3646 S. Tariolle et al. Journal of the European Ceramic Society 25(2005)3639-3647 Conclusion Different types of boron carbide composites have been 60 elaborated by tap se types of C555 composites had never been studied before with boron car bide materials. Different composites with either porous in- 40 terlayers obtained by layers obtained without addition of sintering aid, or weak B4c-BN interlayers obtained by a mixture of boron carbide and Cs45 C550 boron nitride, or weak interfaces in graphite or boron ni- tride have been realized. Most of them presented reinforce- ment by crack deflection as we can see on the values of Fig. 16. Work of rupture in the different composites work of rupture: 38.07kJm-3for composites with interlay ers with corn starch(55 vol %) 40.25 kJ for compos- ites with B4C-BN interlayers, 30 11 kJm-3 for composites The composite NSA presented againof 175%for the work with weak interlayers in bN and 38.64kJm-3 for compos- of rupture compared with dense material whereas no crack ites with weak interlayers in graphite. An increase is ob- deflection was observed: in this case, there was no reinforce- served compare with the value for a dense boron carbide ment by crack deflection. The composite with interlayers ob-(25.09kJm-) tained by the lowest quantity of corn starch(CS45) presented Concerning the most promising materials, further re- no gain of work of rupture and small crack deflection: there searches should be carried out concerning(i) the influence is no reinforcement. In these two cases, no friction stress was of relative thickness on weak interlayers obtained with lower contents of pore forming agent and(ii)mixtures of B4 C-BN All other composites presented reinforcement by crack varying the content of BN. Concerning weak interfaces, the deflection Concerning composites with interlayers obtained technique of deposition of the interlayers should be better by the use of corn starch(Cs), the reinforcement was bet- mastered ter for a large value of porosity in the interlayers: a gain of 50% for the work of rupture compared with dense ma- terial was observed and long crack deflection were mea- sured for CS55 containing 51 vol. of porosity. A slight Acknowledgement gain of apparent fracture toughness (16%)was also no- ticed for the composite. The composite with interlayers This work is a part of the thesis of s. tariolle made with a mixture of boron carbide and boron nitrido presented a significant reinforcement by crack deflection: a gain of 60% in work of rupture and significant crack de- References flections. Both the composites with weak interfaces with graphite (l-G)and boron nitride(l-BN) presented a gain in 1. Clegg, w.J., The fabrication and failure of laminar ceramic compos- work of rupture (54% and 20%, respectively)and a gain ites. Acta Metall. Mater, 1992, 40(11), 3085-3093 in apparent fracture toughness(13% and 105 2. Liu, H. Y. and Hsu, S. M, Fracture behavior of multilayer sili- on nitride/boron nitride ceramics. J. Am. Ceram. Soc., 1996, 79(9) tively) 2452-2457 3. Kuo, D. H and Kriven, W M, Fracture of multilayer oxide compos- ites. Mater. Sci. Eng. 4, 1998 4. Blanks, K. S, Kristoffersson, A, Carlstrom, E. and Clegg, w. J Crack deflection in ceramic laminates using porous interlayers u: Ceram.Soc,1998,18,1945-1951. 5. Davis, J B, Kristoffersson, A, Carlstrom, E and Clegg, W. J, Fab- mean per layer rication of laminates with crack deflecting porous interlayers J.Am. Cera.Soc.,2000,83(10),23692374 6. He, M.-Y. and Hutchinson, J. W. Kinking of a crack out of the xoo interface.J. Appl. Mech., 1989, 56, 270-278 CS50 7. Thevenot, F, Boron carbide: a comprehensive review. J. Eur Ceram Soc,1990,6(4),205-225 8. Tariolle B4C-BN H-BN 1-G osites lamellaires. Elaboration, propri Ph.D 502 thesis. 328TD. Ecole des mines de saint-Etienne. france NSA 9. Reynaud, C, Thevenot, F and T, Processing and microstruc- ture of Sic laminar J. Refract. Met. Hard Mater Fig. 17. Lengths of crack deflection in the different composites 2001,19,425-4353646 S. Tariolle et al. / Journal of the European Ceramic Society 25 (2005) 3639–3647 Fig. 16. Work of rupture in the different composites. The composite NSA presented a gain of 175% for the work of rupture compared with dense material whereas no crack deflection was observed: in this case, there was no reinforce￾ment by crack deflection. The composite with interlayers ob￾tained by the lowest quantity of corn starch (CS45) presented no gain of work of rupture and small crack deflection: there is no reinforcement. In these two cases, no friction stress was observed. All other composites presented reinforcement by crack deflection. Concerning composites with interlayers obtained by the use of corn starch (CS), the reinforcement was bet￾ter for a large value of porosity in the interlayers: a gain of 50% for the work of rupture compared with dense ma￾terial was observed and long crack deflection were mea￾sured for CS55 containing 51 vol.% of porosity. A slight gain of apparent fracture toughness (16%) was also no￾ticed for the composite. The composite with interlayers made with a mixture of boron carbide and boron nitride presented a significant reinforcement by crack deflection: a gain of 60% in work of rupture and significant crack de- flections. Both the composites with weak interfaces with graphite (I-G) and boron nitride (I-BN) presented a gain in work of rupture (54% and 20%, respectively) and a gain in apparent fracture toughness (13% and 105%, respec￾tively). Fig. 17. Lengths of crack deflection in the different composites. 5. Conclusion Different types of boron carbide composites have been elaborated by tape casting and lamination. These types of composites had never been studied before with boron car￾bide materials.8 Different composites with either porous in￾terlayers obtained by pore forming agent, or weak inter￾layers obtained without addition of sintering aid, or weak interlayers obtained by a mixture of boron carbide and boron nitride, or weak interfaces in graphite or boron ni￾tride have been realized. Most of them presented reinforce￾ment by crack deflection as we can see on the values of work of rupture: 38.07 kJ m−3 for composites with interlay￾ers with corn starch (55 vol.%), 40.25 kJ m−3 for compos￾ites with B4C-BN interlayers, 30.11 kJ m−3 for composites with weak interlayers in BN and 38.64 kJ m−3 for compos￾ites with weak interlayers in graphite. An increase is ob￾served compare with the value for a dense boron carbide (25.09 kJ m−3). Concerning the most promising materials, further re￾searches should be carried out concerning (i) the influence of relative thickness on weak interlayers obtained with lower contents of pore forming agent and (ii) mixtures of B4C-BN, varying the content of BN. Concerning weak interfaces, the technique of deposition of the interlayers should be better mastered. Acknowledgement This work is a part of the thesis of S. Tariolle. References 1. Clegg, W. J., The fabrication and failure of laminar ceramic compos￾ites. Acta Metall. Mater., 1992, 40(11), 3085–3093. 2. Liu, H. Y. and Hsu, S. M., Fracture behavior of multilayer sili￾con nitride/boron nitride ceramics. J. Am. Ceram. Soc., 1996, 79(9), 2452–2457. 3. Kuo, D. H. and Kriven, W. M., Fracture of multilayer oxide compos￾ites. Mater. Sci. Eng. A, 1998, 241, 241–250. 4. Blanks, K. S., Kristoffersson, A., Carlstrom, E. and Clegg, W. J., ¨ Crack deflection in ceramic laminates using porous interlayers. J. Eur. Ceram. Soc., 1998, 18, 1945–1951. 5. Davis, J. B., Kristoffersson, A., Carlstrom, E. and Clegg, W. J., Fab- ¨ rication of ceramic laminates with crack deflecting porous interlayers. J. Am. Ceram. Soc., 2000, 83(10), 2369–2374. 6. He, M.-Y. and Hutchinson, J. W., Kinking of a crack out of the interface. J. Appl. Mech., 1989, 56, 270–278. 7. Thevenot, F., Boron carbide: a comprehensive review. J. Eur. Ceram. Soc., 1990, 6(4), 205–225. 8. Tariolle, S., Carbure de bore monolithique poreux et com￾posites lamellaires. Elaboration, propri´et´es, renforcement. Ph.D. thesis, 328TD, Ecole des Mines de Saint-Etienne, France, 2004. 9. Reynaud, C., Thevenot, F. and Chartier, T., Processing and microstruc￾ture of SiC laminar composites. Intern. J. Refract. Met. Hard Mater., 2001, 19, 425–435