D Jianxin et al. Materials Science and Engineering A 444 (2007)120-129 m-m5a-m1723-m (a 3939423.854 50.349 213s9(b) 48093 (c) 94347 51.139 Fig 10. Distribution of (a) axial(oz).(b)radial(o, ) and (c)circumferential(aa) residual thermal stresses of GN-2 laminated nozzle 3.3. Erosion behaviour of the Sic/w,li)C laminated nozzle that of the worn GN-2 and GN-3 laminated nozzles, especially at the nozzle entry region. The exit diameter of the worn GN-3 The erosion behaviour of Sic/w,Ti)c laminated ceramic laminated nozzle is greatly reduced compared with that of the nozzle(GN-2 and GN-3) in dry sand blasting processes was GN-2 laminated nozzle. investigated in comparison with the stress-free ceramic nozzle The results of the nozzle entry bore diameter variation with (CN-2). Fig. 12 shows the cumulative mass loss of GN-2, GN- the erosion time for GN-2, GN-3, and CN-2 nozzles are shown 3, and CN-2 nozzles in dry sand blasting processes. It can be in Fig. 15. It is indicated that the entry bore diameter enlarges seen that the cumulative mass loss continuously increased with greatly with the operation time for CN-2 stress-free nozzle the operation time. Compared with GN-2 and GN-3 laminated While the entry bore diameter increases slowly with the opera nozzle, the cn-2 stress-free nozzle showed higher cumulative tion time for gn-2 and gN-3 laminated nozzles. Fig. 16 shows mass loss under the same test conditions the comparison of the erosion rates for GN-2, GN-3, and CN-2 The entry bore profiles of worn GN-2, GN-3, and CN-2 noz- nozzles in sand blasting processes. It is obvious that the erosion zles after dry sand blasting for 540 min are shown in Fig. 13. rate of the stress-free nozzles is higher than that of the laminated It is showed that the entry bore of CN-2 stress-free nozzle was nozzles. Therefore, It is apparently that the GN-2 and GN-3 lam everely worn. While the entry bore of GN-2 and GN-3 lami- inated nozzles exhibited higher erosion wear resistance over the nated nozzle had worn slightly compared with that of the former CN-2 stress-free nozzle under the same test conditions Fig. 17 shows the SEM micrographs of the entry bore surface The worn ceramic nozzles were cut after operation in longitu- of the worn ceramic nozzles. From these SEM micrographs, dinal directions for failure analysis. Fig. 14 shows the photos of different morphologies and fracture modes of the nozzles can the inner bore profile of the whole ceramic nozzle after 540 min be seen clearly. The CN-2 stress-free nozzle at the entry area operation. It is showed that inner bore diameter of the worn CN- failed in a highly brittle manner, and exhibited a brittle fracture 2 nozzle along the nozzle longitudinal directions is larger than induced removal process. There are a lot of obvious pits locatedD. Jianxin et al. / Materials Science and Engineering A 444 (2007) 120–129 125 Fig. 10. Distribution of (a) axial (σz), (b) radial (σr), and (c) circumferential (σ) residual thermal stresses of GN-2 laminated nozzle. 3.3. Erosion behaviour of the SiC/(W,Ti)C laminated nozzle The erosion behaviour of SiC/(W,Ti)C laminated ceramic nozzle (GN-2 and GN-3) in dry sand blasting processes was investigated in comparison with the stress-free ceramic nozzle (CN-2). Fig. 12 shows the cumulative mass loss of GN-2, GN- 3, and CN-2 nozzles in dry sand blasting processes. It can be seen that the cumulative mass loss continuously increased with the operation time. Compared with GN-2 and GN-3 laminated nozzle, the CN-2 stress-free nozzle showed higher cumulative mass loss under the same test conditions. The entry bore profiles of worn GN-2, GN-3, and CN-2 noz￾zles after dry sand blasting for 540 min are shown in Fig. 13. It is showed that the entry bore of CN-2 stress-free nozzle was severely worn. While the entry bore of GN-2 and GN-3 lami￾nated nozzle had worn slightly compared with that of the former one. The worn ceramic nozzles were cut after operation in longitu￾dinal directions for failure analysis. Fig. 14 shows the photos of the inner bore profile of the whole ceramic nozzle after 540 min operation. It is showed that inner bore diameter of the worn CN- 2 nozzle along the nozzle longitudinal directions is larger than that of the worn GN-2 and GN-3 laminated nozzles, especially at the nozzle entry region. The exit diameter of the worn GN-3 laminated nozzle is greatly reduced compared with that of the GN-2 laminated nozzle. The results of the nozzle entry bore diameter variation with the erosion time for GN-2, GN-3, and CN-2 nozzles are shown in Fig. 15. It is indicated that the entry bore diameter enlarges greatly with the operation time for CN-2 stress-free nozzle. While the entry bore diameter increases slowly with the opera￾tion time for GN-2 and GN-3 laminated nozzles. Fig. 16 shows the comparison of the erosion rates for GN-2, GN-3, and CN-2 nozzles in sand blasting processes. It is obvious that the erosion rate of the stress-free nozzles is higher than that of the laminated nozzles. Therefore, It is apparently that the GN-2 and GN-3 lam￾inated nozzles exhibited higher erosion wear resistance over the CN-2 stress-free nozzle under the same test conditions. Fig. 17 shows the SEM micrographs of the entry bore surface of the worn ceramic nozzles. From these SEM micrographs, different morphologies and fracture modes of the nozzles can be seen clearly. The CN-2 stress-free nozzle at the entry area failed in a highly brittle manner, and exhibited a brittle fracture induced removal process. There are a lot of obvious pits located