Silicon Nitride and YMgSiAlON Glass Study by Mechanical Spectroscopy

Abstract
Si₃N₄/TiN and YMgSiAlON/SiC composites have been studied by isothermal mechanical spectroscopy over a large frequency range. Internal friction curves obtained for the composite Si₃N₄-TiN(30%vol)-Al₂O₃,Y₂O₃(7.5%vol) exhibit a thermally activated pseudo peak superposed on a non purely exponential background. We can assume that this maximum is due to relaxations in the compressed intergranular glassy films. The apparent dynamical parameters deduced from its shift (11.2 eV and 3.10^-45 s) are unusual as observed in amorphous materials. YMgSiAlON glass has a composition very similar to the one of the intergranular phase of Si₃N₄/TiN composite. The damping curves obtained for YMgSiAlON/SiC composites above the glass transition temperature are pure exponential backgrounds. An original analysis of these curves allows to determine an activation energy of about 3.6 eV. This value is more realistic for an elementary diffusion mechanism in a glass near Tg.