Z Krstic, V.D. Krstic/Jounal of the European Ceramic Sociery 28 (2008)1723-1730 33 审审1 293 当汤 :m-+26 E SN-BN 681012141618 Number of layers Number of layers Fig. 6. Change of Youngs modulus and relative density for samples whic Fig. 7. Change of Youngs modulus with the number of Si3 N4 lay containing 50 wt %o BN +50wt %o Al2O3 the interface(SN-(BN+Al O3)) lining 50 wt% BN +50wt% AlO3 designated as SN-(BN +Al2O3)and 10 wt. Si3 N4 in Bn designated as SN-(BN+SN) effect on Youngs modulus in that any small increase in porosity BN and the other consists of 10 wt. Si3 N4 and 90 wt. BN. It (equivalent to decrease in density) leads to a large decrease in can be seen from Fig. 7 that the laminated structure with inter- Youngs modulus faces containing 50 wt% BN and 50 wt %o Al2O3 has a higher Besides the porosity, BNis known to have low Youngs modu- overall Youngs modulus than the laminated structure with an lus (33.86 GPa, in the c direction and 85.95 GPain the a direction interfaces containing 10 wt Si3N4 and 90 wt. BN (at room temperature)and this is the main reason for the reduc- Much larger reduction in Youngs modulus tion of Youngs modulus of the whole system. Fig. 7 shows SN-(BN+SN)laminates(Fig. 7)is caused by the apparent the change of Youngs modulus with the number of layers for level of porosity in the interfacial layers. Careful examination two different interlayer compositions. In one set of samples, the of the interfaces in Fig. 8 revealed the presence of a much weak interfacial layer consists of 50 wt %o Al2O3 and 50 wt %o larger amount of porosity in layers containing BN and Si3n4 Fig. 8. Fracture surface of the interfaces (a)in SN-(BN+SN) and(b)in SN-(Bn +Al O3)laminated structures.1726 Z. Krstic, V.D. Krstic / Journal of the European Ceramic Society 28 (2008) 1723–1730 Fig. 6. Change of Young’s modulus and relative density for samples which containing 50 wt.% BN + 50 wt.% Al2O3 the interface (SN − (BN + Al2O3)). effect on Young’s modulus in that any small increase in porosity (equivalent to decrease in density) leads to a large decrease in Young’s modulus. Besides the porosity, BN is known to have low Young’s modu￾lus (33.86 GPa, in the c direction and 85.95 GPa in the a direction (at room temperature)) and this is the main reason for the reduc￾tion of Young’s modulus of the whole system. Fig. 7 shows the change of Young’s modulus with the number of layers for two different interlayer compositions. In one set of samples, the weak interfacial layer consists of 50 wt.% Al2O3 and 50 wt.% Fig. 7. Change of Young’s modulus with the number of Si3N4 lay￾ers for interlayer containing 50 wt.% BN + 50 wt.% Al2O3 designated as SN − (BN + Al2O3) and 10 wt.% Si3N4 in BN designated as SN − (BN + SN). BN and the other consists of 10 wt.% Si3N4 and 90 wt.% BN. It can be seen from Fig. 7 that the laminated structure with inter￾faces containing 50 wt.% BN and 50 wt.% Al2O3 has a higher overall Young’s modulus than the laminated structure with an interfaces containing 10 wt.% Si3N4 and 90 wt.% BN. Much larger reduction in Young’s modulus in SN − (BN + SN) laminates (Fig. 7) is caused by the apparent level of porosity in the interfacial layers. Careful examination of the interfaces in Fig. 8 revealed the presence of a much larger amount of porosity in layers containing BN and Si3N4. Fig. 8. Fracture surface of the interfaces (a) in SN − (BN + SN) and (b) in SN − (BN + Al2O3) laminated structures