EFFECTS OF ENVIRONMENT ON CREEP BEHAVIOR OF NEXTEL™720/ALUMINA-MULLITE CERAMIC COMPOSITE AT 1200°C

摘要

The tensile creep behavior of an oxide-oxide continuous fiber ceramic composite was investigated at 1200 °C in laboratory air, in steam and in argon. The composite consists of a porous alumina-mullite matrix reinforced with laminated, woven mullite/ahimina (Nextel™720) fibers, has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. The tensile stress-strain behavior was investigated and the tensile properties measured at 1200 °C. The elastic modulus was 74.5 GPa and the ultimate tensile strength was 153 MPa. Tensile creep behavior was examined for creep stresses in the 70-140 MPa range. Primary and secondary creep regimes were observed in ail tests. Creep run-out (set to 100 h) was achieved in laboratory air for creep stress levels ≤ 90 MPa. The presence of either steam or argon accelerated creep rates and reduced creep lifetimes. Composite microstructure, as well as damage and failure mechanisms were investigated.