Journal of Nuclear Materials 384 (2009)195-211 Contents lists available at ScienceDirect Journal of Nuclear materials ELSEVIER journalhomepagewww.elsevier.com/locate/jnucmat The effect of neutron irradiation on the fiber/matrix interphase of silicon carbide composites T Nozawa*Y Katoh, L L. Snead Materials Science and Technology Division, Oak Ridge National Laboratory, P 0. Box 2008, Oak Ridge, IN 37831-6138, US ARTICLE IN F O ABSTRACT Article his eceived 11 July 2008 Given the good stability of mechanical properties of silicon carbide (SiC) under neutron irradiation. ultimate irradiation tolerance of Sic composite materials may be limited by the fiber/matrix interphas Accepted 13 November 2008 which is critically important to the performance of these composites. This study investigates the irradi- ation stability of pyrolytic carbon(Pyc)monolayer and Pyc/sic multilayer interphases by tensile and sin- le fiber push-out test techniques. Neutron irradiation was performed to doses of 0.7-7.7 dpa at temperatures from 380 to 1080C. Both interfacial debond shear strength and interfacial friction stress parently decrease by irradiation, although this is not so dramatic when Tir < 1000C. In contrast, the interfacial shear stresses are most affected by the higher temperature irradiation(>1000C). Noteworthy these irradiation effects depend on the type of interphase material, i.e for the pyrolytic carbon or mul layer SiC variants studied. In the range of irradiation temperature and dose, the degradation in interfa- al shear properties, while measurable, is not of a magnitude to degrade the mechanical performance of he composites. This was observed for both interphase types studied. In particular, the proportional limit tensile stress decreases slightly by irradiation while the tensile fracture strength undergoes very minor e 2008 Elsevier B V. All rights reserved. 1 Introduction adopted as an F/M interphase, which serves to intercept and tie- up propagating cracks. Since the enhanced fracture tough Silicon carbide(Sic) has been widely used for high-temperature and ultimate performance of composites is critically dependent engineering applications due to its inherently high thermo-chem- on this interphase, its irradiation stability, and the combined ef- ical stability, good oxidation resistance and strength retention at fects of environment and irradiation on the fiber, matrix, and inter- high-temperatures. Moreover, its resistance to neutron irradiation, phase is of critical importance. e.g., low-induced radioactivity and low irradiation-induced after- The effect of neutron irradiation on the F/M interface was first heat, gives scope for a potential application in fusion and advanced evaluated on Nicalon /CVI-SiC composites with Pyc as an F/M nuclear fission energy systems [1. Additionally, it has been proven interphase [5,6]. In this composite system. the crystalline CVI-SiC that Sic in a stoichiometric form offers exceptional retention of matrix swells by irradiation depending on irradiation temperature mechanical properties neutron irradiation. High-purity and neutron dose, typical of ceramic materials. However, the chemical-vapor-deposited (cvd) sic reportedly retains its strength tallized glassy Nicalon" fiber underwent densification by neutron irradiation at to 20 dpa [2-4 Due to this differential irradiation-induced dimensional change be- Due to inherent brittleness of Sic in its monolithic form, Sic is tween Nicalonand CVI-SiC, comparably large stresses generate a being developed for use in the composite form, combining a Sic fi- the F/M interface, resulting in shear failure of the composites, i.e., ber, a Sic matrix, and a fiber/matrix(F/M)interphase. Near-stoichi- shape instability probably induced by strong contribution of ometric and highly-crystalline Sic, e.g., Hi-Nicalon M Type-s or trans-interface tensile stress [5]. Meanwhile, this shape instability TyrannoM-SA SiC fibers, and a chemical-vapor-infiltrated(cvi) issue has been solved by adopting near-stoichiometric and highly SiC matrix, are generally adopted because of their better irradiation crystalline advanced third generation Sic fibers such as Hi-Nic tolerance. a poorly graphitized pyrolytic carbon(Py c)is typically alon m Type-s and Tyranno m-SA Since both advanced Sic fibers CVI-SiC matrix swell in similar manners. irradiation-induced shear stresses at the F/M interface are minimized. Indeed, no major macroscopic deformation by irradiation has been identified for Hi-Nicalon" Type-S/CVI-SiC composite system [7]. Moreover, no 1195. Japan.Tel:+81292826416:fax:+81292843589 significant deterioration of flexural and tensile properties has been a. takashi67@jaea. go jp(T Nozawa). reported[8-10]. 'S- see front matter e 2008 Elsevier B v. All rights reserved. nuchaL2008.11.015The effect of neutron irradiation on the fiber/matrix interphase of silicon carbide composites T. Nozawa *, Y. Katoh, L.L. Snead Materials Science and Technology Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6138, USA article info Article history: Received 11 July 2008 Accepted 13 November 2008 abstract Given the good stability of mechanical properties of silicon carbide (SiC) under neutron irradiation, the ultimate irradiation tolerance of SiC composite materials may be limited by the fiber/matrix interphase, which is critically important to the performance of these composites. This study investigates the irradi￾ation stability of pyrolytic carbon (PyC) monolayer and PyC/SiC multilayer interphases by tensile and sin￾gle fiber push-out test techniques. Neutron irradiation was performed to doses of 0.7–7.7 dpa at temperatures from 380 to 1080 C. Both interfacial debond shear strength and interfacial friction stress apparently decrease by irradiation, although this is not so dramatic when Tirr < 1000 C. In contrast, the interfacial shear stresses are most affected by the higher temperature irradiation (>1000 C). Noteworthy, these irradiation effects depend on the type of interphase material, i.e., for the pyrolytic carbon or mul￾tilayer SiC variants studied. In the range of irradiation temperature and dose, the degradation in interfa￾cial shear properties, while measurable, is not of a magnitude to degrade the mechanical performance of the composites. This was observed for both interphase types studied. In particular, the proportional limit tensile stress decreases slightly by irradiation while the tensile fracture strength undergoes very minor change. 2008 Elsevier B.V. All rights reserved. 1. Introduction Silicon carbide (SiC) has been widely used for high-temperature engineering applications due to its inherently high thermo-chem￾ical stability, good oxidation resistance, and strength retention at high-temperatures. Moreover, its resistance to neutron irradiation, e.g., low-induced radioactivity and low irradiation-induced after￾heat, gives scope for a potential application in fusion and advanced nuclear fission energy systems [1]. Additionally, it has been proven that SiC in a stoichiometric form offers exceptional retention of mechanical properties under neutron irradiation. High-purity chemical-vapor-deposited (CVD) SiC reportedly retains its strength by neutron irradiation at least to 20 dpa [2–4]. Due to inherent brittleness of SiC in its monolithic form, SiC is being developed for use in the composite form, combining a SiC fi- ber, a SiC matrix, and a fiber/matrix (F/M) interphase. Near-stoichi￾ometric and highly-crystalline SiC, e.g., Hi-NicalonTM Type-S or TyrannoTM-SA SiC fibers, and a chemical-vapor-infiltrated (CVI) SiC matrix, are generally adopted because of their better irradiation tolerance. A poorly graphitized pyrolytic carbon (PyC) is typically adopted as an F/M interphase, which serves to intercept and tie￾up propagating cracks. Since the enhanced fracture toughness and ultimate performance of composites is critically dependent on this interphase, its irradiation stability, and the combined ef￾fects of environment and irradiation on the fiber, matrix, and inter￾phase is of critical importance. The effect of neutron irradiation on the F/M interface was first evaluated on NicalonTM/CVI-SiC composites with PyC as an F/M interphase [5,6]. In this composite system, the crystalline CVI-SiC matrix swells by irradiation depending on irradiation temperature and neutron dose, typical of ceramic materials. However, the poorly-crystallized glassy NicalonTM fiber underwent densification. Due to this differential irradiation-induced dimensional change be￾tween NicalonTM and CVI-SiC, comparably large stresses generate at the F/M interface, resulting in shear failure of the composites, i.e., shape instability probably induced by strong contribution of trans-interface tensile stress [5]. Meanwhile, this shape instability issue has been solved by adopting near-stoichiometric and highly￾crystalline advanced third generation SiC fibers such as Hi-Nic￾alonTM Type-S and TyrannoTM-SA. Since both advanced SiC fibers and CVI-SiC matrix swell in similar manners, irradiation-induced shear stresses at the F/M interface are minimized. Indeed, no major macroscopic deformation by irradiation has been identified for Hi-NicalonTM Type-S/CVI-SiC composite system [7]. Moreover, no significant deterioration of flexural and tensile properties has been reported [8–10]. 0022-3115/$ - see front matter 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jnucmat.2008.11.015 * Corresponding author. Present address: Fusion Research and Development Directorate, Japan Atomic Energy Agency, 2-4 Shirakata Shirane, Tokai, Ibaraki 319- 1195, Japan. Tel.: +81 29 282 6416; fax: +81 29 284 3589. E-mail address: nozawa.takashi67@jaea.go.jp (T. Nozawa). Journal of Nuclear Materials 384 (2009) 195–211 Contents lists available at ScienceDirect Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat