Effects of Environment on Creep Behavior of Nextel 720/Alumina-Mullite Ceramic Composite at 1200 deg C
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH GRADUATE SCHOOL OF ENGINEERING AND MANAGEMENT
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The creep behavior of an oxide-oxide ceramic matrix composite CMC was investigated at 1200 deg C in Laboratory air, in steam and in argon. The composite consisted of a porous alumina-mullite matrix reinforced with laminated, woven mullitealumina Nextes720 fibers. The composite had no fiber coating and relied on its porous aluminamullite matrix for flaw tolerance. Tensile stress-strain behavior was investigated and the tensile properties were measured at 1200 deg C in laboratory air. Tensile creep behavior of the CMCs was examined for creep stress level of 73, 91, 1114 and 136 MPa. Creep run-out, set to 100 h, was achieved for stress levels 91 MPa in air. The presence of steam or argon accelerated the creep rates the N720AM composite. Optical and scanning electron microscope SEM micrographs were used to examine fracture surfaces and to evaluate failure mechanisms. Fracture surfaces of the N720AM composite were predominately planar. Limited areas of short fiber pull-out were observed for specimens tested at low creep stress levels in air.
- Laminates and Composite Materials