Assessment of the high temperature elastic and damping properties of silicon nitrides and carbides with the impulse excitation technique

The impulse excitation technique (IET), based on resonant vibration analysis, was used to determine the high temperature elastic and damping properties of hot-pressed silicon nitride (Si3N4) and silicon carbide (SiC) materials with Al- and Y-additives. The Si3N4 materials were doped with 2 wt.% of TiN to suppress the crystallization of intergranular glassy pockets. Near 1000 degreesC the investigated materials display a characteristic damping peak, which is essentially unaffected by temperature excursions up to 1400 degreesC. Two existing models which aim at linking elastic and damping properties with microstructural and micromechanical details, are considered. One of the models is used to provide an estimate of the amount of amorphous intergranular pocket phase. This type of information is of particular relevance since the high temperature deformation resistance of silicon based ceramics is severely dependent on the presence and amount of amorphous multiple grain pockets. (C) 2002 Elsevier Science Ltd. All rights reserved.