Effect of Prior Exposure at Elevated Temperatures on Tensile Properties and Stress-Strain Behavior of Three Oxide/Oxide Ceramic Matrix Composites.

摘要

Thermal stability of three oxide-oxide ceramic matrix composites was studied. The materials studied were Nextel(trademark)610/aluminosilicate (N610/AS), Nextel(trademark)720/aluminosilicate (N720/AS), and Nextel(trademark)720/Alumina (N720/A), commercially available oxide-oxide ceramic composites (COI Ceramics, San Diego, CA). The N610/AS composite consists of a porous aluminosilicate matrix reinforced with laminated woven alumina N610 fibers. The N720/AS and N720/A composites consist of a porous oxide matrix reinforced with laminated, woven mullite/alumina (Nextel(trademark)720) fibers. The matrix materials are aluminosilicate in N720/AS and alumina in N720/A. All three composites have no interface between the fibers and matrix, and rely on the porous matrix for flaw tolerance. The N610/AS and N720/AS CMCs were heat treated in laboratory air for 100 h at 1100 deg C and for 10, 20, 40 and 100 h at 1200 deg C. The N720/A CMC was heat treated in laboratory air for 100 h at 1200 deg C and for 10, 20, 40 and 100 h at 1300 deg C. The room-temperature tensile properties of all composites were measured after each type of heat treatment. Effects of prior heat treatment on tensile strength were evaluated. Heat treatment at 1100 deg C had little effect on tensile strength of the N610/AS and N720/AS composites, while heat treatment at 1200 deg C caused dramatic loss of tensile strength. Poor strength retention after heat treatment at 1200 deg C is attributed to degradation of the aluminosilicate matrix. The N720/A composite exhibited excellent thermal stability, retaining about 90% of its tensile strength after heat treatment at 1300 deg C. Results indicate that the aluminosilicate matrix is considerably more susceptible to localized densification and coarsening of the porosity than the alumina matrix.