Availableonlineatwww.sciencedirect.com SCIENCE DIRECT● E噩≈S ELSEVIER Journal of the European Ceramic Society 25 (2005)3485-3493 www.elsevier.com/locate/jeurceramsoc Influence of SiC whisker morphology and nature of SiC/Al2O3 interface on thermomechanical properties of SiC reinforced Al2 O3 composites V Garnier G. Fantozzi, D. nguyen, J. Dubois, G. Thollet INSA de Lyon, GEMPPM UMR CNRS 5510, Villeurbanne 69621, france Received 9 July 2004; received in revised form 13 September 2004: accepted 18 September 2004 Available online 20 June 2005 Abstract Thermomechanical properties of a 35 vol. SiC whiskers/Al,O3 matrix composite were investigated as a function of whisker surface quality. Two batches of Sic whiskers(Tateho-SCw-l-S)were studied. Whisker surface chemistry, as determined by X-ray photoelectron pectroscopy and whisker morphology, as determined by SEM or TEM, was correlated to the thermomechanical properties of the composites The surface oxygen content of the whiskers was shown to strongly affect the composite thermomechanical properties. High oxygen surface ontent appears to affect the whisker/matrix interfacial bonding thus decreasing the amount of crack deflection, whisker pullout and whisker bridging which are required to reach high fracture toughness values C 2004 Elsevier Ltd. All rights reserved. Keywords: SiC; Whiskers; Interfaces; Composites; Thermal properties; Mechanical properties; Al2O3/SiC 1. Introduction Recent works on ceramic matrix composites have demon strated that fracture toughness and flexural strength of poly In ceramic matrix composites, whisker reinforcements crystalline Al2O3 can be significantly improved by addi are primarily used to enhance the fracture toughness and tion of SiC whiskers. Becher and Wei, 3 Wei and Becher, 14 the flexural strength of the composite at temperatures Becher et al., 15 and Homey et al. 6 have achieved frac- 1000C. Essentially, the whisker reinforcement prevents ture toughness values approaching 10 MPam.and flexural catastrophic brittle failure by providing processes that dis- strength values approaching 800 MPa. Furthermore, Homeny spate energy during the fracture process. Toughening mech- and Vaughn have demonstrated that the fracture toughness anisms, such as crack deflection, -whisker pullout, -and could vary with whisker type from 4 to 9 MPam>when whisker bridging 8-10 depends to a large extent on the na- utilising whiskers that were similar in all aspects, except for ture of the whisker/matrix interface. Several factors affect surface chemistry. They have associated the high fracture the whisker/matrix interface, including matrix chemistry, toughness with the presence of carbon and silicon oxycarbide whisker surface chemistry, whisker morphology and ther- phases on the whiskers surface Tiegs et al. I8 have also per- mal expansion mismatches. The internal stresses are also formed a detailed study on whiskers from numerous sources pected to affect the toughening behaviour of SiC-whiskers- and have correlated the oxygen and carbon concentrations of et al. and Li and Brad. 2 omposite as shown by Predecki reinforced alumina matrix the whisker surfaces with the fracture toughness. According to them as well, the high fracture toughness is associated with of carbon excess on the surfa fracture toughness is attributed to oxygen excess Corresponding author The present work deals specifically with the effect of E-mail address: Vincent Garnier@insa-lyon fr(V. Garnier) hiskers quality on the thermomechanical properties of Sic 0955-2219/S-see front matter c 2004 Elsevier Ltd. All rights reserved doi: 10. 1016/j. jeurceramsoc. 2004.09.026Journal of the European Ceramic Society 25 (2005) 3485–3493 Influence of SiC whisker morphology and nature of SiC/Al2O3 interface on thermomechanical properties of SiC reinforced Al2O3 composites V. Garnier∗, G. Fantozzi, D. Nguyen, J. Dubois, G. Thollet INSA de Lyon, GEMPPM UMR CNRS 5510, Villeurbanne 69621, France Received 9 July 2004; received in revised form 13 September 2004; accepted 18 September 2004 Available online 20 June 2005 Abstract Thermomechanical properties of a 35 vol.% SiC whiskers/Al2O3 matrix composite were investigated as a function of whisker surface quality. Two batches of SiC whiskers (Tateho-SCW-1-S) were studied. Whisker surface chemistry, as determined by X-ray photoelectron spectroscopy and whisker morphology, as determined by SEM or TEM, was correlated to the thermomechanical properties of the composites. The surface oxygen content of the whiskers was shown to strongly affect the composite thermomechanical properties. High oxygen surface content appears to affect the whisker/matrix interfacial bonding thus decreasing the amount of crack deflection, whisker pullout and whisker bridging which are required to reach high fracture toughness values. © 2004 Elsevier Ltd. All rights reserved. Keywords: SiC; Whiskers; Interfaces; Composites; Thermal properties; Mechanical properties; Al2O3/SiC 1. Introduction In ceramic matrix composites, whisker reinforcements are primarily used to enhance the fracture toughness and the flexural strength of the composite at temperatures to 1000 ◦C. Essentially, the whisker reinforcement prevents catastrophic brittle failure by providing processes that dis￾sipate energy during the fracture process. Toughening mech￾anisms, such as crack deflection,1–2 whisker pullout,3–7 and whisker bridging,8–10 depends to a large extent on the na￾ture of the whisker/matrix interface. Several factors affect the whisker/matrix interface, including matrix chemistry, whisker surface chemistry, whisker morphology and ther￾mal expansion mismatches. The internal stresses are also ex￾pected to affect the toughening behaviour of SiC-whiskers￾reinforced alumina matrix composite as shown by Predecki et al.11 and Li and Bradt.12 ∗ Corresponding author. E-mail address: Vincent.Garnier@insa-lyon.fr (V. Garnier). Recent works on ceramic matrix composites have demon￾strated that fracture toughness and flexural strength of poly￾crystalline Al2O3 can be significantly improved by addi￾tion of SiC whiskers. Becher and Wei,13 Wei and Becher,14 Becher et al.,15 and Homeny et al.16 have achieved frac￾ture toughness values approaching 10 MPa m0.5 and flexural strength values approaching 800 MPa. Furthermore, Homeny and Vaughn17 have demonstrated that the fracture toughness could vary with whisker type from 4 to 9 MPa m0.5 when utilising whiskers that were similar in all aspects, except for surface chemistry. They have associated the high fracture toughness with the presence of carbon and silicon oxycarbide phases on the whiskers surface. Tiegs et al.18 have also per￾formed a detailed study on whiskers from numerous sources and have correlated the oxygen and carbon concentrations of the whisker surfaces with the fracture toughness. According to them as well, the high fracture toughness is associated with the presence of carbon excess on the surfaces, while the low fracture toughness is attributed to oxygen excess. The present work deals specifically with the effect of whiskers quality on the thermomechanical properties of SiC 0955-2219/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2004.09.026