HEAT-TREATMENT EFFECTS ON THE TENSILE PROPERTIES AND MICROSTRUCTURE OF A SIC RBSN COMPOSITE IN NITROGEN/

The room-temperature tensile properties and constituent microstructure s of a unidirectionally reinforced SiC/RBSN composite have been invest igated after heat treatments at 1400, 1600, or 1800 degrees C in nitro gen for up to 100 h. The composite consisted of similar to 24 vol% of aligned 140 mu m diameter, continuous length, chemically vapour deposi ted SiC fibres in a similar to 40% porous silicon nitride matrix. The composites heat treated at 1400 degrees C for up to 100 h showed elast ic modulus, first matrix cracking strength and ultimate tensile streng th values similar to those of the as-fabricated composites, but those heat treated for 1 h beyond this temperature displayed losses in all t hree properties. Recrystallization of the SiC fibres, loss of carbon f rom the carbon-rich interface coating on the fibres, and dissociation of the RBSN matrix are the reasons for the loss of mechanical properti es. Published by Elsevier Science Limited and Techna S.r.l.