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 and 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 performed for the in situ formation of intermetallic compounds - MoSi2 and WSi2; the nitridation in an N2-base atmosphere with a total cycle of 1350°C × 20 h + 1400°C × 20 h + 1450°C × 2 h in order to realize the complete conversion of Si into Si3N4; post-hot-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°C. Si3N4/MoSi2 composite shows a maximum value of bend strength at about 1200°C, whereas the bend strength of Si3N4/WSi2 composite slightly increases from room temperature up to 1000°C.