Composites Science and Technology 68(2008)3305-3313 Contents lists available at ScienceDirect Composites Science and Technology ELSEVIER journalhomepagewww.elsevier.com/locate/compscitech Tensile creep and fatigue of Sylramic-iBN melt-infiltrated Sic matrix composites Retained properties, damage development, and failure mechanisms Gregory N Morscher Greg Ojard, Robert miller Yasser Gowayed, Unni Santhosh Jalees Ahmad Reji john Materials and Manufacturing Directorate, Air Force Research Laboratory, AFRL/RXLMN, Wright-Patterson AFB, OH, USA SA Glenn Research Center, 21000 Brookpark Road, MS 106-5, Cleveland, OH 44135, US pRatt and Whitney, East Hartford, CT, USA d Auburn University, Auburn, AL, USA Research Applications Inc, San Diego, CA, USA ARTICLE INFO ABSTRACT An understanding of the elevated temperature tensile creep, fatigue, rupture, and retained properties of eceived in revised form 8 August 2008 ceramic matrix composites( CMC)envisioned for use in gas turbine engine applications is essential for omponent design and life-prediction. In order to quantify the effect of stress, time, temperature, and oxi- Accepted 21 August 2008 Available online 11 September 2008 dation for a state-of-the-art composite system, a wide variety of tensile creep, dwell fatigue, and cyclic fatigue experiments were performed in air at 1204C for the SiC/SiC CMC system consisting of Sylram- ic-iBN SiC fibers, BN fiber interphase coating, and slurry-cast melt-infiltrated( Mi)SiC-based matrix. Tests were either taken to failure or interrupted. Interrupted tests were then mechanically tested at room tem- perature to determine the residual properties. The retained properties of most of the composites sub- jected to tensile creep or fatigue were usually within 20% of the as-produced strength and 10% of the s-produced elastic modulus. It was observed that during creep, residual stresses in the composite are Tered to some extent which results in an increased compressive stress in the matrix upon cooling nd a subsequent increased stress required to form matrix cracks Microscopy of polished sections and the fracture surfaces of specimens which failed during stressed-oxidation or after the room-temperature etained property test was performed on some of the specimens in order to quantify the nature and extent of damage accumulation that occurred during the test. It was discovered that the distribution f stress-dependent matrix cracking at 1204C was similar to the as-produced composites at room tem- perature; however, matrix crack growth occurred over time and typically did not appear to propagate through-the-thickness except at the final failure crack Failure of the composites was due to either oxi- dation- induced unbridged crack growth, which dominated the higher stress regime(>179 MPa)or con- trolled by degradation of the fibers, probably caused by intrinsic creep-induced flaw growth of the fibers or internal attack of the fibers via Si diffusion through the Cvi SiC and or microcracks at the lower stress regime(≤165MPa) e 2008 Elsevier Ltd. All rights reserved. understand the mechanisms that lead to degradation in stress-strain behavior and ultimate creep or fatigue rupture Silicon carbide fiber-reinforced silicon-carbide matrix compos- The effect of damage development in some 2D-woven 0/90 SiC- ites are currently being evaluated for aircraft engine hot-section reinforced non-oxide reinforced composites has been determined components [1-3. Elevated temperature creep and fatigue condi- for CVI SiC matrix systems with lower modulus Sic-based fiber- tions under oxidative environments are a primary concern for these types(Nicalon"and Hi-Nicalon")for creep and fatigue conditions types of applications. Therefore, it is essential that the effect of ele- between 1100 and 1400C in air and argon environments [4-6]. In vated temperature creep and fatigue conditions be well understood those composite systems, with increasing stress and time, micro in order to predict useful lives for these types of composites. As part cracks are formed in the 90 minicomposite bundles with increas- of this effort, it is critical to understand the development of damage ing stress and or time, the cracks grow and extend through the cvi in these materials over stress, time, and environment in order to Sic into the load-bearing 0 fiber minicomposite bundles produc ing through-the-thickness matrix cracks. Eventually a"master Corresponding author. Tel : +1 216 433 5512. crack"[6 will form that becomes the site of ultimate failure. For mail address: gmorscheresbcglobal net (G N Morscher these composite systems, fairly high strains to failure(0.5% to 3538/s-see front matter o 2008 Elsevier Ltd. All rights reseTensile creep and fatigue of Sylramic-iBN melt-infiltrated SiC matrix composites: Retained properties, damage development, and failure mechanisms Gregory N. Morscher b,*, Greg Ojard c , Robert Miller c , Yasser Gowayed d , Unni Santhosh e , Jalees Ahmad e , Reji John a a Materials and Manufacturing Directorate, Air Force Research Laboratory, AFRL/RXLMN, Wright-Patterson AFB, OH, USA bOhio Aerospace Institute, NASA Glenn Research Center, 21000 Brookpark Road, MS 106-5, Cleveland, OH 44135, USA c Pratt and Whitney, East Hartford, CT, USA d Auburn University, Auburn, AL, USA e Research Applications Inc., San Diego, CA, USA article info Article history: Received 28 March 2008 Received in revised form 8 August 2008 Accepted 21 August 2008 Available online 11 September 2008 Keywords: A. Ceramic matrix composites B. Creep B. Fatigue B. Matrix cracking D. Acoustic emission abstract An understanding of the elevated temperature tensile creep, fatigue, rupture, and retained properties of ceramic matrix composites (CMC) envisioned for use in gas turbine engine applications is essential for component design and life-prediction. In order to quantify the effect of stress, time, temperature, and oxi￾dation for a state-of-the-art composite system, a wide variety of tensile creep, dwell fatigue, and cyclic fatigue experiments were performed in air at 1204 C for the SiC/SiC CMC system consisting of Sylram￾ic-iBN SiC fibers, BN fiber interphase coating, and slurry-cast melt-infiltrated (MI) SiC-based matrix. Tests were either taken to failure or interrupted. Interrupted tests were then mechanically tested at room tem￾perature to determine the residual properties. The retained properties of most of the composites sub￾jected to tensile creep or fatigue were usually within 20% of the as-produced strength and 10% of the as-produced elastic modulus. It was observed that during creep, residual stresses in the composite are altered to some extent which results in an increased compressive stress in the matrix upon cooling and a subsequent increased stress required to form matrix cracks. Microscopy of polished sections and the fracture surfaces of specimens which failed during stressed-oxidation or after the room-temperature retained property test was performed on some of the specimens in order to quantify the nature and extent of damage accumulation that occurred during the test. It was discovered that the distribution of stress-dependent matrix cracking at 1204 C was similar to the as-produced composites at room tem￾perature; however, matrix crack growth occurred over time and typically did not appear to propagate through-the-thickness except at the final failure crack. Failure of the composites was due to either oxi￾dation-induced unbridged crack growth, which dominated the higher stress regime (P179 MPa) or con￾trolled by degradation of the fibers, probably caused by intrinsic creep-induced flaw growth of the fibers or internal attack of the fibers via Si diffusion through the CVI SiC and/or microcracks at the lower stress regime (6165 MPa). 2008 Elsevier Ltd. All rights reserved. 1. Introduction Silicon carbide fiber-reinforced silicon-carbide matrix compos￾ites are currently being evaluated for aircraft engine hot-section components [1–3]. Elevated temperature creep and fatigue condi￾tions under oxidative environments are a primary concern for these types of applications. Therefore, it is essential that the effect of ele￾vated temperature creep and fatigue conditions be well understood in order to predict useful lives for these types of composites. As part of this effort, it is critical to understand the development of damage in these materials over stress, time, and environment in order to understand the mechanisms that lead to degradation in stress-strain behavior and ultimate creep or fatigue rupture. The effect of damage development in some 2D-woven 0/90 SiC￾reinforced non-oxide reinforced composites has been determined for CVI SiC matrix systems with lower modulus SiC-based fiber￾types (NicalonTM and Hi-NicalonTM) for creep and fatigue conditions between 1100 and 1400 C in air and argon environments [4–6]. In those composite systems, with increasing stress and time, micro cracks are formed in the 90 minicomposite bundles. With increas￾ing stress and/or time, the cracks grow and extend through the CVI SiC into the load-bearing 0 fiber minicomposite bundles produc￾ing through-the-thickness matrix cracks. Eventually a ‘‘master crack” [6] will form that becomes the site of ultimate failure. For these composite systems, fairly high strains to failure (0.5% to 0266-3538/$ - see front matter 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.compscitech.2008.08.028 * Corresponding author. Tel.: +1 216 433 5512. E-mail address: gmorscher@sbcglobal.net (G.N. Morscher). Composites Science and Technology 68 (2008) 3305–3313 Contents lists available at ScienceDirect Composites Science and Technology journal homepage: www.elsevier.com/locate/compscitech