Creep in Interlaminar Shear of an Oxide/Oxide Ceramic-Matrix Composite at Elevated Temperature1

Abstract

Creep behavior in interlaminar shear of an oxide–oxide ceramic composite was evaluated at 1100 °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™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.

Effect of thermal exposure on the microstructure and strength of an alumina‐silica ceramic fiber

“…[1][2][3][4][5][6] The mechanical properties of oxide/oxide composites are closely related to the properties of oxide fiber, especially after exposure at elevated temperatures. [7][8][9][10] All commercial polycrystalline oxide fibers used in oxide/oxide composites up to now are based on alumina. 11,12 High alumina content provides increased chemical stability and good strength up to 1000 • C. However, the strength of alumina fiber such as Nextel 610 fiber decreases significantly after exposure above 1000 • C, as a result of grain growth and the formation of defects associated with this process.…”

“…Oxide/Oxide ceramic matrix composites have seen significant advancement over the past few decades, due to their low density, high temperature capability and oxidative stability 1–6 . The mechanical properties of oxide/oxide composites are closely related to the properties of oxide fiber, especially after exposure at elevated temperatures 7–10 . All commercial polycrystalline oxide fibers used in oxide/oxide composites up to now are based on alumina 11,12 .…”