C. Li et al. Materials Letters 57(2003)3473-3478 Table 1 Mechanical properties of the laminated Si N//BN ceramics Materials Work of fracture Work of fracture MPa). RT (MPa),1300°C m2).1300°C MYA-LCs 700.46±25.62 2100±44 26.56±33.75 1300±140 LYA-LCS 650.57±46.28 3500±100 325.85±48.76 2400±220 on the side, which was normal to the hot-pressing thirds of that of LYA-LCs. However, the cases are direction and would experience tension stress during different at elevated temperature. At 1300C, the testing. The two edges near the tensile surface were bending strength and woF of the LYA-LCs are much rounded with a 15-mm diamond grinding wheel. The higher that those of MYA-LCs, twice and once higher mechanical properties of the samples were determined than those of MYA-LCs, respectively. This can be with the mechanical test machine(Astron AG2000A). explained based on the feature of the glass phases The test direction and the orientation of the laminated resulted from the sintering aids. It is well known that Si3N4/BN ceramics bars are shown schematically in Fig. 2. The strength measurement was carried out sing a three-point bending method with a span of 30 mm and a crosshead speed of 0.5 mm/min. Also, work MYA-LCS of fracture(WOF) measurement was conducted using a three-point bending method with a span of 30 mm and a crosshead speed of 0.05 mm/min Crack deflec tion and polished surface parallel to the hot-pressing direction were examined with scanning electron microscopy (SEM). Microstructure analysis with scanning electron microscopy(SEM) was carried out on test bars polished with diamond pastes to 1 um and etched in a platinum crucible with melting NaoH at 400C for 1.5 min and cleaned with boiling water repeatedl Displacement (um) 3. Results and discussion LYA-LCS 3.1. Mechanical properties In this work, the bending strength of the specimen was calculated using three-point bending stress equa tion, whereas the WoF was calculated by dividing the area under the load-displacement curve by twice the 3 150 MYA-LCS cross-sectional area of the specimen. The mechanical properties of testing materials at room temperature and at 1300C are given in Table 1 From Table 1, it can be seen that the type of sintering aids remarkably affects the mechanical prop erties of the laminated Si3 N4/BN ceramics. At room Displacement (um) temperature, the bending strength of MYA-LCs is 50 MPa higher than that of LYA-LCs, even though Fig 3. Load-displacement curves of both materials(a)at room the work of fracture(WOF)of MYA-LCs is only two- temperature and(b)at 1300C.on the side, which was normal to the hot-pressing direction and would experience tension stress during testing. The two edges near the tensile surface were rounded with a 15-mm diamond grinding wheel. The mechanical properties of the samples were determined with the mechanical test machine (Astron AG2000A). The test direction and the orientation of the laminated Si3N4/BN ceramics bars are shown schematically in Fig. 2. The strength measurement was carried out using a three-point bending method with a span of 30 mm and a crosshead speed of 0.5 mm/min. Also, work of fracture (WOF) measurement was conducted using a three-point bending method with a span of 30 mm and a crosshead speed of 0.05 mm/min. Crack deflec￾tion and polished surface parallel to the hot-pressing direction were examined with scanning electron microscopy (SEM). Microstructure analysis with scanning electron microscopy (SEM) was carried out on test bars polished with diamond pastes to 1 Am and etched in a platinum crucible with melting NaOH at 400 jC for 1.5 min and cleaned with boiling water repeatedly. 3. Results and discussion 3.1. Mechanical properties In this work, the bending strength of the specimen was calculated using three-point bending stress equa￾tion, whereas the WOF was calculated by dividing the area under the load –displacement curve by twice the cross-sectional area of the specimen. The mechanical properties of testing materials at room temperature and at 1300 jC are given in Table 1. From Table 1, it can be seen that the type of sintering aids remarkably affects the mechanical prop￾erties of the laminated Si3N4/BN ceramics. At room temperature, the bending strength of MYA-LCs is f 50 MPa higher than that of LYA-LCs, even though the work of fracture (WOF) of MYA-LCs is only two￾thirds of that of LYA-LCs. However, the cases are different at elevated temperature. At 1300 jC, the bending strength and WOF of the LYA-LCs are much higher that those of MYA-LCs, twice and once higher than those of MYA-LCs, respectively. This can be explained based on the feature of the glass phases resulted from the sintering aids. It is well known that Table 1 Mechanical properties of the laminated Si3N4/BN ceramics Materials Bending strength (MPa), RT Work of fracture (J/m2 ), RT Bending strength (MPa), 1300 jC Work of fracture (J/m2 ), 1300 jC MYA-LCs 700.46 F 25.62 2100 F 44 126.56 F 33.75 1300 F 140 LYA-LCs 650.57 F 46.28 3500 F 100 325.85 F 48.76 2400 F 220 Fig. 3. Load – displacement curves of both materials (a) at room temperature and (b) at 1300 jC. C. Li et al. / Materials Letters 57 (2003) 3473–3478 3475