Availableonlineatwww.sciencedirect.com DIRECT. COMPOSITES CIENCE AND TECHNOLOGY ELSEVIER Composites Science and Technology 66(2006)2089-2099 www.elsevier.com/locate/compscitech Creep behavior of NextelM610/Monazite/ Alumina composite at elevated temperatures M B. Ruggles-Wrenn ,S.s. Musil, s Mall, K.A. Keller Department of Aeronautics and Astronautics, Air Force Institute of Technology, Wright-Patterson Air Force Base, OH 45433-7765, USA Received 7 June 2005: received in revised form 8 December 2005: accepted 22 December 2005 Available online 6 March 2006 Abstract The creep behavior of a N610/LaPO/Al,O3 composite was evaluated in this work. The composite consists of a porous alumina matrix reinforced with Nextel 610 fibers coated with monazite in a symmetric cross-ply(0%/90/0 90)s orientation. The te stress-strain behavior was investigated and the tensile properties measured at room temperature and in the 900-1200oC range the a tion of monazite coating resulted in 50% improvement in ultimate tensile strength (UTS) at temperatures <1100C, and in improvement in UTS at 1200C. Tensile creep behavior was examined at temperatures in the 900-1100C range for creep stresses rang- ing from 40 to 150 MPa. Primary and secondary creep s were observed in creep tests at 900C. At temperatures above 900C, the composite exhibited primary, secondary and tertiary creep. Minimum creep rate was reached in all tests. Creep rates accelerated with increasing temperature and creep stress. At 900C creep run-out, defined as 100 h at creep stress, was achieved for stress levels <120 MPa. The residual strength and modulus of all specimens that achieved run-out were characterized. Comparison with results obtained for N610/Al2O3(control) specimens revealed that the use of the monazite coating resulted in improved creep resistance at 900C Creep performance deteriorated rapidly as temperatures increased above 900 C. Composite microstructure, as well as damage and failure mechanisms were investigated e 2006 Elsevier Ltd. All rights reserved Keywords: A. Ceramic-matrix composites(CMCs): A Oxides; A. Fibres; A. Coatings: B Creep; B. High-temperature properties; B. Mechanical prop- erties: D. Fractography 1. Introduction and fracture toughness at high temperatures and they therefore continue to attract attention as candidate materi- The severe conditions encountered by aerospace compo als for such applications. Additionally, the lower densities nents require structural materials that have superior long- of CMCs and their higher use temperatures, along with a term mechanical properties and retained properties under reduced need for cooling air, allow for improved high-tem high temperature, high pressure, and varying environmen- perature performance when compared to conventional tal factors, such as moisture [1]. Ceramic-matrix compos- nickel-based superalloys [2]. Alternately, it is recognized ites(CMCs) are capable of maintaining excellent strength that the thermodynamic stability and oxidation resistance of CMCs are vital issues The views expressed are those of the authors and do not reflect the Non-oxide fiber/non-oxide matrix CMCs such as SiC/ official policy or position of the United States Air Force, Department of SiC generally show poor oxidation resistance [3, 4, partic Defense or the US government larly at intermediate temperatures(800C). The degrad Corresponding author. Tel: +1937 255 3636x4641: fax: +1937 656 tion involves the oxidation of the fibers fiber coatings and 4032 aruggles -wrenn(@afit. edu (M. B. Ruggles. matrices and is typically accelerated by the presence of moisture [5-11]. Using a non-oxide fiber/oxide matrix or I Under USAF Contract F33615-01-C-5214 an oxide fiber/non-oxide matrix composite generally does 02663538/S. see front matter 2006 Elsevier Ltd. All rights reserved doi:10.1016j.compscitech.2005.12.026Creep behavior of NextelTM610/Monazite/Alumina composite at elevated temperatures q M.B. Ruggles-Wrenn a,*, S.S. Musil a , S. Mall a , K.A. Keller b,1 a Department of Aeronautics and Astronautics, Air Force Institute of Technology, Wright-Patterson Air Force Base, OH 45433-7765, USA b UES, Inc., 4401 Dayton Xenia Road, Dayton, OH 45433-7817, USA Received 7 June 2005; received in revised form 8 December 2005; accepted 22 December 2005 Available online 6 March 2006 Abstract The creep behavior of a N610/LaPO4/Al2O3 composite was evaluated in this work. The composite consists of a porous alumina matrix reinforced with Nextel 610 fibers coated with monazite in a symmetric cross-ply (0/90/0/90)S orientation. The tensile stress–strain behavior was investigated and the tensile properties measured at room temperature and in the 900–1200C range. The addi￾tion of monazite coating resulted in 50% improvement in ultimate tensile strength (UTS) at temperatures 61100 C, and in 37% improvement in UTS at 1200 C. Tensile creep behavior was examined at temperatures in the 900–1100 C range for creep stresses rang￾ing from 40 to 150 MPa. Primary and secondary creep regimes were observed in creep tests at 900 C. At temperatures above 900 C, the composite exhibited primary, secondary and tertiary creep. Minimum creep rate was reached in all tests. Creep rates accelerated with increasing temperature and creep stress. At 900 C creep run-out, defined as 100 h at creep stress, was achieved for stress levels 6120 MPa. The residual strength and modulus of all specimens that achieved run-out were characterized. Comparison with results obtained for N610/Al2O3 (control) specimens revealed that the use of the monazite coating resulted in improved creep resistance at 900 C. Creep performance deteriorated rapidly as temperatures increased above 900 C. Composite microstructure, as well as damage and failure mechanisms were investigated. 2006 Elsevier Ltd. All rights reserved. Keywords: A. Ceramic-matrix composites (CMCs); A. Oxides; A. Fibres; A. Coatings; B. Creep; B. High-temperature properties; B. Mechanical prop￾erties; D. Fractography 1. Introduction The severe conditions encountered by aerospace compo￾nents require structural materials that have superior long￾term mechanical properties and retained properties under high temperature, high pressure, and varying environmen￾tal factors, such as moisture [1]. Ceramic–matrix compos￾ites (CMCs) are capable of maintaining excellent strength and fracture toughness at high temperatures and they therefore continue to attract attention as candidate materi￾als for such applications. Additionally, the lower densities of CMCs and their higher use temperatures, along with a reduced need for cooling air, allow for improved high-tem￾perature performance when compared to conventional nickel-based superalloys [2]. Alternately, it is recognized that the thermodynamic stability and oxidation resistance of CMCs are vital issues. Non-oxide fiber/non-oxide matrix CMCs such as SiC/ SiC generally show poor oxidation resistance [3,4], particu￾larly at intermediate temperatures (800 C). The degrada￾tion involves the oxidation of the fibers, fiber coatings, and matrices and is typically accelerated by the presence of moisture [5–11]. Using a non-oxide fiber/oxide matrix or an oxide fiber/non-oxide matrix composite generally does 0266-3538/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.compscitech.2005.12.026 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 US Government. * Corresponding author. Tel.: +1 937 255 3636x4641; fax: +1 937 656 4032. E-mail address: marina.ruggles-wrenn@afit.edu (M.B. Ruggles￾Wrenn). 1 Under USAF Contract # F33615-01-C-5214. www.elsevier.com/locate/compscitech Composites Science and Technology 66 (2006) 2089–2099 COMPOSITES SCIENCE AND TECHNOLOGY