D Jianxin et al./ Materials Science and Engineering A 444(2007)120-129 05e1115gy氵i:u a) ()L6561169:636n ?虑 Fig 8. SEM micrographs of each polished layer of SiC/(W,Ti)C laminated ceramic nozzle material (GN-2):(a)the first layer(entry zone). (b)the second layer, (c) the third layer, (d)the fourth layer, (e)the fifth second layer, and(f)the sixth layer(exit zone) SiC:E=450GPa,u=0.16.,a=46×10-6K-1 and the maximum value is.003 MPa,-130949 MPa, and k=33.5W/(mK) -265.368 MPa, respectively. Therefore, laminated structures in ceramic nozzles can form an excess compressive residual stresses in the nozzle entry (or exit)region during fabricating Owing to the symmetry, an axisymmetric calculation was process preferred Presume that it was steady state boundary conditions The FEM gridding model of the laminated nozzle is shown in Fig 9. The results of the distribution of axial (oz), radial(or), and circumferential(oe)residual thermal stresses in the GN-2 laminated nozzle in cooling process from sintering temperature to room temperature are showed in Fig. 10. As can be seen, an excess residual thermal stress is formed in the nozzle entry region for the GN-2 laminated nozzle. It is indicated that axial(oz), radial(o), and circumferential(oe) residual thermal stresses at the nozzle entry zone are compressive, and the maximum value is -71.018 MPa,-121578 MPa, and -276 204 MPa, respec- tively Fig. 11 shows the distribution of axial (oz), radial (or). and circumferential(oe)residual thermal stresses in the GN-3 laminated nozzle in cooling process from sintering tempera ture to room temperature. It is obvious that an excess resid ual thermal stress is formed both in nozzle entry and exit region for the GN-3 laminated nozzle, and the axial(oz), radial (or), and circumferential(oe) residual thermal stresses both at the nozzle entry zone and at the exit zone are compressive Fig. 9. FEM gridding model of the laminated nozzle.124 D. Jianxin et al. / Materials Science and Engineering A 444 (2007) 120–129 Fig. 8. SEM micrographs of each polished layer of SiC/(W,Ti)C laminated ceramic nozzle material (GN-2): (a) the first layer (entry zone), (b) the second layer, (c) the third layer, (d) the fourth layer, (e) the fifth second layer, and (f) the sixth layer (exit zone). SiC : E = 450 GPa, ν = 0.16, α = 4.6 × 10−6 K−1, k = 33.5 W/(m K). Owing to the symmetry, an axisymmetric calculation was preferred. Presume that it was steady state boundary conditions. The FEM gridding model of the laminated nozzle is shown in Fig. 9. The results of the distribution of axial (σz), radial (σr), and circumferential (σ) residual thermal stresses in the GN-2 laminated nozzle in cooling process from sintering temperature to room temperature are showed in Fig. 10. As can be seen, an excess residual thermal stress is formed in the nozzle entry region for the GN-2 laminated nozzle. It is indicated that axial (σz), radial (σr), and circumferential (σ) residual thermal stresses at the nozzle entry zone are compressive, and the maximum value is −71.018 MPa, −121.578 MPa, and −276.204 MPa, respec￾tively. Fig. 11 shows the distribution of axial (σz), radial (σr), and circumferential (σ) residual thermal stresses in the GN-3 laminated nozzle in cooling process from sintering tempera￾ture to room temperature. It is obvious that an excess resid￾ual thermal stress is formed both in nozzle entry and exit region for the GN-3 laminated nozzle, and the axial (σz), radial (σr), and circumferential (σ) residual thermal stresses both at the nozzle entry zone and at the exit zone are compressive, and the maximum value is −94.003 MPa, −130.949 MPa, and −265.368 MPa, respectively. Therefore, laminated structures in ceramic nozzles can form an excess compressive residual stresses in the nozzle entry (or exit) region during fabricating process. Fig. 9. FEM gridding model of the laminated nozzle.