Availableonlineatwww.sciencedirect.com SCIENCE DIRECT● E噩≈S ELSEVIER Journal of the European Ceramic Society 25(2005)1717-1722 www.elsevier.com/locate/jeurceramsoc Subcritical crack growth processes in SiC/SiC ceramic matrix composites R.H. Jones, C H. Henager Jr Pacific Northwest National Laboratory, MS P8-15, PO. Box 999, Richland, WA 99352, USA Available online 2 February 2005 Abstract Ceramic matrix composites have the potential to operate at high temperatures and are, therefore being considered for a variety of advanced energy technologies such as combustor liners in land-based gas turbo/generators, heat exchangers and advanced fission and fusion reactors Ceramic matrix composites exhibit a range of crack growth mechanisms driven by a range of environmental and nuclear conditions. The crack growth mechanisms include: (1) fiber relaxation by thermal (FR) and irradiation(FIr) processes, (2)fiber stress-rupture(SR),(3)interface removal (Ir)by oxidation, and(4)oxidation embrittlement(OE)resulting from glass formation including effects of glass viscosity. Analysis of these crack growth processes has been accomplished with a combination experimental/modeling effort. Dynamic, high-temperature, in situ crack growth measurements have been made in variable Ar+O2 environments while a Pacific Northwest National Laboratory(Pnnl) developed model has been used to extrapolate this data and to add radiation effects. In addition to the modeling effort, a map showing these mechanisms as a function of environmental parameters was developed. This mechanism map is an effective tool for identifying operating regimes and predicting behavior. The process used to develop the crack growth mechanism map was to: (1) hypothesize and experimentally verify the operative mechanisms, (2)develop an analytical model for each mechanism, and (3)define the operating regime and boundary conditions for each mechanism. A map for SiC/SiC composites has been developed for chemical and nuclear environments as a function of temperature and time o 2004 Elsevier Ltd. All rights reserved. Keyords: Composites; Corrosion; Creep; Fracture; Carbides, Engine applications; Structural applications 1. Introduction peered interfaces between the fiber and matrix, provide ex- cellent fracture properties and fracture toughness values on Silicon carbide is a refractory semiconductor with unique the order of 25 MPam/2. The strength and fracture tough- properties. Because of its thermal, mechanical and chemi- ness are independent of temperature up to the limit of the cal stability, it can be used in extremely harsh environments. fiber stability. Also, these fiber/matrix microstructures im- Pure SiC also provides exceptionally low radioactivity un- part excellent thermal shock and thermal fatigue resistance to der neutron radiation, making it a top candidate for use in these materials so start-up and shut-down cycles and coolant advanced fission and fusion reactors. However, these appli- loss scenarios should not induce significant structural dam cations will require that these composites be optimized for age. For nuclear applications, the radiation resistance of the maximum performance. To accomplish this it will be neces- B phase of Sic imparts excellent radiation resistance. The B sary to understand their high-temperature mechanical, chem- phase of SiC has been shown by numerous studies to have a ical and radiation properties. Ceramic composites made from saturation swelling value of about O 1-0.2%at 800-1000C silicon carbide fibers and silicon carbide matrices(SiCf/Sic) This suggests that composites of Sic/Sic have the poten- are promising because of their excellent high-temperature tial for excellent radiation stability. The purpose of this pa- strength, fracture, creep, corrosion and thermal shock resis- per is to describe the subcritical crack growth behavior of tance. The continuous fiber architecture, coupled with engi- SiCf/SiC composites as this is an element in the creep behav ior of these materials. This analysis is based on the develop- Corresponding author. Tel. +1 509 3764276: fax: +1 509 3760418. ment of crack growth models and the supporting experimental E-mail address: rh. jones @pnl. gov(R H. Jones). 0955-2219/S-see front matter c 2004 Elsevier Ltd. All rights reserved doi: 10.1016/j-jeurceramsoc. 2004.12.015Journal of the European Ceramic Society 25 (2005) 1717–1722 Subcritical crack growth processes in SiC/SiC ceramic matrix composites R.H. Jones ∗, C.H. Henager Jr. Pacific Northwest National Laboratory, MS P8-15, P.O. Box 999, Richland, WA 99352, USA Available online 2 February 2005 Abstract Ceramic matrix composites have the potential to operate at high temperatures and are, therefore being considered for a variety of advanced energy technologies such as combustor liners in land-based gas turbo/generators, heat exchangers and advanced fission and fusion reactors. Ceramic matrix composites exhibit a range of crack growth mechanisms driven by a range of environmental and nuclear conditions. The crack growth mechanisms include: (1) fiber relaxation by thermal (FR) and irradiation (FIR) processes, (2) fiber stress-rupture (SR), (3) interface removal (IR) by oxidation, and (4) oxidation embrittlement (OE) resulting from glass formation including effects of glass viscosity. Analysis of these crack growth processes has been accomplished with a combination experimental/modeling effort. Dynamic, high-temperature, in situ crack growth measurements have been made in variable Ar + O2 environments while a Pacific Northwest National Laboratory (PNNL) developed model has been used to extrapolate this data and to add radiation effects. In addition to the modeling effort, a map showing these mechanisms as a function of environmental parameters was developed. This mechanism map is an effective tool for identifying operating regimes and predicting behavior. The process used to develop the crack growth mechanism map was to: (1) hypothesize and experimentally verify the operative mechanisms, (2) develop an analytical model for each mechanism, and (3) define the operating regime and boundary conditions for each mechanism. A map for SiC/SiC composites has been developed for chemical and nuclear environments as a function of temperature and time. © 2004 Elsevier Ltd. All rights reserved. Keywords: Composites; Corrosion; Creep; Fracture; Carbides; Engine applications; Structural applications 1. Introduction Silicon carbide is a refractory semiconductor with unique properties. Because of its thermal, mechanical and chemi￾cal stability, it can be used in extremely harsh environments. Pure SiC also provides exceptionally low radioactivity un￾der neutron radiation, making it a top candidate for use in advanced fission and fusion reactors. However, these appli￾cations will require that these composites be optimized for maximum performance. To accomplish this it will be neces￾sary to understand their high-temperature mechanical, chem￾ical and radiation properties. Ceramic composites made from silicon carbide fibers and silicon carbide matrices (SiCf/SiC) are promising because of their excellent high-temperature strength, fracture, creep, corrosion and thermal shock resis￾tance. The continuous fiber architecture, coupled with engi- ∗ Corresponding author. Tel.: +1 509 376 4276; fax: +1 509 376 0418. E-mail address: rh.jones@pnl.gov (R.H. Jones). neered interfaces between the fiber and matrix, provide ex￾cellent fracture properties and fracture toughness values on the order of 25 MPa m1/2. The strength and fracture tough￾ness are independent of temperature up to the limit of the fiber stability. Also, these fiber/matrix microstructures im￾part excellent thermal shock and thermal fatigue resistance to these materials so start-up and shut-down cycles and coolant loss scenarios should not induce significant structural dam￾age. For nuclear applications, the radiation resistance of the
phase of SiC imparts excellent radiation resistance. The
phase of SiC has been shown by numerous studies to have a saturation swelling value of about 0.1–0.2% at 800–1000 ◦C. This suggests that composites of SiC/SiC have the poten￾tial for excellent radiation stability. The purpose of this pa￾per is to describe the subcritical crack growth behavior of SiCf/SiC composites as this is an element in the creep behav￾ior of these materials. This analysis is based on the develop￾ment of crack growth models and the supporting experimental data. 0955-2219/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2004.12.015