The internal friction which originated from sliding and diffusional flow along grain boundaries was monitored (as a function of temperature and damping frequency) in model SiC polycrystals with an intergranular SiO2 glassy film. Emphasis was placed upon the change in internal friction characteristics upon adding Ca cations. It was expected that Ca cations would segregated to the intergranular glass phase and modify its network structure. The presence of an internal-friction relaxation peak, due to grain-boundary sliding, permitted a quantitative evaluation of the activation energy for viscous flow of the intergranular glass and of the magnitude of the related viscosity. A peak-analysis procedure, involving the peak-shift method (monitoring the peak shift after damping frequency changes), was proposed which quantitatively revealed the activation energy for viscous flow in various impurity-doped intergranular glasses. The presence of chemical gradients at grain boundaries was also analyzed by taking account of the dependence of peak morphology upon damping frequency.

Internal Friction Analysis of CaO-Doped Silicon Carbides. H.Nishimura, Y.Ikuhara, K.Ota, G.Pezzotti: Materials Transactions, 2002, 43[7], 1552-6