Availableonlineatwww.sciencedirect.com SCIENCE E噩≈S Journal of the European Ceramic Society 23(2003)1987-1996 www.elsevier.com/locate/jeurceramsoc The measurement and characterization of the interfacial toughness of Si3 N4/BN composites by a three-point bending test Linhua Zoul a, b, * Yong Huang, Ruifeng Chen, Chang An Wanga, Dong-Soo Park astate Key Lab of New Ceramics and Fine Processing, Department of Material Science and Engineering, Tsinghua University, Beijing 100084, PR China Ceramic Materials Group, Korea Institute of Machinery and Materials, 66 SangNam-Dong, Chang-Won City, KyongNe th korea Received 20 June 2002: received in revised form 30 October 2002: accepted 11 November 2002 In this paper, a simpler method has been proposed for measuring and characterizing the interfacial toughness of Si3N4/BN composites. A sandwiching material, with one preset crack source connecting directly to a Bn interphase in the middle of a single half-Si3 N4 matrix, were designed and fabricated by sandwiching a thinner bn layer with two Si3 N4 green bodies obtained by die ompaction at room temperature. The bn layer had been made by tape casting. The sandwiched sample bars measured with 3x4x50 mm were cut and machined. The interfacial toughness of Si3 N4/BN composites was measured by three-point bending test for pure BN interphase, and interphases modified by different amounts of Si3 N4 or AlO3. The interfacial toughness values were calculated based on three-point bending fracture mechanics model. The interfacial toughness values we obtained were 38.20, 104.03 nd 116. 14 J/m2 for pure BN, BN+15vol %Si3N4 and BN+25vol %Si3 N4 interphases: 46.86, 53.90, 73.64 J/m2 for BN+16vo- L %ALO3, BN+36vol %Al2O3 and BN+63vol %ALO3 interphases, respectively. When the amounts of modified Si3N4 or Al,O3 increased the interphase was strengthened and crack deflection and propagation within interphase could not occur, the interfacial toughness was not obtainable for the corresponding samples, but it could be obtained by extrapolation based on the value obtained in each kind of interphase systems. The results show that the method is simple and effective for measuring and char- acterizing interfacial toughness, compared with some other related works in literatures C) 2003 Elsevier Science Ltd. All rights reserved. Keywords: Composites: Interfaces: Toughness; Measurement: Si3Nr-BN: Testing 1. Introduction >4000 J/m2. Huang et al. 8, also fabricated the materi als with the two structures, the materials had bending Si3N4 ceramic is a very promising, high-temperature strength of about 600-800 MPa and work of fracture structural material with its excellent mechanical prop- >4000 Jm. Among all the studies mentioned earlier erties, but due to its brittleness, its wide application has most of them lacked of interface design and control long been restricted. With the emergence of the two More often it was followed by manufacturing material, structures Si3 N4/ BN composites, i.e. laminated and measuring and characterizing material properties, and fibrous monolithic ceramics, the toughness of the finally evaluating interface by the properties of the Siy N4 has been greatly improved. Haiyan Liu et al. 5 materials. This was a very passive process to fabricate made the multilayer Si3N4/BN ceramics, which has 430 material. In order to design, tailor the material, and MPa of average bending strength and about 6500 Jm- optimize its bending strength and work of fracture, we of average work of fracture. Halloran et al. 6. 7 manu- must know how to characterize interphases with differ factured the Si3N4/BN composites with the two struc- ent compositions and give a quantitative evaluation on tures respectively, the materials had bending strength of its bonding strength. Usually, the fracture toughness of about 400-600 MPa and work of fracture values of this kind of composite was characterized indirectly by measuring the work of fracture. Sometimes. it was also characterized by Single Edge Notched Beam (SENB) method. However values obtained from both of the two methods cannot reflect the toughness of interface 0955-2219/02/S. see front matter C 2003 Elsevier Science Ltd. All rights reserved. PII:S0955-2219(02)00430The measurement and characterization of the interfacial toughness of Si3N4/BN composites by a three-point bending test Linhua Zou1,a,b,*,Yong Huanga ,Ruifeng Chena ,Chang An Wanga ,Dong-Soo Parkb a State Key Lab of New Ceramics and Fine Processing, Department of Material Science and Engineering, Tsinghua University, Beijing 100084, PR China bCeramic Materials Group, Korea Institute of Machinery and Materials, 66 Sang-Nam-Dong, Chang-Won City, Kyong-Nam, South Korea Received 20 June 2002; received in revised form 30 October 2002; accepted 11 November 2002 Abstract In this paper,a simpler method has been proposed for measuring and characterizing the interfacial toughness of Si3N4/BN composites. A sandwiching material,with one preset crack source connecting directly to a BN interphase in the middle of a single half-Si3N4 matrix,were designed and fabricated by sandwiching a thinner BN layer with two Si3N4 green bodies obtained by die compaction at room temperature. The BN layer had been made by tape casting. The sandwiched sample bars measured with 3
4
50 mm3 were cut and machined. The interfacial toughness of Si3N4/BN composites was measured by three-point bending test for pure BN interphase,and interphases modified by different amounts of Si3N4 or Al2O3. The interfacial toughness values were calculated based on three-point bending fracture mechanics model. The interfacial toughness values we obtained were 38.20,104.03 and 116.14 J/m2 for pure BN,BN+15vol.%Si3N4 and BN+25vol.%Si3N4 interphases; 46.86,53.90,73.64 J/m2 for BN+16vo￾l.%Al2O3,BN+36vol.%Al2O3 and BN+63vol.%Al2O3 interphases,respectively. When the amounts of modified Si3N4 or Al2O3 increased,the interphase was strengthened and crack deflection and propagation within interphase could not occur,the interfacial toughness was not obtainable for the corresponding samples,but it could be obtained by extrapolation based on the values obtained in each kind of interphase systems. The results show that the method is simple and effective for measuring and char￾acterizing interfacial toughness,compared with some other related works in literatures. # 2003 Elsevier Science Ltd. All rights reserved. Keywords: Composites; Interfaces; Toughness; Measurement; Si3N4–BN; Testing 1. Introduction Si3N4 ceramic is a very promising,high-temperature structural material with its excellent mechanical prop￾erties,but due to its brittleness,its wide application has long been restricted. With the emergence of the two structures Si3N4/BN composites,i.e. laminated and fibrous monolithic ceramics,14 the toughness of the Si3N4 has been greatly improved. Haiyan Liu et al.5 made the multilayer Si3N4/BN ceramics,which has 430 MPa of average bending strength and about 6500 J/m2 of average work of fracture. Halloran et al.6,7 manu￾factured the Si3N4/BN composites with the two struc￾tures respectively,the materials had bending strength of about 400–600 MPa and work of fracture values of >4000 J/m2 . Huang et al.8,9 also fabricated the materi￾als with the two structures,the materials had bending strength of about 600–800 MPa and work of fracture >4000 J/m2 . Among all the studies mentioned earlier, most of them lacked of interface design and control. More often it was followed by manufacturing material, measuring and characterizing material properties,and finally evaluating interface by the properties of the materials. This was a very passive process to fabricate material. In order to design,tailor the material,and optimize its bending strength and work of fracture,we must know how to characterize interphases with differ￾ent compositions and give a quantitative evaluation on its bonding strength. Usually,the fracture toughness of this kind of composite was characterized indirectly by measuring the work of fracture. Sometimes,it was also characterized by Single Edge Notched Beam (SENB) method. However,values obtained from both of the two methods cannot reflect the toughness of interface 0955-2219/02/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved. PII: S0955-2219(02)00430-2 Journal of the European Ceramic Society 23 (2003) 1987–1996 www.elsevier.com/locate/jeurceramsoc * Corresponding author. 1 Now at Korea Institute of Machinery and Materials. E-mail address: linhua_zou@hotmail.com (L. Zou).