SICFO'-SIALON COMPOSITE - PROPERTIES AND OXIDATION RETAINED PROPERTIES

A composite of O'-SiAlON (Si2-xAlxN2-xO1+x, with x similar to 0.14) re inforced with 20 vol.% SiC monofilaments was fabricated by hot-pressin g at 1600 degrees C for 2 h under 34 MPa pressure. The mechanical and interfacial properties of the composites, as-fabricated as well as pos t-oxidized, were investigated. The composite exhibited a significant i mprovement in ultimate flexure strength (640 MPa) and work of fracture (42 kJ m(-2)) compared with that (350 MPa and 1.8 kJ m(-2), respectiv ely) of the monolithic material. These mechanical properties were slig htly increased after the composite was heat treated for 24 h in air at 1200 and 1300 degrees C. However, the composite exhibited a significa nt degradation in ultimate strength, while the work of fracture (WOF) remained unchanged after exposure in air at temperatures beyond 1400 d egrees C. The as-fabricated composite revealed a low interfacial shear strength (6.2 MPa) and a frictional sliding stress (3.2 MPa). After t he composite was oxidized at elevated temperatures, the interfacial bo nding and sliding stresses were reduced to noticeable extents, resulti ng from the degradation of the carbon coating layer of the SiC monofil aments.