Creep in Interlaminar Shear of an Oxide/Oxide Ceramic-Matrix Composite at Elevated Temperature

Creep behavior in interlaminar shear of an oxide-oxide ceramic composite was evaluated at 1100 degrees C in laboratory air and in steam environment. The composite (N720/AS) consists of a porous aluminosilicate matrix reinforced with laminated, woven mullite/alumina (Nextel (TM) 720) fibers, has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. The interlaminar shear properties were measured. The interlaminar shear strength (ILSS) was determined as 7.6 MPa. The creep behavior was examined for interlaminar shear stresses in the 2-6 MPa range. Primary and secondary creep regimes were observed in all tests conducted in air and in steam. Tertiary creep was noted in tests performed at 6 MPa. Creep run-out defined as 100 hrs at creep stress was not achieved in any of the tests. Larger creep strains and higher creep strain rates were produced in steam. However, the presence of steam had a beneficial effect on creep lifetimes. Composite microstructure, as well as damage and failure mechanisms, was investigated.