Preparation and Mechanical Properties of Si-C-O Long Fiber/Alumina Matrix Composite

Abstract

Si-C-O long fiber (20vol%)/alumina matrix composites have been fabricated by infiltration of aqueous alumina suspensions into fiber-sheets and sintered at 1000-1400°C by firing in air, vacuum (0.01Pa) and hotpressing (39MPa). The sinterability of monolithic alumina and the composites was higher in an atmosphere of air rather than under vacuum. The flexural strength of composites sintered in vacuum showed a maximum (300MPa) at a sintering temperature of 1300°C. The vacuum sintering at 1200°C-1300°C produced a significant non-linear fracture behavior in stress-strain curves based on the pull-out of fibers from the matrix. Increase of sintering temperature of the composite to 1400°C resulted in brittle fracture behavior, suggesting that the interfacial strength increased with an increase in density of the composite. Sintering of the composite in air produced the intermediate layers of the SiO₂-Al₂O₃ system between the alumina matrix and the Si-C-O fibers due to oxidation of the fibers. The formation of SiO₂-Al₂O₃ layers reduced the strength of composite with brittle fracture behavior. Hot-pressing of the composite at 1200°C using Si-C-O fibers coated with fine BN particles led to an increase in strength (420MPa) as well as in non-linearity of the fracture behavior.