J. Deng et al. /Ceramics international 36(2010)299-306 nozzles. and the other is the thermal stress inside the cws [2] Z Ding. J. Deng, J. Li, Wear behavior of ceramic nozzles in coal water nozzles. Once the CwS ceramic nozzle possesses a layered slurry burning, Ceramics Intemational 34(2004)591-596 structure, the hardness and fracture toughness at the nozzle [3] R. Lakshminarayanan, D K Shetty, R.A. Cutler, Toughening of layered xternal layer are improved(see Table 3), and the temperature eramic composites with residual surface compression, Journal of Amer- ican Ceramic Society 79(1996)79-87 gradients and the thermal stresses at the nozzle exit can be greatly [4] P.Z. Cai, DJ. Green, G L Messing, Mechanical characterization of ALO3/ reduced due to the different thermal expansion coefficients of the ZrO2 hybrid laminates, Journal of the European Ceramic Society 5(1998) individual layers during Cws burning processes. Therefore, 025-2034. layered ceramic nozzles exhibited an apparent increase [5] G. de Portu, L. Micele, G. Pezzotti, Laminated ceramic structures from xide systems, Composites: Part B 37(2006)556-567 erosion wear resistance over the unstressed reference one, the [6] V.M. Sglavo, M. Bertoldi, Design and production of ceramic I mechanisms responsible were found to be that layered structure with high mechanical resistance and reliability, Acta Materialia s in the CWS nozzles can improve the hardness and fracture 4929-4937 toughness of the external layer, and reduce the temperature [7] S. Guicciardi, M. Nagliati, C. Melandri, G. Pezzotti, D. Sciti, Effects gradients and the thermal stresses at the exit of the nozzle residual stresses on the fracture properties of non-oxide laminated omposites, Journal of the European Ceramic Society 27(2007)351 4. Conclusions [8] H. Tomaszewski, H. Weglarz, A. Wailer, M. Boniecki, D. Kalin Multilayer ceramic composites with high failure resistance, Journal of Al2O/W,Ti)C Al2O3/TiC layered ceramics with different the European Ceramic Society 27(2007)1373-1377 thickness ratios among constituent layers were developed to be [9] V. Sergo, D.M. Lipkin, G. De Portu, D.R. Clarke, Edge stresses in alumina/zirconia laminates, Journal of American Ceramic Society 80 used as nozzles in CWs boilers. The performance and wear 997)1633-1638 characteristics of these nozzles were investigated. The [10]G De Portu, L. Micele, D. Prandstraller, G. Palombarini, G. Pezzotti, following conclusions were obtained: brasive wear in ceramic laminated composites, Wear 260(2006)1104- The layered ceramic nozzles (LNl, LN2, and exhibited an apparent increase in erosion wear resistand [11] A. Tarlazzi, E. Roncari, P. Pinasco. S. Guicciardi, C. Melandri, G. de the unstressed reference nozzle(n5)in industry CWs I Portu, Tribological behaviour of Al2O,/ZrOr-ZrO2 laminated composites, wear244(2000)29-40. The mechanisms responsible were found to be that layered [12] M Hadad, G. Bluga bler. E. Rosset. L. Rohr. J. Michler. Tribo- structure in the CwS nozzles can improve the hardness and logical behaviour of Si,N4 and Si3N4 -% tin based composites and fracture toughness of the external layer, and can reduce the ti-layer laminates, Wear 260(2006)634-64 temperature gradients and the thermal stresses at the exit of the 13] J. Deng, Wear behaviors of ceramic nozzles with laminated structure at their entry, Wear 266(2009)30-36. nozzle during CWs burning processes 14] J. Deng, L Liu, M. Ding, Effect of residual stresses on the erosion wear of It is suggested that layered structures in ceramic nozzles is laminated ceramic nozzles, Materials Characterization 59(2008)1-8. an effective way to improve the erosion wear resistance over the [15] J. Deng, L. Liu, M. Ding, Erosion wear behaviours of SiC/(w,)c stress-free ceramic nozzles in industry Cws boilers laminated ceramic nozzles in dry sand blasting processes, Materials Science Engineering A 444(2007)120-129. Acknowledgements 16]x. Al. Z. Li, J. Deng. Development and perspective of advanced ceramic ng tool materials, Key Engineering Materials 108(1995)53-66. 17]J.Barry, G. he machining of hardened steels. This work was supported by the"Taishan Scholar Program Part I. Alumina/TiC cutting tool wear, Wear 247(2001)139-15 Foundation of Shandong", the"Outstanding Young Scholar [181. Deng. X. Yang Wear mechanisms of Al/nic/Mo/Ni ceramic wire- Science Foundation of Shandong", and the"Key Science and 9]RF. Cook, B.R. Lawn, A modified indentation toughness technique. Technology Project of Shandong Province(2006GG2204017) Journal of American Ceramic Society 66(1983)200-201 [20] J. Deng, D. Yuan, Y. Tan, Design, fabrication and performance of Al2O3/ References Wo.7Tio.3)C+ Al2O,TiC multilayered ceramic nozzles, International Journal of Refractory Metals Hard Materials 27(2009)734-739 [I J. Deng, Z Ding, D. Yun, Erosion wear mechanisms of coal-water-slurry 21 Z. Ding, Development of assembled coal-water-slurry ceramic nozzles (CWS)ceramic nozzles in industry boilers, Materials Science Engineering and study on their failure mechanisms, Ph D. Dissertation, Shandong A417(2006)1-7nozzles, and the other is the thermal stress inside the CWS nozzles. Once the CWS ceramic nozzle possesses a layered structure, the hardness and fracture toughness at the nozzle external layer are improved (see Table 3), and the temperature gradients and the thermal stresses at the nozzle exit can be greatly reduced due to the different thermal expansion coefficients of the individual layers during CWS burning processes. Therefore, the layered ceramic nozzles exhibited an apparent increase in erosion wear resistance over the unstressed reference one, the mechanisms responsible were found to be that layered structure in the CWS nozzles can improve the hardness and fracture toughness of the external layer, and reduce the temperature gradients and the thermal stresses at the exit of the nozzle. 4. Conclusions Al2O3/(W,Ti)C + Al2O3/TiC layered ceramics with different thickness ratios among constituent layers were developed to be used as nozzles in CWS boilers. The performance and wear characteristics of these nozzles were investigated. The following conclusions were obtained: The layered ceramic nozzles (LN1, LN2, and LN3) exhibited an apparent increase in erosion wear resistance over the unstressed reference nozzle (N5) in industry CWS boilers. The mechanisms responsible were found to be that layered structure in the CWS nozzles can improve the hardness and fracture toughness of the external layer, and can reduce the temperature gradients and the thermal stresses at the exit of the nozzle during CWS burning processes. It is suggested that layered structures in ceramic nozzles is an effective way to improve the erosion wear resistance over the stress-free ceramic nozzles in industry CWS boilers. Acknowledgements This work was supported by the ‘‘Taishan Scholar Program Foundation of Shandong’’, the ‘‘Outstanding Young Scholar Science Foundation of Shandong’’, and the ‘‘Key Science and Technology Project of Shandong Province (2006GG2204017)’’. References [1] J. Deng, Z. Ding, D. Yun, Erosion wear mechanisms of coal-water-slurry (CWS) ceramic nozzles in industry boilers, Materials Science Engineering A 417 (2006) 1–7. [2] Z. Ding, J. Deng, J. Li, Wear behavior of ceramic nozzles in coal water slurry burning, Ceramics International 34 (2004) 591–596. [3] R. Lakshminarayanan, D.K. Shetty, R.A. Cutler, Toughening of layered ceramic composites with residual surface compression, Journal of Amer￾ican Ceramic Society 79 (1996) 79–87. [4] P.Z. Cai, D.J. Green, G.L. Messing, Mechanical characterization of Al2O3/ ZrO2 hybrid laminates, Journal of the European Ceramic Society 5 (1998) 2025–2034. [5] G. de Portu, L. Micele, G. Pezzotti, Laminated ceramic structures from oxide systems, Composites: Part B 37 (2006) 556–567. [6] V.M. Sglavo, M. Bertoldi, Design and production of ceramic laminates with high mechanical resistance and reliability, Acta Materialia 54 (2006) 4929–4937. [7] S. Guicciardi, M. Nagliati, C. Melandri, G. Pezzotti, D. Sciti, Effects of residual stresses on the fracture properties of non-oxide laminated composites, Journal of the European Ceramic Society 27 (2007) 351– 356. [8] H. Tomaszewski, H. Weglarz, A. Wajler, M. Boniecki, D. Kalinski, Multilayer ceramic composites with high failure resistance, Journal of the European Ceramic Society 27 (2007) 1373–1377. [9] V. Sergo, D.M. Lipkin, G. De Portu, D.R. Clarke, Edge stresses in alumina/zirconia laminates, Journal of American Ceramic Society 80 (1997) 1633–1638. [10] G. De Portu, L. Micele, D. Prandstraller, G. Palombarini, G. Pezzotti, Abrasive wear in ceramic laminated composites, Wear 260 (2006) 1104– 1111. [11] A. Tarlazzi, E. Roncari, P. Pinasco, S. Guicciardi, C. Melandri, G. de Portu, Tribological behaviour of Al2O3/ZrO2–ZrO2 laminated composites, Wear 244 (2000) 29–40. [12] M. Hadad, G. Blugan, J. K¨ ubler, E. Rosset, L. Rohr, J. Michler, Tribo￾logical behaviour of Si3N4 and Si3N4 – % TiN based composites and multi-layer laminates, Wear 260 (2006) 634–641. [13] J. Deng, Wear behaviors of ceramic nozzles with laminated structure at their entry, Wear 266 (2009) 30–36. [14] J. Deng, L. Liu, M. Ding, Effect of residual stresses on the erosion wear of laminated ceramic nozzles, Materials Characterization 59 (2008) 1–8. [15] J. Deng, L. Liu, M. Ding, Erosion wear behaviours of SiC/(W,Ti)C laminated ceramic nozzles in dry sand blasting processes, Materials Science Engineering A 444 (2007) 120–129. [16] X. Ai, Z. Li, J. Deng, Development and perspective of advanced ceramic cutting tool materials, Key Engineering Materials 108 (1995) 53–66. [17] J. Barry, G. Byrne, Cutting tool wear in the machining of hardened steels. Part I. Alumina/TiC cutting tool wear, Wear 247 (2001) 139–151. [18] J. Deng, X. Yang, Wear mechanisms of Al2O3/TiC/Mo/Ni ceramic wire￾drawing dies, Materials Science Engineering A 424 (2006) 347–354. [19] R.F. Cook, B.R. Lawn, A modified indentation toughness technique, Journal of American Ceramic Society 66 (1983) 200–201. [20] J. Deng, D. Yuan, Y. Tan, Design, fabrication and performance of Al2O3/ (W0.7Ti0.3)C + Al2O3/TiC multilayered ceramic nozzles, International Journal of Refractory Metals & Hard Materials 27 (2009) 734–739. [21] Z. Ding, Development of assembled coal-water-slurry ceramic nozzles and study on their failure mechanisms, Ph.D. Dissertation, Shandong University, 2004. 306 J. Deng et al. / Ceramics International 36 (2010) 299–306