic matrix composites. Accord should exhibit microstructures containing a ingly, the fracture toughness( K,d)of materials large amount of elongated grains increasing the which reveal mainly debonding and pullout fracture toughness of the material without exag- (crack deflection is neglected) depends on the gerated grown grains, which would deteriorate matrix toughness(KTe), a constant(A)as wel the materials strength. Therefore, these cera the volume fraction (V) and the diameter mics are expected to combine both high (Dmi)of the reinforcing particles (egn(6)) strength and high fracture toughness. The rela Herewith the constant (A)depends on the tion between microstructure and mechanical strength and elastic moduli of the reinforcing properties is discussed in the following para graph phase as well as the Poisson ratio, elastic mod ulus and fracture energy of the matrix and the 4.1.3 Microstructure and mechanical properties of fracture energy of the interface between the Si,N ceramics reinforcing phase and the matrix The interconnection between the Si, Na-cera mics microstructure and its fracture toughness KIe=[(KI)2+A V Dmin] 10 D/E104/96 0102030405,060 010203,04,0506.0 Leng th lum Length fum D/E1020/80 20 886=0E 01,02,03040506,0 °102080405060 gth fum] Length lum ig. 6. Microstructural development of Si, N.-ceramics. E10: a-Si, N,(UBE SN-E10, UBE Industries, Japan) containi 4. 1 vol% B-Si3N4; D/E10 4/ 96: a-Si3N4(E10) seeded with 4 vol %o B-Si3N )DE102080 vol% B-Si,N, (D); D: B-Si, N,(SN-BS, Denka, Japan) containing 2. 5 vol% x-Si, NSilicon-based non-oxide structural ceramics 21 product the starting powders should possess a narrow fl-Si3N4 grain size distribution and have faceted, elongated fl-Si3N4 crystals. Ceramics prepared from such Si3N4-powders should exhibit microstructures containing a large amount of elongated grains increasing the fracture toughness of the material without exag￾gerated grown grains, which would deteriorate the materials strength. Therefore, these cera￾mics are expected to combine both high strength and high fracture toughness. The rela￾tion between microstructure and mechanical properties is discussed in the following para￾graph. 4.1.3 Microstructure and mechanical properties of Si3N4-ceramics The interconnection between the Si,N4-cera￾mics microstructure and its fracture toughness can be analyzed in terms of the pullout model developed by Becher et al. 93 This model explains the toughening behavior of whisker reinforced ceramic matrix composites. Accord￾ingly, the fracture toughness (K,c) of materials which reveal mainly debonding and pullout (crack deflection is neglected) depends on the matrix toughness (K','c), a constant (A) as well as the volume fraction (V 0 and the diameter (D,,~n) of the reinforcing particles (eqn (6)). Herewith the constant (A) depends on the strength and elastic moduli of the reinforcing phase as well as the Poisson ratio, elastic mod￾ulus and fracture energy of the matrix and the fracture energy of the interface between the reinforcing phase and the matrix. KI~=[(K¢]~c)2-kA. Vf. Dm,~]'/2 (6) / ..~'° ....""" ." .. ............................................................................................. ~' 4o ..." .. ........................................................................................................................ ....."" SO ' , " ' ........................................................................................................................................... T SO : .."" ... • ........................................................................................................................... ..~Pl~ -- ..... - .-. --" - """""""'"I 0 , ... ...... ." . ..... P=~+:4 ° .... 0 ~ i I.'" v' "(::" i:::~""i:::"~i""i::~V~1 2 ~,~X 0 1,0 2,0 3,0 4,0 5,0 8,0 -- 0 1,0 2,0 3,0 4,0 5,0 6,0" -- Length rum] Length rum] Z o,o,o,l l .................................................................................... o ....................... ~)~o~ ~ .............. I ~ ...... ..... • = " • , :: if:! > o~~::f_2L~<~ - > ,, ..... :::: :::i:,ii I 0 1,0 2,0 3,0 4,0 5,0 6,01 Y~ 00¢" 1,0 Length rum] Length rum] Fig. 6. Microstructural development of Si.~N4-ceramics. El0:0~-Si3N4 (UBE SN-E10, UBE Industries, Japan) containing 4.1 vol% fl-Si~N4; D/E10 4/96: 0~-8i3N 4 (El0) seeded with 4 vol% fl-Si3N4 (D); D/E10 20/80:~-Si~N4 (El0) seeded with 20 vol% fi-Si3N4 (D); D: fl-Si~N4 (SN-BS, Denka, Japan) containing 2.5 vol% ct-Si3N4. '~