J Mater Sci(2007)42:5046-5056 DOI10.1007/s10853-006-0579-5 Microstructural characterization and fracture properties of SiC-based fibers annealed at elevated temperatures J.J.Sha·T. Hinoki·A. Kohyama Received: 6 April 2006/ Accepted: 15 June 2006/Published online: 22 February 2007 Springer Science+Business Media, LLC 2007 Abstract Ceramic matrix composites(CMCs)have Introduction been proposed as potential structural materials for application of high temperature technologies. Excel- Currently, ceramic matrix composites(CMCs)have lent high temperature performance of CMCs requires been proposed as potential structural materials for that fibers must have high enough thermal stability and application of high temperature technologies, such as sufficient mechanical properties throughout the service advanced energy-generation systems and propulsion life. In order to clarify the correlation between the systems [1-3]. The key to successful application of mechanical properties and the microstructure of Sic- CMCs is judicious selection and incorporation of based fibers, Sic-based fibers were annealed at ele- ceramic fiber reinforcement with proper chemical vated temperatures in Ar for 1 h After annealing, the physical and mechanical properties. For high temper- fracture strengths on these fibers were evaluated at ature operation, the most critical fiber properties are room temperature by tensile test; the microstructural high strength and its reliable retention throughout the features were characterized by X-ray diffraction service life. Low fiber strength and thermal stability (XRD) and field emission scanning electron micros- could result in low fracture toughness and accelerate copy(FE-SEM). Furthermore, the fracture mechanics sub-critical crack propagation in CMCs was applied to estimate the fracture toughness and the Recently developed Sic-based fibers witi critical fracture energy of these fibers. As a result, stoichiometric composition and high-crystallite excellent microstructure and mechanical stabilities structure, such as Hi-Nicalon type s [4 and Tyran- were observed for SiC fibers with near-stoichiometric noM-SA [5], are promising reinforcement for CMCs composition and high-crystallite structure Combining fabrication. These fibers experienced a pyrolysis or the microstructure examination with tensile test indi- sintering process during fabrication and their micro- cates that the thermal and mechanical stabilities of Sic structure and mechanical properties depend on the fibers at high temperatures were mainly controlled by thermal history. On the other hand, CMCs may be their crystallization and composition as well as other applied or fabricated above the fiber's processin temperature [1-3, 6, 7. In many cases, SiC fibers were expected to expose to an environment with very high temperature and low oxygen partial pressure in which case, the performance of fibers could be changed by J.Sha(凶) hermal exposure, since the thermal and mechanical International Innovation Center, Kyoto University, stability of Sic fibers, which can vary with processing Sakyo-ku, Kyoto 606-8501, Japan conditions, are very sensitive to high temperature e-mail: shajianjun@iic. kyoto-uac jp environment T Hinoki·A. Kohyama The processing, structure and composition on Institute of Advanced Energy, Kyoto University, Gokasho, as-received Sic fibers have been presented in literature Uji, Kyoto 611-0011, Japan 8. These authors confirmed the chemical composition 2 SpringerMicrostructural characterization and fracture properties of SiC-based fibers annealed at elevated temperatures J. J. Sha Æ T. Hinoki Æ A. Kohyama Received: 6 April 2006 / Accepted: 15 June 2006 / Published online: 22 February 2007 Springer Science+Business Media, LLC 2007 Abstract Ceramic matrix composites (CMCs) have been proposed as potential structural materials for application of high temperature technologies. Excel￾lent high temperature performance of CMCs requires that fibers must have high enough thermal stability and sufficient mechanical properties throughout the service life. In order to clarify the correlation between the mechanical properties and the microstructure of SiC￾based fibers, SiC-based fibers were annealed at ele￾vated temperatures in Ar for 1 h. After annealing, the fracture strengths on these fibers were evaluated at room temperature by tensile test; the microstructural features were characterized by X-ray diffraction (XRD) and field emission scanning electron micros￾copy (FE-SEM). Furthermore, the fracture mechanics was applied to estimate the fracture toughness and the critical fracture energy of these fibers. As a result, excellent microstructure and mechanical stabilities were observed for SiC fibers with near-stoichiometric composition and high-crystallite structure. Combining the microstructure examination with tensile test indi￾cates that the thermal and mechanical stabilities of SiC fibers at high temperatures were mainly controlled by their crystallization and composition as well as other factors. Introduction Currently, ceramic matrix composites (CMCs) have been proposed as potential structural materials for application of high temperature technologies, such as advanced energy-generation systems and propulsion systems [1–3]. The key to successful application of CMCs is judicious selection and incorporation of ceramic fiber reinforcement with proper chemical, physical and mechanical properties. For high temper￾ature operation, the most critical fiber properties are high strength and its reliable retention throughout the service life. Low fiber strength and thermal stability could result in low fracture toughness and accelerate sub-critical crack propagation in CMCs. Recently developed SiC-based fibers with near￾stoichiometric composition and high-crystallite structure, such as Hi-NicalonTM type S [4] and Tyran￾noTM-SA [5], are promising reinforcement for CMCs fabrication. These fibers experienced a pyrolysis or sintering process during fabrication and their micro￾structure and mechanical properties depend on the thermal history. On the other hand, CMCs may be applied or fabricated above the fiber’s processing temperature [1–3, 6, 7]. In many cases, SiC fibers were expected to expose to an environment with very high temperature and low oxygen partial pressure in which case, the performance of fibers could be changed by thermal exposure, since the thermal and mechanical stability of SiC fibers, which can vary with processing conditions, are very sensitive to high temperature environment. The processing, structure and composition on as-received SiC fibers have been presented in literature [8]. These authors confirmed the chemical composition J. J. Sha (&) International Innovation Center, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan e-mail: shajianjun@iic.kyoto-u.ac.jp T. Hinoki A. Kohyama Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan 123 J Mater Sci (2007) 42:5046–5056 DOI 10.1007/s10853-006-0579-5