Z Krstic, V.D. Krstic/Joumal of the European Ceramic Sociery 28(2008)1723-1730 1727 3 SiN, layers 0 0000 10 Si, N, layers 人 00000000000 9 Si,N, layers 7 SiN, layer 7 Si,N, layers B-SA N,B-s, 400队5 0000 S-S,N, S,N, 2 Theta(degree) 2 Theta(degree) Fig.9.X-ray diffraction pattems of SN-(BN+Al203)laminates with different Fig. 10. X-ray diffraction patterns of SN-(BN+SN) laminates with different number of layers sintered at 1760C. number of layers sintered at 1760( Laminates with interfacial layers containing 10 wt %o Si3N4 in with an increase in the number of Si3 N4 layers. It is found that a Bn appear to be less effective in promoting densification and certain amount of Al2O3 present in the interface diffuses into the results in a lower relative density and consequently a lower Si3N4 layers and some Y2O3(after decomposition of B-phase) diffuses into BN-based interfacial layers. Finally, both Y203 and Figs. 9 and 10 show the X-ray patterns of cross-section Al2 O3 react with each other to form the YAG phase. An increase of the Si3N4/BN-based laminates having different numbers in the number of Si3 N4 layers decreases the thickness of the lay of Si3N4 layers for compositions SN-(BN+Al2O3) and ers and increases the number of the BN-based interfaces. The SN-(BN+SN), respectively. According to the X-ray data, consequence of this is that the diffusion path for mass transport the microstructure of the Si3N4 layers consists of a major p- within the layers at the sintering temperature becomes shorter Si3N4 phase and two minor phases, Y2SiAIOSN(B-phase) and allowing easier diffusion and partitioning of Y203 and Al2O3 Y2035Al2O3(YAG). It can also be inferred from Figs. 9 and 10 within the layers that the amount of YAG phase increases continuously with the The X-ray diffraction patterns(Fig. 11)of the BN-based increase in the number of Si3N4 layers from 5 to 13 and 4 to interfaces, when layers were broken/separated along the Bn 16. It can also be noticed that the increase in the amount of interface, show that, in addition to the presence of B-Si3N4 YAG phase takes place at the expense of B-phase, indicating phase, three other phases are present: BN, B-phase and YAO that the Y2SiAIOSN(known as B-Phase)decomposes to YAG Again, the content of the YAG phase increases with an increase and Sin of the number of Si3N4 layers for up to 9 layers. When the It is also noticed that the entire amount of a-Si3N4 phase is number of layers is more than 9, the YAG phase becomes transformed to B-Si3N4 phase in both compositions. It appears the major phase in the interfaces. This behaviour is consis that the addition 10 wt %o of oxides(7 wt %o of Y203 and 3 wt tent with the ability of the Y203 component to diffuse fron of Al2O3) provides sufficient amount of liquid phase for com- the Si3N4 layer to the interfacial layer and react with Al2O plete a to B-Si3 N4 phase transformation. The slow cooling rate As pointed out earlier, as the number of layers increases, of 10C/min used in the present experiment was another favor- their thickness decreases creating shorter diffusion paths for ble factor which contributed to complete decomposition of Y2O3 and faster reaction with Al2 O3. The result of this is B-phase at temperatures between 1000 and 1100C. Another the larger amount of YAG phase formed in the interfacial interesting finding of this work is the increase of YAG phase layer. The decomposition of B-phase can be expressed by theZ. Krstic, V.D. Krstic / Journal of the European Ceramic Society 28 (2008) 1723–1730 1727 Fig. 9. X-ray diffraction patterns of SN − (BN + Al2O3) laminates with different number of layers sintered at 1760 ◦C. Laminates with interfacial layers containing 10 wt.% Si3N4 in BN appear to be less effective in promoting densification and results in a lower relative density and consequently a lower Young’s modulus. Figs. 9 and 10 show the X-ray patterns of cross-section of the Si3N4/BN-based laminates having different numbers of Si3N4 layers for compositions SN − (BN + Al2O3) and SN − (BN + SN), respectively. According to the X-ray data, the microstructure of the Si3N4 layers consists of a major - Si3N4 phase and two minor phases, Y2SiAlO5N (B-phase) and 3Y2O35Al2O3 (YAG). It can also be inferred from Figs. 9 and 10 that the amount of YAG phase increases continuously with the increase in the number of Si3N4 layers from 5 to 13 and 4 to 16. It can also be noticed that the increase in the amount of YAG phase takes place at the expense of B-phase, indicating that the Y2SiAlO5N (known as B-phase) decomposes to YAG and Si3N4. It is also noticed that the entire amount of -Si3N4 phase is transformed to -Si3N4 phase in both compositions. It appears that the addition 10 wt.% of oxides (7 wt.% of Y2O3 and 3 wt.% of Al2O3) provides sufficient amount of liquid phase for com￾plete  to -Si3N4 phase transformation. The slow cooling rate of 10 ◦C/min. used in the present experiment was another favor￾able factor which contributed to complete decomposition of B-phase at temperatures between 1000 and 1100 ◦C. Another interesting finding of this work is the increase of YAG phase Fig. 10. X-ray diffraction patterns of SN − (BN + SN) laminates with different number of layers sintered at 1760 ◦C. with an increase in the number of Si3N4 layers. It is found that a certain amount of Al2O3 present in the interface diffuses into the Si3N4 layers and some Y2O3 (after decomposition of B-phase) diffuses into BN-based interfacial layers. Finally, both Y2O3 and Al2O3 react with each other to form the YAG phase. An increase in the number of Si3N4 layers decreases the thickness of the lay￾ers and increases the number of the BN-based interfaces. The consequence of this is that the diffusion path for mass transport within the layers at the sintering temperature becomes shorter allowing easier diffusion and partitioning of Y2O3 and Al2O3 within the layers. The X-ray diffraction patterns (Fig. 11) of the BN-based interfaces, when layers were broken/separated along the BN interface, show that, in addition to the presence of -Si3N4 phase, three other phases are present: BN, B-phase and YAG. Again, the content of the YAG phase increases with an increase of the number of Si3N4 layers for up to 9 layers. When the number of layers is more than 9, the YAG phase becomes the major phase in the interfaces. This behaviour is consis￾tent with the ability of the Y2O3 component to diffuse from the Si3N4 layer to the interfacial layer and react with Al2O3. As pointed out earlier, as the number of layers increases, their thickness decreases creating shorter diffusion paths for Y2O3 and faster reaction with Al2O3. The result of this is the larger amount of YAG phase formed in the interfacial layer. The decomposition of B-phase can be expressed by the