Availableonlineatwww.sciencedirect.com °scⅰ ence Direct c000055 Part A: applied science and manufacturing ELSEVIER Composites: Part A 37(2006)2029-2040 www.elsevier.com/locate/compositesa Effects of steam environment on high-temperature mechanica behavior of Nextel M720/alumina(N720/A)continuous fiber ceramic composite M B. Ruggles-Wrenn", S Mall, C.A. Eber, L B. Harlan Department of Aeronautics and Astronautics, Air Force Institute of Technology, WPAFB, OH 45433-7765, US.A Received 15 February 2005: received in revised form 30 November 2005; accepted 13 December 2005 Abstract Mechanical behavior of an oxide-oxide continuous fiber ceramic composite( CFCC)consisting of a porous alumina matrix reinforced with laminated, woven mullite/alumina fibers(Nextel M720)was investigated at 1200 and 1330oC in laboratory air and in 100%steam environments. CFCC has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance Tension-tension fatigue behavior was studied for fatigue stresses ranging from 100 to 170 MPa at 1200C, and for fatigue stresses of 50 and 100 MPa at 1330C. Tensile creep behavior was examined for creep stresses ranging from 80 to 154 MPa at 1200C, and for creep stresses of 50 and 100 MPa at 1330C. At 1200C, the CFCC exhibited excellent fatigue resistance in laboratory air. The fatigue limit(based on a run-out condition of 10 cycles)was 170 MPa(88% UTS at 1200C). The material retained 100% of its tensile strength. Presence of steam caused noticeable degradation in fatigue performance at 1200C Fatigue resistance at 1330C was poor In creep tests, primary and secondary creep regimes were observed. Minimum creep rate was reached in all tests. At 1200oC, creep rates were 10-8-10-s-I and maximum time to rupture was 255 h. At 1330oC, creep rates were 10-7-10-5s-I and maximum time to rupture was 87 h Presence of steam accel erated creep rates and dramatically reduced creep life Published by elsevier Ltd Keywords: A Ceramic-matrix composites(CMCs); A Fibres; A Creep 1. Introduction aerospace applications. Compared to the conventional nickel-based superalloys, CMCs offer improved high- Aerospace components require structural materials that temperature performance at reduced weight. Advanced have superior long-term mechanical properties and can be reusable space launch vehicles will likely incorporate exposed to severe environmental conditions, such as high fiber-reinforced CMCs in critical propulsion components temperature, high pressure, or water vapor. Ceramic- In these applications, CMCs will be subjected to mechani- matrix composites(CMCs), capable of maintaining excel- cal loading in complex environments. For example, a typ- lent strength and fracture toughness at high temperatures ical service environment for a reusable rocket engine continue to attract attention as candidate materials for turbopump rotor includes hydrogen, oxygen and steam, at pressures >200 atm [l]. Ceramic-matrix composites are also being considered for aerospace turbine engine applica- The views expressed are those of the authors and do not reflect the tions. Higher material operating temperatures and official policy or position of the United States Air Force, Department of decreased cooling air requirement are the significant Defense or the u.s. government Corresponding author. Tel. +937 255 3636x4641; fax: +937656 4032 advantages that CMCs offer to the aerospace engine design E-mailaddress:marina.ruggles-wrenn(@afit.edu(M.B.Ruggles.community.However,theseapplication sure to oxidizing environments. Recently CMCs have been 1359-835X/S.see front matter Published by Elsevier Ltd doi:10.1016/j.compositesa.2005.12.008Effects of steam environment on high-temperature mechanical behavior of NextelTM720/alumina (N720/A) continuous fiber ceramic composite q M.B. Ruggles-Wrenn *, S. Mall, C.A. Eber, L.B. Harlan Department of Aeronautics and Astronautics, Air Force Institute of Technology, WPAFB, OH 45433-7765, USA Received 15 February 2005; received in revised form 30 November 2005; accepted 13 December 2005 Abstract Mechanical behavior of an oxide–oxide continuous fiber ceramic composite (CFCC) consisting of a porous alumina matrix reinforced with laminated, woven mullite/alumina fibers (NextelTM720) was investigated at 1200 and 1330 C in laboratory air and in 100% steam environments. CFCC has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. Tension–tension fatigue behavior was studied for fatigue stresses ranging from 100 to 170 MPa at 1200 C, and for fatigue stresses of 50 and 100 MPa at 1330 C. Tensile creep behavior was examined for creep stresses ranging from 80 to 154 MPa at 1200 C, and for creep stresses of 50 and 100 MPa at 1330 C. At 1200 C, the CFCC exhibited excellent fatigue resistance in laboratory air. The fatigue limit (based on a run-out condition of 105 cycles) was 170 MPa (88% UTS at 1200 C). The material retained 100% of its tensile strength. Presence of steam caused noticeable degradation in fatigue performance at 1200 C. Fatigue resistance at 1330 C was poor. In creep tests, primary and secondary creep regimes were observed. Minimum creep rate was reached in all tests. At 1200 C, creep rates were 108 –105 s 1 and maximum time to rupture was 255 h. At 1330 C, creep rates were 107 –105 s 1 and maximum time to rupture was 87 h. Presence of steam accel￾erated creep rates and dramatically reduced creep life. Published by Elsevier Ltd. Keywords: A. Ceramic-matrix composites (CMCs); A. Fibres; A. Creep 1. Introduction Aerospace components require structural materials that have superior long-term mechanical properties and can be exposed to severe environmental conditions, such as high temperature, high pressure, or water vapor. Ceramic– matrix composites (CMCs), capable of maintaining excel￾lent strength and fracture toughness at high temperatures continue to attract attention as candidate materials for aerospace applications. Compared to the conventional nickel-based superalloys, CMCs offer improved high￾temperature performance at reduced weight. Advanced reusable space launch vehicles will likely incorporate fiber-reinforced CMCs in critical propulsion components. In these applications, CMCs will be subjected to mechani￾cal loading in complex environments. For example, a typ￾ical service environment for a reusable rocket engine turbopump rotor includes hydrogen, oxygen and steam, at pressures >200 atm [1]. Ceramic–matrix composites are also being considered for aerospace turbine engine applica￾tions. Higher material operating temperatures and decreased cooling air requirement are the significant advantages that CMCs offer to the aerospace engine design community. However, these applications also require expo￾sure to oxidizing environments. Recently CMCs have been 1359-835X/$ - see front matter Published by Elsevier Ltd. doi:10.1016/j.compositesa.2005.12.008 q The views expressed are those of the authors and do not reflect the official policy or position of the United States Air Force, Department of Defense or the U.S. Government. * Corresponding author. Tel.: +937 255 3636x4641; fax: +937 656 4032. E-mail address: marina.ruggles-wrenn@afit.edu (M.B. Ruggles￾Wrenn). www.elsevier.com/locate/compositesa Composites: Part A 37 (2006) 2029–2040