Damage tolerant oxide/oxide fiber laminate composites

Oxide-fiber/oxide-matrix composites were developed using non-infiltrated wo ven fiber layers between matrix-infiltrated fiber layers in order to achiev e damage tolerant behavior. A fiber interface coating was not used. This te chnique enables damage tolerance in materials with strong fiber-matrix bond ing and under oxidizing conditions. Fabrication of composites was carried o ut through a slurry infiltration technique. Slurries for fiber (Nextel(TM) 720, 3M) infiltration were prepared using a submicron alpha-Al2O3 powder co ated with an amorphous SiO2-layer through a sol-gel process. Hot-pressing w as used to densify and bond the laminate layers together, followed by press ureless heat-treatment to allow mullite to form. Room temperature three-poi nt bending tests were performed on as-received samples and on samples which underwent long-term annealing at high temperatures (1200-1300 degrees C) i n air. Subsequent examination revealed that due to the lack of a fiber inte rface coating, matrix-infiltrated fiber layers behaved in a quasi-monolithi c manner with little or no crack deflection. Layers of non-infiltrated fibe rs, however, provided damage tolerance by deflecting cracks in the plane of the laminate and by serving as a mechanical bond between matrix-infiltrate d layers. The laminate composites demonstrate reasonable room-temperature f racture strength both in the as-received state (88 MPa) and after exposure to 1300 degrees C air for 200 h (72 MPa) along with extensive fracture defl ection through the layers of non-infiltrated fiber. Composite properties, s pecifically fracture strength and damage tolerance, can be tailored by vary ing lay-up and processing parameters such as fiber-matrix ratio and type of fiber weave. (C) 2000 Elsevier Science Ltd. All rights reserved.