IN-SITU FORMATION AND HIGH-TEMPERATURE REINFORCING EFFECT OF MOSI2 AND WSI2 ON REACTION-BONDED SI3N4

A three-step procedure consisting of presintering, reaction-bonding an d post-hot-pressing was employed to prepare Si3N4/MoSi2 and Si3N4/WSi2 composites, using as starting materials powder mixtures of Si-Mo and Si-W, respectively. A presintering step in an Ar-base atmosphere was p erformed for the in situ formation of intermetallic compounds-MoSi2 an d WSi2; the nitridation in an N-2-base atmosphere with a total cycle o f 1350 degrees C x 20 h + 1450 degrees C x 20 h + 1450 degrees C x 2 h in order to realize the complete conversion of Si into Si3N4; post-ho t-pressing was employed for the further densification of the reaction- bonded specimens. The 3- and 4-point bend tests were performed at 25, 1000, 1200 and 1400 degrees C. Si3N4/MoSi2 composite shows a maximum v alue of bend strength at about 1200 degrees C, whereas the bend streng th of Si3N4/WSi2 composite slightly increases from room temperature up to 1000 degrees C. (C) 1997 Elsevier Science S.A.